Restorative dentistry

BLUK133-Jacobsen January 5, 2008 21:39

Restorative Dentistry

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To Charlotte, Matthew and Christopher – may their dreams come true.

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Restorative DentistryAn Integrated Approach

Second Edition

Peter Jacobsen, MDS (Lond), FDSRCS (Eng), FHEA

Reader in Restorative Dentistry, Division of Adult Dental Health,Wales College of Medicine, Cardiff University, Cardiff, UK;Honorary Consultant in Restorative Dentistry,Cardiff and Vale NHS Trust, Cardiff, UK

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C© 2008 by Blackwell Publishing Ltd

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First published 2008 by Blackwell Munksgaard

ISBN: 9781405167994

Library of Congress Cataloging-in-Publication Data

Restorative dentistry : an integrated approach / Peter Jacobsen. – 2nd ed.p. ; cm.

Includes bibliographical references and index.ISBN: 978-1-4051-6799-4 (pbk. : alk. paper)1. Dentistry, Operative.[DNLM: 1. Dental Restoration, Permanent. WU 300 AR435 2008] I. Jacobsen, P. H. (Peter H.)RK501.R473 2008617.6–dc22

2007032687

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Contents

Contributors viiPreface ixAcknowledgements xi

Section I The Patient

1 The Patient – His Limitationsand Expectations 3

2 History and Examination 5

3 Diagnosis and Stabilisation 15

4 General Principles of TreatmentPlanning 25

Section II The Restoration and Its Environment

5 Applied Biology of the Teeth 35

6 The Pathology of Caries and PulpalDisorders 46

7 The Periodontium in Health and Disease 56

8 Functional Anatomy of the Occlusion 62

9 Properties of Restorative Materials 74

Section III Clinical Management andTechniques

10 Intracoronal Restorations 91

11 Management of the Deep Cavity 107

12 Root Canal Treatment 115

13 Management of the PeriodontallyInvolved Dentition 135

14 Principles of Occlusal Management 143

15 Fixed Prosthodontics – Crowns 157

16 Colour and Aesthetics 175

17 Impression Materials and Techniques 187

Section IV Fixed and Removable Prosthodontics

18 Diagnosis and Treatment Planning forFixed and Removable Prosthodontics 199

19 Fixed Prosthodontics: Resin-RetainedBridgework 210

20 Fixed Prosthodontics: ConventionalBridgework – Design and Planning 217

21 Fixed Prosthodontics: ConventionalBridgework – Clinical Procedures 226

22 Fixed Prosthodontics: Basic Principlesof Implants 240

23 Fixed Prosthodontics: ClinicalAspects of Implants 249

24 Removable Prosthodontics: PartialDentures – Design 263

25 Removable Prosthodontics: PartialDentures – Clinical Procedures 273

26 Removable Prosthodontics: CompleteDentures 278

Section V Problems

27 Tooth Surface Loss 295


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28 Temporomandibular Dysfunction 302

29 Management of Failure in theRestored Dentition 1: FixedRestorations 310

30 Management of Failure in theRestored Dentition 2: Dentures 322

Bibliography 329Index 333


Contributors

Robert Adams, MSc (Lond),MSurgDent, BDS (Wales),FDSRCS (Eng)Specialist Dental Practitioner,

Wilmslow, CheshireHonorary Lecturer in Dental

Implantology, Wales College ofMedicine, Cardiff University,Cardiff, U.K.

Implantology

Martin Addy, PhD, MSc,BDS (Wales), FDSRCS(Eng)Professor of Periodontology,

University of Bristol DentalSchool, Bristol

Honorary Consultant inRestorative Dentistry, UnitedBristol HealthCare NHS Trust,Bristol, U.K.

John Moran, PhD, MScD, BDS(Wales), FDSRCS (Eng)Senior Lecturer in Periodontology,

University of Bristol DentalSchool, Bristol

Honorary Consultant inRestorative Dentistry, UnitedBristol HealthCare NHS Trust,Bristol, U.K.

Periodontology

Alan Harrison, TD, QHDS, PhD,BDS (Wales), FDSRCS (Eng)Emeritus Professor of Dental Care

for the Elderly, University ofBristol Dental School, Bristol

Formerly Honorary Consultant inRestorative Dentistry, UnitedBristol HealthCare NHS Trust,Bristol, U.K.

Removable Prosthodontics

Gavin J Pearson, PhD,BDS (Lond), LDSRCS(Eng)Professor of Biomaterials in

relation to Dentistry, QueenMary Westfield College,London, U.K.

Dental Biomaterials

David K Whittaker, PhD(Wales), BDS (Manc),FDSRCS (Eng)Emeritus Professor of Oral

Biology, Wales College ofMedicine, Cardiff University,Cardiff

Formerly Honorary ConsultantDental Surgeon, Cardiff andVale NHS Trust, Cardiff,U.K.

Oral Biology and Pathology


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Preface

This book began life in the mid-1980s when threefriends mused about the state of the world as theywalked around a churchyard in Northleach, Glouces-tershire, after a very good lunch in a restaurantlong since gone. The product was ‘ConservativeDentistry – an Integrated Approach’ published byChurchill Livingstone in 1990. The intention of thatbook was to distil the essentials of the subject andmerge them with the appropriate aspects of the sup-porting sciences to try to avoid the compartmental-isation of dental education and show the relation-ships that extend from oral biology, oral pathologyand dental biomaterials into clinical practice.

The original book was expanded in the mid-1990sand was published as ‘Restorative Dentistry – an In-tegrated Approach’ by Butterworth–Heinemann in1998. This book sold well but is now clearly pastits sell by date – hence this new edition.

The new book embraces the new and, I hope, re-tains the old where this has been seen to be clinicallysuccessful and relevant to modern practice. The prac-tice of dentistry has gone through many transitions inits history and the present time is no different. Thereis the saying ‘What goes around, comes around’ andthis applies to dentistry too.

So, Dear Reader, please indulge this old man in theautumn of his career with a little time for reflectionon the 20 years since his first book was published andthe 40 years since he qualified.

A trip down memory lane into the textbooks andwritings of the late Victorian era and early part ofthe twentieth century provides a fascinating histori-cal perspective on what our professional forefathersthought and did. It may come as a shock to readthat many of the principles we expound now wereexpounded then. Bridgework was taught as needinghigh standards of construction with an appreciationof the role of the occlusion and the need for soundabutments. Today’s strategy for the management ofperiodontal disease is the same as that practised in1900 though the role of the occlusion in causing thedisease, prevalent in the 1960s, has gone.

The overriding impression is that our forefatherswere just as clever as us, sometimes cleverer, butthey were restricted by their materials and equipment.Look at the Bing Bridge of 1868. It is instantly recog-

nisable as a resin-retained bridge with wings and apontic but instead of being glued on, it was pinnedon. There were no air turbines, no polymers; therewere arsenic root fillings and poor local analgesics.In the early twentieth century, all the precision re-tainers we would recognise today had been designedfor the then preferred ‘removable bridgework’.

As a student in the 1960s, I learnt the Baldwintechnique of glueing in an amalgam restoration witha wet mix of zinc phosphate cement. What are theYoung Turks doing now? – glueing them in withpolymers.

The cycle of ignorant rediscovery continues. Fiftyyears ago deep caries was managed by superficial re-moval and then the placement of a tannic acid dress-ing to ‘harden’ the dentine. Six months later the tannicacid was removed and the tooth restored. Today wehave the ‘new’ ‘stepwise’ excavation of caries.

The quest for aesthetic restorations has led to‘amalgam-free’ dental practices and the prescrip-tion of polymeric composites for all intracoronalrestorations. Milled ceramics with CAD/CAM tech-nology have arrived together with durable adhesives.The Young Turks now reject dentine pins and postcrowns – see one and glue one! How much longer willthe principles of the preparation geometry of near-parallelism be taught for crown retention?

Endosseous implants represent the biggest develop-ment of the last 20 years. How long will it be beforeendodontics disappears? Crown-retained bridgeworkwith its use of dubious abutments is also a candidatefor the history books.

The practice of dentistry and indeed the teachingof dentistry is about managing transitions – silicatesto composites, copper rings to elastomers, vulcan-ite to acrylic. But there is a need to beware of falsedawns – the self-polymerising filling materials of the1950s, the sandwich technique of the 1980s, mul-tiple ‘generations’ of dentine adhesives, discardinggold inlays – and dental academics have to be con-servative with a small ‘c’. It is no use allowing theYoung Turks to take over with their revolutionaryideas only to find that 2 or 3 years of students havequalified not knowing techniques that turn out to bestill fundamental; you cannot call them back and startagain!


x Preface

Modern educational theory reveals the difficultythat all learners have in making links between ‘boxes’of information that are actually connected but aretaught in ‘modules’. This problem is compounded bythe modular style of education now provided in mostschools in the United Kingdom. Dentistry, of course,has a multitude of these boxes and it seems to be tak-ing longer for students to establish the links betweenthe boxes – to ‘integrate’ the information. Studentsseem to finish one year of study and pass on to thenext, consigning the first to the filing cabinet, withoutrealising the importance of the ‘continuum of dentaleducation’.

The ‘Integrated Approach’ attempts to developthe links that make for success in restorativedentistry.

This new edition of the book tries to balance the oldtried and tested with the new kids on the block. It triesto hit the moving target of developments in materialswithout losing the basic techniques that have servedour patients well and will continue so to do. The daysof molar endodontics and conventional bridgeworkmay be numbered but until many more dentists aretrained in the use of implants, messing about up rootcanals and trying to cut parallel-sided preparationswill still be required.

P.H.J.Cardiff 2007.


Acknowledgements

Many people, friends and colleagues have helped inthe gestation, writing and production of this bookand its predecessors.

My sincere thanks are due to all the specialist con-tributors. To Alan Harrison and David Whittakerfor the chapters they wrote for the first editionwhich have stood the test of time and needed lit-tle change. Thanks to John Moran for revisingMartin Addy’s chapters. I welcomed our implantol-ogist Robert Adams to the team and thank him forsuffering the indignities of being ‘integrated’. Lastly,to my dear friend Gavin Pearson, who has been a stal-wart supporter, adviser and co-conspirator for moreyears than we both want to remember, my sincerethanks not only for updating the biomaterials textbut also for his personal support and advice.

Mr Frank Hartles and the staff of the AudiovisualAids Unit at Cardiff have contributed greatly throughthe clinical photographs and the new artwork – inparticular Mr Sam Evans and Miss Ruth Bowen de-serve a personal mention and thanks. Artwork from

the first edition was done by Mr Peter Cox, freelanceMedical Artist, and by Mrs Jo Griffiths and I thankthem again for their efforts.

Within the clinical chapters, many of the cases il-lustrated are from my own clinical practice withinthe University Dental Hospital, Cardiff, and here Iwould like to emphasise the need for such cases tobe planned and treated by the efforts of an integratedteam. Without the skills and support of Mr Jeff Lock,Chief Dental Technologist, who has worked with mefor over 20 years and seems to be able to see mycrown margins when I cannot, together with a verylarge number of dental nurses, the quality of care thatthese patients received would have been considerablyreduced.

The staff of Blackwell Publishing, particularly MissKatrina Chandler and Miss Amy Brown, have assistedin the development and publication of the book.

Finally, all my undergraduates and postgraduatesprovided the inspiration to put this thing together(again) – I hope they like it.

P.H.J.


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BLUK133-Jacobsen December 7, 2007 16:38

Section IThe Patient


“I’m ready when you are.”

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Chapter 1The Patient – His Limitations and Expectations

The provision of high-quality restorative dentistry depends upon the dentist:

� Making an accurate diagnosis� Devising a comprehensive and realistic treatment plan� Executing the treatment plan to a high technical standard� Providing subsequent continuing care

There is a very strong tendency, particularly in thefield of fixed prosthodontics, for the dentist to becomeover-interested in the technical execution of treat-ment. There is a vast range of materials and equip-ment to stimulate this interest and compete for hisattention. It is perhaps inevitable that dentists can be-come obsessive about types of bur or root canal file,the pros and cons of various materials and the precisetechniques of restoration.

This is not to decry such interest because a highstandard of technical execution is essential for thelongevity of restorations. However, technical execu-tion must be seen in the context of the four-point se-quence listed above. Without a sound diagnosis andtreatment plan, even the best technical execution willbe doomed to failure.

A major influence on the formulation of the treat-ment plan is:

� The Patient (Frontispiece)

It is usually by his own volition that he seeks restora-tive advice and treatment, and he usually brings withhim certain problems and limitations that influencetreatment planning and the delivery of care.

Each patient also attends with strong preconcep-tions based on his previous experience of dentistry.This could be good or bad, with a single traumaticepisode being able to reverse many years of coopera-tion. The patient will have some idea of what dentistrycould or might do for him, and what he wants fromhis dentist. Some of his concepts could well be lim-ited or unambitious, and education has a major role toplay here. Conversely, sometimes his concepts couldbe over-ambitious, complex bridgework for instance,

and here re-education is often necessary to bring himdown to the practical and feasible.

It might be that the dentist has the skills and tech-nical facilities to perform advanced procedures, butbefore he puts bur to tooth, he must stop and askwhether this is really what this patient needs andwants. If the answer is no, then to proceed is an actof pure selfishness that might also be regarded asnegligent!

Certainly the dentist may have certain treatmentgoals for all his patients – no pain or caries, healthyperiodontium, complete occlusion – but the way inwhich he prescribes and delivers his care has to betempered by the patient’s aspirations for his ownmouth and his readiness to accept care.

A prolonged treatment plan could be very incon-venient to a shift worker or to a mother with youngchildren or those with no personal transport. It mightcreate restorations that will be beyond the mainte-nance capacity of the lazy or disinterested, or thosewith inadequate washing facilities.

Perhaps the patient is a reluctant attender, ex-tremely apprehensive of dental care and its possiblediscomforts, and will require some form of therapeu-tic help just to get the simple things done. The short,unambitious treatment plan is more likely to succeedhere, and if the patient’s confidence can be obtained,the more complex treatment could be providedlater.

Advanced restorations require skill and facilities,and these have to be paid for, either by the state orby the patient. Both have limited resources and bothdeserve value for money. Committing resources toan ambitious treatment plan should involve judge-ment on the likely lifespan of the restorations in that

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4 I. The Patient

Treatment Plan

Dentist

AbilityTrainingFacilities

Materials andtechniques

DurabilitySimplicity

Patient

NeedsAspirations

Mouth

Caries ratePeriodontal index

Level of care

Fig. 1.1 Influences on the formulation of a treatment plan.

particular mouth and its conditions, and whether theexpense is justifiable – cost benefit analysis.

The intra-oral conditions bring as much influenceto bear. The caries rate, the number of missing teeth,the periodontal condition, the presence of denturesand the quality of previous restorative work all actas limitations to the scope of the treatment plan. Allof us like to provide our best work for those whowill appreciate it and look after it. Disinterest on thedentist’s part is created by the appearance of largeplaque deposits and evidence of little care.

The other side of the equation is what may be avail-able and this relates to the dentist’s skills and train-ing, the materials and techniques at his disposal, andthe facilities available for providing care (Fig. 1.1).These, in turn, could well modify or even dictate thepatient’s aspirations – a clean, well-equipped and ef-ficient practice would indicate a good level of careto the average patient, whilst the reverse could welllower his expectations.

The dentist should offer only what is realisticallyavailable and work within his own limitations. It iscertainly no disgrace to say that certain options arebeyond your capabilities and it is possible to considerreferral to an appropriate specialist. It could also bethat the options the patient has aspirations towardsare those with a lower success rate, and it is sensibleto tell him this frankly.

There is considerably more awareness of the cos-metic possibilities of modern dentistry and thus de-mand for new materials and techniques. Much of thisis expensive and has not been fully evaluated over asufficient period for total confidence in its durability.The patient deserves a proper explanation about thereservations there are about particular lines of treat-ment.

The provision of restorative treatment is a complexarrangement wherein the patient, the dentist, the tech-nical support and the materials must be in harmony toproduce a satisfactory result. The limitations of oneelement will inevitably change the effects of the oth-ers. It is important to remember that the treatment isonly as good as its weakest link – don’t let that beyou!

The key to success throughout is communication –listen and learn from what the patient says, explainwhat can be done for him, and then decide jointlyon what should be done. If you are not sure, do notcommit yourself, but delay the decision and take ad-vice from your colleagues or even your local con-sultant.

This book begins by talking about how to find outwhat’s wrong with the patient and what does he wantdone about it, coupled with the limitations the patientbrings to formulating a treatment plan and then toexecuting it.

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Chapter 2History and Examination

It is very important to listen to what the patient has to say about his problems.

This aspect of care can be neglected in an obsession to ‘get inside the mouth’.

The history is the basis for diagnosis and treatment planning – there is potential for harm to the patient if itis neglected.

The history should provide a clear account of the pa-tient’s experience of health care prior to the currentattendance. It should establish an organised body ofknowledge about the patient’s dental past and his fit-ness to receive future treatment – it forms part of therationale for his management.

The history, though, is very subjective and proneto differences in the perceptions and aspirations ofthe patient and the dentist. These differences may bereduced or exaggerated by the level of communica-tion between the two, and the dentist must bear thisproblem in mind.

Clearly, it is the dentist’s responsibility to create theright atmosphere for the patient to tell his story. Thepatient must be sitting comfortably in quiet surround-ings and be confident in the dentist’s sympathetic at-tention. He should be sitting upright, not supine andvulnerable, and facing the questioner with his eyes atthe same level. This avoids the ‘operating’ position,with its overtones of discomfort and interrogation.The dentist should sit in front of the patient facinghim, and not out of sight behind him.

The most limiting aspect of the history is that to acertain extent it is not strictly factual. It is the pa-tient’s perception of events or circumstances. Evenitems of medical history can be incorrectly remem-bered and misunderstood, and in difficult cases thepatient’s medical practitioner must be contacted forinformation.

The dental aspects are often muddled, particu-larly in the identification of a troublesome tooth inamongst 30 or so others.

The dentist has to sift this information and organ-ise it, give it the weight it deserves, and then recordit and draw conclusions from it. He has to pick up

inconsistencies in the story and use a systematic ap-proach so as not to miss anything. However, he mustbeware of the too precise patient with an obsessivelydetailed history, which can be just as misleading orunhelpful as that provided by someone who is vague.

Patient’s memories or understanding of previoustreatment are often confused or just blank. Some maynot remember having root treatment; the dentist justspent a long time fiddling with the tooth!

The history should be taken slowly, with pauses forwriting in the notes; this helps the patient relax andlets further information come to his mind.

Evaluation of Dental Pain

Of all the aspects of history taking, this is the onewhere a systematic approach is essential. The patientin pain can often be rambling and disjointed. Thedentist must have a clear plan in mind and must bringthe patient back to it by firm questioning.

The following questions are important:

� Where is the pain, e.g. tooth, gum, face, ear?� Does it change position, i.e. radiate elsewhere?� Describe the pain, e.g. throbbing, sharp, dull.� How long has the pain been there?� How strong is it?� How long does it last?� What brings it on?� What takes it away?� Does it come at any particular time day or night?� How often does it occur?� Is it getting worse or getting better?� Are there any associated symptoms, e.g. swelling,

bad taste?

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6 I. The Patient

Frequency of attack

Pain

inte

nsi

ty (

analo

gue)

10

9

8

7

6

5

4

3

2

1

Durationof attack

Stimulationand timing

Intensityof attack

Relievingfactor

Fig. 2.1 Schematic characterisation of pain. The diagram shows the initiation of the pain, the frequency of the pain, itsintensity, its duration and the effect of any relieving factors.

It can be useful to have the patient scale the intensityof the pain from 1 to 10 and give some pictorial rep-resentation of the intensity, duration and frequencyof each attack (Fig. 2.1).

Do not lead the patient; questions should bephrased so that a positive reply, rather than a plain‘yes’ or ‘no’, is required.

The description of the pain will lead to certain pro-visional diagnoses and also allow the exclusion ofothers.

Pulpal disorders

The correlation of symptoms with actual pulp state isvery poor. It is possible for several grades of pathologyto be present within the same pulp. For instance, asingle pulp could have an area of necrosis, an area ofchronic pulpitis and an area of acute pulpitis (Chapter6), but it would almost certainly be the acute pulpitisthat provoked the painful symptoms.

So bearing in mind the pitfalls of the precise diag-nosis, the following generalisations about symptomscan be made.

Physiological responseThe pulp will respond to extremes of temperaturethrough a sound crown, but the pain will be transientand stop as soon as the stimulus is removed.

When dentine is exposed by caries, trauma or sim-ply gingival recession, then saliva and acid or alkaliions will reach the odontoblastic processes. The dis-turbance of the neutral pH will cause symptoms, usu-ally of a transient and mild nature.

Temperature changes may stimulate pain, eitherwhen larger areas of cervical dentine are exposed orwhen caries has spread well into the tooth. However,the pain stops when the stimulus is removed, thoughin dentine hypersensitivity, the pain can be quite un-pleasant.

Once toxins or bacteria reach the pulp, the symp-toms become more severe.

Acute pulpitisThe symptoms are classically an intense throbbingpain, initiated by heat, sometimes relieved by cold,well localised to one tooth, though sometimes radiat-ing to the ear from the lower molar region. The pa-tient is kept awake at night, and standard analgesicsare not very effective. It is usually episodic, with in-creasing frequency and intensity of each episode, untilit becomes continuous. It stops when the pulp dies oris removed.

Chronic pulpitis/slow dying(moribund) pulpThis condition often produces no symptoms, but maygive rise to vague, dull and diffuse pain along a

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2. History and Examination 7

quadrant; i.e. it is poorly localised. Examination willoften reveal several teeth with deep restorations, anyone of which could be the cause.

Apical infectionChronic apical infection is usually symptomless –hence the need for continued radiographic review ofroot-treated teeth. Acute apical periodontitis usuallycreates an intense throbbing pain, not affected by tem-perature, fairly continuous, worse at night and initi-ated or made worse by biting or knocking the tooth. Itis usually well localised, and percussing the teeth fordiagnostic purposes is unnecessary (and cruel!). Rou-tine analgesics are not very successful and the paingoes immediately the pressure within the bone is re-lieved, usually when the infection has caused perfo-ration of the cortical plate followed by a soft tissueabscess, or sinus formation. If pressure builds again inthe soft tissues, then a throbbing pain is again likely,but not as intense as that produced by the rigidly con-fined infection.

In the latter case, swelling will be an accompanyingcomplaint.

Periodontal diseaseGeneral acute conditions will give rise to generalisedsoreness of the mouth with perhaps ‘bleeding gums’,a ‘bad taste’ and ‘painful eating’ as accompanyingsymptoms.

Local conditions, such as pericoronitis or a lateralperiodontal abscess, will cause more localised painand soreness, particularly on eating.

Chronic periodontal disease is usually painless, butsymptoms of bleeding or a bad taste are good indica-tors. Mild acute exacerbations sometimes occur as aresult of occlusal trauma, and these cause vague dif-fuse pain, similar to the moribund pulp.

Temporomandibular dysfunction andother facial painThis is discussed in more detail in Chapter 28, but theclinician must be careful not to place the difficult diag-nostic pain problem into this category for want of anybetter ideas! Remember that the most common causeof pain around the jaws arises from pathology of thepulp and the periodontal ligament (odontogenic pain)and these must be investigated first.

Derangements and inflammation of the temporo-mandibular joint can lead to pain that is localised tothe joint area, sometimes felt within the external au-ditory meatus, and often accompanied by clicking orcrepitus in the joint.

The more common symptoms arise from the mus-cles of mastication and give rise to facial pain andheadaches. The pain is usually in the area of the af-fected muscles, though occasionally retro-orbital painis described. The character of the pain is typical of allacute muscular problems – soreness, tenderness, diffi-culty with movement, and sometimes a clear startingpoint is remembered, such as a wide yawn, removalof wisdom teeth, etc.

Pain described outside the muscle areas may not befrom temporomandibular dysfunction; for instance,the maxillary antrum sometimes produces overlap-ping anterior pain.

The most classic pain picture is that of trigeminalneuralgia, with its trigger zone and paroxysms of in-tense pain. However, this character can be modifiedinto atypical facial pain that may be trigeminal inorigin, psychotic or due to central nervous system le-sions. Pain that crosses the midline is often psychoticin origin.

However, in all these cases, the purely dental causesmust be eliminated first.

Diagnosis of pain – summary

Obtain a full description of the pain; this will un-doubtedly lead to an incomplete provisional diagno-sis. However, an open mind is important until afterthe clinical examination, so beware of early categori-sation of pain.

Caries tends to affect several teeth in the samemouth, and so these teeth could exhibit differentstages of the pathology. Symptoms of each could co-exist in the same quadrant, and confuse the pain pic-ture completely. Here, each facet of the symptomsneeds to be dissected out, and analysed separately.

Medical History

Information about the patient’s general health is es-sential for the planning of his dental care. Some med-ical conditions will influence the component itemsof a treatment plan or change its whole direction,whilst others will influence the way in which ‘nor-mally’ planned care is delivered. This is discussed indetail in Chapter 4.

Past and present disease experience should be ques-tioned together with information about current drugtherapy. A structured series of questions is the mostreliable way of taking a medical history (Table 2.1),but the questioner must be careful not to miss

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8 I. The Patient

Table 2.1 Medical history taking

Have you suffered from:

� any serious disease?

� any heart or chest trouble?

� rheumatic fever, chorea, growing pains?

� pneumonia or bronchitis?

� jaundice, hepatitis?

Do you have:

� bleeding disorders?

� diabetes?

� epilepsy?

Have you ever had a blood transfusion?

Have you ever given blood, or been turned down as a donor?

Are you allergic to any drugs, antibiotics or any other

substances?

Have you ever taken penicillin, and were you alright after?

Have you ever been in hospital or had any operations?

Are you taking any tablets or medicines at the moment

(beware anticoagulants, steroids, drug abusers)?

Do you smoke or drink alcohol?

Have you been ill recently or consulted your doctor?

anything because the patient misunderstands ormishears the questions. The series of questions willneed to be expanded if particular problems areevident from the history. For example, if the patientcomplains of soreness or ulceration of the mouththen questioning on possible causative or modifyingfactors must be explored. If there is any doubt aboutthe patient’s general health, it will be necessary tocontact their general medical practitioner for infor-mation, particularly to ascertain whether the patientis suitable for the delivery of dental care withoutproblems.

Previous Experience of Dentistry

The patient’s previous experience will condition himto expect certain things of dentistry in general. Thesecould be good or bad. His attitude in turn is con-veyed to the dentist, who may respond by tailor-ing the treatment plan to his perceptions of theattitude.

The patient may have high aspirations based on hisprevious experience, or vice versa. The dentist willjudge the extent of the previous experience and maybe influenced to continue the same basic pattern.

The important aspects to question are:

� Range of treatment experience� Method of delivery of care, e.g. sedation� Experience of analgesia/anaesthesia� Prostheses: age, comfort, function� General satisfaction with previous care� Any particular problems

The answers will indicate any special needs, such asnon-adrenaline containing local analgesic, use of se-dation and so on.

The patient’s opinion of his dentures will helpthe decision about possible replacement or relining(Chapter 24).

A patient dissatisfied with his previous care couldcontinue to be dissatisfied, even if the new dentist pro-vides the best care possible. Unfortunately, dentistryand plastic surgery attract perfection seekers!

Family and Social History

The general home and work environment may dictatehow easy or difficult it might be to carry out oralhygiene procedures or maintain a non-cariogenic diet.The home might also contain entrenched attitudes todental care.

Work patterns – shiftwork, absences from home –or young children, may reduce the ability to attendfor prolonged courses of treatment.

Anxiety and emotional problems can be initia-tors of stress-related facial pain and muscle disorders(Chapter 28).

History Taking – Summary

The efficiency of history taking will be related to theconfidence of the patient in the listening powers of hisdentist and the ability of both to communicate witheach other.

History taking should not be a rigid system ofchecklists, though there must be a consistent basisfor the dentist’s questions. The programme of ques-tioning must be flexible and adapted towards the in-dividual patient – it is his story.

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Clinical Examination

The clinical examination must establish the status ofthe oral tissues as a basis for diagnosis and treatment.It is important to observe and record health as well asdisease, and to be as accurate as possible when doingit. These observations must be part of a continuing ex-ercise that should be performed briefly at every visit,particularly over long courses of treatment – nothingremains static!

Comprehensive, sequential, up-to-date and easilyread records are necessary to assess the progress ofconditions, particularly when a preventive approachis being used, e.g. application of fluoride to earlyenamel caries. A brief scan of the records should re-inform the dentist of the patient’s background at eachvisit. Many minutes spent thumbing back over oldentries is wasteful, so updated summary sheets areessential.

Reviewing the summary sheets will provide thebackground for each visit and the decisions to bemade as problems occur.

The examination begins as soon as the patient en-ters the surgery. How mobile is he, is he breathless,flushed? Does he look fit and alert? Does he ap-pear nervous or apprehensive? This series of obser-vations may give clues about the patient’s attitudeto treatment, motivation or an underlying medicalcondition.

An immediate extra-oral examination may be in-dicated if there is a facial swelling or if the patient

has complained about tenderness in muscles or joints.However, in restorative dentistry, in contrast to oralsurgery, all the important signs will be in the mouth.For example, routine palpation of lymph nodes is notuseful when in many cases these may be enlarged fromtrivial facial infections.

Intra-oral examination should commence with aquick, general assessment of the condition of themouth which will indicate the context in which thedentist will have to work. Is it clean and well main-tained? Or are there large areas of plaque, open cari-ous lesions and failed restorations?

Then turn to the area of the main complaint, if thepatient has one. Certainly if there is pain, then someform of stabilisation will be necessary that could beprevented if time is taken for a full examination first(Chapter 3).

Soft tissues should be examined, looking at theirshape, integrity and colour. Look for swellings, ulcer-ation, inflammation of all areas from the lips back tothe fauces and pharynx.

The Basic Periodontal Examination (BPE) is an im-portant and simple screening examination. (It wasknown as the Community Periodontal Index of Treat-ment Needs – CPITN.) The periodontium is exam-ined with a World Health Organisation CPITN probeto determine pocket depth, bleeding response and todetect calculus. The probe is light with a ball tipof 0.5 mm diameter that is designed to detect sub-gingival calculus without penetrating the floor of thepocket (Fig. 2.2).

(a) (b)

Fig. 2.2 The BPE examination: (a) the profile of the probe; (b) the probe inserted into a gingival crevice.

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10 I. The Patient

Table 2.2 The Basic Periodontal Examination

Score Tissue assessment Probe appearance

0 Health

1 Bleeding on probing

only

The black band on the

probe does not enter

the pocket

2 Plaque retentive factor,

e.g. calculus/restoration

overhang

3 Pocket 3.5–5.5 mm The black band enters

the pocket and is partly

visible

4 Pocket >5.5 mm The black band

disappears in the

pocket

– No teeth present in the

sextant

In addition to these scores, the symbol * should be added tothe sextant score when there are clinical abnormalities suchas furcation involvement, mobility, mucogingival problemsor recession extending to the black area of the probe (3.5mm or greater).

The mouth is divided into sextants, the gingivalcrevice of each tooth is examined in at least foursites and the worst clinical finding in that sextant isrecorded as the code for that sextant.

If the probing depth is more than 3 mm and theprobing is accompanied by bleeding, this would indi-cate periodontitis. The findings and clinical implica-tions are shown in Table 2.2. Whilst this is a usefuland easy system, it is limited in terms of overall treat-ment planning. It certainly records signs of existingpathology but the treatment plan can only be com-pleted when the diagnosis is qualified by considera-tion of modifying factors. This is discussed in detailin Chapter 13.

Observations of plaque deposits may be recordedon a chart which is a useful baseline against which tojudge success of oral hygiene procedures.

These observations may be summarised as an oralhygiene index. There are several oral hygiene or de-bris indices, but the simplest is that of Greene andVermillion, which uses six teeth, an upper and lowermolar on opposite sides, an upper and lower premo-

lar on opposite sides and an upper and lower incisoron opposite sides. Both lingual and buccal surfacesare scored by:

0 = no plaque present1 = plaque present on cervical third2 = plaque present on both cervical third and middle

third3 = plaque present on whole surface

The index is the total scored divided by the numberof surfaces examined.

The examination of the teeth for caries and restora-tion defects should be done after a thorough prophy-laxis to remove stains and debris which would oth-erwise obscure observation. A dry field and a goodlight are traditionally necessary, but a probe shouldonly be used with caution.

The probe should not be used to test a ‘stickyfissure’ since the application of pressure will sim-ply break it down further. Occlusal caries shouldbe diagnosed principally by appearance – darknessunderlying the cuspal slopes – aided in the deeper le-sions by radiography (see later). Additionally, trans-illumination is useful for unrestored teeth, and thistechnique can also reveal cracks in the enamel.

The margins of existing restorations are difficultto examine, particularly approximal, without usinga probe, because such areas cannot be seen clearlyand may be obscured by the restoration on radio-graphs. The probe must be used gently, though, toavoid creating a defect that did not exist previously(Fig. 2.3).

Fig. 2.3 Recurrent caries around the distobuccal marginof the amalgam restoration in 5|. This is shown by thefracture of the enamel margin and the white zone aroundthe buccocervical corner.

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The recording of caries and restorations is based onthe use of the dental chart, which can easily becomea static record. It is valuable as a record of the teethand the planned restorations at the beginning of treat-ment, but as work proceeds, it becomes out of date.Periodic re-charting should be done so that there isnot just a chart of the teeth some years ago, when thepatient joined the practice, with line upon line of re-stored holes at each course of treatment, but a singlecurrent chart.

Detailed examination of the periodontium re-quires observation of gingival shape, size, texture andcolour, and also crevice depth. Several indices havebeen developed for the assessment of the periodon-tium including measurement of plaque accumulation,gingival health, pocket depth, bleeding and treatmentrequirements.

Examination of the occlusion is discussed in detailin Chapter 14, but briefly, arch form, missing teethand their effects, restoration of the occlusion by den-tures, crowns and bridges should be assessed. Cen-tric occlusion, centric relation and lateral and protru-sive movements should be observed and noted, andwhere appropriate, a diagnostic articulated mountingshould be used.

Special Investigations

Pulp sensitivity (vitality) testing

An indication of the condition of the pulp is of greatdiagnostic value, but the methods available fall veryfar short of the absolute. Most methods rely on nervestimulation by electricity, thermal change or mechan-ical interference, but really the vitality of a pulp de-pends on its blood supply, which cannot be testedeasily. Hence the change of term to pulp sensitivitywhich is the response elicited by testing.

Complications also arise because of the varyingstate of the tissues in a single diseased pulp. Multi-rooted teeth can have one root containing healthypulp, and the other containing necrotic debris – a falsepositive could be recorded. Pus or inflammatory exu-date in the root canal can conduct electricity and thisis another reason for a false positive result.

False negative results can occur because the pulpis insulated by much secondary dentine, or where theenamel is unable to transmit the stimulus because ofits thickness or its proximity to large restorations.

Teeth restored with insulating materials, such asceramics or polymers, are also difficult to test.

Electric pulp testing passes a low current at highpotential through the tooth. The current must havea square wave form because it must pass throughenamel and dentine, which are relatively poor con-ductors, and reach the other side at sufficient poten-tial to stimulate the nerves of the pulp.

Unfortunately, numbers are ascribed to the pa-tient’s response, and this gives the test more apparentscientific validity than it actually possesses. It really issubjective with a yes or a no as the response. The pa-tient’s expectation of the test influences the result, par-ticularly if the sensation from the first, control toothis very painful. A pre-emptive response is very likelyin the subsequent tests.

Because false positive and false negative results arepossible with electric pulp testing it should be comple-mented with thermal tests to increase the informationavailable. Ice sticks, or ice crystals made by evapo-rating ethyl chloride from a large pledget of cottonwool, can be used but the amount of ice applied mustbe substantial to create sufficient temperature differ-ential to affect the pulp. Because the tooth crown is agood heat sink, a small pledget of cotton wool withice crystals may have no effect.

Hot gutta-percha or impression compound shouldbe applied to a lubricated tooth surface to contrastwith the cold results. Interestingly, the effect of heatis often less than that of cold since the temperaturedifference is larger when dropping from 37 to 0◦C,compared to the rise from 37 to about 65◦C.

The most reliable pulp test is the test cavity, andthis can be done quite simply by starting a cavity inthe tooth under test without local analgesia havingexplained the purpose of this to the patient; the dentiststops as soon as there is a response.

Non-operative pulp tests must be interpreted withcaution, but they produce one more piece of the di-agnostic jigsaw to be placed alongside the clinical ex-amination and the radiographic findings.

Blood tests

The oral tissues may be the first to reflect systemic dis-ease and a full cell count and haemoglobin estimationmay be indicated in cases of abnormal gingival inflam-mation to exclude blood dyscrasias such as leukaemiaor anaemia.

Patients on anticoagulant therapy may require aninternational normalised ratio (INR) estimation priorto dental treatment that carries a risk of bleeding. Pro-cedures such as scaling and polishing, root planing,infiltration analgesia and single extractions may be

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12 I. The Patient

done with an INR less than 4. Inferior dental blocksand multiple extractions carry the most risk and theINR level needs to be less than 2.5 for these. Changesto anticoagulant therapy should be done in consulta-tion with the responsible physician. This, of course,requires support from the local hospital, and if thisis not forthcoming, the treatment plan would have tobe modified accordingly.

Radiography

Radiographs are essential for proper diagnosis andtreatment planning in restorative dentistry.

Three views are important: the orthopantomogram(OPT/OPG), the bitewing and the periapical. The in-formation they provide is as follows.

OPT

� General but imprecise scan of the teeth and jaws� Buried teeth, roots and cysts� Apical infection (sometimes)� Existence of root fillings� Temporomandibular joint (sometimes)

Bitewing

� Caries: approximal and occlusal� Depth of restorations� Restoration integrity� Interdental bone height� Pulp chamber morphology

Periapical

� Apical infection� Integrity of root fillings and posts� Interdental bone� Root fractures and perforations� Resorption� Root canal morphology

The OPT has some value as a scan for new patientswho have had considerable dentistry; patients oftencannot say what type of treatment has been per-formed. However, the value of a repeat OPT at anytime must be questioned. As will be discussed below,there are radiographs that give a better definition withlower exposure of the patient to ionising radiation. Ifthe posterior region of the body of the mandible needsto be seen, then a lateral oblique film will provide abetter image.

Fig. 2.4 Part of an OPT showing an apparent apicalradiolucency on |1. Root canal therapy was started on thebasis of this film.

Only structures in the OPT focal corridor will be infocus and there may not be sufficient definition for thediagnosis of caries or for the accurate estimation ofinterdental bone height. In some areas, there may bemasking of the root apices by overlapping structures,and occasionally apparent apical radiolucencies maybe seen, which are just artefacts. Overlap of the ver-tebral column in the midline is a particular problem.

In addition, because of variable image densitiesand the angulation of the beam in certain areas, dra-matic misdiagnoses are possible. Figure 2.4 showspart of an OPT that shows a very precise radiolucency,apparently associated with the lower left centralincisor.

Based on this film only, and without a vitalitytest, root canal therapy was started. The tooth waspainful! An apical film was then ordered (Fig. 2.5),which suggests that the radiolucency is more asso-ciated with the lateral incisor than the central. Thelateral incisor was vital to pulp testing.

The radiolucency is not ‘right’ for an apical area –it is round, not merging smoothly with periodontalspace and is higher than it should be. A surgical explo-ration was undertaken and the radiolucency turnedout to be a lateral periodontal cyst.

Clearly then, bitewing and the periapical films arerequired to investigate OPT observations and to showprecise detail.

It must be remembered that the radiograph is a two-dimensional picture of a three-dimensional entity andis dependent on mineral densities for its image. Thedepth of a carious lesion can be underestimated by asmuch as a third on a bitewing, and pulp horns can besuperimposed on the caries, whereas they are actuallyin a different plane.

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Fig. 2.5 Apical film of the suspicious area in Fig. 2.4. Theradiolucency is centred on the |2, not arising from the apexand turned out to be a lateral periodontal cyst.

Root concavities, particularly in the approximalcervical areas, maybe shown as apparent areas ofdemineralisation – ‘burn out’ (Fig. 2.6).

Angulation is critical for both films when assessingrestoration integrity. Unless the X-ray beam is pre-cisely aligned along a cervical margin, the restorationwill obscure the margin and appear sound (Fig. 2.7).The periapical film taken using a film holder andbeam-aiming device provides an image with mini-

Fig. 2.6 A periapical radiograph of 76| showing cervicalradiolucencies (arrowed) mesially on 8| and distally on 7|that are artefacts caused by the curvature of the teeth.Contrast these with the more clearly defined recurrentcaries under the distal margin of 6|.

mal distortion which is not the case if the bisect-ing angle technique is used. Bitewing films pro-vide good definition of the crowns of the posteriorteeth.

All radiographic findings should be confirmedwherever possible by repeating the clinical examina-tion with the films alongside. Thus cervical overhangsor apparent approximal caries should be confirmedby gentle probing.

Summary sheets for radiographs taken and theirfindings should be an integral part of the notes, al-lowing easy reference and review.

(a) (b)

Fig. 2.7 (a) Periapical film of |45 taken using the bisecting angle technique showing a bridge retainer with apparently goodadaptation at the distal margin; (b) bitewing film with its different angulation reveals a deficiency of the distal margin.

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14 I. The Patient

Of course, it almost goes without saying, that thequality of radiographs – both in the taking and in the

History and Examination – Summary

The meticulous collection and collation of all the information provided by the history, clinical examination,special tests and radiographs should provide the basis for the diagnosis and the treatment plan, and thecontinuing care of the patient. There can never be enough information, but be careful about guessingor taking things for granted. With clinical experience this might be acceptable, but for precision, theinformation must be accumulated carefully and as fully as possible.

processing – has to be of the highest order for accurateconclusions to be made.

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Chapter 3Diagnosis and Stabilisation

The diagnosis is the key to proper treatment planning and therefore of primary importance in the care ofpatients. In many simple conditions it is too easy to jump from examining the mouth to items of operativetreatment. This avoids the discipline of:

� Diagnosis first� Treatment plan second

Without this discipline, the management of the complex case becomes impossible. Decide what is wrongfirst before you decide what to do about it!

The diagnosis is the summation and conclusionsdrawn from the assembly of all the separate pieces ofinformation gathered from the patient’s story, clinicalobservations, special tests and radiography (Fig. 3.1).It is an intellectual jigsaw puzzle that is completed as alist of pathological conditions and simple restorativedisorders. Each piece of the jigsaw must be placed inits correct position to make the diagnosis (Fig. 3.2).However, in distinction from the conventional jigsawpuzzle there is no picture on a box for guidance andthe incorrect interpretation of one or more pieces cancreate the wrong picture (Fig. 3.3).

The aetiology of each condition should also be es-tablished so that this can be eliminated, if appropri-ate, to prevent recurrence of the problem.

In some cases, it will be necessary to carry outsome operative investigation, either to confirm aprovisional diagnosis or to determine the actualdiagnosis.

For example, a deep carious lesion will usually needto be opened and investigated to reveal its extent, andto detect the presence of a pulpal exposure. Planningthe restoration of such a tooth before investigationwould be premature.

Stabilisation is a series of procedures that is de-signed to control actively progressing pathologyrapidly, to achieve:

� Pain relief� Arrest of tissue destruction� Final diagnosis� The basis to plan the definitive management

The operative phase is instituted immediately,sometimes before the history and examination hasbeen completed, so that no time is wasted in reliev-ing symptoms. The treatment should be planned tobe completed as quickly as possible and the proce-dures will be short and sharp, e.g. pulp extirpation,extraction.

Diagnosis

Caries

Some conditions are obvious; cavitation of the enamelcoupled with a brown base and whitened edges usu-ally means caries. Indeed, the jump from what is seento the diagnosis is so rapid that the intermediate list-ing of physical signs is somewhat superfluous.

However, the aetiological factors may not be ob-vious. Is this one of many sites of primary caries, oran isolated recurrent carious lesion around a failingrestoration? Is this the middle-aged onset of cervicalcaries with its problems of rapid spread, or just fis-sure caries, which in some population groups wouldhardly qualify for a raised eyebrow?

So the caries rate is important, and the Decayed,Missing and Filled (DMF) score helps reflect this. Butalso the number of active lesions must be consideredas an indication of the severity of the current pathol-ogy. Diet analysis would be appropriate for many pa-tients with a high active caries rate, in order to deter-mine the aetiology.

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16 I. The Patient

Investigation

Confirmeddiagnosis

Stabilisation

Provisionaldiagnosis

History Examination Special tests Radiography

Fig. 3.1 The route to a confirmed diagnosis.

Fig. 3.2 The diagnostic jigsaw correctly completed.

If it is an isolated recurrent lesion, this could bethe result of operator error, and, if so, this must notbe repeated on replacement of the restoration. Was itincorrectly sited margins, poorly finished enamel orthe abuse of a matrix band? How deep has the cariesspread around the restoration? Does the radiographhelp, or is the lesion masked by the radio-opacity ofthe amalgam? Only removal of the restoration andthe caries will answer this.

Restorations

The faults that can be diagnosed with long-standingrestorations are numerous. There could be corrosion,ditching and fracture of amalgam, or discoloura-tion, marginal staining and surface loss of compos-ite. There could be the technical faults of cervical

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3. Diagnosis and Stabilisation 17

Fig. 3.3 An incorrect assembly of the pieces will lead misidentification of the diagnosis.

overhangs, negative edges, incorrect occlusion, poorshade matching and perforations.

Having identified the fault, however, there is onevery important question to be answered – ‘Has thefault induced any pathology?’ The reason for thequestion is that some faults are just minor techni-cal errors or normal material behaviour, and to re-place restorations purely for these reasons would bewrong.

Where pathology is associated with the fault, thenclearly something must be done. Figure 3.4a showsditched and corroded amalgams, which are techni-cally less than pleasing, but in the absence of a pos-itive diagnosis of associated pathology, they shouldnot be replaced. Contrast them with that in Figs. 3.4band c, with its suspicious fracture line and underlyingcaries.

Pulpal disorders

The history, pulp tests and radiography (Chapter 2)would have given some information about thepossible state of the pulp. A deep carious lesion withno response to hot and cold, and electric pulp test-ing, together with apical radiolucency on radiograph,would lead to a certain diagnosis of pulp necrosis andapical periodontitis.

However, what about the painless deep lesion withan ambivalent pulp testing response and normal api-cal anatomy on radiograph? Here it would be ap-propriate to make a provisional diagnosis of chronicpulpitis to be confirmed or refuted by operative in-vestigation.

Episodes of intense pain, localised to one tooth,with the pain lasting after the initiating stimulus

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18 I. The Patient

(a)

(c)

(b)

Fig. 3.4 (a) Ditched and corroded amalgams, but still satisfactory restorations. (b) A ditched and corroded occluso-palatalamalgam, but with a central fracture in it. This is much more suspicious. (c) Removal of the amalgam revealed deep caries intwo sites occlusally, together with a mesial lesion. The bitewing of this tooth (6|), Fig. 10.12, was not very helpful.

has been removed, with normal apical radiographicappearance would suggest acute pulpitis.

Apical conditions

The diagnosis usually relies on the radiographic ap-pearance of a radiolucent area at the root apex. Fordifferential diagnostic purposes, a negative responseto pulp testing is necessary to eliminate neoplasia,such as cementoma, overlying fissural cysts or sim-

ply an anatomical structure, such as a foramen. If thetooth in question is already root filled, the diagnosiscan be more difficult. Here, any symptoms and thehistory of the tooth would be important. Where thetooth is symptomless, an apical area may not bepathological, and serial radiographs are necessary todifferentiate between a healing lesion and progressingpathology (Fig. 3.5). A static area may indicate heal-ing by fibrous tissue without calcification that wouldnot be infected.

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(a) (b)

Fig. 3.5 (a) Periapicalradiograph of |2 immediatelyafter apicectomy and retrograderoot filling; (b) complete apicalin-fill. This took 2 years and thedecreasing area shown on filmstaken in the meantime must bedistinguished from apicalpathology.

If the history is not clear then the dentist is left tofall back upon his skill in radiographic interpretation.Figure 3.6a shows a central incisor that was apicected18 months previously. The referring dentist thoughtthat this was a recurrence of infection but there wereno symptoms. The periodontal space should be tracedaround the tooth; does the radiolucency have its ori-gins there? Does it blend with the space? Can the

periodontal space be seen ‘through’ the radiolucency;i.e. is there superimposition? The circular shape ofthe radiolucency should raise suspicion that it is aforamen. The second film (Fig. 3.6b) confirms that itis the incisive canal.

If there are symptoms, and pain on percussion, thenacute apical periodontitis is the diagnosis. A ‘silent’apical area coupled with a negative pulp test will be

(a) (b)

Fig. 3.6 The incisive canalmasquerading as an apical area:(a) Radiolucency associated witha retrograde root filling;(b) second film at a differentangulation reveals the true natureof the radiolucency.

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20 I. The Patient

chronic apical periodontitis, an apical granuloma oran apical cyst. The differential diagnosis between agranuloma and a cyst relies essentially on biopsy, asclinical and radiographic features do not distinguishthem from each other.

Periodontal disease

The complaint of ‘bleeding gums’, the signs of red-dened gingival margins with slight enlargement andbleeding on probing with no pocket formation leadsto the conclusion of the almost ubiquitous chronicmarginal gingivitis.

But the severity of this, together with the amountof plaque and debris present, must accompany the di-agnosis. Is there hyperplasia present as well, or justenlargement due to inflammatory oedema? Is the aeti-ology just poor oral hygiene, or are there other localfactors such as faulty restoration margins that pre-vent the patient cleaning efficiently? Could there besystemic disorders, such as blood dyscrasias, presentthat modify the tissue response to the plaque?

Where soreness and even pain accompany theredness and bleeding, then an acute gingivitis may bepresent.

A plaque index is essential to accompany the diag-nosis. Simple disclosing and the scoring of the ex-tent of plaque coverage as described in Chapter 2provides a good baseline against which to judge im-provements.

The presence of a pathologically deepened gingivalcrevice, a pocket, accompanied by bleeding on prob-ing indicates chronic marginal periodontitis. Radio-graphs, particularly bitewings, may reveal vertical orhorizontal bone loss caused by the inflammation. Ver-tical bone loss leads to the diagnosis of an infra-bonypocket (Fig. 3.7).

Occlusal disorders

Impacted and malpositioned teeth are obvious diag-noses here. But also, the signs of occlusal derange-ment following tooth loss should be diagnosed. Theseare tilting, drifting and over-eruption of the adjacentteeth into the space, which, in turn, may bring pathol-ogy such as caries of approximal root surfaces, andperiodontal disease from food impaction and plaqueaccumulation (Chapter 18).

The inefficient restoration of the occlusion by den-tures or crowns and bridges should be diagnosed, andthe effects of occlusal interferences noted (Chapter 8).

Fig. 3.7 Radiograph showing an infra-bony pocketdistally at 7|.

Investigation of Provisional Diagnoses

The need for investigation in relation to the diagno-sis of pulpal disorders has already been mentioned,but perhaps the most dramatic area where consid-erable investigation is necessary is the diagnosis offacial pain. Detailed descriptions of the various con-ditions is outside the scope of this book, but there isa considerable overlap of the symptoms of caries andpulpitis, and those of sinusitis, temporomandibulardysfunction, trigeminal neuralgia and atypical facialpain.

It is so important to remember that the most com-mon cause of pain around the lower face and jaws ispathology of the teeth and periodontium.

The dying or moribund pulp can produce the quiteatypical symptoms of diffuse pain, unrelated to anystimulus, and radiating to areas served by the trigem-inal nerve of the same side. The pulp will often becovered by a large, radio-opaque restoration, quiteimpervious to X-rays, and impossible to examine bynon-invasive vitality tests. Worse still, because of thenature of caries, several of these restorations mayexist together.

It is essential that all these restorations are inves-tigated thoroughly, before a committed diagnosis ismade. It is very embarrassing to relieve long-standingfacial pain by the extraction of a non-vital tooth,when the patient has been taking tegretol for severalmonths!

After careful clinical examination, pulp tests andradiographs, the next step is to remove individualrestorations. Clinical experience will tend to suggest

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which teeth look suspicious, and which could beinnocent.

The restoration removal can be started without lo-cal analgesia as a very reliable mechanical pulp test.Explain the purpose of this to the patient, and thatan analgesic will be given as soon as any pain is felt.Inspect the pulpal aspects of the cavity carefully, andif no exposure is found and the tooth is vital, place asedative dressing. If, on the other hand, an exposureis present then several different lines of treatment willbe possible. These are discussed in Chapter 11.

Stabilisation

Caries

Figures 3.8a and b illustrate a case of so-called acutecaries. There is caries in most teeth, with some ex-tensive loss of dentine. It would be quite wrong toapproach the definitive restoration of |6 first, find acarious exposure, root fill it, and then construct apinned core and a full veneer crown. Whilst this wasbeing done, the caries in the other teeth would bespreading ever onwards. So stabilisation of the cariesin the whole mouth is required.

The actual plan must be based on an overall assess-ment of the patient’s expectations and the restorativepossibilities. The extent of the caries does not reflectkeen dental awareness! However, education is possi-ble, if interest is there.

First of all, make an estimate of how many teethcould be restored simply, how many would requireroot canal therapy and how many would requirecrowns. Present this estimate and the implications of

time and effort to the patient, and await the reaction.A keen, motivated reaction would suggest opening,investigating and dressing all the lesions, stabilisingthe pulp as appropriate (see later) and extracting onlythose that turn out to be absolutely unrestorable.

A disinterested reaction, on the other hand, wouldlead to extraction of those teeth whose prognosis wasnot assured after simple restoration – i.e. those withdeep lesions.

Acute pulpal and apical conditions

The most rapid and effective way of treating these is toextract the tooth. The pulp is removed, and drainageof an apical abscess is very clearly established by thisprocedure. However, if conservation of the tooth isindicated and root canal therapy is possible and itis restorable after such therapy, then rather differentmeans must be used.

Acute pulpitisThis should be stabilised by pulp extirpation. How-ever, this may not be straightforward, since localanalgesia may be sometimes difficult to achieve. Thisdifficulty may be related to the persistence of the painstimulus altering the nerve impulse conduction andmaking blocking by analgesic more difficult.

The first approach is to repeat the local analgesic in-jection, but use a different agent. For instance, if xylo-caine was given first, repeat with prilocaine. The twoagents potentiate each other. If this does not work,apply a topical corticosteroid paste to the exposeddentine. This will reduce inflammation and ease pain,and in 48 hours or so the patient should return foranother attempt under local.

(a) (b)

Fig. 3.8 (a) and (b) Bitewing radiographs showing extensive caries which requires stabilisation before definitive treatment isprovided. There is deep primary caries in 7|67, recurrent caries cervically in 76| and early lesions in almost all the otherteeth.

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22 I. The Patient

Failing all these, the pulp will have to be extirpatedunder a general anaesthetic.

Ideally, the pulp should be extirpated from the fulllength of the root canal, so that remnants are not leftbehind to continue the pain. However, a diagnosticradiograph is necessary to assure this, and the dura-tion of analgesia may not be long enough to allow it.

If only partial extirpation has been achieved, applya topical corticosteroid as a root canal dressing andcomplete the extirpation at the preparation stage.

Total extirpation should be followed by root canaldressing with calcium hydroxide in propylene glycol.

Apical periodontitis and apical abscessThis diagnosis presumes pulp necrosis and the pres-ence of infection or leakage of toxins beyond theroot apex. The canal must be cleared of debris anddrainage established for the apical exudate, whoseaccumulation causes the pain.

If an abscess has formed, then cutting an endodon-tic access cavity will be rewarded by pus leaking fromthe tooth. Pain relief can be instantaneous. If no pusor exudate appears, then a barbed broach should beused, well short of the apex, to clear any obstruction.If drainage is still not achieved, then passage of a fine(No 8) file through the apical foramen must be con-sidered. This diameter will establish drainage, but willnot create the later difficulties in root filling caused bylarger apical perforations.

The use of local analgesic should be cautious inthe presence of acute inflammation. Restriction of theblood supply to the area could result in spread of theinfection. Also, the analgesic may not be effective.

It is better to use an air turbine as much as possibleto reduce vibration, and support the tooth, perhapswith a composition splint at the same time. Use aconventional speed handpiece to break the final half-millimetre or so of dentine overlying the pulp.

If an abscess has pointed in the sulcus, this shouldbe incised. Hot salt water mouthwashes should beused to apply heat to the alveolus and drainage shouldbe maintained by the patient sucking the tooth to keepthe access clear.

Systemic antibioticsThese should be restricted to cases where systemicinvolvement is apparent, i.e. raised temperature,malaise, tender regional lymph nodes, or there issome medical indication. In these circumstances, twohigh doses of oral amoxycillin are very effective; 3 Gimmediately and 2 G 24 hours later. Systemic antibi-otics should be avoided wherever possible for local‘mechanical’ problems where the bacteria are within

a root canal and sheltered from the blood and phago-cytosis.

ReviewOpen drainage through the root canal should be re-stricted to 24–48 hours. After this, more will go up thecanal, than will come down. To complete the stabili-sation, the canal must be fully prepared (Chapter 12).The reason for this is that the walls of the root canalwill be infected (in contra-distinction to the acute pul-pitis case) and simply irrigating and sealing the canalwill not remove the infection.

Traumatic injuries to the teeth

The immediate objective is the relief of pain and theprocedure required will depend upon the site of anyfracture and the state of the pulp. The pulp, however,can be concussed by a blow and may not providea pulp test response for some weeks. Therefore, im-mediate stabilisation must be followed by review fordefinitive diagnosis and management.

A complete history is essential in case of future lit-igation regarding the cause of the accident. All teethin the area of the trauma should be pulp tested andradiographed, and if there are any soft tissue lacera-tions and missing tooth fragments, the tissues shouldbe radiographed also.

Where there is any doubt on the whereabouts offragments, the possibility of facial fractures or anygeneral injury, the patient should be referred to thelocal casualty department for complete investigation.

The treatment schemes for traumatised teeth aresummarised below but for more detailed considera-tion the reader is referred to a specialised text.

Enamel-only fractureSmall fracture areas can be simply smoothed, whilstlarger defects, which may affect aesthetics or function,should be restored with acid-etch-retained composite.The teeth should be reviewed in 4–6 weeks and thepulp tests and radiographs repeated. Negative pulptests may indicate that root canal therapy is necessary.

Enamel/dentine fractureSuperficialThe tooth should be dressed with zinc oxide/eugenolcement in a temporary crown to aid pulp recovery.The crown must allow access to enamel for later pulptesting. If vital at review, then an acid-etch-retainedcomposite restoration should be placed. Non-vitalitywould probably indicate root canal therapy.

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DeepThis should be treated as if there was a pulp exposure.

Enamel/dentine/pulp fractures and deepenamel/dentine fracturesWith these the pulp is unlikely to recover and themanagement depends on whether the root apex hasclosed or is still open.

Root formation completeConventional root canal therapy is indicated plussemi-permanent restoration of the crown, usually bycomposite. A post crown should be avoided if at allpossible, especially for young patients playing contactsports.

Root apex openRoot formation should be encouraged to finish. If thepulp is vital, pulpotomy is used to remove the coronalpulp, leaving radicular pulp to continue root forma-tion.

If the pulp is non-vital, the canal should be care-fully filed short of the apex, and filled with calciumhydroxide in propylene glycol. This material createsconditions favourable for root formation.

In both cases, when the apex has closed, the canalshould be root filled.

If the apex does not close, then root canal ther-apy should be done – this is technically difficult(Chapter 12).

Root fracturesApical thirdIf symptomless and vital, leave and review. Otherwise,root fill to the fracture line and review. Remove theapical fragment if there is evidence of pathology.

Middle thirdIf the coronal fragment is mobile, it should be splintedto the adjacent teeth. In the absence of symptoms orpathology, it may be possible to place a post throughboth fragments to increase stability. If the fragmentsare not in line, this will not be possible, and the toothshould be root filled to the fracture line and reviewed.The fragment may need to be removed and it is pos-sible to use a long post extending into the bone asan implant to increase the stability of the crown. Theprognosis for the middle third root fracture is poor.

Coronal thirdThe prognosis depends on the extent to whichthe fracture goes beyond the epithelial attachment,

usually palatally. A very oblique fracture will bedifficult to restore, and the tooth should be ex-tracted.

A more shallow fracture would indicate root fillingand the provision of a cast post and diaphragm to pre-vent root splitting later. The immediate stabilisation isto extirpate the pulp and provide a temporary crown.The easiest way to do the crown is to use the toothfragment and to acid etch it to the adjacent teeth, overthe sealed root access.

Dislocation and avulsion

The dislocated tooth can be repositioned and splintedfor about a week. Pulp recovery is unlikely and theroot canal treatment should be done whilst the splintis in place.

The avulsed tooth can be replanted, but the successof this depends on the length of time it has been outof the mouth and how it was stored during that time.Milk is probably the best storage medium, though aparent could keep the tooth in their own buccal sulcusto be kept moist by saliva.

Before replanting, the tooth should be washed innormal saline, but no other cleaning should be done.Splint the tooth in place and carry out root canal ther-apy whilst the splint is on. It is unwise to leave the rootcanal empty.

Calcium hydroxide has been shown to inhibit ex-ternal resorption, and this can be left in the canalfor some time, with periodic replacement. The splintshould be removed after a week.

ReviewA traumatised tooth will require regular review by ra-diography, and if vital at the outset, pulp tests. Slowdentine formation can be induced by trauma, lead-ing to the obliteration of the canal and difficult rootcanal therapy. If this is seen, the tooth should be rootfilled immediately whilst it is still possible. Late lossof vitality is also possible.

The other main complication of trauma is root re-sorption, either internal or external. Internal resorp-tion is treated by removal of the pulp followed by rootfilling.

External resorption can sometimes be arrested bycalcium hydroxide being placed in the canal. Hy-droxyl ions diffuse to the outside of the root and raisethe pH there. This seems to inhibit cell activity. As asequel to the resorption, the periodontal ligament isreplaced by ankylosis of the tooth to bone, and thetooth can remain firm for many years even though it

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24 I. The Patient

Fig. 3.9 A re-implanted tooth showing externalresorption. The tooth was symptomless and firm, suggestingankylosis of the root.

has little root (Fig. 3.9). If infection supervenes, thetooth will require extraction.

Acute gingival conditions and severe chronicperiodontal disease

Acute gingival conditions should be treated bymouthwash and systemic antibiotics appropriate tothe causative organism.

Diagnosis and Stabilisation – Summary

� Draw conclusions from the history and examination – the diagnosis� If the data are inconclusive, make a provisional diagnosis� Investigate to confirm the diagnosis� Control active pathology as rapidly as possible� When stable, draft the definitive treatment plan

Fig. 3.10 Chronic marginal gingivitis associated withcrowns on 321|123. The crown margins must be correctedbefore the gingivae will resolve.

In the presence of severe chronic periodontal dis-ease, most restorative work will be impossible be-cause of gingival bleeding or exudate, or incorrectlevel of the gingival margin. Scaling and polishing,and instruction in oral hygiene are required first, fol-lowed by review. However, if the standard of the ex-isting restorations is contributing to plaque retention,then the faulty ones should be removed, and well-fitting provisionals placed, pending resolution of thegingival problems (Fig. 3.10).

Intracoronal cavities can be provisionally restoredwith polycarboxylate cement, placed with the aid of amatrix, or even amalgam. This will provide the bettergingival and contact area contour. Replacement of thetemporary amalgams should be done after resolutionof the soft tissue inflammation.

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Chapter 4General Principles of Treatment Planning

Whilst making a diagnosis is an intellectual challenge, the formulation of the treatment plan has to combineexperience, ability and common sense.

There is absolutely no use in compiling an elaborate and technically demanding series of procedures thatis inappropriate for this particular patient, with this particular pathology in these particular circumstances.

Once the diagnosis is made, there may be two or three equally ‘correct’ treatments for the condition.

Making the decision as to which is appropriate is the skill of treatment planning.

The Treatment Plan

The treatment plan is the basic blueprint for the de-livery of care. It combines priorities for therapy withthe organisation and management of that therapy. Itmust combine prevention of disease with the eradica-tion and repair of pathology.

The treatment plan must fit the profiles of both thepatient and the dentist (Fig. 4.1). As was discussed inChapter 1, the patient will have some ideas about hisdental future, and the dentist will have some resourcesand technical skills at his disposal to fulfil treatmentobjectives.

Basically, the resources available, governed bythe dentist and his techniques, should, through themedium of the treatment plan, match the resourceconsumption by the patient, governed by his expec-tations and his pathology.

Figure 4.2 projects the patient from diagnosis,through agreement and formal consent to the treat-ment and its delivery, to oral health and the very im-portant concept of continuing care.

To a large extent, the left side of Fig. 4.1 willbe dealt with in the succeeding chapters, and prob-lems created by the patient himself will be consideredhere.

The Patient’s Influence on TreatmentPlanning

Motivation, expectations and availability

These go hand in hand – a well-motivated patient willalmost always find a way to make himself availablefor treatment. A string of failed appointments beliesinitial protestations of interest and desire for treat-ment!

If there are doubts about the patient’s commitment,then this should be reflected in a cautious start tothe treatment plan. One or two visits to the hygienistfollowed by a short appointment with the dentist for asimple restoration and review of oral hygiene wouldbe appropriate. Provided active pathology has beenstabilised, then the weaker patient might well benefitfrom a repeated oral hygiene lesson, together with themessage that unless oral hygiene improves, restorativework will not be started. Certainly, this must be thecase prior to advanced restorations.

As was discussed earlier, the extraction of a toothmay fit a patient’s expectations more than attendancefor four or five visits for root canal therapy and acrown. It may be that the restorative treatment iswell within the dentist’s capabilities, but it will be

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26 I. The Patient

Treatment Plan

Dentist

AbilityTrainingFacilities

Materials and techniques

DurabilitySimplicity

Patient

NeedsAspirations

Mouth

Caries ratePeriodontal index

Level of care

Fig. 4.1 The factors influencing a treatment plan.

somewhat wasted if the patient looses interest afterthe first hour, when the root canals were being iden-tified. Of course, this is not to suggest that the dentistshould not try to educate and inform about restora-tive possibilities. It could be that the patient neverrealised the scope of modern dentistry. However, ini-tial enthusiasm must be maintained so that it is notjust the product of the dentist’s ambitions alone.

Confirmeddiagnosis

Availabilityof care

Acceptanceof care

PrioritiesManagement

Delivery of care

Treatment plan

Oral health

Continuing care

Fig. 4.2 The route to oral health and continuing care.

Consent to treatment

As has been mentioned, there may be several waysin which a particular pathology could be treatedor several methods for restoring or replacing teeth.Whilst the dentist might already have decided whattreatment to recommend, for the patient to provideinformed consent to treatment it is essential thathe is made aware of and understands all the pos-sible options that are available not only with thisdentist but elsewhere as well. The patient must re-ceive a full explanation of the advantages and dis-advantages of the treatment options and their likelyoutcome.

Apprehension

No one likes visiting the dentist, mainly in view of theprospect of minor surgery to a very tender area of theanatomy, but also because of the folklore surroundingthe profession.

The majority of those who actually come for treat-ment are able to control their apprehension success-fully, but a minority have tremendous difficulty. Of-ten, their apprehension stems from a single unpleas-ant experience, perhaps as a child, and frequently painfrom poor analgesia is remembered vividly. Many ofthese will respond to sympathetic listening, carefulexplanations about treatment, an unhurried, relaxedchairside manner and a great deal of patience – tenderloving care (TLC).

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4. General Principles of Treatment Planning 27

Simple procedures with complete analgesia shouldbe done first to establish confidence, and then morecomplex work may be possible. The more intractablecases may be candidates for:

� Oral sedation� Inhalation sedation� Intravenous sedation� General anaesthesia

Oral sedationThe use of a low dose of an anxiolytic drug may re-duce mild apprehension so that dental care can be de-livered normally. Diazepam is probably the most usedand 5–10 mg the night before the appointment andrepeated 1 hour before, having arranged the appoint-ment to be in the early morning, is a suitable dosage.However, this must only be a short-term measure; theuse of such drugs should be limited to the lowest pos-sible dose for the shortest possible time.

Inhalation sedationThis technique involves the administration of be-tween 20 and 40% nitrous oxide together with a min-imum of 30% oxygen. The level of nitrous oxide isset by observing the patient’s response. Appropriatetraining and facilities are required and these are listedin the national guidelines cited in the Bibliography.

The operator must encourage and reassure the pa-tient during induction and treatment. There is cer-tainly an element of hypnosis in the procedure. Localanalgesia must be used for painful procedures.

It is not possible to use inhalation sedation if thenasal airway is obstructed, the patient cannot liesupine or is in the first trimester of pregnancy.

Intravenous sedationA few patients are not able to respond to inhala-tion sedation, and for these the administration of asedative intravenously is usually successful. Modern,short-acting benzodiazepines, such as midazolam, arevery suitable for outpatient sedation. Midazolam hasa very short half-life and therefore a short recoveryperiod. It also induces amnesia, which can be veryhelpful.

The patient should not have eaten for 4–6 hoursbefore the sedation is begun, but may drink smallquantities after that. No alcohol should be taken,but regular medication should be taken as usual. Anyanxiolytics will probably reduce the dose of sedationrequired.

The patient should be supine and the drug shouldbe administered through an in-dwelling venous

cannula in the antecubital fossa, hand or forearm. Thedrug is injected slowly and carefully titrated againstthe patient’s response; oversedation particularly withthe elderly is a potential risk. Oximetry is essential todetect hypoxaemia that may result from respiratorydepression. Again the reader is referred to nationalguidelines for further information.

Communication is important as the patient will re-spond slowly to command. Local analgesia is alsonecessary. If the sedation becomes less, then a furtherincrement titrated against response should be given.

After the treatment is completed, recovery shouldbe observed and the patient can go home escorted,when he is lucid and capable of walking unaided.The patient must avoid driving, sport and alcohol for12 hours.

General anaesthesiaIntubated general anaesthesia in day stay facilitiesshould be reserved for those who cannot be treated inany other way. It may also be appropriate for stabilis-ing urgent cases who will subsequently have definitivetreatment under inhalation sedation.

It is really the last resort and is a compromise be-cause of the limited time available – say, about anhour – and the difficult working conditions of an op-erating theatre. Only very basic conservation shouldbe planned and any teeth of dubious prognosis shouldbe extracted.

The patient should be screened by urinalysisand blood pressure determination to ensure fitnessfor anaesthesia. Haemoglobin estimation and bloodcount has been discontinued by most anaesthetistsexcept where a general indication exists. The patientmust be starved and not have any acute respiratoryinfections. Patients with medical problems should beadmitted for observation before and after the anaes-thetic.

Care must be taken during treatment not to floodthe pharynx with water and to ensure that all piecesof tooth, amalgam, etc., are removed from the mouth.

The patient must be accompanied home and lookedafter for 24 hours. They should return for a normaloutpatient appointment for review and occlusal ad-justment of restorations, which is not possible in the-atre.

This review visit should also begin an acclimati-sation programme to help the patient accept normaldental care. Many patients dislike the experience somuch that they are very susceptible to conversion toless traumatic techniques.

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28 I. The Patient

Age

Age per se has a limited effect on treatment planning.The young patient with an immature dentition wouldprobably be unsuitable for conventional bridgeworkdue to large pulps and a developing gingival mar-gin. Playing contact sports would also hazard anteriorcrowns and bridges but such activity is not necessar-ily age related. Implants would be contra-indicatedbecause of continuing bone growth.

In the older patient it is the combination of agewith infirmity that limits the delivery of care. A fit70-year-old could well have the same treatment as a fit50-year-old. However, an unwell 50-year-old couldwell be more disadvantaged.

Having established this, there are changes in thedentition that will affect the incidence of certainpathologies and make some aspects of dental caremore difficult. These changes are discussed in Chap-ter 5. Gingival recession, a predisposition to rootcaries and sclerosis of root canals are all problemsthat may influence the technical aspects of restorativedentistry. These will be compounded if the patienthas already had a high experience of dental disease.It is more difficult to maintain an ageing dentition ofcomplex restorations than one with no restorationsat all!

An elderly patient may have more difficulty in per-forming oral hygiene procedures and this difficultycould be compounded by the presence of complexrestorations provided in the past. He might not beable to tolerate long periods in the dental chair forcomplex care and will certainly have more difficultyin adapting to dentures (Chapter 26).

The influence of medical history on treatmentplanning and management

The taking of the medical history and its importancewas outlined in Chapter 2. Medical conditions mayinfluence:

� The content of the treatment plan and/or� The way in which care is delivered

For example, some conditions may indicate the ex-traction of a tooth rather than its restoration, whilstothers may indicate that restorations, planned nor-mally, are carried out under special conditions.

Cardiovascular conditionsProbably the most confusion arises from the influ-ence of a history of rheumatic heart disease. Transient

bacteraemias may lead to bacteria colonising scarredareas of the endocardium, usually the valve edges,causing bacterial endocarditis. Bacteraemias occurevery day from chewing or defecation, and certaindental procedures may cause them.

The precise relationship between dental proceduresand the development of bacterial endocarditis is stillthe subject of considerable debate. There are manypatients who have had no antibiotic cover for manyyears of dentistry, including extractions, with no ap-parent ill effects.

The reader is advised to follow the nationallyagreed recommendations which are to provide an-tibiotic cover for susceptible patients for dental pro-cedures that carry a high risk of major bacteraemia.These procedures are:

� Extractions� Scaling and polishing, pocket probing, root plan-

ing� Surgery involving the gingival margin

There is currently no incontrovertible evidence thatendodontic procedures are incriminated in the aeti-ology of endocarditis, though care must be taken toremain within the confines of the root canal. (This istrue for all root canal therapy, anyway.) Suggestionsthat minor procedures, such as pulp extirpation, gin-gival retraction or placing a matrix band, are incrim-inated in the aetiology have been made. The support-ing evidence for this is patchy and the provision ofan appropriate antibiotic regime for multiple visitsfor routine dentistry is difficult. Such suggestions willencourage the continued misuse of antibiotics. In allcases, the gingival margins should be cleaned with anantiseptic, such as chlorhexidine prior to treatment.

The definition of the susceptible patient is more dif-ficult. Not all patients who give a history of rheumaticfever will have scarred endocardia, revealed by thepresence of a murmur. To prescribe antibiotics forthese patients would appear to be wasteful, if not afurther misuse of antibiotics. It is safer to request anopinion from a medical practitioner, preferably a car-diologist, as to whether cover is indicated.

Other cases where cover is definitely indicated arepatients with:

� A previous history of endocarditis� A prosthetic heart valve� Congenital cardiac defects

These patients are at a high risk from endocarditis.The regime for prophylaxis is based on the degree

of risk and any recent therapy with antibiotics. The

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current recommendations will be found in the BritishNational Formulary (BNF).

All patients in the at-risk groups should be in-formed of the need to maintain good oral hygiene andthose patients who are candidates for cardiac surgeryshould be well restored first.

Treatment planningThe healthy patient with a history of rheumatic fevershould be treatment planned as normal. The higherrisk patient, particularly if there is a history of endo-carditis, should be planned more radically, becausethe risks that are much higher. A tooth requiring apossibly difficult root filling should be extracted, andany areas of chronic infection should be regarded withsuspicion, and the teeth not given the benefit of thedoubt.

Other cardiovascular conditions may make pro-longed courses of treatment risky or difficult. Thisgroup includes stroke and cardiac infarction. Full re-covery from such an episode, of course, should bringno problems, though the dentist ought to be preparedfor a recurrence in the chair and revise his manage-ment of collapse.

For those patients with incomplete recovery, treat-ment should be planned to be simple, and providedin short appointments. Blood pressure measurementbefore, during and after treatment is useful for theassessment of patient stability. The trauma from ex-traction should be avoided if at all possible.

Stroke patients with residual paralysis may needadvice on oral hygiene aids, such as electric tooth-brushes, to assist them. It will be sometimes necessaryto train the patient’s carer to perform oral hygieneprocedures.

Blood-borne viruses and the preventionof cross-infectionThe two most important blood-borne viruses in den-tistry are hepatitis B virus (HBV) and human immun-odeficiency virus (HIV).

Patients who are ill with hepatitis B or AIDS shouldreceive dental treatment under hospital conditions.Those people who are known to be infectious, butare well, may be treated in normal dental practiceand should be treatment planned as ‘normal’.

Many carriers are unidentified, and these aretreated unknowingly as normal patients. These andthe known ones constitute a combined hazard to thedentist and his staff, and to the patients followingthem in the surgery. The basic routine for the pre-vention of cross-infection should be applied to all

patients – universal precautions – and the recommen-dations are referred to in the Bibliography.

In brief, the key recommendations are:

� Protection of the operator and close-support den-tal nurse by gloves, masks and glasses or visors

� Decontamination and sterilisation of all instru-ments and equipment that have touched the pa-tient or have been handled by ‘contaminated’ staff

� Use of single-use equipment wherever possible� Use of precise surgery routines to avoid contami-

nating areas, such as inside drawers or the stock oftemporary crowns, that will be difficult to steriliselater

� Clean contaminated surgery surfaces and protectthem by using tray systems, towels and cling film

� Decontaminate items such as impressions beforethey are sent to the laboratory

� Decontaminate laboratory work before it reachesthe chairside

Other medical conditionsGeneral infirmity or terminal illness would indicate aminimum of complex work being attempted. The planshould be to stabilise sources of pain and discomfortas simply as possible.

Blood dyscrasias and diabetes may give rise to gin-gival problems because of the reduced resistance toinfection and these will preclude anything but sta-bilisation being carried out. The medical conditionshould be resolved prior to definitive conservation.

The operator would wish to conserve teeth wher-ever possible in epileptics to avoid dentures, inhaemophiliacs to avoid extractions, and in cases withirradiated bone where post-extraction healing can beprolonged and difficult.

It is important to see patients before radiotherapy,whenever possible, to remove any teeth of dubiousprognosis. There should be no exposed bone in themouth prior to radiotherapy. After radiotherapy thedentist may have a role in advising on the care andmanagement of mucositis, xerostomia and radiation-induced caries.

The management of xerostomia will involve adviceon the elimination of anything that impairs saliva-tion, such as alcohol consumption and smoking, useof sugar-free chewing gum and use of saliva substi-tutes containing fluoride.

Altered management of a normal treatment planwould be appropriate for a controlled diabetic, wheretreatment is best carried out immediately after a mealwhen the blood sugar is higher.

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30 I. The Patient

Patients having orthopaedic joint prostheses or in-dwelling catheters do not require antibiotic prophy-laxis for dental treatment, provided there is no otherindication for prophylaxis.

Restorative dentistry for pregnant patients requiressome minor modifications. The generally held viewis that invasive procedures are best avoided in thefirst and third trimesters, and radiography avoidedtotally throughout. However, where urgent treatmentincluding radiography is required, this should be donein any event. It is also important to complete treat-ment and reach stability in the second trimester, sothat treatment is not required later when the pa-tient will be uncomfortable, or immediately afterthe baby is born, when the mother will have otherpriorities.

Level of previous care

The well-restored and cared-for mouth encouragesmore of the same. It indicates the patient’s desire forcontinuing care and his ability to maintain restora-tions in plaque-free and caries-free conditions.

Unfortunately, the quality of the previous restora-tive care, rather than its volume, can also modify atreatment plan. If the restorative work has not beenprovided to a high standard then, even though thepatient has been a regular attender, the sheer volumeof replacement work required may inhibit a totallyrestorative approach (Fig. 4.3).

Fig. 4.3 Orthopantomogram of a patient who hasexperienced extensive restorative dentistry. There is nowgross caries and periodontal disease. The chances ofsuccess for future work are small, and, in any case, thevolume of work required is daunting. The patient wastreatment planned for a clearance and full dentures.

Several missing teeth and a partial denture mightwell lead to extraction of a difficult restorative prob-lem and its addition to the denture.

Oral hygiene and periodontal disease

A high active caries rate may dictate extractions andsimple restorations only, and generalised periodontaldisease might indicate the same. Oral hygiene mustbe effective before advanced restorations are con-templated and the use of fluoride and chlorhexidinemouthwashes or gels may be of assistance.

Occlusion

Evidence of deterioration in occlusal relationshipsfollowing tooth loss would indicate bridges or par-tial dentures (Section IV). Inadequate occlusion onbridges or dentures might indicate their replacement.

Radiographic findings

The major use of radiography is in diagnosis (Chap-ter 2). However, it is absolutely essential in the plan-ning of endodontics. The presence of patent rootcanals, absence of obstruction by secondary dentine,pulp stones or curvature can only be decided by goodradiographs.

Having diagnosed acute pulpitis clinically, the ra-diograph will lead the planner to contemplate rootcanal therapy, or to recommend extraction. It mightbe very desirable to save the tooth, but it might betechnically impossible.

The General Structure of a Treatment Plan

Priorities

The simple treatment plan designed to treat chronicgingivitis, caries and failed restorations would be-gin by preparing the supporting tissues for restora-tive work – scaling and polishing, and preventing therecurrence of gingivitis – instruction in oral hygiene.This phase is better carried out by the dental hygienistor therapist, leaving the dentist free to perform morecomplex functions.

The priorities for simple restorations would relateto size, doing the largest first, unless the periodon-tium was being influenced by a poor contact area oroverhanging margin.

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Oral hygiene should be reviewed continually dur-ing treatment with encouragement, or further re-minders if necessary. If advanced work – crowns orendodontics – is planned, this should be placed at theend of the plan after gingival resolution and the com-pletion of simple restorations. Oral hygiene reviewshould also be satisfactory.

Extractions are best regarded within the frame-work of stabilisation, since the affected teeth couldgive rise to pain whilst other work is being done.Also, there is the possibility of damaging new restora-tions during surgery, particularly of impacted teeth.If the patient is to be referred for oral surgery, thenthis should be arranged early, but almost certainly thework will not be carried out until after the generalpractitioner has completed other treatment. At thetime the referral is made, it is important to includeinformation on proposed treatment of other teeth,so that the referring practitioner’s responsibilities areestablished.

Any surgery involving the gingival margin, e.g.apicectomy, should be done well in advance of crownsor veneers proposed for the affected teeth.

Partial denture planning should be built-in along-side the planning of restorations since the design mayrequire rest seats, or specially modified crowns.

Structure

A schematic arrangement for a treatment plan couldbe:

1 Prepare supporting tissues – scale and polish2 Preventive measures – topical fluoride, fissure

sealing, oral hygiene instruction, dietary advice3 Design bridges or partial dentures4 Large intracoronal restorations5 Simple restorations6 Root canal therapy7 Review oral hygiene and periodontal condition8 Periodontal therapy, if necessary – root planing,

surgery9 Crowns

10 Construct dentures/bridges11 Recall and continuing care

Review and Recall

The simple treatment plan has within its structure thereview of oral hygiene procedures, but some other

procedures would require formal review prior toprogress in treatment.

For example, apical surgery should not be followedimmediately by crowns on the affected teeth. Two orthree months should elapse whilst the gingival tissuesstabilise and the margins reach a constant level, andan indication of apical healing is apparent.

Extractions and alveolar remodelling should be fol-lowed by review, perhaps 6 months later, before per-manent bridges are considered.

The listing of a formal recall as part of thetreatment plan is essential to indicate the respon-sibility for continuing care. The actual recall inter-val can be decided as appropriate to the patient’scondition.

It is essential to perform a risk assessment andassessment of prognosis. What is the likelihood offurther pathology or a failed restoration in the next3 months, 6 months, 1 year or 2 years? When will it benecessary to see the patient again to monitor plaquecontrol and caries status, and to check for other oralpathology?

Patients with poor plaque control and periodontaldisease might be seen at 3-monthly intervals. Youngpatients with active caries might be seen at 6-monthlyintervals. Older and well-maintained patients withgood oral hygiene could be left to their own devicesfor as long as 2 years. A conscious decision must bemade that involves the patient’s understanding of theissues.

However, it must be remembered that risk canchange with a patient moving from a low-risk gradeto a higher one. Diet changes, such as starting to usesugar in hot drinks, will upset any previous risk as-sessment.

Radiographic review of crowns and endodonticsis essential. Symptomless loss of vitality under acrown preparation must be detected by the apicalcondition changing. Progressing healing of an api-cal lesion following root canal therapy should bemonitored. Symptomless crowns, endodontics andbridge retainers should have periapical films takenat about 1 year after treatment and 4-yearly afterthat.

Teeth with symptoms or signs of continuing pathol-ogy will need to be radiographed more frequently.

Again this is based on a risk assessment andthe likely diagnostic yield of the radiograph, bal-ancing the risks caused by the ionising radiationagainst the information that may be gleaned from thefilm.

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32 I. The Patient

Treatment Planning – Summary

1 Decide on items for prevention and treatment2 Order these according to priority in the patient as a whole3 Consider the treatment methods that are appropriate:

� for this patient� at this time� in this practice� with this dentist

4 Review oral hygiene and prevention5 Recall to commit the patient to continuing care

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Section IIThe Restoration and Its

Environment


34


Chapter 5Applied Biology of the Teeth

The techniques for the restoration of tooth structure require a detailed knowledge of the tissues againstwhich the material is to be placed. The purpose of this chapter is to describe the hard tissues of the humantooth and their relationship with their environment. The implications for restorative dentistry of enamel anddentine structure and pulp physiology are discussed.

Introduction

Caries is a microbially initiated disease causing lo-calised destruction of mineralised tissues in the body,including bone. For the purpose of this book onlycaries of the teeth will be considered and the signsof presence of the disease will be described as thelocalised destruction of enamel, dentine and morebriefly, of cementum. As is the case with other patho-logical conditions, a clear understanding dependsupon a knowledge of the basic structure of the tis-sues involved.

Enamel Structure and Chemistry

Enamel is the outer protective covering of the crownof the tooth and is an extremely hard, brittle, white,shiny substance. It is composed basically of billionsof crystals of hydroxyapatite that are roughly octago-nal in cross section with a diameter of about 360 nm.The length of the crystals has proved difficult to de-termine but they are thought to be long and ribbon-like, extending for some distance through the enamel.The crystals are tightly packed together so that or-ganic matrix lying between them is minimal, consti-tuting only about 2% by weight of the enamel butmuch more than this by volume. Between the crystalsare therefore micropores or pores, the size of whichcan be measured with some accuracy, and changes inthese spaces is one of the methods of indicating thepresence of carious attack. Under these conditions theenamel is said to have developed increased porosity.The methods available for such studies will be dis-cussed in Chapter 6.

Prisms

The crystals of enamel are not randomly arranged butare grouped together to form rods or prisms of mate-rial, extending from the enamel–dentine junction tothe surface of the tooth. In the original English litera-ture the preferred term is that of ‘prisms’ whereas inmore recent writings the term ‘rod’ is preferred andin fact induces a clearer image of the structure in themind of the reader. Because the remainder of this bookwill use the word ‘prism’, the old-fashioned term willbe used here.

Each prism has a mean cross-sectional diameter ofabout 5 μm but because the surface area of the outerenamel is greater than that of the enamel–dentinejunction the prisms tend to increase in diameter fromthe junction to the outer surface. The cross-sectionalshape of the prisms has been variously described asoctagonal to fish scale or keyhole shaped but this de-pends to some extent on the angle of section throughthe prisms. The keyhole concept is the classical con-struction in human enamel and is shown diagram-matically in Fig. 5.1. The broad part of the keyhole isoften referred to as the head and the narrow part asthe tail. There is controversy as to what constitutesthe boundary of each prism. Current research sug-gests that prism boundaries may be formed both bysudden changes in hydroxyapatite crystal orientationand by an increased concentration of organic matrix.

Matrix

The nature of the organic matrix has received muchattention but because of its small amount has proveddifficult to analyse with certainty. In the immaturetooth the matrix consists of two distinct proteins,amelogenin and enamelin, and during maturation

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36 II. The Restoration and Its Environment

Pulp

Pulp

Enamel rods (prisms)

Prism head

Crystallites

Prism tail

Perikymata

Incremental lines

Dentinal tubules

Odontoblast cell body

Predentine

Odontoblast process

Intertubular dentine Peritubular

dentine

Fig. 5.1 Schematic diagram of the structure of a tooth showing the main features of enamel and dentine.

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5. Applied Biology of the Teeth 37

much of the amelogenin is removed. The cells respon-sible for secreting and maturing the enamel during de-velopment are the ameloblasts and they migrate out-wards from the putative enamel–dentine junction fora distance equal to the thickness of the enamel at thatpoint on the tooth.

When the ameloblasts have completed their se-cretory activity, the final thickness of the enamel isdetermined and this cannot be altered throughout life,since the ameloblasts then degenerate. In principle,enamel is a dead tissue which cannot repair itself.However, we will see later that chemically speakingsome repair or re-structuring of enamel is possible.

Incremental nature

The enamel is laid down by the ameloblasts in in-crements, arranged rather like the layers in an onionover each cusp of the tooth. In cross section, theseappear as concentric rings through the enamel andare known as incremental lines or brown striae ofRetzius (Fig. 5.1). Each line represents the point thatthe ameloblasts had reached at a particular time intheir functional activity. The incremental line is notpigmented as the name brown striae would suggestbut is probably caused by a slight change in directionand diameter of the enamel prisms. These incrementallines reach the surface of the tooth at an acute angleand there is evidence that they modify the progressionof caries in the natural lesion.

Surface structure

Although the enamel prisms have been depicted as ex-tending from the junction out to the surface, in prac-tice this is often not the case. Many of the prisms incertain parts of the tooth and in certain teeth stopshort of the surface. The surface layers of the toothare therefore made up of aprismatic enamel thatmay have been produced because the activity of theameloblasts changes before they cease secretory activ-ity. Too little attention has been paid to this outer layeron the teeth and it is conceivable that it may be relatedto caries susceptibility and is certainly of importancewhen etching and bonding techniques are considered.

Ionic exchange

Once the teeth have erupted, ionic interchange is pos-sible between the crystals of the enamel and ions inthe surrounding environment. For example, the cal-cium ions may be exchanged for strontium and the

hydroxyl part of the molecule may be replaced byfluoride which appears to protect the tooth againstcarious attack. Epidemiological studies have shownthat newly erupted teeth may be more susceptible tocaries than teeth in more mature individuals, so thatgreat efforts are now made by restorative dentists toprevent so far as possible the commencement of car-ious attack which will become much less likely in theolder individual.

Morphology of Teeth

The overall shape and detailed morphology of theteeth varies considerably between teeth and evenwithin tooth types. Thus, the incisors are quite dif-ferent in shape to the canines, premolars and molarsand in different individuals premolars may themselvesvary somewhat in shape. These factors are importantin restorative dental procedures and should be studiedin greater depth in standard texts of tooth morphol-ogy. It is usual in current dental practice to distin-guish to some extent between restorative proceduresin deciduous teeth and permanent teeth and this is be-cause there are structural differences between them,the most important of which are the relative size ofthe teeth, the thickness of the enamel and underly-ing dentine, the relative size of the pulp chamberswhich are larger in deciduous teeth and the bulbosityof the enamel of deciduous teeth at the cervical mar-gin. However, there is evidence accruing recently thatthe structure of the enamel of deciduous and perma-nent teeth may differ and this may affect the rate ofprogression of caries. For instance, it has been shownusing microradiographic techniques that deciduousteeth are somewhat less well mineralised than theirpermanent counterparts. This may account for theirwhiter appearance since more porous enamel tendsto be less translucent so that the yellowness of theunderlying dentine does not show through so clearly.

Dentine Structure, Chemistry andSensitivity

Dentine

The bulk of the structure of the tooth, both crownand root, is made up of a less well mineralised butmore flexible tissue known as dentine. This also iscomposed of hydroxyapatite crystals but in a lessconcentrated form than in enamel. The majority of

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the crystals are arranged more or less parallel to theenamel–dentine junction but in the three-dimensionalsense are much more random than those in enamel.They are laid down in a matrix composed of gly-cosaminoglycans, in which have been laid downcollagen fibrils secreted by the odontoblast cells intheir movement inwards from the enamel–dentinejunction towards the future pulp. The matrix of den-tine therefore consists of a rather dense, rubberymaterial, the general shape of which is retained evenafter removal by acids of all of the mineral compo-nent. Whilst caries of enamel results in cavitation andloss of the material, at least initially in dentine a rub-bery, stained matrix may be retained for some time.

Odontoblast processes

As the odontoblasts migrate inwards from the junc-tion towards the pulp they leave behind them a cellprocess which becomes enclosed in a tubule incorpo-rated into the matrix. The dentine is therefore per-meated by millions of cell processes radiating outfrom the odontoblasts through the whole thicknessof the dentine at least in the younger tooth. Theseprocesses may have side communicating branches sothat a syncitium of cells is formed. When the dentinemineralises, crystals are laid down in the ground sub-stance and fibres of the matrix but are not laid downin the cell processes. In the mature dentine, there-fore, the cell processes are contained in mineralisedtubules running through the dentine. With increasingage these tubules narrow by the deposition of miner-alised material in their walls (intra-tubular dentine)and there is still disagreement as to whether maturedentine possesses viable cell processes throughout thelength of its tubules.

Dentinal tubules

Although these tubules radiate from the pulp tothe enamel–dentine junction, they do not travel instraight lines. In the longitudinal plane they tend tofollow a sigmoid curve from the outer dentine to-wards the pulp so that the cell body is placed moreapically than the periphery of the process (Fig. 5.1).This arrangement has some clinical significance whichwill be discussed later.

Mineralisation

Unlike enamel, dentine matrix does not mineralise assoon as it is produced. There is a delay between laying

down the matrix and its mineralisation in the formof calcospherites which finally coalesce to producea more or less homogeneously mineralised tissue. Insome parts of the tooth a failure in this fusion of cal-cospherites seems to occur. Firstly, in the coronal por-tion large non-mineralised, star-shaped spaces are leftin many teeth following an incremental line below theenamel–dentine junction. These defects are knownas interglobular spaces and the cell processes of theodontoblasts run straight through them. Their signif-icance in relation to spread of caries is not known. Atthe periphery of the root just below the cementum,much smaller defects in mineralisation are observed,known as the granular layer of Tomes. No clinicalsignificance has been ascribed to this structure.

Secondary dentine

As the odontoblasts migrate pulpally they lay downthe adult form of the tooth completing the root some21/2 to 31/2 years after eruption of the tooth. If theywere to continue at this rate of production of dentinethen clearly the pulp chamber would be obliteratedwithin a few years of establishment of the dentition.Once the mature outline of the tooth has been com-pleted the odontoblasts slow down and although con-tinuing to migrate inwards, do so at a rate enablingthe pulp chamber to survive into old age. The dentinelaid down in the initial stages of tooth developmentis known as primary dentine and that laid down af-ter the odontoblasts have slowed is known as regularsecondary dentine. As we will see in Chapter 6, theodontoblasts may change their rate of production ofdentine and its type under the influence of cariousattack.

Dentine sensitivity

In order to enable dentine to react in this mannerit must be responsive to outside stimulus and manypatients who have suffered cavity preparation underinadequate anaesthesia will testify that this is the case.The exact mechanism is still not clear, largely becausetechnical problems of fixation and examination of tis-sue remain unsolved. The pulp is well supplied bynerves, both non-medullated (controlling blood vesseltone) and medullated (capable of transmitting com-mon sensation and pain). These latter nerves haveendings in a plexus close to the odontoblast cell bod-ies and also have nerve endings on the cell bodiesthemselves. There is clear evidence that some of thesenerve fibres extend some distance into the dentine and

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have presumably been incorporated into it during itsformation. About 1 in 2000 tubules appear to containnerve fibres but only for quite short distances. It is in-teresting to consider that this so-called sparse innerva-tion is probably greater than that found in the finger-tips! As has been already stated, there is some doubtas to whether living odontoblastic cell processes ex-tend throughout the thickness of the dentine in themature tooth. If they do, then loss of enamel may re-sult in osmotic changes at the peripheral end of theprocesses, thus resulting in fluid exchange and distor-tion of the processes. This event may be transmittedalong the process and then converted by transductioninto nerve impulses either at the inner third of the pro-cesses themselves or at the cell body region. If the cellprocesses do not extend throughout the thickness ofthe dentine then it is conceivable that fluid balancechanges in the outer part of the tubules may initiatedistortion of the processes resulting in impulses even-tually to the nerve plexus.

Enamel–Dentine Junction

The junction between the enamel and the dentine lieson the original basement membrane separating theenamel organ on the outside from the papilla or meso-dermal tissue on the inside at an early stage of toothdevelopment. In most human teeth it is not a flat sheetbut is deformed into a crater-like appearance produc-ing on section the appearance of scallops. The con-cavities of these scallops face towards the enamel andthe convexities towards the dentine. That is to say theouter surface of the dentine, if the enamel were to beremoved, appears like the surface of the moon withirregularly shaped craters. The inner surface of theenamel is composed of convexities fitting into thesecraters. This has the effect of increasing the surfacearea between the two tissues. In some parts of the hu-man tooth, particularly near to the neck of the tooth,the enamel–dentine junction may be more or lessflat.

Smear Layer

During restorative procedures, removal of decayedenamel and dentine and extension of the cavity forprevention, retention and access may be carried outusing hand instruments such as chisels and hatchetsbut is more commonly done using rotary instrumentsof various types and speeds. Rotating instruments

may result in smearing of the crystal and organiccontent of both enamel and dentine over the cut sur-face. This smearing may be a purely physical effector may be engendered by heat at the point of cut-ting and grinding. Hand instruments, however sharp,may also cause heavy smearing on the enamel surfaceespecially on the floor of an approximal box. The clin-ical implications of the smear layer will be discussedlater.

The Pulp

The pulp and the dentine cannot be separated ei-ther anatomically or functionally. Anatomically, thecell bodies of the dentinal processes lie in the pe-ripheral region of the pulp and the odontoblast cellsand their processes are therefore intimately associatedboth with dentine and pulp tissue. Functionally, thereaction of both dentine and pulp to external stimuli isdependent upon both the cell processes and bodies ofthe odontoblasts and therefore reaction is a combinedfunction of both tissues. The three-dimensional shapeof the pulp chamber varies in different teeth. Thus, inan upper incisor the coronal part of the pulp cham-ber is somewhat flattened buccolingually and broadmesiodistally and the radicular portion of the pulpchamber is roughly triangular in shape and conicalin length. In multirooted teeth such as the molars theform of the pulp chamber is obviously much morecomplex. It is important for the restorative dentist toappreciate the general form of the pulp chamber ineach tooth type, although variations exist even be-tween teeth of similar notation. A standard text ontooth morphology will provide this information. Ithas already been stated that the relative size and shapeof pulp chambers in deciduous teeth is larger than thatin permanent teeth and therefore exposure of the pulpchamber is considered by many to be a greater hazardin deciduous dentitions.

The healthy pulp is of a jelly-like consistency havinga ground substance of glycosaminoglycans in whichis interspersed a loose and sparse network of collagenfibres. These collagen fibres are produced and main-tained by fibroblasts which are the commonest celltype in the healthy pulp. There are also macrophages,pluripotential histiocytes and occasional monocytes.There is a complicated vascular supply consisting ofarteries entering the apical foramen and dividing intoan extensive network of arterioles, particularly in theperipheral parts of the pulp. These arterioles connectdirectly with venules so that arterio-venous shunts

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exist. There is an extensive capillary plexus particu-larly in the region of the odontoblast cell bodies at theperiphery of the pulp. Although difficult to demon-strate, there is an adequate lymphatic drainage fromthe pulp and veins and lymphatics leave togetherthrough the apical foramina. Innervation of the pulphas already been discussed in relation to sensitivity ofthe dentine.

The Periodontium

The tooth is supported in its bony socket by a spe-cialised connective tissue – the periodontal ligament.At the cervical margin or neck of the tooth it is contin-uous with the connective tissue underlying the gingi-vae. At the apex, it is continuous with the tooth pulp.It bridges the gap between the root cementum andthe alveolar bone and is approximately 0.2 mm inwidth. It is composed of fibres in a gel-like groundsubstance that contains nerves, blood vessels andcells.

Fibres

Most of the fibres in the ligament are Type I collagen,although some Type II collagen and specialised oxy-talan and elastin fibres are present in small amounts.The collagen fibres are arranged in bundles which pur-sue a complex wavy course. At their cementum endthe bundles are smaller in diameter than at their alveo-lar bone end. They form branching networks aroundthe neurovascular bundles but no single fibre bun-dles appear to traverse the whole distance from toothto bone. The collagen bundles are incorporated intobone and cementum in the same way as are tendons,that is to say, in the form of mineralised Sharpey’sfibres. The fibre bundles are ‘crimped’ along theircourse and the fibre bundles overlap each other. Ithas been suggested that this allows response to load-ing under occlusal forces. The functional activity ofthe ligament will be described later. The fibre bun-dles are arranged in specific named groups associatedwith the gingival, crestal, radicular, apical and inter-radicular portions of the tooth. Their arrangement isshown diagrammatically in Fig. 5.2.

The oxytalan fibres lie parallel to the length of thetooth root and are attached to cementum at one end.They have been implicated in both tooth eruption andsupport and may be involved in support of blood ves-sels.

Ground substance

The major components are hyaluronic acid, glyco-proteins and proteoglycans. Hyaluronic acid and thepolysaccharide components of proteoglycans are gly-cosaminoglycans. Water content is about 70%.

Vasculature

The periodontal ligament is well supplied with bloodvessels that are mainly derived from the superior alve-olar branches of the maxillary artery or from the in-ferior alveolar artery in the mandible. There may beother sources deriving from the buccal, masseteric orlingual arteries in the mandible or from the palatalor facial arteries in the maxilla. The veins drain intolarger veins in the inter-alveolar bone and usually donot follow the route of the arteries. Within the liga-ment itself the blood supply is most extensive in thecervical part and least extensive in the middle third.Most of the vessels enter the ligament as perforatingarteries from the intra-bony vessels and they run par-allel to the long axis of the tooth, passing betweenthe principal fibre bundles of the ligament. Manybranches arise from these vessels and they form a cap-illary plexus that is more complex at the bone surfacethan at the cementum surface of the ligament. Thereappear to be arterio-venous shunts in the cervical partof the ligament and these resemble renal glomeruli.There is some evidence that in older patients, the vas-cularised spaces are larger and encroach upon areaspreviously occupied by fibres and bone.

The actual rate of blood flow has not yet been re-liably determined but is controlled by both α- andβ-adrenoreceptors, allowing both constriction anddilation of vessels.

There are lymphatics present, although not ingreat numbers, and they tend to follow the venousdrainage.

Nerves

These are derived from either the superior or inferiordental nerves. Some of the bundles of nerve fibres runfrom the apical region of the periodontium towardsthe cervical margin of the tooth. They are joined bynerves passing through foramina in the bone to en-ter the ligament horizontally. Large fibres are myeli-nated and terminate in specialised nerve endings thatare associated with mechanoreceptor activity. Thesemonitor forces on teeth and may be involved in re-flex jaw opening and masticatory control. Small fibres

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c

a

d

b

4

5

3

1

2

Fig. 5.2 Schematic diagram of the structure of the periodontium. Principal fibre groups: (1) alveolar crest, (2) horizontal,(3) oblique, (4) inter-radicular, (5) apical. Gingival ligament groups: (a) dentogingival, (b) dentoperiosteal,(c) alveogingival, (d) circular.

terminate as free nerve endings associated with ap-preciation of pain. Autonomic nerves are present andthey control regional blood flow in the ligament.

Cells

Most of the cells of the ligament are fibroblasts. Theyare responsible for the unusually high ‘turnover’ ratein this tissue resulting in the fibres being constantlysynthesised, removed and replaced. The fibroblastsare spindle shaped, large cells and they align them-selves along the length of the fibre bundles. Theyare able to both produce and remove collagen fibresso that diseases affecting their function can seriouslydamage the ligament.

Some of the epithelial cells (Hertwig’s sheath) re-sponsible for mapping out the shape of the tooth root

remain in the ligament as cell ‘rests’ and they may sub-sequently proliferate to produce periodontal cysts.

There are undifferentiated cells of mesodermal ori-gin and it is probable that they can differentiate intoany type of mesodermal cell in the ligament.

Since the ligament is bounded on the tooth surfaceby cementum and the outer surface by alveolar bone,there are cementoblasts and osteoblasts present. Boneremodels readily so that osteoclasts are seen in the lig-ament. Cementum is much more stable so that in adultteeth (but not deciduous) cementoclasts are rarelyseen.

Response to movement and load

Clearly, the ligament is responsible for the support ofthe teeth and attaches the tooth to the bone. There is

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still debate, however, as to how the ligament functionsduring normal physiological activities such as erup-tion or response to loading in an axial or tangentialdirection. It has been suggested that the ligament maycontract during eruption, that migration or contrac-tion of fibroblasts may occur, or that pressure may beexerted by vascular or fluid elements. The evidenceis complex and largely derived from experiments onrodent teeth. It seems that the vascular theories arethe most probable.

Mesial drift or movement of erupted teeth towardsthe mid-line has been attributed to activity in the peri-odontal tissues. At the present time there is conflictingevidence and physiological mesial movements in re-sponse to tooth loss or wear cannot be fully explained.

In respect of functional loading on the teeth there isalso controversy. The weight of evidence suggests thatthe ligament does not behave purely as a suspensoryligament but that it behaves in a viscoelastic manner.It is now thought that all the components act togetherlike a hydraulic shock absorber. In this case the fibres,ground substance, blood in the vessels and tissue flu-ids are all important. The system is very complex andis as yet imperfectly understood.

Age Changes in Teeth

It is sometimes difficult to distinguish betweenchanges occurring in tissues due to age and changesoccasioned usually in the older person because of in-creased exposure to external stimulation. This is par-ticularly so in the case of the hard tissues of the teeth.

Enamel

In the case of enamel, although it is in principle anon-reactive tissue, most of the changes that occur asage progresses are due to ionic exchange between theexternal environment and the tooth. These have beendescribed earlier. They may result in an enamel with aslightly changed refractive index so that the colour ofa person’s tooth may change somewhat with age, usu-ally becoming rather darker. The small but importantorganic content of the teeth, especially in relation tolamellae, may also take up staining as life progressescontributing to this change in colour. Because enamelis non-replaceable in bulk, certain parts of the toothtend to become worn as age progresses. Whilst nota true age change, this phenomenon of surface lossis often used by anthropologists to age individuals

although considerable information is required as tothe diet responsible for the wear pattern.

Dentine

In the case of dentine there do seem to be changesmore directly associated with age. There is evidencethat the amount of intra-tubular mineralisation in-creases with age and this occurs from the peripheryof the odontoblast tubules working inwards towardsthe pulp. The effect of this is to produce sclerotic den-tine where the refractive index and homogeneity ofthe tissue is more uniform. This phenomenon occursparticularly under regions of surface wear or caries inthe crown but is strikingly evident in the apical partof the tooth, spreading upwards from the apex to, inold age, two-thirds or more of the way along the root.On tooth section, this sclerotic dentine gives a trans-parent appearance to the root dentine and its extentprovides a standard method of ageing dead bodies inforensic investigations. Its clinical significance will bediscussed later.

The pulp

The pulp, although reducing in size as age progresses,may also change in consistency. It is reported that thefibrous content of the pulp increases relatively withage and there is evidence that the number of viableodontoblasts reduces.

Cementum

Cementum was a tissue of lesser interest to restorativedentists in the past but with the advent of interest inroot caries may assume a greater importance in thefuture. It is for this reason that the tissue structurehas not been discussed in detail. It has been reportedrecently that incremental lines in cementum may berelated to seasonal changes and therefore may be usedto age an individual. Whilst this seems a possibilityin hibernating animals, the prospect seems unlikely inthe human tooth.

The Microenvironment of the Tooth

When the tooth erupts into the mouth any cellularremnants on its surface are quickly lost. This bringsthe enamel surface in direct contact with the saliva,some of the proteins of which are instantaneously de-posited on the enamel surface.

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Saliva

Flow rates of saliva are at a maximum during masti-catory activity and there is also a diurnal rhythm. Itis not clear whether salivary flow rates are reducedto zero during sleep but they are certainly very low.Saliva contains anti-bacterial agents and is also ofsome importance in the initial digestion of food. Thisis brought about by its content of amylase. It is alsofunctionally necessary for the sense of taste since sub-stances can affect the taste buds only when in solu-tion. To the restorative dentist, apart from the phys-ical problems of dealing with it clinically, saliva islargely viewed as a protective medium for the teeth. Itcontains mucus mainly secreted by the submandibu-lar and sublingual glands and it is this mucus whichforms the protein coating on newly erupted teeth. It isa self-cleansing material since it washes the teeth fol-lowing meals and as already mentioned it has someanti-bacterial and possibly anti-viral activity (secre-tory IgA). Two features of saliva, however, are of greatinterest to the restorative dentist. Firstly, saliva is anexcellent buffer, largely due to its content of bicar-bonates and to some extent its proteins. A buffer isa substance which tends to prevent changes in pH.During mealtimes when perhaps acid substances areingested or when the products of breakdown of foodproduces acid, the buffers in saliva tend to neutralisethis acid. The increased flow of saliva at mealtimesproduces increased buffering activity. Secondly, salivais supersaturated with calcium and phosphate ions.It is therefore largely the source of ionic interchangebetween the microenvironment of the mouth and thetooth itself. Fluorides may be contained in saliva andmay be concentrated by plaque forming on the sur-face of teeth.

Dental plaque

Plaque is a bacterial deposit on the protein pellicle ofthe tooth and its ecology is complex and variable. Inmost people it consists of a basic bacterial flora of thestreptococcus mutans type perhaps along with lacto-bacilli. In older plaque, filamentous organisms of theactinomyces type become apparent. Many of theseorganisms, particularly streptococcus mutans, break-down refined carbohydrates producing extracellularglycans and large amounts of acid. As will be seenlater, the relationship of the numbers and types ofvarious micro-organisms to the prevalence of cariesis an extremely difficult problem and it must be re-membered that caries is a multifactorial disease and

studies of any one factor may be unrewarding. As anillustration of this point it is known that plaque onthe surface of teeth is capable of concentrating fluo-rides so that in an external environment of one partper million there may be eight to ten parts per mil-lion in the plaque. This concentration of fluoride maybe toxic to some bacteria, although there is evidencethat many bacteria combine the fluoride and remainmetabolically active. The suggestion has been madethat the presence of some young plaque capable ofconcentrating fluoride may be useful to the tooth sur-face in that interchange with the surface hydroxyap-atite crystals may be aided. Most clinicians, of course,would recommend removal of plaque, thereby deny-ing the production of low pH and the formation ofcarious lesions.

Restorative Implications

In our descriptions of enamel, dentine, saliva andplaque, the reader will have detected that the infor-mation is rarely academic but is necessary for a fullunderstanding of the process of carious attack and ofthe dentist’s ability to prevent or repair it. Importantaspects of basic dental science and clinical restorativedentistry will be emphasised by a few examples.

Enamel prisms

The reader will have appreciated that the detailedorientation of the enamel prisms is complex since itvaries in different parts of the tooth. In the cuspal re-gion the prisms follow a wavy and complex course,probably adding to the strength of this part of theenamel. In the cervical region they may slope towardsthe cervical margins and in deciduous teeth, may bemore horizontal in this part of the tooth.

Surface preparation

It is important that unsupported prisms are not leftsince these may be extremely friable and the restora-tive dentist seeks to ensure that the periphery of hispreparation lies along the general direction of theprisms. This produces maximum strength and reducesthe likelihood of future fracture at the periphery of hisrestoration. Clinical practice must be tempered withcommon sense and it is recognised by most restora-tive dentists that sometimes the load on a particu-lar part of a restoration part is minimal and it maynot be necessary to follow these guidelines. The same

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principles apply to the preparation of the surface ofa cavity and attempts are often made to avoid leav-ing loose enamel crystals present even though theseare invisible to the operator. Thus, some operatorsadvocate the cleaning and disinfection of a cavitybefore placing a restoration. It is probably less im-portant in relation to enamel than to dentine unlessbonding techniques are anticipated, in which case theprisms of the enamel must be exposed in order toproduce a good key for the bond. This latter con-sideration may be important not only in relation tofinishing cavity margins but in preparing surfacesof enamel where bonding to unprepared enamel isrequired.

Remineralisation

It will be clear from the description of enamel that inbiological terms it is a non-healing tissue. This is whymost approaches to dental caries in the past have beennot so much treatment as repair of an untreatable de-fect. This has now changed and it has become estab-lished that at least in the early stages of carious attackdemineralisation or increased pore spacing in enamelmay be repaired to some extent by removing the at-tacking medium and allowing the super-saturated na-ture of saliva to take its effect or if necessary by ap-plying super-saturated remineralisation solutions tothe early carious lesion. It is now well recognised thatcaries is not a continuous process but is a start–stopphenomenon. It seems logical to assume therefore thatthe condition in its early stages is reversible and thisfact forms the basis for most restorative, preventiveand early treatment regimes.

Saliva and plaque

The importance of saliva and its consequent plaqueformation on teeth has already been touched upon.Current opinion holds that removal of plaque by ad-equate oral hygiene procedures, especially during thefirst two decades of life, will prevent or markedly re-duce the prevalence of caries. Extensive restorativeprocedures are therefore contra-indicated in patientsunable to control their plaque formation and initiallythe prevention of caries in children and eventually themanagement of established caries in adults dependsas much upon oral hygiene procedures, diet and flu-oride application as upon excellent technical restora-tive procedures.

Secondary dentine

Odontoblastic processes in their tubules follow a sig-moid course as they traverse towards the pulp. This isespecially the case in the radicular part of the tooth.This means that the cell bodies associated with a par-ticular tubule are much more apically placed than thecarious attack at the periphery of the tubule. Any re-active secondary dentine will therefore not be devel-oped directly at the base of the cavity but will beplaced more apically. This is important to recognisesince the protective effect of secondary dentine dis-tancing the attack from the pulp is useful in the apicalportion of the cavity but exposure of the pulp is muchmore likely more cervically.

Progress of caries

The rate of progression of caries through enamel anddentine is not known with precision but it appears totake 3–4 years for an early lesion to progress throughenamel. It is then believed that the rate of progres-sion through dentine is much more rapid. Clinically,it is obvious that when the lesion reaches dentine itspreads laterally along the enamel–dentine junctionand this may be a reflection of the lower mineral con-tent of the dentine and also of the inter-connectinglateral processes of the odontoblastic processes. Theimportance clinically is that caries has to be followedlaterally at the enamel–dentine junction, thereby pro-ducing undermined enamel which will need to beremoved subsequently.

Dentine sensitivity

The question of reaction of dentine to external stim-uli is one of the most important factors in aiding thedentist in his control of carious attack. We have al-ready noted that progress of caries through dentine ismore rapid than through enamel but this is limited bythe fact that the dentine will react to attack produc-ing irregular secondary dentine, sometimes knownas tertiary dentine. Perhaps the interesting questionconcerning the sensitivity of dentine is not how it isbrought about but why it is necessary in the first place.Sensation in most parts of the body is a defence mech-anism, allowing the organism to withdraw from nox-ious stimuli. A patient cannot readily withdraw theteeth, although they might conceivably seek to placeunpleasant foods in another portion of the mouth.It may be that the sensitivity of dentine is concernedmore with trophic mechanisms controlling the health

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of the pulpal tissue and may be associated in someway with the response of the odontoblast and theirprocesses to outside stimuli. A major difference be-tween dentine and enamel is that the former is capableof responding to carious attack or wear or fracture ofthe tooth and has a potential for healing. This will

be discussed in greater depth in Chapter 6, but theliving nature of the odontoblastic processes, cell bod-ies of the odontoblasts and the continuing ability ofthe tissue to lay down pre-dentine mineralising intodentine, enables the tissue to respond to loss of toothsubstance by walling off the vulnerable pulp tissue.

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Chapter 6The Pathology of Caries and Pulpal Disorders

An understanding of the pathology of caries and the way it affects the pulp is fundamental to much ofrestorative dentistry. This chapter considers the scientific evidence associated with the aetiology of caries,the ways in which enamel and dentine are destroyed and the effects on the pulp. The clinical implicationsof these processes are discussed.

Introduction

Caries is essentially an attack on the mineralised tis-sues of the body, resulting in demineralisation andin some cases in destruction of the matrix. In prin-ciple, it may occur in all of the hard tissues includ-ing bone but for the purposes of this book discussionwill be restricted largely to enamel and dentine. In theyoung, healthy human the dentine of the tooth is en-tirely protected by enamel or by the gingivae and peri-odontal tissues in the root area. Caries therefore mustcommence at the enamel surface. In older individualswhere gingival recession and loss of periodontal andbone support have occurred the root of the tooth maybe exposed to the mouth and caries may then occurde novo on the cementum and dentine.

Factors Influencing Caries

The crown of the tooth is in a microenvironment ofits own, mainly that of the saliva, microbial depositsderived from the saliva and other sources, food de-bris and other dietary constituents. Whether cariescommences or not seems to depend upon the qual-ity of this environment, the ability of the tooth to re-sist demineralisation, immunological reactions by thehost and the length of time for which all these factorsare in operation. The disease therefore has been de-scribed as multifactorial and in some texts as many as50 factors have been described in relation to cariousattack. It is more profitable to group the factors intothree: firstly, those associated with the host includingthe quality of the saliva and the bacterial flora therein;secondly, outside factors associated with diet and thesubstrate on which these bacteria act and finally, the

tooth itself and those features which either predisposeto or resist carious attack (Fig. 6.1).

Host factors

When a tooth is developing within the alveolar pro-cess its enamel surface is protected by means of anorganic pellicle and cellular covering. As it erupts intothe oral cavity much of this protection is lost but im-mediately on contact with the saliva a secondary or-ganic pellicle is immediately laid on the enamel sur-face and it is to this that organisms within the oralcavity attach themselves.

Micro-organismsInitially most of the organisms are streptococcal innature, producing an immature plaque on the surfaceof the tooth. If this is allowed to be maintained, otherorganisms of filamentous nature such as actinomyceswill also be involved and the plaque is said to be ma-ture. The organisms colonising the plaque will dependupon those present in the oral cavity and may there-fore vary from individual to individual. However, ithas been shown that breast-fed children may acquirestreptococcus mutans from their mother so that inthis sense caries may be thought of as an infectiousdisease.

There has been a great deal of research to estab-lish the nature of organisms associated with den-tal caries, much of which lies outside the scope ofthis chapter. Some of this work has been carried outon gnotobiotic animals where it was shown that thedifference between animals which were caries activeand those which were caries resistant lay in the factthat the latter lacked particular micro-organisms. Inhuman enamel caries large numbers of organismshave been described on the enamel surface but in

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6. The Pathology of Caries and Pulpal Disorders 47

Toothsusceptibility

Hostsaliva

Oralflora

CariesDiet

substrate

Time

Fig. 6.1 Factors influencing the onsetand spread of dental caries. Microbialbreakdown products of dietarycomponents may produce an adverselocal environment that, if operative forsufficient time, may result in caries in asusceptible tooth.

caries-susceptible individuals it seems that the mostobvious organisms are lactobacilli and streptococ-cus mutans. In older plaques, actinomyces species arepresent but most studies have not implicated theseparticularly in the development of the early lesion. Inthe case of root caries the most commonly isolatedorganisms are of the actinomyces type followed bylactobacillae, Streptococcus mutans and Streptococ-cus sanguis.

SalivaNot only is the saliva responsible for the microenvi-ronment of plaque organisms but is also in itself im-portant in the development of early carious lesions.This is because caries is essentially a demineralisingdisease requiring a fall in pH at the surface of thetooth. If the saliva is capable of resisting this changein pH because of buffering capacity then caries is lesslikely to ensue. It is known that high flow rates ofsaliva improve its buffering capacity so that caries isdependent not only on the quality of the saliva butalso upon its quantity. It is for instance well knownthat caries increases in patients with xerostomia fol-lowing irradiation of tumours in the oral region but

there may also be changes of diet associated withthese problems. Saliva is a super-saturated solution ofcalcium, phosphate, hydroxyl and fluoride ions andthese may reduce the solubility of enamel and promo-te remineralisation of early lesions. In addition, thesaliva contains non-specific antibacterial agents suchas lysozyme, lactoperoxidase and lactoferin and in ad-dition contains immunoglobulin ICA molecules andin those patients with inflammation of the periodon-tal tissues IGC may be present in the serum exu-date. It has been suggested that it may be possible toimmunise patients against caries but in western soci-ety where caries prevalence seems to be falling it seemsunlikely that this will be an acceptable procedure.

Oral hygieneThe final host factor of importance in caries is theability to improve oral hygiene thereby removing theplaque from the surface of the teeth and preventingthe production of acids initiating caries. Oral hygieneis usually considered to be mechanical using tooth-brushes, toothpastes, floss and similar methods, butit must be remembered that oral hygiene is also a nat-ural phenomenon which some individuals do well and

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others do not. The use of the tongue as a means oforal hygiene has received relatively little study butmay well be a factor in reducing caries.

Diet

The second main group of factors associated withcaries of the teeth is that of diet. Microbial plaque onthe surface of teeth is disastrous only if there is suffi-cient substrate for these bacteria to work upon. Fer-mentable carbohydrates need to be present for acidto be formed. The problem is that in the presence offermentable carbohydrates, the plaque bacteria pro-duce acid rapidly so that the pH in relation to theplaque falls precipitously very quickly. The recoveryfrom this position to normal pH levels is an extendedprocess. The major part of our dietary fermentablecarbohydrate is sucrose, but lactose is present in milkand maltose is derived from the hydrolysis of starch. Itseems that it is the frequency of fall in pH which is im-portant and this information enables dentists to plandietary advice for their patients. Attempts have beenmade to replace these fermentable carbohydrates byother types of sugar such as xylitol which is a sugaralcohol but is not metabolised to acid by the plaqueorganisms. There are however difficulties in changingthe habits of a lifetime.

Tooth susceptibility

The third factor related to caries incidence appears tobe the structure of the teeth themselves.

MorphologyCaries tends to occur at certain points on the teethsuch as the depth of the fissures and below the con-tact areas and cervical margins and this suggests thatthe shape and morphology of the tooth is importantalong with its ability or otherwise to shed food debrisor to be cleansed by the patient’s musculature or sali-vary flow. Packing of food between teeth which aremalaligned may also constitute a problem. Fissureswhich are deep and difficult to cleanse may well bemore liable to caries than shallow, cleanable fissuresbut the details of tooth morphology are best studiedin texts related to that subject.

ChemistryUsing techniques of microprobe analysis and micro-biopsy, it has been possible to show that tooth struc-ture varies chemically between different individuals.For example, fluoride levels vary between individuals

and this in itself may have an influence on their cariesresistance.

Surface structureIt has become clear that the outer surface structureof enamel is extremely variable and indeed in manypatients in some of their teeth and at certain sites theprisms of the enamel may in fact not reach the sur-face. The surface of the tooth in contact with the mi-croenvironment is therefore said to be aprismatic butthe relationship of this structural variation to cariesresistance is not clear.

Research Methods

Most of the modern techniques of scientific investi-gation have been applied to caries over the decades.These have included epidemiological studies on theincidence of the disease and biochemical studies onthe environment of the mouth and of the teeth them-selves. It is beyond the scope of this book to discussthese in any detail. However, in order to understandthe principles of restorative dentistry it is necessaryto have a working knowledge of the pathology of thelesion itself.

Ground sections in polarised light

Most of the early work in this area consisted of theproduction of ground sections through teeth contain-ing natural early lesions and much of it was directedtowards the technology of producing sufficiently thinsections to be of use in these studies. Sections between50 and 100 μm in thickness have now been achievedand these may be examined either in the light mi-croscope or more profitably and commonly in thepolarised light microscope. Polarised light is vibrat-ing in one plane and this plane may be rotated bysuitable crystalline materials. Enamel is such a mate-rial as is dentine by nature of its hydroxyapatite con-tent and its collagen matrix. When polarised light ispassed through enamel it is rotated both by the crys-tals themselves and by the arrangement of the crystalsin the form of prisms. The former is said to be intrin-sic birefringence and the latter form birefringence. Inthe case of dentine the light is rotated by the crystalsof hydroxyapatite and also by the repeat pattern ofthe collagen. Carious attack affects both the size andthe shape of the crystals and the spaces between themand the overall outline of the enamel prisms. In thecase of dentine it may alter the collagen component

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as well. For these reasons carious lesions exhibit al-tered birefringence, the direction and extent of whichnot only indicates the extent of the lesion but may beused quantitatively to deduce the degree of deminer-alisation.

Transmission electron microscopy

The availability of the transmission electron micro-scope (TEM) in the early 1960s held promise ofdetailed investigation both of normal and cariousenamel, but it proved almost impossible to producesections of sufficient thinness for this technique tobe fully exploited. Thin sectioning is possible in par-tially demineralised enamel but there is doubt as towhether the sectioning procedure may alter the crys-talline structure of the material being examined. At-tempts were made to solve this problem by cuttingthick sections through the lesions and taking carbonreplicas which themselves could be examined in theTEM and considerable progress was made using thistechnique.

Scanning electron microscopy

A decade later the scanning electron microscope(SEM) became available and since this records infor-mation from a cut surface by excitation of secondaryelectrons, thin sectioning was no longer needed. Al-though the method has been exploited to some extentin studies of caries, interpretation of the images andparticularly the formation of smear layers during sec-tioning has proved difficult. Methods of removal ofthe smear layer using either chemical or preferably ionetching techniques are now in progress and back scat-ter electron imaging which provides information frombeneath the cut surface is a recent promising advance.Modern SEMs allow analysis of emitted X-rays fromthe specimen being studied and electron microprobeanalysis of this nature allows chemical analysis to bemade in various parts of the lesion. X-ray and elec-tron crystallography have also featured in studies ofcaries.

Microradiography

Since carious lesions in both enamel and dentine arecharacterised by loss of mineral, microradiographscan be used to demonstrate changes of mineral den-sity within the lesions. It is necessary to use a grad-uated step wedge in order that a standard may becompared with the radiographic image and plane or

parallel sections of known thickness are required inorder to make the necessary calculations of mineralloss.

Microbiopsy

Microbiopsy techniques have been evolved so thatsmall portions of a carious lesion from a known po-sition can be excised and analysed using some ofthe methods previously described. These biopsies arealso available for biochemical study. Using such tech-niques the distribution for instance of fluoride ionwithin a lesion may be determined.

All of these methods have now been applied bothto natural human lesions and to artificially inducedlesions in human and in animal teeth so that the pro-cess of caries in mineralised tissues is now more fully,but still incompletely, understood.

Caries of Enamel

When mineral is removed from the enamel by cariousattack, the individual crystals making up the prismsdiminish in size and the enamel is said to become moreporous.

White spot lesion

Even a slight increase in porosity of the enamelchanges its optical characteristics and in the initialstages it becomes less translucent so that the earliestevidence of caries is known as a white spot lesion. Atthis stage the surface of the enamel is still intact andthe lesion may be difficult to detect clinically. Histo-logical studies using polarised light have shown thatthe lesion at this stage is not continuously progres-sive but may remineralise so that processes of bothdestruction and repair are occurring simultaneously.When examined under the polarising microscope inwater, the lesion is described as cone shaped with itsbase just below an intact surface zone. The body ofthe lesion appears to be dark in colour and the incre-mental lines are accentuated. The use of quinoline asan inhibition medium of different refractive index al-lows further details of the early lesion to be described.Four zones may be seen in an early white spot lesion(Fig. 6.2).

Advancing frontZone 1 is a translucent zone present at the advancingfront of the lesion and is usually only seen in sections

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Fig. 6.2 Scanning electron micrograph of a ground section of an early ‘white spot’ carious lesion. It consists of four zones:(1) translucent zone; (2) dark zone; (3) body of the lesion; (4) surface zone.

examined in quinoline. This zone is more porous thansound enamel having a pore volume of about 1%compared with 0.1% in intact enamel.

Dark zoneZone 2 is known as the dark zone and lies superficialto the translucent zone. It appears dark when exam-ined in quinoline. Polarised light studies have shownthat the pore volume is increased to 2–4% in thisregion. It is thought that the dark appearance is oc-casioned because some of the pores are too small toallow quinoline to enter so that they retain air follow-ing sectioning. It has been speculated that some rem-ineralisation may be occurring here reducing some ofthe pore sizes.

Lesion bodyZone 3 is the body of the lesion and since more than5% of the enamel is porous and the size of the poresare large enough to allow water to enter, the bodyappears dark when examined under polarised light inwater but translucent when examined in quinoline. Insome parts of the body the pore volume may increaseto 25%.

Surface zoneThe fourth zone is known as the surface zone and isbest seen in sections examined in water. It is an intactsurface layer with a pore volume of less than 1% andis usually between 20 and 50 μm in thickness. Thus,the early lesion is more demineralised in its depth thanat its surface and although it was first thought that thesurface zone was caused by a hyper-mineralised zoneat the surface of the tooth, it may be reproduced fol-lowing removal of this surface layer. It is now thoughtthat it may be caused by re-crystallisation of dissolvedmineral elements from deeper in the lesion.

Fissure caries

The foregoing description is that of an early lesion onthe smooth surface of a tooth and in the case of earlyfissure caries similar appearances are noted aroundthe fissure wall. It should be noted that in many fis-sures examined in sections there is an enamel defectat the base so that the lesion spreads very quickly intodentine. This may explain the recently described phe-nomenon of ‘bomb’ caries in teeth that have beensubjected to fluoride ions during development or

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subsequently. The enamel around the sides of the fis-sure is resistant to carious attack by reason of its flu-oride content but the lesion spreads rapidly into den-tine spreading along the enamel dentine junction andcavitating the dentine although the fissure may appearclinically to be intact.

Electron microscopyElectron microscope studies on early carious lesionshave provided conflicting evidence. In most cases theinter-prismatic regions seem to be preferentially dis-solved but also larger, unusually shaped crystals maybe seen in this region and these may represent aremineralisation phenomenon. The biopsy techniquespreviously described have shown that in the translu-cent zone the cross section diameter of the crystals is25–30 nm compared to 30–40 nm in sound enamel.In the dark zone of the lesion crystal diameters maybe 50–100 nm whereas in the main body of the lesionthey may be only 10 nm in diameter. These findingsagain support the view that remineralisation of crys-tals is occurring in various parts of the early cariouslesion.

MicroradiographyMicroradiographs of sections through the early lesionare sufficiently sensitive to demonstrate loss of min-eral if this is more than about 5%. The body of thelesion therefore shows up well using this techniqueand the intact surface zone is also readily seen. Inhigh-resolution microradiography the outline of theincremental lines may be visible within the body ofthe lesion.

Biochemical studies using biopsies of the lesion orelectron probe microanalysis have confirmed thesechanges in enamel caries and have also shown thatfluoride levels are high in this artificially porousmaterial.

Progress of the lesionAs the lesion progresses through the enamel its apexmay reach the enamel–dentine junction before col-lapse of the intact surface zone occurs so that lesionsmay be quite deep before they are easily detectableclinically. The enamel lesion, however, is extremelyporous by this stage so that acids are able to diffuseeasily across the junction and into the dentine. Theimplication is that dentine may be involved even whenlesions appear to be restricted to enamel on standardclinical radiographs.

Caries in Dentine

Caries spreading to dentine may be either subsequentto enamel caries having reached the enamel–dentinejunction or in certain circumstances, that is, exposureof the root of the tooth, it may commence de novo inthe cementum and spread to the dentine directly.

Coronal caries

Involvement of dentine in the crown of the tooth maybe either underneath smooth surface caries, usually atthe contact area or immediately below it, or may bean extension of caries in an occlusal fissure. When thecarious process reaches the enamel–dentine junction,it tends to spread laterally involving the dentine on awider front. In this way the enamel is undermined sothat the resultant cavity preparation requires removalof sound enamel in order that the infected dentinemay be approached and also to remove unsupportedenamel prisms which under areas of stress will tend tofracture. Lesions of the occlusal fissures may directlyinvolve dentine since in many cases enamel is deficientat the base of the fissure.

Root caries

In patients where the root surfaces have become ex-posed usually due to chronic inflammatory periodon-tal disease, but also in continuing eruption to com-pensate for occlusal wear, the root becomes directlyexposed to plaque and carious attack. Chronic infec-tive periodontal disease and continuing eruption dueto occlusal wear are both commonly seen in olderpeople so that root caries tends to be a disease ofold age. Root caries may extend from lesions at thecervical margin of the enamel or may attack dentineexposed directly by the aforementioned means. Rootcaries can be of two types. Active root caries is softand pale in colour, whereas arrested lesions, possiblycaused by good oral hygiene techniques, tend to stainand be hard and dark brown.

Dentine is a living reactive tissue and must be con-sidered in association with the living pulp tissue be-neath. Reactions to dentine caries therefore involveconsideration of both the dentine itself and the un-derlying pulp tissue. The reaction and response of thepulp will be considered later.

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Micro-organisms

Once the enamel has been penetrated, bacteria cangain access directly to the dentinal tubules and so thetissue becomes infected. The initial invasion of den-tine appears to be mainly acidogenic, the acid presum-ably diffusing ahead of any micro-organisms. The firstorganisms to invade the dentine appear to be lacto-bacilli and also cariogenic streptococci, notably strep-tococcus mutans. Underneath the enamel–dentinejunction the microbiological population is mixed andorganisms producing proteolytic hydrolytic enzymesmay be found. At the advancing edge of the denti-nal lesion is a zone of demineralised dentine thatbacteria have not yet penetrated. This is because thetubules are smaller than the diameter of most bacteriaand only when the tubules have become laterally en-larged by dissolution of the inter-tubular matrix dobacteria enter. Superficial to the demineralised den-tine is a zone of penetration in which bacteria arepresent in the tubules. Superficial to that again is azone of complete destruction where the mineral con-tent and organic matrix of the dentine have both beendestroyed.

Effect on dentinal tubules

Once the dentine is infected it may react in sev-eral different ways. Those tubules directly located inthe centre of the demineralised zone may appear tobe empty because the cell processes of the odonto-blasts have withdrawn. During section preparationthese empty tubules may be filled with air produc-ing a dark colour under the light microscope oftenreferred to as a dead tract. Odontoblastic cell pro-cesses less acutely involved in the carious process,that is, usually those at the periphery of the lesionmay react by laying down calcified material as thecell processes withdraw, thereby equalising the refrac-tive index of the dentine and producing a transpar-ent or translucent sclerotic zone. The crystals in thesetubules, when examined in the electron microscopemay have larger and more irregular crystals than inthe normal dentine. They are considered to representthe result of remineralisation. Sclerotic dentine maybe considered as an extension of the normal process ofproduction of peritubular dentine. The sclerotic den-tine may consist initially of fine crystals of whitlockiteand at later stages of mineralisation of a mixture ofwhitlockite and hydroxyapatite. The final oblitera-tion of the tubule appears to be by hydroxyapatitecrystals.

Secondary and tertiary dentine

The lesion eventually spreads towards the pulp of thetooth and the stimulus may cause reactionary tertiarydentine to be laid down in the pulp at the depth of thelesion in an attempt to wall off the advancing cariesfrom the pulp. It may be a relatively well-formed tis-sue containing dentinal tubules and may be similar instructure to normal secondary dentine. It may also bean abnormal tissue with very few tubules and numer-ous inter-globular zones. Reactionary dentine is mostfrequently formed when the stimulus is mild and theblood supply to the pulp is good so that it is morelikely to be seen in younger teeth. If the stimulus isoverwhelming, the odontoblast cells lining the pulpmay be killed and then of course no reactionary den-tine can be produced. Under these circumstances thecarious lesion will directly involve the pulp and thiswill be discussed in the next section.

Response of the Pulp

In the early stages of infection, the pulp reacts aswould any other healthy tissue.

Hyperaemia

An inflammatory reaction occurs and in its initialstages this is characterised by hyperaemia. The pul-pal blood vessels dilate, become more permeable andfluid and defence cells pass out into the surround-ing pulp tissue. This increases the pressure within thepulp and this pressure, unlike in soft tissues, cannotbe relieved because of the enclosed nature of the pul-pal tissue. The pressure, therefore, rises and the pa-tient suffers pain. Initially, this may be the case whentransient stimuli such as very hot liquids or very coldliquids are placed in contact with a carious lesion.The pain may only last as long as the stimulus is ap-plied. Once the carious lesion has approached closelyto the pulp the stimulus may be continuous and thereaction of the pulp will depend upon the durationand the intensity of this stimulus.

Chronic inflammation

If the lesion is progressing slowly towards the pulpthen toxins and thermal stimulation may be of alow-grade nature and the result is chronic inflamma-tion. Lymphocytes, plasma cells, macrophages and

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monocytes can be seen in the pulpal tissue and thetissue may survive. There may be no increase in intra-pulpal pressure and therefore no symptoms.

Acute inflammation

If the stimuli reaching the pulp are stronger, then theblood vessels dilate, fluid passes out into the tissuesand the pressure builds up to such an extent that thearterioles entering through the apical foramina maybe occluded. Polymorphonuclear leucocytes are themain cells involved in acute inflammation. The in-crease in intra-pulpal pressure leads, usually, to severepain.

Pulpal necrosis

The rise in intra-pulpal pressure may occlude thepulp’s blood supply. This may be accompanied by anoverwhelming bacterial infection from the carious le-sion. The result of both of these is pulp death and theceasing of any pain.

It is possible for a necrosed pulp to remain quies-cent for many years with no evidence of such pathol-ogy. The apical foramen may become blocked withcalcific deposits – a natural root filling.

On the other hand, the apical foramen may remainpatent and there will be pathological effects in theperiapical region.

Periapical Involvement

The first effects of the pulpal infection will be the leak-ing of bacterial toxins and tissue breakdown productsthrough the apical foramina to the periapical tissues.The response of these tissues may also be either acuteor chronic in nature, depending upon the severity ofthe stimulus. Later, bacteria may pass out into thetissues.

Acute periapical infection

The acute inflammatory reaction at the apex is alsoenclosed, this time by bone. The fluid exudate andthe presence of oedema tends to force the tooth outof the socket and it will be painful to bite on andthere will be a continuous throbbing pain. If this isleft untreated then there will be continued pressurebuilt up and the pain will become intense. The pres-sure of the exudate and pus so formed will lead tobone resorption and the fluid will track through the

bone along the line of least resistance. Eventually theperiosteum may be penetrated resulting in a releaseof pus and consequent reduction or relief of pain.A symptomless, progressively enlarging swelling is acommon finding.

Chronic periapical infection

This is the more common sequel to pulp death andmay arise from low-grade irritation from the rootcanal, i.e. bacterial by-products leaking out into theapical tissues, or from the partial resolution of anacute response.

The precise pathology is again related to the viru-lence of the organisms and the host tissue reaction.The lower grade activity results in a more gradualremoval of bone and the formation of granulationtissue. It is usually symptomless and often only dis-covered by radiography.

Alternatively, the chronic response may, if the bal-ance changes in the lesion, exacerbate into an acuteone with the symptoms described above appearing.

The apical response is usually induced by toxinsand tissue breakdown products only. The bacteria re-main within the pulp chamber undisturbed by phago-cytes. If any do pass beyond the apical foramen theyare usually killed by inflammatory cells. If on theother hand the bacteria leave the root canal in suffi-cient numbers and/or the inflammatory response losesits potency, then infection of the apical tissues, as op-posed to irritation, will follow. The lesion may remainchronic though, with no evidence of the differentcircumstances.

The apical tissue response in a chronic lesion isusually granulomatous and may be accompanied byproliferation of epithelium. The epithelium originatesfrom the cell rests of Malassez that are the remnantsof the epithelial root sheath of Hertwig. The inflam-matory process appears to stimulate the growth ofthe cells. The chronic apical granuloma is a massof chronic inflammatory cells, variable amounts ofstrands or sheets of epithelium and perhaps some pus,all surrounded by a fibrous tissue capsule.

In certain circumstances the epithelium forms aperiapical cyst. Various theories of cyst formationhave been proposed. These are:

� The block of proliferating cells enlarges and thecentral cells break down to form a cavity

� Cavities in the granuloma due to pus formation al-low the epithelium to proliferate along the surfaceto from a continuous lining

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� Strands and sheets of epithelium join up into a shellby chance

Once the epithelium lines a cavity, osmosis occurs.Fluid passes through the cell layer and the osmoticpressure causes slow expansion. For all this to happenand be seen takes some time, maybe 2 years.

In the chronic periapical lesion therefore there maybe a cyst or small cysts within a granuloma or a lesionthat is essentially a cyst surrounded by a fibrous cap-sule, with no granulation tissue outside it. The cystmay become infected, depending upon the movementof bacteria from the root canal.

Relationship to Clinical Management

It should be clear from this description of the pathol-ogy of the carious lesion that in its earliest stages,i.e. the white spot lesion, there may be considerabledifficulties in clinical diagnosis.

Early caries

The surface of the enamel will still be intact and there-fore the lesions can only be diagnosed either visuallyor radiographically. The use of a mirror and stronglighting may indicate a slight change in optical den-sity below the contact area and high-intensity transil-lumination with a small fibreoptic probe may be moreuseful. Bitewing radiographs are unlikely to pick upthe very early lesion and it is said that by the time alesion is visible using this means it may well have pro-gressed towards the enamel–dentine junction. All isnot lost however, since changes in oral hygiene prac-tice, removal of plaque, administration of fluoridesand good dietary control may cause such lesions toremineralise even though they were never diagnosed.

RemineralisationSince these early lesions are cycling between destruc-tion and repair, the clinician aims to tip the balancetowards repair. There is some evidence that such rem-ineralised lesions may resist further attack better thannormal enamel. It may be that many patients diag-nosed as caries free have in fact remineralised earlylesions from their own saliva.

Once cavitation of the surface has occurred, rem-ineralisation will not replace the normal contour ofthe tooth. For this reason probing should not be usedin diagnosis of early lesions, since cavitation may be

produced by the clinician. The early diagnosis of car-ious lesions has been discussed in Chapter 2.

Very early caries is perhaps best diagnosed by astudy of the risk factors to which the patient is sub-jected. Therefore, a good diet history will be neededand it is clear that the younger patient is at greaterrisk than the older. The adequate secretion of salivaand its buffering capacity should be investigated andit may be useful to look at the types of organismspresent in the saliva so that the high-risk Lactobacilliand Streptococcus mutans may be discerned.

Excavation of caries

Once the caries has involved the dentine it will benecessary to remove softened and infected necroticmaterial. It is clear from the progression of the lesionthat this may involve a larger cavity than at first ap-preciated since the lesion will have extended alongthe enamel–dentine junction. It is believed necessaryto remove all of the infected dentine at the junction.When the softened dentine in the bulk of the lesionhas been removed the decision has to be made on howto deal with the infected area of dentine overlying thepulp. The approach that has been followed for manyyears is to remove the infected dentine leaving thedemineralised but unifected translucent zone over thepulp intact.

Newer techniques involve leaving bacteria in situand killing them with a disinfection process. This isdiscussed in Chapter 11. Providing that the tooth hasbeen symptomless and appears to be vital, the translu-cent area of dentine covering the pulp may be cappedwith a calcium hydroxide paste, the rationale herebeing to protect the pulp and induce the formationof reparative dentine. If there is clinical evidence ofacute or chronic inflammation of the pulp, usually bysymptoms, then the inevitable sequel may be deathof the pulp requiring eventual root canal therapy orextraction.

The reactions of the pulp underlying carious le-sions may give some clinical information to the den-tist as to the health or otherwise of the tissues. Thus,a patient who complains of transient pain followinghot and cold drinks, the pain lasting for the dura-tion of the stimulus, may well have pulpal hyperaemiawhich may be reversible if stabilisation of the cavityis achieved using the methods described. Once thepulp has become infected it may, if the inflamma-tion is chronic, produce no symptoms. Under thesecircumstances the patient may complain of no painand the pulp may eventually recover. However, it may

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slowly die without symptoms and the dentist shouldbe aware of this possibility and keep future checks onthe health and vitality of that particular tooth. If thepatient complains of continuous lancing pain then thetooth pulp is almost certainly acutely inflamed and avital removal of the pulp or the tooth is probably in-dicated. In patients where this has not occurred theacute continuous pain may eventually resolve for atime as the inflammation expands through the apicalforamen and the pressure is released. During hyper-aemia the patient may be able to localise the intermit-tent sharp pain to a particular tooth but when acutepulpitis intervenes the pain may radiate over a largerarea. As the inflammation extends into the periapicaltissues and in the absence of the satisfactory responseby the patient it may eventually involve alveolar bone.The pain may then become deep seated and throbbingand may be localisable because the tooth is tender to

percussion or biting. If the infection extends throughthe bone, producing a localised osteitis, it may trackthrough the bone, reducing the pressure somewhatand therefore the pain but then raise the periosteumeither buccally or lingually to again produce severepain and the presence of an apical abscess. If this ab-scess discharges into the buccal or lingual sulci thepain may again cease because of reduction of pres-sure. However, it may spread above the level of at-tachment of the muscles of the mandible and maxillaand the final sequel is a cellulitis or facial swelling overthe area. Patients are likely to seek emergency dentaltreatment at any point where the pressure is high ei-ther in the pulp, the periapical tissues, the bone orin the facial tissues. Reduction of pressure at certainstages of the advance of the infection explains whypatients may report decrease or absence of symptomseven though the lesion is progressing. Se

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Chapter 7The Periodontium in Health and Disease

This chapter and Chapter 13 will summarise those areas of periodontology that are of clinical relevanceto an understanding of the disease, its treatment and restorative dentistry. The text will be almost entirelydevoted to gingivitis and chronic periodontitis. The space available does not allow for an exhaustive texton periodontology and readers are referred to the Bibliography for additional reading.

Introduction

Periodontal disease, which encompasses gingivitisand periodontitis, is highly prevalent in all popula-tions. The development of gingivitis is due to the accu-mulation and maturation of supragingival plaque andsubgingival plaque is associated with the advancinglesions of periodontitis. As periodontitis progresses,bone loss will compromise the integrity of teeth re-sulting in looseness and/or drifting out of their normalalignment. In planning restorative dental proceduresthe periodontal status of the individual must be con-sidered and rectified, if unhealthy, before commenc-ing restoration of the dentition. As importantly, theconsequences of particular restorative procedures toperiodontal health should be evaluated, particularlyin the treated periodontal patient who clearly has asusceptibility to the disease.

The Healthy Periodontium

Definition

The periodontium comprises the tissues investing andsupporting the teeth, namely the gingiva, alveolarbone, periodontal ligament and cementum.

The gingiva

The gingiva is the only tissue of the periodontium thatis visible and comprises the marginal and attachedgingiva that are separated from each other by the freegingival groove and from the alveolar mucosa by themucogingival junction. The tissue is pink in colourand may be stippled to produce an ‘orange peel’

appearance. The colour may be modified by differentdegrees of melanin pigmentation and keratinisation.

The structure consists of keratinising stratifiedsquamous epithelium attached to the alveolar boneby connective tissue. There are collagen fibres em-bedded in an extracellular matrix that are arrangedin groups by virtue of their orientation and named:

� Circular (around the teeth)� Transeptal (joining teeth)� Dentogingival (cementum to free gingiva)� Dentoperiosteal (cementum to attached gingiva)� Crestal (alveolar crest to attached gingiva)

The marginal gingiva forms a cuff 1–2 mm widearound the tooth and fills the interdental space as alabial and lingual papillae joined by a gingival colbetween the tooth and below the contact point. Itforms the gingival crevice (0–2 mm deep) and here islined by crevicular epithelium that is non-keratinisingstratified squamous epithelium.

The marginal gingiva is joined to the tooth at or justabove the cemento–enamel junction by the junctionalepithelium that has cells arranged parallel to the toothsurface with wide intercellular spaces, and containssmall numbers of neutrophils.

The attached gingiva is a mucoperiosteum tightlybound to the alveolar bone and has a variable widththat does not correlate with health. The absence ofattached gingiva is not necessarily pathological pro-viding plaque control is adequate.

Alveolar bone consists of cancellous bone coveredby a thin layer of compact bone that supports theteeth and is tooth dependent; it resorbs to a variabledegree when teeth are lost. The bone adjacent to thetooth root is perforated (the cribriform plate) and re-ceives the insertion of the periodontal ligament fibres.

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7. The Periodontium in Health and Disease 57

The alveolar crest maintains a relatively constant dis-tance of 1–2 mm from the cemento–enamel junction(biologic width).

The periodontal ligament suspends the tooth in thesocket and acts like a viscoelastic shock absorber per-mitting small movements of the teeth when underload. It consists of principal collagen fibre bundles(Sharpey’s fibres), namely alveolar crest, horizontal,oblique and apical, all of which extend from the ce-mentum to the alveolus. It has a very high connectivetissue turnover.

Cementum is the usually thin layer of calcified con-nective tissue covering the whole of the root surfaceand into which the periodontal ligament fibres are in-serted. There are two types, acellular (cervical area)and cellular (mid and apical area), depending on thepresence of cementocytes within the structure.

Periodontal Disease

This section will consider gingivitis and periodonti-tis as essentially separate entities. At present, thereis insufficient evidence to permit the conclusion thatfactors relevant to gingivitis are relevant to periodon-titis. The concept that plaque causes gingivitis and, intime, gingivitis inextricably progresses to periodonti-tis that in turn, left untreated, leads to tooth loss, isno longer accepted.

Nevertheless, gingivitis and periodontitis are notmutually exclusive nor unrelated; indeed gingivitis isone aspect of periodontitis (see definition of periodon-titis). Data indicate that not all gingivitis progresses toperiodontitis and populations with poor oral hygieneand severe gingivitis have incidences of periodontitislittle different from those populations with less plaqueand gingivitis.

Gingivitis is thus a poor predictor of future peri-odontitis in the as yet unaffected individual or toothsite. Even in individuals treated for periodontitis andtherefore by definition susceptible to the condition,the recurrence of gingivitis is a poor predictor (30%)of recurrence of periodontitis.

Conversely, and most importantly, the absence ofgingivitis is highly predictive (99%) of no recurrenceof periodontitis. Taken together, the evidence sup-ports the concept that periodontitis is always pre-ceded by gingivitis and the prevention of gingivitisthrough supragingival plaque control will prevent theoccurrence or recurrence of periodontitis. This con-cept has widespread implications for public healthpreventive programmes for periodontal disease and is

also of major relevance to the total care and long-termmanagement of the restorative patient. A high stan-dard of supragingival plaque control must be prac-tised by all patients, particularly those who alreadyexhibit a susceptibility to periodontitis.

Gingivitis

DefinitionGingivitis is inflammation of the marginal gingivawithout loss of attachment.

Clinical featuresInflamed gingiva exhibits redness, variable swelling,bleeding, usually in response to minor trauma such astooth brushing, and increased flow of the crevicularfluid. Pain is not usually present, although vague sen-sory symptoms may be reported by some individuals(wedging, tingling, itching).

AetiologyEpidemiological data have shown a strong correlationbetween plaque and gingivitis (correlation coefficient� 0.8).

Controlled clinical trials have proved a direct causeand effect relationship between plaque and gingivitis.This forms the basis for the prevention of gingivi-tis and logically, therefore, periodontitis through thecontrol of supragingival plaque.

Plaque formationEnamel in the mouth is always covered by a salivarypellicle of glycoprotein that increases in thicknesswith time to several micrometres. Even if removed bypolishing, pellicle reforms in minutes. Primary plaqueforming bacteria, gram-positive facultative strepto-cocci such as Streptococcus sanguis and some gram-negative actinomyces species, attach to this pellicle.These primary plaque formers are essential for theattachment of other bacteria.

The adsorption mechanism is complex and involvesa number of forces and physical interactions betweenthe bacteria and oral surfaces. Compatible surfacefree energies, hydrophobicities and specific attach-ment sites are important factors in bacterial adher-ence. Bacterial seeding is slow and the plaque massincreases mainly by bacterial division.

Over a period of a few days increased proportionsof anaerobic gram-negative cocci attach and prolifer-ate. These are followed by rods and filamentous bac-teria such as fusiforms and finally spirochaetes andother motile rods can be found. Supragingival plaque

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thus develops in thickness and complexity and theseare almost certainly mutually dependent processes. Itis in association with the later stages of plaque devel-opment that the clinical features of gingivitis appear.

Pathogenesis of gingivitisBacteria are not thought to penetrate crevicular ep-ithelium but induce an inflammatory response in thegingiva by chemical by-products. Bacteria release arange of enzymes capable of damaging all cellular andsupporting tissues of the gingiva and these also allowthe penetration of high-molecular-weight bacterialendotoxins through crevicular epithelium. The net re-sult is an inflammatory response with elements akinto both acute and chronic inflammation. Neutrophilsand macrophages accumulate in the connective tissueand pass into the gingival crevice. Vascular dilata-tion and vascularity increases with fluid extravasationand lymphocytes and plasma cells appear within thetissues.

Epidemiological considerationsGingivitis is considerably less prevalent and less se-vere in the primary dentition whilst periodontitis af-fecting deciduous teeth is rare and usually a feature ofan underlying systemic disease affecting host defence,e.g. cyclical neutropaenia.

Gingivitis is highly prevalent (100%) in the perma-nent dentition from a young age whilst the severityand number of sites affected varies at the extreme inindividuals. The most important factors influencingthe severity of gingivitis relate to those that influencethe oral hygiene practices of individuals by either di-rectly or indirectly affecting compliance and dexterity.

In general, oral hygiene and gingival health areworse in:

� Low social classes� Males compared to females� Pre-teenage years compared to teenage (further in-

crease in age has little affect on oral hygiene)� Individuals who brush less than twice daily (fur-

ther increases in tooth brushing frequency do notimprove oral hygiene)

� Smokers� Physically and mentally handicapped individuals� Right buccal quadrants of the dental arches in

right-handed tooth brushers� Individuals wearing removable dental prostheses

or fixed or removable orthodontic appliances

Oral hygiene and gingival health is little affected by:

� Tooth crowding� Mucogingival anomalies such as high fraenal at-

tachments and shallow sulci� Narrow zones or absence of attached gingivae

Gingival health is always compromised by restora-tions that encroach upon the gingival crevice.

Modifying factorsThe gingival response to supragingival plaque ap-pears to be exaggerated or changed by certain localand systemic factors including:

� Incompetent lips and mouth breathing, particu-larly during adolescence

� Puberty� Pregnancy� Contraceptive pill� Drugs – notably epanutin, ciclosporin, nifedipine

and other calcium channel blockers, notably am-lodipine, felodipine and lacidipine, that may resultin gingival hyperplasia

� HIV infection� Neutropaenias, notably cyclical neutropaenia� Leukaemias, particularly acute leukaemias where

marked swelling may occur due to gingival infil-tration with large numbers of leukaemic cells

� Nutritional deficiency, notably of ascorbic acid

Note. Some of the modifying factors listed above forgingivitis do not appear or have not been proven tomodify periodontitis (see Periodontitis).

Strategies for the prevention of gingivitis

The basis for the management of gingivitis issupragingival plaque control. Two aspects are impor-tant:

� Preventing the development of a maturepathogenic plaque (primary control)

� Removing or modifying factors that facili-tate plaque formation and retention (secondarycontrol)

Primary control may be achieved by mechanical andchemical approaches namely:

� Preventing bacterial attachment (antiadhesiveapproach)

� Preventing bacterial proliferation (antimicrobialapproach)

� Regularly removing accumulated plaque (mechan-ical and chemical cleaning approach)

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All of these approaches are possible and have beenachieved in other conditions where microbial plaquespose problems. In the oral cavity success to datehas only been achieved realistically with the an-timicrobial and mechanical cleaning approaches (seeChapter 13).

Secondary control has preventive and therapeuticimplications for restorative treatment that involves:

� The preparation and placement of restorations� Positioning of margins in relation to the gingiva� The design and precision of construction of fixed

and removable prostheses

Therapeutic considerations concern the replacementor removal of fixed or removable restorative plaquetraps, treatment of carious cavities and the removalof supragingival calculus.

Periodontitis

DefinitionPeriodontitis may be defined as gingivitis with lossof attachment, typically producing a periodontalpocket. This is a useful definition since it describesthe histological lesion of periodontitis and suggestsan approach to management that is based on preven-tive and therapeutic strategies.

Clinical featuresLoss of attachment whereby the junctional epitheliummigrates along the root surface resulting in the forma-tion of a pocket. The true pocket is measured fromthe cemento–enamel junction to the base of the at-tachment, whereas pocket depth is the distance fromthe gingival margin to the base of the pocket.

Pocket depth may therefore be greater than the lossof attachment when the gingival height is above thecemento–enamel junction or be less than the loss ofattachment when the gingival margin is below thecemento–enamel junction (recession).

Colour change is variable in periodontitis. The gin-gival margins may exhibit all the features of gingivitisor appear perfectly normal. Usually, however, there isbleeding on probing when the probe is inserted to thebase of the pocket and a purulent exudate may alsobe seen at the pocket orifice. Pain is not a feature ofperiodontitis although vague sensory symptoms maybe reported, such as awareness of the teeth.

Aetiology of periodontitisSub-gingival plaque, derived from supragingivalplaque, is always associated with the advancing

lesions of periodontitis. The progression of gingivitisto periodontitis is thought to occur when periodontalpathogenic micro-organisms act upon a susceptiblehost.

Periodontal pathogensIn excess of 400 species of micro-organisms have beenfound in periodontal pockets and about a third ofthese have yet to be identified. To date approximately20 are considered putative pathogens and most ofthese are obligate anaerobes.

Strong evidence exists for the following organismsto be considered actual pathogens:

� Aggregatibacter actinomycetemcomitans (faculta-tive anaerobe)

� Porphyromonas gingivalis� Tannerella forsythia

Less strong evidence supports Campylobacter, Eu-bacterium, Fusobacterium, Prevotella, Peptostrepto-coccus and Eikenella as periodontal pathogens. Themere presence of these organisms in periodontallesions is not necessarily indicative of progressingdisease.

Microbiological diagnosis is therefore of little or novalue in the diagnosis and management of periodontaldisease; this includes the decision to use antimicrobialtherapy and the choice of agent.

The micro-organisms associated with periodontitiscan be found at several sites:

� Periodontal sites:

Root surfacePocket lumenPocket epitheliumDentinal tubules

� Oral sites:

TongueTonsil

� Extra-oral sites:

Spouse/partnerFamily pet

SusceptibilityThere is some evidence for a major gene effect in someforms of aggressive periodontitis that dictates suscep-tibility. Similarly, a specific variation of the IL-1 genecluster regulating IL-1 production has been associ-ated with increased susceptibility to severe chronicperiodontitis.

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Neutrophil defects are associated with increasedor rapid periodontal breakdown that even affectthe deciduous dentition. These include cyclical andother neutropaenias, leukaemias, Chediak–Higashisyndrome, Down’s syndrome and Papillon–Lefevresyndrome.

Smoking is a risk factor, probably due to adverseeffects on host defence mechanisms, and the responseto treatment in smokers appears compromised.

Limited evidence suggests diabetes mellitus,particularly when uncontrolled, is a risk factor andconversely periodontitis may compromise diabeticcontrol.

Stress is suspected as a risk factor for periodon-tal breakdown but evidence is lacking. Part of theincreased susceptibility with smoking, diabetes andstress may be adverse effects on polymorph function.

Excessive occlusal loading and food packing ap-pear to be co-destructive factors in periodontitis, al-though a definition of what constitutes ‘excessive’loading is elusive.

PathogenesisPeriodontal lesions typically develop as loss of ep-ithelial attachment at the cemento–enamel junction.Associated with this is widening of epithelial spaces,ulceration of the sulcular epithelium, breakdown ofcollagen and ground substance and bone resorption.

For this to occur, pathogenic factors must over-come or exceed protective mechanisms. The latter arederived from the intact nature of the sulcular epithe-lium, gingival crevicular fluid, rapid tissue turnoverand non-specific and specific defence and immune sys-tems. The major pathogenic factors are the bacterialenzymes and toxins that can have direct destructiveeffects and/or initiate adverse host immune responses.These adverse host immune responses include theproduction of cytokines and host enzymes such ascollagenase, probably initiated by bacteriallipopolysaccharide.

Epidemiological considerationsChronic periodontitis shows a very low incidence inthe second decade of life but increases progressivelyin succeeding decades. Approximately 60% of 60- to70-year-olds will have chronic periodontitis affectingone or more teeth. The average rate of progression ofperiodontitis, measured by radiographic bone loss orloss of attachment, is approximately 0.1 mm/year.

In any population only a small proportion (8–10%) exhibit advanced periodontitis (loss of attach-ment >6 mm) at one or more sites. A relatively small

proportion of individuals and a small percentage ofsites in those individuals account for most of the ad-vanced periodontitis in any population.

The Periodontium and Restorations

The relationship between the periodontium and theprovision of restorations involves certain key areas:

� Prevention� Treatment planning� Technical execution� Maintenance

Whilst gingivitis is almost universal, the accurate pre-diction of the susceptibility of individuals and partic-ular intraoral sites to periodontitis is not possible.Even in those patients who are known to be suscep-tible, the site specificity for rapid breakdown cannotbe predicted. Therefore, prevention of gingivitis or therecurrence of periodontitis must be a high priority forall patients undergoing restorative dentistry.

The provision of restorations for most patientsmust be viewed as having the potential to influenceadversely their susceptibility to gingivitis and possiblyperiodontitis. Virtually all restorations compromiseplaque control and the procedures used to place themmay be harmful too. The more complex the restora-tion so the higher the risk. Treatment plans shouldtherefore be based on providing the minimum num-ber of restorations of the simplest and least plaqueretaining types.

When considering the design of bridgework (Sec-tion IV) whilst direct masticatory loads are modifiedby biofeedback where the periodontium is reduced,excessive twisting or tilting forces widen the peri-odontal membrane space and can cause tooth move-ment and/or physiological mobility but not loss of at-tachment. The viscoelastic nature of the periodontalligament has to be considered when restorations arelinked between teeth as in fixed bridgework or whenteeth are linked to osseointegrated implants, that haveno mobility.

Technical aspects of restorations of importance inprevention or initiation of periodontal disease relateparticularly to the effects on the gingival sulcus.

Mechanical instrumentation and restoration mar-gin placement in the gingival sulcus may directlyproduce loss of attachment, particularly if there is en-croachment on the biologic width. The gingival sulcuslimits the subgingival extent of restorations and maytherefore introduce aesthetic restrictions, particularly

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in the anterior region. Subgingival restoration mar-gins always result in a variable degree of bacterial-associated gingival inflammation but this may notnecessarily progress to periodontitis. However, over-hanging subgingival restorations cause loss of attach-ment and alveolar bone loss.

Lost interdental papillae can also have implicationsfor aesthetics and surgical mucogingival techniquesto rebuild papillae are difficult and unreliable. Oncegingival recession occurs, loss of cementum rapidlyresults thereby predisposing sites to dentine hyper-sensitivity.

The Periodontium – Summary

Plaque control is the key to prevention and management of periodontal disease.Periodontitis is not a natural progression from gingivitis; patient factors influence the disease process.Restorations of all types contribute adversely to plaque retention.

Operative treatment may be required to remove ae-tiological or co-destructive influences on periodon-titis, such as marginal overhangs, negative edges orincorrect restoration contour.

For the maintenance of periodontal health, restora-tive dentistry must be of the highest quality both indesign and in execution. In addition, patients havean equal role to play in performing regular and ef-ficient plaque control. The dentist must ensure thatappropriate oral hygiene measures are taught and pe-riodically reinforced as part of the continuing careprogramme.

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Chapter 8Functional Anatomy of the Occlusion

Occlusion is probably the most daunting and confusing subject within restorative dentistry. Much of thisconfusion arises because there is little scientific evidence to support clinical practice and terminology isoften random. There is considerable work on the anatomy and physiology of occlusal function but theestablishment of generally agreed principles for occlusal restoration and therapy remains elusive.

This book tries to take a pragmatic approach and considers:

� What constitutes ‘normal’ occlusal anatomy and physiology (Chapter 8)?� What are the basic requirements for restoration of the occlusion (Chapter 14)?� What are the causes and management of ‘occlusal dysfunction’ (Chapter 28)?

Whilst the word ‘occlusion’ refers strictly to the actof closing the teeth together, it has come to includethe way in which:

� The mandible moves in relation to the skull� The teeth are aligned in each jaw� They contact each other during the complicated

movements of chewing or speaking� The dentition should be restored� Disorders of the masticatory apparatus should be

managed

The study of occlusion in a functional sense there-fore includes the temporomandibular joints and theneuro-muscular control of mandibular movement, aswell as the teeth themselves.

The masticatory apparatus is unique in the wholebody because of the close interactions between dif-fering structural entities. Malfunctions in the jointsthemselves, the muscles operating them, the neuro-muscular reflexes controlling them or imperfectionsin the interdigitation of up to 32 teeth may all re-sult in dysfunction of the masticatory apparatus as awhole.

The Temporomandibular Joints

The articulation between the fused right and left por-tions of the maxilla and mandible is by the temporo-mandibular joints (TMJ). Each is unique in the bodyin terms of function since it is the only place in whichleft and right joints are linked via a relatively inflexi-

ble bone, the mandible. This means that movementsof each joint may not take place independently of theother and therefore it is possible that undue stresseson one joint may be transmitted to the other. Thejoints are also unique in that their pattern of move-ment and the forces transmitted to them are modifiedby the teeth.

Anatomy

The upper part of the TMJ is composed of the glenoidfossa which is an oval depression in the base of thetemporal bone. This depression is bounded anteri-orly by the articular eminence, a bony swelling downwhich the head of the mandibular condyle will moveduring function.

The glenoid fossa lies immediately in front of theexternal auditory meatus, and its posterior border islimited by the squamo-tympanic fissure and the post-glenoid tubercle. The tubercle is a small, conical em-inence separating the articular surface from the ante-rior margin of the tympanic part of the bone.

The roof of the glenoid fossa is sufficiently thinto be transparent if transilluminated in a dried skullwhich suggests that the joint is not adapted to bearmuch stress.

The other half of the joint is the condylar process ofthe mandible, a rounded structure about 15–20 mmin the mesiolateral dimension and 8–10 mm antero-posteriorly. The long axis of each condyle is angulatedso that lines drawn through them will meet at a pointposterior to the mandible itself. This is because the

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8. Functional Anatomy of the Occlusion 63

condyles appear to be set at right angles to the mainbody of the mandible on each side.

In the adult, the articulating bony surfaces of bothcondyle and glenoid fossa are composed of dense cor-tical bone that is covered by dense fibrous connectivetissue.

Ligaments

The ligaments probably do not support the joint dur-ing normal function, but restrict the border move-ments of the mandible, and therefore define the en-velope within which all movements occur. There arefour ligaments associated with the joint.

The temporomandibular ligament extends from thebase of the zygomatic process of the temporal boneand the articular tubercle, and runs downwards andbackwards to be inserted into the neck of the condyle.It appears to be separate from, and lateral to, the cap-sular ligament that forms a kind of collar around theneck of the condyle and runs upwards to be attachedaround the periphery of the glenoid fossa.

The capsular ligament completely surrounds thejoint cavity to form a synovial capsule.

During opening of the jaw, the temporomandibularligament restricts hinge movement, but when wideropening occurs, the head of the condyle moves for-ward onto the articular eminence. This relaxes thetemporomandibular ligament and causes the third lig-ament, the sphenomandibular, to become taut. Thisligament is situated some distance from the joint itself,and arises from the spinous process of the sphenoidbone, passing downwards and forwards to be insertedinto the lingula on the lingual side of the ramus of themandible.

The fourth ligament is the stylomandibular, whichextends from the styloid process to the posterior bor-der of the angle. This also limits the anterior move-ment of the mandible.

The temporomandibular disc

The joint cavity is divided into upper and lower com-partments by a bi-concave, oval-shaped disc of fi-brous tissue that is sandwiched between the head ofthe condyle and the bone of the glenoid fossa. Its in-ferior surface is concave and its superior surface isconvex, and it has the appearance of a baseball capplaced over the head of the condyle with the peakpointing anteriorly.

The crown of the cap is thickened by a posteriorband of dense connective tissue, and, at the junction

of the crown and the peak of the cap, there is a secondthickening, the anterior fibrous band. Between thesebands is a less dense intermediate zone, and behindthe posterior band is the bilaminar region, consistingof an upper part attached to the posterior wall of theglenoid fossa and a lower part attached to the backof the condyle (Fig. 8.1).

The borders of the disc are attached to the fibrouscapsule of the joint, except anteriorly, where the peakof the disc is attached to fibres of the lateral pterygoidmuscle. There may be some attachment of the disc lat-erally to fibres of the masseter and temporal muscles.

Posteriorly, the disc is attached to a thick layer ofvascularised connective tissue, and in this region thedisc contains elastic fibres. The part of the capsule in-serted into the disc from above, and which is attachedto the glenoid fossa, is loose and therefore permitsextensive sliding movements of the upper joint com-partment.

The lower part of the capsule that attaches the discto the neck of the condyle is much denser, allowingonly hinge movement in the lower joint compartment.A synovial membrane, composed of connective tissuewith many capillaries, lines the peripheral parts of thedisc and the capsule but does not cover the articulat-ing surfaces. It secretes synovial fluid into the jointspaces. This fluid has a jelly-like consistency and iscomposed largely of hyaluronic acid. The amount ofsynovial fluid present in normal function is very smalland it is assumed that the joint spaces are normallycollapsed.

Microscopic anatomy of the joint

The bonesThe articular surfaces consist of fibrous connectivetissue overlying undifferentiated mesoderm that itselfoverlies a thin layer of hyaline cartilage. This carti-lage is most predominant in younger joints, and is agrowth cartilage taking part in the normal develop-ment of the joint, and may be involved in remodellingprocesses in adulthood.

Below the layer of cartilage is compact bone cov-ering the cancellous bone of the internal structure ofthe mandible. In old age, not only may the cartilagezone be lost, but so may the fibrous tissue covering atleast some areas, resulting in denuding of the compactbone layer.

The discThe central part of the disc consists of dense connec-tive tissue, but peripherally it has a looser texture, rich

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Anterior band

Lateral pterygoid muscle

Condylar head

External acoustic meatus

Posterior band Bilaminar zone

Fig. 8.1 Schematic diagram of the anatomy of the temporomandibular joint showing the articular disc (meniscus) as theshape of a ‘baseball cap’ lying over the condylar head, and dividing the joint space into upper and lower compartments.

in vessels and nerves, particularly posteriorly in thebilaminar region. The capsule and parts of the discare enervated by branches of the auriculo-temporalnerve that are arranged so that they are not com-pressed during movements of the joint.

The blood supply to the temporomandibular jointis from the superficial branch of the external carotidartery.

The Muscles of Mastication

These may be divided simplistically into closing andopening muscles. However, it must be rememberedthat relaxation of the closing muscles is necessaryto allow the opening muscles to operate, so that allthe muscles are operational during mandibular move-ment.

The masseter is made up of two main bundles ofmuscle fibres originating from the lower border of thezygomatic arch and running downwards and slightlybackwards, to be inserted on the lateral side of theramus of the mandible. Its major function is to close

the jaws together with great force, although it mayalso protrude the mandible slightly during this move-ment.

The temporal muscle has a broad origin from thelateral surface of the parietal bone and its anteriorfibres run more or less vertically, its middle fibresobliquely, and its posterior fibres almost horizontally,all to be inserted into the coronoid process. It is usedto position the mandible during closing movements.Usually, the anterior fibres contract first, elevatingthe mandible, followed by the others to control finepositioning.

The activity of the temporal muscle is extremelycomplex and unilateral contraction is involved in lat-eral mandibular excursions. The muscle is extremelyimportant in dysfunction (Chapter 28), since the painarising from its spasm is reported by patients asheadache.

The medial pterygoid muscle originates in thepterygoid fossa and its fibres run downwards, back-wards and outwards to be inserted into the inner as-pect of the ramus. It is able to elevate the mandibleand position it laterally. During protrusive and lateral

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movements, the activity of this muscle is greater thanthat of the temporalis.

The lateral pterygoid muscle has two heads, onearising from the outer part of the lateral pterygoidplate and the other from the base of the sphenoidbone. The two heads come together and are insertedinto the neck of the condyle and, through the anteriorwall of the capsule, into the disc. The main functionof this muscle is to draw both the head of the condyleand the disc forwards during opening movements.Unilateral contraction will produce lateral movementof the mandible in association with the other muscles.

There are minor muscles of mastication, which in-clude the digastric and the buccinator.

The digastric is an opening muscle running fromthe mastoid process to a bursa on the hyoid bone andup to the genial tubercles of the mandible. Contrac-tion will draw the chin downwards, but this is aidedconsiderably by gravity so that the muscle is mostprominent in the final opening movements.

The buccinator muscles are concerned with main-taining the muscular activity of the cheeks and retain-ing food on the occlusal surfaces of the teeth.

Temporomandibular Joint Function

As was described above, the TMJ is capable of twomovements:

� Rotation� Sliding (translation)

Rotation occurs in the lower compartment and theaxis for this is the mandibular hinge axis. When thecondylar heads are in their most posterior superior(retruded) positions in the glenoid fossae, the axisof rotation is referred to as the terminal hinge axis.The path of rotation is then called the retruded arc ofclosure or reflex arc of closure.

Sliding or translation occurs in the upper compart-ment.

The disc should locate on the head of the condylethroughout, though during sliding it lags behind thecondyle somewhat so that the condyle comes tobear on the anterior fibrous thickening. The lateralpterygoid muscles are the principal protruders of themandible, moving the discs anteriorly as well. The re-turn movement of the mandible is caused by the eleva-tor muscles of mastication but the disc is returned pos-teriorly only by the elasticity of the bilaminar zone.

If the discs get out of phase with the condylarheads or the bilaminar zones lose their elasticity, then

‘clicks’ occur during movement. The disc may becometrapped anteriorly to the condylar head on closureand the click occurs as the condylar head rides back-wards on the posterior band. On the next openingmovement the disc is released and moves sharply pos-teriorly as the condylar head moves forward.

When the mandible moves to open the mouth fromits retruded position with the teeth touching, it willinitially describe an arc about the terminal hinge axis.At about 15 mm open, further hinge movement is im-possible and the condyles slide forwards, taking theirdiscs with them, and continue the rotation on a widerarc until maximum opening is reached (Fig. 8.2). Thepathway described forms the posterior boundary ofthe envelope of border movements (Posselt’s enve-lope). The superior boundary of the envelope is de-termined by the teeth and the remainder to a largeextent by the ligaments around the TMJ.

Lateral movement of the condyles within the fossaeoccurs as the mandible moves to the left or right andis called side shift.

The Teeth

Centric occlusion

Centric occlusion (CO) is the position of maximumintercuspation of the teeth and is also referred to asthe intercuspal position (ICP); because it is usually theposition where exact interdigitation occurs it may becalled the position of ‘best fit’.

CO is used in function to stabilise the mandible forswallowing or as a position for resting during mas-tication. Most individuals swallow with their teethtogether with the lips forming the anterior oral seal.Whilst individuals close their teeth into CO automat-ically, the position is learnt behaviour and appears tobe in the short-term memory.

As a minority behaviour, tooth apart swallowingis recognised. This may be caused by discrepanciesin arch form, tooth position or soft tissue morphol-ogy; the reader is referred to texts on orthodontics forfurther reading on this subject.

CO is a position that is used hundreds of times eachday for swallowing saliva and is the major referenceposition for occlusal restoration. The vast majorityof restorations are adjusted to CO with the patientbeing asked to ‘close together onto their back teeth’.

The basic unit of centric occlusion is the cusp/fossarelationship, with a supporting cusp occluding witha centric stop (Fig. 8.3a). The centric stop may be a

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(a) (b) (c)

Fig. 8.2 Opening the mouth from the retruded contact position (a), the mandible first describes an arc on the terminalhinge axis (b), followed by protrusion and rotation to wide opening (c). This movement is the posterior border of Posselt’senvelope. Opening from centric occlusion would trace an arc slightly anterior to this.

fossa or a pair of marginal ridges or a single sluiceway(Fig. 8.3b). Each cusp will rest in a fossa in a stablerelationship having reached this position by eruption.The position of the teeth in CO is maintained as oc-clusal stability with either inclined planes opposingeach other (Figs. 8.3 and 8.4) or by the tips of cuspsoccluding with flat areas – either as a result of wearor because of a natural shallow fossa anatomy. Thepalatal cusps of the upper teeth and the buccal cuspsand incisal edges of the lower teeth are all supportingcusps occluding into central fossae, marginal ridge orcingulum contacts.

If three inclined planes interact to form thecusp/fossa relationship, this is called a tripod(Fig. 8.4). Some authorities believe this to be a fun-damental occlusal relationship. It is, though, exceed-ingly difficult to reproduce in restorations and evenif it is, the properties of the restorative material maynot maintain it (see Chapter 14).

Loss of the cusp/fossa relationship contacts willlead to loss of occlusal stability and tooth move-ment may follow leading to over-eruption, tilting orrotation.

The buccal cusps and incisal edges of the upperteeth and the lingual cusps of the lower teeth donot participate in the arrangement for occlusal sta-bility and are termed non-supporting cusps. Thesecusps have no opposing contacts in centric occlusion

but may contact teeth in the opposite arch in lat-eral excursions and protrusion (see later). An alterna-tive terminology uses stamp cusp instead of support-ing cusp and shear cusp instead of non-supportingcusp.

Centric relation

When centric occlusion has been lost, in full denturesfor instance, or is unsatisfactory, another referenceposition must be used for restoring the occlusion. Thisis centric relation (CR). It is important to recognisethat this position has been defined for the convenienceof restorative dentists and is not a physiological po-sition. This may explain the several definitions thatexist for the position.

CR, sometimes referred to in removableprosthodontics as centric jaw relation (CJR), isa position of the condyles within the glenoid fossaeunrelated to tooth position. The most commondefinition used in the United Kingdom is ‘the mostretruded position of the condyles in the glenoidfossae from which unstrained lateral movementsare possible’. However, this is a difficult concept tooperate in practice and a rather better definition forpractical, clinical use is ‘the most superior, posteriorposition of the condyles in the glenoid fossae’.Some American authorities prefer two other closely

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Uppersupportingcusp

Lowersupportingcusp

Buccal

(a)

(b)

Fig. 8.3 (a) Cusp/fossa relationship in bucco-lingual section. Stability is provided by the accurate meeting of the inclinedplanes. (b) Cusp/fossa relationships in mesio-distal section. The upper supporting cusp may occlude with two marginalridges, or into a sluiceway.

related positions; ‘the most superior position’ and‘the most superior anterior position’. It is outsidethe scope of this book to consider the argumentsproposed for these but the most important consid-eration is to obtain a reproducible and symmetricalmandibular position around which to reconstruct thedentition.

CR is usually found by manipulating the mandibleand pushing the condyles upwards and backwards.The condyles will then be centred on the terminalhinge axis and the mandible can be ‘rotated’ by theoperator on the retruded arc of closure.

As the operator moves the teeth together, therewill usually be tooth contact before CO; this is theretruded contact position (RCP), and the teeth in-volved exhibit a premature contact. The movementof the mandible from RCP to CO will have a su-perior or ‘vertical’ component, an anterior or ‘hor-izontal’ component and perhaps a lateral component(Fig. 8.5). The magnitude of this mandibular slideor displacement is often defined as the ratio betweenthe vertical and horizontal movement. The shorthandfor the ratio is either Vh (pronounced as ‘big V, littleh’) where the vertical component is greater than the

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Supportingcusp contacts

Fossa contacts

(a)

(b) (c)

Fig. 8.4 Cusp/fossa relationships. (a) Occlusal view of an upper premolar showing classic tripod contacts, one set in thesluiceway fossa and the other on the tip of the supporting cusp. (b and c) Clinically, this may be obscured by folding of thearticulating paper in the fossae, or by natural variations in relationships. The fossa contact in (c) is almost a tripod, whilst thatin (b) is a flat contact on the top of the marginal ridge.

horizontal or Hv (pronounced ‘big H, little v’) wherethe horizontal component is greater.

In a minority of patients no mandibular displace-ment will be seen such that centric relation is coinci-dent with centric occlusion. However, this diagnosiscan be suspect in view of the difficulty that can beexperienced in the manipulation of the mandible (seeChapter 14).

The significance of mandibular displacements isdisputed. A posterior–anterior slide with Vh is verycommon and it would appear that a separationof CR and CO is natural. The condylar positionin CO is between 0.5 and 2 mm anterior to cen-tric relation in the majority of individuals. It maybe that this posterior–superior position whilst use-ful for dental reconstruction is not a position thatis used physiologically. When reconstructing the

dentition, the new centric occlusion is made withthe condyles in CR, though some limited evidenceexists to suggest re-establishment of a more poste-rior CR within 2 years of reconstruction in dentatepatients.

Lateral displacements are less common as are thosewith Hv. It is possible that a slight asymmetry inmandibular position might lead to muscle fatigue asmight a long horizontal component in the mandibu-lar displacement. This is discussed in more detail inChapter 28.

When individuals close naturally into CO, the pre-maturities are not contacted; it is part of the learntbehaviour mentioned above to avoid them. Closureoccurs straight to CO on a favoured arc of closure.Intrusion by stress, anxiety and so on, into the centralnervous system may interfere with the co-ordination

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(a)

(b)

Terminal hinge axis

Retruded arc of closure

Upward and backward pressure from operator

Retruded arc of closure

Centric occlusion contacts

Premature contact and slide

Retruded contact position on premature contact

Forward and upward into centric occlusion

Codylar position in centric occlusion

Posterior, superior position in glenoid fossa

Hinge axis

Fig. 8.5 (a) The retruded arc of closure and a precentric premature contact on two premolars. Following this contact, themandible slides upwards and forwards into centric occlusion; (b) plan view of articulating paper contacts made during themovement made in (a).

of this behaviour. This may lead to temporomandibu-lar dysfunction (Chapter 28).

Mandibular guidance

The hard tissue guidance of mandibular movementscomes from the condyles and their relationship withthe glenoid fossae – the condylar guidance, and ifthe teeth are in contact, the tooth-to-tooth contacts –tooth guidance. Tooth guidance is made up of an-terior (incisal and canine) guidance and posteriorguidance.

Because the condyles can turn and slide, and thusadapt to tooth positions, in practical terms, the

condylar guidance is not as important as the toothguidance.

ProtrusionAnterior movement of the mandible from CO re-sults in contact of the lower incisors with the palatalsurfaces of upper incisors and the mandible has toopen. It moves forward and downwards to incisaledge contact. The posterior teeth are discluded, butthe amount of disclusion depends upon the heightof the anterior guidance, the steepness of the curveof Spee, the cusp height of posterior teeth and theirslopes (Fig. 8.6a). The anatomy of these features mustbe in harmony so that the posterior teeth do not pre-vent incisal edge contact.

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(a) (b)

(c) (d)

Fig. 8.6 Tooth guidance. (a) Anterior guidance. In sliding forwards with the upper and lower incisors together, themandible also moves downwards, discluding the posterior teeth. This patient has a high anterior guidance. (b) Canineguidance. The movement of the mandible to the right and downwards is dictated by the contact of the upper and lowercanines and the slope of the condylar guidance on the left, non-working side. (c) Group function. There are multiplecontacts between the upper and lower teeth when the patient moves to the left. (d) Non-working interference between theupper and lower second molars (arrowed).

Lateral excursionsThis is also referred to as mandibular side-shift. Thelateral movement is usually also accompanied by adownwards movement caused by the tooth guidance.The side towards which the mandible is moving is theworking side. The opposite side is the non-workingside. In complete denture prosthetics the non-workingside is referred to as the balancing side because of itsrelationship to denture base stability (see Chapter 26).

During lateral excursions, the non-working ororbiting condyle moves smoothly down the articu-lar slope and medially towards the working side.The angle of the medial movement is the progres-sive side-shift. The working side condyle merely turnswithout coming forward. In some individuals, theremay be also a bodily movement of the mandible

and both condyles as soon as the lateral movementcommences – the immediate side-shift.

The tooth guidance for the lateral movement maybe canine guided/protected or in group function. Incanine guidance, the lateral movement is guided onlyby upper canine to lower canine contact, coupledwith the condylar guidance from the non-workingside condyle (Fig. 8.6b). All other teeth should be dis-cluded. In group function, on the other hand, multiplecontacts of the cheek teeth occur (Fig. 8.6c).

There have been arguments as to which of theseguidance arrangements should be used in reconstruc-tion of the dentition. The ‘popularity’ of group func-tion as a restorative scheme arose from studies ofprimitive peoples who ate an abrasive diet, thus los-ing cusp tips and bringing several teeth into contact

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in lateral movement. This is therefore argued as the‘correct’ scheme for man. However, in western races,canine guidance predominates in people under 40years of age, whilst group function tends to occurafter this age due to tooth wear.

Therefore, to favour one scheme to the exclusionof the other would seem to be illogical. As will bedescribed later, it is better to conform to the schemealready present, unless there are positive contraindi-cations.

In both canine guidance and group function thereshould be no tooth contact on the non-working side.If there is contact, this is referred to as a non-workinginterference. Classically, on lateral excursion, the sec-ond molars of the non-working side may be in contact(Fig. 8.6d). This is considered to be a departure fromocclusal norms and might be a predisposing factor intemporomandibular dysfunction. The ‘proper’ rela-tionship is that the mandible should have tooth guid-ance on the working side, but only condylar guidanceon the non-working side.

Tooth contacts in functionThe teeth do not usually meet during masticationsince the food is between them. They attain tooth con-tact in centric occlusion for swallowing or for rest be-tween a series of chewing strokes. During eating, themandible describes some form of ‘tear-drop’ pathway,with a favoured chewing side.

Mouth empty movements, parafunction, may in-volve tooth contacts and these may be habitual. Interms of restorations, it is important to reproduce ex-act and accurate tooth morphology so that this typeof sub-conscious movement is not impeded with thepossible result of occlusal dysfunction.

The Physiology of Mastication

When an individual is at rest, with maximum relax-ation of the jaw muscles, the teeth are not in contactbut are separated by the so-called freeway space ofabout 2 mm. This is the physiological rest position ofthe mandible. There appears to be electrical activityin the jaw muscles even when at maximum rest, sug-gesting that the freeway space is maintained by mus-cle tone monitored by muscle spindles (see below),rather than by the elastic properties of the musclesand surrounding tissues.

The control of mastication is an extremely com-plicated activity and only the main principles can becovered here (Fig. 8.7). Insofar as brain mechanisms

are concerned, it appears that there are centres in thecortex, in the hypothalamus and limbic systems, andin the brain stem itself, each of which has central path-ways to the trigeminal nucleus and thus controllingthe muscles of mastication. In addition, the jaw move-ments used during speech are controlled quite sepa-rately. Disturbances in the central mechanisms con-trolling mandibular movements may result in clinicalconditions such as bruxism (Chapter 26).

The direct control of the muscles of mastication isvia the trigeminal motor nucleus lying in the middlelevel of the pons. Each individual muscle is innervatedby a motor neurone in a particular region of the motornucleus.

The activity of the muscles is monitored contin-uously via their proprioceptive reflexes, which arelargely controlled via the muscle spindles that exist inall the masticatory muscles. They are found in largenumbers in the jaw elevator muscles, but much less inthe depressors. The muscle spindles consist of spe-cialised intrafusal fibres enclosed in a thin capsuleand lying parallel to the main extrafusal muscle fibresor ordinary contractile fibres. Each muscle spindlecontains both nuclear bag and nuclear chain fibres,the stretch in which is monitored by primary myeli-nated group I afferent nerves and thinner myelinatedgroup II nerves. Stretching of the main muscle resultsin stretching of the muscle spindles, resulting in in-formation being sent to the central nervous system.These spindles therefore monitor the stretch reflex ofthe muscles.

Information from the central nervous system andalpha efferent nerves returns to the extrafusal or mainmuscle fibres causing them to contract. The sensitivityof the muscle spindles is adjusted by motor enerva-tion of the intrafusal fibres within the spindle. Theseconsist of two types called static and dynamic fusimo-tor fibres, and are supplied by gamma I or gamma IInerve endings. This system means that when normalmuscle tone is maintained, the spindles are detectingstretching or shortening of the muscle.

However, if the muscle contracts considerably, thespindles would no longer detect slight changes oflength. At this point, the gamma motor neuronesshorten the spindle so that it is again able to monitormuscle tone. Information is also sent to the centralnervous system from Golgi tendon organs that aremuch less sensitive than muscle spindles. Informationfrom these appears to have an inhibitory effect on themotor neurones so that the muscle spindles and Golgitendon organs work together to maintain functionalactivity of the muscles.

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Higher centres

Reflex activity

ProprioceptorsExteroceptors

Muscle contractionMuscle relaxation

Oralmucosa

Joint

Motor end plates

Muscle spindle

Periodontalligament

Fig. 8.7 Schematic diagram ofthe neural control ofmastication. Proprioceptive andexteroceptive information fromthe muscles and oral tissues isprocessed in the brain stem.Under the influence of highercentres, motor impulses arerelayed to the muscle endorgans.

These reflex arcs control various reflexes in themasticatory cycle. These are jaw-opening reflexes, avariant of which is the horizontal jaw reflex occurringin lateral or horizontal movement.

There is also a jaw-closing reflex, which ‘operates’the reflex arc of closure. However, the normal pathof closure is not the reflex one, but the habitual onethat achieves centric occlusion efficiently.

In addition to the information from the musclespindles and Golgi tendon organs, information is fed

to the central nervous system from receptors in thejoints, particularly in the capsule of the TMJ andin the peripheral parts of the articular disc. Thereare also receptors in the periodontium that rangefrom non-specialised nerve endings to more com-plex structures. Pain is monitored via sensory nerveendings and directional sensitivity may be associatedwith mechano-receptors. The presence of food in themouth is monitored by exteroreceptors in the oralmucosa.

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The masticatory cycle

It seems that when food is placed in the mouth itscontact with the oral mucosa initiates, through sen-sory nerve endings, the commencement of the masti-catory cycle. The size, hardness, taste and texture ofthe food is appreciated and this information is pro-cessed by an ‘oscillator’ system in the brain stem closeto the trigeminal nucleus so that rhythmic chewingmovements begin. These movements are modified byreflex activity originating from nerve endings in themuscles of mastication, the periodontium, the oralmucosa and the TMJs, and are modified by the guid-ance planes provided by the joints, but more particu-larly by the teeth themselves.

When the information reaching the central nervoussystem suggests that the food is well comminuted and

Functional Anatomy of the Occlusion – Summary

The anatomy and physiology of the temporomandibular joints, ligaments and muscles of mastication andtheir relationship to the function of the teeth is the basis of occlusion.

The many terms used in describing the function of the teeth and the joints are a source of confusion andthere are conflicting forms of terminology proposed by different authorities. The terms defined here areused throughout the book.

The success of much restorative dentistry depends upon the correct shaping of the functional surfaces ofrestorations to comply with the functional anatomy described here.

formed into a bolus, deglutition begins. The rele-vant part of this is that the mandible goes into cen-tric occlusion to be ‘locked’ in that position so thatthe pharyngeal constrictors and the tongue can op-erate from a firm base, and an anterior seal can beprovided.

In such a complex system, instability of teeth, miss-ing teeth, teeth in malocclusion or premature con-tact, pain in any tissues of the mouth, disturbances inthe joint itself or influence from the central nervoussystem require considerable adaptation by the indi-vidual to maintain efficient function. Clinical dentalprocedures are aimed at restoring the harmony be-tween all the components of the masticatory systembut often depend on the patient tolerating and man-aging to use the restorations.

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Chapter 9Properties of Restorative Materials

Understanding the formulation, basic properties and clinical behaviour of restorative materials is the keyto their correct usage. All materials have limitations and must be used to their best advantage within awell-considered treatment plan. Restoration design is to a large extent governed by the properties of thematerial chosen. This chapter considers the commonly determined physical and chemical properties ofmaterials, how these compare with those of tooth substance and the implications, in general terms, forclinical practice.

The mouth is a hostile environment for restorativematerials. Within this environment they are subjectedto physical and chemical stresses from the occlusion,the diet, plaque and the behaviour of the patient. Thevarious effects are listed in Table 9.1. It is against theirbehaviour in this environment and their ability to behandled easily that materials must be judged.

The requirements of an ideal restorative materialare:

� Physical properties equivalent to those of tooth� Insoluble in oral fluids and diet� Adhesive to tooth, sealing and stabilising the

tooth/restoration interface� Dimensionally stable� Chemically inert, non-toxic� Cariostatic and bacteriostatic� Tooth coloured� Easy to handle� Cheap

In relation to the first requirement, various physicalproperties of tooth tissues are shown in Table 9.2, butwhat these values do not reveal is the way in which atooth, a very complex composite structure, functions.Also, as with many physical properties, the physicalvalues vary not only with the site of the tissue, butalso with the way in which it is tested.

Whilst enamel is a brittle crystalline solid, dentineis viscoelastic, being able to deform under load andrecover subsequently. The combination of the twomake a very interesting engineering structure withthe response to an applied load revealing it to bevery durable, much better than if the two tissues actalone. However, in analytical terms their combinedconstants are almost impossible to determine abso-

lutely. Add to this the elasticity of the periodontalligament that absorbs some occlusal loading, and thepuzzle is complicated even further.

Therefore, one can only sympathise with the bio-materials scientist who is called upon to design re-placements for lost or excised tissues.

Physical Properties of RestorativeMaterials

Various physical criteria may be used to describe ma-terials and test their ability to restore teeth. Table 9.3lists some physical properties that are often quoted tojustify clinical usage.

Historically, the basis for acceptance of a new ma-terial was to select a group of clinically successfulmaterials and characterise it by laboratory tests. Thenew material could then be judged against the val-ues for the materials already in use for that particularapplication.

Unfortunately, this approach is very restrictive ofnew developments, and the application and signifi-cance of some ‘standard’ tests is open to question.Also, many materials are used in combination: metal–ceramics, dentine adhesives and composites, gold andluting cements. A successful restoration will dependon the combinations working well. However, themeasurement of the properties of one componentalone will not tell the whole story.

Mechanical properties

Mechanical properties give an indication of materialquality, but the testing method may not mimic the

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9. Properties of Restorative Materials 75

Table 9.1 Possible deleterious effects of intraoral function on restorations

Function Agent Possible effect on restorations

Mastication

Acids in diet or plaque Surface degradation

Abrasive food Discolouration

Dissolution

Deformation by load Fatigue and fracture

Temperature change Dimensional change and

adhesion failure with tooth

Saliva and dissolved or Discolouration

suspended compounds

Habits

Tooth brushing Abrasive Surface loss

Pipe smoking Pipe stem Surface loss

Bruxism Opposing teeth Fatigue and fracture

forces applied clinically; these vary in nature, mag-nitude and rate of application. Whilst considerableefforts have been made to develop clinically realistictests, such as the ‘artificial mouth’, these are inevitablycomplicated and costly.

Mechanical properties tests also give an indica-tion of possible handling problems, in that specimenpreparation is often as crucial as the method of test.If a material causes problems, inconsistent specimensand a large scatter of results will be seen. This point isillustrated by the problems of adhesion testing whereclinical inconsistencies are also reflected in a very widescatter of results in the laboratory.

Modulus of elasticity (Young’s modulus)This is a fundamental property that characterises therigidity of a solid in tension or compression, when itis deformed elastically.

Stiff materials, such as ceramics and metals, havehigh elastic moduli and materials like impressionrubbers have low moduli, with polymeric materialssuch as methyl methacrylates forming an intermedi-ate group. The modulus reflects the amount of de-formation or strain a material will undergo when acertain load or stress is applied.

When stress is plotted against strain, a character-istic curve is produced (Fig. 9.1). The slope of thelinear portion where stress is proportional to strain isthe modulus.

The proportional limit shows where the plot ceasesto be linear and the elastic limit indicates the onset of

plastic deformation, where the removal of the loadis followed by incomplete recovery to the originaldimensions (Fig. 9.2a).

Before the elastic limit, removal of the load wouldbe followed by full recovery. If the recovery took timeto occur (Fig. 9.2b), the material would be viscoelasticand this is a characteristic of the majority of restora-tive materials.

Full recovery is an important property of impres-sion rubbers after they have been removed fromundercut areas of the mouth, so that these may bereproduced accurately. However, because of their vis-coelasticity, recovery is not instantaneous, and theyshould not be cast for at least an hour to allow re-covery to take place first. If, though, the undercutswere severe, the material might be taken beyond itselastic limit and recovery would not be; it would havea permanent set.

On the other hand, if ductility is required of a metalfor swaging, then the permanent deformation beyondthe elastic limit, but before the yield point, is an es-sential property.

A complication of viscoelastic behaviour is that therate at which loading takes place influences the strain,and results for modulus will vary accordingly.

Brittle materials, such as ceramics, do not have anelastic limit, and exhibit rapid brittle failure whenthe stresses exceed the proportional limit. Viscoelasticmaterials subjected to low loads that are intermittent,may eventually fatigue, i.e. show reduced recoveryand then deterioration by ductile failure.

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Tabl

e9.

2So

me

prop

ertie

sof

rest

orat

ive

mat

eria

lsco

mpa

red

with

toot

hsu

bsta

nce

(indi

cativ

eva

lues

)

Gla

ssio

nom

er

Prop

erty

Enam

elD

entin

eA

mal

gam

Com

posi

tece

men

tsC

emen

tbas

eG

old

type

III

Mod

ulus

ofel

astic

ity

(GPa

)

8515

55H

ybri

d20

Mic

rofin

e6

Aci

dba

se4

RM

GIC

8

Poly

carb

oxyl

ate

5

Zin

cox

ide

Euge

nol2

100

Com

pres

sive

stre

ngth

(MPa

)

380

300

350–

510

250–

400

Aci

dba

se25

0

RM

GIC

300

Poly

carb

oxyl

ate

70

Zin

cox

ide

Euge

nol

26

N/A

Tens

ilest

reng

thdi

amet

ral

(MPa

)

1010

548

–60

50–9

0A

cid

base

40

RM

GIC

80

(Uni

axia

l)

Poly

carb

oxyl

ate

12

Zin

cox

ide

euge

nol3

450

(Uni

axia

l)

Vic

kers

hard

ness

(kg/

mm

2)

300

6010

060

4040

400

Ther

mal

coef

ficie

ntof

expa

nsio

n×

10−6

/◦C

11.4

(acr

ossc

row

n)

8.3

2525

–60

Aci

dba

se10

RM

GIC

15

3540

0

76



Table 9.3 Physical properties of restorative materials

Mechanical properties

� Modulus of elasticity

� Creep

� Compressive strength

� Tensile strength

� Flexural strength

� Fracture toughness

� Abrasion resistance

Physical constants

� Coefficient of thermal expansion

� Thermal conductivity and diffusivity

� Dimensional changes on setting

Degradation

� Sorption and solubility

� Corrosion

� Colour stability

Handling characteristics

� Mixing time

� Working time

� Setting time

� Surface finishing

As a concept it is important to decide which typeof failure mode will occur in a given circumstance,and it is then possible to design a material for theapplication. However, as both types of failure may

Plastic

deformatio

nUltimatestrength

Elastic limitProportional limit

Ela

stic

def

orm

atio

n

b

a

Strain (change in length/unit length)

Str

ess

(fo

rce/u

nit

are

a)

Fig. 9.1 Stress/strain curve. The ratio of a/b is the modulusof elasticity.

be seen intraorally, depending on the material in use,design decisions are difficult, if not impossible!

Progressive time-dependent permanent deforma-tion under load is termed creep, which is a particularfailing of dental amalgam. The loading by the occlu-sion causes the restoration to deform, and the mar-gins, being thin, are the first areas to fatigue duringthe repeated loading. Corrosion of the metal hastensthe fatigue cracking. The more successful amalgamshave low creep values and lower corrosion rates. In-terestingly though, the very lowest creep values do notseem advantageous, possibly because this is accompa-nied by brittle behaviour, with the material being toorigid to absorb stress.

Creep is measured by applying a static load for agiven time and measuring the change in length of thespecimen. However, intermittent loading is more re-alistic and dynamic creep is the measure of this.

Compressive strengthThis is determined by applying a steadily increasingcompressive stress to a cylindrical specimen until thespecimen fractures (Fig. 9.3). It might represent theloading of a restoration by the occlusion, but takes noaccount of the support provided by the cavity wallsor absorption of stress by the periodontal ligament.Further, the incidence of compressive loading dependsupon the site of the restoration, with Class III and Vtypes receiving none.

The test gives some indication of the quality of amaterial but is not a definitive guide, since there islittle point in having values above that of enamel,and this could be deleterious to opposing teeth. Itis also not a very discriminatory test in terms ofdifferentiating between materials of similar generictype.

The rate of loading of the specimen can significantlyaffect the results; strain rates during test of 1 mm/minare common, but apparently higher strengths can berecorded if higher rates are used. Attempts have beenmade to relate strain rates to those encountered dur-ing chewing, and 190 mm/min has been suggested.

Misleading results can also be obtained in compos-ite materials whose filler particles will be compactedduring testing, increasing the forces recorded prior tofracture.

The rapid attainment of an adequate compressivestrength is an essential requirement for a cavity basethat must resist the subsequent forces of restorationinsertion. Compressive strengths of lining cementsmeasured at 24 hours, rather than the realistic 10 min-utes, therefore have little clinical relevance.

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Load removed

Recovery

Permanentdeformation

Strain(change in length / unit length)

Str

ain

Load removed

Return tooriginal dimensions

Str

ess

(fo

rce

/un

it a

rea

)

Load applied Recovery Time

(a) (b)

Fig. 9.2 (a) Stress/strain curve showing loading of a specimen past its elastic limit, resulting in a permanent deformationafter the load has been removed; (b) strain plotted against time for a viscoelastic material. After the load has been removed,some time is necessary for full recovery to take place.

There is some correlation between the early (1 h)compressive strength of amalgam and its clinicalsuccess.

Tensile strengthTo determine this property, two opposing pullingforces are applied to the specimen in its long axis(Fig. 9.3). Tension is quite likely to be encountered inthe mouth, for instance, across the occlusal isthmusof a Class II restoration under occlusal load.

It is a better test of material quality than compres-sion, but the test specimens are more difficult to makeand alignment during testing is critical to ensure theloading is uniaxial. The results are much lower thancompressive strengths, partly due to sensitivity to thespecimen defects mentioned above as well as the dif-ficulties of test. As with the compressive strength test,the results are strain rate dependent.

To overcome these difficulties, diametral tensilestrength has become popular. Here, the load is ap-plied to a cylindrical specimen on its side (Fig. 9.3).

The application of a compressive load in one planeis converted to a tensile strain at right angles to it. Itis, however, only suitable for brittle materials sinceit is assumed in the calculation that there is no dis-tortion of the specimen prior to fracture. This is notthe case with polymers and many composite materi-als and quite erroneous results can be obtained thatwill flatter the material under test.

Flexural strengthThe application of a bending force to a beam (Fig. 9.4)induces both compressive and tensile forces, andtherefore the results should indicate a combined

property. The test is useful for polymers and ceramics,and is simple to perform. Again, the results are strainrate dependent and can be affected by specimen de-fects as with other tests.

More recently biaxial flexure tests have becomepopular. Here the specimen is a disc supported onan annular knife edge and the load is applied to thecentre of the disc. This removes the concerns aboutedge effects as these are outside the area of the speci-men under test. In both uniaxial and biaxial flexuralstrength tests, if the deflection of the specimens ex-ceeds more than 10%, the theory for calculation isinvalidated.

Fracture toughnessComplex tests under this heading endeavour to mea-sure the energy required to propagate a crack within amaterial and create new surfaces. This is superficiallyattractive since crack formation is an integral part ofintraoral failure. However, results are often modulusdependent and ranking of materials by using this typeof test can be at variance with clinical findings.

Hardness and abrasion resistance

These properties give some guidance on the possibleeffects of surface degradation by physical as opposedto chemical agents. However, because of the very com-plex processes involved intraorally, their results canbe very misleading.

Several types of wear tests have been devised thattry to mimic oral conditions, but these have beendisappointing as they tend to produce a ranking orderthat only fits one generic group of materials.

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Compression Tension

Diametral tension

Plane oftensileforces

Fig. 9.3 Schematic diagrams of thetest configurations for thedetermination of compressive strength,tensile strength and diametral tensilestrength.

Coefficient of thermal expansion

A mismatch of the coefficients of thermal expansionof the restoration and tooth will result in differentialexpansion and contraction during intraoral tempera-ture changes. This will stress the restoration/materialinterface and a space will form between the two. Thisallows the ingress of fluids and bacteria, known asmicroleakage (see later).

These transient temperature changes lie between5 and 65◦C and their effects are made worse bycapillary action as the expansion/contraction occurs.

The worst material from this respect is unfilledacrylic, whilst the best are ceramic and glass ionomercement.

Thermal conductivity and diffusivity

Thermal conductivity indicates the amount of heatpassing through a standard volume of material whenthe specimen and its surroundings are at a steadytemperature. This steady state is rarely reached inthe mouth and it is better to consider the thermal

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Bending – Flexural strength

Induced compressive stress

Induced tensile stress

Fig. 9.4 The fracture of a beam to determine flexuralstrength by three point loading. During bending, the uppersurface is subjected to compression and the lower totension.

diffusivity of any material which shows the rateof temperature change from one side of a speci-men to the other during transient changes in tem-perature. This type of change is typical of intraoralconditions.

With metals, these properties are of considerablesignificance since the heat transference is so rapid thatthe underlying structure will reach oral temperaturevery rapidly. With polymers, the rate of heat trans-fer will be considerably slower and composites showa surprising range of diffusivities that may relate tofiller loading, size and type. The less well-appreciatedphenomenon is that once the temperature of these ma-terials changes, recovery to oral temperature is muchslower.

The ideal would be to match the material’s diffu-sivity as closely as possible to that of dentine, as thisacts as a very effective heat sink, both because of itsbulk and its low diffusivity value.

Dimensional changes

Ideally, materials should undergo no change afterplacement in the cavity, but almost all setting ma-terials shrink as new compounds are formed.

Polymerisation of monomers leads to contractionand it may be quoted as volume or linear shrink-age. Whilst this gives some guide as to the amountof space that may form around restorations, its ef-fects are moderated by the strength of mechanicalor chemical bonds between the cavity wall and the

material, and its configuration. The development ofhigh-molecular-weight monomers of low shrinkage isvery important.

Conversion of monomer to polymer during settingis usually inefficient in dental materials, about 40%for chemical initiation and 60% for light activation,and exposure to temperature changes intraorally in-duces further reaction leading to a post-cure shrink-age.

Water sorption causes expansion of dental poly-mers including composites, but the effect is reducedby the containment of the material by the cavity andcompensation for shrinkage does not occur.

The acid/base setting reactions of cements such aszinc cements and conventional glass ionomer cementsare usually dimensionally stable if they are main-tained at constant humidity. Loss of water leads notonly to shrinkage but to weakening of the cementmatrix, hence the need to coat glass ionomer cementswith an impervious polymer layer during cement mat-uration.

The setting reaction of amalgam is complex,with an initial shrinkage caused by solution ofthe components, followed by expansion caused bycrystallisation of new phases. The net result inmodern mechanically mixed materials is a smallshrinkage.

Intraoral Degradation

As was mentioned at the beginning of this chapter,the hostility of the mouth towards restorations causesmany forms of degradation. All materials are affectedin some way or other.

Sorption and solubility

Ideally, these properties should have values of zero.The sorption of fluid by polymers depends on theirdegree of cross-linking. Polymethyl methacrylate ab-sorbs about 2% by weight of water and, in thelong term, this reduces its physical properties. Otherpolymer-based materials, such as composites, exhibitless uptake, but the amount still has a significant effecton their properties.

Similarly, there is a loss of material from most poly-mers with time, as the lower molecular weight com-pounds slowly dissolve out. The solubility decreasesas the molecular weight of the polymer increases andas more efficient conversion occurs during polymeri-sation.

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These properties are usually measured over a pe-riod of 7 days for standard tests, but in the mouth theexchange of fluid continues for a considerable timeuntil equilibrium is reached. This is frequently notfor many months.

Loss of material, which tends to include plasti-cisers, inevitably affects the mechanical propertiesadversely.

Whilst water is the recognised test medium, othersolvents found intraorally, such as ethyl alcohol, andacetic and lactic acids, are likely to have deleteriouseffects. The solubility values for luting cements areimportant as an indicator of these materials’ durabil-ity. Polycarboxylate and glass ionomer cements, whenfully matured, have the lowest values.

Corrosion

This affects both metals and glasses, but by differentmechanisms.

AmalgamThere may be some advantage in some corrosion ofamalgam since the products are bactericidal and alsoseal the cavity wall/material interspace. However, thecorrosion occurs in the weakest phase of the set amal-gam and causes the whole structure to weaken andparticularly leads to ‘ditching’ of the margins.

The main product of the setting reaction of conven-tional alloys is a cored structure of unchanged alloypowder surrounded by the silver–mercury γ1 and thetin–mercury γ2 phases. The removal or the reductionof the latter phase has been the prime objective, sinceit is by far the weakest of the phases. The presenceof saliva and plaque sets up corrosion cells that re-sults in the slow breakdown of the γ2 phase with theformation of sulphides and chlorides, and alsothe liberation of mercury that continues to react withthe unchanged alloy.

The high copper amalgams show a marked reduc-tion or even elimination of the γ2 phase. The copperhas a greater affinity for the tin than the mercury,and copper–tin complexes are formed preferentially.These are themselves not entirely resistant to corro-sion but the rate of corrosion is considerably reduced.The end products take some time to form and theelimination of the γ2 phase is very dependent on mer-cury concentration during mixing.

Corrosion and creep are all increased by the pres-ence of excess mercury and the mixing and han-dling of the materials must be carefully controlled.Certain high copper materials perform better than

others and there is an overlap in performance withthe poorer high coppers and the best conventionalmaterials.

GlassesThe ceramics employed in both composite materialsas reinforcing fillers, and as inlays and crowns arecorroded by saliva.

In the composites, water is absorbed by the poly-mer and comes into contact with the filler. Metal-lic ions pass from the glass and the accumulationof corrosion products causes stress cracking in thepolymer. Long-term immersion studies have showndramatic decreases in strength of conventional com-posites. Glasses containing barium strontium or zincsalts to confer radio-opacity are more vulnerable thanalumino–silicate combinations.

However, the microfine materials are more resis-tant to corrosion because the filler particles are sur-rounded by heat-cured polymer that exhibits a lowerwater uptake. The clinical durability of the microfineshas been greater than would be expected from sim-ple mechanical properties tests and this illustratesanother problem in predicting clinical performance.Their performance clinically was very similar to themore highly filled composites but the trend has beento abandon the microfines in favour of hybrid fillerconfigurations.

Ceramic materials used in the construction ofcrowns and inlays are also liable to a form of corro-sion. This is particularly common where glazing ma-terials are applied the surface of cast ceramics. Therate of material loss is slow but leads to an irregularsurface that may be quite abrasive. The corrosion ofthe body of the ceramic is a cause of fracture in thelong term.

Colour stability and staining

This applies principally to the polymer-based mate-rials. Loss of tooth matching colour may be due tosetting reaction by-products, degradation of the basepolymer or the accumulation of extrinsic stains on adegraded surface.

Amines are used as initiators in both self-cured andlight-cured materials and they remain after the re-action as potential discolourants. If the amine con-centration is too high, perhaps in order to acceleratesetting, then colour instability will result in the longterm. Accelerated ageing tests will reveal this.

The principal base monomer of many compos-ites is bis-GMA and this yellows gradually when

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exposed to ultraviolet light. UV absorbers are addedto counteract this, but they are not wholly satis-factory. The polymer also changes colour due tosorption.

However, the most critical aspect of the compositesis their tendency to accumulate stain on the surface.This is partly due to the degradation of the silanecoupling agent that bonds the filler to the polymerand partly to the abrasion of surface polymer leav-ing a rough surface. Porosity, that results from airinclusions during mixing and placement, also collectsstain.

Microleakage

The interface between restoration and cavity wall isan area of weakness that is under the influence ofthe properties discussed above. In the absence of anadhesive, mechanical interlocking between tooth andrestoration is all that maintains a seal. As shrinkageand subsequent temperature changes occur, the linksare broken, and fluid and bacteria pass in. The spacebecomes an area of transit for all types of compoundsthat cause staining and pulpal sensitivity. Bacteria arethe least welcome as they are able to colonise thedentine surface and are implicated in the pulpal re-actions to restorative materials.

Various techniques and materials have been devel-oped to overcome the problem, the first being the cav-ity varnishes used with amalgam. Even these were sol-uble and the success of the restoration depended uponcorrosion products blocking the space.

The development of dentine adhesives or restora-tives that adhere to dentine offers the best hope forthe reduction of leakage (see later).

Ion exchange across the interface is of considerableinterest. For example, fluoride migrates from the glassionomer cements and inhibits caries initiation at therestoration margins. The fluoride is incorporated inthe glass as a flux to aid manufacture and intraorallyit slowly diffuses into the surrounding matrix fromwhich it passes into the tooth tissue (Fig. 9.5). Thecompomers are the best fluoride releasing polymer-based restoratives available but the rate of releaseis substantially less than that from conventional andpolymer-based glass ionomer cements. Surprisingly,there is little evidence of the appropriate levels of flu-oride release needed for restorative materials. Recentwork has shown that the higher levels of fluoride re-lease may have some effect on inhibition of bacterialgrowth on the restoration leading to reduced plaqueformation.

Plaque

Bacteria

Saliva

Metallic salts in solutionSolvents

ElectrolytesBacterial by-products

Plaque

Enamel Material

Dentine

Corrosion products

Diffusion products

Tissue fluidTubules

Secondarydentine

Pulp

Fig. 9.5 Microleakage. Tissue fluid together with corrosionand/or diffusion products from the material passes out andbacteria, toxins and various salts in solution pass in.

Handling Characteristics

Materials must be formulated so that they can be ma-nipulated easily. Any material that is difficult to useor is oversensitive to handling techniques is likely tobe a failure, no matter how good its final properties.

Mixing

The most efficient way of ensuring the correct pro-portions of components and a satisfactory mix is touse encapsulated materials. With amalgam, encapsu-lation has the added advantage of improving mercuryhygiene.

The cements, particularly glass ionomers, are themost sensitive to errors in proportioning and mixing.Care must be taken to follow the manufacturer’s in-structions exactly.

Mixing also incorporates air into the material thatmay lead to surface problems. Single component ma-terials, particularly those, such as the light-cured com-posites, that are vacuum packed as well as being

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delivered in single dose ‘compules’, help reduce theproblem.

Working time

Adequate time must be available to mix and form therestoration before the setting reaction increases theviscosity of the material to a level at which it is notworkable. The self-cured composites were the mostdramatic example of this problem. They tended tobe overinitiated to please the clinician with a shortsetting time. Unfortunately, this severely restricted theworking time leading to poor cavity wall adaptationand surface clefts if placement was not rapid. Thiswas one of the driving forces for the development oflight-activated materials.

These materials have become known as ‘commandsetting’ materials. They use external energy, currentlylight within the wavelengths 410–490 nm, to excite aninitiator in the material. However, the working timeis not unlimited as the operating light also emits lightof a similar wavelength. Unless an appropriate filteris fitted to the operating light, the working time canbe quite restricted. This may lead to the placement ofmaterial that is already starting to polymerise.

Rapid setting amalgams, mainly spherical parti-cle or microcut types, also have a restricted workingtime. If this is exceeded, increments may not amalga-mate with each other, leading to ‘layering’ within therestoration.

Setting time

A rapid set seems to be clinically desirable to reducechairside time. However, this brings with it the loss ofworking time discussed above, and also in polymericmaterials, the chain growth is restricted, leading toinferior physical properties. A long setting time canbe equally deleterious, since great patience is requiredfrom the clinician. The early glass ionomer cementswere very slow setting due to the low reactivity of theglass and early contamination with saliva led to rapidbreakdown of the restoration.

Surface finishing

The final restoration should have very low surfaceenergy so that it does not collect plaque and otherintraoral deposits. Often, the ‘as set’ material will re-quire a finishing stage to impart a smooth surface.This must be as simple as possible and ideally doneat the placement stage. However, very few materials

have achieved their optimum properties at this timeand finishing must be delayed until maturation hasoccurred.

Adhesion

Many attempts have been made to achieve chemi-cal attachment of the restoration to both the enameland dentine. These may be divided into two distinctgroups:

� Bonding directly to the substrate by the restorative(polyacid-based cements)

� Bonding to the substrate by the use of an interme-diate bonding compound

Bonding directly to the substrate by therestorative

The oldest successful adhesive system is that usingpolyacrylic acid as found in the polycarboxylate andglass ionomer cements. Two reactions appear to-gether. The first is a simple chelation reaction in whichthe calcium in the enamel and dentine reacts with thepolyacrylate ion. The carboxylic acid groups of the ce-ment polyacid displace phosphate and calcium fromthe hydroxyapatite surface with the formation of anintermediate layer of fluoridated carbonoapatite. Thesecond is a limited chemical reaction between the or-ganic phase of the dentine and the polyacrylate ion.This mechanism of attachment has not been clearlydefined but it is reported that the bond to decalcifieddentine is very difficult to break.

The bond appears to be a dynamic phenomenon.The polymeric nature of these cements ensures a mul-tiplicity of bonds between substrate and cement sothat under clinical conditions the severance of a sin-gle bond does not lead to failure. Although the bondstrength of glass ionomer cement to dentine is nothigh in comparison with other adhesives, the bondappears to be the most durable and reliable of thecurrently available materials.

The surface must be clean and free of pellicle. Var-ious cleaners, or conditioners, have been used, start-ing with citric acid. This, though, produced mild pul-pal irritation and rapidly degraded. More recently theuse of tannic acid and, more commonly, polyacrylicacid has become more accepted. It is now thought,however, that the bond strengths to freshly cut den-tine are no different from those found with treateddentine.

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Fig. 9.6 A scanning electron micrograph of a smear layerat the cavity margin. It is an incomplete layer with somepatches of underlying enamel showing through.

Bonding to the substrate by the use of anintermediate bonding compound

The smear layerThe cutting of both enamel and dentine produces alayer of amorphous material, rich in calcium, thatis smeared over the surface of the enamel and den-tine, the smear layer (Fig. 9.6). While the smear layeron dentine has been well defined that on enamel isstill not elucidated clearly. Dentine smear consists ofglobules approximately 0.05–0.1 mm diameter sepa-rated by water-filled channels. It is thought that theseglobules contain aggregations of fractured inorganiccrystallites bound together with denatured collagen.Etching this type of structure will not result in com-plete dissolution and small fragments of crystallitesmay remain within the collagen gel. The enamel smearis thought to be larger fractured crystallites boundtogether by salivary proteins forming a crust to thesurface of the cut enamel.

The amount of smear created depends on the typeof bur used. The ranking order from most to leastis white stone, blank metal, diamond and tungstencarbide burs. The tenacity of the smear layer has neverbeen determined, but it appears to be rather variable.Its presence confers two advantages:

� Sealing of the dentinal tubules� Provision of a calcium rich layer

The smear layer blocks the cut ends of the dentinaltubules and therefore may be a factor in pulp protec-tion from microleakage.

Bonding mechanismBonding to both enamel and dentine is now regardedas a hybridisation process infiltrating the tooth tissue

to provide a complex polymer–tooth tissue contin-uum.

Bonding to enamel is achieved primarily by etchingthe enamel surface with an acid using phosphoric acidgel and then impregnating the etched surface with alow viscosity monomer forming what is classicallyknown as a ‘tag’ layer that mechanically locks thesubstrate to the polymer.

More recently the ‘total etch’ of both enamel anddentine has led to the use of systems that containhydrophilic monomers. These appear to optimisethe infiltration of the acid-etched enamel encourag-ing the hybridisation of the enamel by encapsulat-ing and infiltrating the crystallites exposed by theacid-etching process. This has culminated in the useof self-etching adhesives. These are not regarded asideal for use on enamel as they are particularly ag-gressive and may completely dissolve thin sections ofenamel.

Bonding to dentine is now regarded as a substi-tution of monomer for the inorganic constituents ofthe dentine. The monomer diffuses into the intersticesof the dentine after removal of the inorganic phaseby etching. Once this monomer substitution has oc-curred, the polymerisation process leads to micro-mechanical interlocking with the remaining toothtissue.

There is some evidence of additional bonding be-tween residual calcium and some monomers, but thisis not entirely certain. Predicting the outcome ofbonding to dentine is a much harder than that toenamel as the dentine substrate contains inorganicand organic moieties and also a large proportion ofwater. Further the bonding site on the tooth and anypulpal fluid outflow will influence the outcome. Thecommon adhesive systems fall into two groups: etch-and-rinse adhesives and self-etch adhesives. The maindifference between these two groups is that when us-ing an etch-and-rinse adhesive, the process involves atleast two stages. Initially the dentine is etched and thesmear layer removed, either in its entirety or in part,and the residue is rinsed away before the applicationof the monomer phase.

In the self-etch group both processes are carriedout without the removal of the decalcified mate-rial, which is incorporated within the hybridisedlayer.

There was originally some concern as to the ef-fect of the adhesive primers on the underlying dentinestructure and the odontoblast processes but this ap-pears to be unfounded, except where the floor of thecavity is close to the pulp.

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The process of dentine hybridisation involves thedemineralisation of the outer surface of the den-tine using a range of acids to partly remove thesmear layer and widen the lumen of the dentinaltubules. This also partly demineralises the inter-tubular dentine leaving the collagen as a fibre web.This is then impregnated by the monomer produc-ing micromechanical entanglement within the fibrescaffolding.

The effect is confined to the outer 10–15 μm ofthe dentine. Polymer tags pass down the lumen ofthe fluted dentinal tubules and the intertubular den-tine is hybridised to a depth of 1–3 μm. Care mustbe taken during the priming process since excessivedemineralisation of the dentine leads to a collapseof the collagen network and less penetration of themonomer with a resulting reduction in bond strength.Currently, the bond strengths that are obtainable arein excess of 20 MPa (exceeding the bond strengthsobserved to enamel). However, the results are some-what variable and depend on the type of dentineused to conduct the test and the method of test itself(see below).

One of the main reasons for bond failure is theforce exerted by the polymerisation shrinkage of thecomposite.

Methods of adhesion testing

Bond strengthThe demonstration of effective bonding and its ab-solute measurement is desirable to support the effi-cacy of a particular system. Mechanical bond strengthmeasurement is unfortunately fraught with potentialsystematic and random errors.

Forces designed to rupture the bond can be appliedin several ways. The most common are tensile andshear forces (Fig. 9.7) and many individually designedtest apparati have been proposed to apply these.

Sources of error in testing may be due to the use ofan incorrect substrate, surface preparation and stan-dardisation, specimen handling, and peel and shearforces created as a result of the alignment of the spec-imen during testing.

In view of the shortage of human teeth, severalsubstitutes have been used. These include animalteeth, particularly bovine, and synthetic hydroxyap-atite. Both types of substitute are similar chemicallyto human teeth, but have structural differences. Theyare useful in screening potential adhesives, but finallythere is no substitute for human teeth.

Variations in bond strength will also be found inparallel with compositional differences of the teeth.

Material

Adhesive

Tooth

Uniaxial tension Shear

Fig. 9.7 Adhesion testing. The arrangement for the determination of tensile and shear bond strengths.

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For example, age or position of dentine in relation tothe pulp will vary the mineral content of the specimensurface.

The surface area for bonding must be carefullyand accurately defined and the method must notcontaminate the surface. For ease of analysis, thesurface must be flat and, to avoid mechanical in-terlocking contributing to the bond, as plane aspossible. Handling the specimen after bonding willneed extreme care if the bond is not to be stressedprematurely.

A universal joint system is usually incorporatedinto tensile testing assemblies to align the specimenand substrate with the direction of the applied force.However, during this alignment the bond can bestressed non-axially by peel and shear forces.

Microleakage

The measurement of the intrusion of an agent, suchas a dye, into the space between the material and thetooth also is a common test for the demonstration ofadhesion. This should reflect the effects of inclusionin a cavity rather more than the simple flat surfacebond strength tests.

Many intrusion agents have been used such asradio-isotopes, bacteria, electrolytes and air. How-ever, the hydrodynamics of the dentine cannot be re-produced, and results may not correlate with clinicalobservations.

Biological Compatibility

Biological compatibility is of paramount importancefor any material that is placed permanently in livingtissues. By virtue of compounds leaching from thematerial, local or systemic effects are possible.

Dental materials are often placed at a time whenthey are chemically active, after which they set andbecome essentially inert. A series of in vitro and invivo tests have been devised to screen the biologicalproperties of restorative materials.

The in vitro tests begin with a simple screeningof cell cytotoxicity, after which the material will betested in animals. The animal tests are implanta-tion in the tissues and simulated in-use tests in theteeth.

For the in-use tests, the material is placed in stan-dardised cavities and the pulpal response noted atvarious time intervals after placement. There are a

number of problems with this test in terms of repro-ducibility and variability but, in the absence of anyreliable alternative, it is the best guide to compatibil-ity for restorative materials.

The laboratory tests at the cellular level tendto eliminate materials that are acceptable in othertests. For instance, the cytotoxicity is reduced iffully set material is used instead of freshly mixedmaterial.

The presence or absence of an intervening layer ofdentine between material and pulp alters the responseof pulp tissue to the material very considerably. Zincoxide/eugenol cements are the classic example of this,in that if they are applied to exposed pulp, they induceinflammation, whilst they are obtundent to the closedpulp.

In recent years there has been concern about long-term cumulative effects of small amounts of chemi-cals passing from dental materials. These may haveeffects locally on soft tissues, for example, bis-GMAhas been implicated in the formation of lichenoid le-sions of the oral mucosa. There may also be systemiceffects following ingestion that are even more diffi-cult to investigate and quantify. Latex allergy is nowa serious problem with the use of protective glovesand rubber dam.

The dentist and his staff are at risk from han-dling materials. There may be allergic reactions inthe skin and the effects of inhalation of volatile ma-terials such as methylmethacrylate monomer. Mer-cury has been recognised as a health hazard to den-tal personnel for many years but is now consid-ered to be more of an environmental hazard (seeChapter 10).

Clinical Testing

Following laboratory testing, the materials are sub-jected to clinical trials. An initial explanatory trialusing controlled conditions and a small number ofclinicians is followed by a field trial where the ma-terial is used by many operators in general practiceconditions.

The time scale for these assessments is inevitablylong and the trials are costly. It might be as longas 5 years between invention of a material and itsmarketing, but there is no avoiding this. Realis-tic accelerated tests are difficult to devise in pri-mates and are not representative of human intraoralconditions.

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Conclusion

The combination of laboratory tests, animal stud-ies and clinical trials ought to provide the clinicianwith considerable valuable information on the likelybehaviour of a material when it is placed in themouth.

Unfortunately, this is not the case, since there areso many unquantifiable biological factors that influ-ence clinical success. Not least of these is the skill ofthe clinician in handling materials. Proper attentionto detail and the understanding of the quirks of eachmaterial is an essential component of the dentist’seducation.

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88


Section IIIClinical Management

and Techniques


90


Chapter 10Intracoronal Restorations

The evolution of materials, cutting instruments and techniques, together with a better understanding of thestructure of the dental hard and soft tissues and of the carious disease process, has resulted in modificationsto the principles of cavity design propounded by G. V. Black over a hundred years ago. The advent ofadhesive materials coupled with the more precise diagnosis of caries by radiography has led to differentconcepts. The need for retention created by the cavity shape has been reduced and the lesion is treatedat a much earlier stage. These factors have led to smaller cavities and greater conservation of sound toothtissue. The range of materials available for the restoration of an intracoronal cavity is large.

Indications for Treatment

Primary carious lesions

There is considerable evidence to support the reminer-alisation of the early carious lesion in enamel (Chap-ter 6). Only when the lesion shows positive evidenceof having reached the dentine should operative treat-ment be commenced. Figure 10.1a shows a radio-graph of an early lesion for which the applicationof topical fluoride coupled with regular radiographicreview would be appropriate.

Figure 10.1b, on the other hand, shows clear ev-idence of caries in dentine, and this lesion shouldbe excised and the tooth restored. The diagnosisof caries must be aided by high-quality radiographsthat have been taken and processed by standardisedtechniques.

Failed restorations

Restorations may fail because of recurrent caries, de-terioration of restorative materials or fracture of thesurrounding tooth. The diagnosis of these was dis-cussed in Chapter 3 as was the difficulty associatedwith accurate diagnosis of when to replace a restora-tion or when to accept apparently minor faults.

Cavity Design and Preparation

The extent of the excision of the caries and the finalshape of the cavity depend upon:

� The size of the lesion, or cavity to be re-restored� Its position with regard to aesthetics� The need to conserve tooth substance� The choice of restorative material� Caries incidence and oral hygiene

These factors are interrelated considerably. The se-quence for cavity preparation is:

1 Obtain access and explore the lesion2 Choose the restorative material3 Complete the cavity design and preparation

This is in total contrast with the old traditional teach-ing of cavity preparation, blamed on Black thoughperhaps aided by subsequent teachers, where particu-lar ‘standard’ cavity shapes were defined and applied,without thought being given to the lesion, the toothand its environment.

The lesion

An initial assessment of the extent of the lesion willbe based on clinical and radiographic appearance.However, both methods may underestimate the ac-tual size and exploration is essential prior to mak-ing a decision on restoration type. Remember thatenamel and dentine cannot be replaced once removedso a cautious approach is necessary. Use small ro-tary instruments to gain direct access to the lesion,clear the enamel–dentine junction and the dentinefloor and then consider the likely restoration type(Fig. 10.2).

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92 III. Clinical Management and Techniques

(a)

(b)

Fig. 10.1 (a) Bitewing radiograph showing early enamelcaries (arrowed) which should receive topical fluorideapplication, rather than restoration; (b) Bitewing radiographshowing an approximal carious lesion (arrowed) whichextends into dentine. This lesion should be excised and thetooth restored.

Choice of restorative material

The choice for intracoronal cavities is often a com-promise between aesthetics and long-term durability.The principles of the material types and adhesion totooth were discussed in Chapter 9. The range of ma-terials available for intracoronal restorations is large.It includes:

� Direct composite� Glass ionomer cement� Silver amalgam� Compomer� Composite inlay� Ceramic inlay� Gold inlay

CompositeForty years of relatively successful usage has seen thisgroup of materials become well established for ante-rior use. They are now becoming more established foruse in minimal cavities in posterior teeth and there isa worldwide trend to use composite exclusively forall intracoronal restorations. This is partly becauseof patient demand for good aesthetics and partly be-cause of concerns about the safety of amalgam (seebelow).

The composites are currently regarded as the prin-cipal material for small to moderately sized cavities.In spite of developments, their use in occlusal loadbearing restorations ought to be viewed with cau-tion since they are technically much more demandingto use than amalgam and may not maintain occlusalcontacts as well. They have acceptable wear charac-teristics in small cavities but in larger cavities surfaceloss may be seen within five or so years (Fig. 10.3).Marginal breakdown may be associated with the oc-clusion and the late effects of polymerisation shrink-age.

Current materials are almost exclusively of theblue light/camphoroquinone initiated type thoughnewer photoinitiators, such as phenylphosphine ox-ides, have been developed. Two component self-initiating materials are now reserved for practice loca-tions with poor electricity supply. The by-products ofthe amine–peroxide self-curing system lead to colourinstability, and in light-activated materials there is noperoxide, and the amine concentration is reduced.However, even these materials will change colourslightly during the polymerisation process and willstill darken with age.

Light-activated materials are dispensed in a singlecomponent format and this permits the manufacturermore flexibility in the production of the material, andmulti-functional monomers are common. The orig-inal bis-GMA polymer has been replaced in manymaterials by others such as urethane dimethacrylate;these have enhanced physical properties. Further, thesingle component can be packed at the factory un-der vacuum, mixing is eliminated and the risk of airinclusions is reduced.

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10. Intracoronal Restorations 93

(a) (b) (c)

(e)(d)

Fig. 10.2 Clinical exploration of a carious fissure. (a) The occlusopalatal fissure is darkened with shadowing under theenamel; (b) a small round bur is used to obtain access to explore the lesion; (c) the lesion turns out to be large; (d) theperiphery is cleared and then the pulpal floor is excavated. Some residual staining is left; (e) the completed amalgamrestoration. (A composite might be suitable for this cavity.)

The other principal development has been in fillertechnology with denser fine particle hybrid materialsnow being the commonest formulation. The microfinematerials have provided good clinical service but thevagaries of the market place have reduced their usage.

The restriction of the light-initiated materials istheir depth of cure. Only those parts of the materialthat are reached by the light are initiated and there-fore if either the light source is too far away or theunpolymerised layer is too thick, there will be incom-plete polymerisation. Restorations that are deeperthan 2 mm must be built in separately polymerisedlayers. This makes the restoration tedious and costlyto construct.

Glass ionomer cementGlass ionomer cement (GIC) has undergone consid-erable development in the past 15 years. The originalacid–base reaction setting materials are still regarded

as being effective but the incorporation of polymersin the composition has led to several different ma-terial types – the resin-modified glass ionomer ce-ments (RMGIC). These materials were produced tocounter the limitations of the conventional GIC thatwere slow build-up of mechanical properties and sen-sitivity to moisture.

All RMGICs have, to a greater or lesser extent,an acid–base setting reaction that is accompaniedby a polymerisation reaction. The accompanyingwater-soluble monomer system, usually 2-hydroxy-ethylmethacrylate (HEMA), may be polymerisedby:

� Blue light via a photoinitiator, usually camphoro-quinone – light cure

� A redox amine–peroxide self-initiating system –dark cure

� A combination of the two – dual cure

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Fig. 10.3 Occlusal wear of a direct composite restoration.

Monomer substitution of the water using HEMA hasproduced materials that have early mechanical prop-erties that are similar to those of a mature (three tofour months old) conventional GIC. The initiationof the polymerisation reaction by light provides aform of command set although the acid–base reac-tion will continue for some time afterwards. The ma-terials leach fluoride in a similar manner to the GICsbut they are less susceptible to changes in moisturecontent.

The addition of HEMA has led to a settingexotherm that is markedly greater than the compos-ites and there is a substantial polymerisation shrink-age. It has been suggested that this can be compen-sated for by the high water sorption but saturation ofthe restoration takes several weeks. The marked poly-merisation shrinkage subjects the bond to tooth tissueto substantial stress during the setting stage and thedurability of the bond is uncertain. On the evidencecurrently available, the RMGIC are more appropriatefor the restoration of anterior teeth.

Attempts to achieve radio-opacity for conventionalGICs have been made with varying degrees of success.The majority have been associated with the modifica-tion of the glass to include a radio-opaque element,frequently strontium.

Silver particles may be sintered with the glass dur-ing its production to form a cermet. Another methodis the addition of amalgam alloy particles at the chair-side. Both these methods provide radio-opacity and

also enhance the mechanical properties if added inappropriate proportions.

The cariostatic properties are advantageous. Flu-oride ions released from the glass during the settingreaction leach out from the filling matrix to the sur-rounding tissue. There is also evidence that there isa reverse flow when fluoride ion concentration in thesurrounding medium is raised. It is now inferred fromthis that the GICs may act as reservoirs for variousions. This is of considerable significance since it hasbeen demonstrated in a number of studies that thereis caries inhibition around these restorations.

Conventional GICs may in the long-term sufferfrom erosion in areas where plaque accumulationoccurs. This phenomenon leads to substantial lossof material but the underlying tissue appears to besound.

CompomersThis further group of materials has been developedto combine some aspects of GICs with those of com-posites. The filler is generally a fluoro-alumino silicateglass. These materials, more precisely known as ‘poly-acid modified composites’, have a novel monomerthat contains both carboxylate groups and methacry-late side groups. The setting reaction, usually bluelight initiated, is the same as that of the conven-tional composites where the methacrylate groupspolymerise. However, once the restoration is exposedto the oral environment, water is absorbed and anyfree carboxylate groups will react with this and thesurface of the glass filler. This leads to an acid–basereaction. The carboxylate groups react with the sur-face of the filler to form a salt matrix, and fluorideis released. The mechanical properties of these ma-terials are similar to the hybrid composites. As withcomposite materials, they require the use of an inter-mediate dentine bonding agent to achieve adhesion tothe tooth tissue.

SummaryThe bewildering array of materials described abovecan be regarded as occupying a spectrum rangingfrom pure acid–base reaction ‘salt matrix’ materials atone end, to purely polymer-based materials, the com-posites, at the other. In between there are various com-binations of the two with a lack of clarity about whatthe user should expect from a particular formulation.

Clinical choice is to a large extent personal andempirical and in Table 10.1 the basic properties arecompared. There is no doubt that the average gen-eral dental practitioner is attracted to a rapid setting

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Table 10.1 A comparison of glass ionomer cements, composites and their derivatives as restorative materials

Resin-modified glass ionomercements (RMGIC) (blue lightactivated/dual cure)

Glass ionomer cement (GIC)(acid–base reaction)Property Composites and compomers

Adhesion Intermediate agent(s) required Inherently adhesive Intermediate agent(s) usually

required

Fluoride Composites – mostly none

Compomers – low diffusion

Good diffusion Good diffusion

Setting reaction Blue light – rapid

Surgery light initiates cure

Slow Blue light – rapid

Self-cure component of dual

cure – slow

Setting shrinkage

(average)

Significant (1–3%) Minimal Significant (3%)

Flexural strength

(average)

High (120–150 MPa) Low (60 MPa) Moderate (80 MPa)

Finishing Immediate Delay until mature Immediate (with care)

Colour stability Marginal staining and darkening in

time

Surface stain Surface stain

Abrasion resistance Good except under occlusal load Poor Moderate

Aesthetics Good Variable Good

material that can be finished immediately, is not sen-sitive to water content and has good aesthetics. Thesecriteria reduce the popularity of the original acid–basereaction GICs in favour of the RMGICs and compos-ites. The implications of this are that dentists seemwilling to accept having to use additional bondingagents and the deleterious effects of polymerisationshrinkage.

Silver amalgamThe material of choice in the posterior teeth where thecavity is moderate to large and involves substantialocclusal contacts remains amalgam. It is simple touse and is durable. The major question is over itssafety and a review is cited in the Bibliography. Tosummarise:

� Mercury is a tissue poison and the prime risk is tothe dentist and his staff. Improvements in mercuryhygiene with capsulated amalgam and the carefulcontrol of waste have reduced this risk to a mini-mum. Good mercury hygiene is the primary meansof reducing risks to staff. This includes the properdisposal of the unused material.

� Environmental concerns have led to legislationin some countries seeking to eliminate amalgamfrom use. Other legislation concerns the disposal

of amalgam waste into the public sewers and amal-gam separators may be installed on dental unitsto prevent this. However, it is possible that nor-mal particle filtration systems found in suction andspittoon units are as effective as some separators.

� The most emotive area is the allegation of healthrisks to the patient. Reports on this are far fromconclusive and to date no clear unequivocal sci-entific evidence exists to support the eliminationof amalgam from dental practice; notwithstandingthis, advice has been given that removal or place-ment of amalgam restorations should be avoidedin pregnant women where clinically reasonable.

� As was mentioned in Chapter 9, there are vari-ous components of other restorative materials thatmay have local adverse effects or that are ingestedwith possible systemic effects. Essentially, there isno material that can be described as risk free.

Clearly, reduction in the use of amalgam is possible.Where restorations will be lost in a short period, as indeciduous teeth, then other materials should be used.However, the current amalgam replacements are allmaterials that introduce technical difficulties in place-ment and their long-term performance in larger cav-ities is not as cost effective and durable as amalgam.Their general popularity is driven by aesthetics.

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Composite inlaysComposite inlays have now fallen out of use. Theywere initially produced as a means of compensatingfor the polymerisation shrinkage of direct compositematerials. The shrinkage took place in the laboratoryand the use of a fine luting resin was considered aneffective means of cementation. The disadvantages ofthe systems are the cost of the additional processingand the inherent weakness of the luting composite.The inlays were vulnerable in occlusal contacts andmarginal staining and fracture where the lute was bro-ken down was common. This type of material may beuseful for provisional crowns and bridges.

Ceramic inlaysCeramic materials are the most durable of the toothcoloured materials and have been in use for manyyears as very successful crown materials (see Chapter15). Refinements in formulation and firing techniquehave now made the construction of accurate inlayspossible. They have the advantages of maintainingthe occlusion more reliably than polymers and theyhave far superior colour stability (Fig. 10.4). In partic-ular, the milled or cast materials offer much enhancedfit when compared with the original furnace-firedceramics.

Their disadvantages are the inherent brittleness ofceramic that may lead to marginal fracture and theproblem that besets all indirect restorations, the lack

Fig. 10.4 Ceramic inlay. An MOD in an upper molar.

of durability of the cementing material and interfacialbond failure.

Gold inlaysGold inlays are very much out of favour even thoughwhen well constructed they are arguably an excel-lent restoration. They are the restoration of choice formaintaining occlusal stability and have no adverse ef-fects on the opposing enamel surface. However, theskills required, coupled with the weakness of the ce-ment lute, make them inferior in the majority of oper-ator’s hands to the average amalgam restoration. Thisis not to say that the placement of amalgam does notrequire a high level of skill – it does – but the techniqueis more forgiving.

Treatment of the minimal dentine lesion

Occlusal caries – the preventive resinrestorationA minimal lesion in an occlusal fissure should betreated by local excision of the carious dentine,through the overlying enamel. The access should be ofsufficient size to allow good vision of the affected den-tine. The other fissures on the occlusal aspect shouldbe inspected for evidence of caries, rather than juststaining, and should not be removed unless cariousdentine can be seen under them. Occlusal stops willbe unlikely to be removed by such a preparation, andtherefore GIC can be used because of its adhesionto dentine, low pulp irritation and fluoride diffusion.Composite may also be used.

The remainder of the fissure pattern should be acidetched prior to the insertion of the GIC, and fis-sure sealed after insertion. The fissure sealant shouldbe extended over the GIC to protect it from water(Fig. 10.5).

If the fissure is very steep, so that the sealant will notenter it fully, or there is suspicious staining, then fis-sure widening may be used. A fine tapered diamondis run along the fissure at the depth of the enamel–dentine junction (Fig. 10.6). Any caries revealed bythis can be removed locally by a round bur runningslowly and the cavity extended and restored appro-priately.

Approximal cariesA number of designs to deal with minimal lesionshave been suggested. All of these rely on very precisecontrol of fine cutting instruments, and the uniqueproperties of GIC. It is essential to use magnification

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(a) (b)

Fig. 10.5 The preventive resin restoration. The deeper part of the cavity is filled with glass ionomer cement, and this, plusthe fissure system, has acid etch resin applied to it.

(a) (b)

(c) (d)

Fig. 10.6 Fissure exploration. (a) An apparently innocent pit; (b) careful exploration reveals extensive caries under theenamel; (c) the periphery has been cleared and some altered dentine has been left on the pulpal aspect; (d) the completedamalgam restoration.

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(a) (b) (c)

Fig. 10.7 Tunnel preparation. (a) Bitewing radiograph of 5| showing minimal approximal caries in dentine; (b) Theapproximal lesion is approached via an occlusal access having placed a section of matrix band to protect the adjacent tooth;(c) Glass ionomer cement is placed to restore the ‘tunnel’. This must be chemically cured since the marginal ridge willobscure the approximal section from the curing light. The GIC and the fissures are covered with fissure sealant.

for accurate vision whilst cutting this type of prepa-ration.

The commonest of these is the tunnel preparation(Fig. 10.7) that maintains the marginal ridge, but caremust be taken not to touch the adjacent tooth as thetunnelling emerges approximally. Sight of the approx-imal lesion is obtained by widening the occlusal ac-cess bucco-lingually. GIC is suitable for small lesions;in a larger cavity it can be used for the approximalpart, but it may be surfaced with composite occlusally.Modern condensable GICs may be an alternative ma-terial for the whole restoration. The principal dis-advantage of the tunnel preparation is the limitedaccess it creates to the lesion and therefore the in-ability to be sure of removing the caries. An alter-native design involves removal of the marginal ridge(Fig. 10.8).

Moderate lesions

Conservative Class II cavityThe overriding considerations are:

� Conserve as much tooth substance as possible� Maintain occlusal contacts on enamel

The preparation is begun by obtaining access to theapproximal lesion to inspect its extent and make aprovisional decision on the likely restorative material.The occlusal section will be prepared in accordancewith any carious attack in the fissures and should

extend just below the enamel–dentine junction so thatthis may be inspected for caries. Localised areas ofcaries should be removed either with excavators orwith slow running large round burs. It is necessaryto avoid cutting enamel centric stops if at all possi-ble since occlusal stability may be lost if the restora-tive material is not shaped correctly or loses its shapeduring function.

One of the main problems associated with the ap-proximal preparation is a failure to be aware of the

Fig. 10.8 Diagram of a minimal restoration involving themarginal ridge.

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site of the carious lesion in all three planes beforestarting. The initial penetration of the marginal ridgeshould be made directly towards the lesion with ex-treme care. If the lesion is not located properly, theremay be a tendency to remove more tissue than is nec-essary. Slightly rotated teeth are a particular problem.

The margins of the preparation should just clearthe contact with the adjacent tooth, buccally, lin-gually and cervically, meaning that the outline fol-lows the embrasure shape as well as the shape of thelesion.

Thought must also be given to the mechanics ofplacing the restoration. If the margins are not clearedfrom contacting the adjacent tooth there may be prob-lems in placing the matrix later (see below). Adequatespace must be provided for the entry of instrumentsto place bonding agents and the final material (Black’s‘Convenience Form’).

When using composites, microleakage is reducedby the bond to acid etched enamel. To achieve thisbond, prisms must be etched in their long axis andbevelled margins are necessary to expose prism endsin certain areas. The approximal preparation mar-gins should be bevelled, but not the occlusal section.Here the enamel is cut transversely by the normalpreparation because of its slope towards the fissure(Fig. 10.9).

Fig. 10.9 Model of a cavity for composite withapproximal bevelled margins.

InstrumentationLimits on the extent of cavity preparation are imposedby the bur dimensions, the precision and state ofthe handpiece bearing, and the visual acuity of theoperator.

BursBurs used may be divided into those that abrade awaythe surface and those that cut the surface. The firstcategory includes the diamond instruments that havea fine grit of diamond embedded in the matrix of thebur. Their method of production limits their effectivediameter to not less than 0.8 mm, and the wear on abur of such a size is very rapid. These abrade away thesurface of the dentine producing a surface of uniformroughness.

Tungsten carbide burs have blades with cuttingedges that may be serrated to increase the cutting rate.Even these burs tend to grind the tooth rather thantruly cut the surface. Here again there is a limit tohow narrow these burs can be before the risk of frac-ture of the metal becomes unacceptable; their diame-ters must be greater than 0.8 mm. At any thickness,though, they are very prone to fracture if any lateralstress is placed on them. This fracture will be eitherat the shank or within the structure of the bur itself,depending on the design. This limitation plus the ec-centricity of the handpiece means that the minimumpossible width of cavity that can be obtained realisti-cally is about 1 mm.

Burs with a sharp terminal profile, such as the in-verted cone or flat fissure, introduce stress concentra-tions in the line angles of a cavity, and round profileburs, such as the dome fissure, are preferred.

Anterior restorations

Here all that is required is excision of the lesion withthe minimum removal of tooth substance. The oldkidney-shaped Class V cavity is aesthetically unsatis-factory and quite unnecessary.

Cervical lesions may be restored with composite,GIC or RMGIC if they have enamel margins andby GIC if they are sited in dentine alone. GIC hasdurable bonding to dentine and the important advan-tages of fluoride exchange and better stain resistance.The compomers, the fluoride releasing acid modifiedcomposites, may also be used. There is some evidenceof reasonable survival but the initial poymerisationshrinkage appears to put any adhesive bond at risk.RMGICs show even greater polymerisation shrinkageand are therefore less suitable. Where cervical root

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Fig. 10.10 Direction of access to a mesial lesion on anincisor. The marginal ridge is preserved by this line ofapproach.

caries has appeared in areas of gingival recession, orin sensitive abrasion cavities, GIC is the material ofchoice.

Because the adhesion of both composite and GICis variable, it is unwise to rely on it totally for re-tention, and mechanical undercuts must be provided.However, as was discussed in Chapter 9, marginalleakage is considerably reduced.

For Class III lesions it is desirable to adopt a palatalapproach for the approximal lesion wherever possi-ble for aesthetic reasons, and to angle the bur into thelesion under the marginal ridge to maintain enamelin the occlusion (Fig. 10.10). The labial extensionshould be just through the contact, and whilst thismay result in a very thin layer of enamel and den-tine or enamel alone, the modern aesthetic materialsoffer the advantage of supporting this layer throughbonding; this produces a better aesthetic result. Aswith the Class V, though, it is still preferable to in-clude some mechanical retention as well. This wouldtake the form of gingival and incisal pits and grooves,providing these do not weaken the remaining tooth.

The choice of restorative material is between GICand composite and their hybrid relatives, with theGIC having a positive advantage in individuals withhigh caries rates. Composites and compomers havean advantage in respect of colour match and translu-cency.

Large lesions and amalgam replacement

Here it must be remembered that the amalgamrestoration is a solid block of metal that has no adhe-sion to tooth and that the interface between the ma-terial and the tooth allows marginal leakage and onthe surface is a plaque trap. In addition, the materialis weak in tension and cannot reinforce unsupportedenamel.

Therefore, the cavity design for amalgam restora-tions needs:

� Mechanical retention by undercut walls� Margins placed in zones that can be cleaned� Sufficient width for strength of the material� Removal of enamel that is not supported by

dentine

Approximal sectionUsually referred to as a ‘box’, this area is created byremoving the lesion (and the failed restoration) andextending the margins to the buccal and lingual em-brasures and cervical to the approximal contact area.Unsupported enamel should be removed from thesemargins. Resistance to displacement in an occlusaldirection (retention or stability) is provided by un-dercutting the lateral walls of the box in relation toeach other (Fig. 10.11).

In addition, the approximal box requires resistanceto prevent displacement towards the adjacent tooth,and this should be provided by the occlusal portionof the cavity.

Occlusal sectionThe occlusal key or lock is cut to one-quarter to one-fifth the inter-cuspal distance; this reduces the riskof weakening the remaining tooth structure to a

Fig. 10.11 Approximal box for an amalgam cavity.

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Fig. 10.12 Two composite restorations that have replacedamalgam. The outlines are not ideal for minimising theexposure of material to the occlusion.

minimum and may maintain the enamel occlusalstops. It is shaped so that it is wider at its opposite endfrom the box to create the resistance to approximaldisplacement of the box. If there are two approximalboxes, as in an MOD cavity, these will be mutuallysupporting.

The floors of both the occlusal section and the boxshould be flat to resist loading from the occlusion.

Amalgam replacementWhen replacing an amalgam restoration with a differ-ent material, the choice is between a composite andan inlay. The difficulty is that the cavity will have beenextended to suit amalgam and not composite and thatit will be undercut which is not appropriate for aninlay.

Figure 10.12 shows two composite restorationsthat, on the request of the patient, were replacementsfor amalgam. There is considerable exposure of thecomposite to the occlusion which may lead to deteri-oration of the composite surface.

Ceramic and gold inlays are discussed below.

Cavity finishing

Different opinions exist as to whether cavity wallsshould be left as they are cut or smoothed with someform of blank or multi-bladed finishing bur. The sur-face produced by different burs is striking but did notseem to be critical for clinical results until the arrivalof adhesives.

The quality of the adhesive bond is dependent toa large extent on the morphology of the substrate towhich it is applied; this will vary according to theinstruments used. The rougher the surface, the moredifficult will be the wetting of this by the adhesive.The result will be air pockets under the restorationthat will be a route for microleakage, in spite of the

adhesive. Theoretically the smoother the surface, themore efficient will be the adhesive process.

Pulp Protection – Linings

On completion of the cavity a decision should bemade regarding the need for further pulpal protec-tion. In the majority of minimal cavities, the protec-tion afforded by the dentine from both chemical andmechanical irritation is adequate. But once the cavityextends beyond minimal size, additional pulpal pro-tection is required.

Lining materials may be bases or liners.

Bases

The primary purpose of these materials is to pro-tect the pulpal tissue from mechanical and chemi-cal irritation. Their properties also allow their useas a dentine replacement. They are usually used inthick section to act as thermal insulators. For clini-cal use, it is important that they reach a substantialstrength quickly, otherwise the restoration placement,particularly the condensation of amalgam, will becompromised.

The principal bases are zinc oxide–eugenol materi-als, polycarboxylate and GIC. Zinc phosphate is nowlittle used.

Zinc oxide eugenol cementsThese are derived from the original simple zinc ox-ide eugenol (ZOE) cement that was used as a seda-tive dressing. In its crudest form the material was notstrong enough to be used as a base or as a long-termtemporary dressing. It did, however, have an obtun-dent effect on pulp symptoms as long as dentine re-mained over the pulp. On exposed soft tissue, thematerial is an irritant.

The basic ZOE cements have been modified by theaddition of a variety of materials. Zinc stearate andzinc acetate were first included as a means of increas-ing the strength and shortening the setting time, andeither polystyrene or ethoxybenzoic acid have beenadded to reinforce the materials further.

Whilst still the weakest of the bases, mixed cor-rectly it provides good service. However, incorrectproportioning is common, which means that the ma-terial is used at powder/liquid ratios well below thosewhich would achieve the optimum properties.

The importance of having a strong base has beendemonstrated by work which shows that there is a

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displacement of the restoration under load and thatthe displacement is directly related to the type of ce-ment used as a base.

The other disadvantage of the eugenol-based mate-rials is that they are not compatible with all restora-tive materials. Polymer-based materials are plasticisedby the eugenol and their polymerisation is retarded.

Polycarboxylate cementThe powder consists of a mixture of zinc oxide andmagnesium oxide with vacuum dried polyacrylic acid;this is simply mixed with water.

The resulting material, that has a zinc polyacrylatematrix, is stronger than the ZOE bases but its mainadvantage is that it possesses adhesive properties totooth structure. Its disadvantage is that it is difficult tomix and tends to stick to instruments. Some versionshave added fluoride salts which will permit a limitedshort-term release of fluoride ions into the dentine.

Glass ionomer cements andResin-modified glass ionomer cementsThis family of materials has, in addition to therestorative materials described earlier, derivatives foruse as linings. The conventional GICs provide amaterial with similar compressive strength to poly-carboxylate cement and have a tenacious bond totooth. The RMGICs offer greater mechanical strengthinitially but at the expense of a considerable poly-merisation shrinkage and a marked exotherm dur-ing this setting phase. This may well affect the ad-hesive properties of the cement. Some concern hasbeen expressed about the monomer addition to thesematerials, HEMA. This has been reported to have ad-verse effects on skin and allergic reactions have beenreported.

Liners

These materials form a thin layer over the pulpal floorof deep cavities and the commonest form is the cal-cium hydroxide cements whose therapeutic action isdiscussed in Chapter 11. The calcium hydroxide iscombined with a polymer base that may be self-curingor light activated.

Self-curing liners have poor mechanical propertiesin comparison with the bases discussed earlier, butthey are valuable as chemical insulators in shallowcavities and as sub-linings in deep ones. In deep cav-ities, it is desirable that they should be covered by astructural base because of their weakness.

The development of light-activated polymer-basedliners has changed the materials considerably. Theiradvantage is the increase in the mechanical properties,but there is a reduction in the pH of the cement from11 down to 7 and this property influences secondarydentine deposition that is reduced. It is possible thatthese materials will not be as effective as pulp cappingagents. They also set by an exothermic reaction andthis can lead to substantial temperature rises.

Linings – conclusionThe use of bases is reduced in current clinical practicebecause of the use of dentine bonding agents and the‘total etch’ techniques referred to in Chapter 9. Theease of use of the calcium hydroxide liners has re-sulted in these being the most popular lining for mostsmall to moderate restorations. It is now consideredthat one of the main requirements for any materialused beneath the restorative should be to effectivelyseal the underlying tissue from bacterial ingress.

Matrices

A plethora of matrix retainers and bands is availableand it is difficult to single out any one particular typeas being the ideal. However, there are a number ofdesirable features for any system:

� The approximal contour should be reproducedaccurately

� The band should be thin enough to provide anadequate contact and yet be rigid enough not tobuckle or crease

� The bands must be of sufficient variety to matchvarious tooth shapes

� The retainer should be stable and allow correcttightening of the band at the cervical margin

The problems of the current systems are that only afew produce the concavo–convex outline of the nat-ural tooth and most produce a flat surface with thecontact usually at the marginal ridge rather than one-third of the way down the approximal surface.

The Siqveland type is usually the easiest to usebut will produce a poorly contoured approximal sur-face unless it is burnished to shape. It should also becut after packing, so that it can be removed laterallythrough the contact. If this is not done, there is a dan-ger that removal will take the marginal ridge with it.

It is essential to wedge all bands, and failure todo this will result in overhangs that are difficult to

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(a) (b)

Matrix band

Wedge

Fig. 10.13 Wedging technique. The subpart (a) shows the correct position for the wedge and (b) shows it too high, bucklingthe band.

remove in amalgam but almost impossible to detect orremove with composites without damaging the tooth.

The choice and use of wedges is also important.The wedge must hold the band against the cervicalmargin of the cavity. Frequently, this is not achievedand the wedge rests on the margin interfering withthe contour (Fig. 10.13).

Matrices for the anterior region are ill developed,and improper use can ruin the restoration. The mostdifficult restoration is the Class V, since the acute con-vexity of the buccal aspect together with the complexshape in the longitudinal plane of the teeth will fre-quently result in poor contour. The contoured softmetal matrices are the most satisfactory but are un-usable with light-activated materials.

Transparent matrices for anterior cavities are welldeveloped but those marketed for approximal cavitieswere difficult to adapt and metal bands are better.

Restorative Materials – Handling

Composites

Clinical usage of light-activated composites is com-plicated by:

� Restricted depth of cure� Activation by the operating light� Occlusal shaping� Deterioration in the halogen-light-activating units� Differing wavelengths available from LED light

sources

The activating light intensity is reduced if it is ob-structed by tooth or is some distance away from thematerial, as with the floor of the approximal box ina Class II restoration, and therefore the restoration

must be built in individually cured increments thatare no more than about 2.0 mm thick. The depth ofcure is also reduced with the use of darker or opaqueshades.

Halogen curing units produce light over a rangeof wavelengths between 410 and 510 nm and havevarying energy outputs. This can seriously affect thecuring potential of the system. It may also be affectedby variations in the power supply voltage that reducethe energy emitted at the 470-nm wavelength. A re-duction in the voltage shifts the energy distributiontowards the higher wavelengths. The bulb should alsobe changed at least every 6 months to maintain effi-ciency, and the continuity of fibres in the fibre optictype should also be checked regularly as these areprone to breakage.

Devices are now available for testing the light out-put and this should be done regularly.

The newer LED light curing units avoid some ofthe problems of the halogen systems but themselvescreate difficulties. The emission characteristics meanthat while they have a constant energy output fromtheir delivery until failure, the wavelengths emittedare much narrower than those from a halogen bulb.This means that the peak excitation of the photo-initiator must be more closely matched to the wave-length of light emitted. Failure to do this will meanthat the composite will not polymerise satisfactorily.With newer initiators being included in some materi-als it is essential that the user confirms that his LEDunit is suitable for the material he has chosen to use.

Class II restorationsThe placement of composite in a Class II cavity re-quires meticulous completion of each stage in turn,and consequently much time.

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The sequence of placement is:

1 Pre-wedge to open contact area2 Prepare cavity with rounded line angles and

bevelled approximal margins3 Line with eugenol-free base4 Acid etch enamel, apply thin layer of ‘enamel bond-

ing agent’ and air-disperse5 Place dentine bonding agent – follow manufac-

turer’s instructions6 Place matrix, re-wedge7 Apply and cure 0.5 mm of composite at the cervical

margin to avoid shrinkage and marginal failure8 Build and cure remainder in 2-mm increments9 Complete occlusal surface

The occlusion is difficult to restore, as free hand carv-ing leaves an oxygen-inhibited surface that shouldbe cut back. This may be avoided by overfilling andcutting back after curing. This is tedious and pro-duces a relatively inaccurate occlusal morphologywith the inherent risk of removal of tooth tissue sincedifferentiation between tooth and restorative is fre-quently difficult. An occlusal index can be preparedpre-operatively to mould the composite, or, rubberdam permitting, the patient can close into centric oc-clusion with the composite covered with a piece ofcling film. This latter technique gives a quick and sim-ple guide to the occlusal stops.

There is a higher incidence of post-operative painfollowing composite placement. The polymerisationshrinkage causes cuspal flexure and marginal leakage,and halogen light is a potent source of heat. Some ma-terials stick to instruments and are thus pulled awayfrom cavity floors, leading to leakage (Fig. 10.14).

Glass ionomer cements

All the materials are sensitive to water contaminationin the early stages of setting and should be protectedfrom early exposure to saliva after placement by ei-ther copal ether varnish or unfilled polymer. However,a certain amount of water is required, and they mustnot be allowed to dry out, otherwise they will crum-ble.

Mechanically mixed encapsulated materials pro-vide a much more reliable and consistent materialsince the method of mixing is the greatest problemwith GICs at present. Poor results are usually dueto incorrect proportioning and mixing, and the ma-terials are often blamed rather than the operator ornurse’s inability to follow the instructions.

Fig. 10.14 Bitewing radiograph of 6| restored withposterior composite. There is a failure of adaptation at themesial cervical margin (arrow).

Amalgam

The variables that can seriously alter the propertiesof the material and the durability of the restorationare:

� Proportioning� Mixing� Condensation� Carving� Polishing

ProportioningFor hand mixing it was necessary to use an ex-cess of mercury, with mercury/alloy ratios of 8:5 or7:5, and even after condensation, excess mercury re-mains, with consequent reduction in physical proper-ties. This problem has been reduced considerably bymechanical mixing and encapsulation which, becauseit is more efficient, requires a ratio of about 1:1.

MixingThe correct ratio must be mixed for the correct time.An under-mixed amalgam will be dry and crumbly.The ideally mixed material should be a cohesive ballthat can be pushed to thin film without breaking up,with the over-mixed material being soupy, difficult toremove from the capsule and frequently hot to touch.Over-mixing reduces the working time and increasescreep values, whilst under-mixing leads to an unus-able mix.

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CondensationUndercondensation by using inadequate pressure or alarge surface area condenser will result in inadequateexpression of excess mercury and also lead to mi-croporosity. Here the admixed and spherical particlealloys show some advantage, since they may be con-densed with less pressure, and puddling of the alloyproduces a satisfactory restoration. In fact, the use ofa small condenser is contra-indicated with these al-loys as the tip will push through the amalgam andleave sub-surface porosities. Mechanical condensa-tion is also disadvantageous.

CarvingCorrect reproduction of the occlusal contacts, to-gether with removal of the mercury rich excess layer,is essential. In Chapter 8, the difficulty of reproduc-ing exact anatomical cusp/fossa relationships was de-scribed. Occlusal stability can be achieved, togetherwith axial loading of the tooth, by carving flat cen-tric stops to receive the opposing supporting cusps,rather than attempting tripods (see Fig. 14.12). If thetripods have one or more contacts missing, the toothwill move to find a stable position. This may createocclusal interferences.

The amalgam restoration should hold shimstock,and if it does then a shiny mark(s) will be seen onits surface; this is not necessarily a ‘high spot’, andan amalgam with no shiny marks will be out of oc-clusion. Unfortunately, the majority are taken outof occlusion for this reason and occlusal instabilityensues.

PolishingPolishing should correct any carving errors, such asexcess at the margins or occlusal problems, but mustnot eliminate the occlusal stops already produced.When using finishing burs or polishing pastes, it isundesirable to produce local hot spots on the surfacesince this will probably cause changes in the phasesof the amalgam. It will also cause excess mercury tocome to the surface and this will in turn weaken thematerial.

Inlay techniques for gold, composite andceramic

The basis for all indirect restorative techniquesis the cutting of a non-undercut preparation, thereproduction of this through an impression andlaboratory model, laboratory construction of the

restoration and finally its fitting and cementation inthe mouth.

Variations around these basic principles arebrought about by the physical properties of the in-lay material and the cementing medium.

Gold inlaysHere the technique has been developed over manyyears to compensate for the lack of adhesion and thesolubility of the cement, originally zinc phosphate.Gold inlays have to be mechanically retentive with-out the cement being present. This is achieved bynear-parallelism of cavity walls and by having a singleand long path of insertion. A cavity taper of 5–10◦ isnecessary.

The cement is protected from oral fluids by abevelled margin on the inlay that can be swagedon to the tooth surface, covering the cement lute.The excellent strength of gold alloys allows thisthin layer to be manufactured and manipulated(Fig. 10.15).

The cement provides the final stability for the inlayby mechanical interlocks with the cavity wall.

Fig. 10.15 Model of a cavity for a gold inlay. The cavitymust not have any undercut and requires a marginalbevel.

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Ceramic inlaysA bevel cannot be constructed in this type of mate-rial because it is brittle and will fracture in thin sec-tion. There will therefore be no protection for thecementing medium that is exposed to both oral flu-ids and the occlusion. Retention of these inlays isheavily dependent on the adhesion of the cementingmaterial.

Intracoronal Restorations – Summary

Techniques for small restorations have changed dramatically in the last few years. Advances in the diagnosisof caries, materials and cavity design have eclipsed Black’s original concepts. Understanding the pathologyof caries, the anatomy of the tooth and the properties of restorative materials is essential for the design ofmodern cavities. These designs are based on individual circumstances and not learnt by rote.

Tooth tissue should be regarded as a precious resource, only to be removed if essential. Small cavities causeless trauma and do less harm to the natural occlusal relationships.

A large range of restorative materials is available. All have limitations and some have not been in generalclinical service for long enough for their longevity to be established.

The cements may be fluid polymer composites oflow filler concentration whose physical properties areconsiderably lower than those of restorative compos-ites. These are literally the weak link. Their degrada-tion leads to marginal staining and lack of supportfor the inlay margin that is then prone to fracture.

Clinical studies suggest that these problems are seenat about 5-year service.

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Chapter 11Management of the Deep Cavity

Management of the deep cavity requires accurate assessment of pulpal condition, the restorability of thetooth and the method of restoration.

This chapter discusses pulp testing, pulp capping, the use of auxiliary retention and the choice of restorativematerial.

In distinction from the treatment of the small to mod-erate carious lesion, the deep cavity requires not onlya decision on the restorative technique to be used, butalso, and most importantly, an assessment of the stateof the pulp.

Clinical assessment of pulp conditions can be unre-liable, and for this reason it is far preferable to insti-tute regular and risk-assessment-based examinationsto avoid, amongst other things, the problems of man-aging deep caries. This is particularly important inthe young patient, where there is less mineralisationof the dentine, and the response to carious attack bythe pulp cannot keep pace with the advancing lesion.

In the older patient the rate of spread is slower,and the pulpal response of laying down secondarydentine and increasing the mineral content of the den-tine, is able to provide some chance of pulp defence(see Chapter 6).

Pulp Assessment

The clinician has very poor information to guide him– he has no opportunity to biopsy the diseased tissue!He needs to make the fullest use of:

� Symptoms� Clinical appearance� Vitality (pulp sensitivity) tests� Radiographic appearance

The correlation of symptoms with pulpal pathologyis poor. However, the following sequence may act asa guide:

1 Transient low grade pain on eating sweet foods –early lesion in dentine, pulp normal

2 Transient mild pain on hot and cold foods – deeperlesion in dentine, pulp normal

3 More severe pain lasting after the stimulus hasgone – pulp pathology

Provided the symptoms are transient, it is fairly cer-tain that the pulp tissue is not involved in the pathol-ogy, and the response can be regarded as essentiallyphysiological. It is only if the pain continues after thestimulus is removed that there is a strong possibilitythat the pulp has started to respond at a cellular level.

The more severe the pain, the less chance there isof pulp recovery after removal of the caries.

Of course, this nicely ordered picture may not beseen, since the chronic nature of the lesion may notgive rise to symptoms at all. Alternatively, there maybe odd diffuse pain which is poorly localised.

Unfortunately, the absence of pain is no guaran-tee of pulpal health and the possible maintenance ofvitality.

The visual appearance of the lesion – extent ofbreakdown, colour of tooth and so on – will pro-vide a valuable indication of the likely depth of thelesion. This, coupled with the radiographic appear-ance and the results of vitality tests (Chapter 2), willput the clinician on the right track on the flow chart(Fig. 11.1).

Operative Treatment

This is best done under rubber dam to reduce therisk of salivary contamination of any exposure to aminimum.

The objective is to remove all the peripheral caries,thus obtaining good access to the body of the lesion,

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DEEP CARIOUS LESION

Save

Open and explore

No exposure

VitalNo pain

Directpulp cap

Restore

Indirectpulp cap R.C.T.

Non-vital

Exposure

Extract

General assessmentVitality/radiograph

Remainder of mouth

Fig. 11.1 Management of the deep carious lesion.

and then carefully remove the caries that lies directlyover the pulp.

Management of the lesion without exposingthe pulp

The ideal is to excise the whole lesion, leaving sounddentine as the base of the cavity. However, when a pul-pal exposure might result, it is permissible to leave azone of altered dentine at the base. It is the identifica-tion of the proximity of the pulp and the dentine thatmay be left, which present the problems.

It is very difficult to be sure of the three-dimensionalrelationship of the lesion with the pulp, though, withexperience, an educated guess is possible.

In all circumstances, soft mushy dentine must beremoved. However, where there is slight softening,but the dentine appears structurally intact, it is pos-sible to leave this, if the risk of exposure is high. Themeans of determining the extent of the penetration ofthe caries are very limited and the use of the conven-tional dental probe to detect softening could easilylead to penetration of a very thin layer overlying thepulp.

The dentinal caries is explored carefully with eitheran excavator or a large slow running round bur. Itis important to understand the two zones within thelesion:

1 Zone of destruction – extensively or total dem-ineralised dentine, containing a large volume ofbacteria

2 Zone of bacterial penetration – areas of partialdemineralisation of dentine with invasion by clus-ters of bacteria

The structure of the first more superficial zone is to-tally disorganised, whilst the second deeper zone re-tains the basic ordered structure of dentine. It is thedeeper zone that can be remineralised in favourableconditions (Fig. 11.2).

There is no infallible method for determining whereZone 1 ends and Zone 2 begins; clinical experience isnecessary to make the judgement.

If the removal of the infected material has beencompleted, and no exposure has resulted, and if thetooth is restorable, an indirect pulp cap is placed.

The most reliable material is calcium hydroxide,usually in a polymer base, which has two effects.Its high pH of 9–11 will reduce the activity of anybacteria still remaining as the environment changesfrom acid to alkaline, and also it provokes reminer-alisation of the softened dentine and the depositionof secondary dentine beneath the lesion by the pulp.Since this effect appears to relate to pH, there is someconcern about the therapeutic efficacy of recently pro-duced materials that have a pH of 7.

However, these new materials do have the advan-tage of being stronger mechanically and can morereadily withstand the occlusal load transmitted viathe restoration. The older materials required an extrastructural base to absorb this.

Other techniques attempt to kill the residual bac-teria in the zone of bacterial penetration and therebymean less removal of dentine. These include the use ofozone or photo-activated disinfection. Special equip-ment and chemicals are required for these techniqueswhose early results are encouraging.

Yet another suggestion is to seal and entomb thebacteria within the dentine, thereby leaving much ofthe original lesion intact. Provided the bacteria aredeprived of substrate, they will die. However, thispresupposes that the restorative materials are capa-ble of maintaining a long-term seal and this cannotbe guaranteed.

There has also been the reintroduction of an oldtechnique, now called stepwise excavation. Here

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11. Management of the Deep Cavity 109

E. D. J. caries REMOVE

Unsupported enamel REMOVE

Necrotic debris REMOVE

Infected dentine REMOVE

Uninfected, stained dentine MAY BE LEFT

Fig. 11.2 Schematic diagram of the zones of a deep carious lesion.

some of the lesion is removed, the cavity sealed andthen in several months time, the cavity is opened andmore of the lesion removed. The expectation is thatin the intervening period, reparative dentine will beformed and the complete removal of the lesion willnot expose the pulp.

Management of the lesion with a pulpexposure

If the removal of the softened dentine results in an ex-posure, then the whole lesion should be excised imme-diately. Contamination of the pulp will have occurredand infected dentine should not remain in the area. Itis now necessary to consider direct pulp capping.

Again success depends upon the absence of cellularchanges in the pulp, as may be indicated by symp-toms. A number of physical criteria also determinethe success of the procedure:

� Size of the exposure: the larger the exposure, theless likely is a successful outcome since contam-ination of the pulp with infected dentine debriswill have occurred. Also, haemorrhage will be in-creased. Ideally the exposure should be less than0.5 mm in diameter, and one over 1 mm in diam-eter has a very poor prognosis.

� Contamination with saliva: this will reduce thesuccess rate greatly since there will be bacterialcontamination.

� Marginal leakage: any leakage can result in bacte-rial ingress and direct access to the pulp.

Once the exposure has been located, all the dentinedebris should be removed. Any haemorrhage must bearrested, preferably without massive blood clot for-mation. Evidence suggests that the presence of a largeclot reduces the success rate.

The exposure is then treated with calcium hydrox-ide materials that are free from zinc oxide/eugenol.Again the use of a structural base to prevent displace-ment of the calcium hydroxide liner is necessary.

Success rate is variable for carious exposures,whilst traumatic exposures are considerably better.

It is, of course, very important to see that there ispulp tissue present. Calcium hydroxide applied to anempty pulp chamber has little value.

Pulpotomy may be attempted for large exposures.This involves opening the pulp chamber and ampu-tating the coronal pulp, leaving what is hoped to behealthy pulp in the roots. The root canal pulps arecovered with calcium hydroxide.

The success of the procedure depends on the in-fection being limited to the coronal pulp only, andthis will be far from certain. However, if the rootcanals cannot be negotiated by conventional instru-ments, pulpotomy gives some hope of retaining thetooth.

Post-operative assessment

The patient should be warned of possible pulp symp-toms and told to return immediately if there is pain.Regular review using vitality tests and radiographs isessential to ensure that any changes in pathology of

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the apical tissues may be detected. Calcium hydroxidemay cause excessive deposition of secondary dentinethat may occlude the root canal. Should this occur, in-tervention and endodontic therapy may be indicatedbefore the canal is obliterated.

Restoration

In many cases where indirect or direct pulp cappinghas been necessary, the tooth will have lost a con-siderable amount of tissue. The plan for restorationshould consider, in particular, the retention and sta-bility of the proposed restoration, and the occlusion.Interim temporary dressing should be avoided if pos-sible, since subsequent removal of this and morepreparation can insult the pulp further.

Anterior teeth may be restored by acid etch retainedcomposite, but as will be discussed in Chapter 15, thismay have some limitations aesthetically and function-ally. Once large amounts of what are small teeth arelost, then elective devitalisation, root filling and a postcrown are almost inevitable.

In posterior teeth, where all cusps remain intact,or only a single cusp has been lost, restoration withamalgam is the most reliable solution. Here retentionwill usually be obtained from the remaining toothsubstance and free-hand carving will reproduce oc-clusal stability adequately.

Where more tooth has been lost, then the accuratereproduction of the occlusion will almost certainlyrequire a crown or inlay. In order to provide a properfoundation for the crown, a core will be necessary.

Choice of core material

Three materials may be used for core construction:

� Amalgam� Metal reinforced composite� Glass ionomer cement

AmalgamThis has several advantages. It can be well condensedaround pins and may be contoured to anatomicalform easily. It has good long-term durability if crownconstruction is to be delayed, perhaps whilst oral hy-giene is being improved. If there is any dissolutionof the cement lute during the life of the crown, corro-sion of the amalgam will provide a barrier to leakage.Amalgam offers resistance to the burs used in crownpreparation which is therefore more easily controlled.

Metal reinforced compositeSeveral materials have been developed specifically ascore materials. They are self-curing composites withmetal particles, such as titanium, added to improvethe resistance to crown preparation cutting. The darkcolour of these materials provides good contrast withtooth so that the core/tooth junction can be seenclearly.

However, these materials are more difficult to han-dle than amalgam and may not adapt completelyaround pins. Crown failures have been reported dueto separation of the core from the pins. Ideally, thematerial needs to be placed with pressure rather thanby condensing as if using amalgam. Some manufac-turers have produced core-forming moulds for thispurpose. Alternatively a temporary crown form is agood substitute. Care must be taken to remove cer-vical excess when using either technique, hence therequirement for a contrasting colour to permit easyidentification of the excess.

The materials are often used in conjunction withdentine adhesives and thereby avoiding pins. How-ever, it is unwise to rely on current adhesive systemsalone to retain large volumes of composite without agood bulk of supporting tooth tissue.

Glass ionomer cementCurrently, it is essential that GICs are supported by aconsiderable volume of tooth structure for their suc-cessful use as core materials. Cermets and condens-able glass ionomers have increased the applicationsof GIC derivatives for cores but clinical results arefew. Whilst the presence of fluoride, adhesive prop-erties and their dimensional stability are advantages,manipulation is more difficult, and amalgam has theproven durability. It would be unwise to rely on theadhesion of GICs to support a crown and not usepins.

Core placement

Amalgam will always require auxiliary retention,though when it is not to be reduced by subsequentcrown preparation, careful use of the remaining toothtissue to provide undercuts can be successful.

It is important to remember that any additional aidto retention will weaken the tooth and the dangers ofexcessive use of pins must be recognised.

The principal means of adding retention are:

� Pits and grooves� Pins

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Pits and groovesThe objective is to place the grooves or pits in oppos-ing walls to resist the displacement of the restorationeither vertically or laterally. However, their effective-ness can be limited, and they certainly weaken re-maining walls. To be of use, any groove must be op-posed by another groove or other retentive feature.The two features will then act in concert.

Unless they are of adequate depth and undercutto allow for the setting contraction of the amalgamor composite, they will serve little purpose. It is alsoimperative that the core material is adequately con-densed into them.

It is important to visualise what tooth substancewill be left after preparation of the crown. If thepreparation will remove the tooth tissue that was usedto retain the core, the process will be wasted.

PinsPins, whilst aiding retention of the restoration, alsointroduce planes of weakness in the material andstress concentrations in the tooth. A balance must beestablished between adequate retention and a restora-tion that fractures under occlusal stress.

Three types of pin are available:

� Self-threading� Friction grip� Cemented

Self-threadingThe pin hole is prepared by a twist drill, the diameterof which is slightly smaller than the pin. The pin,usually integral with a bur shank, can then be tappedinto place using slow speed. The pin shears off thebur shank as it meets the resistance at the base of thepin hole. These are the most convenient and safest ofthe types available, but a number of difficulties canoccur during placement:

1 Oversized pin hole. This is either the result of thehandpiece chuck running eccentrically due to aworn bearing or by lack of positive control of thehandpiece as the hole is cut

2 Dentine failure. The speed of rotation or weaknessof the dentine can lead to the thread that has beentapped, shearing as the pin reaches the bottom ofthe hole. The pin then comes back with its shank

3 Incomplete seating. This is a particular problemwith the self-shearing varieties and can be causedby running the handpiece too fast, or by variationsin the elasticity of the dentine resulting in the pinshearing early

The first two may be corrected by either cutting thenext larger hole and trying again with the larger pin,or cementing the pin in place. The latter is difficult,but may be the only solution.

The failure to seat properly may lead to excess pinintruding into the occlusion and also weakness in thesupport for the pin. If the pin is secure, then it willneed bending or cutting. It is better, though, to try toremove it and start again.

Even the successful placement of this type of pin ispotentially damaging to the dentine causing crazingand stress concentrations.

Friction gripHere again the pin hole is prepared to a slightlysmaller size but the pin is pushed home using a holder.This type of pin relies on the elasticity of the dentineto accommodate and retain it, and again there is a riskof stresses and fracture of the dentine under load.

CementedThese pins are cemented into place in slightly over-size holes using low viscosity polycarboxylate orcyanoacrylate cements. Increased retention may beobtained by sandblasting the pin to produce a me-chanical interlock between the dentine, cement andpin. Introduction of the cement and the pin into thepin hole can be a challenge!

Pin placementThis is particularly important since the pin mustbe placed in an area that provides support for therestoration and that does not weaken the tooth. Itmust also not perforate the pulp or periodontal tis-sues. There are, therefore, a limited number of siteswhere pins may be positioned.

Pins should be placed in dentine and to en-sure an adequate bulk of dentine surrounding them(Fig. 11.3), they should be about 1 mm inside theenamel–dentine junction. Any closer to the junction,there will be a high risk of fracture of a plate of enameland dentine away from the side of the tooth. Repairof this, so far below gingival margin level, can beimpossible.

The anatomy of the pulp chamber and the interfacebetween the root and the periodontal ligament dictatethe angulation of the pin. The pin hole should be par-allel to the external root surface and a good guideto this is to place the tip of the bur, or the blade ofa flat plastic, in the gingival crevice against the root.The bur may then be placed at the same angle on thedentine.

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Fig. 11.3 The position of a pin. It should be surroundedby dentine, 1 mm inside the enamel–dentine junction,2–3 mm deep and bent to fall within the contour of therestoration.

The commencement of the pin hole may be assistedby the cutting of a small depression with a small roundbur. The pin hole itself should be cut to a depth ofabout 2–3 mm, with some brands having a collar fit-ted to the burs to limit the depth of the hole. The pinshould extend the same length above the surface.

After placement, pins should be bent to fall withinthe contour of the final restoration and sufficientamalgam must overly the pin so that it does not crackaway either during carving or subsequent crownpreparation (Fig. 11.4).

Considerable care is necessary during bending sinceinjudicious bending will stress the dentine and causecrazing. A number of devices are available to do thisand they work on the principle of gripping the pinjust above the point of entry into the dentine. The ce-mented pins offer the advantage of pre-bending priorto cementation.

Adequate clearance must be obtained between thetop of the pin and the surface of the restoration. Fail-ure to do this will result in the exposure of the pineither during carving or subsequently during crownpreparation. Reduction of the length of the pin is dan-gerous, and the most effective way is to use a diamondin an air turbine. Under no circumstances should a

Fig. 11.4 Three pins in place and correctly contoured.

tungsten carbide bur be used as it is likely to fracture.Care should be taken with both self-threading andfriction grip pins that they do not start to work looseduring this procedure and the patient’s pharynx mustbe protected against swallowing or inhaling the pin.

A rough guide to the number of pins that should beplaced is one per cusp lost, with a minimum of two.There should be at least one at each end of a coreso that when the occlusal reduction for the crownpreparation is done, one section of the core does notdrop away (Fig. 11.4).

It is possible to overstate the risks of pin placementand become averse to placing pins and rely solely ontooth undercuts or adhesives. This is unwise. A crownis an expensive restoration and without a sound, firmfoundation, it will not give appropriate service. Asan example, Fig. 11.5a shows a premolar that haslost its palatal cusp leaving a large unsecured MODamalgam. Removal of the amalgam leaves only thebuccal cusp; the pulp was vital. In order to provide acrown, a core is necessary and there is clearly insuffi-cient tooth tissue to retain this; two pins were placed(Fig. 11.5b).

MatricesPlacement of matrices on the badly broken downtooth presents a particularly difficult problem. TheSiqveland can be very difficult to use since as theband is tightened, it may ride up the tooth and slipover the cavity margin resulting in a negative marginor a space through which amalgam will be exuded.Careful stabilisation of the retainer by one handduring packing can help.

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(a)

(c) (d)

(b)

Fig. 11.5 (a) An upper premolar that has lost its palatal cusp; (b) the amalgam removed and two pins placed; (c) the cavitylined and a matrix placed and wedged; (d) the completed core.

The Tofflemire holder with its larger selection ofbands may be better and is usually easier to adapt toirregular margins.

Wedging is essential for any matrix so that theband is firmly adapted to the margins of the tooth(Fig. 11.5c). Care is necessary to avoid the wedge rid-ing up over the preparation margin (see Fig. 10.13).Failure to establish a stable, adequately contouredmatrix will lead to difficulty in the construction ofthe core.

Packing and carvingSeveral successive mixes of amalgam should be used,rather than one large one, since the later ones willbe workable at the end of packing. Carving of a core

Fig. 11.6 A completed pinned amalgam which would besuitable as a medium-term restoration.

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should aim to maintain the contacts with adjacentteeth and stabilise the occlusion. Elaborate anatom-ical detail is not necessary, provided the crown is tobe prepared within a short time (Fig. 11.5d).

Management of the Deep Cavity – Summary

1 Assess the pulpal condition as accurately as possible2 Remove all peripheral caries3 Remove pulpal caries with caution and attempt to prevent an exposure4 Can the tooth be restored? Is a crown necessary?5 Indirect pulp cap/direct pulp cap with calcium hydroxide6 Provide auxiliary retention, often by pins7 Restore with amalgam posteriorly, composite anteriorly8 Review pulpal and apical condition regularly

However, if the aim is to produce a medium-term restoration, then tooth anatomy should be re-produced to maintain the occlusion and periodontalhealth (Fig. 11.6).

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Chapter 12Root Canal Treatment

The field of endodontics and root canal therapy in particular has seen a large number of changes intechniques, equipment and materials in the last few years.

There are now more methods of preparing and filling a root canal than for any other small restorativeprocedure – the subject is ‘technique intensive’!

Fortunately, the basic principles underlying all methods remain the same and this chapter considers theseto the exclusion of detailed descriptions of all the various twists and turns of new techniques.

The maintenance of pulp vitality should be one ofthe primary objectives of restorative dentistry. How-ever, as more teeth are retained by a populationof increasing average age, so the incidence of pulppathology increases. Whilst the prevention of the needfor root canal treatment is very desirable, knowl-edge of its techniques is essential for modern daypractice.

The object of root canal treatment is to maintain afunctional tooth with a healthy periodontal ligamentin the dentition following pulp pathology and its se-quelae (Chapter 6).

Diagnosis and Treatment Planning

The choices in formulating the treatment plan dependvery much on the general factors discussed in SectionI, and the local need to keep a particular tooth withinthe context of the mouth as a whole.

The investigation of the deep cavity and the prin-ciples of pulp management were discussed in Chap-ter 11 and this chapter deals with the extremely lo-cal problems of dealing with the restorable, non-vitaltooth or a tooth chosen for elective devitalisation.

Diagnostic procedures for root canal treatment fol-low the same basic guidelines presented in Section I,but particular note should be made of:

� Symptoms� Problems of pulp testing� Radiographic appearance� Restorability of the crown

The first two relate to the achievement of a pre-cise diagnosis of pulp condition, the third to themechanical problems of preparing a root canal andthe fourth to the subsequent and final stage ofrestoration.

Following the decisions that the pulp is non-vital and the tooth should be conserved if possi-ble, the crucial factors are that the root(s) must beamenable to root filling and that the tooth shouldbe restorable afterwards. The treatment plan shouldinclude a provisional decision on the restorationtype.

The technical objectives of root canal treatment areto:

� Remove all accessible infected and contaminatedtissue

� Disinfect infected tissue that cannot be removed� Shape the canal to an appropriate form to receive

the chosen filling material� Obturate the whole canal to block and seal the

dead space to prevent recurrence of infection

To remove all infected tissue, which includes bothpulp and dentine, the full length of the root canalmust be prepared to the apical constriction.

The root filling material must be chosen beforethe preparation is started, so that the preparation isshaped accordingly. For example, an apical mastercone system will require precise preparation of theapical region of the root, whilst a fluid injectable sys-tem might be able to penetrate areas that simply havehad infected tissue removed.

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Root canal morphology

As a basis for successful root canal therapy the den-tist must have a comprehensive knowledge of theanatomy of the pulp chambers and root canals ofall teeth. Variations in anatomy are common andcanals cannot be regarded as simple tubes runningfrom crown to apex. Single roots often contain morethan one canal and there will be other features such astransverse anastomoses, fins, lateral canals and api-cal deltas. Accessory canals are important also; thesemay pass from the pulp chamber into the furcationareas of molars or occur in the main root area.

The most common variations in root canalanatomy are:

� A single canal running to the apical foramen� A root containing two separate small canals that

unite in the apical region and exit through a singleforamen

� A root containing two completely separate canalsthat exit through separate foramina

� A root containing a single canal that divides intwo in the apical region and exits through twoforamina

The most likely teeth to have more than one canal ina single root in descending order of incidence are:

� Lower molars: mesial roots� Single-rooted upper premolars� Upper first molar: mesio-buccal root� Lower incisors� Lower premolars

The canal anatomy for an individual patient thoughmust be assessed by radiography, and the radiographsmust be of high quality and free from distortion.

When looking at the radiographs, each root to betreated should:

� Have evidence of a patent, unobstructed root canalreaching the apex

� Be negotiable by root canal instruments, i.e. notexcessively curved

The actual canal though is usually nothing like therather reassuring image seen on a conventional ra-diograph. Figure 12.1 shows a lower incisor X-rayedin the usual labio-lingual view accompanied by themesio-distal view, which, of course, is not seen andcan only be guessed. Far from being a conical tube,the canal is irregular, probably has two main branchesfor part of its length, and exhibits sharp curves. Inaddition, the microscope would reveal connecting

(a) (b)

Fig. 12.1 Radiographs of a lower incisor, showing (a) theconventional labio-lingual view and (b) the ‘unseen’ shapeof the canal when seen from the side.

branches of pulp, blind and patent lateral canals, andvarious fin-like projections.

This type of appearance may also be seen in thesections of two extracted premolars (Fig. 12.2). Fig-ure 12.2a shows the bucco-lingual view with its re-assuring tube-like image whilst Fig. 12.2b shows themesio-distal view with a wide canal shape.

Difficulties in interpretation can be produced byoverlying anatomical structures – such as the zygo-matic arch in the upper molar region, sclerosis ofroot canals, hypercementosis and overlap of individ-ual roots. The last problem must be overcome by re-angulating the X-ray tube to throw the roots clear ofeach other (Fig. 12.3).

In some cases, sclerosis may not be complete butthe radiograph may not show a canal. Here it is worthtrying to find canals operatively.

Very thin roots may not have sufficient radiodensityto be visible within the denser bone. An instrumentin such a root can sometimes appear to be leavingthe crown through a perforation. The X-ray tube an-gle should be changed to concentrate on the problemroot.

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12. Root Canal Treatment 117

(a) (b)

Fig. 12.2 Longitudinal sections of lower premolars. (a) thepulp chamber seen from the buccal aspect (the‘radiographic view’) and (b) the pulp chamber seen fromthe mesial aspect (the ‘unseen view’).

Apical anatomy

The apical foramen is not usually at the anatomicalapex of the root and is likely to be on the side of theend of the root. The foramen may be single or mul-tiple and can lie at the confluence of two (or more)root canals. The mature root shows an apical con-striction where the canal narrows dramatically at itsapex, caused by dentine and cementum deposition(Fig. 12.4).

The apical constriction is the upper limit of the idealcanal preparation and is located 0.5–1 mm from theanatomical apex.

The radiographic apex can be distorted by the an-gulation of the X-ray beam in relation to the film,and precise detail of the apical foramen is not usuallyclear on radiographs. Occasionally, though, an apicaldelta can be seen, as can lateral canals.

Pre-Endodontic Preparation

Before root treatment is commenced:

� The tooth must be caries free� The crown should be provisionally restored

Radiographicimage

(b)

X-ray tube angulation

(a)

Fig. 12.3 Angulation of the X-ray tube to separate theimages of two roots on a single tooth. (a) Conventionalperiapical view; (b) the tube is moved mesially to giveseparate root images.

Secondary cementum

Apical foramen

Apical constriction

Lateral canal

Fig. 12.4 Diagram of the anatomy of the root apex. Theapical constriction is between 0.5 and 1 mm below theapical foramen.

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The latter stage should aim to maintain tooth posi-tion, seal the entrance to the canal(s), provide supportfor the rubber dam and restore aesthetics.

The removal of caries might well have been done atthe provisional planning stage to assess restorability,but all stained dentine and unsupported enamel mustbe removed prior to root canal preparation so thatdisease progression is stopped.

Posterior teeth will often need pinned amalgamcores or well-retained temporary crowns. Somethought must be given to the final restoration, be-cause when the root treatment is completed, a newcore will be required, and the old pins could well belost. Some ‘free’ dentine should be left to receive thepermanent pins later.

When constructing the pre-endodontic restoration,it is important not to obstruct access to the rootcanal(s). If, for example, the whole crown was filledwith amalgam, it would be exceedingly tedious anddangerous to find the root canals through this. Theroof of the pulp chamber should be overlaid with aweak cement that is easy to remove later.

Anteriorly, if enough coronal dentine is present,a composite provisional restoration will be satisfac-tory. Problems arise if there is little coronal dentineand the root canal must be used to retain the crown.Here a conventional provisional post crown is madethat is removed at each preparation and filling stage.Of course, this brings complications for rubber damplacement (see later).

Canal Preparation

Isolation

Rubber dam is essential to:

� Protect the oro-pharynx� Minimise contamination of the open root canal� Retract soft tissues

In some areas, it is possible to avoid the use of clampswhich has the advantage that the radiographic ap-pearance is not obscured by metal.

The problem of isolating the crownless root has tobe dealt with by using the adjacent teeth for stability,and joining the holes in the dam (Fig. 12.5). A caulk-ing compound may be applied around the marginsof the dam to assist sealing. However, care must beexercised if chemical irrigants, other than saline, areused. There would be a risk of fluid passing into themouth.

Fig. 12.5 Rubber dam applied to |5 which has had itstemporary post crown removed to allow root canaltreatment. A caulking compound may be applied to the cutedges of the dam to improve sealing.

Vision and magnification

Manipulation of small instruments into root canalsrequires precise control and this is aided by im-proving visibility. Magnifying loupes or, now morepopular for endondontics, operating microscopes arerecommended.

Access

Pulp chamberAccess must be obtained through the coronal tissuesto reach the apical constriction. The preparation ofthe access cavity must remove the ‘roof’ of the pulpchamber so that the floor of the chamber and theopening(s) of the root canal(s) can be seen clearly.The access cavity must be placed so that it lies in asnear a straight line with the apex as possible; thisallows efficient instrumentation with little bending ofthe instruments.

The final breakthrough into the pulp chamber mustbe done with slow speed, and not the air turbine, toprevent air or water under pressure entering the rootcanal and passing into the apical tissues. Also, andperhaps more importantly, when obtaining access tomolars, the roof of the pulp chamber is often veryclose to the floor, and rapid cutting may perforatethe roof, the floor and the furcation! In some circum-stances the use of an excavator to remove the roof isa distinct advantage.

There is a compromise between excellent endodon-tic access, where removal of the crown to gingivallevel would expose the root canals very obviously (!),and the restorative requirement where as much toothsubstance as possible should be conserved.

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The access cavity must be extended to enable re-moval of all coronal pulp, particularly in anteriorteeth where residual necrotic tissue may cause dis-colouration.

Root canal orifice enlargementAccess into the root canal system and preparation ofthe coronal one-third of the root canal is performed atthis stage. Fine canal orifices will be located with ISO08 or 10 files and knowing where to look is essentialto avoid excessive removal of dentine.

Orifice enlargement should create a smooth entryroute for files later and also begin the straighteningof curved canals (Fig. 12.6). Once the orifices havebeen positively identified and slightly enlarged by fil-ing, Gates–Glidden burs, size 1 or 2 initially, or orificeenlargers, are used to remove dentine rapidly. Caremust be taken to remove dentine appropriate to thecanal straightening objective and not to enlarge theorifice symmetrically around the original canal intoareas of little dentine. The pulp chamber must be ir-rigated continually during this procedure (see later).

Pulp extirpation

The timing of pulp extirpation, if necessary, is diffi-cult. It will be facilitated by the orifice enlargement

Fig. 12.6 The preparation of a curved root requiresremoval of the shaded areas, so that it is effectivelystraightened.

but it needs to be done at the peak of local analgesia.Pragmatically, many dentists choose to remove thepulp as soon as pulp chamber access has been doneto avoid causing pain.

A barbed broach should be inserted carefully alongthe canal wall and kept short of the apex to avoid api-cal perforation. To engage the broach in the pulp tis-sue, it should be twisted and withdrawn in a smooth,gentle action. Sharp movements should be avoidedto prevent tearing and incomplete removal. In finecanals, a Hedstroem file of small diameter may bebetter, since the barbed broach could bind and lodgein the canal.

If the tooth is non-vital, then necrotic tissue shouldbe removed with a file and by irrigation with a 1%sodium hypochlorite solution. The apical portion ofthe canal must not be prepared in any way before theworking distance has been determined.

The problems of obtaining local analgesia for pulpextirpation were discussed in Chapter 3.

Working distance determination

The position of the apical constriction in relation to afixed reference point on the crown of the tooth shouldbe determined as accurately as possible (±0.5 mm).This is essential to ensure correct mechanical prepa-ration that, if short, will leave:

� Necrotic material and bacteria at the apex� Untreated pulp space apically

If the working distance is long, the preparation will:

� Destroy the apical constriction� Damage the apical tissues� Make filling difficult

The working distance may be determined by anelectrical conductivity measurement device, an apexlocator, by radiography or a combination of thetwo. Apex locators are now more reliable but maygive erroneous values. It is recommended that rootlengths determined by apex locators be confirmed byradiography.

The sequence for the radiographic technique is:

1 Select the largest file that will pass easily into thecanal for good radiographic definition

2 Measure the pre-operative radiograph and com-pare the root length with average values and iftaken, the apex locator result. Decide on the likelyworking length and set a stop on the file to thislength

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3 Note a reference point on the crown (if no crown,use an adjacent tooth)

4 Insert the file slowly; stop and X-ray if obstructed5 When at provisional working distance, X-ray

Note: X-ray film holders for use in conjunction withendodontic instruments can be very cumbersome anddifficult to use, particularly with rubber dam ob-scuring the area. Rigid digital sensors make thisproblem worse; thinner phosphor sensors should beconsidered even though these introduce a delay inreading the image. Patients find this stage very un-comfortable.

6 Measure the radiographic image of the file – itshould be ±1 mm of reality to indicate minimaldistortion; retake if wrong

7 Measure the distance from the tip of the file to theradiographic apex

8 If this is greater than 5 mm, increase the insertionof the file, re-X-ray

9 From an undistorted radiograph, and when thetip of the file is close to the apex, measure thedistance from the tip to the apex and add this tothe known file length, in millimetres

10 Subtract 1 mm from the measurement – this is theaverage position of the apical constriction and isthe working distance (Fig. 12.7)

11 Record the distance in the patient’s notes

Canal preparation

The preparation must:

� Remove accessible infected or degraded dentine� Modify the shape of the pulp space so that it can

be filled efficiently� Disinfect areas of the canal system that are inac-

cessible to instruments

The properties of the root filling material will influ-ence preparation shape and this principle is the sameas that applying to cavity preparation (Chapter 10).Table 12.1 lists the types of root filling materials thatare available. The ideal material would be:

� Easy of use within the canal confines� Controllable during application to avoid over or

underfilling� Condensable into canal wall irregularities� Biocompatible� Unaffected by tissue fluid� Non-resorbable� Adhesive to dentine� Dimensionally stable

Known length of file

Fig. 12.7 The determination of the working distance.(X − 1) mm is added to the known length of the file, aslong as the radiograph is not distorted and X is small.

� Radio-opaque� Easy to remove in the event of problems

Currently the preferred technique is to use gutta-percha in the form of a master cone and accessorycones together with a root canal sealer. Whilst tediousto use, the control provided in the positioning of theroot filling exactly at the apical constriction and thedensity of the filling achieved is not provided reliablyby any other material.

The optimum shape to receive laterally condensedand sealed gutta-percha is a smooth-walled tube witha continuous taper from the apical constriction tothe access cavity. The last 1 mm of the apical regionshould be of round cross-section to receive the mastercone (Fig. 12.8).

Perhaps the most important thing to remember dur-ing canal preparation is that the canal morphologyis extremely variable, some of which cannot be pre-pared mechanically. Therefore, all that is preparedare the main, accessible areas, and this mechanical

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Table 12.1 Root canal filling materials

Material Principal

type components Technique Advantages Disadvantages

Semi-solid Gutta-percha Cones/lateral

condensation with

sealer

Compressible

Controlled insertion

Difficult to use in fine,

curved canals

Thermomechanical

compaction.

GP melted by friction of

compacting

instrument; minimal

sealer

Good condensation Excessive heat generated

Shrinkage on cooling

Warm vertical

condensation with

heated spreaders; no

sealer

Good condensation Time-consuming

Soft GP may pass through

apex

Thermoplasticised

injection with vertical

compaction

Time saving due to

extraoral softening

Variation between systems

Shrinkage on cooling

Soft GP may pass through

apex

Solid Silver

Titanium

Single cone with sealer Ease of use in curved

canals due to rigidity

Poor adaptation

Canal space blocked with

metal – difficult to remove

Corrosion of silver

Hybrid Gutta-percha coated

steel

Cone heated to soften

GP; then warm

vertical condensation

Good condensation Canal space blocked with

metal core – difficult to

remove

Pastes Zinc oxide–eugenol

based plus various

additives:

iodoform,

paraform, steroids,

antibacterials

Spiral paste filler in

conventional

handpiece spins

material into canal

Simple to use Difficult to control

Extrusion/voids easily done

Vital structure damage

reported from paraform

extrusion

Resorbable

Root canal

sealers

Zinc oxide/eugenol,

Calcium

hydroxide/ZOE

Epoxy resin

Glass ionomer

cement

Mineral trioxide

aggregate (MTA)

All used with master

cones

Biocompatible

Biocompatible

Slow setting

Biocompatible

Biocompatible

Solubility

Solubility

Apical irritation reported

Vulnerable to water

contamination rapid set

Expensive, handling difficult

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Fig. 12.8 Root-filled upper central incisor showing theflared canal preparation.

preparation must be accompanied by an antimicro-bial chemical process.

InstrumentationThere are several instrumentation systems for canalpreparation; they all require the use of files, andthese may be specially developed for the particularsystem.

The principal method for many years has beenthe use of steel hand files but now this is rivalled inpopularity by high-torque slow-speed handpiece mo-tor systems used in conjunction with nickel–titanium(NiTi) files. The two systems may be used in parallel.There are also handpieces that operate in reciprocat-ing motion, and systems that use sonic or ultrasonicenergy.

The files themselves are also being developedrapidly. Whilst some files are sharp tipped and onlycut on the withdrawal stroke, there are newer designsthat have safe, blunt tips that can cut when moved ineither direction. This latter design of file reduces thecanal irregularities, such as zipping and ledges, whichmay be produced by sharp-ended files.

NiTi files are super-elastic having a low modulusof elasticity and therefore greater flexibility. The fileswill recover from greater strains than steel files andcan negotiate sharp curves and return to their originalshape afterwards.

In addition, the NiTi files are produced in greatertapers that the original files; these commonly had a2% taper, but now in order to improve the efficiencyof preparation and improve the funnel shape of thepreparation, tapers of 4 and 6% are common. Handfiles are now produced in orifice enlarger shapes andin greater tapers. Root filling cones are also producedin matching tapers.

TechniquesThe precise manipulation of the file required toachieve the desired canal shape and remove debrishas been the subject of considerable research. Thereare at least eight methods that have been advocatedby endodontists in recent years – there will be more!

Hand filing. The most efficient way to prepare theapical stop and remove debris is to insert the file to-wards the apex until it binds, either at the workingdistance or short of it and make a quarter to half aturn clockwise to engage the cutting blades into thecanal wall.

Then, if using single direction cutting files, with-draw the file completely bringing the debris out withthe file.

If using two-directional cutting files with blunt tips,maintain the apical position of the file and turn itanticlockwise one turn. Provided the file being usedcan cut on the upstroke, this action will remove thedentine that had been engaged by the clockwise turn.This is the balanced force technique.

The preparation should be done with copious irri-gation and with care to clean debris from both thecanal and the files. Irrigants are described later.

When the file reaches the working distance anddoes not bind on turning, change to the next file upand continue with the chosen action.

Do not enlarge the apical stop any more when both:

� The diameter has reached the minimum size forthe material (no. 25 for GP) and

� The canal wall consists of sound dentine

The remainder of the canal (that excluding the apical1 mm) should now be prepared by circumferential fil-ing to flare it outwards towards the crown. It is nowunnecessary to twist the file to engage the blades, sincepressure can be applied via the handle. Also, the canal

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profile will be oval and the simple turning and cuttingaction used for the apical stop will simply cut a roundshape in the oval, leaving the periphery unprepared.The majority of radiographically straight canals havesome degree of curve in the apical third and thestep back technique provides a controlled method ofnegotiating and enlarging this curve.

The canal is prepared progressively short of theworking distance with progressively larger instru-ments. Care must be taken not to create ledges orelbows by trying to take stiff instruments around thebend. Steel files larger than no. 35 will not negoti-ate a curve at the apex, even when pre-curved beforeinsertion in the canal.

The danger of the progressively shortening prepa-ration is the tendency for debris to remain ahead ofthe files. The working distance must be re-establishedat each progression by the original apical stop sizefile – recapitulation, with slight turning to engage anddisplace the debris. The shape will be determined ba-sically by the original canal morphology, and it is nec-essary to remove an even amount of dentine from itsperiphery. Preparation should continue until the eventapered shape is achieved and the canal walls offerfirm resistance to cutting.

Stiff files, used around a curve, may create a sepa-rate channel away from the main canal. A new apicalforamen may be created and whilst this is essentiallya lateral perforation the term apical transportation isused to describe the outcome. As with many of thecanal preparation faults, it is very difficult to correct.Pre-curving a fine file and trying to re-establish accessto the real apical constriction is the only solution.

Canals that are curved in their middle third shouldbe prepared by filing the inner aspect of the curve,to ‘straighten’ the canal within the curved root –anti- curvature filing. The danger here is of filing toomuch and perforating the inner aspect of the root – astrip perforation (Fig. 12.9).

A further technique advocated by some is patencyfiling. This involves passing small instrumentsthrough the apical foramen every so often to re-move dentine debris, pulp tissue remnants and micro-organisms that tend to become lodged at the end ofthe canal and create a plug. This debris can obstructinstruments reaching the working length, thus short-ening the prepared canal, and may deflect instrumentsagainst the canal walls thus creating ledges and zips.However, there is no evidence to support this tech-nique whilst there is some to show that a plug ofclean dentine dust in the apical foramen may act as amatrix for cementum to form during apical healing.

Fig. 12.9 Strip perforation on the inner aspect of themesial root of a lower molar.

Hand instrumentation – summary.

� Use safe-ended instruments that cut on the up-stroke as well as the downstroke

� Use copious irrigation to lubricate instruments andintroduce antibacterial solutions to inaccessibleareas

� Clear debris by frequent cleaning of instruments� Maintain control of the working distance� Never force an instrument if it binds� Do not miss out an instrument in a series� Discard damaged instruments� Clear blockages as they develop by irrigation to-

gether with the use of small, curved file

High torque motor, NiTi files. The great advantageof nickel–titanium alloy is its flexibility which has al-lowed manufacturers to produce instruments with in-creased tapers that will negotiate curves. This type ofinstrument will automatically produce the necessarydegree of flare when preparing canals and therefore

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can be used without the need to stepback. This savesmuch time and wear on the fingers!

The instruments must be used with electric or airmotors that are capable of very slow speeds of around150–600 revolutions per minute with good control oftorque. Different systems require different speeds ofrotation and, in general, more rapid rotation createsstresses within the instruments that may result in frac-ture.

The disadvantages of these systems are that theyare expensive and require training and experienceusing extracted teeth before using them on pa-tients.

The preparation technique requires a crown-downapproach with canal orifices being enlarged foraccess as mentioned earlier. When preparing the bodyof the canal, rotation and movement of the filemust be maintained from before entering the canal,throughout time the file is in the canal and until the fileis out of the canal. A glide path is established so thatthe file passes into and out of the canal with light pres-sure. Much lubrication is required and it is commonto use compounds that include chelating agents, suchas ethylenediaminetetraacetic acid (EDTA), to assistdentine removal. The instrument should only remainin the canal for short periods of about 10 seconds asit is moved in and out; the movement is referred to aspecking.

It is difficult to control apical position of the filein this way and care must be taken not to go beyondthe working distance. Normally the apical stop willbe prepared with a file of 2% taper and the remainderof the canal with progressively increasing tapers (4%,6%) to create the flared shape.

The risk of fracture of files means that damagedfiles must be discarded and narrow files should beused for only one patient. Larger files may be usedon several occasions but the difficulty in stock con-trol may lead to all files being discarded after oneuse.

Rotary systems are not without their problems andit is important to appreciate some of the anatom-ical problems that will interfere with their action.These include canals with acute apical curvatures, ‘S’-shaped canals, wide canals becoming narrow, or withtwo canals merging into one apically.

Because of these problems a general pattern hasbeen evolving such that hand files are necessary forthe control and definition required in the prepara-tion of the apical region but the mechanical systemsmay make bulk preparation of the remaining canaleasier.

General problemsHaemorrhage should not be seen during canal prepa-ration. If it is, this may indicate:

� Pulp remnants still present at the apex� Apical perforation� Lateral perforation� Furcation perforation

A radiograph should be taken with the apical stop filein place and the working distance checked. Pulp rem-nants may be removed by filing since they will oftenbe inaccessible to a barbed broach; local analgesia isnecessary. Apical perforation may allow extrusion ofmaterial at the root filling stage. The correct work-ing distance should be re-established and an apicalstop created. Small lateral perforations and furcationperforations can be sealed at the root filling stageafter the correct line of the canal has been re-established. Large lateral and furcation perforationsare difficult to seal and therefore have a poorprognosis.

After preparation, the canal should be dried firstwith a cotton wool pledget and then by careful use ofpaper points. To dry the apical stop, the paper pointshould be capable of passing into it. That is, do notuse no. 60 points in a no. 25 canal!

Irrigation and antibacterial techniques

As already mentioned, copious irrigation is necessaryto lubricate files and remove debris. In addition, it isnow recognised that removal of bacterial contamina-tion from both within the canal and within the lateralcanals and opened dentinal tubules is important. Suchantibacterial action may also be enhanced by remov-ing any smear layer (Chapter 9) that has formed onthe wall of the canal as a result of the preparation.

So to summarise, an irrigant should:

� Remove debris� Lubricate instruments� Assist the removal of dentine during preparation� Remove smear layer� Disinfect the canal system

There is no compound available that is effective atachieving all of these roles by itself.

For many years, the two common irrigants werenormal saline and 1% sodium hypochlorite. Thehypochlorite dissolves organic matter and is mildlybacteriocidal, whilst the advantage of saline is that itis non-irritant if passed through the apex.

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Fig. 12.10 Biofilm. Scanning electromicrograph ofbacterial biofilm taken from a dentine surface after 24hours. There are substantial numbers of bacteria in a webof extracellular material.

In many cases, bacterial contamination within aroot canal has developed over a long period andthe bacteria have had the opportunity to develop afavourable environment for their survival. Particu-larly, near the apex of the canal a substantial biofilmwill have developed in which a range of bacteria willsurvive symbiotically with one another. The biofilmalso provides protection for the bacteria against bothmechanical and chemical disruption. Thus, during thepreparation of the canal, the biofilm must be mechan-ically disturbed. Failure to achieve this, particularly incases where there is a substantial build up in biofilmthickness, means that any disinfectant will requiresubstantial time to pass into the biofilm and have anyeffect (Fig. 12.10).

The irrigants which are currently used may be splitinto cleaners and disinfectants.

CleanersThe primary role of these materials is to debride andclean out dentine dust from the canal. They may alsohave a secondary function in assisting in the removalof the smear layer created by the root canal prepara-tion. Examples of cleaners are saline, 17% EDTA,20% citric acid and 0.5–5% sodium hypochorite.The only one of these with some bacterial potencyis sodium hypochlorite. There is no evidence to sup-port the use of concentrations of hypochlorite greaterthan 1% and proprietary bleach preparations thatare marketed for household disinfection should beavoided because they usually contain compounds inaddition to the bleach which may be toxic and also al-ter the pH to high alkalinity. They would also be usedoutwith the manufacturers’ intended purpose for the

product with possible legal consequences if there areproblems.

DisinfectantsDisinfection during and after cleaning is essential andsodium hypochlorite is effective if used in copiousvolumes. It is not, however, effective against someof the bacteria associated with persistent infectionssuch as Enterococcus faecalis. Sodium hypochloriteused in conjunction with chlorhexidine and povidoneiodine have been used to address the limited efficacyof hypochlorite alone.

Recent additions to the disinfectants include twosystems, one based on ozone and the other referredto as photo-activated disinfection (PAD). The PADsystem consists of a dilute solution containing phar-maceutical grade tolonium chloride and a low-power635-nm laser light source that activates the solutionthrough a disposable handpiece tip. In this way singletoxygen, which is a potent bacteriocide, is producedin the root canal.

All these systems require that the active agents mustreach the bacteria and this highlights the importanceof biofilm disruption.

Medication

After preparation, canals may be filled by some typeof dressing material that could have an antimicro-bial effect. Many substances ranging from antibioticmixtures to very irritant disinfectants have been used.No conclusive evidence exists regarding the efficacyof canal medication.

The waiting of a week or so between preparationand filling does allow any acute apical reaction to pulpextirpation or debris being pushed through the apexto subside without pain. The inflammatory exudatecan pass into the partly empty canal. It is essentialthat the temporary restoration seals the access to theroot canal effectively.

A mild antimicrobial with very low irritation is cal-cium hydroxide in a propylene glycol vehicle. Whilethis has proved to be reliable, there is some doubtas to its efficacy against the bacteria associated withrecurrent endodontic infections.

Calcium hydroxide is sometimes successful in re-solving a persistently oozing canal if left for 4–6weeks, though replacement is necessary every 10 daysor so to maintain activity.

Single visit root canal therapy is possible, providedthere is no infection present. This has the advantage

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that the canal is open for a relatively short period,there being no temporary dressing that may leak andcontaminate the canal.

Root Filling

After preparation, and before root filling, the toothshould:

� Be symptomless� Not be tender to percussion� Have no exudate in the root canal(s)

If any one of the above is present, it indicates continu-ing pathology. Wash the canal to remove the dressing,dry it, re-establish the working distance with the api-cal stop file, redisinfect and re-dress. Review in a weekto 10 days.

When obturating the canal, the master cone mustmatch the file size as closely as possible, but somevariation in the GP cones is inevitable because of diffi-culties in manufacture. After placement of the mastercone, lateral or accessory cones are condensed intoplace together with the sealer. This means that theworking time of the sealer should be sufficiently longto allow this.

The sequence for root filling is:

1 Remove the dressing from the canal, re-establishthe apical stop with the appropriate file. Wash, dis-infect and dry

2 Select the GP point of the apical stop size and markthe working distance on it; insert it into the canalslowly

3 Make sure the point reaches the working distanceand is a good fit (‘tug back’)

4 X-ray to check that the GP fits to the workingdistance

If the point does not fit to the working distance whentried in, or is short when X-rayed, repeat the prepara-tion of the apical stop to either clear debris, or extendthe preparation if it is short. Re-check the diameterof the GP point on a gauge, and if necessary, try an-other one of the same nominal size. The GP try-inalso checks the preparation in addition to checkingthe master cone fit.

Then:

5 Mix sealer and place a range of accessory coneswith their tips in the sealer

6 Select a file size smaller than the apical stop andcoat this with sealer and, with an anticlockwise

rotation, coat the canal walls with sealer, up to thestop

7 Coat the master cone with sealer, insert it carefully(beware hydraulic effects causing pain or extru-sion) to the marked working distance

8 Using lateral spreaders, beginning with the small-est, make room for accessory cones alongside themaster cone and build up the full filling sequentially

9 Take a post-operative radiograph and seal theaccess cavity

If the canal is overfilled, tell the patient and keep itunder review. If the canal is underfilled because oftechnical error, remove the root filling and start again.

If this underfill goes to the working distance whichis short because of some obstruction, then again tellthe patient, and keep it under review.

Problems Encountered During Root CanalTherapy

The almost blind instrumentation of a series of natu-ral channels of variable anatomy is inevitably accom-panied by risk. Table 12.2 sets out the major problemsthat might be encountered during root canal therapy.Some of these have been or will be discussed in moredetail within the text.

It is important that the patient understands thetechnical difficulties that may be encountered duringroot canal therapy. This will be the basis for their in-formed consent. In the event of a complication, suchas a lateral perforation or a fractured instrument, thepatient must be informed about what has happenedand its likely outcome.

Fractured instrument

The current techniques of filing rather than ream-ing and the construction of modern files means thatbroken instruments are less common. Forcing instru-ments around canal bends or jamming them in theapical constriction are recipes for disaster.

The most likely instruments to fracture will be finefiles in a curved apical region or the tips of Gates–Glidden burs in the canal orifice. The former areusually impossible to remove. The canal preparationshould be completed, perhaps with by-passing of thefragment, and gutta-percha condensed around it.

Overflexing is the usual reason for Gates–Gliddenfracture and the main shank of the bur is supposed tobe the fracture zone of the instrument. However, tips

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Table 12.2 Root canal therapy problems

Stage Problem Action Comments

Access Incomplete

analgesia

1. Repeat LA with 3% prilocaine or 5%

xylocaine

2. Steroid dressing for 48 h; retry LA

3. If all fails, general anaesthesia for pulp

extirpation

1. Second agent potentiates the first

2. Pulpal inflammation is reduced,

neural pain pathway recovers, LA

then becomes effective

3. Ensure that GA is justified on likely

success rate of RCT

Perforation –

furcation or

lateral

Re-establish correct canal line

If small, pack perforation with

calcium hydroxide or MTA; this will

be supported by the RCF later

Prevention is better than cure

Note root angle before cutting

especially if there is an artificial

crown present that may obscure

the true angle

Canal

preparation

Incorrect working

distance

from radiographic

distortion

Retake radiograph Avoid calculating working distance if:

• the image of the file is not 1:1 with

reality

• the file does reach to within 5 mm

of the apexObstructions

Secondary dentine,

pulp stones

Dentine softening agent, e.g. EDTA,

slow reaction – seal and leave

Canal anatomy

Curves, fins, apical

delta, lateral

canals, accessory

canals, internal

resorption,

Prepare only those major channels that

allow file access

Preparation faults

Ledges, zips, elbows Attempt to re-establish correct

preparation path

Apical

transportation

Pre-curve instrument, attempt to reach

correct apex

Hand instruments only

Apical perforation As open apex; see text

Strip perforation,

lateral perforation

Attempt sealing at RCF stage Prognosis for large perforations is poor

If accessible, consider surgery. (see

Chapter 29)

Fractured

instrument

If at the apex and tooth symptomless,

root fill around fragment

If in main body of canal, remove (see

Chapter 29) or by-pass using canal

anatomy

The round instrument will not obstruct

all of an oval canal

If irremovable consider apical surgery Always inform the patient

Fractured root See Chapter 3

Open apex See text

Continued

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Table 12.2 cont.

Stage Problem Action Comments

Post crown present If crown sound, consider apical surgery

If inadequate, remove, re-root fill and

re-restore

Medication Persistent exudate

and/or symptoms

Check working distance and

preparation; re-dress with calcium

hydroxide

Consider apical surgery

Canal obtu-

ration

Overfilling Radiographic review if symptomless

If symptoms, remove or consider

apical surgery

Underfilling/ under-

condensation

Remove RCF and re-fill If found at review: leave if no

pathology

Re-root fill if to have new restoration

even if no pathology

may break in the canal and because these are usuallysuperficial, they can be retrieved using a file or exca-vator. Failing this, the Masserann kit (see Chapter 29)may be used.

Ni–Ti instruments, particularly if re-used, may suf-fer tip breakage. Various innovative techniques havebeen proposed to attempt the removal of these pieces,e.g. bonding a new file to the fractured piece bycyanoacrylate adhesive and removing it.

Open apex

This may occur as a result of incomplete root forma-tion (Chapter 3) or because of instrumentation be-yond the apical constriction (apical perforation). Itmakes root filling difficult because there is no restric-tion to the escape of sealer in to the apical tissues.In the immature root, the canal is funnel shaped,becoming wider towards the apex. Conventional con-densation is then almost impossible.

The preparation of the immature canal should bedone by careful circumferential filing, since the apicaldiameter is usually larger than the largest file. Theroot filling should be made up, by trial and error,from warming and coalescing several GP points intoa large single cone of the right diameter. This can betried-in in the usual way and then sealed carefully,avoiding extrusion into the tissues.

Filling a canal with an apical perforation is alsodifficult. The length of insertion of the master cone

must be controlled carefully, and it should be heldagainst the crown whilst inserting lateral cones, sothat the spreaders do not push it past the apex. Lateralcondensation must be gentle, to avoid extrusion ofsealer.

Review

Apical tissues take time to heal, and progress shouldbe monitored radiographically, in the absence ofsymptoms, at about 1 year after filling, and then every4 years. There is an incidence of recurrent infectionaround apparently successful root fillings that mayrelate to lateral canals, or to short zones of unfilledapical canal.

More frequent radiographs, perhaps yearly, mightbe necessary to monitor the healing of a large api-cal radiolucency to ensure that reduction in size isproceeding.

Healing of the root end is by the laying down ofcementum across the apical foramen and possibly thepresence of clean dentine dust will help this. Theremay be a very small zone of clean compacted den-tine chippings at the final extent of successful rootfillings.

The final coronal restoration should be completedas soon as possible after the root filling. There is ev-idence to suggest that leakage from the crown willcontaminate the root filling and promote bacterialgrowth.

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Fig. 12.11 The removal of a GP point by a Hedstroemfile. This file is ideal because of its rearward facing barbs.

Recurrent Infection

Symptoms, or radiographic appearance of an increas-ing area of radiolucency at the apex indicate pathol-ogy and failure of the root filling. Consider either:

� Removing the root filling and repreparing thecanal(s)

� Apical surgery� Extraction

Do not intervene in cases of long standing, symptom-less over or underfilled canals, though there could bean exception to this if the tooth was to receive a crownor be a bridge abutment. Residual apical radiolucencymay be accepted in the absence of symptoms providedthat the apical area is less than 5 mm in diameter.

Management of old root fillings

This is usually the main problem in retreatment.If the canal is filled by a single GP cone, it isusually possible to insert a file, preferably a Hed-stroem type with its backward facing barbs, along-side the cone, engage the blades and pull the cone out(Fig. 12.11).

On the other hand, if the root filling, or fragmentof instrument, cannot be removed, it may be possibleto by-pass it and then incorporate it into the new rootfilling (Fig. 12.12).

Once the root filling has been removed, it will thenbe necessary to start the root filling preparation fromthe beginning, establish the working distance and pre-pare the canal (Fig. 12.13). Sometimes the old rootfilling may be short because of a canal obstructionwhich may prevent the re-preparation. This can onlybe ascertained once the root filling has been removedso there will be some uncertainty in predicting out-come before commencing retreatment.

Clearly, a further alternative to retreatment is ex-traction of the tooth and the patient must understandthe expected success of the proposed procedure andhave the option of extraction explained. In general,retreatments are not as successful as root treatmentsprovided from scratch. In all cases, teeth with estab-lished apical infection have a poorer outcome in com-parison with uninfected teeth.

Apical Surgery

The surgical approach to the root apex is required toplace an apical seal when the conventional approachthrough the root is impossible, or when an apparentlywell executed root filling has failed. Surgery shouldbe reserved for these cases and should not be used tocorrect symptomless and signless filling errors.

The circumstances in which to consider surgeryare, in the presence of infection, canals that are non-negotiable or difficult to fill because of:

� Secondary dentine, curves, pulp stones� Fractured instruments� Post crowns (Fig. 12.14)� Unremovable root fillings� Lateral canals� An open apex

Surgery may also be used to provide root canal treat-ment rapidly or to deal with infection that persists inspite of repeated dressing.

If the unremovable root filling is an apical silverpoint or a retrograde amalgam, and the remainder ofthe canal is empty, then the cause of the infection maybe leakage past the filling into the canal. Bacteria canobtain their nutrient from the leakage and toxins passout into the tissues. In these cases it is worth trying toprepare the empty canal and fill it up to the existingroot filling (Fig. 12.15).

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(a) (b)

Fig. 12.12 (a) Upper left lateral incisor having an apical area associated with a sectional silver point. Exploration of thecanal led to reaching the apex without removing the point. (b) the canal has been filled around the silver point

Apicectomy technique

Local analgesia is usually acceptable for most sin-gle teeth. Intravenous sedation or general anaesthe-sia may be indicated for several teeth or apprehensiveindividuals.

The analgesia must be effective, with palatal andincisive canal blocks being necessary for upper ante-rior teeth.

The sequence is:

1 Analgesia2 Raise full gingival flap with bevelled incision at

the papillae (Fig. 12.16); this gives good accessand little scarring

3 Identify the apical region by pressure with an ex-cavator to try perforating the cortical plate overthe infected area. Otherwise measure the rootlength from the pre-operative radiograph

4 Remove cortical bone with slow speed burs withcopious irrigation

5 Avoid scarring the root by working higher thanthe apical level initially

6 Obtain clear access to the root apex and iden-tify any anatomical structures of relevance, e.g.antrum, mental nerve

7 Clear any soft tissue around the apex – excisionbiopsy

8 Reduce the apex by a bevelled cut, so that the rootface is angled towards the operator

9 Cut a 2- to 3-mm-deep undercut cavity in theroot canal end; this may be assisted by ultrasonicinstruments

10 Wash, dry and pack the bone with ribbon gauzeto isolate the apex

11 Place retrograde root seal (see below)12 Remove gauze and excess sealant, irrigate, close

and suture

Systemic antibiotics should be prescribed pre-operatively for medical problems, or post-operativelyfor the prevention of infection in a large bony cavity.

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(a) (b)

Fig. 12.13 Retreatment of an upper premolar. (a) The tooth has an apical area associated with two short and underpreparedroot fillings; there appears to be root canal beyond the points. (b) The tooth has been retreated by removing the root fillings,re-establishing the working distance, repreparation and re-filling. The two canals terminated in a single apical foramen.

Fig. 12.14 Extruded GP in |2 associated with symptomsand a sinus. There is a very good post crown present, andthe extruded filling probably could not be retrievedanyway. The tooth was apicected. The post-operativeradiographs are shown in Fig. 3.5.

The more posterior the tooth, the more difficultwill be the surgery and the more likely there will beanatomical complications.

The palatal roots of upper premolars are difficultto reach and see. Palatal roots of upper molars wouldrequire a separate palatal flap, but these roots arestraight and can usually be root filled conventionally.The buccal roots are easily accessible by surgery.

The maxillary antrum lies close to the upper premo-lars and molars. Antral perforation does not usuallygive rise to problems because the flap closes it. Thepatient should be given systemic antibiotics and toldnot to blow his nose.

The mental nerve is a complication with lower pre-molars, and the hazard of mental anaesthesia mustbe mentioned when consent to apicectomy in the re-gion is sought. Many now consider that apical surgeryof lower premolars is contraindicated because of thepossibility of this complication.

The inferior dental nerve is close to the lower mo-lars – do not apicect these teeth.

Finally, always place a retrograde seal; do not relyon the sealing ability of the existing root filling, whichmay be disturbed when cut.

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(a) (b)

Fig. 12.15 (a) Apical infection associated with a non-vital 2| and an apical silver point in 1|. (b) This was treated byconventional root canal therapy of 2| and root filling the 1| up to the silver. The result was complete resolution of theinfection without surgery.

Retrograde root sealerFor many years amalgam was the recommended ma-terial for retrograde root filling. The success rate ofthis material was good but in view of the concernsabout the toxicity of amalgam discussed in Chapter10, other materials for retrograde root filling havebeen suggested.

The glass ionomer cements and EBA reinforced zincoxide–eugenol cements have been used with reportedsuccess equivalent to that of amalgam. The sensitivityto moisture of both materials and the solubility of theZOE cements could be disadvantages when in contactwith tissue fluids.

The preferred material is currently mineral trioxideaggregate (MTA) which is essentially Portland cementmixed with sterile water. The handling of this mate-rial is not easy and it is expensive. However, it hasbeen shown to have good biocompatibility and clini-cal results are favourable.

Through and through techniqueWhere a post crown is to be placed, the post shouldbe made first before the surgery, in case the post-preparation displaces the apical seal later. The surgeryis performed by a through and through techniquewhere the canal is open to both the mouth and the api-cal tissues. The canal is dried and the post cementedwith the apical tissues protected from excess cement(Fig. 12.17). The through and through technique mayalso be used where there is an open apex and an emptycanal. The canal is root filled with the flap raised anda retrograde seal placed afterwards.

Review and treatment optionsApical bone may take several months, sometimes overa year, to fill in. This should be monitored radiograph-ically at regular review (see Fig. 3.5).

When considering apicectomy as a treatment op-tion, it should be remembered that this is an

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Bevelled incision

Fig. 12.16 Full gingival flap for apical surgery. Theincision at the gingival papillae is bevelled to provide abroad area for replacement, which reduces recession.

unpleasant and sometimes painful surgical procedurewith an uncomfortable immediate post-operative pe-riod. Success rate studies suggest an overall rate ofabout 80% but studies running for over 4 years arerare. The success of implant therapy is considerablehigher and more predictable, and this should be con-sidered as being more desirable than trying to save atooth on its last legs (Chapter 22).

Success Rate of Root Canal Therapy

Outcome analysis in restorative dentistry is generallyinadequate, particularly from general practice. Whilstsuccess rate studies have been reported, these are of-ten retrospective and therefore pre-operative criteriaare not established and various techniques may beemployed. The studies often include a large numberof operators. Clinical trials of restorative materialsare an exception, probably because they are easier toconduct with clear trial entry criteria, proper controlgroups, pre-trial training of operators. Assessmentcriteria are well established and short-term analysismeans that most of the original cohort of patients canbe reviewed. On the other hand, the design factors forfixed prosthodontics are very difficult to study.

In root canal therapy, success rate studies rely toa large extent on radiographic interpretation and thereproducibility of some of these is notoriously poor.The acceptance of new instrumentation techniques is

Fig. 12.17 A long post has been inserted in 2| at the timeof apical surgery prior to the placement of the retrogradeseal. A provisional crown is placed at the same time to waitfor gingival healing.

based on laboratory studies rather than clinical out-come studies.

The highest success is found with single-rootedteeth with little or no infection (>90%) whilst thelowest is with multi-rooted teeth with establishedand long standing apical areas particularly in themandible (<60%). Bacteria can remain undisturbedin such tooth sites as lateral canals and non-obturatedareas of main canals and within well establishedapical areas. The problems described in Table 12.2all reduce the success rate. Underpreparation andunderfilling are associated with lower success thanoverfilling.

The clinical studies show that the principal factorsinfluencing success are:

� Root canal morphology� Quality of canal preparation and filling� Presence of apical infection

The overriding requirements of root canal therapy areto remove viable bacteria from the canal system or killthem, and to prevent their re-establishing themselvesthere again.

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Root Canal Therapy – Summary

Base treatment planning on accurate radiographs and a realistic assessment of outcome.

Thoroughly debride as much of the canal system as possible and disinfect the rest.

Shape the canals in accordance with the choice of root filling material.

Obturate all the prepared space.

Review apical condition regularly.

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Chapter 13Management of the PeriodontallyInvolved Dentition

This chapter will consider aspects of diagnosis, treatment planning, treatment and follow-up for a patienthaving periodontal disease together with comments on the broader restorative implications of the manage-ment of the disease.

Introduction

The planning and execution of treatment for any dis-ease or condition is dependent on careful diagnosis.Having defined periodontitis in Chapter 7, the dis-ease should be easily diagnosed by noting gingivitisaccompanied by loss of attachment. Unfortunately,this alone is of little value to treatment planning foran individual patient and the diagnosis of periodonti-tis needs to be qualified. Such qualification requires:

� Identification of aetiological and predisposingfactors

� Qualification of disease severity� Appreciation of patient factors relevant to man-

agement

The disease itself arises from the interaction of apathogenic subgingival flora on a susceptible host.Therapy aims to eradicate the former but can do lit-tle to alter the latter so for this reason recurrence ofthe disease is always a possibility. Long-term success-ful treatment of the patient with periodontal diseasedepends on a considered management programmewhere pre-and post-treatment care is as important asthe actual treatment itself.

Management of periodontitis is based upon initia-tives for:

� Removal of subgingival plaque (therapeutic phase)� Prevention of recurrence through the control of

supragingival plaque (preventive phase)

The therapeutic phase is highly operator dependentwhereas the preventive phase is highly patient depen-dent. Both are based on mechanical debridement ofsupra and subgingival plaques and clearly the effi-ciency of the procedures used, whether in the surgeryor at home, will have a direct bearing on success.

Chemical agents, largely against micro-organismsand antimicrobial, may be employed both locally andsystemically. Modification of the host response toplaque is an alternative possibility.

Diagnosis – Qualifying Factors

Once loss of attachment in the presence of inflam-mation, based on clinical and radiographic examina-tions, has been established, the diagnosis of periodon-titis is made. The diagnosis must then be qualified inorder to prepare a treatment plan.

Plaque scores

Accumulation of dental plaque at the gingival mar-gin is the major aetiological factor in gingivitis andgives rise to the subgingival plaque associated withperiodontitis. Levels of plaque on all or selected teethshould be recorded using a suitable index or scoringmethod (see Chapter 2).

Plaque scoring at various time intervals forms thebasis for diagnosis, oral hygiene instruction, assess-ing response to instruction and for patient informa-tion and encouragement. Clinical probing and radio-graphic examination provide information about thepresence of subgingival deposits, notably subgingivalcalculus, and usefully directs treatment.

Local predisposing factors

Certain factors encourage plaque accumulation andsome make plaque removal difficult by normal toothcleaning methods. These include:

� Supra and subgingival calculus� Carious cavities

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� Subgingival restorations� Overhanging restorations� Poor approximal contact areas� Fixed and removable appliances or prostheses

Perhaps surprisingly, mucogingival anomalies andtooth malpositions have little bearing on plaque ac-cumulation and removal.

Modifying factors of the gingival orperiodontal response to plaque

Local or systemic conditions referred to in Chapter 7should be identified from the history and examinationof the patient. Special tests to determine predisposi-tion or susceptibility to periodontal disease are rarelyneeded and the important factors usually arise fromthe medical history. However, where unusual symp-toms or signs are apparent, particularly in gingival in-flammation, that appear outwith the known medicalhistory or local factors, haematological investigationmust be considered.

It is worth noting that at present the use of microbi-ological methods to qualify the bacterial aetiology ofperiodontitis are of no value in the treatment planningof individual patients with chronic periodontitis andof little, if any, value to aggressive types of disease.

Severity

It is essential to qualify the diagnosis of periodontitisfor severity, particularly in respect of the patient’s age.The following aspects should be examined to deter-mine the severity of periodontitis:

� Gingival inflammation and associated recession orenlargement

� Loss of attachment� Mobility� Bone loss� Tooth position� Tooth vitality

Gingival inflammation may demonstrated by bleed-ing on probing and the observation of gingival en-largement that may be local or general. Localisedinflammation is most likely to be due to local pre-disposing factors such as poorly adapted crownmargins.

Gingival recession may be local or general whereagain a differential diagnosis based on aetiology maybe required. Gingival recession may lead to sensitivity

of dentine and poor aesthetics. These may need to beconsidered in the general treatment plan.

Loss of attachment is observed by using a grad-uated periodontal probe to measure pocket depthwhich in turn may provoke bleeding or exudationof pus. Pocket depths, indicating loss of attachment,are recorded in millimetres. Observation of bleedingin response to probing provides information on thedistribution and severity of gingival pocket inflam-mation.

Multisite probing (6 per tooth) is often recom-mended but a considerable amount of informationcan be derived from mesial and distal probing andprobing to the furcation areas of molar teeth.

Mobility is assessed using the handle of the probealone or together with the handle of the dental mirrorand typically graded on a 0 = none through to 3 =severe basis. Sophisticated instruments are availableto measure mobility but their value to the assessmentand follow-up of the individual patient is question-able. Vertical mobility is usually a poor prognosticsign and care must be taken in distinguishing patho-logical mobility resulting from bone loss and physio-logical mobility due to increased tooth loading, par-ticularly as they may coexist.

Bone loss may be diagnosed from the probingdepths and from bitewings or periapical radiographs(Chapter 2). However, full mouth periapical radio-graphs for diagnosis and follow-up of periodontaldisease are now rarely required because the diagnos-tic yield is low without supplementing to any greatextent the information that can be found by clinicalexamination.

Bone loss both in extent and type (horizontal orvertical) should be noted with particular reference tofurcation defects; the latter being poor prognostic in-dicators to treatment success. The type of bony lesionwill influence decisions concerning non-surgical andsurgical periodontal treatment and the use of guidedtissue regeneration and/or bone grafts.

Tooth position may indicate that drifting and/orovereruption has occurred. Particularly at anteriorsites, aesthetic considerations may have major treat-ment planning implications, and decisions concern-ing orthodontic and restorative treatments have to bemade.

Periodontal lesions may compromise tooth vital-ity and conversely endodontic lesions may createapparent periodontal or furcation lesions. Distin-guishing an endodontic–periodontal lesion from aperiodontal–endodontic lesion is important due tothe poor treatment prognosis of the latter compared

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13. Management of the Periodontally Involved Dentition 137

to the relatively good treatment prognosis of theformer. Clearly, both can coexist making definitivediagnosis difficult. Sinus formation may be importantin the differential diagnosis of apical from periodontalinfections since sinuses are more likely to be associ-ated with apical disease.

Most assessments of disease severity must be corre-lated to age since this provides information concern-ing disease susceptibility and rate of disease progres-sion, prognosis and therefore treatment planning.

A number of methods using chairside test kitshave been used in the past to evaluate disease activ-ity and to demonstrate the presence of certain peri-odontopathogens. Lack of sensitivity and specificityhas largely resulted in discontinuation of their use inroutine periodontal practice.

Patient factors

Patient factors are of considerable importance totreatment planning since they can influence the dis-ease itself and the ability and willingness of the in-dividual patient to participate in the treatment plan.Firstly, there is a need to assess whether an individualcan fulfil the long-term commitment to the preventionphase of management alone or with assistance fromthird parties. Secondly, it is important to determinewhether an individual can receive the ideal treatmentfor the disease. Some of the answers to these com-plex questions can be determined easily from directdiscussions with an individual and a consideration oftheir psychosocial and medical backgrounds. Otheraspects of assessing their ability to participate inthe management programme are difficult sometimesimpossible to evaluate, particularly during initialappointments.

Patient factors that may be relevant to the pre-ventive phase of management are numerous and atpresent many are poorly understood. At the extremes,why some individuals appear able to practise goodplaque control and others not, often cannot be ex-plained. It may be simply related to their apparentcompliance and dexterity with oral hygiene practicesthat has been determined in retrospect, rather thanpredicted prospectively at the initial diagnostic andtreatment planning visits.

Nevertheless, some factors that may contribute todifficulties with oral hygiene can be identified:

� Physical and/or mental handicap� Chronic medical conditions particularly of painful

nature may influence cooperation

� Social or occupational commitments may limittime available

� Social problems can affect ability and willingness

Patient factors that can influence the receipt of treat-ment are usually more obvious but potentially largein number and variable in their impact.

The age and general medical and psychologicalhealth of an individual are most important. As anexample, in the aged it is possible to judge retrospec-tively the susceptibility to periodontal disease andplan treatment accordingly. In such circumstancestreatment is likely to be conservative, even palliative.Conversely, in the young healthy adult, particularlywith advanced periodontitis, treatment planning mayhave to be aggressive.

Specific aspects of the medical history can placeindividuals at risk from periodontal procedures, bothnon-surgical and surgical. These include:

� Previous endocarditis, congenital and acquiredheart valve defects and cardiac valve replacement

� Bleeding diatheses and other acute haematologicaldisorders

� Anticoagulant therapy� Long-term steroid therapy

Medical disorders or conditions may influence thetiming of periodontal procedures, for example:

� Pregnancy� Coincident medical or surgical procedures

Concurrent pharmacotherapy may influence the pe-riodontal state and therefore treatment decisions no-tably those associated with gingival hyperplasia.

Medical conditions or drug therapies can influencethe decision to employ chemotherapy within the pe-riodontal treatment plan. These include where theperiodontal chemotherapy could induce:

� An adverse patient reaction due to allergy, for ex-ample penicillin or aspirin

� An adverse interaction with current medication,for example aspirin and coumarin anticoagulants

� An antagonism of an existing medical condition,for example aspirin and peptic ulceration

� Potential deleterious effects to the foetus duringpregnancy, for example metronidazole

Medical and social problems can affect the patient’sability to attend for treatment particularly since peri-odontal treatment is often continuous and protractedwith regular recalls. These problems could include

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occupation, travel distance, availability of transportand finances.

Treatment planning

Accepting that periodontal disease arises when suit-able pathogens act on a susceptible host suggests threepossible approaches to treatment:

� Removal of the pathogens� Alteration of the host response� Reduction or change of susceptibility

The mainstream approach to management of peri-odontal diseases has been and remains the removalof the subgingival pathogens and the prevention ofrecurrence through supragingival plaque control.

The host response can be altered to advantage bydrugs such as non-steroidal anti-inflammatory drugs(NSAIDs). The role of NSAIDs in therapy is not es-tablished at present with clear concerns over benefitto risk ratio due to potential serious side effects. Atpresent NSAIDs are of interest in researching patho-genesis of periodontal diseases. Daily use of low-dosage tetracycline (doxycycline hyclate) appears ofinterest for potential effects on host collagenase; thelong-term additional benefit of this treatment remainsto be established.

Susceptibility is poorly understood and thereforenothing can be done at present to change the sus-ceptibility of most individuals with periodontitis.Specific aspects of the medical history that increasesusceptibility, notably those influencing polymorphfunction, usually cannot be altered but have to betaken into account in treatment planning. Presentknowledge indicates that patients with periodonti-tis should stop cigarette smoking. Improving diabeticcontrol in Type I and Type II diabetics logically shoulddecrease susceptibility but data are lacking to supportthis suggestion.

Based on the antipathogen approach to manage-ment, the following form the basic treatment plan forperiodontitis:

1 Hygiene phase� Advice and instruction in supragingival plaque

control2 Therapeutic phase

� Thorough debridement of the root surface� The use of surgery to improve access� Adjunctive use of antimicrobials� Recall and maintenance

Interestingly, this ‘modern’ treatment plan can befound almost in its entirety in periodontal textbooksfrom the beginning of the century. Before consideringthe specifics of the treatment plan applied to the aver-age case of periodontitis, important factors concern-ing individual patients have to be considered sincethese may modify treatment planning to a lesser orgreater degree. These include:

� Susceptibility factors influencing disease progres-sion

� Predisposing factors that affect plaque accumula-tion and retention

� Severity factors that affect prognosis

Susceptibility factors include the modification of asmoking habit, diabetic control and the use of antimi-crobials where polymorph function is compromised.

Predisposing factors that are outside patient con-trol need to be removed or modified. These have beendiscussed earlier and frequently involve restorativeprocedures.

Extractions may have to be considered when:

� Periodontal therapy cannot or is unlikely to re-solve the disease

� Aesthetics can only be improved by restorations� Comfort and security problems can only be im-

proved by restorations� Coincident restoration problems exist making the

tooth unsaveable

Decisions concerning the above may have to be takenin consideration of the patient’s wishes, attitude, ageand medical history.

Patient factors are of considerable relevance totreatment planning since they can influence needs anddemands for treatment and affect the type and de-livery of treatment. Some of the important patientfactors that are identifiable from personal details, oc-cupational, social and medical histories have alreadybeen mentioned. Most cannot be changed and there-fore, when possible, the treatment plan has to be mod-ified to accommodate them.

It is not unusual particularly where aesthetic con-siderations are important to the patient that collabo-ration with restorative and/or orthodontic colleaguesis necessary. Based on these consultations, restorativeand/or orthodontic procedures may be planned to im-prove aesthetics and function. It is essential to appre-ciate that such procedures should be consequent upona successful outcome to periodontal treatment. Thereis evidence to suggest that restorative and more partic-ularly orthodontic treatments which place increased

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loading upon individual teeth can act as aggravatingfactors in the progress of active periodontal disease.In the presence of treated periodontal disease such ef-fects appear irrelevant. Therefore, a sound basis forother treatments to the dentition must be a healthyperiodontium.

Hygiene phase

Advice and instruction in oral hygiene methods mustbe tailored to individual needs. There is no scientificbasis for providing any particular type of advice andinstruction and there is little evidence that any methodor device is superior to others. It would seem reason-able that patients or, where indicated, a third caringparty, need to understand the problem. Informationon plaque, gingivitis and periodontitis should be pro-vided and can include verbal and written information.The main aim is to achieve a level of supragingivalplaque control compatible with gingival health. Toachieve this, the clinician must identify individual fac-tors which can affect compliance and dexterity withtooth cleaning habits.

Many individuals appear not to find interdentalcleaning easy and do not follow advice. Some mayhave dexterity problems of varying magnitude andmay require assistance. Certain sites appear diffi-cult to clean with most people spending little or notime cleaning such sites; most notable are lingual andpalatal areas.

Oral hygiene proceduresIn the absence of evidence for the superiority of anyone method, recommendations should be based onindividual needs and ability. Interdental cleaning isimportant in long-term management. Oral hygienewill involve:

� Toothbrushes� Toothpastes� Mouth rinses

ToothbrushesTooth brushing with a toothpaste remains the pri-mary method of oral hygiene in the developed worldand the individual is the major variable in influencingthe outcome of tooth cleaning. Twice daily brushingfor 1–2 minutes appears optimal.

There is little evidence that variations in manualtoothbrush design significantly influence oral hygieneand gingival health. However, it would seem reason-able to suggest that head sizes are not too large for the

specific individual and filaments are soft to mediumwith rounded ends.

Electric toothbrushes can be of benefit to handi-capped individuals. Also there are some recent datato show that electric brushes with a rotary osci-llation action provide some benefit compared withmanual toothbrushes. The cost implications of elec-tric toothbrushes have to be considered for eachindividual.

ToothpastesToothpastes contain ingredients, such as detergents,that provide some plaque inhibitory effects but theseare probably insufficient to benefit gingival health.Recent evidence is available that toothpastes contain-ing chlorhexidine, stannous fluoride or triclosan (witheither zinc citrate or polyvinyl methyl ether maleicacid) provide modest benefits to gingival health.However, chlorhexidine and stannous fluoride tooth-paste have the potential to cause tooth staining dueto interactions with dietary chromogens on the toothsurface.

MouthrinsesMouthrinses containing a small number of agents,of which chlorhexidine is still considered the ‘goldstandard’, have been shown to be effective adjunctsto tooth brushing with a toothpaste. However, as partof the long-term commitment to plaque control, theuse of such rinses may be questioned on the basis ofcost, benefit and local side effects.

For example, mouth rinsing twice daily with a pro-priety product requires an approximate expenditureof four times that spent on toothbrushes and tooth-paste.

The use of antiplaque agents notably chlorhex-idine in the hygiene phase may be questioned.Chlorhexidine in the short-term provides little if anytherapeutic action against established gingivitis andcertainly established periodontitis, since subgingivaldeposits are relatively inaccessible to supragingivallydelivered fluids. The considerable inhibitory prop-erties of chlorhexidine against supragingival plaquemake an assessment of the response to oral hygieneinstruction almost impossible and may therefore bemisleading.

The clinical responsibilities in the hygiene phaseare to provide oral hygiene advice and instructionand to monitor response using plaque and/or gin-givitis scoring. In addition, it may be necessary toremove or modify factors predisposing to plaque ac-cumulation and retention. This includes scaling and

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polishing of teeth to remove supragingival plaqueand calculus and easily accessible subgingival de-posits and the correction of faulty fixed or removablerestorations.

Therapy phase – mechanical

The therapy of chronic periodontitis is almost to-tally based on non-surgical and surgical mechan-ical debridement of the root surface. Indeed, thetreatment of rapid-onset periodontal diseases withfew exceptions always includes these mechanicalmethods.

Non-surgical and, more particularly, surgical pro-cedures result in variable often unpredictable gingivalrecession. The choice of procedure must be made onthe full understanding by the patient on the possibleoutcomes including the possibility of dentine hyper-sensitivity (see gingivectomy).

Non-surgical root surface debridement/scaling/planing techniques are the first line of treatmentfor all forms of periodontitis with the expectationof reductions in inflammation and probing depth,gains in attachment level and beneficial shifts in thesubgingival bacteria. Procedures can be performedwith hand instruments or ultrasonic scaling devices.Ultrasonic devices appear particularly efficient butlack tactile feedback and may be usefully combinedwith manual instrumentation. Local analgesia maybe used as necessary, based on patient wishes andcomfort.

Surgical techniques are used primarily to improveaccess and facilitate removal of subgingival deposits.In the uncomplicated treatment of periodontitis, flapprocedures aimed at minimising loss of tissue shouldbe the first choice. Where infrabony defects or fur-cations are present, surgical flap procedures can alsobe used to facilitate the insertion of bone infill ma-terials. Gingivectomy eliminates pockets at the ex-pense of gingival tissue and this can create aestheticproblems.

Flap and gingivectomy procedures may be used aspart of the restorative therapy, for example crownlengthening.

Guided tissue regenerationThe ultimate goal of periodontal treatment is to re-store lost connective tissue attachment. The heal-ing process following either surgical or non-surgicaltreatment involves the formation of a long junctionalepithelial attachment along the root surface with-

out regeneration of the periodontal tissues. Guidedtissue regeneration at present is the most promis-ing method for restoring periodontal structures. Theaims of this treatment are firstly to prevent apical mi-gration of the epithelial attachment during the ini-tial stages of healing and secondly to create a poten-tial space under the surgical flap so as to facilitateregeneration of periodontal ligament along the rootsurface.

This space can be created by inserting an exclu-sionary barrier membrane under the flap and coveringthe root surface and adjacent bone. Various materi-als have been developed which may be resorbable ornon-resorbable. Initially, most of the clinical evalua-tion was concerned with a non-resorbable expandedpolytetrafluoroethylene (e-PTFE) material. Clinicallyimpressive results, in terms of pocket depth reduc-tion, gain in attachment and bone fill have been notedin Grade II furcation lesions and various infrabonydefects, with less impressive results in Grade IIIfurcations in maxillary molars.

More recently developed resorbable membraneshave the advantage of not requiring a second oper-ation for removal. These materials are based on lac-tide/glycolide copolymers or collagen. Studies havefound the copolymers as effective as e-PTFE mem-branes in attachment gain and reduction in pocketdepth. Bovine and human Type I collagen membranesponges have been used in guided tissue regenera-tion with good results, but there have been no directcomparisons with other materials.

Other approaches to regeneration of lost periodon-tal ligament have included the use of growth fac-tors and an enamel matrix derivative, which do notinvolve the use of a barrier membrane. These ma-terials are simply coated onto the exposed root sur-face prior to suturing of the replaced surgical flap. Atpresent it is too early to ascertain the long-term ben-efits of these biologically active materials, althoughinitial studies appear promising.

Therapy phase – chemoprevention andchemotherapy

Since periodontitis is associated with bacteria antimi-crobial agents may be used as part of treatment. Thesemay have a primarily preventive role or a primarilytherapeutic role, and can be delivered locally or sys-temically.

Chemoprevention is usually directed against thepotential adverse effects of plaque organisms locally

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or systemically. Chlorhexidine mouthrinses, irriga-tion and sprays are the usual forms of local treatment.Indications for their use include:

� Reduction of contamination of the operatory withoral organisms

� Reduction of bacteraemia in the at-risk individualas an adjunct to systemic antimicrobial prophy-laxis (see Chapter 4)

� Control of supragingival plaque when mechanicalcleaning may be compromised

Chemotherapy, either local or systemic, is usuallyused as an adjunct to mechanical surgical or non-surgical techniques.

Local delivery of antimicrobials subgingivally maybe achieved by:

� Irrigation� Slow release devices

This area of local delivery has been extensivelyreviewed and currently it is considered that localchemotherapy should not be used routinely. It is in-dicated where sites have not responded to mechani-cal debridement techniques. Irrigation with either asingle agent or a variety has not been convincinglyproven adjunctive to root planning.

The potential side effects of the development ofbacterial resistance and overgrowth of opportunistorganisms must also be considered.

Some antimicrobials in slow release devices havebeen shown adjunctive to scaling and root plan-ning as measured by a reduction in pocketing and/orgains in attachment levels. These include tetracycline,minocycline, doxycyline and metronidazole. Thevalue of chlorhexidine in slow release vehicles is stilldebated.

Systemic delivery is usually by the oral route andcurrently systemic antimicrobials have little or noplace in the management of chronic periodontitis.They may be considered in the management of aggres-sive and refractory periodontitis. The use of systemicantimicrobials in individuals whose periodontal stateis compromised by a medical condition, e.g. diabetes,while logical, is unproven. It would seem reasonableto delay the decision to determine if such an individ-ual is refractory to conventional therapy.

Systemic antimicrobials that have attracted mostresearch interest are metronidazole, tetracyclines andthe combination of metronidazole and amoxycillin.

The decision to use systemic antimicrobials must bebalanced against possible side effects, namely:

� Hypersensitivity (allergic) reaction� Development of bacterial resistance� Superinfection by opportunist organisms� Toxic side effects of the particular antimicrobial� Drug interaction with concomitant chemotherapy

Mucogingival (perioplastic) surgicaltechniques

These have evolved over a number of years. They havebeen designed to:

� Remove fraenal attachments� Deepen sulci� Augment the width of attached gingivae� Recontour gingiva and or replace missing papillae� Cover exposed root surfaces (recession)

It is now appreciated that neither the mucogingivalproblem nor the treatment outcome to rectify theanomaly have any bearing on the prevention of re-currence or treatment of periodontitis. Mucogingivaltechniques, therefore, rarely feature in the treatmentof the disease. Clearly, these procedures may provideaesthetic and/or functional benefits and are usuallyreserved for such indications. Examples include thecoronally repositioned flap procedure to cover buccalrecession and surgical crown lengthening to exposesound tooth structure.

Maintenance phase

It has been established that whatever the outcomeof treatment, long-term success is dependent onsupragingival plaque control that is improved bythe combination of clinical and personal hygieneprogrammes. Periodontitis is a chronic condition inwhich susceptibility does not change and thereforerecurrence is always a possibility. There is thereforea need for recall, reassessment and re-motivation ofpatients. When necessary, clinical prophylaxis shouldbe given. The timing of recall appears arbitrary andshould be based on patient needs rather than applyingthe same regime to each patient.

Patients who are unable to maintain a satisfactorylevel of oral hygiene or who are not followed up, tendto show relapse over time. Conversely, patients prac-tising over-zealous tooth brushing may cause gingivalrecession and those who are subjected to frequent and

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repeated scaling of teeth, particularly at shallow sites,show iatrogenic loss of attachment.

To summarise, care and maintenance are essentialbut should not be over prescribed. The value of long-

Periodontal Therapy – Summary

The main aspect of pre- and post-treatment management or preparation for the periodontal patient is theachievement and maintenance of satisfactory supragingival plaque control. This is dependent on clinicaland personal involvement in a disease for which susceptibility cannot be altered by means available atpresent. For the foreseeable future, ‘once a periodontal patient always a periodontal patient’.

term chemical plaque control for the susceptibleperiodontal patient who has been treated is notestablished.

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Chapter 14Principles of Occlusal Management

The functional anatomy of the occlusion was described in Chapter 8. This chapter discusses the clinicaltechniques associated with the occlusion, particularly the use of articulators.

Occlusal Analysis

Whilst the examination of the occlusion is part ofthe examination of every patient, the term ‘occlusalanalysis’ implies a more detailed examination and thiswill be aided by articulated models.

An occlusal analysis is necessary for:

� Planning fixed prosthodontics� Designing removable partial dentures� Diagnosing cases of occlusal dysfunction

Clinical examination of the occlusion

The following intraoral aspects are of particularinterest:

� Missing or malposed teeth� Cuspal height and cuspal inclines� Centric occlusion (CO) – intercuspation� Effects of tooth loss – tilting, drifting, overeruption� Tooth surfaces – wear facets, irregular surface loss,

attrition, erosion and abrasion� Curves of Spee and Monson, overbite, overjet,

incisal inclination� Restorations/prostheses – accuracy of fit, occlusal

form and function� Centric relation (CR) and the retruded arc of

closure, pre-centric prematurities� Extent and direction of mandibular displacement

from CR to CO� Tooth guidance in lateral and protrusive excur-

sions and interferences

The examination will be completed, if appropriate,by the examination of the:

� Temporomandibular joints� Muscles of mastication

Detailed examinationThis may be done alongside an articulation to con-firm it, or as a clinical procedure only. The exerciserequires 8-μm metal foil (shimstock) and artery for-ceps, 40-μm smudge proof articulating paper, red andblue, with reverse action tweezers.

Centric occlusionThe shimstock is used to check the existence of sta-ble, contacting cusp/fossa relationships. The patientshould be asked to close until the teeth are just touch-ing, since variable compression of the periodontal lig-aments can bring uneven or open sites into contact.This point is of considerable importance when fittingrestorations since clenching can create apparent even-ness of contacts.

Shimstock is placed between each area of likelycontact, the patient closes, and the foil will either beheld or pull out (Fig. 14.1). This can be noted andchecked against the articulation later.

Next, blue paper is used to mark CO contacts. Theteeth should be dried and the patient asked to closethe teeth together. A variety of markings are possible,from the classic tripod, to single fossa contacts (seeFig. 8.4).

Centric relationRed paper is now used to mark the retruded contactposition (RCP) and mandibular slide from CR to CO.The patient is manipulated onto the terminal hingeaxis and closed into the RCP (Fig. 14.2). Then hecloses of his own volition into CO.

This procedure will lead to:

� Double marking of centric stops, i.e. red superim-posed on blue

� Red alone marking the RCP and slide(s) (seeFig. 8.5b)

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Fig. 14.1 Shimstock being used to check the centriccontact between the upper and lower first premolars.

Lateral and protrusive excursionsExamination of lateral and protrusive excursionsshould demonstrate either canine guidance or groupfunction, and the length and height of the anteriorguidance. This last characteristic is shown by theamount of posterior disclusion.

The most important aspect of the eccentric excur-sions is to look for interferences, i.e. tooth contactsthat are interrupting smooth and even sliding con-tacts. These contacts may cause deviations in side-shift or protrusion. In group function, all buccal cuspson the working side should be in contact. If during theexcursion, a pair of upper and lower cusps ‘lift’ theother cusps out of contact, this pair of cusps consti-tutes a working side interference.

Tooth contacts on the non-working side may inter-fere with condylar guidance and side-shift; these arenon-working interferences (see Fig. 8.6d).

Fig. 14.2 Manipulation onto the retruded arc of closure.The operator’s fingers and thumbs exert upward andbackward pressure to locate the condyles into their mostsuperior, posterior position and ‘rotate’ the mandible.

Temporomandibular jointsThese may be examined for movement and clicks bypalpation with the fingers overlying the joints or in theexternal auditory meatus. In addition, a stethoscopemay be used to listen to joint sounds.

Clicking in the joint may not be revealed by sim-ple movement of the mandible, since the disc posi-tion may change when food is between the teeth. Itcan be useful to ask the patient to chew on somehard wax and listen during the series of functionalmovements.

Muscles of masticationExtra-oral palpation of the temporalis origins overly-ing the parietal bones and the whole lateral aspect ofthe masseters is straightforward. Bi-manual palpationof the masseter is more reliable with one digit withinthe mouth and one external. This same method canbe used for the mylohyoid and digastric.

Intraoral palpation of the medial pterygoid requiresa finger to be placed in the fauces area and this can beunpleasant. The most difficult muscle to palpate is thelateral pterygoid. The first finger is placed aroundthe posterior aspect of the tuberosity and up-wards to the lateral aspect of the lateral pterygoidplate of the sphenoid bone. This is uncomfortablealso.

The discomfort induced by palpation may per-suade the patient to report tenderness which ofcourse is misleading. The muscles that can be pal-pated with reliable results are the temporalis andmasseters.

Articulation of Study Models

Equipment

The equipment available for reproducing the occlu-sion in the laboratory, for either the detailed exami-nation of the occlusion or the construction of restora-tions, ranges from the primitive to the esoteric, frombare hands to microcomputers!

The overriding consideration in the choice of equip-ment is to use that which is appropriate to the jobin hand, and that both the dentist and his techni-cian really know and understand the principles ofthe instruments they use. A badly used articulator isoften much, much worse than using no articulatorat all.

Incorrect articulation will lead to restorations thatwill require considerable chairside time for fitting

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14. Principles of Occlusal Management 145

whilst the occlusal surfaces are modified to suit theactual occlusion.

The very simple articulators, the average path andsimple plane line, are too small to reproduce therelationship between the temporomandibular jointand the occlusal plane. For this reason they do notlocate any hinge axis from the patient and may intro-duce errors if tooth apart occlusal records are used.The incisor angulation may be incorrect because ofthe free-hand orientation of the models and this mayaffect management of aesthetics. These instrumentsare little more than a convenient way of locating twomodels in a fixed position.

At the other end of the scale, the computerised, fullyadjustable articulator will provide the nearest equiv-alent to the patient, with curved condylar guides,immediate and progressive side-shifts, exact inter-condylar width and an exact reproduction of thehinge axis.

The most practical type of instrument is a semi-adjustable articulator and its associated facebow.There are several excellent types available and thechoice depends to a large extent on personal pref-erence. This book shows cases mounted on the Den-tatus ARH and the Denar Mk IIA. The first is a goodinstrument for teaching the basic principles of occlu-sion and the latter is a light, simple instrument that ismore suitable for fixed prosthodontics.

In order to illustrate the design of facebows andarticulators, the Denar Mk IIA and its associatedSlidematic facebow will be described in detail.

FacebowThe purpose of the facebow is to locate the maxil-lary teeth in three planes (superior–inferior, anterior–posterior and lateral) to the temporomandibularjoint. Ideally, the articulator’s hinge should be the ter-minal or true hinge axis of the joint. However, twopieces of equipment, a hinge axis locator, togetherwith a hinge axis transfer facebow are required to dothis accurately.

For simplicity of use, most facebows work in con-nection with an arbitrary hinge axis. A number ofworkers have determined the position of the truehinge axis for a group of subjects and correlated itwith a surface anatomical landmark. Each worker hasthen derived an average position in order to dispensewith true hinge axis location. These positions are usu-ally claimed to be within 5 mm of the true hinge axison all patients.

The most commonly used arbitrary hinge axis is apoint 12 mm anterior to the posterior border of the

Fig. 14.3 The Denar Slidematic earbow in place. Thebow is self-centring and locates to the side of the nose forits vertical reference point. The registration fork is stabilisedby the operator.

tragus along a line drawn from the superior borderof the tragus to the outer canthus of the eye. Thisposition would be transferred by a facebow to thecondylar axis of the articulator.

However, it is easier to use an earbow that locatesinto the external auditory meatus, with the articula-tor having an earbow mounting site that is posteriorto the articulator hinge. (Remember that the ear isposterior to the TMJ!) Alternatively, the design of thearticulator and its mounting system takes account ofthis anatomy.

The Denar Slidematic facebow (Fig. 14.3) is a self-centring earbow that can also measure the inter-condylar distance. The bow is located in the verticalplane by an arbitrary point on the side of the nose,43 mm from the upper lateral incisor edge.

The registration fork should locate the upper modelaccurately but without engaging tooth undercut toavoid distortion of the wax. Three layers of base platewax, softened and firmly sealed to the metal are suf-ficient, and a ZOE wash can be added for extra accu-racy if required.

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In taking the record, ensure that:

1 The ear lugs are firmly engaged on bone2 The reference plane locator points to the nose point3 The registration fork is accurately and evenly lo-

cated on all the teeth and stabilised by the clinicianduring recording

4 All screws etc. are tightened firmly to avoid slip-page during mounting

The record is assembled on the articulator by meansof an index system that avoids the need to send thewhole earbow to the laboratory. It is useful to havethe articulator at the chairside to check the earbowsettings and discover spurious recordings whilst thepatient is still available.

ArticulatorThe Denar Mk IIA (Fig. 14.4) is a simple, light‘Arcon’-type semi-adjustable articulator. The ‘Arcon’classification (short for ARticulator-CONdyle) de-scribes the fact that the condyles are attached to thelower member in comparison with the Dentatus ARHthat is ‘non-Arcon’ having the condyles on the uppermember (Fig. 14.5).

The Arcon design is more realistic anatomically,since in protrusion the condyles move forward withthe mandible. In the non-Arcon, the condyles movebackwards in protrusion. Some minor technical ad-vantages are also claimed for the Arcon type.

The Denar can be set to vary the condylar angles,the progressive side-shift and the immediate side-shift.

Fig. 14.4 The Denar MkIIA articulator. This is a lightArcon instrument, with adjustable condylar angles,progressive side-shift and immediate side-shift. Theintercondylar distance is fixed.

Fig. 14.5 The Dentatus ARH articulator. This is anon-Arcon instrument, with adjustable condylar angles andprogressive side-shift. It has no provision for immediateside-shift.

The antero-posterior position of the condyles can beadjusted to provide separate identifiable positions forcentric relation and CO. It has a fixed intercondylardistance. The incisal guide can be ‘customised’ to theanterior guidance (see later).

Occlusal recordsThere are three types of static occlusal records, eachfor a different purpose. In addition, dynamic recordscan be used for certain articulators.

Centric relation recordThis is a tooth-apart record, taken with the patient onthe retruded arc of closure. It is used to carry out apre-operative occlusal analysis where problems havebeen diagnosed with the existing CO. Alternatively itmay be used for the construction of restorations whenCO is lost, as in complete dentures.

Centric occlusion recordThis is a tooth-together record of the position of max-imum intercuspation. This position would be used formounting pre-operative and master models when nochange to the existing CO is proposed.

Lateral and protrusive check recordsThese are used to set the articulator condylar an-gles and the instruction manual of the articulator willspecify those required for a particular instrument.

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Fig. 14.6 A kinematic facebow in use. Two styli areattached to the mandible and two sensor pads are fixed tothe head alongside the area of the temporomandibularjoints.

Dynamic recordsA detailed description of these is outside the scopeof this book. Basically, these are usually tracings ormicro-computer signals from specialised kinematicfacebow systems (Figs. 14.6 and 14.7).

They can be used to:

� Assess the amount of immediate and progressiveside-shift

Fig. 14.7 The output from the facebow. The lower tracesare the condylar paths and the upper traces are the lateralbodily movements. Settings for the articulator arecomputed from the traces.

� Assess the condylar inclination� Trace the condylar path shape� Trace the incisal guide� Trace the chewing cycle� Assess muscle activity and functional disturbances

Recording mediaThe essential requirements are that the recordingmedium should:

� Not interfere with the path of closure of themandible

� Record sufficient detail to permit accurate orien-tation of the models

� Be sufficiently rigid to stabilise the models duringmounting on the articulator

The commonly used wax squash bite has the majordisadvantage of interfering with the path of closureand also obscures the tooth position that is beingrecorded. Softer materials, such as alginate and im-pression rubbers, have been used to overcome thisproblem, but they give imprecise mounting positionsfor the models during articulation.

The best way of orientating the models for a centricocclusion articulation is to avoid the use of an inter-dental record altogether and place them into the posi-tion of ‘best fit’. This position can be checked againstthe patient and marked on the models.

However, if CO is not reproducible by a positionof best fit, a registration will be required. Islands ofacrylic or a silicone registration polymer fulfil the re-quirements listed above. It is important not to use a‘horseshoe’ of material as this interferes with seeingthe teeth in contact. Figure 14.8 shows red acrylicislands on the teeth after registering CO.

There are several techniques for registering centricrelation. The technique described here offers rigidityand the minimum interference with closure.

Fig. 14.8 Registration of centric occlusion using acrylicislands.

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Fig. 14.9 Occlusal record for centric relation. Aluminiummesh is cut to fit exactly to the palatal surfaces of the upperteeth. The mesh supports the wax wafer and preventsdistortion.

The starting point is accurate study models, takenin an elastomer and cast with die stone occlusalsurfaces.

The record consists of two thicknesses of very hardbaseplate wax supporting by a metal mesh. The meshis cut to fit exactly to the palatal surfaces of the upperteeth (Fig. 14.9) and the wax is trimmed to the buccalsurfaces (Fig. 14.10). This ensures good vision of thetooth relationships.

Fig. 14.10 Two thicknesses of hard wax have been addedto sandwich the mesh. The wax is trimmed to the buccalsurfaces so that the occlusal relationship can be seenduring the registration.

Bi-manual manipulation of the mandible ontothe terminal hinge axis or retruded arc of closureis now performed. The patient is asked to halfopen the mouth and relax. The operator’s fingersand thumbs exert upwards and backwards pres-sure on the mandible to locate the condyles intothe posterior, superior position in glenoid fossae(Fig. 14.2).

The wax wafer is softened in hot water and placedon the upper arch and the mandible manipulated onthe hinge axis so that the lower teeth indent the waxvery lightly. The wafer is removed and chilled in coldwater. This first stage creates a matrix to support theactual recording medium.

The detail of the tooth relationships can now berecorded using a zinc oxide–eugenol wash. The washis ‘dotted’ into the tooth indents on both surfaces ofthe wax with just enough used to record the cusp tipsonly. Any more may record occlusal surface detail notincluded on the models and therefore prevent seatingof the record.

The wafer is replaced in the mouth and themandible manipulated again onto the terminal hingeaxis and onto the record.

After the ZOE has set, the record is removed andcarefully placed on each model in turn to check for ac-curate seating (Fig. 14.11). This checks the accuracyof both the record and the models.

To confirm the reproducibility of the record, twofurther wafers can be taken and the mounting doneby a split cast technique. Here, the upper modelis grooved and a separating medium applied. It ismounted to the facebow in the usual way, and thelower model plastered to the first record. When theplaster has set, the record is removed and the uppermodel separated from its mounting plaster leaving the

Fig. 14.11 The completed record has the cusp tipsreproduced in ZOE and should fit each model accurately.

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Fig. 14.12 An occlusal deprogrammer. This removes thememory of centric occlusion and, after removal,manipulation onto the retruded arc of closure should beeasier.

locating points. The other two records are then usedto orientate the upper model onto the mounted lowermodel and the articulator closed. If the records areidentical, then the location grooves and points willmeet exactly. Two matching out of three is an accept-able reproduction, given the difficulty that may beexperienced in manipulating the mandible.

In the case of patients whose musculature resists themanipulation, a ‘deprogrammer’ may be needed toremove the short-term memory of CO. The applianceis made at the chairside from cold cure acrylic andforms a flat bite plane on the incisal edges (Fig. 14.12).The record is re-attempted after about 10 minutes,with the deprogrammer out.

The same wax wafer arrangement may be usedfor lateral and protrusive records for articula-tor settings in accordance with the manufacturer’sdirections.

Confirmation of articulated mountingThe articulation should be compared with the patient.This will involve the use of articulating paper andshimstock and general observation of the tooth rela-tionships created by articulator movements.

When the pre-centric record is removed, the ar-ticulator should reproduce the retruded arc of clo-sure, with the RCP and then close into CO via slidingfrom the prematurities (Fig. 14.13). In CO, shimstockshould be retained by centric stops on the articulatoras it is in the mouth (Fig. 14.14). Wear facets shouldbe observed in particular, to see that these approxi-mate to each other on the models as they do clinically.

Comparison of the articulating paper markingsmade clinically in CO, RCP and in eccentric excur-sions with those on the articulator should show goodagreement. The adjustment of the antero-posteriorposition of the articulator condyles facilitates the clo-sure directly into CO if a centric relation mountinghas been done.

Errors in articulationThese can occur as a result of the compromises madein articulator design and particularly as a result ofusing an arbitrary hinge axis. It may be possible tocompensate for some errors by adjusting the condylarassemblies to bring appropriate teeth into contact, butgross inaccuracies will require remounting to a newocclusal record.

Possible sources of error in articulation are:

� Distortion of the impression� Air blows on the occlusal surface� Slippage of the facebow� Use of the arbitrary hinge axis� Expansion of the mounting plaster

(a) (b)

Fig. 14.13 (a) Articulated models with pre-centric record in place. (b) The record has been removed and the articulatorclosed. There has been an upward and forward movement, as shown by the marks on the premolars, to reach centricocclusion.

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Fig. 14.14 The centric occlusion contacts on anarticulator being checked with shimstock.

� Incorrect occlusal record� Articulator design compromises� Compression of the periodontium not reproduced� Incorrect angles set

Restoration of the Occlusion

Conformative and re-organised approaches

As was discussed in Chapter 8, each individual adaptssuccessfully to his occlusal irregularities, and will usu-ally continue to adapt as teeth are lost or restored.However, there must clearly be a limit to the capacityof this adaptation and so the golden rule of occlusalrestoration is not to create further problems.

This principle is enshrined in the ‘conformativeapproach’ to occlusal restoration. Where CO andits associated lateral and protrusive movements arefunctioning satisfactorily, then no procedure mustchange this. No doctrinaire philosophies of therights or wrongs of a particular occlusion shouldintrude on treatment. Each new restoration shouldblend harmoniously with the functional patternalready present, provided that is satisfactory.

The converse of this is the ‘reorganised approach’.Here changes are made to the existing occlusionfollowing a diagnosis that there is some major oc-clusal problem present or, of course, when there isno CO.

An example of when the reorganised approachwould be appropriate is the replacement of restorative

work that introduces occlusal interferences and/or de-viations on mandibular closure that the patient hasnoticed, usually as discomfort. This type of case re-quires an articulation in centric relation to make theinitial diagnosis followed by careful planning of thenew occlusion using diagnostic waxing to developappropriate tooth relationships.

Occlusal stability

The maintenance of a stable CO position is impor-tant for occlusal harmony. This may be influenced byrestorative work and the behaviour of materials.

Intracoronal restorationsThe natural cusp/fossa relationship, especially onethat is based on tripods, is very difficult to reproduceby freehand carving. The result of inaccurate con-tacts, or no contacts at all, will be tooth movement toseek a stable position (Fig. 14.15).

In moderate to large restorations, the natural fossashould be replaced by a flat plateau (Fig. 14.16),which receives the supporting cusp of the opposingtooth. This provides good stability and also directs theocclusal loads axially. It is also easier to carve and ad-just in comparison with anatomically shaped fossae.

However, the best restoration from the occlusalviewpoint is the small one. Absolutely minimal cut-ting of the occlusal surface will allow the occlusionto be maintained by enamel in its original state (seeFigs. 10.7 and 10.8).

Choice of materialsThe choice of materials to restore occlusal surfacesis equally important. No wholly satisfactory materialexists; all direct restorative materials deform underload (creep) or undergo surface loss (see Chapter 9)and, of the indirect materials, ceramic is the most dif-ficult to use efficiently. Table 14.1 summarises factorsthat influence the choice between cast metal and ce-ramic for the restoration of occlusal surfaces in fixedprosthodontics.

The relationship of preparations to pulpal andtooth size will be discussed in Chapter 15.

A low anterior guidance leads to very little poste-rior disclusion in protrusion and lateral excursionsand therefore the occlusal clearance required to ac-commodate ceramic may result in a very short prepa-ration. A larger posterior disclusion will permit ce-ramic coverage.

The average technician is usually skilled in handlingwax and will be able to make a functional surface in

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(a) (b)

Fig. 14.15 Occlusal stability. (a) Poorly carved amalgam restoration without buccal supporting cusps, (b) overeruption ofthe upper molar is the consequence. To correct this, the upper occlusal plane must be realigned by adjusting the displacedmolar, or crowning it, followed by a veneer crown on the lower to restore the occlusion and maintain the new position.

metal very adequately. However, when firing ceramicit is much more difficult to achieve accurate contacts.

Perhaps the most important veto is provided bythe last factor on the table. Marking, adjustment andrepolishing of metal is much less time consuming clin-ically than the procedure for ceramic, which shouldinclude reglazing.

Unless aesthetics are of overriding importance, thebetter material for occlusal surfaces is cast metal(Fig. 14.17). For anterior crowns, two-thirds of theguidance should be in metal, allowing translucencyat the incisal tips (Fig. 14.18).

Fig. 14.16 Amalgam restoration with flat plateaux centricstops to provide accurate occlusal stability.

BridgeworkIt is essential that bridgework replaces all the func-tional contacts in CO. It used to be suggested thatloads on the abutment teeth could be reduced by nar-rowing the occlusal table of the pontics. This is ques-tionable, but more importantly such a pontic may nothave correct centric contacts.

Figure 14.19 shows a case where occlusal contactswere not provided, leading to considerable problems.

The patient was a 45-year-old man, who was com-plaining that the gap between the lower left lat-eral incisor and the canine was opening progressively(Fig. 14.19a). This, in fact was caused by overerup-tion of the canine, and the bridge pontic opposing thistooth (Fig. 14.19b) had no centric stop.

Orthodontic therapy was provided to realign thecanine (Fig. 14.19c), and the upper bridge was re-made with a positive fossa relationship with the repo-sitioned tooth (Fig. 14.19d). This course of treatmenttook almost 2 years.

Table 14.1 Factors involved in the selection of materialsfor occlusal surfaces

Metal Ceramic

Large pulps Small pulps

Small teeth Large teeth

Low anterior guidance High anterior guidance

Average technical support Excellent technical support

Simple clinical adjustment Difficult clinical adjustment

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Fig. 14.17 Upper arch bridgework, with most of thefunctional surfaces reproduced in metal.

Anterior guidance

The functional contours of upper anterior teeth areparticularly important, and when making crowns orbridges for that region, the articulator must be ‘cus-tomised’ to reproduce conformative movement path-ways. This is done at the diagnostic mounting stageand either an adjustable incisal guide can be set tothe appropriate angles or, for better accuracy, a cus-tomised incisal table can be made (Fig. 14.20).

Fig. 14.18 Two anterior crowns with two-thirds of theincisal guidance reproduced in metal. The incisal tips needtranslucency for aesthetics.

Cold curing acrylic is added to the incisal table,and whilst it is soft, the articulator is moved throughthe functional pathways dictated by the teeth. Whenhard, the articulator will reproduce these movementswhen, say, a series of crowns is being constructed.

A change in the anterior guidance may be indicatedwhen a key functional tooth is being replaced.

This problem tends to be centred on the canine. Ifthis tooth is lost in a canine-guided occlusion, thenconsideration must be given to changing the occlusalscheme to group function, so that the prosthetic re-placement, whether bridge pontic or denture tooth,is not subjected to unfavourable forces. Figure 14.21shows a bridge replacing a canine, in lateral excur-sion. The pontic receives all the lateral load and trans-mits rotational forces to the premolar. This lattertooth was mobile and painful. The bridge requiredreplacement and a change in the functional patternto group function so that the lateral forces could beshared with other posterior teeth.

Occlusal Equilibration

Indications

This procedure, sometimes referred to as ‘selectivegrinding’, involves the recontouring of tooth surfacesso that the occlusion conforms to certain norms. Theindications are contentious and there is much dis-agreement on whether the procedure should be per-formed at all.

Various workers have proposed occlusal equilibra-tion:

� To establish occlusal harmony as a preventive mea-sure

� To treat temporomandibular dysfunction� As part of periodontal therapy� As pre-operative mouth preparation for crown

and bridge work� Following oral surgery

The doctrinaire ‘equilibration for all’ is not indi-cated by the available evidence that suggests that al-most all people have occlusal interferences but onlya small proportion are suffering from an occlusal re-lated disorder (see Chapter 28). The use of equili-bration for an established disorder is also consideredlater.

The occlusal imbalance as a primary aetiologicalagent in periodontal disease is currently discredited.

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(a)

(c)

(b)

(d)

Fig. 14.19 Loss of occlusal stability. The lower canine has overerupted (a) because there is no centric stop on the upperbridge pontic (b). The tooth was realigned orthodontically (c), and a new bridge made with a positive centric stop (d).

Fig. 14.20 Customised incisal guidance table on a DenarMk IIA.

Fig. 14.21 Cantilever bridge replacing 3| retained by 4|only. In lateral excursion, the occlusion is canine guided,and the pontic transmitted rotational forces to the premolar.The occlusal scheme should have been changed to groupfunction to balance the forces on the bridge and the secondpremolar should have been included in the design.

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(a)

(c)

(b)

BuccalSC

SC

Buccal

SlideSC

SC

Centric occlusion contacts

Premature contact and slide

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(d)

(e)

(f)

Right

Right

Buccal

Buccal

Right

SC

or

SC

SCSC

SC

SC

Direction of movement to right working side

Direction of movementto right working side

SC

Protrusion

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Work from Scandinavia has suggested that occlusalforces are regulated by a feedback mechanism thatrelates them to the amount of support available.There is evidence of secondary effects of occlusal ir-regularities once the primary lesion is established (seeChapter 7).

However, there is some evidence that limited equi-libration is of value prior to crown and bridgework.The preparations will remove occlusal surface andin doing so may remove existing prematurities or in-terferences. This will change the tooth guidance andmay also change the CO position. The practical re-sult might be the loss of occlusal clearance when therestoration is tried in.

If the occlusal surface of the lower molar shownin Fig. 8.6d was reduced, then the condylar guidancewould take over the progressive side-shift pathwayand no crown could fit in between.

Finally, an excellent indication is following thereduction and healing of maxillofacial fracturesor orthognathic surgery when there may be slightdiscrepancies in occlusal positions remaining.

Technique

Equilibration must be approached with extremecare – the enamel cannot be put back! Further, theremoval of apparently simple and localised prematu-rities can have the knock-on effect of creating moreelsewhere.

Full mouth equilibration requires the application ofan occlusal ‘philosophy’. There are essentially two:

� Freedom in centric� CO coincident with centric relation

Freedom in centric has some sense attached to it,though little scientific support. The basic concept isto allow closure on multiple arcs of closure into a COposition that has a range of 1 mm or so both antero-posteriorly and bucco-lingually – a ‘long centric’.

Occlusal Management – Summary

The overriding consideration is that most patients are able to tolerate many minor anatomical and technical‘faults’ in tooth relationships and restorations. Dentists must avoid being dogmatic about occlusal theoryand remember the old saw – ‘If it ain’t broke, don’t fix it!’

Restorations must be constructed to harmonise with and maintain existing tooth relationships where theseare satisfactory.

Articulators are essential for the construction of fixed and removable prostheses and there is no substitutefor hands-on training with this equipment.

Changes to an occlusion must be planned carefully with proper diagnostic procedures.

The attainment of any position within long centriccan then be achieved without the intrusion of prema-ture contacts. The precise position of CO is thereforeremoved, but not occlusal stability. The neuromus-cular control of mandibular closure therefore doesnot have to be so precise and therefore, it is argued,there will be less susceptibility to temporomandibulardysfunction.

In lateral movements, all teeth on the non-workingside should be discluded, as should all palatal cuspson the working side. In protrusion, all the posteriorteeth should disclude, and the lower anterior teethshould have even and balanced contact with the upperteeth.

The philosophy of CO being made coincident withCR involves the establishment of a precise positionbased on tripods. Much relies on which CR defini-tion is applied; the posterior–superior position willbe too far posterior for natural comfort and in con-trast with freedom in centric, the mandibular posi-tioning on closure will have to be very accurate. Thisapproach seems to ignore the naturally occurring dif-ference between the condylar positions in CO andCR.

The results of clinical studies of equilibration havebeen reported but many of these are retrospective andsometimes no more than anecdotal. There have beena few controlled studies and these are inconclusive.

In carrying out an equilibration to freedom in cen-tric, the following rules should be applied:

� Do not reduce the height of any supporting cusps� Fossae may be widened but must not be deepened� Prematurities and interferences should be removed

by hollowing cusp slopes� Non-supporting cusps can be reduced in height to

remove non-working interferences.

These rules are illustrated in the series of diagrams inFig. 14.22.

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Chapter 15Fixed Prosthodontics – Crowns

Intracoronal restorations will be generally satisfactory provided there is sufficient sound tooth tissue tosupport and retain them and to maintain the occlusion. On the other hand, weakened tooth tissue isvulnerable to fracture and should be protected. Further, large plastic restorations tend not to maintain theocclusion as well as cast metal or ceramic. These are the principal reasons for providing crowns.

Treatment Planning

Indications for crowns

The indications for the provision of a crown are:

� Protection of weakened tooth tissue� Maintenance of the occlusion� Improving aesthetics

The potential disadvantages are:

� The need to remove further sound tooth tissue� Plaque accumulation at the margins� Risk of crown fracture or failure

The treatment of a large cavity in a posterior tooth, asdiscussed in Chapter 11, would in the first instancebe restored by a pinned amalgam restoration. Thismight well give good service for some time, and it iscertainly effective as a stabilisation measure. How-ever, depending upon its size, there might be remain-ing enamel and dentine that has become underminedand therefore weakened and the amalgam might notmaintain occlusal stability in the long term.

A large cavity in an anterior tooth might berestorable by a composite restoration but it is morelikely that retention will be compromised by loss oftooth tissue and the aesthetics of a large compositemight not be satisfactory.

It is likely that a better long-term result would beachieved in both of the cases described above if acrown was constructed.

Crowns may also be used to improve aesthetics andthis is discussed in Chapter 16.

The decision to construct a crown depends not onlyon the individual tooth factors, as listed above, buton other general factors. These are:

� Patient motivation� Oral hygiene status� Periodontal condition� The restorative state of the tooth� The occlusion� The provision of dentures

Patient motivation

As was stressed in Section I, patient motivation is es-sential, and any advanced operative work requiresa commitment from both the patient and the den-tist. The stabilisation phase of the treatment plan willgive the dentist the opportunity to assess the patient’smotivation, and indeed vice versa!

Oral hygiene and periodontal condition

As was discussed in Chapter 13, no matter how accu-rately made the crown, the junction between it and thetooth will promote plaque accumulation. If this extraplaque is superimposed on already established peri-odontal disease, this may make the condition worse.Ideally the periodontium should be stable and thepatient’s oral hygiene excellent.

Restorative state of the tooth

Examination of the tooth should ensure that the toothis either vital or that adequate endodontic treatmenthas been carried out. A periapical assessment withradiographs must be made. If there is doubt aboutthe prognosis of a tooth, it is better not to embarkon a complex restoration until the doubt has beenremoved. Nothing is more frustrating or embarrass-ing to find the necessity for endodontics shortly aftercrown placement.

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If the existing restoration has not been placed bythe present dentist and is of dubious quality, it shouldbe removed. This is really part of the managementof the deep cavity since the dentine can be examinedto ensure it is caries free and the periphery may beexamined to ensure that there is an adequate base ofsound tooth upon which to place a crown margin.

The remaining tooth can also be examined to de-cide on the techniques of core construction. An assess-ment of the tooth support likely to remain after crownpreparation should be made so that weak underminedwalls can be removed. This will influence the type andamount of additional retention to be provided for thecore. It is usually best to plan for the worst and forthe core to be well retained by an adequate numberof pins. It is unwise to place too much reliance on acore that is retained principally by dentine adhesive.

The commonest reason for crown construction isthe fracture of one or more cusps. The position ofthe fracture line may well determine not only the typeof restoration but also the fate of the tooth as well.Subgingival fractures are difficult to treat since thedeeper they are, the more inaccessible they are to in-struments and impression materials. Gingival surgeryis often necessary to expose the margin and assessrestorability.

The occlusion

The ability of an amalgam or composite to maintainocclusal stability will depend on the surface area ofthe restoration in contact with opposing supportingcusps and the accuracy with which the occlusal sur-face has been carved.

Once cusp or incisal tip loss has occurred, the prog-nosis for any direct restoration diminishes. While therestoration may not fail catastrophically, the effectof the oral environment on the physical properties ofthe material will result in slow degradation. The basisfor this was discussed in Chapter 9; both amalgamand composite undergo creep, and the composite isvulnerable to surface deterioration. Occlusal loadingleads to fatigue of both materials.

As a rule of thumb, one cusp can probably be re-stored reasonably with amalgam, but more than thisand crowning should be considered. If an incisal edgeis restored with composite then not only should therestoration itself be reviewed carefully, but alsothe opposing teeth in case surface loss is caused bythe hard filler particles of the composite.

The tooth position relative to the adjacent andopposing teeth will influence the type of crown

preparation to be used. Imbrication and rotation willalter the design of the preparation and may limit theability to position its margins satisfactorily. Tilting ofthe adjacent teeth may limit the path of insertion ofthe restoration and prevent crown construction unlessmodifications are made to the approximal surfaces ofthese teeth as well.

The inter-arch occlusal relationships should bestudied prior to preparation. If there has been dete-rioration in these, there may be opposing cusps maybe intruding beyond the planned occlusal plane andpre-operative equilibration of the area must be done(Chapter 14 and see Fig. 14.15).

The provision of dentures

Partial denture abutments that are heavily restoredmay provide a better relationship with the denture ifthey are crowned. Appropriate contours for claspingand to receive occlusal rests can in incorporated in thecrown, probably to greater advantage than trying toused the existing tooth. The design of a partial denturethat will relate to a new crown must be completedbefore the crown is made (see Chapter 24).

Principles of Preparation

The design of the preparation of any extracoronalrestoration depends on planning the following usingpre-operative study models:

� Path of insertion� Stability of the restoration� Aesthetics and the choice of material� Margin position and type� New occlusal relationships

Path of insertion

This is dictated by the approximal surfaces of the ad-jacent teeth mesio-distally and not by the long axisof the tooth to be prepared. Ignoring this may leadto an inability to seat the crown because its marginis obstructed by a tilted adjacent tooth or a poorlycontoured approximal surface of an adjacent tooth(Fig. 15.1). The bucco-lingual path on the other handis dictated by the tooth inclination (see below).

The path of insertion is also linked to the stabilityof the restoration. A long, single path provides themaximum retention (Fig. 15.2) and on tilted teeth,particularly lower molars, a lingually inclined pathwill provide the longest opposing walls.

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15. Fixed Prosthodontics – Crowns 159

Fig. 15.1 Periapical radiograph showing a full crown onthe lower second molar. The mesial margin of the crown isdeficient because the distal surface of the lower first molarobstructs the path of insertion of the crown. The crownneeds to be removed, the distal surface of the first molarrecontoured and a new crown made with the correct pathof insertion.

Stability of the restoration

This is the resistance provided by the preparation todisplacing forces. These will usually be occlusal inorigin and will give rise to rotational moments. Whilstretention is often considered in relation to the path ofinsertion, it is unlikely that displacing forces in servicewill act in this direction.

Additional resistance to displacement will beprovided by the cementing medium. Traditionally,crowns have been cemented by space occupying lutingagents. These fill the gap between the tooth and thecrown and assist retention by mechanical interlock-ing. There are inorganic cements with an adhesivecomponent, polycarboxylate and glass ionomer ce-ments, that have shown good success. Now there arewell-established polymeric adhesive materials that arecommonly used to cement ceramic veneers and resin-retained bridges (see Chapter 19) and may be usedfor crowns. If the adhesive materials were totally re-liable, then the preparation geometry to be describedbelow that creates resistance to displacement wouldbe unnecessary. However, this is not the case and, fur-ther, if the crown required removal to deal with say,recurrent caries or fractured ceramic, this could bea very tedious and difficult process if the crown waswell bonded to the underlying tooth.

Near-parallelismStability is achieved firstly by the principle of oppos-ing parallel walls that need to be based on the same

level – parallel walls not on the same base do notprovide stability (Fig. 15.3).

The bucco-lingual inclination of the tooth to beprepared should be assessed so that the path of in-sertion creates the maximum amount of parallel andopposite walls (Fig. 15.4).

The preparation of exactly parallel walls is difficult,and near-parallelism, with an angle of convergence ortaper of about 5◦ is more realistic and achievable. Anyincrease in taper above this figure leads to a dramaticreduction in stability.

The tapered rotary instruments used in the prepa-ration are manufactured with this taper, and so allthat is required is to select the path of insertion andcut the bulk of the preparation with the bur heldrigidly in this axis. The temptation to angle the burfor apparently easier access, particularly palatally,must be resisted, as this will produce far too muchtaper.

Basic retention will be created by a cervical col-lar resembling a squashed cylinder that will occupyone-third to one-half of the crown height. The oc-clusal third of the buccal and lingual aspects will needto be curved, so that the overall reduction is even,and the final crown will not be bulbous (Fig. 15.5).Some teeth with short lingual walls will have lessheight bucco-lingually, and so attention must bepaid to the approximal areas to create most of theretention.

Cutting the approximal surface can be made dif-ficult by a long and broad contact area. Upper mo-lars are a particular problem in that the contact isfrequently wide and can extend down to the enamel–dentine junction cervically.

Crown heightA short clinical crown will increase the risk of fail-ure by displacement since the path of insertion willbe very short. Increasing the crown height may beachieved by gingival surgery – crown lengthening –but this can produce very unsatisfactory results. Caremust be taken to ensure that gross irregularities donot occur in the level of the gingival margin as a re-sult of the lengthening of a single short wall. There isalso danger of the exposure of alveolar bone.

Gingival surgery is probably of most use in the dis-tal segment of the lower arch, where frequently thedistal crown height of the last standing tooth is veryshort; the removal of a wedge of tissue can increasethe crown height significantly.

The stability of short preparations can be increasedby the use of slots and grooves. These will usually

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(a) (b)

Single path of insertion Maximum retention

Range of paths of insertion No retention

Over-tapered wallsParallel walls

Fig. 15.2 The geometry of paths of insertion. (a) A long single path provides the greatest stability for the restoration; (b) anovertapered preparation leads to a range of paths and the restoration will have poor resistance to displacement.

need to be placed in the buccal and lingual walls,though approximal grooves are useful where the lin-gual walls are short (Fig. 15.6).

If none of this is possible, then dentine pins incor-porated in the casting or the use of dentine adhesiveswill be necessary.

Occlusal reductionStability is increased by a preparation with a large sur-face area and having an occlusal surface that followsthe proposed cusp outline. A flat-topped preparationhas less stability and also removes more tooth sub-stance than is necessary.

Margin position and type

The finishing margin of any crown is determined bythe gingival contour, the restorative material to beused and the presence of any core.

Where aesthetics is not the primary consideration,the crown margin should be placed supragingivallyto prevent plaque accumulation and subsequent gin-gival inflammation. The margin should therefore fol-low the sinuous outline of the gingival tissue, with nosharp changes of direction.

The margin should, however, extend beyond thejunction of any core, so that it is sited on soundtooth. If the margin is not beyond the core, the

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(a) (b)

Fig. 15.3 Stability in a full crown preparation. The parallel walls in preparation (a) are opposite each other on the samebase, and provide excellent stability. The parallel walls in (b) are not on the same base, and the crown would be vulnerableto rotational forces.

core/tooth/crown junction will be vulnerable to re-current caries.

The profile of the finishing line is determined by thematerial from which the crown will be constructed.Ceramic must have a shoulder with a minimum widthof 1 mm, otherwise the material will be at risk of frac-ture in thin section. Gold may be finished on a cham-fer or a bevelled shoulder, the object being to achievea 135◦ edge to the metal and to create a slip jointthat can allow for slight casting shrinkage. This sizeof margin also allows the gold to be finished withoutrunning the risk of distortion.

The bevelled shoulder is used for partial veneercrowns where the supporting cusps require overlay-

ing and the casting may be vulnerable to flexure. Itmay also be used for metal–ceramic crowns to providemargin strength for the sub-frame, and to provide asmoother enamel finish. The drawback to the bev-elled shoulder is that it sacrifices considerable toothsubstance.

The chamfer is the principal finishing line for thegold veneer crown (Fig. 15.7). It is conservative oftooth structure and provides clear definition of theextent of the preparation for both the clinician whenreading his impression and the technician when wax-ing. It also provides a substantial bulk of metal closeto the margin reducing the risk of flexure under loadand the consequential rupture of the cement lute seal.

(a) (b)

Fig. 15.4 The choice of path of insertion in the bucco-lingual plane. (a) The path shown by the burs will not createopposite parallel sides; (b) angulation of the path creates longer walls that are parallel and opposite each other.

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(a) (b)

Fig. 15.5 The bucco-occlusal reduction on a full veneer crown preparation. (a) The first stage to create a near-parallelcollar in the cervical area for stability; (b) the remainder of the buccal wall must be reduced to conform with the contour ofthe tooth to avoid the final crown being overcontoured.

The shoulderless or knife-edge finishing line(Fig. 15.7) should not be used as its definition is poorand can lead to inadequate thickness of metal thatmay flex under load.

New occlusal relationships

The new crown should harmonise with the existingocclusal relationships where they are satisfactory, butmay be required to modify those that are not.

The occlusion should be examined pre-operativelyfor premature contacts and occlusal plane irreg-ularities in the region of the proposed crown. Ifdeterioration of the occlusal surface has occurred,

the opposing tooth may have overerupted. If thisis not corrected, the new crown will continue thedisharmony.

Crowns may also be used to correct rotations oraesthetic malalignments. The new crown positionmust be stable or the eventual result will be toothmovement and a worse problem subsequently (seealso Chapters 16 and 19).

The occlusal clearance provided by the preparationmust be sufficient to accommodate the chosen mate-rial (see later) and in load bearing areas there must bean adequate thickness to prevent fracture. The shapeof the reduction should indicate the cusp positions tothe technician.

(a) (b)

Fig. 15.6 (a) A short preparation is vulnerable to lateral displacing forces; (b) the incorporation of grooves increases theresistance to displacement.

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ChamferShoulderless

Fig. 15.7 Finishing line profiles for gold crowns.

Choice of material

The choice is between:

� Gold� Laboratory fired ceramic� Milled ceramic� Ceramic fused to metal (metal–ceramic)

GoldGold is still regarded as the most satisfactory extra-coronal restorative material. It has a hardness sim-ilar to enamel, does not undergo creep intraorallyand may be cast accurately. The creation of the oc-clusal contour and axial surfaces is relatively straight-forward by wax carving. It may be used in thinsection and will allow the production of fine mar-gins. It is not, however, regarded as a very aestheticmaterial.

There are a number of gold types with additions ofother metals providing a variety of properties avail-able for use in different parts of the mouth. The clini-cian should specify the type of gold required for eachtype of restoration.

The tooth reduction required to accommodate goldis approximately 1 mm throughout, and 1.5 mm,where possible, on the supporting cusps.

CeramicDental porcelain, or ceramic as it now termed, isregarded as the most aesthetic material used in themouth but is brittle and is liable to fracture in thin

section. It is essential to have a minimum thickness of0.8 mm at the margin and at least 1–1.5 mm incisally.Simple laboratory fired ceramic is not strong enoughto be used alone for full crowns on posterior teeth orfor bridgework. Its weakness is that cracks can origi-nate from micropores on the fit surface, and that thesecan open catastrophically in tension or bending.

In view of the inherent weaknesses of basic den-tal ceramic, a number of methods for strengtheningit have been developed and most seek to increase thestrength and/or translucency of the core; ultimately,there is a desire to eliminate metal from aestheticsystems.

Strengthening methods are:

� Dispersion strengthening� Glass infusion� Crystallisation of glasses� Metal sub-structure

Dispersion strengtheningThe introduction of ceramic crystals of high strengthand elasticity into the basic ceramic matrix reinforcesthe system. The first such system involved the use ofalumina crystals and the aluminous crown was intro-duced in the mid-1960s. This has a high alumina corethat is very opaque onto which conventional enameland dentine ceramics are fired. The improvement ofphysical properties achieved by this has not reallybeen surpassed until very recently.

Other systems of dispersion strengthening are theinclusion of leucite crystals in either a convention-ally fired material (Optec, Jeneric, Connecticut) orin a castable, heat processed form (Empress, Ivoclar,Liechtenstein). Magnesium–aluminium oxide crystalsare incorporated in another castable ceramic, Alce-ram (Innotek, Colorado).

The disadvantage of the castable ceramics is thatspecialised equipment is required for production ofthe restoration. Their advantage is that they canbe produced by the lost wax process and thereforecontouring is easier.

Glass infusionThis produces a denser stronger core by slip casting.In this technique a pure alumina slip cast coping ismade on a special gypsum die and partially fired. Af-ter shaping by milling, the porous alumina is infusedwith a low fusing glass of matching thermal expan-sion that melts and diffuses through the porous alu-mina by capillary action. The result is a very dense andstrong alumina composite. The commercial materials

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Fig. 15.8 The die scanning stylus for a milled ceramiccrown. All changes of direction of the preparation surfaceshould be rounded to allow smooth movement of the stylus.

are Procera (Nobel Biocare, Sweden) and In-Ceram(Vita, Germany).

A variation in finishing line is necessary for milledceramic materials that require the die to be scannedmechanically by a stylus to reproduce the internalcontours (Fig. 15.8). To allow free movement ofthe stylus the preparation geometry should includerounded angles. This means that the shoulder needsto blend with the axial wall of the preparation witha rounded line angle, not a sharp one (Fig. 15.9).

Crystallisation of glassesThis is the strengthening technique found in anothergroup of castable ceramics. It requires an initial firingprocess that produces a ‘green’ ceramic followed by asecond firing that converts this material into a densemass of interlocking crystals. Commercial materi-als are Dicor (Dentsply, Philadelphia) and Cerapearl(Kyocera, California) but these systems are now usedless frequently.

Metal sub-structureThe use of a cast alloy sub-structure is the principaland most common method; it is discussed below.

Clinical implicationsWhilst the newer systems are of considerable interest,they are as yet unproven clinically and some are not

Milledceramiccore

Aestheticceramic

Rounded shoulder

Fig. 15.9 Finishing line for a milled ceramic crown.

in general use because of the cost of the equipment.Perhaps the most important factor in the acceptanceof new ceramics is whether they can be used in themultiple units of fixed bridgework. Most current ma-terials have limited application in this field.

The principle of the preparation for an all-ceramiccrown of any type is to provide dentine support for theceramic throughout, particularly on the incisal andcingulum areas of anterior teeth. Adequate thicknessof material is also essential.

Dental ceramic is harder than enamel and anunglazed surface will abrade tooth surface and fre-quently results in considerable wear to the opposingtooth (Fig. 15.10).

Metal–ceramicThe most reliable and successful method for strength-ening ceramics is the provision of a cast metal sub-frame to which the ceramic is bonded. This preventsthe propagation of cracks from the ceramic inner sur-face and the combination provides good aestheticsand excellent strength. Its disadvantage is that it re-quires considerable tooth reduction to accommodateit.

Ceramic bonding alloysThe alloys intended for ceramic combination shouldhave a:

� Sufficiently high melting point so that they do notdeform during firing of the ceramic

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(a) (b)

Fig. 15.10 Poorly glazed ceramic. (a) Crowns and a bridge with poorly constructed ceramic. Opaque ceramic is exposed tothe occlusion and this is very abrasive, (b) Poorly glazed ceramic on the palatal aspect of 3| has resulted in wear of the (3|).

� Thermal coefficient compatible with ceramic toavoid fracture on cooling after firing

� Capacity to bond chemically with the ceramic

There are four main categories of alloy:

� Precious� Semi-precious – high gold� Semi-precious – low or no gold� Non-precious

The melting points of these alloys are higher thanthose of gold alloys used for crowns and thereforeneed to be used in phosphate bonded investmentsrather than gypsum bonded.

Precious metal alloys contain small amounts ofplatinum and palladium that have been added to goldto raise the melting point. These exhibit good bondingcharacteristics, are relatively easy to cast, and finishto a high lustre. Their disadvantages are cost and theirtendency to sag during firing of the ceramic, particu-larly when long span bridges are being made.

The semi-precious alloys have better sag resistanceand consist principally of silver and palladium, witha variable amount of gold. The silver sometimes leadsto ‘greening’ of the ceramic if the alloy has beenoverheated during casting and is visible at the metal–ceramic junction.

Both precious and semi-precious alloys have smalltraces of base metals (iron, indium, tin or zinc), whichoxidise on firing to form a film that bonds chemicallywith the ceramic.

Non-precious, or base metal, bonding alloys areeither nickel–chromium or cobalt–chromium. Theyare cheap, but more difficult to cast, and harder tofinish. Their high modulus of elasticity gives them thehighest sag resistance of all the bonding alloys. Thenickel and the chromium oxidise on firing to formthe oxide layer for bonding. However, this can beuncontrolled and was one of the major limitations ofthe early alloys.

There are some reservations about the inclusion ofnickel, which may induce a sensitivity reaction in sus-ceptible patients.

The mechanism for bonding the ceramic dependson three factors:

� Chemical – during firing an oxide film is formedon the metal that bonds with the ceramic

� Mechanical – surface irregularities on the castingprovide a key for interlocking with the ceramic

� Compressive – there is a slight mismatch betweenthe thermal coefficients of expansion of the ce-ramic and the alloy. That of the ceramic is higherso that on cooling the ceramic shrinks very slightlymore and grips the metal. A curved surface isnecessary for this to happen effectively

Clinical implicationsThe aesthetics of metal–ceramic restorations presentparticular problems and these are discussed in Chap-ter 16. As mentioned above, the clinical preparationrequires considerable tooth substance removal to ac-commodate the metal and ceramic. This particularly

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Metalsubframe

Shoulderceramic

Shoulder Bevelled shoulder

Fig. 15.11 Finishing lines formetal–ceramic crowns. The metalsubframe does not cover the shoulder andshoulder ceramic is used. The bevelledshoulder is designed to allow metal toextend to the external aspect of the crown.

applies to the occlusal aspect where 2-mm clear-ance is desirable if ceramic is to cover the oc-clusal surface. Other areas for which ceramic cov-erage is desired should have a 1.2-mm reduction,which should be removed evenly from the whole sur-face contour. This means that the final third of thepreparation will curve markedly towards the occlusalaspect.

Finishing lines. As was mentioned above, ceramicrequires a shoulder finishing line that allows suffi-cient bulk of material for strength. In metal–ceramicrestorations it was usual to extend the metal sub-frame to the edge of the shoulder to support the ce-ramic and restrict its shrinkage. Various configura-tions were used and the bevelled shoulder is shownin Fig. 15.11. This creates a very accurate fit atthe cervical margin but has the disadvantage thatthe collar of metal may be visible and spoil theaesthetics.

To obviate this problem, shoulder ceramic was in-vented. This invention is conventional ceramic that ismixed with wax and when this mixture is fired there islittle shrinkage. This means that the ceramic remainsadapted to the shoulder and the metal subframe is notrequired in that area (Fig. 15.11); this creates excel-lent aesthetics.

Under-reduction of the preparation. This is themain clinical fault associated with metal–ceramiccrowns. Under-reduction of the buccal surface maylead to one of two problems:

1 The technician overbuilds the crown to give ad-equate thickness of material for aesthetics. Thecrown is then grossly overbuilt (Fig. 15.12a)

2 The technician attempts to maintain the origi-nal tooth anatomy which leads to a thinning ofthe ceramic and metal, with poor aesthetics andthe subsequent fracture of the porcelain occlusally(Fig. 15.12b)

In order to judge the amount of tooth tissue removedduring the preparation and to ensure this removal iseven and sufficient a silicone index may be used. Asmall local impression is taken of the tooth beforepreparation and cut through in the long axis of thetooth. This may then be positioned on the tooth atstages during the preparation to check the amount ofreduction (Fig. 15.13).

Occlusal considerations. The choice of materialfor the functional surfaces must also be considered.Glazed porcelain is usually the patient’s choice but itis difficult to produce the anatomical form accuratelyand adjust it intraorally. If not reglazed, it will damagethe opposing tooth surface. As was discussed in Chap-ter 14, it may not be possible to provide enough clear-ance in the occlusion to accommodate ceramic. Metalis therefore preferred (see Figs. 14.17 and 14.18).

Restoration of Root-Filled Teeth

By the time caries and/or trauma has destroyed coro-nal dentine and the endodontic access cavity has been

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(a) (b)

Fig. 15.12 Incorrect preparation for metal–ceramic crowns and the consequences. (a) The crown is made bulbous toreproduce the correct shade; (b) the correct contour is reproduced, but this means that the ceramic is too thin.

cut, there will often be little dentine remaining to sup-port a crown (Fig. 15.14). Should a crown thereforebe required on a root filled tooth, some form of postand core will be needed to retain the crown and pro-vide stability, with the post being fixed within the rootcanal.

The post crown has some limitations and risks.These relate to the morphology and size of the roots,and the danger of fracture of the root in the event oftrauma to the crown.

Where the root is of variable shape and size andcannot be seen clearly by radiography, the post crownis a real hazard (Chapter 29). This is true of posterior

Fig. 15.13 Silicone index used to indicate the amount oftooth reduction to ensure sufficient tooth is removed.

teeth, particularly those which have sometimes oneand sometimes two roots.

The two-rooted premolar may also have very nar-row roots, quite unsuitable for receiving posts. Hereit is safer to provide a pin retained amalgam core,rather than embark on two posts with a split core.If there is not enough dentine for the pins, then theroot canals can be used for retention, but using smallcemented preformed posts that only intrude by 3 orso millimetres into the canal.

A further variation is to construct an amalgamcore without pins that is retained within the coronalregion of the root canal(s) – the Nayyar core. This

Fig. 15.14 A carious, non-vital tooth. After removal of thecaries and the cutting of the endodontic access cavity, therewill be little dentine left to retain a crown. The root canalmust be used for retention.

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type of post and core is very poor at resisting lat-eral forces and it is essential that at least 2 mm ofcoronal dentine is present above gingival level to beincorporated in the crown preparation to resist suchforces.

In the anterior teeth, the post and core is therestoration of choice.

Posts and cores

There is a huge range of post and core systems fromwhich to choose. They may be classified into:

� Cast� Prefabricated� Hybrid

Cast post and coreHere the natural shape of the canal is utilised after theelimination of undercuts and irregularities to form aconical preparation. The post shape may either berecorded using the direct technique with inlay waxor a non-residual burnout pattern acrylic, or indi-rectly by taking an elastomeric impression. The coreis waxed to the appropriate shape for the particulartooth and the system has the major advantage that it

is made to fit the tooth, rather than the tooth beingprepared to fit the system.

The major disadvantage of the cast post is that itis weaker than the equivalent diameter of a wroughtpost. Therefore, if fracture of the post is to be avoided,the diameter of the canal must be enlarged to ensurean adequate bulk of metal. This means that the tech-nique sacrifices more tooth and weakens the root incomparison with the prefabricated systems.

The cast post is probably the technique of choicefor large canals, for difficult alignment problems, andwhen a cast diaphragm is required to support the root,or make up subgingival deficiencies.

Prefabricated post and coreThese posts are factory made in a range of sizes with amatching twist drill system to prepare the root canalto receive the post. The posts may be parallel sidedor tapered and these in turn may be smooth, serrated,threaded or vented or various combinations of someof these (Fig. 15.15).

The choice of commercially available systems is im-mense and personal preference has a large part toplay in selection. Of the various types, the taperedthreaded post is the most dangerous, since its inser-tion can generate enough stress to split the root.

(a) (b) (c) (d) (e) (f) (g)

Fig. 15.15 Variations in post configuration: (a) tapered; (b) tapered serrated; (c) tapered threaded; (d) parallel; (e) parallelserrated; (f) parallel threaded; (g) parallel vented.

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Root filling

Post

Core

Jacket crown

Fig. 15.16 The structure of a hybrid post crown.

The majority of non-threaded posts are made ofstainless steel and are therefore strong in narrow di-ameters, whilst the threaded systems tend to be brassor mild steel. Other designs have utilised carbon fibreor composite polymers or titanium.

Parallel posts are effective in most teeth, but caremust be taken with them in small roots, because therisk of perforation of the canal wall is high. Taperedposts are better in narrow canals. The vented postshave channels for the escape of excess cement and aretherefore claimed to permit better seating.

Perhaps the biggest drawback of the basic prefabri-cated system is that the core position, size and shapeis relatively fixed. Some modifications are possible,but are limited in extent. The biggest claimed advan-tage is that they remove one laboratory stage, and aretherefore more economical.

Hybrid – prefabricated post, cast coreThis group has prefabricated posts where the core iscustom made and cast onto the post. This combinesthe strength of the wrought post that can be semi-precious alloy, cobalt–chromium, steel or titanium,with the advantage of being able to shape the coreexactly for the particular tooth.

Figure 15.16 shows the basis of the hybrid tech-nique using a smooth parallel-sided post that fits

into a matched preparation. This post may be tita-nium, steel or, rarely, wrought gold. The core is castgold, and extends into a countersink to reinforce thepost and provide resistance to rotation. The shoul-der, which receives the crown, is cut separately andmay leave a collar of dentine that effectively lengthensthe canal preparation. The collar must have sufficientbulk so that it does not fracture on the die.

Some systems provide plastic impression posts thatcan be used instead of the metal ones but these cancreate some problems. The narrower posts are flexibleand will negotiate curves that the final post will not.The impression post can subsequently be used as partof the pattern for casting but then the disadvantagesof the cast post mentioned above are reintroduced.

The core waxing may be done either in the mouthor in the laboratory.

Other variationsConcerns about the presence of metal in the rootcanal such as possible discolouration and the trans-mission of impact forces directly to the root have ledto non-metallic posts. These include posts made frompolymer impregnated with carbon fibre, glass fibre,or glass particles. The principal advantage claimedfor these posts is that they have moduli of elasticitysimilar to dentine and therefore it is suggested if thecrown receives a blow, the post will absorb some ofthe force and not transmit it directly to the tooth caus-ing root fracture. However, against this is the prop-erty that the post is flexible. Functional loads of thecrown may then flex the post and the cement seal maybe broken. There is no convincing outcome analysisthat supports the use of these posts.

A further technique that has become popular withsome, is the cementing of a prefabricated post af-ter canal preparation and then building a compositecore to the appropriate shape followed by the impres-sion for the crown. This technique may be called ananchor system. Whilst this is a quick technique, thedisadvantage is that the composite relies on mechan-ical interlocking with the post for its retention whichmay be unreliable.

Canal preparation

Whatever system is used, there are a number of com-mon features in the preparations. The following as-pects are important:

� Root canal morphology� Length

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� Diameter� Resistance to rotation� Retention of coronal dentine� Core characteristics

Root canal morphologyAssessment of the root canal morphology is requiredbefore committing the tooth to a post preparation. Itis essential to have an adequate apical seal and theroot filling material should be removable from thecoronal end of the canal. A full-length silver pointis a considerable impediment, and should be replacedwith gutta-percha if possible. If it cannot be removed,then a post will be impossible, and a pinned core willhave to be considered.

The cross section of the canal and the presenceof any curvature should be assessed. A very narrowcanal may make preparation difficult and an exces-sive curvature may limit the extent of the post andreduce retention.

Remember also that the radiograph only showscurves mesially or distally, and not labially orpalatally.

LengthThe length of the post is one of the most critical fea-tures. A short post is capable of exerting enough lever-age to split the root when loaded transversely. It alsodetermines in part its retention and the longer thepost, the greater the load bearing area for dissipationof forces to the surrounding bone.

As a rule of thumb, the post should be as long asthe crown it is expected to retain.

DiameterThe diameter is determined by the anatomy of thecanal, the amount of diseased tooth tissue removedand the type of metal used in the post and core con-struction. In order not to weaken the root, the postshould not be more than one-third the total rootwidth for the whole root length. This suggests su-periority for the tapered post.

However, if the parallel post obeys the rule in theapical danger zone, it will be narrower coronally. Thisis how the addition of the custom core adapts theparallel post to fulfil ideal requirements, since thediameter is increased by the cast-on metal. Theprefabricated core type does not do this.

The range of post diameters that are successful is1.2–1.4 mm. Posts of a smaller diameter are vulner-able to bending in the occlusion and those that are

larger may jeopardise the root through perforationor splitting.

Resistance to rotationA cylindrical post will rotate under stress from theocclusion and may not locate accurately when triedin. Some prefabricated systems require the cutting ofgrooves or notches to provide resistance to rotation.

However, the natural shape of the root canal is ovaland it seems a pity not to utilise this natural featureand to avoid the stress concentrations and weaknesscreated by anti-rotational notches or other devices.

The canal can be simply enlarged coronally to fol-low the root contour smoothly and this area can beengaged by cast-on core.

Retention of coronal dentineIt is desirable to keep some coronal dentine abovethe gingival level. This will effectively lengthen thepost preparation but more importantly it will createa collar allowing the crown margin to be sited belowthe core/coronal dentine margin as seen in Fig. 15.16.This overlapping of the root dentine and core–dentinejunction is referred to as a ferrule. This term comesfrom the thimble-like metal tip to a walking stickor umbrella end that is intended to stop the woodsplitting.

Hence, in post crown designs, the ferrule has beenproposed as a way of stopping the root splitting.There have been designs where the ferrule has beenpart of the post and core, perhaps as a diaphragmover the root face. However, the crown itself acts asthe ferrule and there is no need to modify the post forthis purpose.

Difficulty arises when there is not enough den-tine to provide this collar and then the core toothmargin will be at the same level as the crown-tooth margin. This is not so advantageous in thedistribution of stress away from the canal walls.Also with more stress being transmitted to the post,its mechanical properties become more important.The Nayyar core mentioned above will not succeedwithout a good-sized ferrule because amalgam isweak when subjected to shear forces. Also there ismore risk of the non-metallic posts bending in suchcircumstances.

Core characteristicsThe core should provide retention and stabilityfor the final restoration and should be similar tothe shape of a conventional crown preparation(Fig. 15.17).

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Fig. 15.17 Two posts and cores in place, showing thebasic core shape is similar to the ceramic jacket crownpreparation, but is smaller. A collar of dentine is present asthe base for the core and the ‘ferrule effect’.

It is possible to realign the position of the crownwith the core, which allows derotation or uprightingrelative to the root position. However, this optionmust be used with caution since there is frequentlyan interplay between the hard and soft tissues, andmuscle pressure may well move the altered tooth pro-ducing a bizarre result.

The core can also be smaller than the vital toothpreparation since there is no pulp to worry about.This gives added bulk to the final crown, which is aconsiderable advantage for the strength of a ceramiccrown, and helps the aesthetics of the metal–ceramiccrown.

Provisional Crowns

This aspect of advanced operative work is frequentlyneglected and little time is devoted to the constructionof a good provisional crown.

The functions of a provisional crown are:

� Protection of cut dentine� Maintenance of the occlusion� Maintenance of approximal contacts� Restoration of aesthetics� Maintenance of gingival health

It is good practice to construct the provisional crownprior to the impression of the preparation, since thiswill allow proper estimation of the time remaining forthis.

Provisional crowns may be customised or madefrom prefabricated crown forms.

Customised crowns

An impression in a silicone putty is taken prior tothe start of the preparation and put to one side. Oncompletion of the preparation the putty impressionis used to form a mould for a polymer-based ma-terial. There are currently a number of dimethacry-late polymers based on composite technology thatare available for this application and these may beself-curing or light activated. They may pass througha rubbery phase during setting which is intended toassist removal of the mould and crown prior to fullsetting.

After the tooth has been prepared, the material isplaced in the putty mould which is then replaced onthe tooth. The mould must be located exactly as it waspre-operatively or else the provisional crown will beincorrect. At the rubbery stage the mould and crownis removed with care. It is very easy to tear the crownat this stage. On the other hand, leaving the crown toharden on the tooth may mean that the set materialis locked into approximal undercuts and then it willhave to be cut off; it cannot be left in place in thiscondition because it will be a plaque trap and allowleakage to the preparation.

When polymerisation has completed, the crown istrimmed accurately to the margins of the prepara-tion and the occlusion, and polished. It should becemented with a weak ZOE cement.

Prefabricated crowns

Anterior crown forms can be tooth coloured, usuallypolycarbonate, or transparent cellulose acetate. Theyare available in a range of sizes for each tooth and thesize should be chosen to conform to the mesio-distalwidth. They need to be cut carefully to the cervicalmargins and then based with a self-curing polymer(Fig. 15.18).

The range of sizes can be restrictive, if it fits it isusually good, but if it does not it can be terrible. Itcan be difficult to find one with the correct dimensionsboth bucco-lingually and mesio-distally.

Posteriorly, the best provisionals are anatomicallyshaped silver–tin crowns. These are also designed asburn-out patterns for crown waxing. They are softand can be adapted easily to the occlusion and to thecervical margin.

They do not usually require basing with a polymer,but can be if the fit needs to be refined. Their disad-vantage is that being made of a soft alloy, they have alimited life. They must also be protected from amal-gamation if they are placed on a fresh amalgam core.

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Fig. 15.18 Provisional restorations. They have been madefrom transparent crown forms and self-curing acrylic, andprovide correct aesthetics, occlusion and gingival contour.

Shade and Impressions

These are considered in Chapters 16 and 17.

Occlusal Registration

The construction of a single crown and often a pairof crowns will not require an articulation; hand heldmodels will be satisfactory. However, a crown for astrategic tooth, such as the terminal abutment of abounded saddle, will require articulation to obtainaccurate occlusal contours. Occlusal records were dis-cussed in Chapter 14 and in the absence of a repro-ducible position of best fit the technique of using anocclusal registration coping should be used. This tech-nique is described in Chapter 21.

Fitting a Crown to an Existing Denture

This can be a very difficult operation, particularly ifa rest seat and two clasp arms are involved as wellas the denture base. Clearly the counsel of perfectionis to ensure that denture abutment teeth are soundand well restored before a denture is made. How-ever, further caries and loss of tooth substance mayhappen after a crown has been in service for sometime.

The registration of the denture position in relationto the crown preparation must be supplied to the tech-nician. If there is sufficient clearance between the den-ture and the preparation then the impression can be

taken with the denture in place. The technician maycast the denture area immediately next to the crownpreparation in acrylic to provide a durable index forguiding the waxing of the crown pattern.

A more accurate method, but one requiring an ad-ditional visit, is to take an impression without thedenture and ask the technician to construct an acryliccoping on the die. The coping will normally be madeof a pattern acrylic that burns out of the investmentwith no residue.

Intraorally, the coping is tried on the preparationand the denture seated. Further pattern acrylic is thenadded to the coping to register the position of the den-ture components and the occlusion. The technicianwill use this as a guide for finalising the pattern thatwill be invested and cast.

Try-in and Cementation

The sequence is:

1 Check the restoration on the model before the pa-tient arrives ensuring that there are contacts withadjacent teeth and that the occlusion and shade (ifceramic) is correct. Examine the die and the adja-cent teeth on the model for rub marks which mayhave introduced errors

2 Do not attempt cementation if the tooth displaysany adverse symptoms. If the patient complains ofdiscomfort, diagnose the cause and treat it beforecementation

3 Remove the provisional and clean the preparation,ensuring that all cement is removed. If possible thisshould be done without local analgesic since thiscan prevent the patient assisting in the assessmentof the occlusion

4 Try in the restoration. If it does not seat initiallycheck the contacts with floss (Fig. 15.19a). If therestoration still does not seat, examine the fit sur-face for irregularities such as blebs of cast metaland grind any away

5 Once the crown has been seated, check themarginal adaptation. There should be a smoothtransition from the tooth onto the crown. Checkthe shade in daylight

6 The occlusal contacts should be assessed. Prema-ture contacts may be detected using articulatingpaper and shimstock (Figs. 15.19b,c). The typeof articulating paper can affect the results sincesome are excessively thick and will not allowfor differentiation of the high points and normal

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(a)

(c)

(b)

Fig. 15.19 Fitting a full crown. (a) The approximal contacts are checked with floss; (b) the occlusal relationship is checkedwith shimstock both on the crown itself and (c) at the cusp/fossa relationship mesial to the crown. Both contacts should holdshimstock.

occlusal stops. Fine articulating paper is prefer-able and it often advantageous for the occlusal sur-face of the restoration to have a matt finish in or-der to detect the minor prematurities that may bepresent

7 The occlusal contacts must be checked in all ex-cursions. Heavy contacts must be eased but careshould be taken that the surface is not over-reduced, since this will take the crown out of oc-clusion.

8 Choice of cement. Incorrect selection and manipu-lation of the cement will affect the life of a crowndramatically

There are two principal luting agents, zinc polycar-boxylate and glass ionomer cements, and their prop-erties were discussed in Chapter 9. The polycarboxy-late is the more reliable since there is some concern

about the pulpal response to glass ionomers whenused as luting materials.

The cement should be mixed to the manufacturer’sspecified powder/liquid ratio which should provide aconsistency that will allow it to be displaced as thecrown is seated and excess will flow away.

9 The prepared tooth should be isolated and dried.The fitting surface of the crown should be coatedwith cement, placed on and seated home. Con-siderable pressure should be applied to the seat-ing crown initially to express the excess cementand pressure should be maintained until the ce-ment has set. For a post crown, the canal shouldbe cleaned and filled with cement prior to seatingthe post and crown together with the same mix

10 Once the cement has set, excess is fractured awayfrom the margin and the approximal embrasures

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cleared with floss. It is particularly importantthat the cement has fully set before removal ofexcess is attempted. This is especially so becauseglass ionomer and zinc polycarboxylate cementsgo through a rubbery phase on setting. If theseare disturbed at this point the integrity of themarginal seal may be lost

11 After cementation, the occlusal relationshipshould be rechecked

Fixed Prosthodontics – Crowns – Summary

Ensure that the crown is treatment planned in the context of the patient’s requirements and the generalcondition of the mouth.

Important principles in the preparation of a crown are the choice of the path of insertion and features toensure the stability of the final restoration.

There is a large range of materials available, particularly for the all-ceramic crown. The choice of materialaffects the preparation design, particularly the shape of the finishing line and the amount of tissue to beremoved.

There are many post crown systems. The choice is to a large extent personal but the hybrid types offer thegreatest range of application. Important characteristics in the post preparation are the length and diameter.Tooth tissue should be preserved where possible.

Accurately fitting provisional crowns maintain the relationships to adjacent teeth and the health of thedentition.

High standards of acceptance at the fitting stage will lead to long-lasting restorations.

Review

The crown should be inspected again a week or solater, since natural occlusal function will have beenre-established, and contacts may require further ad-justment

Radiographic review should be carried out 6–12 months later and every 4 years or so, to checkfor symptomless development of apical pathology

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Chapter 16Colour and Aesthetics

Two of the recurring themes of this book are the requirements for durable tooth-coloured restorative materialsand the need to achieve good aesthetics. This is a complex subject and is a mixture of art and science.Advances in both restorative polymers and ceramics have increased the range of techniques available underthe broad heading of ‘Cosmetic dentistry’ and some of these have been described already.

This chapter will consider colour science and shade taking together with the causes and management ofpoor aesthetics of individual teeth. Section IV will consider the aesthetics of fixed bridgework and removableprosthodontics.

Colour

A prerequisite of all aesthetic dentistry is accurateshade taking and matching, and, in respect of indirectrestorations, good shade communication. The techni-cian rarely sees the patient and is therefore relying onthe dentist to describe the shade and its distribution.Perceived colour is highly affected by viewing con-ditions and it is essential that the shade is taken inthe most favourable conditions in order to obtain anaccurate result.

Factors affecting perceived colour

Three factors are involved:

� Light source� Eye response and colour perception� Environment

Light sourceLight is composed of different wavelengths that aredependent upon the source. Incandescent light, suchas that provided by normal light bulbs, accentuatesthe yellow/red range in the spectrum, whilst fluores-cent light accentuates the blue/green range; both affectcolour vision.

Teeth exhibit metamerism, that is the property ofchanging colour in different lighting conditions. Day-light corrected fluorescent tubes and shade takinglights with a standard colour spectrum are commer-cially available and these can help, but they may giverise to more inaccuracies in comparison with good

natural daylight. The daylight for shade taking needsto be diffuse, north light, not direct southern sun-light. Teeth also change colour as they become dry;they must be kept wet during shade taking.

Eye response and colour perceptionWhen concentrating on the colour of a tooth, theretinal cones of the eye will fatigue and sensitivityto colour will be reduced. To overcome this, deci-sions on shade should be made in steps of no morethan 5 seconds. Looking at a pale blue surface, suchas a napkin or piece of card, between evaluations ofshade can help; this accentuates yellow/orange sensi-tivity, which is the dominant range of tooth colour.Prolonged viewing of a tooth results in a negativeafter-image that is the complimentary colour of theoriginal surface viewed.

Colour perception is subjective and varies betweenpeople. In addition, colour blindness is quite commonand obviously creates problems during shade taking.Using two people to take the shade, dentist and nurse,will even out such inaccuracies. A simple eye test isalso useful to discover colour vision acuity.

EnvironmentStrongly coloured light reflected from furniture,clothing or the walls will influence shade taking,partly from the after-image mentioned above andpartly from reflection. Ideally the surgery and itsequipment should be of a neutral colour. Strongcolours from make-up or clothing should be removedor masked.

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Components of colour

In order to communicate subtle variations in colour,it is important to understand the way that a specificcolour is measured. Colours may be broken downinto three components:

� Hue� Chroma� Value

Hue (colour)This is the description or name given to a colour orfamily of colours, e.g. blue, red, green, yellow. Den-tine is the most important hue within a tooth.

ChromaThis is the intensity or strength of a given hue. Forexample, if 10 drops of red dye are added to a glassof water it will become red, if 100 drops are added,the water will still be red, but of a more intense colour.The chroma will have changed but the hue will not.The chroma of dentine is as important as its hue.

ValueThis is the total reflectance or luminance, that is re-lated to the brightness of a colour measured on a scalefrom black to white. For example, if red is the huethen pink or maroon can be made by changing thevalue without changing the original hue. The overly-ing enamel, being essentially colourless, is the prin-cipal determinant of value in a tooth, modifying thedentine hue to the observer. The brightness of a colouris probably the most easily perceived characteristic.

Shade Guides

The most commonly used shade guide is the Vita-Lumin that allocates a letter for the hue, A, B, C, D,and a number, 1, 2, 3, 4, indicating the chroma. Noprovision is made for altering or indicating the value.

The arrangement of basic hues is:

� A1-4: browns� B1-4: yellows� C1-4: greys� D2-4: reddish-greys

This means that the observer must make a decisionabout the combined hue/chroma in almost one step.Selection can therefore be difficult, especially for thenovice, as there is a tendency to jump from one groupto another, rather than follow a progressive pattern.

Neck shade A4

White fleck

Incisal A3

A2

Translucent mesially

Fig. 16.1 Sketch made at the chairside to provideinstructions for the laboratory for shade reproduction.

If the shade tabs are arranged according to value(degrees of brightness), as in most denture tooth shadeguides, selection may be more straightforward. Theappropriate sequence is B1, A1, B2, D2, A2, C1, C2,D4, A3, D3, B3, A3.5, B4, C3, A4, C4.

The shade guide has other limitations. An all-ceramic crown will not be the same thickness as ashade tab, and, of course, light passes through anall-ceramic crown more readily than one of metal–ceramic.

The construction of the guide may be different fromthe layering that the ceramist may use. The shade tabhas subtle in-built colours and nearly always a neckeffect that most ceramists do not include. It is im-portant to ask the ceramist how he uses his shades,and it may be necessary to remove the neck colourfrom the tab to match his system. Many laboratoriesuse just core, dentine, enamel and an external stainand it would be useful to ask the laboratory to pro-vide a customised guide of various thicknesses andcolours.

Informing the technician

Any time spent accurately obtaining the shade willbe wasted unless the information is communicatedclearly to the technician. When taking a shade it isessential to include a sketch diagram of the tooth orteeth marking clearly areas of decalcification, internalflecks, lamellae and so on (Fig. 16.1).

Work cards, or laboratory prescription forms, canbe set out in many ways, but must include the follow-ing information:

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16. Colour and Aesthetics 177

Fig. 16.2 Ceramic crown on |1 showing characteristion.

� Patient’s name and sex� Approximate age – the surface texture of teeth

changes with age and the technician can reproducethis effect

� A drawing of the tooth showing the distributionof the various shades, and characterisation

� The dentine, enamel and cervical shades� Amount of glaze – high, as guide or low� Amount of translucency – high, as guide or low� Type of restoration required� Is a metalwork try-in stage required?� Is a biscuit bake (unglazed) try-in stage required?� Ceramic or metal occlusal surface?

If the information given to the technician is good andthe accompanying impressions are accurate, then thestandard of ceramic crown construction can be excel-lent (Fig. 16.2).

Discoloured Teeth

Discolouration of the teeth may be due to intrinsic orextrinsic stains:

Extrinsic staining:� Plaque and calculus� Mouth washes� Diet� Discoloured restorations� Smoking

Intrinsic staining:� Caries� Erosion� Chemical ingestion, including fluoride and

tetracycline� Trauma

� Non-vitality and root filling� Neonatal jaundice� Genetic and developmental malformations

Extrinsic staining

This is very common and patients may not appreci-ate the effects of tea, coffee, smoking, red wine andchlorhexidine mouth washes. The misinformed pa-tient may resort to home-bleaching kits when all thatis required is a scale and polish and instruction in oralhygiene.

The discolouration and microleakage associatedwith polymeric restorations has been discussed inChapter 9. Corrosion products from amalgam diffuseinto the surrounding dentine, causing a greyish-blackstain.

Intrinsic staining

Developmental disorders vary in intensity from caseto case. Enamel hypoplasia may be seen as localisedinsignificant white spots or more extensive areas ofpoorly formed tissue that are very liable to take up ex-trinsic stains. Other more serious conditions, amelo-genesis imperfecta and dentinogenesis imperfecta maylead to badly discoloured teeth; these are consideredin Chapter 27.

Chemicals may be incorporated in the dentine andenamel during their formation. The most dramaticof these is tetracycline. Different effects are producedby different members of the tetracycline family, bythe dosage and duration of treatment and the age ofthe patient at treatment. Effects range from mild greybands to total blackness. It is surprising, in view ofthis problem being common knowledge, that tetra-cycline is still prescribed for children by the medicalprofession.

The dental profession, on the other hand, in itskeenness to prevent caries has caused a somewhatsimilar problem with fluoride. Systemic fluoride sup-plements, perhaps with their dosage not monitoredaccurately by parents, coupled with ingestion by chil-dren of fluoride toothpaste, has led to a high inci-dence of fluorosis in the more dentally aware popu-lation. This may be seen as grey or white patches inthe enamel.

Neonatal jaundice may lead to incorporation of theyellow pigment of bilirubin in the dentine.

Discolouration caused by caries was discussedin Chapter 10 and erosion will be discussed inChapter 27.

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Trauma, particularly that resulting in loss of vi-tality, may induce dentinal changes. Blood may passfrom the pulp into the dentine and the breakdownproducts of haemoglobin will appear as black orbrown stains. Non-vital dentine can loose its translu-cency, probably as a result of mineral deposition inresponse to the trauma, and become more yellow.

Root canal therapy may cause three staining prob-lems. If all the pulp is not removed from the crown,particularly from the pulpal cornua, this will undergobreakdown and cause staining. The older silver con-taining root canal sealers have to be handled carefullyso as not to leave residues in the access cavity, becausethese can stain the dentine. Finally, the access cavityof an anterior tooth should be sealed with a toothcoloured material and not amalgam; amalgam mayinterfere with the translucency of the crown, makingit look darker.

Management of discolouration

The remedies for extrinsic stains and discolouredrestorations are straightforward – polishing of bothor replacement of the restoration. A stained restora-tion may not be a functional failure but, if the patientis aware of it, it is an aesthetic failure. In respect ofroot canal access discolouration, remove the accessseal, remove stained dentine within the coronal areaand restore it with a lighter shade composite

Intrinsic stains may be more difficult to treat. Thepossibilities, depending upon the cause and the sever-ity, are:

� Microabrasion� Bleaching

� Ceramic veneer� Crown

MicroabrasionStaining or a developmental problem that is fairly su-perficial in the enamel can be eliminated by removingthe stained enamel. Here, ‘fairly superficial’ means tothe depth of several hundred micrometres only. Theremoval must be carefully controlled and very conser-vative. It is important to maintain the overall enamelsurface character.

This procedure may be done using a combinationof abrasive and dilute acid. Commercial products areavailable that use hydrochloric acid together withabrasive impregnated wheels. An effective substituteis dry pumice mixed with phosphoric acid etching geland applied by hand with a composite polishing rub-ber (Fig. 16.3).

The technique removes only superficial stains andmust be abandoned if the stain turns out to be deeperthan originally estimated.

BleachingThe intrinsic pigments of the stained dentine may bebleached by chemical action. The technique uses 35%hydrogen peroxide or similar agents such as urea per-oxidase or carbamide peroxide. The technique is usu-ally used on teeth that have discoloured after rootcanal therapy. The access cavity is reopened underrubber dam and a pledget of cotton wool soakedin the bleach inserted. The cotton wool is sealed inplace for a week and ‘refreshed’ as necessary. Yellowstains respond better than brown or orange. How-ever, the changes are not permanent and relapse iscommon.

(a) (b)

Fig. 16.3 Enamel hypoplasia that is superficial and amenable to microabrasion. (a) Before treatment; (b) after treatment.

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External bleaching of vital teeth has become popu-lar and has been provided by non-clinically qualifiedpeople. The intention is to change the colour of all theteeth making them to be whiter and brighter. To beeffective the underlying dentine must be bleached butthis will take time. Superficial stains may be bleachedby home bleaching kits but these are limited to lowconcentrations of hydrogen peroxide so they are notas effective as treatment provided by the dentist whereconcentrations of up to 35% carbamide peroxide maybe used. The risk of unqualified people providing suchtreatment or of patients deciding to treat themselves isthat any underlying pathology such as a carious lesionmay not be diagnosed. In the United Kingdom suchtreatment has been complicated by its being classedas cosmetic with a limit of 0.1% hydrogen peroxidebeing imposed on dental treatment.

Ceramic veneersThese are effective for masking more substantial hy-poplastic defects of enamel, intrinsic staining andmild malformations. They utilise a half-enamel thick-ness reduction of the labial surface and the acid etchtechnique to bond a thin layer of ceramic to the tooth.They are a valuable conservative alternative to ce-ramic crowns.

The cementing agents are the same as those areused to cement resin-retained bridges (see Chapter19), ceramic and composite inlays. To complete thetechnique, ‘opaquers’ that are fluid composites canbe used to mask strong underlying colours or modifythe shade of the veneer. The mode of adhesion to theceramic relies on etching or sand blasting and thencoating the fit surface with a silane coupling agent.

Adhesion is much better to enamel than to dentineand the best results are obtained with either com-plete attachment to enamel or, where enamel has beenlost, with at least 2 mm of enamel present around theperiphery of the restoration. If too much dentine ispresent bonding will be unreliable and crowns willbe a better alternative.

IndicationsIf the stain or anomaly is deep within enamel or indentine then the choice is between a veneer and acrown.

A suitable check list is:

� Is the discolouration severe enough to warranttreatment?

� Is there enough tooth tissue left to support aveneer?

Fig. 16.4 Root filled and discoloured |2 that requires aveneer.

� Is the discolouration minor enough to be maskedby thin ceramic?

� Is there any occlusal restriction?

The first point is to consider whether the patient isbeing excessively conscious of a minor defect. Somepeople naturally have teeth of a slightly odd colourand these often fall into the shade guide range of Cand D. A careful and sympathetic explanation of nat-ural tooth colour and the disadvantages of operativetreatment may dissuade such patients from sacrific-ing structurally normal enamel to correct a minorproblem.

The second question is whether the tooth is tooheavily restored to support a veneer. For exam-ple, a veneer preparation on a tooth with largemesial and distal restorations plus an endodontic ac-cess cavity might not be supported by much soundtissue.

Figure 16.4 shows an upper lateral incisor thathad been traumatised and was root filled, and alsohas stained composite restorations. The dentine hasbeen darkened in response to the trauma. It was un-likely that bleaching and replacement of the compos-ites would provide lasting improvement. A veneer wastherefore provided.

Very dark staining, such as that of tetracyclinestaining, may not be masked by veneers. Notwith-standing this, even opaque veneers can achieve avery acceptable change from gross staining that isoften appreciated by patients. It is now less com-mon to see such discolouration but mild stainingwith yellow, orange or brown bands is still seen(Fig. 16.5).

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Fig. 16.5 Mild tetracycline staining.

Ceramic in thin section is very vulnerable to chip-ping. If there is parafunction or evidence of excessivetooth wear, veneers may fail.

PreparationThe preparation (Fig. 16.6) involves the reductionof a one-half enamel thickness over the whole sur-face, which means that there is a variable thickness ofenamel removal. The reduction is extended into theapproximal embrasures but not through the contactarea, and should remain on enamel.

Defects, such as acid erosion, should be made goodwith glass ionomer cement and the finishing marginshould be a narrow shoulder or chamfer prepared at

the level of the free gingivae and not placed in thegingival crevice.

The incisal edge should be reduced, utilising a re-verse bevel onto the palatal surface. The thickness ofthe incisal reduction should be at least 1 mm.

Provisional restorations may not be necessary andit is an advantage not to place these because their re-tention would be by adhesives which might interferewith the cementation of the final restoration. If thepatient feels that the appearance of the preparationsis unsightly, a composite layer or a polycarbonate ve-neer can be placed but this should only be tacked ontoa limited area of prepared enamel.

Laboratory stagesThe impression is cast first in divestment refractorystone, i.e. stone that can be heated in the ceramicfurnace without breaking up, and then in die stone.The veneer is built and fired on the divestment andadjusted finally on the die stone model. The ceramicthat is used must be translucent so that the glass coresreferred to in Chapter 15 cannot be used because theyare opaque. Standard dentine and enamel ceramics orthe newer leucite reinforced ceramics are satisfactoryand their translucency enables minor colour correc-tion to be achieved by varying the shade of the under-lying cement.

After adjustment of the margins and the occlu-sion, the fit surface is treated. This is better done, if

(a)

(b)

Chamfer

Ceramic

Enamel

Fig. 16.6 (a) Schematic diagram of the preparation for a ceramic veneer on a central incisor. Note the incisal reduction andthe palatal reverse bevel, (b) Preparation on the |2 shown in Fig. 16.4. Note that the approximal contacts are maintained.

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possible, after clinical try-in because contaminationfrom the mouth may interfere with adhesion.

The techniques for preparation of the veneer fittingsurface are:

� Etching� Sand blasting

Etching is very technique sensitive. The glazed sur-face of the veneer is first protected with wax and thefitting surface etched with 30–40% hydrofluoric acidfor no more than 3 minutes. The etched surface mustbe neutralised by placing it in a furnace at 600◦ C for5 minutes, followed by ultrasonic cleaning in distilledwater for 3 minutes after cooling.

Because of the dangers of hydrofluoric acid, sub-stitutes are available, but the safest way is to avoidetching altogether and grit blast the surface insteadwith 40-μm grit. This grit blasting may be done usinga small unit in the dental practice.

Try-in and cementationThe tooth is cleaned with dry pumice and a slowlyrotating brush to remove plaque and pellicle thatmight otherwise contaminate the veneer. The veneeris placed carefully onto the tooth and the margins andthe occlusion checked. If necessary these may be ad-justed by fine diamond points followed by a diamondpolishing paste.

The shade is observed in natural light in order todecide whether the ‘universal’ cement will be satisfac-tory or whether a lighter or darker shade is required.

The lightly filled composite cements or lutingagents may be dual cured or light cured. Whilst thedual-cure type may provide better polymerisation ifthe activating light is attenuated by the veneer, theircolour stability is poorer because there is an increasedamine concentration for the self-cure system.

Depending upon the product, it will come with thebasic shades grouped into whites, yellows, brownsand perhaps greys. There will be a separate opaquingagent. There may either be individual syringes of eachcolour or a base colour and containers of add-incolours – tinters.

The base paste may be tried first without mixingin the activator. Additions may be made as desired tochange the colour, keeping some on the mixing pad,until the effect under the veneer is correct. The under-side of the veneer must be cleaned for each application– the reserve on the pad will become the final cementin due course.

When the correct effect has been obtained, rubberdam is applied, the underside of the veneer is cleaned

Fig. 16.7 Completed ceramic veneer on |2.

with isopropyl alcohol and, if this has not been donealready, grit blasted. (Wax must be applied to theglazed surface first to protect it.) A silane coating isthen applied to the veneer and air dried. The bond-ing resin comes next; this is air dispersed to preventpooling. Then apply the luting cement and positionthe veneer.

‘Tack’ cure for 10 seconds with the activating lightand check the orientation of the veneer. If this is cor-rect, the cement can be fully cured by exposure to thelight from several angles.

If the orientation is incorrect, the veneer can be re-moved gently and cleaned to repeat the cementation.

After curing, check and remove excess from themargins, check the occlusion both in centric occlusionand lateral and protrusive excursions and show thepatient (Figs. 16.7 and 16.8).

Fig. 16.8 Ceramic veneers on 21|12 masking thetetracycline staining shown in Fig. 16.5.

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Aesthetics

Incorporation of colour and characterisation

Careful selection and use of colour can create illu-sions to apparently change the position or size of acrown. This can be used for a malaligned or poorlyshaped tooth to give it the appearance of being wideror shorter than it really is. By lightening or darkeningselected teeth in a full arch, the illusions of flatnessor more rounded appearance can be created. Wideteeth can be apparently narrowed by the placementof shaders or stains mesially or distally that highlightthe central area.

The contour and texture of a crown should mir-ror its neighbour, enabling the reflection of light tobe equal to that of the natural tooth. A roughenedlabial surface should be left on the core of a crown sothat light entering through the more translucent lay-ers of ceramic will be reflected in different directions,adding vitality.

If the technician has been asked to make six an-terior crowns with just the shade and the sex of thepatient to guide him, he can make the crowns takeon a definite masculine or feminine appearance by at-tention to detail and careful shaping. Labial surfacesmay be made to look flat and therefore wider andmore masculine, or, alternatively they can be rounded,smaller and feminine with greater vitality due to thereflected light from the curved surface coming at avariety of angles.

Artificial ageing can be achieved by creating flatworn incisal edges, loss of lamellae and thin enamel.

Colour may be imparted to a crown by the ap-plication of internal colourant ceramic effect pow-ders. When building colour into the crown, the ce-ramist will remove unfired body ceramic almost tothe opaque layer, hollowing and cutting an angle soas to achieve a blend and carefully introducing eithergingival effect or dilute stain into the depression, andupon firing, the colour will show through the moretranslucent body ceramic. Traces of orange on theincisal edge, decalcifications and so on may all be in-corporated in the same way.

Colour may also be included by cutting back a pre-viously fired crown. A cut is made into the crown witha diamond disc, the selected colour applied, air-dried,and then overlaid and refired. Similarly, the blue effectsometimes present on mesial and distal corners canbe obtained by grinding ceramic away to the desireddepth and painting the prepared surface with a bluewash, overlaying with a clear ceramic and refiring.

The use of clear ceramic and inlaid colours is par-ticularly effective, and imparts a very natural appear-ance. Surface staining is less effective and does notgive the three-dimensional effect achieved with inter-nal segmented building. It is also vulnerable to abra-sion during intraoral service, thus losing its effects.

However, surface stain can be added quickly andeasily, being mixed with a liquid binder and paintedonto the fired crown before glazing and is thereforepopular.

Aesthetic problems

Dark line at gingival marginThis was common with earlier metal–ceramic systemsbut has now been eliminated by the use of shoulderceramic (Chapter 15).

Core shineThis usually occurs in cases where insufficient labialreduction has taken place during clinical preparation.The technician, in an attempt to bring the crowninto line with the adjacent teeth, exposes the un-derlying core by grinding or is forced to cover itby insufficient dentine build-up. This results in anarea of the crown that looks lifeless. Opaque ceramicmust be covered by at least 0.5 mm of dentine ce-ramic to diffuse the reflected light from the opaque.Doing this though in the underprepared tooth re-sults in a bulbous overcontoured crown with pooraesthetics.

The correct treatment is to ensure that a mini-mum of 1.2 mm is removed from the labial sur-face during preparation to allow enough depth of ce-ramic to create a lifelike aesthetic restoration. Themetal substructure needs to be a minimum of 0.3 mmthick, the opaque needs to be a minimum of 0.3 mmwhich leaves only 0.6 mm for the dentine and enamelceramics to create an acceptable result.

Shadowed regionsShadowing occurs in areas where there is an excessiveamount of dentine ceramic or in areas where thereis not an opaque backing. Typically, in bridges theseoccur interstitially or at the cervical margin of pontics.In order to compensate for these darker areas of lowerchroma, ceramics that have an increased opacity andchroma have been developed – these are known asopacious dentines. The opacious dentines can eitherbe blended with conventional dentine powders or beapplied in layers.

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These ceramics can help considerably to increasechroma and to diffuse reflected light, hence improvingthe aesthetic result.

ConclusionWith the advent of these new ceramics and by usinga layered build-up technique it is now possible forthe ceramist to control the reflection and scatteringof light in a similar manner to natural teeth. Withthe use of opacious dentines, control over value andchroma is possible and life-like aesthetic restorationsare now far more easily achieved. However, when pa-tients move from one type of light to another, changesin apparent shade are inevitable. The most dramaticof these is the sight of metal–ceramic crowns in tele-vision arc lights!

Malformed or missing teeth

The most common problems are:

� Peg-shaped upper lateral incisors� Missing upper lateral incisors� Central incisors lost through trauma

More extensive hypodontia and dental problems as-sociated with cleft palate are considered in Chap-ter 20.

Peg-shaped lateral incisorsThe management options are:

� Persuade the patient that it is better to do nothing� Reshape by veneers or crowns� Extract and either open or close the space

No treatmentSome individuals, particularly females, may becomevery concerned that their appearance is not ‘con-ventional’. This was mentioned earlier in relation toshade. Slightly malformed teeth may not be noticedby the casual observer but are glaringly obvious to thepatient who grimaces at herself close to the make-upmirror.

Minor discrepancies in tooth shape need to be putinto perspective (tactfully) together with an explana-tion of the possibly deleterious effects of restorationsand their need for periodic replacement. Often, pa-tients will be reassured and elect to having nothingdone.

ReshapingThe amount of natural tooth will have a bearing onthe choice of treatment. Very small teeth will be im-possible to prepare with sufficient remaining tissue tosupport a crown or a veneer. It is also problematic toincrease the size of a tooth because this usually resultsin an unfavourable gingival contour.

Here the best solution will often be the use ofacid etch retained composite to increase the incisallength and width of the tooth without encroach-ing on the gingival margin (Fig. 16.9). Some com-mercial products are supplied in a range of shadesequivalent to the Vita shade guide together withopaque shades. This may mean a range of at leasteighteen shades providing a comprehensive colourmatching system. The possible disadvantage is thatthe material may need replacing in 5–6 years due todiscolouration.

(a) (b)

Fig. 16.9 Peg-shaped lateral incisors. The appearance has been improved by the addition of acid-etch-retained composite.(a) Before treatment; (b) after treatment.

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(a) (b)

Fig. 16.10 Prominent canines in the lateral incisor position that cannot be corrected effectively by veneering. Crowns arenecessary to create less prominent teeth of the correct shape. (a) Before treatment; (b) after treatment.

Larger pegs can be veneered successfully to increasetheir size but again the gingival relationship will notbe ideal and the patient will need to be taught carefulflossing and brushing techniques.

ExtractionThis would be the last resort and would be reservedfor badly formed and displaced pegs. Orthodonticsshould be considered to either open or close the space.Space closure is probably more desirable since thisavoids a prosthesis to replace the lateral incisor. How-ever, the disadvantage is that the canine may be movedinto a more prominent position and may requirereshaping (see below).

Missing upper lateral incisorsAbsent upper lateral incisors may result in retentionof the deciduous canines and the eruption of the per-manent canines into the lateral incisor position. Alter-natively, the deciduous canines may be shed as normaland spacing results between the central incisors andthe permanent canines.

The management options are:

� Reshaping the permanent canines to resemble lat-eral incisors

� Orthodontic treatment to retract the canines andbridges or implants to replace the lateral incisors

� Veneers/bridgework to correct the aesthetics with-out orthodontic treatment

ReshapingThis is the simplest option but carries with it the prob-lem of making a large tooth look small. The incisaledge can be made square and level by either compositeresin addition or ceramic veneer or in some cases,simply grinding the tooth.

This type of reshaping will remove the ‘Dracula’ ap-pearance but will not change the bulk or prominenceof the tooth which can be a problem if the caninesare labially placed. Here to reduce the prominence ofthe tooth, a radical crown preparation is required toprovide a flatter labial surface. Ideally, a post crownwould provide the best appearance but elective devi-talisation should not be prescribed without a strongindication. Even with a large labial reduction the ce-ramist will have considerable difficulty with shadecontrol (Fig. 16.10).

The case shown in Fig. 16.11 had retained decid-uous canines and the upper permanent canines haderupted into the lateral incisor position. The decid-uous canines had to be extracted because of cariesand root resorption. Two bridges were made to re-place the missing teeth and the permanent canineswere reshaped by crowns to resemble lateral incisors.

Fig. 16.11 Missing upper lateral incisors with retained c|cand the permanent canines in the lateral incisor position.The c|c have been replaced with bridges and the 3|3 havebeen converted to resemble lateral incisors by crowns. Theunderlying size of the canines restricts the reduction inwidth.

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(a) (b)

Fig. 16.12 (a) Missing upper lateral incisors with uneven spacing; (b) the 3| has been recontoured with acid-etch-retainedcomposite and the |2 has been replaced by a bridge retained by a ceramic veneer on |3.

Inevitably the size of the ‘new’ lateral incisors is dic-tated by the underlying canine teeth which cannot beprepared extensively to allow smaller crowns to beconstructed.

OrthodonticsIn certain respects this is an ideal treatment becausethe canines will be moved bodily into their correctpositions. Lateral incisors of the correct shape canthen made as bridge pontics, usually as resin-retainedbridges (see Chapter 19). However, the disadvantagesare that space will be needed for the canine retraction,usually by extraction of posterior teeth and fixed ap-pliance therapy will be needed perhaps taking at leasta year.

Veneers/bridges without orthodonticsThis approach removes the need for prolonged treat-ment and the loss of more teeth. However, it will al-most always be a compromise because of the limitedspace available for extra teeth. Figure 16.12 shows acase where there was enough space for a reasonablelateral incisor on the left side but the space availableon the right is much smaller. The upper right caninewas enlarged by means of acid etch retained compos-ite whilst a veneer bridge (see Chapter 19) was madeon the left.

Figure 16.13, on the other hand, shows a muchmore difficult case because the lateral incisor spacesare neither small enough to allow the enlargementof the canines nor big enough to allow full-sized lat-eral incisors to be made. The case was complicated

(a) (b)

Fig. 16.13 (a) Missing lateral incisors where there is restricted space for their replacement; (b) two three-unit fixed–fixedconventional bridges 3-1|1-3 where the 2|2 have been made to overlap the retainers to achieve extra width.

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by the previous attempts to veneer the incisors andcanines.

The lateral incisors have been made as wide as pos-sible on two fixed prostheses by overlapping the cen-tral incisor and canine retainers. The preparation ofthe four teeth for crown retainers provided more flex-ibility in the final mesiodistal diameters of the newteeth.

Missing central incisorsIf the space has been maintained then these will fallunder the treatment planning decisions discussed inSection IV. However, in a young patient it may bepossible to move the adjacent lateral incisor into thespace or, if the case has been neglected, the lateral in-cisor may drift forward. The conversion of the lateralincisor to look like a central incisor may be done byeither a veneer or a crown. The disadvantage is the

Colour and Aesthetics – Summary

Modern materials and techniques offer much scope for cosmetic dentistry. The artistic aspects of toothcolour and shape are more difficult to teach and come with experience.

Shade taking must be done in good natural light without the influence of strong colours.

Liaison with the technician must be good in respect of shade communication and reproduction.

Composite additions, ceramic veneers and bridgework each has its place in correcting aesthetics. Eachis accompanied by its advantages and disadvantages and sometimes the treatment plan is a compromisebetween tooth conservation, the patient’s aspirations and technical possibilities.

gingival contour and its relationship where the largercrown or veneer joins the smaller root.

Malocclusion

Whilst many malocclusions are corrected orthodon-tically in childhood, it is still common for adults torequest the correction of crowding and other maloc-clusions. These patients often request rapid treatmentand may not wish to wear orthodontic appliances.They usually expect their appearance to be correctedby crown and bridgework.

Notwithstanding their preferences, these patientsneed to be persuaded that orthodontic therapy willprovide the better results in most cases. Irregular in-cisors are difficult to crown or veneer and such treat-ment results in teeth that have thick incisal edges andcreates periodontal problems.

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Chapter 17Impression Materials and Techniques

The long chain of positive- and negative-dimensional pitfalls between completion of the preparation andthe cementation of a cast restoration begins with the impression.

The choice of impression material, the management of the gingival tissues and the clinical technique allcontribute to the accuracy of the final restoration.

An impression material should be:

� Accurate and dimensionally stable� Easy to handle� Pleasant tasting� Compatible with blood and saliva� Non-irritant and non-allergenic� Tear resistant� Compatible with model materials

The patient would like the material to taste pleasantand have a short setting time. Impression taking canbe a messy procedure so the material should be easy toremove from tissues and clothes. It should not damagethe oral tissues or the tooth and, very importantly,the material should not contain constituents likely toproduce sensitivity reactions.

The operator’s requirements are somewhat differ-ent. The material should be easy to mix with a work-ing time that is long enough to allow it to be placedaround a number of preparations before setting starts.

In order to reproduce the details of the prepara-tion, it should flow well and have a low surface ten-sion, so that it will wet the surfaces of the prepara-tions. This is essential in order that the restorationwill fit well and will not fail due to leakage or plaqueaccumulation.

Impression taking would be very easy if the ma-terials were miscible with saliva and tissue fluid.Some of the more recently available materials areclaimed to be hydrophilic, but currently the onlymaterial that is truly hydrophilic is the reversiblehydrocolloid.

After removal from tooth undercuts the materialmust have a high elastic recovery to reproduce theseareas and the rate of this recovery from deforma-

tion must be rapid (Chapter 9). Also, the materialshould not be excessively rigid. If it lacks elasticity, itmay well be difficult to disengage from undercuts andcould traumatise the soft tissues. A stiff material willalso be difficult to remove from its model and stonedies may be damaged.

Perhaps the most significant properties for clini-cal success are dimensional accuracy and dimensionalstability. All the elastomers set by a polymerisation re-action that results in shrinkage; this varies with thetype of material. The result is a contraction towardsthe internal surface of the impression tray, assumingthat the tray adhesive is strong enough to resist theforces.

With simple extra-coronal preparations this con-traction does not present major problems since the dieproduced from the preparation will be slightly largerthan the original preparation. Therefore, the restora-tion will seat on that preparation, but the width ofthe cement lute will be increased.

Greater problems exist with complex intracoronalfeatures, such as slots and grooves. Here, the dimen-sional changes are much more complex and conse-quent variations result in either difficulty or failure ofthe restoration to seat completely.

The material should also have a high tear resis-tance, since once the impression has entered a gingivalcrevice, a thin area of material might well be damagedon removal.

Impression Materials

A general classification of impression materials isgiven in Table 17.1. With the development of elas-tomers, the rigid materials, often used within a

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copper ring, have fallen from grace almost completely,as have the techniques of direct wax pattern makingin the mouth.

The irreversible hydrocolloids, the alginates, areexcellent for preliminary impressions, but because oftheir dimensional instability, have no place as finalimpressions for crown and bridgework though theyare satisfactory for partial and complete dentures.The reversible hydrocolloids, agar–agar, on the otherhand, are excellent for the reproduction of detail andmix well with intraoral fluids. However, they requirespecialised equipment and must be cast immediatelyupon removal from the mouth.

The principal materials now used for fixedprosthodontics are the rubber-based elastomers. Thecurrently available materials fall into three maingroups:

� Silicones (polysiloxanes)� Polyethers� Polysulphides

The elastomers are generally available in one of fourforms described as putty, heavy bodied, regular andlight bodied, the basic difference between the fourforms being the filler loading.

The silicone materials are divided into two separatesubgroups:

� Condensation curing (Type I)� Addition curing (Type II)

Condensation silicones

Until the general acceptance of addition-cured ma-terials, the condensation curing materials were verypopular in general dental practice because of theirclean handling and rapid set. They may come in allfour consistencies, but the most popular are the puttyand wash materials, the wash being light bodied. Theactive constituents are shown in Table 17.2.

The elastomer sets by a condensation polymerisa-tion reaction with the formation of ethyl alcohol asa by-product. The alcohol subsequently evaporatescausing further shrinkage over and above that of thepolymerisation reaction. Shrinkage continues for sev-eral days with 0.5% occurring in the first 24 hours.This is significant if the technical laboratory is somedistance from the practice. The greater setting con-traction occurs in the light-bodied materials wherethe polymer is the largest component.

The light bodied material has the ability to repro-duce the surface detail well, but has a relatively low

tear resistance and many of the materials are difficultto handle.

The setting reaction is temperature dependent witha marked reduction in both working and setting timesin the presence of a relatively small increase in ambi-ent temperature, particularly when the humidity ishigh. This can result in a material being manipulatedat a time when it has already commenced its settingphase. This causes the development of setting stressesin the material that will be relieved after the removalof the impression. This, in turn, will lead to a restora-tion that, whilst fitting the die, will not seat satisfac-torily in the mouth. Failures with these materials aremore commonly associated with complex intracoro-nal preparations and bridgework.

Addition silicones

These are now the most popular of the elastomers andtheir active constituents are shown in Table 17.2. Thesetting reaction here has no low-molecular-weight by-product which results in a material that shows little orno dimensional change. The shrinkage figures quotedare in the range of 0.05–0.07% at 24 hours.

However, a secondary reaction does take place ifincomplete polymerisation has occurred, with the lib-eration of hydrogen gas. A number of the materialshave finely divided palladium added that is supposedto absorb the hydrogen. Because of this, impressionsshould not be poured immediately, otherwise the lib-eration of hydrogen will result in a roughened diestone surface.

The material has low tear resistance and is proneto tear if engaged in deep undercuts or the gingivalcrevice; care is required on removal of the impression.It is also particularly temperature sensitive.

The other main disadvantage is that current trayadhesives are not very effective and this can result inthe impression material pulling away from the trayin places. This is not necessarily always visible andconsequently it is only when the restoration is tried inand does not fit that the problem is seen. It is essentialto use the adhesive in conjunction with a perforatedtray.

The addition silicones have poor wetting charac-teristics and are also hydrophobic; this may lead topoor reproduction of detail and may also make modelpouring troublesome. Wetting agents have been de-veloped for both intraoral and laboratory use toovercome this problem though some have limitedeffectiveness.

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17. Impression Materials and Techniques 189

Table 17.1 Types of indirect impression materials

Rigid Elastomeric

Composition Hydrocolloids Polysulphides Polyethers Silicones

Irreversible Reversible Type I Type II

Alginate Agar–agar Condensation cured Addition cured

The excellent dimensional stability of addition sil-icones often results in very accurately fitting castingsthat may prove difficult to seat, and the master dieshould be treated with the appropriate die spacer (seelater).

Polyethers

These materials have a restricted but enthusiasticfollowing and when used with care produce verysatisfactory results. Their components are shown inTable 17.2. They are usually purchased as a two pastesystem of a regular consistency.

The original materials, whilst apparently being verydimensionally stable, were affected by humidity andshowed variable unpredictable shrinkage when a dilu-ent paste was added. Modifications in formulationhave improved this, but at the expense of the han-dling properties.

Some cases of allergic reactions to the materialcausing a burning sensation in the tissues covered bythe impression and, in severe cases, marked erythemahave been reported. The reformulation has reducedthis although some patients still comment on theburning sensation when the impression is being taken.

The tear resistance of the material is similar to thatof the silicones but its stiffness is considerably higher.This stiffness can result in problems during removal

of the impression from the mouth which can also beimpeded by the hydrophilic character of the mate-rial; it tends to ‘stick’ to the mucosa. It is advisableto have a double-spaced special tray so that there ismore material to flex to facilitate the removal of theimpression. If a stock tray is used, then this shouldhave sufficient rigidity to prevent distortion duringremoval of the impression from the mouth.

The stiffness may also cause difficulty in the lab-oratory, since it is relatively easy to damage the dieson removal of the impression, particularly if they arenarrow. Lower incisor crown preparations can be aparticular problem.

The material is quite temperature sensitive and mayset rapidly on a hot day. This may be critical since theworking and setting times of these materials are theshortest of all the elastomers.

Polysulphides

These are the oldest of the elastomers and in spite oftheir smell and dirty handling are still occasionallyused because of their reliability and strength. How-ever, they have, to a great extent, been displaced bythe addition silicones.

The components are shown in Table 17.2. Thematerial is usually used as a combination of heavyand light consistencies, with the heavy-bodied version

Table 17.2 Components of elastomeric impression materials

Type Base Catalyst Filler

Type I silicone Dimethyl siloxane Stannous octoate Copper carbonate

Alkyl silicate or silica 2–8 μm

Type II silicone Dimethyl siloxane Chloroplatinic acid Silica

Polyether Polyether – ethylene Dichlorobenzene Silica

imine terminated sulphonate

Polysulphide Polysulphide (Thiokol) Lead dioxide Titanium dioxide, silica or

Dibutyl phthalate copper carbonate

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being particularly difficult to mix. There is also a reg-ular consistency material. It is the lead dioxide thatmakes the material unpleasant to use.

The setting reaction is condensation polymerisa-tion with the formation of water as the by-product.Impressions should be kept in a sealed moist bag toreduce the shrinkage that would be caused by theevaporation of the water. There is a small setting con-traction of between 0.13 and 0.25% at 24 hours, withlittle further shrinkage after this.

On the plus side, the material has a much highertear resistance than the other three elastomers, but itdoes not show such good recovery from deformation.The working and setting times are the longest of allthe elastomers and it appears to be the least sensitiveto temperature changes.

Impression Techniques

Management of the gingival tissues

This and excellent control of saliva are the keys tosuccessful impression taking.

The first requirement is that the tissues should bein good health and undamaged. Careless preparation,with abraded gingivae, will repay the operator witha poor impression. Poorly fitting provisional restora-tions will accumulate plaque and cause gingival en-largement and bleeding.

In the interests of periodontal health, crown mar-gins should be at the level of the gingival margin andnot be placed in the gingival crevice unless aestheticswill be improved by such location. Gingival marginsshould be recontoured if the preparation has to en-ter the crevice by more than 0.5 mm, perhaps wherethere is a deep core. Impression taking is made easyby supragingival margins.

If there are problems with bleeding tissues, the im-pression should be abandoned at that visit. Accuratelyfitting provisional restorations should be placed, per-haps cemented with a periodontal dressing material,and the impression taken on a subsequent visit whenthe gingivae have recovered.

Gingival retractionTo provide clear definition of the finishing line, thegingival tissues must be displaced from the prepa-ration and any exudate from the crevice controlled.There are several types of material that may be usedfor this.

Mechanical displacement using a variety of cordis probably the most popular. Cords come in two

forms, braided and twisted. The braided form iseasier to place and may be supplied in several sizes.The twisted type has a tendency to become untwistedduring placement. There are also elasticated ringsthat may be pushed over the preparation and into thecrevice.

All the proprietary brands may be impregnatedwith agents to control oozing from the crevice; thesemay be vasoconstrictors or styptics. Epinephrine(adrenaline) hydrochloride is the most commonof the first group, but must be avoided in certainpatients who have either cardiovascular problems orare sensitive to it. Aluminium trichloride, alum, isa common styptic as is ferrous sulphate. As well asbeing impregnated in the cord, retraction solutionsmay be purchased separately. Care must be exercisedin their use, since excess application can cause irre-versible damage to the tissues, particularly gingivalrecession.

Cord placementCare must be taken in placement of the cord to avoiddamage to the epithelial attachment. The teeth mustbe isolated by cotton wool rolls and a saliva ejectorand blown dry. The cord is laid around the gingivalmargins of the prepared tooth. The width of the cordshould match the depth of the crevice and, if neces-sary, a multi-stranded cord can be split into severalthin strands. It is better, though, to have cords of dif-ferent diameters available.

The cord is pressed gently into the gingival creviceusing a small flat plastic instrument, keeping the cordbetween the blade and the tissue (Fig. 17.1). A localanalgesic is often advisable as the procedure can beuncomfortable.

The cord should not be left in place too long sincepermanent recession may be caused. About 5 minutesis necessary to provide optimum retraction, maintain-ing saliva control all the time.

If the cord does not obstruct the margins of thepreparation, it can be left in place whilst the impres-sion is taken. If this technique is used, it is most im-portant to remember to remove the cord before thepatient leaves the surgery! To remove the cord af-ter the impression has been taken, it should be firstmoistened with water to avoid damaging the friablegingival tissue.

It is more common, though, to remove the cordwhen the impression material is ready to syringearound the preparation. The cord must be removedvery gently to prevent the initiation of bleeding oroozing. It is essential that the preparation site and

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(a)

(c)

(b)

Fig. 17.1 (a) Braided gingival retraction cord beinginserted into a gingival crevice, (b) and (c) Insertioncompleted. Note the lack of gingival trauma following thepreparation of the full crown.

the surrounding area are dry and free from contami-nants prior to impression taking as any residue mayaffect the impression material and the detail of theimpression.

It is sometimes possible to dispense with retractionand blow the light bodied material into the gingivalcrevice with compressed air. This is quite effective, butmay result in a very thin section of rubber because ofthe lack of retraction, and this is liable to distort ortear.

Electro-surgeryThis technique involves the use of a high-frequencyelectric current that may be used to either coagulatebleeding tissues or fulgurate (spark drying by ioni-sation). When used carefully, it can produce a veryclearly defined margin.

There is a risk, however, that the misuse of thistechnique will result in serious gingival tissue dam-age, particularly if the tissues are inflamed and oede-matous at the time of surgery. Its main advantage isthe haemostasis obtained.

Special trays

The main advantage of a correctly made special trayis that it ensures a uniform thickness of the impres-sion material thereby reducing risk of uneven distor-tion. The tray will also confine the material, assistin its adaptation to the teeth and prevent it escapinginto the rest of the mouth. The thickness of the traymaterial can be controlled to give good rigidity thusavoiding flexing and distortion of the impression onremoval from the mouth. This last characteristic isan important factor in the choice of stock/disposabletrays.

Adequate spacing should be provided betweenthe tray and the teeth to accommodate a reasonablevolume of impression material and stops shouldbe placed around the arch to ensure that the traylocates accurately onto the teeth. It should beextended to about 2 mm below the gingival marginof all teeth and should wrap around the end of thealveolar ridge to confine the material to the tray(Fig. 17.2).

The weak link may be the tray adhesive. Thoseused for the polysulphides are very good, but thoseprovided for the addition silicones are poor and per-forations should be incorporated in the tray to assistretention. Whichever type is used, it must be given ad-equate time to dry before the material is mixed; thismay be as much as 15 minutes.

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Fig. 17.2 Special tray with posterior flanges to aidremoval and occlusal stops to locate it on the teeth.

Full arch, rather than sectional, impressions aredesirable for accuracy of occlusal contacts.

Handling the materials

There are three main ways in which impression ma-terials may be used:

� Putty and wash� Regular/universal single mix� Light- and heavy-bodied double mix

Putty and wash techniqueThis technique uses a very stiff putty within a stocktray instead of a special tray, together with a fluid,light-bodied perfecting wash. Care is needed in trayselection because if pressure is used to seat the tray,some stock trays will distort. On removal of thetray, recovery of the distortion will distort the im-pression

Condensation and addition silicones are the onlysuccessful materials that have been produced for thistechnique. The technique has the possible advantagethat no special tray is required, but there are dan-gers of uneven shrinkage setting up stresses withinthe material. The later release of the stresses leads todimensional inaccuracies.

Putty and wash materials may be used in one-stageor two-stage techniques.

One stageHere, both the putty and wash materials are fluid atthe same time. Following mixing, the wash is syringed

Fig. 17.3 Syringing the light-bodied material around thegingival margin. Care must be taken to apply the materialto the tooth surface so that air does not become trapped.

around the preparation, ensuring that the nozzle ofthe syringe remains within the exuding material toreduce the risk of air blows. Syringing should startat the distal margin of the preparation and broughtforward (Fig. 17.3). It is necessary to cover the prepa-ration and the occlusal surfaces of the other teeth witha thin film, the latter being recorded for occlusal reg-istration.

The putty is loaded into a rigid stock tray as soonas the syringe has been filled, and is inserted into themouth immediately the wash is in place. All thesematerials are very rapid setting and working time isexceptionally short.

Considerable pressure will be required to seat thetray because of the stiffness of the putty. It is alsoimportant to insert the tray in the long axis of thepreparations. An oblique seating direction will dis-place the putty away from the teeth and because ofits high viscosity it will not flow back around the teethresulting in flow failure (Fig. 17.4). The result is oftencalled incorrectly drag marks, but ‘drags’ are causedby the withdrawal of a rigid impression material froman undercut or the early removal of an elastic materialfrom an undercut before it is fully set.

The tray and impression material must be sup-ported under moderate pressure until the materialshave set since disturbances will result in distortion.

Two stageThis technique is not recommended. Here a putty‘tray’ is prepared before the wash is mixed. The stocktray is first filled with the putty and seated home. Apolyester sheet may be placed as a spacer on the sur-

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(a) (b)

Fig. 17.4 (a) Flow failure on the palatal aspect of the upper second premolar. There is also failure of the light bodiedmaterial to merge with the putty. The light bodied was setting before the putty arrived, (b) Model showing the result of flowfailure on the palatal aspects of the premolar and molar.

face of the putty before insertion or, alternatively, thetray may be rocked to provide the space necessary forthe wash.

Once the putty has set it is removed, washed anddried and sluice ways cut in the buccal and lingualaspects in the areas adjacent to the preparation. Anymaterial remaining approximally is also removed.These modifications allow escape of excess wash ma-terial in the second stage of the technique. The puttymust be clean and dry and uncontaminated withsaliva.

The perfecting wash is syringed around the prepa-ration and all occlusal fissures to form a thin film overthe area where fine detail is required. The putty ‘tray’is then reseated and the wash and putty will unitechemically as the wash sets.

The results using this technique can be good but anumber of problems may arise:

� Saliva interposed between the putty and the wash� Build up of wash in certain parts of the occlusal

section of the impression that results in an incor-rect occlusal relationship. This usually follows in-adequate sluice way preparation in the primaryputty impression

� Displacement and distortion of the tray during itssecond seating. This can result in uneven distribu-tion of the wash and, worse, distortion of the trayitself

Special tray techniqueThe putty/wash techniques involve the production ofa close fitting ‘tray’ in putty, but this is bulky and can

introduce errors with incorrect seating. A special trayreduces the volume of impression material used andis easier to handle.

Two mix techniqueThe materials used are light and heavy bodied withthe heavy bodied material acting as a support forthe fine detail reproducing light-bodied material. Thelight bodied material is syringed around the prepara-tion and onto the occlusal surfaces of the other teeth,and the heavy-bodied material is loaded into the spe-cial tray that is seated, again, in a direction parallel tothe long axes of the teeth. The tray must be locatedaccurately and held immobile until the material hasset.

If the tray is not placed as soon as the light-bodiedmaterial has been syringed, there is a risk of salivacontamination between the materials and impressionfailure. Impressions of the lower molars are the mostvulnerable, with the tongue often becoming inter-posed at the crucial stage.

This problem may be reduced by not introducingthe light-bodied material until the heavy-bodied ma-terial is almost mixed. However, too much delay maymean handling the material beyond the point when ithas commenced its setting phase.

Quite heavy pressure should be applied for aboutthe first 15 seconds after insertion to ensure that thematerial flows and, at the same time, it is important toensure that the stops on the fit surface of the specialtray locate accurately on the surfaces of the teeth.Without the stops, the tray will come into contactwith tooth surface over a large area, and even in the

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area of the preparation, with a consequent failure ofthe impression.

Single mix techniqueThe special tray technique may be used with materi-als of a single, regular, or medium, bodied consistencyusing the same mix in both the tray and the syringe.Whilst this can be successful, it is sometimes diffi-cult to syringe the material because it is stiffer thanthe light bodied type, and the tray portion can flowrather freely because it is more fluid than the heavybodied type. This technique is commonly used for im-pressions for partial dentures.

Removal of the impressionIt is always tempting to remove the impression as soonas the outer aspect of the material has set. This mayhave disastrous consequences since the light-bodiedmaterials set at a slower rate than the heavy-bodiedmaterials. This is especially the case with some ad-dition silicone materials where there can be a differ-ence of up to 11/2 minutes between the setting timesof the heavy- and light-bodied materials. Prematuredisturbance of the materials will result in the distor-tion of the impression and dragging of the material atthe margins of the preparation.

The best indication that the material has set in themouth is when the material has set on the mixingpad, and a timer may give additional guidance. Ambi-ent temperature and humidity cause large deviationsfrom the manufacturers’ predicted behaviour, and itis better to leave the material in place for as long aspossible.

The impression should be removed without rockingor shaking. One sharp pull in the line of insertion ofthe preparations is the ideal. This is assisted by havingflanges at the side of the special tray, rather than usingthe handle.

Assessment of impressions

After removal, the impression should be thoroughlywashed to remove all contaminants and then dried.Careful examination should made in good light, usinga hand lens or low-power microscope.

A clear outline of the finishing margin all round thepreparation should be visible with a small extent ofimpression material beyond it (Fig. 17.5).

There should be no air blows on the margin butsometimes small air blows on the fit surface may beaccepted. It is important to ensure that the materialhas not pulled away from the tray. This should be

Fig. 17.5 An impression of a chamfer finishing line(arrowed). Clarity here is essential for the technician to beable to see where to finish the waxing. There should beregistration of uncut tooth beyond the finishing line. Thelight-bodied material has merged properly with the putty.

apparent at the periphery of the impression where itis easy to see.

If there is any doubt about the accuracy of theimpression, it may be possible to pour it immedi-ately and examine the preparations. This may savetime and money, but should be done in liaison withthe technician, to ensure that the appropriate castingtechnique is used.

Decontamination

The dentist has the responsibility for ensuring thatimpressions, models and other equipment passing tothe laboratory are not contaminated with body flu-ids or bacteria from the patient. This is one of theprinciples of that should be enshrined in the dentist’sprevention of cross infection policy.

Several agents have been recommended and somelead to dimensional changes in the impression mate-rial and others, such as glutaraldehyde, present risksto the dentist and his team.

Currently, the recommendation is for immersion ofthe impression, etc., in a 1% sodium hypochlorite so-lution for 20 minutes. Items coming from the labora-tory also need decontamination. It should be remem-bered that it is chlorine from the sodium hypochlo-rite which is the disinfectant and this is used upquickly. This means that each impression should beimmersed in a fresh solution of the disinfectant. It isdesirable that the bagged impression be labelled withthe date and time of disinfection and also the typeof disinfectant used. This will reduce the risk of the

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laboratory carrying out a similar procedure. The ra-tionale for this is that prolonged exposure to disin-fectants can have an adverse effect on the impressionmaterial. It is essential that once disinfection has beencompleted that the impression material is thoroughlywashed since residue from the disinfectant can be de-posited on the surface once the impression is dried.This in turn will affect the surface of the model whichis poured.

Model Construction

The laboratory should always be informed as towhich type of impression material has been used sothat the production of the working die may be donecorrectly. As mentioned earlier, addition-cured sili-cones may release hydrogen if cast too soon and thiswill affect the model surface. If metal-plated mod-els are required, the process will be affected by theimpression type. Both types of hydrocolloid materialare adversely affected by water loss, and thereforemust be cast as soon as possible or kept in a humidi-fier.

In order to improve the abrasion resistance ofthe model, stone die and plaster hardeners may beused. These are monomers in solution that are simplypainted directly onto the die and surrounding areas.They harden, seal and waterproof the surface, andprotect the definition of the margins without alteringthe dimensions of the die.

Die relief or spacer solutions can be used to increasethe size of the die by a controlled amount. The claimedadvantages are:

� Surface roughness is reduced, making patternremoval easier

� Space is created to accommodate the cement lute� Adjustment can be made for dimensional prob-

lems in the investment (This applies to the ceramicbonding alloy investments.)

� The casting is larger in the case of a crown orsmaller in the case of an inlay; therefore, it seatsmore easily clinically

The decision to use die spacers should be made jointlybetween the clinician and technician since the amountof relief required will have to match the dimensionalchanges of the impression material. A very accuratematerial, such as addition-cured silicone, ought tohave die relief used on its models. With materials hav-ing higher shrinkages, such as condensation silicones,die relief would create a very loose restoration.

Two thicknesses are available, coloured gold or sil-ver, and the application of four alternate coats in-creases the die by 25 μm. The die spacer should notbe used within 0.5 mm of the margins of the pre pa-ration.

Dimensional changes associated with indirectrestoration construction

Each stage in the construction of an indirect restora-tion is accompanied by dimensional changes, eitherexpansion or contraction. Each of the changes mustbe controlled or counterbalanced such that when therestoration is fitted the interfacial gap between toothand restoration is of the order of 25–50 μm.

The stages and their dimensional changes are asfollows:

� Impression – polymerisation shrinkage of elas-tomer

� Casting model – hygroscopic expansion of modelplaster

� Waxing – expansion and contraction of the waxon heating and cooling

� Investment – hygroscopic expansion on settingand thermal expansion on heating in the furnace

� Alloy – expansion on heating, contraction oncooling

� Ceramic – contraction on firing

The major predicted and counterbalanced process isalloy casting. The alloy expands on heating and willcontract after casting. Since the casting is done at ahigh temperature, the investment mould will havealready expanded. The casting shrinks on coolingto what will be its final dimensions. Dimensionalchanges of the investment must balance the behaviourof the alloy and may be altered by:

� Hygroscopic expansion – mould placed in warmwater on initial set

� Thermal expansion – gradual heating increasesthis

� Alteration of the powder/liquid ratio� Lining (non-asbestos) of casting ring to permit free

expansion

Alloy manufacturers recommend appropriate invest-ments and how these should be treated to produce anaccurate casting with their particular alloy.

If used correctly, die relief offers an opportunityto balance impression material changes with thosethat result finally from casting the alloy or firing theceramic.

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Impression Materials – Summary

The material of choice for one or two preparations is addition-cured silicone in a putty/wash technique.Polyethers are satisfactory as heavy/light bodied or regular bodied in a stock tray.

For multiple preparations, consider a special tray with a heavy-bodied/light-bodied technique.

Gingival management should involve supragingival margins wherever possible, no trauma during prepa-ration and careful use of retraction cord and solution.

Complete moisture control is essential.

Syringe the light bodied material with the nozzle close to the preparation to avoid air inclusions

Insert the tray in the long axis of the preparations to avoid flow failure.

Remove with a single short, sharp tug and avoid rocking.

Check that the impression is free from airblows, flow failure (drag marks) and material discontinuities.

Decontaminate the impression before it leaves the surgery.

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Section IVFixed and Removable

Prosthodontics


198


Chapter 18Diagnosis and Treatment Planning for Fixedand Removable Prosthodontics

Here we consider the possible consequences on the remaining dentition of the loss of teeth, whether toreplace them or not and the general approach to the choice of a prosthetic replacement.

Consequences of Tooth Loss

No matter how good our preventive programmes andconservation skills, teeth will still be lost as a resultof caries, periodontal disease and traumatic injuries.The consequences of the loss of a tooth or severalteeth will vary from patient to patient, but in generalthe following are possible:

� Tilting, drifting and rotation of adjacent teeth� Overeruption of opposing teeth – loss of occlusal

stability� Increased plaque accumulation and periodontal

disease� Abnormal sites for carious lesions� Damage to remaining teeth due to increased func-

tion – tooth wear� Loss of masticatory efficiency� Loss of aesthetics� Speech problems� Alveolar resorption� Loss of support for soft tissues

The principal effects are summarised in Fig. 18.1.

Loss of occlusal stability

The extent to which this may occur depends upon theoriginal tooth relationships. The teeth around a singleunit space may well have stable contacts such thatno deterioration occurs (Fig. 18.2). In other cases,there may be slight changes in tooth position resultingin less than perfect relationships but not necessarilyrequiring restoration of the missing teeth (Fig. 18.3).

However, overeruption and drifting may be dra-matic (Fig. 18.4). The changes in tooth positions maylead to abnormal functional relationships such asnon-working interferences in protrusion and lateral

excursions, and pre-centric prematurities. Space fortooth replacement may be restricted.

Loss of masticatory efficiency

Whilst the loss of a single tooth is unlikely to haveany significant effect on mastication, the loss of twoor more in the same quadrant would probably requirethe patient to modify his chewing pattern to maintaineffective function. It is unlikely that this would be no-ticed and, even with many missing posterior teeth, thevast majority of patients will continue with a normaldiet.

However, once a substantial amount of posteriorsupport is lost, mastication will be transferred to theanterior teeth that have a narrow occlusal table mak-ing them unsuitable for grinding. The consequencewill often be tooth wear or tooth surface loss (seeChapter 25). A typical case of anterior tooth sur-face loss following loss of posterior teeth is shown inFig. 18.5.

Increased plaque accumulation – caries andperiodontal disease

The opening of contacts by tilting, drifting and ro-tation into an edentulous space may encourage foodpacking and plaque accumulation that in turn mayinitiate or increase the progress of periodontal inflam-mation. The same applies to the overerupted toothwhere embrasures and contact relations are changedto an unfavourable relationship for natural plaquecontrol.

Tilted teeth may be more vulnerable to periodon-tal breakdown due to unfavourable loading from theocclusion.

Caries too may be initiated by plaque accumulationin poorly accessible areas, but of course this disease

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200 IV. Fixed and Removable Prosthodontics

Plaque accumulation

Overeruption

Abnormal sitefor caries

Occlusalinterference

Tilting/drifting Fig. 18.1 Schematic diagram of theconsequences of tooth loss.

also requires a carbohydrate substrate. Therefore, theoverall caries rate will be of importance in predictingthe initiation of new carious lesions. In the event ofnew caries, because the contact area of an overeruptedtooth will be resited to an area of thinner enamel, thetooth can be more vulnerable to carious spread.

These effects are not absolutely certain and otherfactors such as the patient’s diet and plaque controleffectiveness will be important. In a mouth with a lowcaries rate and good oral hygiene the effects of tilting,rotation and drifting may be minimal.

Aesthetics, speech, alveolar resorption andsoft tissue collapse

Losing a front tooth clearly affects aesthetics but aposterior tooth is not usually considered essential for

Fig. 18.2 Edentulous spaces at |4 and |6 where toothrelationships have remained stable.

good looks. This of course varies according to thesocial perceptions of the patient’s social group or oc-cupation. Perhaps an actor or public speaker may bemore concerned about the loss of a premolar or molar.

Speech may be affected, particularly in respect ofanterior tooth loss. There may be lisping or spitting onspeaking. However, these effects are not often foundbecause of the general ability of the patient to adaptto such changes.

Alveolar resorption is a natural consequence oftooth loss, there being no need for the bone if thereis no tooth and periodontium to support. Both intra-and extraoral soft tissues may collapse or spread intothe space. The tongue will spread laterally and theperioral soft tissues may collapse inwards. This lattereffect may affect aesthetics considerably, particularlyin middle age and after, when muscle tone is reduced.

Effects of tooth loss – summary

As with many other biological processes the effectsof tooth loss are often unpredictable. Although thelist of possible problems is large, many patients donot exhibit any of these and in others the effects maybe minimal. Clearly, the more teeth that are lost, thegreater the possibility of problems. The most impor-tant are those that could induce further pathology anddeterioration of the remaining dentition.

The Replacement of Missing Teeth

This section must open with the statement that notevery missing tooth needs to be replaced. This might

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18. Diagnosis and Treatment Planning 201

(a) (b)

Fig. 18.3 Slight deterioration of occlusal relationships around missing molars but not indicating tooth replacement.

come as a shock to a well-motivated patient who hasinvested much time and trouble in attending for pro-longed but ultimately unsuccessful endodontic ther-apy, only to learn that the resulting space will remainunfilled!

Such a patient needs to be informed that all meth-ods of replacing missing teeth carry with them thepossibility of causing further damage to the dentitionand other problems.

On the other hand, there are obviously several po-tential benefits to be gained from tooth replacement:

� Restored aesthetics� Restored function� Prevention of deterioration of the remaining

dentition

Of these, the patient will be highly motivated to therestoration of aesthetics but might need some con-vincing as to the value of the other two, particularlythe last. From the treatment planning viewpoint, therestoration of function and the maintenance of the re-maining dentition will need to be balanced against thepossible harm that may be induced by the provisionof a prosthesis (see later).

Missing teeth may be replaced by:

Fixed prostheses – bridgework

which may be

Resin retained (adhesive)Crown retained (conventional)Endosseous implant retained

Removable prostheses – partial or complete dentures

which may be

Tooth borneTissue borneImplant borneAll three combined

The detailed indications, contraindications, designand construction aspects of the above will be consid-ered in the subsequent chapters (Chapters 19–26) butthe general aspects of each will be considered here.

The choice of prosthesis

Once the decision to replace a missing tooth or teethhas been made, many factors will be involved inchoosing the appropriate prosthesis:

General factors� Patient aspirations and motivation� Age and general health of the patient� Ability and training of the dentist� Ability and training of the technician� Clinical and laboratory facilities available� Economic factors

Intraoral factors� Restorative condition of the dentition, in par-

ticular the abutment teeth� Number of missing teeth and their location� Tooth relationships – the occlusion� Periodontal condition, caries and oral hygiene

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(a)

(b)

(c)

Fig. 18.4 Edentulous spaces with associated deterioration of occlusal stability which has restricted the space forreplacement of the missing teeth.

Fig. 18.5 Loss of posterior support has resulted in anteriortooth surface loss due to changes in chewing pattern.

� The presence of an existing partial denture� Alveolar bone volume and position

General factors

The patientThe patient’s prime position in the formulation of atreatment plan was discussed in Chapter 1 and thesesame principles apply here. A patient with low moti-vation, who is unable to attend regularly or who can-not for whatever reason be treated ‘normally’, shouldhave a simple treatment plan. In the context of thechoice of a prosthesis, this will usually mean a partialdenture.

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There should be no general upper age limit affectingthe choice between a bridge and a partial denture butage may bring with it some restrictions that affect thedelivery of dental care. The influence of the medicalhistory in the drafting of a treatment plan and itsdelivery was discussed in Chapter 4.

Young patients will have immature dentitions withlarge pulps and unstable gingival margin position andwill not usually be suitable for bridgework. Also, theymay be involved in contact sports that again wouldcontraindicate bridgework. Continuing growth con-traindicates implants.

The dentist, the technician and their facilities –The construction of fixed prostheses requires excel-lent clinical and technical skills and appropriate fa-cilities. Whilst some aspects of the construction ofpartial dentures require similar skills, in general thisline of treatment is usually simpler and less demand-ing. It may also be that the consequences of a poorlyconstructed partial denture will be less harmful to thedentition than those of a poorly constructed bridge.At least the partial denture can be removed for clean-ing and the tooth preparation for it is usually minimal.

Economic factors including state or private in-surance schemes influence the delivery of advancedrestorative care to a large degree. Endosseous im-plant retained prostheses are outside the scope ofsome schemes and are outside the financial resourcesof many patients. Fixed bridgework is also affected,though to a lesser extent, whilst partial denturessometimes seem to be regarded as the bargain base-ment treatment; this attitude somewhat devaluesthe skills and techniques required for their properconstruction.

Intraoral factors

Restorative condition of the dentition, inparticular the abutment teethThe provision of any prosthesis should be against abackground of a stable and well-restored dentition.The presence of active caries or periodontal diseaseought to preclude the construction of a prosthesis thatshould wait until intraoral conditions are suitable. Aprosthesis may aggravate a pre-existing condition andmake things worse.

However, delaying the construction of a prosthe-sis may not always be possible, for example whenthe patient requires the restoration of aesthetics. Inthese circumstances it is necessary to make a predic-tion of the outcome of the pre-prosthetic periodontaland restorative therapy. If this prediction is guarded,

it would be acceptable to construct a simple inter-mediate partial denture whilst the mouth is beingstabilised. If the dentist has more confidence in theoutcome then provisional bridgework could be con-structed pending stabilisation of the rest of the mouth.

The condition of the abutment teeth is a majorconsideration in the choice of prosthesis. Bridgeworkrequires biologically and structurally sound teeth ofgood prognosis to support and retain it. Each toothshould have a healthy periodontium, even though thiscan be reduced through previous periodontal disease.The pulp should be unquestionably vital or the toothshould be properly root filled with no apical pathol-ogy. There should be enough sound dentine or enamelto support the chosen retainer.

Whilst the abutment teeth are also important inthe support and retention of a partial denture, thealveolar ridge can often be used to supplement them.Their condition therefore will not be as critical as itis for bridgework.

Teeth alongside implant retained crowns or bridgesshould be sound and well restored.

The number of missing teeth andtheir locationIn general, a single missing tooth is best replaced bymeans of a bridge, all other factors being equal. Evenin the presence of moderate periodontal disease thereis evidence to suggest that a bridge creates less un-favourable conditions for plaque control than does apartial denture. Single tooth restoration endosseousimplants (Chapter 23) offer better success rates thana bridge and do not need the preparation of an abut-ment tooth. However, cost and a surgical operationmay inhibit their use.

An edentulous space resulting from two missingadjacent teeth bounded by remaining teeth could berestored by bridgework, either attached to an implantor to the adjacent teeth. Where the space is of threeor more teeth, the partial denture becomes the morereliable simple option with implants providing bet-ter results at higher cost. Here there may be insuffi-cient adjacent teeth to support a bridge adequately orthe technical difficulties in construction may limit thetreatment plan.

Where the edentulous space is unbounded at oneend, i.e. a free end saddle, the restorative options willbe further limited, again if implants are not possible.A bridge may be used to restore one tooth as a distalcantilever design but to restore more will inevitablyrequire a partial denture.

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Several missing teeth, each in different areas of thedental arch, could be replaced by several independentbridges, but usually the most cost-effective and simpleoption is to make a partial denture.

Tooth relationships, the occlusionAs will be discussed in Chapter 20, the design of a sim-ple bridge involving two or more abutments requiresthat these teeth be aligned roughly parallel. The con-struction of a bridge on malaligned teeth is not im-possible, but is more difficult technically. The greaterthe disruption to the normal tooth relationships, themore a partial denture is indicated. Irregularities ofthe occlusal plane will also compromise the designof a bridge and if these are difficult or impossible tocorrect then usually a partial denture is preferable.

Periodontal condition, caries andoral hygieneAs was stated above, all prostheses should be placedinto stable and pathology-free mouths. In the face ofpoor oral hygiene, all types of prosthesis are likelyto fail. It is a matter of some clinical judgement asto whether intraoral conditions will deteriorate morewhere there is a dirty bridge compared to a dirty par-tial denture present. The counsel of perfection is toonly place a prosthesis in a mouth that is properlymaintained by both the patient and by the dentist andwhere active caries and periodontal disease have beeneliminated.

In relation to implant retained prostheses, the pres-ence of periodontal disease is a significant contraindi-cation. There is considerable potential for periodon-tal infection to spread to the implant sites and causeproblems.

The presence of an existing partialdentureWhen a further tooth is lost in close association toan existing denture, the simplest approach is to addanother artificial tooth to the denture. The mixing ofa denture and bridgework in the same arch may leadthe patient to dispense with the denture and to relyon the bridgework alone. This is true particularly ofan anterior bridge combined with a partial denturereplacing posterior teeth; having an anterior tooth onthe denture is a great motivator to proper denturewearing.

Alveolar bone volume and positionThese will be affected by the extent of post-extractionresorption which may in large edentulous areas

continue for many years. The series of sectioned mod-els (Fig. 18.6) shows the results of resorption in theupper incisor region. Resorption in this area andindeed the whole maxilla proceeds from the outeraspects of the alveolar ridge thus reducing its diame-ters. In contrast the resorption in the mandible pro-ceeds from the inside and therefore the diameters ofthe lower arch increase. In an edentulous patient, thishas implications for the construction of complete den-tures (Chapter 26).

The lower model in Fig. 18.6 has little resorptionand this represents favourable circumstances for theplacement of a bridge pontic onto the alveolar ridge.This may be seen in Fig. 18.7 where a single toothpontic is represented in its restorative position. Thetooth inclination is good from an aesthetic viewpointand, as will be seen in later chapters, the alveolarmucosa will mimic gingival tissue. A removable pros-thetic replacement could also be made in this site and,because of the volume of bone, a labial flange wouldnot be required and the artificial tooth or teeth wouldbe gum fitted.

Clearly, the volume of bone seen in Fig. 18.7 wouldbe favourable for the siting of implants.

The worst case shown in Fig. 18.8 has insufficientbone for implants and when an incisor or incisors areplaced in the correct aesthetic and functional positionthere will be a large gap between the alveolar ridgeand the teeth which can only be filled effectively by adenture base.

Where there is moderate resorption as in the mid-dle model in Fig. 18.6, the replacement could be bya bridge, but there would be a need to make up themissing bone demonstrated in Fig. 18.9 by using pinkceramic. A denture base could also provide an effec-tive replacement.

The angle of an implant placed into an area of re-duced bone may also create unfavourable aesthetics.Figure 18.10 shows the moderately resorbed ridgewith the outline of an implant placed in the maximumvolume of bone. The emergence angle will mean thatthe abutment will need to be at an angle to the im-plant for the crown to be in a functional position andtherefore the aesthetics will be poor. To create goodaesthetics the implant will need to be further forwardand angled palatally and this can only be done byridge augmentation prior to implant placement (seeChapter 22).

This same principle applies to the siting of implantsin other areas of alveolar resorption where vital struc-tures such as nerves, blood vessels and the maxillaryantrum would be vulnerable to damage.

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Fig. 18.6 Alveolar resorption. Sections of maxillary models showing the progression of alveolar resorption over severalyears from the lower model where there is little resorption, the middle model where there is moderate resorption and theupper model where there is much resorption.

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Fig. 18.7 Correct central incisor position on an alveolar ridge with minimal resorption.

Fig. 18.8 Correct central incisor position on a grosslyresorbed ridge. The resorbed bone is replaced by denturebase.

Fig. 18.9 Correct central incisor position on a moderatelyresorbed ridge. A bridge would need the resorbed bone tobe replaced by pink ceramic. A denture base does this.

The functional and aesthetic siting of bridge pon-tics or implant retained crowns in areas of consider-able resorption is difficult. The model in Fig. 18.11shows an incisor that has its tip in the correct position.However, it has been angled to bring its neck into con-tact with the resorbed alveolus. Such an arrangementwas made in the case shown in Fig. 18.12 that hasa large anterior bridge. The angle of the incisors cre-ates poor aesthetics and was presumably constructedin this way because the position of the tips was setby the lower incisor occlusion and the necks by thealveolus. Figure 18.13 shows the alveolus after thebridge was removed and the amount of resorption

Fig. 18.10 The outline of an implant has beensuperimposed on the remaining bone in Fig. 18.9. Theaesthetics would be poor if an implant retained crown wasmade in these circumstances.

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Fig. 18.11 Incorrect incisor position on a ridge with much resorption. The acute angulation leads to poor aesthetics.

can be seen. The management of this case is discussedin Chapter 21.

Deleterious Effects of Dental Prostheses

There is no doubt that the placement of a prosthe-sis, whether this is fixed or removable, brings withit certain disadvantages. Principal amongst these isthe possibility of causing further deterioration of thedentition. The possible deleterious effects are:

� Recurrent caries� Loss of pulp vitality� Tooth wear� Periodontal disease

Fig. 18.12 Large anterior bridge with poor aestheticscaused by the incorrect incisor angulation.

� Soft tissue infection and damage� Alveolar bone infection

These effects will vary in incidence and magnitudeaccording to the type and design of the prosthesis.Their management will be discussed in Chapters 29and 30.

Fixed bridgework

The construction of a bridge requires tooth prepa-ration to accommodate the retainers. In the case ofresin-retained bridgework this preparation is mini-mal and this type of bridge is likely to have less un-toward effects on the dentition. Where conventionalbridges are made, the retainers are usually full crownsand here there is the potential for loss of vitality as a

Fig. 18.13 Alveolar ridge with the bridge removedshowing bone loss.

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result of the trauma of the preparation. If the abut-ment tooth has already been carious and restored thispotential is increased.

The retainer margins, no matter how well fitting,and the pontic/retainer embrasure spaces introduceplaque traps that require special oral hygiene mea-sures to be performed by the patient. The conse-quences of plaque accumulation may be periodontaldisease and, in the presence of a substrate, recurrentcaries.

Damage to opposing teeth is possible if ceramic onthe bridge is in functional contact with them. Theceramic is harder than enamel and, if poorly glazedor rough, will cause rapid tooth surface loss.

Bridge abutment teeth may transmit unfavourabletwisting forces to the periodontium. If the periodon-tium is already inflamed these forces may accelerateperiodontal breakdown. On the other hand, if theperiodontium is healthy, it appears that supportinga bridge does not bring any untoward effects (seeChapter 20).

Implant-retained prostheses

Damage to local vital structures (nerves, blood ves-sels, antrum) is possible during placement. The en-dosseous implant is also a potential entry point forbacteria and ‘peri-implant’ infection of the soft tis-sues and bone is possible (Chapter 23).

Partial dentures

The contact areas of clasps and denture base to thesurrounding teeth are sites for plaque accumulationand its consequences of caries and periodontal dis-ease. Movement of the denture base, particularly tip-ping and rotation may accelerate periodontal break-down in the presence of active periodontal disease.

Stagnation under a denture base may create condi-tions favourable to the establishment of infection byCandida albicans (thrush) leading to denture-inducedstomatitis.

Continuing care and replacement

All restorative work brings the requirements of con-tinued maintenance and monitoring by the dentistand scrupulous oral hygiene by the patient.

Perhaps of even greater importance is the realisa-tion that eventually repair and replacement will benecessary for most restorations. This does not reflectupon the standards of care but a realistic apprecia-

tion to be conveyed to the patient that nothing lastsforever. General wear and tear and changes in theoral cavity may lead to local or general failure ofrestorations.

All other things being equal, i.e. that no pre-existingproblem, such as a questionable root filling, existsthen the life expectancy for a bridge would be be-tween 10 and 15 years and a removable partial den-ture perhaps 10 years. Even during that time minorproblems such as the fracture of a component or evenmajor repairs such as root canal therapy through aretainer may be necessary.

Because of their complexity of construction, im-plant retained prostheses require even more intensemaintenance. Failure of joints and superstructurecomponents is possible as well as the basic failureof the implant itself.

A very positive commitment to continuing care inrelation to any prosthesis is required by both the pa-tient and the dentist. Effective oral hygiene and atten-dance for regular review is the patient’s role in this.

Shortened dental arch

Bearing in mind the above description of the dele-terious effects of dental prostheses, a philosophy ofnon-replacement of lost posterior teeth has evolved,known as the shortened dental arch. Whilst this con-cept could be applied to any missing molar teeth, ithas come to refer to dentitions that have no teethdistal to the second premolars in all four quadrants,i.e. all the molar teeth have been lost and deliberatelynot replaced. This arrangement has also been termeda premolar dental arch or a premolarised occlusion(Fig. 18.14).

Fig. 18.14 A case with shortened dental arches.

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There is clinical evidence to support the con-cept in that patients have been observed to func-tion adequately with such a reduced occlusaltable and the possible deleterious effects of aprosthesis on the premolar teeth, in particulartipping and periodontal problems, are preven-ted.

Loss of occlusal stability of the premolars due todistal drifting and wear has been shown to be smalland the poorer aesthetics of missing molars has notbeen considered a problem.

Treatment Planning for Prosthodontics – Summary

The loss of natural teeth may result in the deterioration of the remaining dentition and affect the patientadversely.

The provision of a prosthesis will restore aesthetics and function as well as playing a part in maintainingthe dentition.

The prosthesis, however, may cause deterioration in its own right and the decision to restore the edentulousspace must take into account both the advantages and the disadvantages of the treatment.

The choice of prosthesis is based on a complete assessment of both the patient and the intraoral conditionsand many factors must be considered with the condition of the mouth itself being of principal concern.

The active cooperation of the patient in both the provision of the prosthesis and its subsequent maintenanceis of paramount importance to its success.

The concept may also be applied if the premolararch is not intact, particularly if the second premo-lars are missing. These teeth may be replaced, all otherfactors being equal, by distally cantilevered units at-tached to the remaining teeth or endosseous implants.The biomechanics of this type of arrangement mustbe considered. It is suggested that the distally can-tilevered unit is restricted to one premolar only toreduce tipping forces and if several teeth are involvedin the prosthesis that it is constructed from gold alloyand acrylic resin to allow flexure.

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Chapter 19Fixed Prosthodontics: Resin-RetainedBridgework

The next five chapters consider fixed prosthodontics. In this chapter there are the basic definitions forbridgework. The history, design, treatment planning and techniques of resin-retained or adhesive bridgeworkare described together with the materials involved in their construction.

General Definitions for Bridgework

A bridge, also referred to as a fixed prosthesis or afixed partial denture, is a false tooth, or teeth, per-manently attached to natural teeth or to endosseousimplants. The false tooth, the pontic, is joined by con-nectors to retainers that are cemented to the abut-ment teeth. The retainers may be either wings – (resin-retained or adhesive bridgework) or inlays or crowns– (conventional bridgework) (Fig. 19.1).

Pontic

ConnectorRetainer

Preparation

Abutment

Edentulous ridge

Fig. 19.1 The components of a bridge.

The pontic may be fixed to the retainer by a rigidconnector, or it may have a movable joint (non-rigidconnector). Bridges may be classified according to thetype of connectors either side of the pontic, as eitherfixed–fixed or fixed–movable.

In addition, the pontic may only have one connec-tor and be free at the other end – this is a cantileverbridge. If the pontic is some distance away from theretainer, and the connector is a metal bar, this is aspring cantilever bridge.

Bridges are also referred to by the total number ofretainers and pontics, for example – a five-unit bridge.

Resin-Retained Bridgework

History

The concept of the resin-retained bridge (RRB) isthat metal ‘wings’ are retained by the acid-etch tech-nique to enamel surfaces adjacent to the edentulousspace. The wings are part of a metal sub-frame thatalso supports a resin or ceramic tooth. The use ofmetal and resin in this way was first reported by Ro-chette (1973) who described a perforated metal perio-dontal splint that was adapted to retain a false tooth.Metalwork covered the whole of the lingual enamelsurface and retention to the cementing compos-ite was achieved through small holes in the metal.Other workers developed alternative ways of ob-taining macromechanical retention to the metal butthese and the Rochette system have now beensuperseded.

In the late 1970s, Livaditis and Thompson at theUniversity of Maryland developed an electro-etchingprocedure for non-precious ceramic bonding alloysto provide a microporous surface that a microme-chanical interlock with the cement. This gave riseto the ‘Maryland’ bridge that had the advantagesover the Rochette type of thinner wings and no per-forations. Electroetching, however, was a demand-ing technique and two other techniques, acid etch-ing and grit blasting, were developed. Grit blastingwas the most simple and reliable and the other twohave been largely superseded. This has not stoppedthe incorrect use of the term ‘Maryland bridge’ for allRRBs.

Further improvements in longevity have been ob-tained by the development of specific affinity cementsand by metal primer systems that increase the bond-ing of the cement to the metal.

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19. Fixed Prosthodontics: Resin-Retained Bridgework 211

Design

The original bridges and splints were made withno tooth preparation, but now considerable enamelpreparation is required to promote long-term success;the technique is also referred to as minimal prepara-tion bridgework. The objectives of the preparationare to create features that will enhance the stabilityof the bridge and, to as great extent as possible, toaccommodate the casting within the original toothcontour. Other aspects of RRBs have evolved empiri-cally with clinical experience. Perhaps the most inter-esting of these has been the reduction in the numberof wings used; most single tooth RRBs will now beretained by a single wing to a single abutment. Thisis the result of an appreciation of the twisting forcesapplied during function that translate to peel forcesacross the adhesive. Stress on one side of a two-wingbridge will be transmitted across the structure and thesecond abutment will be moved in its socket. Stresstherefore concentrates in the adhesive layer under onewing.

Clinical experience showed that two wing RRBsoften failed by debonding of one wing. The problemwould be managed by removing the debonded wingintraorally to leave a single-wing bridge. These single-wing bridges were surprisingly successful and this ledto the current design concepts.

This observation of the biomechanics of this bridgesystem has implications for the design of conventionalbridgework (see Chapter 20).

Tooth preparation

The objectives of tooth preparation are to:

� Accommodate the metal within the original con-tour of the tooth

� Provide occlusal clearance if necessary� Direct stress away from the adhesive� Provide as great a surface area of enamel for bond-

ing as possible� Achieve clear finishing lines

To achieve this it is necessary to:

� Identify a single path of insertion� Remove the bulbosity from as wide an area of

enamel as possible without exposing dentine – halfenamel thickness preparation

� Extend the preparation to as much of the buccaland lingual surfaces as possible to create ‘wrap-around’

Fig. 19.2 Resin-retained bridge preparation on apremolar. The bulbosity is removed, a light chamferfinishing line established and a wrap-around created. Anocclusal rest seat is cut in the mesial marginal ridge.

� Avoid the incisal one-third of anterior teeth tomaintain translucency

� Incorporate rest seats, slots and grooves as appro-priate, to increase stability and accurate locationof the casting for cementation

The posterior tooth preparation is shown on a pre-molar (Fig. 19.2). A rest seat is cut in the marginalridge and in some teeth the occlusal morphology mayallow an additional rest. These rests must be at least1 mm deep to be effective (Fig. 19.3).

Fig. 19.3 RRB preparation on an upper premolar. Notethe second rest seat and the fade out of the preparationbuccally, creating a chamfer in that area.

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Fig. 19.4 RRB preparation on an incisor. This includes apalatal wrap-around, cingulum rest and cingulumreduction to clear the occlusion. The yellow lines indicatessites for retention grooves.

The typical anterior tooth preparation, which isshown on an incisor (Fig. 19.4), requires clearancefrom the occlusion to enable correct reproduction ofthe anterior guidance, an internal cingulum rest for lo-cation and stress bearing, approximal reduction in thepath of insertion and a supragingival chamfer finish-ing line palatally. If the cingulum area is small, slots orgrooves should be cut to enhance stability (Fig. 19.5).

There is a danger of producing greyness of incisaledges if the metalwork extends too far incisally. Forthis reason, the preparation should be confined tothe cervical two-thirds of the crown. Care should betaken also to avoid bringing the approximal reductioninto the line of sight and a ‘fade out’ of the reduc-tion should be done to maintain enamel in the labialregion.

Provisional replacement of the missing tooth by abridge is not possible and a removable partial den-

Fig. 19.5 RRB preparation on an upper canine. Grooveshave been incorporated in the preparation to increasestability.

ture is used. The occlusal clearance created by thepreparation can be maintained by attaching compos-ite to the tip of the opposing teeth. An alternativetechnique that some favour is to fit a bridge that ishigh in the occlusion and allow tooth movement toaccommodate the imbalance. Care must be taken ifthis approach is favoured that inclined plane forcesare not created that may procline the abutment tooth.

Treatment planning

Table 19.1 summarises the indications and con-traindications for resin-retained bridgework.

The occlusionThe RRB is useful for short spans and where un-favourable tipping forces are not present. Potentialdisplacing forces from the occlusion are difficult topredict but patients with a clenching or grinding habitor an edge-to-edge incisor relationship may createunfavourable conditions. A further occlusal problemmay be variations in the level of the occlusal planecaused by tilting or overeruption into the edentulousspace. It is preferable to correct this before makingthe bridge as the irregularity may be another sourceof unfavourable displacing forces.

Table 19.1 Indications and advantages for resin-retained bridgework

Indications Contraindications Advantages Disadvantages

Short spans (one or two teeth) Long spans Technically simple Metal visible through tooth

Sound enamel available Heavily restored teeth Cheaper than conventional Debonding problems

Favourable occlusion Multiple upper anterior teeth bridgework

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The abutment teethThese should have sound and well-supported enamel.Whilst small restorations are acceptable, more ex-tensive cavities are likely to have weakened cusps.If there is any doubt about the integrity of the cho-sen abutment, then the existing restoration(s) shouldbe removed and the enamel inspected. Ideally, theabutment tooth restoration should be composite orglass ionomer cement because of the better bond-ing of the adhesives to these materials (see later).However, small sound amalgam restorations areacceptable.

The precise choice of abutment is somewhat empir-ical but as a general rule the more posterior tooth ofa bounded space is more suitable. The rationale forthis is that the more posterior the tooth usually thelarger and the less visible it is. The exception is theupper lateral incisor and this tooth should be avoidedas the sole abutment because of its small crown andreduced root support.

The amount of etchable surface and potential wraparound varies from tooth to tooth because of vari-ation in size and position. The size is of particularsignificance in the lower arch, where the lingual sur-faces of the anterior teeth are relatively small, and inthe posterior region, where the lingual crown heightis often low. Similarly, very severely tilted or rotatedteeth might be difficult to use as abutments. All in-cisor and canine teeth have short palatal or lingualwalls and here slots or grooves are useful to increasestability.

Bridge spanWhile it is possible to replace more than one toothwith an adhesive bridge, more failures appear to oc-cur with multiple replacements. The use of morethan one abutment on either side of the space isalso rather risky since the differential stresses areapplied to bonds of varying areas, and debondingis likely. A single molar should be regarded as twotooth ‘elements’ and two wings, one at each endare usually prescribed for retention (Fig. 19.6). Anovel design splitting the molar pontic into twooffers the advantage of two single wing bridges(Fig. 19.7).

The upper central incisor may be replaced by a sin-gle wing cantilever from the other central incisor oras a cantilever from two wings on the upper lateralincisor and canine. In this latter design it is importantto incorporate slots, grooves and rests in the prepa-rations to increase stability.

Fig. 19.6 RRB replacing a lower molar using two wings.

Design variationsThe introduction and development of adhesive tech-niques has lead to many variations in design as den-tists attempt to establish the limits of the techniques.

For example, a buccal wing could be used if enamelis better there and the aesthetics are acceptable. Thebridge could be constructed completely in ceramic,with the wing being a veneer preparation (Fig. 19.8).This is useful if the adjacent tooth is to be veneeredanyway.

Spacing is difficult to reproduce but connectors canbe constructed to lie below the space, out of sight.However, the stresses on the wings may be increasedby this design.

Hybrid designs have been used that combine a con-ventional crown on one side of the pontic with a

Fig. 19.7 An alternative design for the replacement of amolar. The molar is replaced by two half-tooth pontics,each attached by a single wing to the abutments.

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Fig. 19.8 Ceramic veneer retained bridge replacing |2cantilevered from |3.

bonded wing on the other but with the experienceof the success of single wing cantilevers; these designshave little value and complicate treatment. The sameapplies to designs that incorporate joints within a hy-brid structure; these are not needed.

Immediate RRBsThis type of bridge can be very successful as an imme-diate replacement for an extracted tooth. The abut-ment is prepared and the bridge constructed beforethe extraction. The tooth to be extracted is removedfrom the model and the model relieved to allow thepontic to be placed superficially in the socket. Afterextraction, bleeding may be controlled if necessary byplacing cellulose mesh in the socket prior to placingthe rubber dam.

The only problem of this technique is that alve-olar resorption may change the relationship of thepontic to the alveolar ridge. If the patient’s lip line islow, the gap may not be noticed. However, if the pa-tient notices food collecting in the gap, a new ceramicfacing can be made for the pontic. This technique isdescribed in Chapter 29.

Cementation

Cementation must be carried out in a dry field and theapplication of rubber dam is essential, particularly inthe lower arch because of the potential for contami-nation of the etched tooth and the fit surface of themetalwork (Fig. 19.9).

Before the dam is placed, the following must bechecked:

� The shade� The seating of the metalwork� The occlusion (if possible)

These cannot be checked with the dam on.The cementing sequence is as follows:

1 Try in and check margins and the occlusion. Ifthe casting is not stable, the occlusion cannot bechecked easily until after cementation

2 Place the rubber dam3 Prophylaxis of the abutment teeth using a slurry

of pumice and water. Non-oil-based prophylaxispastes may be used but they may contain fluoride.This will reduce the effectiveness of the etching

4 Grit-blast the bridge wing or, if there is no ac-cess to a grit-blaster, clean the bridge wing withabsolute alcohol or a proprietary cleaning agent

5 Prime the metal, if required6 Acid etch the area of the tooth preparations

Fig. 19.9 Rubber dam applied for the cementation of theRRBs shown in Fig. 19.7. It is important that the dam isslack over the alveolar ridge so that it is not under tensionwhen the bridge is placed.

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7 Mix and place the cement on the bridge and seathome

8 Remove excess prior to setting and place oxygenbarrier, if required

9 Remove the dam, clean the margins and adjustthe occlusion

10 Check that the embrasures are clear for oral hy-giene measures

Dental materials aspects

Metal subframe and ponticThe choice of metal alloy relates particularly to themethod of adhesion of the retaining wings. Theelectro-etched (Maryland) system is particularly af-fected by the alloy composition and the principalalloy used in this technique was a nickel–chromium–beryllium ceramic bonding alloy. Non-beryllium al-loys did not electroetch well. However, the berylliumcontent of such alloys represents a health hazard oninhalation of the grinding dust and these are thereforenot recommended.

The more universal use of grit blasting has lead tothe use of cobalt chromium ceramic bonding alloys.Nickel-containing alloys should be avoided becauseof the risk of allergy.

The cobalt chromium alloys are harder, denser andmore difficult to cast than the semi-precious alloysdescribed in Chapter 15 and also more time consum-ing to adjust and finish clinically. The higher meltingpoint requires the use of a phosphate-bonded invest-ment and the wax pattern for the bridge is usuallymade on a divestment model similar to those usedfor ceramic veneers. The accuracy of fit of the cast-ing can be less than that achieved with crowns andthe technician may often need to spend considerabletime adjusting the casting to achieve a good fit to themaster model.

However, in spite of this the alloys have the ad-vantage of being strong in thin section and thereforethe retaining wings can be thinner – of the order of0.3–0.4 mm. They also form an oxide layer on theirsurface which is utilised for bonding (see below).

Pontics may be made from ceramic or polymers.Ceramic is the most durable with oven-processedcomposites being a second choice.

Adhesive cementsThere are two basic types:

� Fine particle composite luting cements� Dual affinity polymer cements

These are mostly two-component autopolymerisingsystems but there are also some ‘dual-cure’ mate-rials available that are initiated by visible light butalso have a slow autopolymerising component. Thismeans that polymerisation will take place even whenthe curing light does not reach the full thickness ofthe material. Care must be taken however as the au-topolymerising process is slower. The setting processmay be disturbed if occlusal adjustment is undertakentoo soon after the initial ‘tack’ setting with the light.

The formulation of the first group is based onrestorative composites with very much less filler ofsmaller particle size diluted with lower molecularweight monomers. This results in a material with ahigher polymerisation shrinkage. They rely on mi-cromechanical interlocking to both the etched enameland to the metal wing for their retention.

The second group has a similar basic formulationbut also has a chemical agent present to aid adhesion,particularly to the metal. The individual materialsare based on 4-methacryloxyethyl trimellitic acid an-hydride (4-meta), 4-meta with methyl methacrylate,4-meta with bis-GMA or the halogenated phosphateester of bis-GMA. Some of these have shown veryhigh bond strengths to enamel and apparently offeradvantages over the purely mechanical retention ofthe other types of cement. Their chemical bonding tothe metal is dependent on there being a metal oxidelayer present.

The setting reaction of some cements is inhibitedby oxygen and air must be excluded from the bridgemargins to permit polymerisation. Vaseline is effec-tive and similar compounds are supplied with thematerials.

Metal surface conditioningThe success of resin-retained bridgework depends to agreat extent on the adhesive bond between the metal,cement and tooth. Therefore, an understanding of thevarious methods for conditioning the metal fit surfaceis crucial.

The electroetching technique creates a surface thatenables the polymeric cement to make a microme-chanical interlock with it. Surface contamination withwater, saliva or organic debris will prevent the in-terlocks from forming, which explains the care thatmust be taken with the bridge once it has beenetched. The electroetched surface does not allow thechemical affinity cements to use this aspect of theirformulation.

Grit blasting of a cobalt chromium ceramic bond-ing alloy with 40–50 μm aluminium oxide grit creates

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a surface disruption of the metal that allows sim-ilar micromechanical interlocking but also leaves awell-bonded oxide-rich layer. The dual affinity ce-ments react with this oxide layer to enhance theiradhesion.

Semi-precious ceramic bonding alloys on the otherhand do not form this oxide layer on grit blastingand to obtain the reactive oxide surface they must betin plated and then be heated in a ceramic furnace tooxidise the tin.

A further treatment method is the deposition ofsilicon and silane compounds onto the metal surface.This requires special equipment but bonding is onlymoderately improved and the coating is also easilycontaminated.

Debonding

The catastrophic failure of RRBs by sudden debond-ing is the major drawback of the technique. It is nowmore dramatic with the use of single wings being morecommon. A two-wing bridge might fail on one wingfirst allowing the patient a little warning of impend-ing disaster. One way of providing reassurance is tosupply the patient with an emergency stand-by partialdenture.

Debonding may occur either almost immediatelyafter placement or much later.

The immediate type occurs in the first 48 hours af-ter cementation and the debond is likely to be caused

Resin-Retained Bridgework – Summary

The development of the technique and materials has proceeded rapidly. It is now the treatment of choicefor single tooth replacement. Unfavourable occlusal factors and heavily restored abutment teeth may con-traindicate the technique.

Minimal tooth preparation is required to enhance mechanical stability. Retention is achieved through adual-affinity polymer-based luting cement via the acid-etch technique to enamel and grit-blasting to thebridge alloy. Base-metal-bonding alloys are preferred.

Patients should be warned of the possibility of catastrophic failure and perhaps supplied with an emergencypartial denture to have in reserve.

Fig. 19.10 Single-wing debond in a two-wing bridge.Extensive caries has resulted.

by contamination during cementation and failure atthe tooth-adhesive interface.

The later failures can occur at either of the twointerfaces but, increasingly, evidence of failure withinthe cements has been found. This is presumed to bethe result of fatigue.

Debonding appears to be more common in caseswhere multiple abutments have been used.

When partial debonding occurs, it is essential thatthe bridge is removed and re-cemented, otherwisethere is a high risk of recurrent caries under the loosewing (Fig. 19.10). Alternatively, the loose wing canbe cut off and the bridge thereby converted to a can-tilever type.

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Chapter 20Fixed Prosthodontics: ConventionalBridgework – Design and Planning

Here we consider the replacement of teeth by crown-retained conventional bridgework. The principlesunderlying the choice of design and treatment plan are described. Of particular importance are the conditionof the abutment teeth and their periodontal support. The problems of hypodontia, changes in appearanceand cleft palate are discussed.

Introduction

The more routine use of adhesive bridgework of vari-ous designs and its long-term success has lead to con-siderable reduction in the indications for bridgeworkretained by inlays and crowns. In sound mouths, theresin-retained bridge is now the treatment of choicefor a single tooth, with or crown-retained conven-tional bridges being used for cases where the abut-ment teeth cannot support an adhesively retainedwing. Further changes in the provision of crown-retained bridges have been brought about by the useof implant supported crowns and bridges.

Design Considerations

There is very little scientific evidence to support manyof the principles of conventional bridgework. Theseprinciples have evolved empirically through clinicalexperience and some documentation of failures. Ex-perience in the biomechanics of resin-retained bridge-work has called into question some of the previouslyaccepted tenets of conventional bridgework.

The design of conventional bridgework dependsupon:

� Biological factors� Mechanical factors� Aesthetic factors

Biological factors

The longevity of conventional bridgework dependsfirstly on the biological integrity and prognosis ofeach of the abutment teeth chosen in the provisionaldesign. The crown must be caries free and the pulp

must either be healthy or be replaced by a sound rootfilling with no apical pathology. The periodontiummust also be healthy and well maintained.

Teeth that have suffered previous periodontalbreakdown are not excluded from being abutments,but the disease must have been stabilised and theplaque control maintained at a high level.

The number of abutments required to support theproposed pontics is often a matter of opinion. Anteproposed that the combined surface area of the peri-odontium of the abutment teeth should be equal toor greater than that of the teeth to be replaced. Thisseems to assume that the abutments will be subjectedto greater loading, possibly up to one and a half timesmore.

However, work from Scandinavia, where exten-sive bridges were provided for periodontally dubi-ous teeth, together with clinical experience, suggeststhat Ante was being over-cautious and that occlusalloading is reduced by a bio-feedback mechanism toa level appropriate to the support available. Thisconcept is also supported by experience with resin-retained bridgework where the single-wing cantileverdesign has been found to be successful. For the caseshown in Fig. 20.1, the ‘older’ conventional bridgedesign would almost certainly have involved twoabutments.

Rather than looking at the axial occlusal loads onabutments, it seems more important to consider thepossible leverage and torque that may be applied. Thiswill arise during function and parafunction in lateralexcursions and protrusion, and the assessment of theocclusion is crucial in bridge design. For example, ina canine-guided occlusion, lateral stresses on otherteeth are small, and perhaps this is more favourablewhen they are used for abutments.

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(a) (b)

Fig. 20.1 Single retainer cantilever bridge replacing 1|. This design would not have been used prior to the experience withsingle-wing resin-retained bridges.

This is not to say that a large number of ponticscan be supported by a few abutments, because theretention of the bridge is also important. Rather thatbridges made with less than the traditionally ideallevel of support can be clinically successful.

The periodontal surface area of the abutment teethis clearly important, though. The upper canine andthe upper first molar have the largest areas makingthem ideal for bridge support, whilst at the otherend of the scale, the upper lateral incisor has a verysmall root and is often unsuitable as a terminal abut-ment. Pragmatically, then, it would seem sensible toadopt designs that utilise the teeth with the largestperiodontal surface areas available in the particularcircumstances.

Mechanical factors

Each abutment tooth must also be structurally sound.It must either have dentine of sufficient quality andquantity to allow the preparation of a retentivecrown, or, in the absence of such sound tissue, be ca-pable of being restored, depending upon its position,by a pinned core or a post and core.

Each preparation should provide excellent mechan-ical retention, achieved by near-parallelism of walls(Chapter 15). In a multi-abutment bridge each of thepreparations must individually provide proper stabil-ity. If, for example, a short preparation is included,this will be a site for stress concentration and subse-quent cementation failure.

The most retentive retainer is a full crown withthe partial veneer crown being a close second. Forsimplicity of preparation and reliability of fit, the full

crown has become the most used retainer. The use ofinlays as bridge retainers has died out – mainly be-cause a tooth that is suitable for an inlay would alsobe suitable for a resin-retained wing and therefore theconventional bridge would be contraindicated. Par-tial veneer crowns leave the buccal surface uncut andcan therefore be aesthetically better and are more con-servative of tooth tissue. However, the preparation ismore technically demanding.

Parallel preparationsThe abutment preparations for a fixed–fixed bridgemust be parallel. The bridge will eventually be in-serted in one piece and this will not be possible if eachpreparation has a different path of insertion, causedusually by abutment tooth tilting. This aspect of eachcase must be assessed using a model surveyor. Theproblem of non-parallel alignment of abutment teethmay be solved by:

� Pre-operative orthodontics� Compromises in preparation angulation� Assembly joints� Telescopic retainers or copings

Orthodontics may be used to upright the malalignedtooth or teeth. However, this may not always be prac-tical due to the length of time required or the reluc-tance of the patient to undergo the treatment thatusually requires fixed appliances.

Preparation angulation may be changed from theideal for each abutment to a compromise in keepingwith that required for the bridge design. However,such alterations may result in:

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20. Conventional Bridgework – Planning 219

Fig. 20.2 Tilted teeth – the problemof a fixed–fixed bridge. The seatingof the bridge is prevented by themesial aspect of the last molar, eventhough the preparations have beencut with a common path of insertion.Also, the retention of the preparedmolar is reduced by the angulation.

� Loss of retention of individual retainers� Inability to seat the bridge

Figure 20.2 shows this diagramatically. It is possi-ble to cut parallel preparations on tilted teeth butadjacent teeth may prevent the bridge from beinginserted. Also, changing the path of insertion mayreduce the preparation height and the extent of prepa-ration walls that are parallel to each other thus reduc-ing the retention.

Assembly jointsTo overcome this loss of retention, the paths of in-sertion of each retainer can be made in the long axisof each abutment crown and the bridge assembled inthe mouth at cementation by means of a joint in oneof the connectors parallel to the path of insertion ofthe other element of the bridge (Fig. 20.3). The dove-tail slot may either be milled in the casting or be apreformed precision retainer (Fig. 20.4).

Non-rigid connectors/movable jointsIn addition to permitting the assembly of individualelements of bridges, joints have been used for manyyears as non-rigid connectors, also referred to as mov-able joints. The concept is that even when a bridgemay be made fixed–fixed from the angulation of theabutments, empirical biomechanical considerationssuggest that one retainer may either take more stressthan another or that one is less retentive than another.

The design factor of stress breaking has been appliedto these circumstances.

Stress analysis suggests that this concept is flawed.The type of joint shown in Figs. 20.3 and 20.4 is ca-pable of very little freedom of movement. Loading inthe long axis of the joint might allow some indepen-dent movement of the bridge elements but, of course,most masticatory movement would cause lateral andshear forces on the bridge. In the face of these forcesthe joint would, in effect, be a rigid connector and notbreak stresses at all.

This concept is a very good example of scientificallyunsubstantiated clinical opinion.

Telescopic crowns or copingsAn alternative way of overcoming discrepancies inpaths of insertion is to use telescopic crowns based onmetal copings (Fig. 20.5). Each abutment is preparedto receive a casting in whatever path of insertion isappropriate for that abutment. Each casting or cop-ing has its outer aspect shaped to the common pathof insertion for the bridge and slots/grooves may beincorporated to increase retention.

This structural system, whilst solving the angula-tion problem, also has the advantage that the individ-ual abutments are capable of being treated separatelyin the event of failure. Very often the overlying bridgeis cemented with a temporary cement that allows easyremoval of the bridge if problems arise.

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Dovetail

Slot

Path of insertion of premolar crown

Slot Dovetail

Path of insertion of bridge

Fig. 20.3 Tilted teeth – the assembly joint. Each abutment has its preparation cut in its long axis. The crown on thepremolar has a dovetail-shaped slot cut in its distal aspect (the preparation must be reduced to accommodate it) and thepontic has the dovetail-shaped piece to fit the slot. The line of the dovetail is the path of insertion of the molar preparation.

Fig. 20.4 A precision retainer that can be used as anassembly joint.

Aesthetic factors

This may well be one of the major reasons for pro-viding bridgework and a decision must be madeabout which teeth should have tooth-coloured com-ponents and which can remain all metal. The all-metal retainer utilises a minimal preparation andis technically less demanding than an aestheticone.

The aesthetic component has to have space in thepreparation to accommodate it and requires highertechnical skills for its construction, particularly if it isto function in the occlusion.

Aesthetic materials tend to be applied directly toa metal sub-frame and may be ceramics or polymer-based composites. Pre-formed cemented facings areno longer used.

The newer castable and milled ceramics describedin Chapter 15 may also be used for all-ceramic bridge-work. However, the brittleness of ceramic means thatthe connectors in such bridges need to be substantial.Such connectors may impinge on the gingival tissueto achieve the required cervico-occlusal dimension.Also, caution should be exercised when considering

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Path of insertion of bridge

Path of insertion of telescopic base

Fig. 20.5 Tilted teeth – the telescopic crown. The preparations are in the long axis of each tooth. A gold coping is made forthe molar, which is milled to receive a partial veneer crown with slots and grooves. The path of insertion of the bridge isthen aligned with the premolar preparation.

all-ceramic cantilever bridges; these may end with thepontic breaking away.

When metal–ceramics are used, wherever possible,and with the agreement of the patient, the occlusalsurfaces should be reproduced in metal (Chapter 14).

If the purpose of the bridge is to alter the aesthetics,then this must be carefully planned at the diagnosticstage (see later).

Pontic Design

Pontics may require a functional component and wellas an aesthetic one.

For its functional aspects, the pontic should provideocclusal stability by the inclusion of centric stops andsupporting cusps as appropriate. Its participation inthe new occlusal scheme should be decided (see later)and it should not create any interferences.

Pontic function could be fulfilled by a flat ‘plate’of metal and the wash-through or sanitary ponticsare useful from the periodontal viewpoint, in that thetissues around the pontic are readily accessible forcleaning. However, their use is usually confined tothe molar region and is now rare because of theiraesthetic limitations.

The majority of pontics will need to be aestheticand this will mean the inclusion of a tooth colouredfacing in conjunction with the metal functional sur-face. The aesthetic component will need to repro-duce the embrasure spaces and contact the soft tis-sue of the alveolar ridge. This tissue contact must be

firm, but not intrusive, to reduce plaque accumula-tion under the pontic. Contact should be confined tothe buccal or labial aspect of the ridge, with the re-mainder accessible to the tongue for natural cleansing(Fig. 20.6).

Special oral hygiene techniques are required tomaintain the undersurface of the pontics and connec-tors in a plaque free condition, and the most usefulaid is superfloss (Fig. 20.6c).

If alveolar resorption has been extensive, the pon-tics will not have an aesthetic relationship with thealveolar ridge (Fig. 20.7). The patient shown inFig. 20.7 had difficulty with speech because air es-caped through the teeth as well as having food par-ticles collecting in the gaps. The bridge required re-making with the incorporation of pink ceramic at thenecks of the pontics to ‘seal’ them to the alveolarridge.

Pre-Operative Considerations forConventional Bridgework

The patient

The patient must be well motivated and clearly in-formed of his responsibilities in maintaining the pro-posed restoration and understand the sequence of ap-pointments and what is to be achieved at each. Hemust be capable of maintaining good plaque controland any caries, periodontal disease and poor restora-tions must have been stabilised.

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(a)

(b)

(c)

Metal sub-frame

Connector

Ceramic

Alveolar ridge

Fig. 20.6 Features of bridge pontics. (a) The ridge contact of a premolar pontic. Ceramic covers the soft tissue, (b) Theembrasure spaces are made wide enough to allow cleaning, (c) Superfloss being used to clean the embrasures and fittingsurface of an anterior pontic.

The occlusion

A pre-operative occlusal analysis should have beenperformed (Chapter 14) and consideration given topossible tooth movement in order to achieve morefavourable tooth relationships.

Fig. 20.7 A bridge replacing 21| where there isconsiderable alveolar resorption. The spaces between thepontics are unaesthetic, collect food debris and interferewith speech. The bridge needs to be remade with pinkceramic blocking the spaces.

Orthodontics has an important role to play inmouth preparation where there are malposed teeth oruneven spacing, particularly anteriorly. Uneven spac-ing is illustrated in Fig. 20.8. The two spaces havebeen ‘collected’ into the correct place for a singlepontic.

Equilibration of pre-centric prematurities is desir-able on those teeth that are destined for preparation.If a prematurity is removed by the preparation with-out knowledge of its relationship, the occlusal patterncan be changed leading to loss of occlusal clearanceof the preparation (Chapter 14).

The pattern and strength of occlusal function inlateral and protrusive excursions is of great impor-tance in anterior bridgework. For example, an upperlateral incisor can be replaced as a cantilever bridgefrom the canine in favourable cases. But this designshould not be used if the pontic will receive lateralstresses from the lower incisors in lateral excursions.This would result in unfavourable rotational forcesbeing applied to the canine. In these circumstances,the bridge should either have positive canine guid-ance, thereby discluding the lateral incisor pontic, or

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(a) (b)

Fig. 20.8 Pre-bridge orthodontics. (a) The uneven spacing caused by the loss of one central incisor would makebridgework difficult; (b) the lateral incisor has been retracted by a simple appliance and the single tooth space can now berestored with a cantilever bridge.

involve the central incisor as well in a fixed–fixed de-sign (Fig. 20.9).

Abutment tooth assessment

The biological integrity of all the teeth must be clearfrom the start. Those teeth to be included in the bridgeshould not have pulps of dubious vitality nor have anyroot fillings of questionable prognosis.

Loss of periodontal support does not in itselfpreclude the use of particular teeth as retainers,but the disease must be controlled and stable. Thiswill involve a thorough periodontal assessment andassociated therapy. If the patient has worn a partialdenture before bridgework was contemplated, there

Fig. 20.9 The |2 has been replaced as a cantilever bridgefrom the |3. In left lateral excursion, the pontic takes all theload and transmits this as rotational forces to the canine,which was painful. The bridge should have been made tomaintain canine guidance.

may be gingival complications if the denture was tis-sue borne. This has been discussed in Chapter 13.

These points, then, imply that a very thorough ex-amination of the mouth aided by vitality tests andradiographs (Chapter 2) is essential prior to the pre-scription of bridgework.

Teeth that are provisionally designated for retain-ers should have any restorations of unknown originor quality removed, and the remaining tooth exam-ined to determine its physical and biological state(Fig. 20.10). Even if the restoration’s natural historyis well known, it must be assessed for its possibledurability under a retainer when prepared. A simple

Vitality testRadiograph

Open and investigate

Remove coronal restorationsRemove caries

Pulp OK Pulp dead or dubiousInsufficient dentine

Root canal therapy

Impossible

Avoid use with bridge

Pulp OK

Posteriortooth

Pinned core

Anteriortooth

Post/core

Fig. 20.10 The treatment of potential abutment teeth.

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example is the replacement of a non-pinned amalgamby a pinned core because the tooth substance provid-ing the retention of the former might well be removedduring preparation.

Aesthetics

The provision of good aesthetics is clearly an impor-tant goal for both the patient and the continuing rep-utation of the clinician!

The basic design outline will detail those areas to betooth coloured and those to be constructed in metal.The patient should be aware of and approve such rec-ommendations. Now further consideration must begiven to the particular characteristics of tooth colourand position. The technician must be involved at thisstage so that he can give advice about any shadematching problems that might dictate a change in de-sign or might require special techniques.

If the existing tooth shape and position is satisfac-tory for appearance and function, then this must becopied exactly. This original template may be in theform of a denture or a semi-permanent resin-retainedbridge. However, if a change in aesthetics is proposed,then this needs to be clearly defined at the planningstage.

Small changes, such as the closure of a diastema,can be easily accomplished, but major changes, suchas reduction of overjet, are far more complicated. Thismay involve elective devitalisation of teeth outside theproposed arch line, together with post and cores, and,worse still, the positioning of retainers or pontics inzones where tongue activity may make them unstable.

This type of major cosmetic change should only beattempted when the patient’s objectives and motiva-tion are clearly established, and the clinician is clearin his own mind that these can be satisfied. Additionalabutments will need to be included in the design towithstand the unfavourable muscle forces.

The management of aesthetics is discussed in moredetail in Chapters 21 and 23.

A word of warning – dentists and plastic surgeonsare prone to the attention of perfection seeking indi-viduals. If the patient appears to be making unrea-sonable or strange demands, the dentist should besuspicious. It is better to refuse to provide treatment,tactfully.

Basic Bridge Designs

Much (if not all) bridge design is empirical, basedon the accumulated, acquired wisdom of clinical

experience, or simple personal prejudice! As has al-ready been stated, very little objective work has beencarried out on the biomechanics of the subject and it isdoubtful as to how much in the way of physical lawswould be appropriate in an area that is so dependenton biological status and response. It is a truism to saythat every case is different.

A few basic guidelines can be advanced, such as:

� Keep designs as simple as possibleFor example, if two upper incisors are being re-

placed, make two three-unit bridges, rather thanone six unit

� Use canine or molar teeth as abutments whereverpossible

� Avoid upper lateral incisors as strategic abutments

The experience with resin-retained bridgework dis-cussed earlier has led to the use of fewer abutmentsfor crown-retained bridges and single crown-retainedsingle pontics are used to replace incisors, canines andpremolars.

However, the upper lateral incisor must be avoidedas a single abutment; its root is not sufficiently sub-stantial. If a central incisor cannot be retained by theother central, then it is necessary to involve the canineand construct a three-unit bridge.

Perhaps the principal limiting factor in crown-retained bridgework is the condition of the poten-tial abutments. Longevity studies show that posts andcores are the worst retainers and of course the qual-ity of the root filling is yet another problem. Dubiouspulps should be avoided.

As will be discussed in Chapters 22 and 23, theuse of implants removes the uncertainty of usingteeth of dubious quality to support expensive restora-tions. The days of extensive crown-retained bridgesare numbered!

Precision Retainers

Simply, these are connectors that retain dentures with-out the use of externally visible clasps. The denturemay be a complete denture or a partial, unilateralor bilateral. The unilateral partial denture is some-times called a removable bridge. This is consideredto have an advantage over a conventional bridge inthat it is partly tissue borne, and therefore largerspans can be contemplated. Again, this is an empiricaldecision.

Precision retainers consist of two precisely inter-locking parts, a male and a female, one of which is sol-dered into the retaining crown and the other which is

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processed into the denture. The part fitting the retain-ing crown may be intra or extracoronal. The intra-coronal type requires a more extensive tooth prepa-ration to accommodate it within the crown profile.

There are many designs, most named after theirinventors. Some include internal springs and stressbreaking devices, and others fix the denture perma-nently by means of minute screws. They were devel-oped in the late nineteenth century when many den-tists believed that all prostheses needed to be removedfor cleaning and fixed bridgework was decried for thisreason.

Precision retainers are expensive and technicallydemanding to use, but do have advantages in a fewparticular cases. Where there has been extensive alve-olar loss, denture base material is often necessary tomake up the deficiency and this can be retained byadjacent teeth without an extensive denture base andclasps. Larger partial dentures may be aestheticallymore pleasing without clasps, but teeth having theprecision retainers on them must be splinted for sup-port to other teeth, thus making the overall treatmentplan complicated, costly and technically demanding.

The use of precision retainers in complete denturesis discussed in Chapter 26.

Special Problems

Cleft palate

With modern orthodontic and plastic surgical man-agement of the cleft palate, the cases with massive

Design of Conventional Bridgework – Summary

Much of bridge design is empirical.

The important considerations are choosing abutment teeth that are biologically and structurally sound andhave healthy periodontiums.

Full assessment of the occlusion and tooth alignment using a diagnostic mounting is essential.

Full crown retainers of gold or ceramic fused to metal are the simplest and most reliable retainers.

Malaligned teeth may be incorporated in bridgework after re-alignment by pre-operative orthodontics orby using assembly joints or copings.

crown work to retain obturators are a thing of thepast. The cases treated by modern techniques, though,may require crowning of teeth which are malalignedin the cleft, or bridges to replace missing teeth in thecleft area, particularly the lateral incisor.

Bridgework design must be modified so that thebridge is not fixed on either side of the cleft. Thisapplies equally to resin-retained bridges and conven-tional bridges. The cleft may only be stabilised by fi-brous tissue, and movement between the maxilla andpremaxilla is possible. The forces generated by suchmovement will be easily sufficient to debond a resin-retained bridge of a fixed–fixed design, and cantilevertypes will be more reliable.

Hypodontia

Congenitally absent teeth can present considerablerestorative problems. The common occurrence ofmissing upper lateral incisors and retained deciduouscanines was discussed in Chapter 16.

Cases with several missing teeth are usually associ-ated with considerable drifting of the other teeth andthese usually have small crowns. These cases must betreatment planned with the orthodontist to discusstooth movement into more favourable positions tosupport bridgework. If each missing tooth can havea natural tooth on each side, and these natural teethhave reasonably sized crowns, then bridgework willbe possible. Larger spaces coupled with small crownswould be treated ideally by using implants but usuallycommits the patient to partial dentures.

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Chapter 21Fixed Prosthodontics: ConventionalBridgework – Clinical Procedures

The decision to construct a bridge has been made and its design decided. The abutment teeth are stable withappropriate foundations in place. This chapter discusses the clinical, practical stages in bridge construction.

The sequence of clinical stages in constructing abridge is:

1 Pre-operative diagnostic mounting and model sur-veying

2 Register shade and plan provisional bridge3 Preparations4 Working impression5 Occlusal registration6 Try-in and trial cementation7 Permanent cementation8 Review and recall

Pre-Operative Diagnostic Mounting

The original diagnostic mounting may be adequatefor this stage, but, if any teeth have been equilibrated,or major changes in tooth contours have been madeby cores, then new impressions should be taken anda new mounting made.

The mounting should be in centric occlusion unlessthis position cannot be defined accurately. In this casecentric relation will be used (see Chapter 14).

The occlusal registration for a centric occlusionmounting should be without an inter-occlusal recordif at all possible. The orientation of the models to theposition of best fit, together with checking this po-sition against the patient, marking it and mountingshould be satisfactory for most patients.

If missing teeth prevent the accurate orientationof the models, then occlusal rims will be necessary,but these should be adjusted carefully to ensure thatcentric occlusion is being recorded, and not a po-sition influenced by the presence of the rims in theocclusion.

If there are enough teeth, but the position is impre-cise, two ‘islands’ of registration material, one in eachquadrant of the lower arch, will provide the minimum

interference with closure, and will locate the modelsaccurately for mounting with tooth to tooth contact.

The incisal table should be customised to the pro-trusive and lateral excursions (Chapter 14).

The mounting will provide a record of centric oc-clusion before it is destroyed by tooth preparation,and will be the basis for the provisional bridge. Ac-curate surveying to decide the path of insertion willbe done and a duplicate mounting will allow trialpreparations to be carried out as a rehearsal to pre-dict problems of angulation and paralleling.

Shade and Provisional Bridge

The shade and tooth characteristics should berecorded at the planning stage, particularly beforeteeth are cut.

The provisional bridge must also be planned beforethe teeth are cut. Its functions are:

� Protection of cut dentine� Maintenance of the occlusion� Maintenance of gingival health� Restoration of aesthetics� Maintenance of abutment position and in some

cases� Diagnosis of changes to the occlusion and/or aes-

thetics

The provisional bridge may be made at the chair-side after the preparations have been completed orin the laboratory either before or after the prepara-tion stage. The majority will be polymeric, but spansof more than four units will need a metal sub-frameand polymer facings for durability. The provisionalmay be in use for as long as six weeks and thereforeneeds to be constructed carefully.

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21. Conventional Bridgework – Clinical Procedures 227

Chairside construction of provisionals is appro-priate for short spans of uncomplicated bridgework.These may only be in place for a matter of a coupleof weeks, and for this relatively short period, the in-ferior aesthetics and lower strength are not usually aproblem.

Chairside construction technique

The pre-operative model is used as a template withthe shape of the pontics and retainers being providedeither from the diagnostic waxing or from the addi-tion of denture teeth to the model. The areas of thebuccal and palatal surfaces that will have minimal re-duction should be overcontoured by adding wax sothat eventually this will be reproduced in the provi-sional as thicker walls. Without this, the overlyingpolymer would be too thin for adequate strength.

An impression is made of the area of the bridge insilicone putty. Only a sectional impression is required,but this must extend by at least one tooth either side ofthe abutment teeth so that the impression, or mouldas it is to become, can be stabilised in the mouth. Arefinement of the technique is to use a vacuum formedpolymer sheet that is moulded to the pre-operativemodel or diagnostic waxing.

At the chairside, following the completion of thepreparations, the seating of the mould is checked foraccuracy, gingival retraction cord placed to protectthe gingival tissues, a smear of petroleum jelly ap-plied to the dentine surfaces and a self-curing poly-mer, preferably one designed for provisional bridges,mixed and syringed around the necks of the preparedteeth and into the mould. The filled mould is seatedonto the teeth, located correctly and left in place untilthe initial set of the polymer has occurred. The mouldis then removed together with the new bridge and itsexcess. The excess is trimmed carefully back to thepreparation margins and the pontic gingival marginsrounded. The embrasures, particularly at the cervicalmargins, must be cleared carefully.

The bridge is replaced onto the teeth, and themarginal adaptation checked. The occlusion is thencorrected using abrasive points following identifica-tion of inaccuracies with shimstock and articulatingpaper. Additions can be made easily to the polymeras necessary (Fig. 21.1a).

Laboratory construction technique

The all-polymer bridge can be made by flaskingthe waxed trial preparations model, perhaps having

incorporated denture tooth facings as appropriate,and processing in the same way as a denture. Atthe chairside, the fit of the bridge is likely to be in-accurate because the free-hand cutting of the teethis unlikely to match the free-hand cutting of themodel. The bridge will therefore need to be relinedin polymer on the preparations to achieve accuracy(Figs. 21.1b,d).

The metal-based bridge, whether cast in silver, stu-dent’s alloy or even bonding alloy, requires exactlythe same technique as that required for the finalrestoration. It needs to be made from an impres-sion of the finished preparations as quickly as pos-sible, with an all-polymer bridge made at the chair-side as a very temporary intermediate restoration(Fig. 21.1c).

If the provisional has been used to verify a newocclusal scheme and has been adjusted for this or fortooth shape and position, an impression of the archincluding the bridge must be taken and remountedto the existing mounted opposing model. The incisaltable should then be re-customised.

Preparations

Whilst each abutment will be prepared in accordancewith the basic principles discussed in Chapter 15, themajor consideration in most bridgework is achievinga single path of insertion for the bridge.

The desired path of insertion should be decidedfrom the diagnostic mounting using a model surveyorand the path should be marked on the model abut-ments. If an assembly joint is to be used with differ-ent paths for each abutment, these paths can again bemarked on the model.

In short span bridges, with two or three abutments,the path can usually be transferred to the mouth byeye, with extreme care being taken to keep the bursin this single path whilst cutting.

For longer spans and multiple abutments, someadditional help will be necessary. Proprietary paral-lelometers can be purchased, the simplest being a pairof parallel pins on an extending arm.

This may not be sufficient for cross-arch work andsome reference device can be made for the particularpatient in the laboratory. A flat sheet of 4-mm acrylicsheet is trimmed to fit the arch to be prepared, andmodified with cold curing acrylic to locate to the oc-clusal surfaces accurately. It should extend laterallybeyond the buccal surfaces of the abutment teeth byabout 2 mm.

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(a)

(c) (d)

(b)

Fig. 21.1 Provisional bridges. (a) Polymeric, chairside made type. This has very bland aesthetics and has to beovercontoured for strength. It is satisfactory for short spans, or for a few days whilst a more accurate provisional is made,(b) and (d) All polymer, laboratory constructed type. The labial aspects are made from denture tooth facings and theremainder is made from a waxing and hydroflask-cured acrylic. This is suitable for trying new occlusal schemes andchanges in aesthetics. If it is made from trial preparations on the diagnostic mounting, the retainers will need rebasing in themouth with the addition of cold curing acrylic. Laboratory-cured composite is also satisfactory, (c) Cast silver/polymer type.This is necessary for long spans. The incisors are denture tooth facings, retained to the metal by hydroflasked acrylic. Theocclusion and aesthetics can be checked accurately on this type of provisional.

The model is mounted on a surveyor whose sur-vey rod is aligned with the chosen path of insertion.The acrylic sheet is placed on the model and holesare drilled by a surveyor-mounted handpiece to lo-cate pins at the side of each abutment. The pins canbe screwed in, or glued by cyanoacrylate cement. Thisdevice will locate in the mouth to indicate the desiredpaths for each abutment.

Additional help can be provided during the toothpreparation by cutting the teeth roughly and thentaking an alginate impression. This is cast in plastermixed with hot water for a rapid set, and the resultingmodel checked with a surveyor for accuracy of paral-

leling whilst the patient remains in the chair and thenhas the preparations defined finally afterwards.

The presence of posts and cores in the design can beused to aid paralleling. Preparation for the posts is thefirst stage and an impression is taken of the post holes.The cores can then be waxed parallel to the predictedpath of insertion (Fig. 21.2a), and when cemented,provide a very accurate guide for the preparation ofthe other abutments (Fig. 21.2b).

Modification to the basic design of abutment pre-parations is also necessary in the connector region.Tooth removal should be increased here to provideadditional strength in the subsequent casting. Where

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(a) (b)

Fig. 21.2 (a) Waxing the cores for an anterior bridge. The model has been mounted on a surveyor to align the coresprecisely with the chosen path of insertion, (b) The cores cemented. The bridge is to replace 21|1 from 43|23, and thepreparations have been completed using the cores as alignment guides. Note the shape of the vital tooth preparations givinggood retention and the contour allowing correct thickness of ceramic. Note also the lack of gingival trauma after preparation.

precision retainers or other non-rigid connectors areto be used, box preparations will usually be necessaryto accommodate them.

Impression and Shade

These have been dealt with in Chapters 16 and 17.


Centric occlusion is required, with clear tooth totooth contacts. If a position of ‘best fit’ is still present,in spite of occlusal reductions, this should be usedwithout an inter-occlusal record; reproduction ofthe position from the pre-operative mounting will bepossible.

If centric occlusion has been lost by the tooth prepa-ration, then the most accurate method of registra-tion is by registration copings. These are shells ofacrylic or metal that fit the prepared teeth accuratelyand onto which cold curing acrylic is added to reg-ister the tooth relationships (Fig. 21.3). The copingcan be made on the master die and used to checkthat the preparation margins have been accurately re-produced. Metal, such as cast silver, is better thanpolymer for this purpose if the margins are reallyquestionable.

Alternatively, copings can be made intraorally onlubricated preparations by free-hand application ofpolymer and the occlusion registered at the same time.Clearly, these cannot be used to check margins.

The master model, when completed, is mountedto the untouched opposing arch of the pre-operativemounting. A further face-bow registration is thereforenot necessary.

Articulator angles will have been determined fromthe diagnostic mounting and can be set again for themaster models. However, when constructing crownsand bridges, it is common to use condylar angles thatare slightly lower than average. This has the effectof making cusp heights lower, cusp slopes shallowerand fossae more open. Therefore, the likelihood of in-troducing occlusal interferences unwittingly is muchreduced.

Upon completion of the impression and registra-tion, the provisional bridge should be cemented witha weak ZOE cement, or a proprietary temporarycement.

Try-in

This is possibly the most critical stage, wherein the es-tablished errors are either seen and accepted, or com-pletely missed. It depends on the level of perfectionand perception of both the dentist and the technicianas to what passes and what is rejected. Only the ob-vious needs stating – the larger the errors, the less thechances of success for the restoration.

Metal sub-frame

The try-in of the metal sub-frame before the additionof ceramic has several advantages:

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(a)

(b)

(c)

Fig. 21.3 Laboratory-made copings of pattern acrylic for occlusal registration. (a) Occlusal view; (b) buccal view inocclusion; (c) occlusal view of registration imprints.

� The accuracy of the casting can be checked. If thereare errors, then the time and cost of adding theceramic to a deficient base are avoided

� The localisation between abutments can bechecked and changed if necessary without jeop-ardising the ceramic by resoldering

� The occlusion can be checked and adjusted with-out damaging the ceramic glaze

For short spans, where the dentist and technician areconfident in the impression, then a metalwork try-in could be omitted. For longer spans there shouldalways be one (Fig. 21.4). Now that the use of shoul-der ceramics is routine, the metal sub-frame does notneed to extend to the outer edge of the shoulder.However, for the purposes of a metal try-in the tech-nician should extend the metal to the outer edge ofthe shoulder so that the fit can be checked. This excessmetal will be cut back before the ceramic is added.

Where one retainer fits and the other(s) does notseat fully, there can be a localisation error. The bridge

Fig. 21.4 A metalwork try-in showing the examination ofthe margins.

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(a)

(c)

(b)

Fig. 21.5 Relocalisation of a metal sub-frame. (a) The try-in did not seat on the premolar. The bridge has been sectionedbetween the pontic and the premolar retainer, and now seats correctly. (b) A zinc oxide–vaseline paste has been applied tothe fitting surfaces to stabilise the bridge during application of the fluid acrylic. (c) The acrylic must be extensive to makesure that there is no movement upon removal of the bridge and during its journey to the laboratory.

should be sectioned carefully into individual pieceswith one connector being maintained to hold eachpontic. Each retainer should be tried on its abutmentindividually (Fig. 21.5a). If each seats accurately, thenew arrangement should be fixed by the addition ofcold curing pattern acrylic in the mouth.

To stabilise the retainers for this procedure, a smallamount of non-setting paste, e.g. zinc oxide in Vase-line, should be applied to the retainers’ fit surface (Fig.21.5b). A non-residue, burn-out pattern polymer isthen carefully applied to the sectioned joint to sta-bilise it rigidly (Fig. 21.5c). The relocalised bridge isthen removed, cleaned and returned to the laboratoryfor soldering.

Failure of a sectioned retainer to seat requires a newimpression after the preparation has been inspectedcarefully for undercuts. These may have created animpression fault not seen on the die.

If the dentist is at some distance from his labora-tory, relocalisation may be impractical and it is thenmore common for a complete new impression to betaken.

Final bridge

The bridge should be examined carefully with theteeth dried and isolated, and where possible, a packin place to prevent loss of the bridge into the pharynx.The following must be checked:

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� Marginal adaptation of retainers� Retention and stability� Integrity of contact areas with adjacent uncut teeth� Adaptation of the pontics to the soft tissues� Occlusal relationships in centric occlusion, centric

relation and excursions� Aesthetics – colour, shape and tooth position� Speech� Patient approval

Marginal adaptationA probe should traverse all the margins smoothlyfrom tooth to retainer without catching. Positiveedges can be trimmed back, but negative edges area deficiency and the retainer must be modified orremade. If the master die does not reproduce thedefective margins, then a new impression of theproblem abutment is needed. The new die can berelocated alongside the satisfactory dies in a newmodel and the new retainer soldered into the newrestoration.

If the margin was reproduced on the original die,then ceramic could be added to the retainer. Soldering,though, to build out a deficient metal margin is notusually acceptable.

If a retainer is not seating onto the abutment mar-gin, then the following should be checked:

� Fit surface of preparation – temporary cement re-maining

� Fit surface of retainer – ceramic present, castingexcess from airblow in investment

� Contact areas – tight, preventing seating� Movement of abutments under provisional bridge� Localisation of retainers – one seats and the

other(s) lifts off

The first four are fairly easy to overcome. Carefulinspection will reveal extraneous material and use offloss will demonstrate tight contacts.

Small tooth movements may have occurred whilstthe provisional bridge was in place. This may be dueto occlusal forces or due to slight displacement by thetemporary cement. Not every bridge seats home ex-actly at the first attempt, and small discrepancies canbe overcome by ‘stressing’ the periodontal ligamentby alternate loading and releasing.

Cotton wool rolls or a tongue spatula may beplaced on the occlusal surface of the bridge, and by

alternate clenching and relaxing, the patient can in-duce minor movements of the abutments. This worksonly for small seating problems.

Retention and stabilityThe bridge should not be dependent on its cementlute for retention. Looseness may be caused by over-tapered preparations or poor adaptation of castings.The fit of the individual dies on their retainers shouldbe checked and if these are loose, the bridge should beremade. If the dies are tight, then an impression faultis possible; the impression will need to be retaken afterchecking the parallelism of the preparations.

The bridge should not rock when pressure is ap-plied to each retainer and if it does there is likely tobe a casting error on an individual retainer or seatingproblems referred to earlier.

Contact areasCheck these with floss. A correct contact allows flossto ‘click’ through on pressure. Slack contacts will re-quire the addition of solder or more ceramic to correctthem. Tight contacts should be eased and repolished.

Adaptation of ponticsThe pontic should touch the underlying soft tissuelightly on insertion of the bridge. The neck of thepontic should blend smoothly with the alveolar ridgeto promote natural cleaning during function.

Occlusal relationshipsOcclusal stability should be checked by marking eachnew cusp/fossa relationship with articulating paperand checking that each holds shimstock on light clo-sure. The natural cusp/fossa relationships should alsobe checked with shimstock to ensure that the bridgeis not preventing even occlusion elsewhere.

Check mandibular closure on the retruded arc ofclosure to centric relation to ensure that the bridge isnot introducing new pre-centric premature contacts.

Adjust cusp slopes or fossa width but not support-ing cusp height, as the removal of the cusp tip willalso remove occlusal stability.

Check lateral and protrusive excursions for free-dom of movement and for the presence of non-working interferences. If the bridge is reproducing ca-nine guidance, this must be steep enough to discludethe non-working side. If interferences are introduced,the bridge must be modified, rather than equilibratingother teeth. Similarly, incisal length should provide

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(a) (b)

Fig. 21.6 (a) A non-working interference in protrusion (arrowed). The patient has a provisional bridge at 21|1. In protrusionthe incisal edges are not in contact because of the interaction between |3 and |4. The choice is either to lengthen theincisors to disclude the interference or to equilibrate. (b) In this case, the appearance was satisfactory and therefore theinterference was equilibrated.

enough depth of incisal guidance to disclude the pos-terior teeth (Fig. 21.6).

AestheticsThe patient should be the final arbiter of the appear-ance. Aesthetics were discussed in Chapter 16.

SpeechA standard passage of prose to be read by the pa-tient can be used, but it is better for natural speechto be the deciding factor. This means a period of trialcementation.

Trial Cementation

Once a bridge is cemented permanently, the modifica-tions that can be done subsequently are very limited.Therefore, it is better to fit the bridge with a weaktemporary cement and allow the patient to try it forabout 4 weeks for speech and function, and for theother members of the family to approve the appear-ance.

The patient must be warned, though, of the weak-ness of the cement, and to return immediately if thereare any symptoms. This will usually mean cement fail-ure in a retainer.

Permanent Cementation

The patient’s opinion and experience are discussedafter the trial cementation, and the occlusal relation-ships rechecked. Modifications to tooth shape, colourand size are possible by refiring the ceramic. This maymean the refitting of the provisional bridge, whilst thepermanent one is away in the laboratory.

If further modifications are made or the patient hasany reservations, another period of trial cementationis indicated.

Only when all are satisfied should the bridge becemented permanently. After the cement has set,check the marginal adaptation again and clean ex-cess cement from the embrasures and from under thepontics.

Teach the patient the appropriate oral hygiene pro-cedures (Chapter 20).

Review and Recall

Finally, check the bridge again a week or two aftercementation and make sure the patient is perform-ing the oral hygiene required and that there are noproblems with this. The bridge should be examinedagain 6 months later and the apical condition of allthe abutments reviewed radiographically at 1 yearafter fitting. Further radiographs should be taken

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routinely every 4 years or so. Silent pulp death andapical infection of abutment teeth are possible.

Anterior Bridgework

This presents the dual problems of combining aes-thetics with function. It is an important part of bridge-work, since the cosmetic aspect is a strong motivatingfactor for the patient. This, coupled with the desire tobe rid of the intrusion of a partial denture, providesa demand which can only be satisfied by the highestclinical and technical standards. The ability to makegood anterior bridgework is a good practice builder;the converse is also true.

The patient will either have a partial denture or anintermediate bridge and there are two possible lines oftreatment. The existing prosthetic teeth may be satis-factory from the aesthetic and functional viewpoint,in which case they should be copied exactly in com-bination with the new retainers.

On the other hand, one or both aspects may beunsatisfactory and this will necessitate more in theway of diagnosis and planning and a longer stage withthe provisional bridge.

Replacement of existing aesthetics andfunction

Where the patient is to have a denture or bridge re-placed that has satisfactory aesthetics and function,the sequence following stabilisation is:

1 Diagnostic mounting and examination of theocclusion with old prosthesis included

2 Customise the incisal guidance table of the articu-lator

3 Provisional bridge, tooth preparations4 Provisional bridge approval5 Final bridge – trial cementation and permanent

cementation

Changing aesthetics and/or function

Where the existing teeth and/or function are unsatis-factory, the sequence is:

1 Diagnostic mounting and examination of theocclusion

2 Diagnostic waxing to establish new aestheticsand/or function

3 Customise incisal guidance table to diagnosticwaxing

4 Preparations and impression, chairside provi-sional

5 Construct provisional bridge on master model todiagnostic waxing

6 Check function and aesthetics of provisional,modify if necessary

7 Approval of provisional8 If modifications have been made, impression of

provisional in situ9 Articulate model of approved provisional, re-

customise incisal guide10 Mount master model, construct final bridge11 Trial cementation12 Permanent cementation

Improving poor aestheticsThe re-establishment of original aesthetics when thesehave been changed by a poor bridge or partial den-ture will be greatly helped by old photographs of thepatient. Figure 21.7a shows a case where the uppercentral incisors were originally replaced by a partialdenture following trauma. Some years later, the pa-tient’s general dental practitioner offered her a bridgeinstead of the denture.

The bridge design was a six-unit fixed–fixed bridgefrom the upper lateral incisors and canines. Thebridge was fitted, apparently without the patient’sagreement, and this is shown in Figs. 21.7b,c. Thepatient was unhappy with the appearance and if thisis compared with the old photograph reproduced inFig. 21.7a, it can be seen that the incisor angulationhas been changed. The shade was also incorrect; thenew bridge was Vita A1 in comparison with the shadeof the adjacent teeth that was C2.

The sequence for the management of the casewas that described earlier for changing aestheticsand function. Following the visit for the diagnosticmounting, the old bridge was removed by cuttingeach retainer with a serrated tungsten carbide bur (JetBeaver). The underlying preparations were inspectedand checked for vitality and were found to be satis-factory. An impression was taken and a ‘temporary’provisional bridge made at the chairside.

With the aid of the old photograph a provisionalbridge was made in the laboratory on the mas-ter model. It was fitted at the next visit with tem-porary cement. The patient wore this for 4 weeksand returned with the approval of her family andherself.

An impression was taken of the provisional bridgein place and the model from this provided the guidefor the technician for the tooth shape and position.

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(b)

(a)

(c)

Fig. 21.7 Unsatisfactory replacement of a partial denture by bridgework 1. (a) The patient seen in a family photograph witha partial denture replacing 1|1, (b) and (c) The first bridge showing poor contour and shade.

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(a) (b)

Fig. 21.8 Replacement of the bridge shown in Fig. 21.7.

The bridge design was changed for simplicity froma single six-unit bridge to two three-unit cantileverbridges. The trial cementation was uneventful andthe bridges were cemented permanently 4 weeks later(Fig. 21.8).

Alveolar resorption

The case described above has the pontics touchingthe edentulous ridge directly and, because there hasbeen little resorption, the mucosa appears as naturalgingival tissue in the pontic embrasures.

Where there is more resorption, as was seen in thecase shown in Fig. 20.7, the embrasures need to befilled with pink ceramic to eliminate the dark spacesseen between the pontics (Fig. 21.9).

The case shown in Figs. 18.12 and 18.13 illus-trated the problem of aligning the incisors in re-lation to more alveolar resorption. The angulationof the incisors with their tips in the correct place andthe necks against the resorbed alveolus leads to poor

aesthetics. This case had a diagnostic articulation andpre-operative periapical radiographs. The old bridgewas removed in one piece and the condition of theabutments (vitality, coronal dentine) checked.

Fig. 21.9 Bridge replacing the upper incisors. Pinkceramic has been incorporated in the embrasures to hideminor alveolar resorption.

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(a) (b)

Fig. 21.10 Replacement of the bridge shown in Fig. 18.12. (a) A provisional denture has been made to establish the correcttooth position; (b) the tooth position incorporated in an acrylic provisional bridge.

(a)

(c)

(d)

(b)

Fig. 21.11 (a) Labial view of the permanent bridge at the trial cementation stage, showing pink ceramic replacing lostbone, (b) Palatal view showing the line of the arch and its relationship to the incisive papilla, (c) The patient, (d) The oldbridge shown again for comparison.

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(a)

(c)

(b)

Fig. 21.12 (a) This case has extensive alveolar resorption and 21|12 have been restored by a precision retained denturewhich is very worn; (b) wax-up of a provisional denture to establish the correct tooth position, (c) Provisional denture inplace. The crowns on 43|34 have been removed, the preparations inspected and the crowns replaced with periodontaldressing to promote resolution of gingival inflammation.

The next stage was to establish the correct posi-tion for the incisors. This is most easily done using aprovisional partial denture. An impression was takenafter removal of the bridge and the old bridge re-placed with temporary cement. At the next visit, thewax-based provisional denture was tried in and thetooth position checked. This can be changed easily ifnecessary and it is possible to replace the tooth mouldif the size and shape is wrong.

The processed denture was fitted at the next visit(Fig. 21.10a), and the old bridge was sectioned toprovide temporary crowns for the abutments. Theupper right canine, which was non-vital, was left asa root with an overdenture tooth; this allowed moreflexibility in the position of the teeth. Three weekslater, the patient agreed to the new tooth positionand the denture was replaced by a provisional bridgewith the shape copied from the denture (Fig. 21.10b).

The upper right canine was prepared for a post andcore.

When the bridge was approved by the patient, amodel of it was mounted on the articulator and the in-cisal guide customised. To customise the incisal guide,cold curing acrylic was placed on the incisal table,and whilst soft, the incisal pin was moved in it withthe tooth to tooth contacts being maintained in pro-trusion and lateral excursions. When hard, the tablereproduced the movement paths that were guided bythe provisional bridge contours (see Chapter 14).

The permanent bridge was then constructedthrough the stages of post/core cementation, impres-sion, metal try-in, trial cementation and permanentcementation (Fig. 21.11).

If there is even more resorption then the use ofsimple pontics will be difficult. Then it would be

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(a)

(c) (d)

(b)

Fig. 21.13 (a) and (b) New soldered crowns with Mini-Dalbo precision retainers. Note the extent of the alveolar resorption,(c) and (d) The removable bridge in place.

better to use a denture base to make up the tissue lossand this can be incorporated in a precision retainedremovable bridge, rather than use a partial denturebase.

The original denture (Fig. 21.12a) was worn andthe tooth position was not correct. The new tooth

Clinical Procedures for Conventional Bridgework – Summary

Detailed planning on an accurate diagnostic mounting is essential.Planning will involve choice of the path of insertion, retainer and pontic design.A provisional bridge will be needed to stabilise the abutments and restore aesthetics and function.Retentive preparations parallel to the path of insertion will provide stability for the final bridge.Use occlusal registration copings for accuracy of articulating the master model.The try-in stage will reveal deficiencies in the fit and occlusion of the retainers and pontics.Aesthetics must be approved by the patient; always use a trial cementation phase.Always choose bridge designs that are simple.

position was established by a provisional denture(Figs. 21.12b,c). The retainers on the upper ca-nines and first premolars were replaced as solderedunits with Mini-Dalbo precision retainers attached.The final denture, or removable bridge, is shown inFig. 21.13.

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Chapter 22Fixed Prosthodontics: Basic Principlesof Implants

Intraosseous implants are now well established for the support and retention of crowns, bridges and re-movable dentures.

This chapter describes the basic principles associated with their use.

Historical Background

In 1941, Gustav Dahl introduced the sub-periostealimplant. This was designed for the treatment of pa-tients with edentulous mandibles and consisted of ametal frame of vitallium (cobalt chromium molybde-num) fitted on the surface of the bone of the mandiblebelow the periosteum. The technique involved surgi-cal exposure of the boney ridge followed by an im-pression of it. The vitallium framework was made ona plaster model and was placed in the patient at a sec-ond surgical procedure. Such subperiosteal implantsproved to have moderate success.

The first commercially available intraosseous im-plants were called blade implants, which were blade-shaped and generally made of steel. Initial cuts weremade in the bone and the blades were tapped in with amallet. These blade implants were designed more forsingle tooth replacement or short-span bridgeworkrather than denture support. Again they were mod-erately successful and there are many still in functiontoday.

Professor P. I. Branemark is regarded as the fore-father of modern dental implantology. Whilst under-taking microscopic studies of vital rabbit femurs, hediscovered a unique bond between titanium view-ing chambers and the bone. He described this bondas osseointegration, which he defined as ‘a directstructural and functional connection between orderedliving bone and the surface of a load-carrying im-plant’.

Branemark and co-workers undertook a 15-yearstudy between 1965 and 1980 in which they treatededentulous patients using machined titanium im-plants with high levels of success. The reported suc-

cess rates of the implants were as high as 81% in themaxilla and 91% in the mandible over this 15-yearperiod.

Terminology

Implant

The implant is the intraosseous portion of the wholedevice. It can also be termed a fixture. Impressionstaken of the implant head are called fixture-level orimplant-level impressions.

Abutment

The abutment is the transmucosal portion that con-nects the implant to the restoration, e.g. a crown, ora bridge. Abutments are available in a choice of ma-terials of which the most common are titanium, zir-conium, gold and alumina. The combination of theimplant fixture and a separate abutment can be de-scribed as a two-piece implant.

Osseointegration

The process by which bone is formed against the im-plant after its surgical insertion. At this stage the im-plant is often covered by mucosa.

Healing abutment

This is placed on the implant head following exposureof the implant after osseointegration or at the time ofimplant placement. It allows healing of the gingivaearound the implant prior to provision of the implantrestoration.

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22. Fixed Prosthodontics: Basic Principles of Implants 241

Crown

Abutment

Abutment screw

Implant

Fig. 22.1 External connection type implant.

Platform

The platform is the head of the implant to which abut-ments are connected. Implants are available in differ-ent diameters (platform size) termed narrow, regularand wide platform sizes. The different-sized implantsare used at different sites in the mouth. For example,narrow platform implants are used for replacing miss-ing lateral incisors, whilst wide platform implants areused to replace missing molars.

Platform switching

The use of an abutment that is narrower than the sizeof the platform. Platform switching can avoid verticalbone loss at the connection between the implant andthe abutment.

Connection

The junction between the abutment and implant fix-ture. Implants can have external or internal connec-tion with the abutment.

Crown

Abutment

Abutment screw

Implant

Fig. 22.2 Internal connection platform switching typeimplant.

External connection

The abutment sits on the implant platform. It is con-nected to the implant by an abutment screw. Figure22.1 shows a typical external connection implant.

Internal connection

The abutment fits within the structure of the implantand again is generally screwed to the implant with anabutment screw. Figure 22.2 shows a typical internalconnection implant with a platform switching typeabutment.

Screw-retained prosthesis

The implant prosthesis is screwed onto the abutmentby a bridge screw or directly onto the implant head.The main advantage of a screw-retained prosthesis isits retrievability. It is simple to unscrew the implantprostheses to gain access to the implants.

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Cement-retained prosthesis

The crown is retained onto the abutment by means ofluting cement as in conventional crown and bridge-work. Cement-retained prostheses are more difficultto remove for access to the implants but they generallyoffer better aesthetics.

One-piece implant

In a one-piece implant the implant fixture and abut-ment are joined. There is no connection betweenthem. The crown fits directly to the implant.

Implant Materials

The most common materials for dental implants are:

� Commercially pure titanium� Titanium alloy (Ti6Al4V)� Zirconium

Commonly commercially pure titanium is the mate-rial of choice for implants as it has a predictable inter-action with biological tissue. The metal is highly reac-tive and oxidises passively almost immediately whenin contact with air or tissue fluids. This is of partic-ular benefit when used as an implant since it reducesthe risk of corrosion. Any damage to the surface ofcommercially pure titanium structures is immediatelyprotected by an oxide layer about 12 A thick.

The other physical attributes which make titaniumpopular is that it has a low density, just under half thatof stainless steel, but high strength. It therefore has ahigh strength to weight ratio. It has a modulus of elas-ticity about half that of stainless steel alloys, makingit more elastic. However, the modulus is about fivetime that of bone.

Titanium is regarded as highly biocompatiblethough there is still some release of titanium ionsinto tissue where tissue fluid and blood act as an elec-trolyte. Raised levels of titanium have been identifiedaround implants and systemically in major organs.The amounts observed do not appear to be sufficientto produce an untoward reaction on current evidence.

The biological response to titanium is affected sig-nificantly by the surface character of the implant. Itis suggested that contamination of the implant sur-face may have an adverse affect on the survival of theimplant. Recent attempts have been made to modifyimplant surfaces to enhance the performance. Thesetreatments include plasma spraying or coating the

surface with a film of calcium phosphate ceramic. Thisis designed to encourage bone growth and enhanceosseointegration. These ‘bioactive’ implants offer po-tential for better bone integration but the success isdetermined by the durability of the bond between thecoating and the substructure.

Titanium and its alloy with aluminium and vana-dium is stronger than commercially pure titanium andis easier to machine. However, it is reported to pro-mote a less favourable tissue reaction. More recentlyzirconium implants have become commercially avail-able. Like titanium, zirconium is biocompatible andits main advantage is its colour. It is white rather thangrey, which means that it may offer a more satisfac-tory aesthetic outcome.

Implant Placement Techniques

Standard drilling sequence

Different implant manufacturers recommend differ-ent drilling protocols. In general, preparation of theosteotomy site starts with a small round bur or a sharpstraight drill of 2 mm diameter with drill speeds vary-ing between 800 and 2000 rpm. The drills are cooledwith cold saline irrigation, which can be deliveredinternally to the drills or from an external source.Overheating the drills will cause excessive damageto the bone. The osteotomy preparation continueswith gradually increasing diameter drills and duringdrilling the planned direction of the implant can bechecked by the use of a direction indicator. The finaldrill is generally 0.5–1.0 mm narrower than the di-ameter of the implant. The hole in the bone can bethreaded by use of a screw tap at 50 rpm followingwhich the implant is screwed in at speeds of between25 and 50 rpm with a machine driver or by hand. Themaximum torque developed during placement shouldnot exceed 45 N/cm2 otherwise excessive damage mayoccur to the bone. The drills used to prepare the im-plant site are usually up to 1.5 mm longer than theactual implant. This needs to be taken into accountduring the planning of implant surgery as, for exam-ple a good margin of error needs to be allowed abovethe inferior dental nerve.

Osteotomes/site formers

Some implant systems require the use of osteotomesor site formers to prepare the socket for implant place-ment. Osteotomes are solid hand instruments with aconcave end that come in a range of diameters. The

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smallest diameter osteotome is used first and thenones with gradually increasing diameters until the sitehas been prepared to match the chosen implant. Theyare slower that twist drills in the creation of the im-plant site.

Osteotomes can also be used in soft (type IV) bone(see later) to compact the bone around the implantsite.

Principles of Osseointegration

Following the drilling of the bone and placement ofthe implant a number of events occur within the bone.Both procedures cause damage to the bone up to afew millimetres beyond the extension of the implantwhich can be limited by the use of cooled irrigation,drilling at slow speeds, the use of sharp drills and theuse of a torque controller whilst placing the implant.

A cascade of wound healing events is triggered bythis bone damage. On placement of an implant, thereis not full contact between the bone and the implantand several gaps will exist around the implant sur-face. Bone healing has to occur in these gaps but alsoin the damaged pre-existing bone adjacent to the im-plant. Not all bone sites have the same wound healingpotential and consequently the healing process occursat different rates at different sites.

Healing process in the gaps (de novo boneformation)

The sequence is:

1 Bleeding occurs after drilling. The gaps betweenthe implant and bone fill with blood

2 Wound healing factors are released from the blood(Angiogenesis)

3 Under the influence of the wound healing factors,osteoprogenitor cells migrate into the blood clot

4 Osteocytes differentiate into osteoblasts5 Osteoblasts form woven bone6 Woven bone compacts to form lamellar bone7 Remodelling occurs with the creation of new

osteons

Healing process in pre-existing bone

Despite good surgical technique up to 1 mm of boneadjacent to the implant undergoes necrosis and micro-cracks are found in the bone up to 3–4 mm beyondthis area of microdamage.

Healing in this bone occurs by the followingprocess:

1 Activation of osteoclastic cutter cones2 Resorption of the damaged bone by osteoclasts3 Formation of osteoblasts/new bone deposition by

osteoblasts

On studying the interface between implants and boneat the light microscope level there appears to be directbone–implant contact (BIC). The bone does not con-tact the implant around the whole surface but variesfrom approximately 30% on initial implantation to50–70% following successful osseointegration.

Implant Failure

Implant failures can occur early or late. Early failuresare classified as those occurring before the first yearof loading (placement of the restoration) and late fail-ures are those occurring after the first year of loading.

Early failure

This is a failure to achieve osseointegration. The causeis multifactorial and is thought to include:

� Placement technique� Micromotion of the implant caused by early

loading� Level of experience of the operator� Use of antibiotics and antimicrobials� The cause of tooth loss� The timing of implant placement� Patient-related factors

Placement techniqueThe use of blunt drills and inadequate cooling of thedrills can lead to overheating of the bone. The useof osteotomes in dense bone can be associated withincreased bone resorption around an implant.

Micromotion of the implant caused byearly loadingExcessive movement of an implant during the heal-ing process can lead to fibrous repair and soft tissueencapsulation of the implant.

The level of experience of the operatorStatistically, inexperienced implant surgeons will ex-perience more failures than experienced surgeons.This is probably related to treatment-planning fac-tors and case selection.

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Use of antibiotics and antimicrobialsThere is some weak evidence that the use of pre-operative antibiotics is associated with a lower failurerate of implants than not using them or using post-operative antibiotics alone.

The cause of tooth lossPlacement of implants at sites of teeth that have beenlost through periodontal disease can be associatedwith a higher failure rate. Placement of implants in pa-tients with untreated periodontal disease is associatedwith a higher failure rate and is a contra-indicationto treatment.

The timing of implant placementThere is some weak evidence that immediate place-ment of implants can be associated with a higher fail-ure rate than implants that are placed later.

Patient-related factorsSystemic and local factors can affect the early failurerates of implants. These include smoking, poorly con-trolled diabetes mellitus, radiotherapy and bisphos-phonate medication for the treatment of osteoporosis(see Chapter 23).

Late failure

This is a failure to maintain osseointegration. Thebone at the implant interface is dynamic and is con-stantly remodelled. Fatigue microdamage occurs atthe interface triggering this remodelling process. If themicrodamage is in excess of the repair process thenbone loss will occur.

Causes are:

� Overloading� Peri-implantitis (see Chapter 23)

Overload may be caused by occlusal forces, insuffi-cient implants for the planned restoration or para-functional habits.

Implant Stability

Primary stability

Primary stability of an implant is the stability thatis created during the surgical placement of the im-plant. It is purely a frictional force created be-tween the implant and bone. An implant is morelikely to be successful if good primary stability hasbeen achieved. Primary stability can be recorded by

resonance frequency analysis (RFA). This will give animplant stability quotient (ISQ). The torque (N/cm2)that is achieved during implant placement will alsogive an indication of the primary stability.

Primary stability is influenced by:

� Implant shape� Implant surface topography� Bone quality� Bone quantity

Secondary stability

Secondary stability occurs following the bone heal-ing process as bone is deposited around the implantduring healing and is influenced by:

� Implant material� Implant shape� Implant surface topography� Implant surface chemistry� Bone quality

Timing of Implant Surgery

The original concept of implant surgery as describedby Branemark was that a cover screw was placed onimplants and the mucosa was sutured over them al-lowing the implants to heal undisturbed for up to 6months in the maxilla and 3 months in the mandible.After this period of osseointegration the implantswere exposed into the mouth and healing abutmentsplaced. This is called a two-stage procedure.

It is now common to undertake a one-stage proce-dure. This involves the placement of a healing abut-ment at the time of implant placement (first-stagesurgery) thus allowing the mucosa to heal at the sametime as osseointegration. The advantages are a reduc-tion in healing time, as mucosal and osseous healingcan occur concurrently, and only one surgical proce-dure is required. Following modifications to implantsurfaces, there has been a reduction in the healingtime of implants. Traditionally, implants were left toheal for 6 months in the maxilla and 3 months inthe mandible. It is now more common to leave im-plants 2–3 months in the maxilla and 6–8 weeks inthe mandible.

Immediate placement

Sometimes it is possible to place an implant directlyinto an extraction socket. This is termed immediate

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placement. One of the reported advantages of imme-diate placement is that the healing potential of the im-plant site is at its greatest immediately after extractionof the tooth. There is a suggestion that the bone andgingival profile of the implant site will be preservedby immediate placement. There is also a reduction intreatment time as only one surgical procedure is re-quired. The disadvantage is that there can be a risk oftransmission of infection to the implant at the time ofsurgery. This risk depends on the cause of loss of thetooth and is greatest in patients with multiple causesof tooth loss, e.g. periodontal disease, fractured rootsand caries. Some studies report higher failure rates ofimplants placed immediately into extraction sockets.

Delayed placement

Delayed implant placement generally refers to place-ment 6–8 weeks after extraction of a tooth. The ad-vantages of this include utilising the early wound heal-ing potential of an extraction socket. There shouldalso be resolution of any acute infection present andthere will be an increase in soft tissue volume allowingprimary closure of the site if a two-stage procedureis required, e.g. following bone grafting/guided boneregeneration or treatment in aesthetic areas.

Disadvantages are that multiple surgical proce-dures are required, treatment times are longer andthere will be some resorption of the buccal bone fol-lowing removal of the tooth. Delayed placement re-quires surgical access to the site by raising a flap andthis can be associated with up to 1 mm of resorptionof bone. In areas where aesthetics are important, thismay lead to a poor appearance.

Late placement

Late placement refers to at least 3-month elapsing af-ter removal of a tooth and the placement of an im-plant. Advantages include complete resolution of in-fection prior to placement and it is technically easierto undertake the procedure. The main disadvantage isthat resorption of the bone will have occurred. Lateplacement generally occurs if patients have delayedrequesting treatment. The main indication for lateplacement is if immediate or delayed placement mayrisk damage to a nearby vital structure, e.g. abovethe inferior dental canal or if it is felt that primarystability will not be achieved at immediate or delayedplacement, e.g. upper molars and premolars in closeproximity to the maxillary antrum.

The resorption of bone associated with late place-ment can be overcome by site preservation. Socketvolume preservation is undertaken by guided boneregeneration at the time of tooth extraction. Follow-ing bone healing the implant placement can be under-taken without the need to raise a flap thereby avoidingunnecessary bone resorption.

Immediate loading/Immediate function

Placement of a temporary restoration on an implantwithin 24 hours of implant placement is termed im-mediate loading and can be considered only if im-plants achieve a high primary stability at the time ofplacement.

The advantage of immediate loading is the immedi-ate provision of fixed temporary restorations. How-ever, some studies report higher failure rates of im-plants that are immediately loaded when comparedto delayed loading.

Anatomical Considerations

Before undertaking dental implant surgery it is es-sential to have a good understanding of the three-dimensional surgical anatomy of the maxilla andmandible because there are a number of vital struc-tures that can complicate treatment. To gain detailedknowledge of the surgical anatomy of the maxilla andmandible readers should consult an anatomy text-book.

Vital structures of relevance to dentalimplant surgery

MaxillaNasopalatine nerve/incisive canalFloor of noseMaxillary antrum

MandibleInferior dental nerveMental nerveLingual concavity/floor of mouth

When planning implant surgery 2–3 mm of clearanceneeds to be allowed above the inferior dental nerve.A clearance of 5 mm is usually allowed in front ofthe mental nerve to allow for the anterior loop of thisnerve.

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(a) (b) (c) (d)

Fig. 22.3 Classification of bone quality. (a) Type I – Predominantly cortical type bone. (b) Type II – Dense cancellous/thickcortical plate. (c) Type III – Dense cancellous/thin cortical plate. (d) Type IV – Porous cancellous/thin cortical plate.

Bone quality

The success rates of implants can be site-dependentand failures in the maxilla have been reported as be-ing three times higher than the failure rate in themandible. Implants in posterior regions of the jawalso have a higher failure rate than implants in ante-rior regions.

This is related to the density and quality of thebone. Lekholm and Zarb introduced a bone qualityindex in 1985 (Fig. 22.3).

� Type I – Predominantly cortical type bone� Type II – Dense cancellous/thick cortical plate� Type III – Dense cancellous/thin cortical plate� Type IV – Porous cancellous/thin cortical plate

Type IV bone is most commonly found in the poste-rior maxilla. The failure rate of machined implants intype IV bone has been reported as high as 35%.

Success rates in poor-quality bone have been im-proved by the use of rough surface implants, taperedimplants, osteotomes and the under-preparation ofosteotomy sites to improve the frictional fit ofimplants.

Bone quantity

Following the extraction of teeth there is resid-ual ridge remodelling. This resorption occurs mostrapidly within the first 6 months after tooth

extraction but can continue for life and generally oc-curs horizontally from the buccal aspect.

Resorption at potential implant sites can have twoimplications for implant surgery. First, the bone ridgecan be too thin to accommodate an implant and sec-ond the aesthetic outcome of the implant restorationcan be compromised.

Several bone quantity indices are available.

1 The Lekholm and Zarb classification which is morerelevant to edentulous jaws:� A – Unresorbed alveolar bone� B – Some resorption of alveolar bone� C – Complete resorption of alveolar bone� D – Some resorption of basal bone� E – Extreme resorption of basal bone

2 The Seibert classification is generally more usefulfor partially dentate patients:� Class I – Horizontal resorption� Class II – Vertical resorption� Class III – Combined horizontal and vertical re-

sorption

Bone grafting can be undertaken to increase bone vol-ume to allow implant placement but also to improvethe aesthetic outcome of the final implant restoration.Bone grafting is much more predictable for horizontal(class I) resorption cases than vertical and combinedcases (class II and class III).

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Pattern of residual ridge remodelling

In edentulous patients the pattern of resorption in themaxilla is in a horizontal and vertical direction withbone being lost from the buccal aspect of the alveolarridge. In the mandible the residual ridge remodellingis generally in a vertical direction only, with mandibu-lar basal bone being more resistant to resorption thanmaxillary bone. As a result there is a tendency to-wards a class III skeletal relationship in edentulouspatients. This can have an impact in providing fixedrestorations in patients with severe resorption.

Radiographic assessment of bonevolume/relationship of vital structures

To assess the bone volume and the proximity of vitalstructures, good clinical examination and plain pan-oral and intraoral radiographs are sufficient for thevast majority of patients. If the inferior dental nerveis not clearly identifiable on pan-oral radiographs(OPT) or if any doubt exists then it is advisable toobtain cross-sectional imaging such as cross-sectionaltomograms, cone beam CT or MRI scans.

Bone – Implant Interface

When an implant is placed in bone a number of eventsoccur at the implant surface. Titanium readily formsan oxide layer when exposed to air and on implan-tation the oxide layer is 2–6 nm thick. This increasestwo to three times during healing. Proteins are ad-sorbed onto the surface of the implant that mediatebone healing and there is also a change of the chemicalcompositional of the oxide layer with incorporationof calcium phosphate and calcium sulphate salts.

Any disruption of the bone–implant interface dur-ing healing will lead to fibrous repair and soft tissueencapsulation. This will lead to failure of the implant.

Nature of bone–implant interface

There is no direct contact between bone and the sur-face of the implant seen when studied using electronmicroscopy. There is an afibrillar interfacial zone.

1 The initial layer is similar to cement lines foundaround teeth. Its dimensions are 15–20 A. It con-tains non-collagenous bone matrix proteinsa Osteopontin (OPN)b Bone sialoprotein (BSP)

Both OPN and BSP have arg-gly-asp (RGD) as theirterminal amino acid sequence. This is thought toplay a role in cell adhesion and the binding ofmineral.

2 A lamina limitans layer is found adjacent to theafibrillar interfacial zone. Osteoblasts, osteoid andmineralised matrix is observed at the lamina lim-itans. Bone is therefore deposited adjacent to thislayer

Modifications to implant surfaces to improvebone–implant contact

The initial Branemark implant system was of ma-chined titanium with a smooth surface. Over timemany modifications have been made to improve thebone healing potential of implant systems and mostof these modifications have been made to the initial0.1–1.0 nm of the implant surface, which is termedthe primary interaction zone.

Modifications include:

� Physiochemical methods

Increasing the surface energyCreating a surface chargeChanging the surface composition, e.g. by the use

of hydroxyapatite coating� Morphological methods

Changing the implant shape, e.g. tapered implantsIncreasing the surface roughness, e.g. sand

blasting, acid etching and titanium blasting(TiOblast)

Changing the surface topography, e.g. double-thread design

Research has also been aimed at biomechanical meth-ods to improve implant healing. This has included theuse of growth factors such as bone morphogenic pro-tein (BMP).

Implant–Mucosal Interface

The implant–mucosal interface (IMI) consists of twoprincipal layers, epithelium and underlying connec-tive tissue and has many similarities to the tooth–mucosal interface (Fig. 22.4).

Epithelial layer

Three levels of epithelium have been identified.

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Fig. 22.4 Schematic diagram of the implant–mucosalinterface.

� Oral epithelium – This is keratinised epitheliumthat terminates at the crest of the gingival margin

� Sulcular epithelium – This is a 5- to 15-cell-thicklayer of non-keratinised epithelium

� Junctional epithelium (aJE) – This is a 2- to5-cell-thick layer of non-keratinised epitheliumcharacterised by the presence of desmosomes be-tween cells and hemidesmosomes between junc-tional epithelium cells and the surface of the im-plant/abutment.

Connective tissue layer

The main difference between IMI and the tooth–mucosal interface is the lack of periodontal cemen-tum around implants. As a result there is no directattachment between connective tissue fibres and pe-riodontal cement. Connective tissue fibres are foundto run parallel to the implant surface. This is termedthe circular ligament.

Connective tissue fibres consist of predominantlytype I collagen with some type III and type IV colla-gen. The connective tissue layer is between 0.75 and2 mm thick.

The vascular topography of the IMI also differsfrom the tooth–mucosal interface as the blood vesselsare exclusively derived from periosteum as there is noperiodontal vasculature.

Differences between the tooth–mucosalinterface and the implant–mucosal interface

� Lack of periodontal cementum around implants� No direct attachment between connective tissue

fibres and periodontal cementum around implants� Direction of connective tissue fibres. The connec-

tive tissue directly around implants runs parallel tothe surface of the implant/abutment, the circularligament

� Vascular topography. The vasculature of thetooth–mucosal interface is derived from both peri-odontium and periosteum. The vasculature of theimplant–mucosal interface is solely derived fromthe periosteum.

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Chapter 23Fixed Prosthodontics: Clinical Aspectsof Implants

Implants can be used to support an individual crown, as abutments for bridgework (both partial- andfull-arch bridgework cases) or to help retain dentures (either partial or complete dentures).

The techniques are complex and this chapter provides a simple description of these together with someclinical examples.

Indications for the Use of Implants

The indications for replacing lost teeth and the gen-eral treatment options were discussed in Chapter 18.There is no single treatment option that is right to theexclusion of the others, simply an appropriate treat-ment in the particular circumstances of an individualpatient.

Implants offer some advantages over other treat-ment and these include:

� The ability to reproduce spacing between the teeth� No abutment tooth preparation is required� The condition of the adjacent teeth is not critical

to the success of the implant� Bone and soft tissue volume is preserved

There are, however, some disadvantages of implanttreatment which include:

� Surgical procedures are required� Implant treatment may take several months� Complications of treatment (both surgical and

restorative)� Cost

Most implant treatment, including hard and softtissue augmentation procedures, is possible usinglocal analgesic. Oral or intravenous sedation canbe provided for nervous patients or for prolongedprocedures.

Contra-Indications to Implant Treatment

Dental implant surgery is essentially a routine mi-nor oral surgery procedure and the same contra-

indications and pre-operative precautions apply toit as to any other type of elective minor oralsurgery.

In addition to this there are some contra-indications and precautions that are specific to dentalimplant surgery.

Medical contra-indications to elective minororal surgery

� Unstable angina pectoris� Recent myocardial infarction (elective surgery

should be avoided for 6 months)� Decompensated congestive heart failure� Hypertension

� Systolic blood pressure greater than 180 mmHg

� Diastolic blood pressure greater than 110 mmHg

� Severe aortic stenosis

Medical precautions� Antibiotic prophylaxis protocols for infective

endocarditis apply as for routine minor oralsurgery

� Anti-coagulant therapy. It is generally not nec-essary to discontinue anti-coagulant therapy be-fore surgery. Local haemostatic measures includ-ing tranexamic acid mouthwash, gelatin sponge,resorbable cellulose mesh and sutures are usuallysufficient to control post-surgical bleeding

� Steroid cover. The same indications and steroidcover regimes apply as for routine oral surgery

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� Insulin-dependent diabetes mellitus. The same pre-cautions for minor oral surgery apply to implantsurgery

If any doubt exists, the patient’s general medical prac-titioner should be consulted prior to treatment.

Contra-indications to implant treatment

Contra-indications to implant treatment can eitherbe for local or systemic reasons. Relative contra-indications to treatment are conditions that are as-sociated with higher failure rates of implants but donot necessarily preclude such treatment as long as therisks are understood by the patient.

Systemic contra-indications

� Unfinished cranial growth with tooth eruption.Implant surgery prior to completion of growth canlead to infraocclusion of implant restorations andan unaesthetic appearance

� Alcohol and/or drug abuse� Active chemotherapy� Unrealistic patient expectations

Systemic relative contra-indications

� Diabetes mellitus� Smoking. Smoking probably does not affect the

initial rate of integration of implants. It is how-ever associated with increased coronal bone lossaround implants and an increased risk of peri-implantitis particularly in the maxilla

� Syndromal hypodontia� Age. Some studies show an increased failure rate in

the over 60s age group, whilst other studies reportno difference

� Osteoporosis (particularly with bisphosphonatetreatment)

Local contra-indications

� Head and neck radiotherapy. Failure rates of up to30% have been reported in patients who have hadradiotherapy. The failure rate is thought to be doserelated, with the greatest failure found in patientsreceiving radiation dosage of greater than 50 Gy

� Acute infectious disease� Pathological conditions in the maxilla or mandible� Poor oral hygiene

� Untreated periodontal disease� Insufficient restorative or surgical space for the

implant

Local relative contra-indications

� Poor bone quality� Poor bone volume or severe bone resorption� Para-functional habits

Whilst it is possible to find case reports of implantsbeing successfully used in patients with most chronicillnesses, common sense should be exercised whendeciding which patients are suitable for implanttreatment.

Implants and Aesthetics

It is clear from long-term clinical studies that therecan be confidence in the success and durability of os-seointegration. Attention has now moved from sim-ply achieving an implant that stays in bone retaininga restoration successfully to improving the aesthet-ics of these restorations. Aesthetics is determined notonly by the position and angulation of the implantin relation to the desired restoration position butalso by the surrounding soft tissue and its supportingbone.

It is no longer acceptable to place implants in anyavailable bone with total disregard for the appear-ance that will be created by their position. The prin-ciples discussed in Chapter 21 in relation to anteriortooth-supported bridgework apply equally to implantsupported restorations. Similar techniques may beemployed to decide on tooth position such as diag-nostic waxing and provisional dentures. The two flowcharts, Figs. 23.1 and 23.2, summarise the guidelinesdiscussed below.

Assessment of the anterior edentulous site

The following factors are important:

� Lip line� Space available for the restoration� Functional relationships� Adjacent teeth� Soft tissue phenotype� Gingival line� Muco-gingival line� Interdental papillae

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23. Fixed Prosthodontics: Clinical Aspects of Implants 251

Implants in non-aesthetic areas

Is there sufficient 3-D space for a restoration?

Is there sufficient 3-D bone volume

for implant replacement?

Proceed with implant treatment

Can space be made with restorative or

orthodontic treatment?

Consider alternative treatments

Can bone volume be increased by

bone graft or GBR

Will the patient consider bone graft / BGR?


Bone graft or GBR

NoNo

YesYes

Yes

Yes

Yes

No No

No


Fig. 23.1 Flow chart showingconsiderations for implants innon-aesthetic areas.

� Emergence profile of the implant� Bone contour

Lip lineThe lip line is generally classified as low, medium orhigh. In patients with a low lip line only the incisalthird of the crown is visible during normal function.In patients with a high lip line the margin betweenteeth and gingiva is visible during normal function.The lip line influences how demanding the aestheticswill be. Patients with a low lip line are more likelyto accept an aesthetic compromise than patients withhigh lip line, simply because they will show less of therestoration.

Space available for the restorationThe implant restoration needs to be in harmony withthe adjacent teeth and will be compromised if there is

not enough space available for it. Consideration mayneed to be given to changing the dimensions of theedentulous space by either orthodontic or restorativetreatment.

Functional relationshipsThe occlusal relationships need to be defined includ-ing occlusal contacts in centric occlusion, the inter-arch relationship, the occlusal vertical dimension andthe role that the planned restoration will have inmandibular guidance.

Adjacent teethThe state of the neighbouring teeth is important sothat the implant is considered in the context of thelocal conditions. It is clearly not good to place animplant alongside teeth of poor prognosis or wherethey may restrict the achievement of good aesthetics.

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Implants in aesthetic areas

Is there sufficient 3-D space for an

aesthetic restoration?

Is there soft tissue deficiency or thin soft tissue

phenotype?

Is there sufficient bone for implant placement in a position that

allows an aesthetic emergence profile for the restoration?

Proceed with implant treatment

Can space be made with restorative or

orthodontic treatment?


Consider soft tissue graft

Will the patient accept an aesthetic

compromise?

Proceed with implant

treatment accepting aesthetic

compromise

Will the patient consider bone graft / BGR to improve

emergence profile?


Bone graft or GBR

NoNo

YesYes

Yes

Yes

Yes

Yes

No

No

No

No

Fig. 23.2 Flow chart showingconsiderations for implants inaesthetic areas.

There can also be bacterial contamination of implantsfrom adjacent periapical or periodontal pathology.The following aspects of the adjacent teeth need tobe assessed:

� Position and angulation� Structural integrity and condition� Periodontal and endodontic status� Crown-to-root ratio� Root inclination in relation to the vertical plane� Presence of spacing

Soft tissue phenotypeThe soft tissue phenotype is classified as either thick(approximately 85% of the population) or thin(approximately 15% of the population). A thin softtissue phenotype is more prone to post surgical reces-sion. A titanium abutment may also show throughthe thin soft tissues.

Gingival lineThe course of the gingival line of the implant restora-tion should be in harmony with the adjacent teeth orrestorations.

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Muco-gingival lineThe level of the keratinised mucosa at the implant siteshould be in harmony with the adjacent teeth.

Interdental papillaeThe interdental papillae of the restoration need to bein harmony with the adjacent teeth. The papilla levelshave been classified by Palacci as follows:

Class I – intact or slightly reduced papillaClass II – limited loss of papillaClass III – severe loss of papillaClass IV – absence of papilla

Alternative treatments may be necessary with type IIIor IV papillae or accept an aesthetic compromise.

The level of the soft tissues is dependent on theunderlying bone level. If the contact point betweenrestorations is vertically 5 mm or less from the levelof the interdental bone then there is a 97% chance ofretaining a full dental papilla. If the position of thecontact point is 6 mm from the crest of the interden-tal bone then the chance of retaining a full papillafalls to 56% and at 7 mm the chance of a full papillais 27%. Raising a full thickness flap can be associ-ated with up to 1 mm of gingival recession. This canobviously have an impact on the aesthetic outcome.Careful consideration needs to be given to flap de-sign. Papilla relieving incisions involve raising a flapbut a 1- to 2-mm cuff at the papilla should be left in-tact and such incisions are recommended in aestheticregions.

With single tooth implants, as long as the bonelevels are good around the adjacent teeth then thereis a very good chance of retaining a full interdentalpapilla.

However, adjacent implants may create a problem.In healed alveolar ridges, there is a pre-existing ver-tical deficiency of hard and soft tissue. The averagemucosal thickness around implants is 3–3.5 mm. Thisrepresents a soft tissue deficiency of approximately2 mm. There is a high risk of interdental papilla lossbetween adjacent implants.

The restoration of multiple missing teeth in ante-rior areas using bridgework rather than individualcrowns often results in better aesthetics. Placing sev-eral implants adjacent to each other often leads to apoor aesthetic result (Fig. 23.3).

Emergence profileThis term refers to the angle and position of theimplant restoration in relation to the contours of

the alveolar ridge. The emergence profile of theimplant should be the same as the emergence pro-file of the adjacent teeth. The development of a har-monious emergence profile is dependent on correctthree-dimensional positioning of the implant. Boneresorption may lead to an implant being placed morepalatally and at a more acute angle than the root it isreplacing. The consequence will be that a large anglewill be created between the crown and the implantwith poor aesthetics.

It is often necessary to consider bone grafting orguided bone regeneration (GBR) to improve the bonecontour allowing a better emergence profile.

Bone contourThe bone contour apical to the implant restorationshould be in harmony with the adjacent bone con-tour. It is often necessary to consider bone grafting,GBR or connective tissue grafts to improve the bonecontour. It is often better to preserve bone and softtissue volume at the time of tooth extraction (socketpreservation) rather than having to deal with post-extraction resorption.

Implant position

The three-dimensional position of the implant can in-fluence dramatically the aesthetic outcome of the im-plant restoration. The ideal position is to have thebuccal aspect of the implant head 2–3 mm palatal orlingual to the emergence point of the crown at thegingival margin and 2–3 mm apical to the verticalemergence point of the implant restoration.

The ideal implant position depends on a number offactors which include the use of internal or externalconnection implants, one piece implants, the size dis-crepancy between the implant diameter and the sizeof the implant crown, the buccolingual position of theimplant and the soft tissue phenotype.

Antero-posterior positionImplants that are more buccally placed than the idealwill create the risk of the abutment of being seenthrough the soft tissue or loss of buccal bone causingsoft tissue recession and exposure of the implant orabutment (Fig. 23.4). Buccal inclination of an implantcan also lead to a loss of the buccal tissues leading toa long clinical crown or exposure of the abutment(Fig. 23.5).

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(a) (c)

(b)

Fig. 23.3 (a) Implants supporting 21|2 that are too close together; (b) the result is loss of interdental papilla and pooraesthetics; (c) another case with poor gingival contour.

(a) (b)

Fig. 23.4 Implant placed too far buccally resulting in loss of buccal plate and exposure of the abutment.

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(a) (b)

Fig. 23.5 Implant with buccal angulation resulting in loss of buccal plate and soft tissue recession.

Mesio-distal positionImplants should be placed at least 1.5–2 mm fromadjacent teeth and there should be at least 3 mm be-tween adjacent implants. Following exposure of theimplant into the oral environment, there is establish-ment of the epithelial and connective tissue interfacewith the implant. This soft tissue interface is calledthe biological width and is approximately 1.5 mm. Ifan implant is within 1.5–2 mm of an adjacent tooth,there can be a vertical loss of bone, as the biolog-ical width establishes, leading to loss of the papillabetween the implant and tooth.

Vertical positionImplants that are placed too superficially do not al-low sufficient vertical space to allow the developmentof an aesthetic emergence profile. Implants that areplaced too deeply allow the establishment of a peri-implant pocket, which is a risk factor for peri-implantitis.

Surgical stent

In order to transfer the diagnostic information duringsurgery, the diagnostic waxing or provisional denturetooth position can be replicated as an acrylic surgicalstent. The use of this during drilling the implant siteswill allow correct spacing of implants and can be usedto assess the vertical position of implants in relationto the implant restoration (Fig. 23.6).

Linking Implants to Natural Teeth

Natural teeth and implants behave differently whenloaded by the occlusion and differential movement ispossible in both vertical and horizontal planes. Onapplication of a force of 0.1 N, teeth will show dis-placement of between 50 and 200 μm. This is as aresult of compression of the periodontal ligament. Im-plants will displace by less than 10 μm when subjectedto the same 0.1 N force. This can have a number ofimplications on implant treatment.

When patients occlude their teeth firmly there willbe some intrusion of the natural teeth. This is im-portant in determining the occlusal scheme of im-plant restorations. An implant restoration should beslightly out of occlusal contact in centric occlusionbut should be in occlusal contact on tight clenching

Fig. 23.6 Surgical stent to align drills in correct unitspacing and angulation of final restoration.

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(following slight intrusion of the adjacent teeth). Im-plant restorations should be able to just hold shim-stock on tight clenching. Over time there may begradual intrusion of natural teeth adjacent to implantrestorations. Implants that have the correct occlusalscheme on insertion of the restoration may developinterferences as a result of movement of the adjacentteeth. As a result the occlusion needs to be checkedintermittently on any patient with a combination ofnatural teeth and implant restorations.

There is a further risk caused by the differentialmovement of teeth and implants linked by bridge-work. Unless the implants are absolutely rigid andact as a splint keeping the teeth immobile, the teethwill be depressed into their sockets by loading thusflexing the bridge structure. On recovery, stress willbe induced in the cement lute risking de-cementationand possibly caries of the abutment teeth.

In general, linking teeth to implants should beavoided if possible though it can be acceptable insome circumstances. In these cases, rigid connectorsare recommended.

Circumstances where linking teeth to implants maybe acceptable are as follows:

� Close proximity of vital structures. Implant place-ment may damage vital structures

� Gross bone resorption. Implant treatment wouldrequire bone grafting prior to placement. In thesecases if the patient is unwilling to have grafting un-dertaken then linking implants to teeth may avoidgrafting

� Highly aesthetic regions. In patients with missingupper central and lateral incisor teeth placement oftwo implants can lead to an aesthetic compromise.The options in these cases can be either to place onimplant at the upper central incisor position andplace a fixed–fixed bridge using the canine as anabutment or accept a cantilever bridge from theone implant.

Tissue Augmentation Procedures

Augmentation procedures are frequently necessary aspart of implant treatment. This can include hard tis-sue augmentation (bone graft or GBR) or soft tissueaugmentation.

Bone augmentation

The indications for bone augmentation are either tocorrect bone volume deficiency or for an improve-

Fig. 23.7 Ramus bone graft at 1| position.

ment of the aesthetic outcome of the implant restora-tion (Fig. 23.7). Bone grafting is most predictablein a horizontal direction (class I horizontal ridgedefects).

Donor sites for bone grafting can be either intraoralor extraoral. The most common extraoral donor siteis the anterior iliac crest. Intraoral bone donor sitesinclude the mandibular symphysis, mandibular ramusand maxillary tuberosity.

Intraoral donor sites offer many advantages overextraoral:

� Treatment is possible using local analgesic withsedation if necessary

� Intraoral bone is intramembranous bone whilstextraoral is endochondral. Intramembranousbone gains quicker re-vascularisation and is moreresistant to resorption

� There is less donor site morbidity

Intraoral bone grafts can be supplemented by theaddition of bone graft substitutes. These can havethe benefit of lessening the degree of post-operativeresorption. The only limitation of intraoral bone isthe volume of graft that can be harvested. Forlarge volume deficiencies extraoral bone grafting isrequired.

Common augmentation procedures includecortico-cancellous block grafts to broaden the ridgewidth and maxillary sinus augmentation.

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Guided bone regeneration

GBR involves the use of a cell–occlusive barriermembrane. The membrane prevents epithelial down-growth into a bone defect or socket. Following a toothextraction or creation of an osseous defect, a mem-brane is placed over it. This allows the coagulum toheal and reorganise as bone tissue without the in-growth of epithelium. GBR is usually coupled withthe use of a filler material.

Common filler materials in GBR

� Autogenous bone� Allogenic bone� Xenogenic materials

� Bovine bone� Corals� Algae

� Synthetic materials� Tri-calcium phosphate� Calcium sulphate� Hydroxyapatite� Bio-active glass

Soft tissue augmentation

Soft tissue grafts can be harvested from the palate.They can be of split thickness (connective tissue graft),full thickness (free gingival grafts) or a combinationof the two. Indications for soft tissue grafting includepatients with thin mucosal phenotype, soft tissue de-ficiency or a deficiency of keratinised mucosa at animplant site (Fig. 23.8).

Complications of Implants

Complications of implant surgery

� Bleeding. This can be intraosseous bleeding or per-foration of the lingual plate leading to bleedingfrom floor of mouth

� Nerve damage. The nerves that can be damagedare the inferior dental nerve, incisive nerve, mentalnerve and nasopalatine nerve

� Damage to the roots of adjacent teeth� Infection of the implant� Haematoma formation. This can occur under the

chin following mandibular implant placement� Wound dehiscence� Perforation of the mucosa� Mobility of the implant (poor primary stability)

Fig. 23.8 Harvest of split thickness connective tissue graftfrom palate.

Peri-implantitis

Peri-implantitis is a destructive inflammatory pro-cess affecting the hard and soft tissues around an os-seointegrated implant in function, resulting in loss ofsupporting bone leading to the formation of a peri-implant pocket. It generally causes a saucer-shapedloss of bone superficially with the apical portion ofthe implant often remaining osseointegrated so thatno mobility is discernible (Fig. 23.9).

Clinical signs of peri-implantitis� Bleeding on gentle probing� Suppuration from peri-implant pocket� Swelling and erythema of overlying soft tissues

(not always present)� Mobility of implant

Pain is not typically a feature of peri-implantitis.

Microbiology of failing implantsThe bacteria associated with peri-implant disease aregenerally the same bacteria that are associated withchronic adult periodontal disease and these are:

� Actinobacillus actinomycetemcomitans� Prevotella intermedia� Porphyromonas gingivalis� Fusobacterium species� Non-pigmented bacteroides species

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Fig. 23.9 Implants at 54| showing ‘saucerisation’ boneloss associated with peri-implantitis.

Risk factors for peri-implantitis� Periodontal disease� Implant depth� Surface roughness of the transmucosal portion of

implant� Poor oral hygiene and plaque retention� Foreign-body reaction in the peri-implant pocket� Smoking

Bacteria commonly move from periodontal pocketsto implant sites so untreated periodontal disease is acontra-indication to implant placement. Conversely,implants placed immediately into extraction socketsof teeth lost through periodontal disease carry an in-creased risk of peri-implantitis as do implants placeddeeper than 4–5 mm subgingivally.

Bacterial colonisation of abutments begins at sur-face irregularities and therefore rough surfaces aremore prone to biofilm formation and adhesion of bac-teria. To avoid damaging the surface of the implantabutment, carbon fibre or plastic hand scalers are rec-ommended for scaling implants.

Subgingival misfit of implant components offers anideal environment for the formation and retention of

plaque and similarly poor oral hygiene is a high riskfactor for marginal bone loss and peri-implantitis.

Extrusion of cement into a peri-implant pocket iscommonly associated with an acute peri-implantitisthat usually resolves after removal of the cementremnants.

Smoking is also associated with marginal bone lossand peri-implantitis.

Treatment of peri-implantitisManagement of peri-implantitis includes the follow-ing measures:

� Oral hygiene instruction� Subgingival curettage of the implant� Topical antimicrobial agents� Systemic antibiotics� Surgical treatment for mechanical debridement of

the implant surface and elimination of residualpocketing.

� GBR around the implant surface, although thelong-term results of this are uncertain

Restorative complications

� Implant fracture� Fracture of components/prosthesis� Speech complications due to tooth position and

gaps between the teeth� Lip trapping above fixed maxillary prostheses� Prosthetic complications caused by poor implant

positioning� Late implant failure

Clinical Review

The following aspects need to be reviewed annually:

� Implant stability� Osseointegration and bone contour and volume

by radiography� Surrounding tissues – gingivae and mucosa

Particular attention should be paid to the followingthat will cause concern:

� Clinical signs of infection around the implant, e.g.presence of pus

� Pain or sensitivity� Mobility of the implant� Radiographic evidence of bone loss (saucerisation)� A dull sound at percussion

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(a)

(b)

(d)

(e)

(c)

Fig. 23.10 (a) Patient with metal–ceramic crowns 1|1 with poor shade match; (b) pre-operative radiograph showinginternal resorption 1|; (c) post-operative radiograph showing implant at 1|; (d) post-operative appearance showing milledceramic crowns 1|1 and ceramic veneers 2|2; (e) harmonious smile.

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(a) (b)

(c) (d)

(e) (f)

Fig. 23.11 (a) A patient with bilateral maxillary free-end saddles; (b) occlusal view showing titanium abutments at 46|46 ;(c) titanium abutments at |46 ; (d) implant metal–ceramic bridgework |4 – 6; (e) completed bridgework with harmonioussmile; (f) occlusal view of completed bridgework.

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(a) (b)

(c) (d)

Fig. 23.12 A patient who had experienced difficulty managing a lower complete denture. (a) Pre-treatment OPT ofedentulous mandible; (b) gold bar supported by two mandibular implants; (c) post-treatment OPT showing two mandibularimplants and gold bar; (d) fitting surface of overdenture showing gold clips.

General conclusions from clinical implantsurvival studies

Studies of single tooth implants show consistentlyhigh levels of success with individual centre reportsof over 98% at 5 years, 96% at 8 years and 97.4%at 10 years.

The long-term survival rates of implants used tosupport partial bridgework though are not as consis-tently high as single tooth implant cases. The cumu-lative survival rate of maxillary implants was 90.2%and of mandibular implants was 93.7% at 10 yearsin one study. The survival rate for implant treatmentin partially edentulous jaws followed up for 20 yearsin clinical function was 91% in another study.

A meta-analysis of long-term results of bridgeworksupported by a combination of teeth and implants

were not as favourable as wholly implant-supportedcases. The 5-year survival rates of the implants were90.1% and 10-year survival rates were 82.1% butthe survival rates of the bridgework were found to beworse. At 5 years, 94.1% of the bridges were still infunction but at 10 years this figure had dropped to77.8%.

Studies of full arch bridgework cases show that im-plant survival rates are not as consistently high as forsingle tooth cases. Quoted cumulative survival ratesare very similar as for partial bridgework cases andare of the order of 85–90%.

On the other hand, the survival rates of implantssupporting mandibular overdentures are consis-tently high, probably amongst the highest achievableimplant success rates, though the success rate in themaxilla is not as high.

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Clinical Cases

Single tooth replacement

The patient shown in Fig. 23.10 suffered traumato the upper incisors and in picture (a) has metal–ceramic crowns on the upper central incisors withpoor shade match. The radiograph of the upper rightcentral incisor (b) shows internal resorption. The up-per right central incisor was extracted and an acrylictemporary bridge was provided supported by the up-per left central incisor. Six weeks later a BranemarkMk IV TiU regular platform implant was placed toreplace it (c). The root filling of the upper left cen-tral incisor, although imperfect, has been present forover 10 years; the tooth is asymptomatic and thereis no evidence of pathology and therefore interfer-ing with the root filling is not indicated. A titaniumceramic abutment and ceramic crowns with milledceramic cores were placed after 3 months on the cen-tral incisors and ceramic veneers placed on the lateralincisors.

The result is a very harmonious smile and the im-plant has been present for over 5 years.

Bridgework case

The patient shown in Fig. 23.11a had bilateral free-end saddles in the maxilla. Branemark Mk IV TiUregular platform implants were placed to replacethe upper first premolars and first molars and theseare shown at the healing stage in Fig. 23.11b. Pro-cera titanium abutments were placed 3 months later(Fig. 23.11c) followed by gold–ceramic bridgework(Figs. 23.11d–g).

Overdenture case

Implants may be used to stabilise a complete dentureand can be particularly useful if a patient is havingdifficulty in managing a non-retentive denture. Fig-ure 23.12 shows such a case. Two Astra-Tech im-plants were placed and abutments placed 6 weekslater (Fig. 23.12c). A gold bar was attached to theabutments and gold clips in the denture were retainedby this (Figs. 23.12d–e).

Papers Used in the Summary ofCumulative Success Rates

Henry PJ et al. (1996) Osseointegrated implants for single-tooth replacement: a prospective 5-year multicentre study.Int J Oral Maxillofac Implants 11:450–455.

Bianc G et al. (2000) Osseointegrated implant for single-tooth replacement: a retrospective multicentre study onroutine use in private practice. Clin Implant Dent RelatRes 2(3):152–158.

Priest G (1999) Single-tooth implants and their role in pre-serving remaining teeth: a 10-year survival study. Int JOral Maxillofac Implants 14:181–188.

Lekholm U et al. (1999) Survival of the Branemark implantin partially edentulous jaws: a 10-year prospective multi-centre study. Int J Oral Maxillofac Implants 14:639–645.

Lekholm U (2006) Outcome of oral implant treatment inpartially edentulous jaws followed 20 years in clinicalfunction. Clin Implant Dent Relat Res 8:178–186.

Jemt T, Johansson J (2006) Implant treatment in the edentu-lous maxillae. A 15-year follow-up study on 76 consecu-tive patients provided with fixed prostheses. Clin ImplantDent Relat Res 8:61–69.

Adell R et al. (1981) A 15-year study of osseointegratedimplants in the treatment of the edentulous jaw. Int J OralSurg 10:387–416.

Schwartz-Arad D et al. (2005) A long-term study of implantssupporting overdentures as a model for implant success.J Periodontol 76:1431–1435.

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Chapter 24Removable Prosthodontics: PartialDentures – Design

This chapter considers the first stages in the provision of partial dentures and the principles of their design. Astep-by-step development of the design should be used to create the components for support and retention.Clinical experience and a detailed knowledge of the materials available will produce rational designs.

Diagnosis and Treatment Planning

Supplying a partial denture to a patient is usually thelast phase of a course of restorative treatment. The de-cision to make a partial denture will have been madefollowing a thorough history and examination anddiscussion with the patient.

The dental history should include details of previ-ous denture wearing experience (if any) such as:

� Do you wear a partial denture?� If so, do you find it satisfactory?� How long have you worn it?� If unsatisfactory, what are the complaints?

If the patient has never had a partial denture then itis helpful to ascertain if they would like one and ifso, why. These questions will help to clarify patientmotivation and help in the decisions firstly, whether toprovide a denture and, secondly, the type of denturethat should be provided.

The examination of the mouth and oral tissuesshould include the condition, location and numberof remaining teeth, condition of the soft tissues, thenature of the saddle areas, i.e. the height, width andconsistency of the residual ridges and an assessment ofthe oral hygiene. The denture(s) should be inspectedfor fit, retention and stability, occlusal relationship,wear and cleanliness.

When all the information has been gatheredand considered, a diagnosis can be reached and atreatment plan formulated. The plan will includea provisional partial denture design in order thatother dental treatment can be completed appropri-ately and the mouth prepared to receive the partialdenture.

The design, therefore, must be decided before em-barking on other restorative procedures since it may

affect the type and material of the other restorationsto be placed. This will optimise the function of thedenture and maintain the health of the mouth. Fur-ther information and investigation is necessary inorder to consider the design of the appliance thisincludes:

� Analysis of the occlusion� Radiographs� Model surveying

Study models serve a number of uses of which themost important are:

� Examination of the occlusion� Model surveying – analysis of path of insertion

and withdrawal, location of undercuts� Trial preparation of the teeth� Construction of special trays� Communicating with the patient and the labora-

tory technician

Examination of the occlusion

Although the occlusion can be assessed initially dur-ing an intraoral examination, the use of models per-mits a more detailed inspection and it is, of course,also possible to view the teeth from the lingual aspect.This enables tooth contact to be examined more eas-ily to determine whether sufficient space exists forcomponents of the partial denture design, e.g. oc-clusal rests. In many cases sufficient information canbe gained by examining hand held models. However,this only reproduces the occlusion in a static stateand therefore, for a more detailed analysis of oc-clusal function and articulation (movements of themandible into and out of the position of maximumintercuspation), it is necessary to mount the modelson a semi-adjustable articulator (Chapter 14).

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Model surveying

Model surveying is performed in order to determinethe path of insertion and removal of the denture andto locate undercuts on the dento-alveolar tissues suit-able for its retention.

Trial preparation of the teeth

The earlier analysis of the occlusion and the modelsurveying might reveal the necessity for modificationof the teeth either to improve or eliminate occlusalinterferences or to alter the shape of the crown of thetooth, e.g. reduction of the height of contour on theproximal surface of the molar or premolar to pro-duce a guiding plane parallel to the path of inser-tion in order to gain a more intimate contact betweenprosthesis and tooth. Such modifications can be re-hearsed on the model before being performed in themouth.

Construction of special trays

Special trays are essential for subsequent impressionprocedures to ensure accuracy and reproduction ofdetail and, where appropriate, proper tissue mouldingof the borders.

Communication

Study models provide an excellent aid when dis-cussing or explaining treatment to the patient and arean essential part of the prescription to the technician.An outline of the partial denture design can be drawnon the model to give a three-dimensional apprecia-tion in those cases where a drawing on paper couldbe open to misinterpretation.

Partial Denture Design

Designing the denture is a clinical responsibility sincethe dentist is the only person with all the informationconcerning the condition of the mouth and teeth. Li-aison with the dental technician is perfectly appropri-ate and the technician may have suggestions to makefrom his point of view. However, the denture remainsthe dentist’s overall responsibility.

Partial dentures should be designed using basicprinciples in a logical step-by-step sequence. Beforedetail of the design is considered four guidelinesshould be borne in mind:

� Simplicity� Support from the teeth� Relief of the gingival tissues� Rigidity of the connectors

Simplicity

A partial denture is more likely to be tolerated by thepatient if the design is kept as simple as possible. Com-ponents should only be added for good reason andto serve a definite function. For example, the small-est number of clasps should be used compatible withretention and stability.

Support from the teeth

In the lower arch, with its reduced mucosal areaavailable for support, it is especially important totake advantage of the remaining natural teeth forsupport.

Relief of the gingival tissues

Plaque is more likely to accumulate around teeth thatare covered by a denture and the problem is greatlymagnified in patients with poor oral hygiene. Wheregingival coverage is unavoidable, the impression sur-face of the denture should be closely adapted to theunderlying soft tissue so that this does not grow to fillthe potential space.

Rigidity of the connectors

A thin flexible connector can easily be distorted dur-ing function or if gripped too firmly whilst cleaning.

Design Stages

Provided a step-by-step sequence is followed no im-portant components will be omitted and the de-sign will be functional and satisfy the necessary cri-teria for clinical success. Several choices are usu-ally available when designing and this means thatit is possible to produce several different designsfor the same patient. The final selection is basedon many factors including knowledge of the clini-cal condition of the mouth, shape and length of theedentulous saddles, the patient’s motivation and pre-vious dental experience, availability of technical sup-port and the overall costs of the treatment to thepatient.

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24. Partial Dentures – Design 265

(a) (b)

Fig. 24.1 Surveying an alveolar ridge: (a) The survey rod illustrates a path of insertion that is at right angles to the occlusalplane; the denture base would not enter the tissue undercut; (b) the surveyor is tilted to provide a path of insertion thatallows the denture base direct access to the tissue undercut. In view of the likely displacing forces in function, this undercutarea will now provide direct and possibly indirect retention.

Path of insertion/withdrawal

The path of insertion/withdrawal can be defined asthe path followed by the denture from its first contactwith the supporting tissues until it is fully seated. Ineffect this relates to the direction in which the patientwill insert and remove the denture. There may be asingle path or multiple paths of insertion and it mayor may not coincide with the path of displacement,i.e. the direction in which the denture tends to bedisplaced in function (assumed for the purposes ofdesign to be at right angles to the occlusal plane).

The path of insertion must allow the individual sad-dle areas to be seated but in addition, varying thepath may improve the ability to engage tooth under-cuts with clasps (see later). It is therefore necessary toconsider three areas of the proposed denture at thisstage:

� Alveolar bone undercut� Undercut caused by the approximal surfaces of

abutment teeth overhanging the saddles� Buccal and lingual tooth undercut in relation to

clasping

The path of insertion is chosen whilst surveying themodel. Surveying is usually undertaken with the oc-clusal plane horizontal but a tilt may allow hardor soft tissue undercuts to be engaged and therefore

improve the fit of the denture to the tissues. An ex-ample of this would be when upper anterior teeth aremissing and there is a labial bony undercut present.Tilting a model with the heel down may permit moreefficient utilisation of the labial undercut (Fig. 24.1),always assuming that this does not compromise theinsertion of the denture in other areas.

Many partial dentures have multiple saddles andthe final path insertion of the denture is likely to bea compromise between the ideal paths for each in-dividual saddle together with the clasping sites. Theapproximal surfaces of abutment teeth may over-hang the edentulous space and influence the path ofinsertion adversely (Fig. 24.2a). Here considerationshould be given to modifying the approximal surfaceby grinding to produce guiding planes or, in severecases of tilting, the provision of a restoration withthe correct contour (Fig. 24.2b). If undercuts remainin the approximal aspects, these will be blocked outon the master model to prevent the denture base fromengaging them during processing and later at the fit-ting stage.

Having obtained the desired tilt, the path of in-sertion should be recorded on the model. This can bedone either by ‘tripoding’ (marking the model at threewidely spaced points with the analysing rod fixed atthe same vertical height) or by making vertical markson the side of the base of the model in the anterior

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(b)(a)

Lead

Survey line

Limit of denture base

Path of insertion

Fig. 24.2 Approximal undercut: (a) The survey line on an edentulous ridge showing an area of the tooth that could not becontacted by the denture base. This is a potential site for plaque accumulation, (b) Modification to the approximal surfacewill eliminate this undercut. In cases of tilting, a crown may be constructed to create a favourable relationship.

and posterior regions. Recording the path of inser-tion allows the model to be reorientated to the sameposition during later stages.

Once the path of insertion has been chosen it isnecessary to:

� Outline the saddles� Define the support� Provide direct retention� Consider the provision of indirect retention� Join the components with connectors

An integral and important component of these stagesis the choice of materials.

Denture base materials

Partial dentures may be constructed from polymethylmethacrylate (acrylic) alone or, more commonly, inassociation with cast metal and/or wrought metal.The common alloys that may be used are cobalt–chromium, stainless steel and wrought and cast gold.Acrylic or ceramic may be used for the teeth.

SaddlesPolymethyl methacrylate is universally used for re-placing alveolar bone. Its ease of use and generalphysical properties are well suited to this. The onlyquestion mark over its use relates to the possibility ofresidual monomer within the material causing tissuereaction. This applies to both partial and completedentures and is discussed in Chapter 30.

Clasps and connectorsWhilst acrylic is cheap and simple to use, it is not anideal material for partial denture connectors. It needsto be at least 2 mm thick for strength and thereforecan be intrusive, particularly on the palate. Its plaqueretaining ability is higher than the metal alloys andtherefore its potential to initiate or aggravate peri-odontal disease is large.

Clasps and connectors should therefore be con-structed from metal and the choice will relate to theproposed design. Cobalt–chromium alloys are almostuniversally used for connectors whilst clasp materialsare chosen according to the undercut that they are toengage.

It is generally accepted that a cobalt–chromiumclasp should only engage 0.25 mm of undercut be-cause this material has a high elastic modulus andwill deform or fracture if a deeper undercut is en-gaged. Cast gold has a modulus of elasticity of ap-proximately half that of cobalt–chromium and can,therefore, engage greater undercut (0.5 mm) and awrought structure, in the form of gold or stainlesssteel wire, has a lower modulus and good recoveryand can be used in deeper undercuts (up to 0.75 mm).

TeethAcrylic denture teeth have the advantages of beingeasy to adjust, chemical bonding to an acrylic den-ture base and cheapness. They have the disadvan-tages of having low wear resistance and the poten-tial for becoming discoloured. Ceramic teeth, on theother hand, are more durable, retain their colour andare therefore more aesthetic in the long term. Their

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disadvantages are that they are more time consum-ing to adjust, both clinically and in the laboratory,and mechanical retention to the denture base must beprovided.

The edentulous saddles

A classification of the edentulous saddles allows den-tists and technicians to use a simple ‘shorthand’ de-scription when referring to a particular case. TheKennedy classification is probably the most widelyaccepted:

Class I bilateral edentulous areas (of any length)which lies posterior to the remaining teeth

Class II a single edentulous area (of any length) whichlies posterior to the remaining teeth

Class III a single edentulous area (of any length)bounded by one or more teeth anteriorly andposteriorly

Class IV a single edentulous area (of any length)which lies anteriorly to the remaining teeth

An early decision is required on which (if any) miss-ing teeth need to be replaced. Guiding factors willinclude aesthetics, function, stability of the occlusionand wear of remaining teeth. The outline of the sad-dle(s) of the teeth to be replaced should be drawn onthe design sheet.

Support

Support for the saddles can be provided by:

� Teeth� Mucosa� Teeth and mucosa in combination

As a general guide, permanent mucosa borne den-tures with no tooth support should be avoided in themandible because of the danger of overloading lim-ited support area.

A tooth borne design is only possible when the sad-dles are bounded by natural teeth, i.e. in KennedyClasses III and IV. In these cases the load is trans-ferred to the natural teeth through extensions of thepartial denture positioned on appropriate areas of theteeth and named accordingly:

� Occlusal rests – molars and premolars� Cingulum rests – upper canines and incisors� Incisal rests – lower canines and incisors

In Kennedy Classes I and II, the support is providedby both teeth and mucosa. In these cases the saddle

Support

Bracing

Retention

Fig. 24.3 The component parts of a clasp unit. Thereciprocating arm will be on the opposite side of the tooth.

should cover as large an area as possible to distributethe load widely.

Direct retention

A clasp, or direct retainer, is the component that re-sists dislodgement of the partial denture along thepath of withdrawal. It is a flexible metal arm thatengages the undercut region on a natural tooth andforms part of a clasp unit, i.e.:

� Retentive arm� Reciprocating arm� Occlusal rest

The reciprocating arm is used as a bracing componentto prevent displacement of a tooth by a direct retainerin its active phase, i.e. when it is being inserted orwithdrawn over the survey line. The retentive armshould always be used in combination with a rest toensure a proper and constant position. The portionof the clasp arm above the survey line is thicker andprovides bracing against lateral movement whilst theportion below the survey line must flex to engage theundercut after insertion (Fig. 24.3).

The teeth chosen as potential retaining sites are ex-amined with the analysing rod on the model surveyorand suitable undercuts and the survey lines markedwith a lead marker. Undercut gauges can then be usedto measure the depths of undercuts available in or-der to define the position of the retentive portion ofthe clasp arms in relation to the choice of material(see above). Three gauges are used, one for cobalt–chromium, one for cast gold and one for wroughtgold. If the tooth surface is bulbous the clasp armwill be closer to the survey line whilst if it is shallow,the clasp will be more distant, i.e. the clasp arm is en-gaging a ‘standard’ degree of undercut for the chosenmaterial (Fig. 24.4). On the other hand, if a retentivearm is placed in excessive undercut either the arm will

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(a) (b)

Fig. 24.4 An undercut gauge determines the position ofthe retentive part of a clasp arm within the tooth undercut:(a) The arm will be nearer the survey line on a bulboustooth; (b) the arm will be more gingivally placed on a lessbulbous tooth.

be permanently deformed and no longer functional orit will fracture.

Although there are numerous designs of clasps,many linked with the names of their original protag-onists, there are only two basic types (Fig. 24.5):

� Occlusally approaching – those which approachthe undercut from the occlusal surface – supra-bulge clasps

� Gingivally approaching – those which approachthe undercut from the gingival surface – infra-bulge clasps

The type of clasp used will be determined by:

� The depth of undercut� Position of the survey line� Prosthetic considerations

The depth of undercut that can be utilised has beendiscussed previously in relation to the choice ofmaterials.

The position of the survey line will have an impor-tant influence on the choice of clasp type. There arebroadly four types of survey line (Fig. 24.6).

� Steep oblique� Shallow oblique� Occlusal third� Gingival third

As was mentioned earlier, the survey line can be variedby changing the path of insertion. Whilst this can besuperficially attractive in terms of the retentive arm,it must not be forgotten that the reciprocating armand the denture base must also be capable of be-ing inserted. For example, the low survey line maynot allow the placement of a clasp arm. It could be‘raised’ by the tilting of the model towards this side to

(a)

(b)

Fig. 24.5 The two basic types of clasp: (a) Occlusallyapproaching. This may engage undercut directly from themarginal ridge or from the opposite marginal ridge as anencircling clasp, (b) Gingivally approaching. This is able toengage a low undercut and also reduces tipping forces onthe tooth if the denture base moves into the alveolar tissues.

produce a higher line. However, the result of thiswould perhaps be to reduce undercut on the oppo-site side and also prevent seating of the denture base.

The low survey line may be engaged by a gingivallyapproaching clasp (Fig. 24.5). This has the advantagethat the arm is longer and more flexible and, becauseof its position, is often less visible and therefore aes-thetically more acceptable to the patient. However,because of its length and relationship to the gingivait is more likely to cause food stagnation around theneck of the tooth.

If the survey line is very close to the gingival mar-gin then there will not be space for the clasp arm.Here the contour of the tooth could be increased bya restoration, perhaps simply an acid etch retainedcomposite supplement.

The design of restorations that are needed for abut-ment teeth should include consideration of providingretentive contours, shoulders and ledges for claspsand denture bases and rest seats within the overallcontour (Fig. 24.7). This is why it is so importantto decide upon the denture design before embarkingupon restorations.

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(a)

(b)

(c)

(d)

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Fig. 24.7 A full crown denture abutment with a rest seatand clasp ledges. The clasps will be constructed within thenormal tooth contours rather than adding bulbosity to thetooth.

Indirect retention

Indirect retention is retention obtained by the exten-sion of the partial denture base to provide the fulcrumof a Class II lever. The retainer(s) providing direct re-tention lie(s) between the fulcrum and that part ofthe denture which is subject to the displacing force.In practice, indirect retainers assist clasps in resistingdisplacement of the partial denture in function by pro-viding resistance to rotational dislodging forces. Themain need is with tooth/mucosa borne (free-end sad-dle) partial dentures especially in the maxilla becauseof the constant additional effect of gravity tending todislodge the saddles.

Indirect retention can be provided by, for example,an extension of the major connector on the palate,additional rests on the natural teeth and the use of alingual plate instead of a lingual bar connector in themandible.

Connectors

As the term suggests connectors join the componentparts of the partial denture and are the final stagein the design sequence. They can be classified as ei-ther minor or major connectors. The role of minorconnectors is to link the rests and clasps to the ma-jor connector or denture base. They should be strongenough to withstand heavy occlusal loads and usu-ally be positioned to lie in embrasures in order to beunobtrusive.

Major connectors join the saddles and should berigid so that the partial denture transfers forces to allthe supporting structures on both sides of the arch andtherefore functions as a single unit. The major connec-tor should, ideally, lie at least 3 mm from the gingivalmargin in order to maintain the health of the tissues.

In the mandible the major connectors can be clas-sified into five categories:

� Lingual bar� Sublingual bar� Lingual plate� Dental bar� Buccal bar

Variations are, however, possible and include thecombination of lingual bar and ‘continuous clasp’(a misnomer since no part of the structure engagesundercut – it functions as an indirect retainer). Thelingual bar and lingual plate are the most commonlyused. The lingual bar does not overlay the gingivalmargins and therefore does not promote plaque accu-mulation but requires approximately 8 mm of heightmeasured from the gingival margin to the depth ofthe sulcus, i.e. 3 mm from the gingiva to the bar, atleast 3 mm depth of bar and a further 2 mm belowthe bar to the sulcus.

The lingual plate covers the lingual surface of theanterior teeth and the upper portion of the lingualaspect of the alveolar process. It provides excellentindirect retention and is generally well tolerated bypatients but is likely to lead to an increase in plaquedeposition and so is best avoided if there is evidenceof susceptibility to periodontal disease.

The sublingual bar lies in the floor of the mouth andfills the entire depth and width of the lingual sulcus.It is an attempt to lessen tongue irritation. Since itis shorter than the lingual bar, and also thicker, it ismore rigid. A very careful impression technique withfunctional moulding of the lingual sulcus is requiredotherwise the bar will cause irritation of the tissues.

The dental bar is a modified ‘continuous clasp’which lies on the lingual surface of the anterior teethand is clear of the gingival margins. Although ideallypositioned since it can be used regardless of lingualalveolar ridge depth and there is no gingival coverage,it needs to be made sufficiently thick to be rigid andthis can reduce its acceptability to the patient.

If the anterior teeth are markedly retroclined andit is impossible to develop a suitable lingual path ofinsertion, a buccal bar can be used. This is positionedin a similar relationship to the gingival margins andsulcus as the lingual bar. Since it has a wider arch

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Fig. 24.8 Schematic partial denture designs:(a) Upper bilateral free-end saddle (Kennedy Class I). Thecomponents are:

Saddle areas: 765|67, denture base and teeth in acrylicTooth support: Occlusal rests 4|5 and cingulum rests 2|2Direct retention: (i) gingivally approaching clasp 4|

wrought gold – this has better aesthetics on the moreanterior tooth(ii) occlusally approaching clasp unit |5cobalt–chromium

Indirect retention: The posterior aspect of the denture willtend to drop about the fulcrum of the occlusal rests.Components anterior to this fulcrum will resist thisdisplacement. These are cingulum rests 2|2 and anterioraspect of the palatal ring

Connector: Palatal ringFramework material: Cobalt–chromium

Fig. 24.8 (b) Upper bilateral bounded saddle (KennedyClass III)

Saddle areas: 76|67, denture base and teeth in acrylicTooth support: Occlusal rests 85|58Direct retention: (i) occlusally approaching clasp units 5|5,

buccal arms engaging mesial undercut(ii) occlusally approaching clasps 8|8 again engagingmesial undercuts but because the origin of the clasps ismesial as well the clasps must come from the distalaspects as encircling clasps

Indirect retention: None requiredConnector: Posterior palatal barFramework material: Cobalt–chromium

Fig. 24.8 (c) Lower bilateral free-end saddle (KennedyClass I)

Saddle areas: 76|76 denture base and teeth in acrylicTooth support: Occlusal rests mesially 5|5Direct retention: Gingivally approaching clasps 5|5, I-barsIndirect retention: NoneConnectors: Major – lingual bar

Minor – to rests 5|5Framework material: Cobalt–chromium

Occlusal forces on the denture will cause rotation around afulcrum joining the mesial occlusal rests – See RPI (mesialrest, distal plate and I-bar clasp) system in text – and thegingivally approaching clasps will be disengaged.Unfavourable tipping forces will therefore not be applied tothe abutments.

Fig. 24.8 (d) Upper anterior saddle (Kennedy Class IV)

Saddle areas: 21|12, denture base and teeth in acrylicTooth support: Occlusal rests 6|6 and cingulum rests 3|3Direct retention: Occlusally approaching encircling clasp

units 6|6Indirect retention: The clasp units on 6|6 approach the

mesial undercuts from the distal. Therefore when thedenture tends to drop around the fulcrum between theocclusal rests the clasp arms are engaged to prevent it

Connector: Middle and anterior palatal barsFramework material: Cobalt–chromium

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than a lingual bar it is longer and therefore needs tobe made thicker to maintain the rigidity. In practiceit is rarely used.

In the maxilla there is greater flexibility in the de-sign and type of major connector(s) that can be used.The main requirements are, as with lower connec-tors, that the structure is rigid, well tolerated by thepatient and that it is compatible with gingival health.The following designs are generally recognised:

� Palatal plate� Anterior palatal bar� Mid palatal bar� Posterior palatal bar� Open ring (anterior and posterior palatal bar

combination)� Horseshoe, U shaped

The term ‘bar’ can include connectors that are widerthan the term suggests when compared to use in thelower arch. In these cases others have favoured theterm ‘strap’.

Indicative Designs

Figure 24.8 illustrates four designs that incorporatefeatures that have been discussed above. As with fixedprosthodontics, there are no ‘standard’ designs with

Partial Denture Design – Summary

The design of partial dentures is the responsibility of the dentist and not the technician.

All partial dentures should, wherever possible and particularly in the lower arch, utilise teeth for supportto complement support provided by the alveolus.

Cast metal frameworks (direct and indirect retainers and connectors) are recommended for strength, dura-bility, periodontal health and patient comfort in comparison with acrylic.

Whilst there are many options for inclusion in a denture design, the overriding consideration is to keep thestructure as simple as possible.

clinical experience being a large factor in choice andthere being little biomechanical evidence for manyempirical principles.

The RPI Case System

The RPI (mesial rest, distal plate and I-bar clasp) sys-tem was originally described in the 1960s and furtherdeveloped in the 1970s, although its usage is still lim-ited. The concept attempts to distribute the mastica-tory loads between the saddles and abutment teeth.For each saddle the occlusal rest is placed mesially (asFig. 24.8c) since there is evidence that this gives morefavourable and even load distribution. Guide planesmesially and distally are utilised by the minor con-nector joining the rest to the major connector and thedistal plate. This plate lies on the 3- to 4-mm guideplane so that when the denture is fully seated the platecontacts only the lower 1 mm of that surface. (Theportion over the gingiva is relieved.)

The I-bar clasp tip is positioned on, or anteriorto the midpoint of the buccal surface and is bracedby the guide plane contacts. The load on the saddlecauses the denture to rotate about the occlusal restand the distal plate and I-bar tend to disengage pre-venting further stress being posed on the abutmenttooth.

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Chapter 25Removable Prosthodontics: PartialDentures – Clinical Procedures

The clinical stages in the construction of a partial denture are described together with their practicalproblems.

The stages in the construction of a partial denture are:

� Preliminary impressions� Secondary (working) impressions� Occlusal registration� Try-in of metal framework� Try-in of waxed dentures� Fit� Review

Preliminary Impressions

An elastic impression material is required to repro-duce the details of the natural teeth and tissue under-cuts. Alginate is the material of choice but it requiressupport from an adequate stock tray made fromeither metal or plastic. Metal is more rigid, whilst theplastic type may be prone to deformation, dependingon its design.

A suitable size should be chosen that encompassesall the teeth and extends into the labial and buccalsulci. In areas where there are several missing teeth,for example free-end saddles in the lower arch, thetray should be modified by the addition of impres-sion compound (suitably moulded) to take up someof the excess space and also extend the tray into thesulcus. This will ensure that the alginate is adequatelysupported and hence used within its functional lim-its for maximum accuracy of reproduction. Althoughonly one partial denture may be required, it is nec-essary to take impressions of both jaws in order torecord the occlusion.

After trying in, the impression trays should be driedand an even, thin layer of adhesive applied to aid re-tention of the impression material to the trays. Thealginate should be mixed according to the manufac-turer’s instructions using water at room temperature

and transferred immediately to the lower tray us-ing a spatula. It is preferable to take the lower im-pression first since this is generally tolerated betterand allows the patient to become accustomed to theprocedure.

When taking the upper impression, two techniquesare commonly described. In the first the posterior por-tion of the tray is seated first and then the anterior por-tion. This is intended to force the alginate upwardsand forwards away from the sensitive posterior areasof the palate and fauces. For the second, the anteriorportion is inserted with the lip held away from thetissues to aid inspection and then the tray graduallypushed up posteriorly until a slight excess of mate-rial exudes from the border of the tray at which pointthe tray is held firmly in position until the alginatesets.

When the surface of the alginate is no longer tackyit is set and the impression tray can be removed fromthe mouth. Removal should be performed with a sin-gle firm motion after breaking the seal between im-pression and tissues by pulling the cheeks or lips awayfrom the periphery of the tray. Alginate has poor me-chanical properties and is likely to tear when removedfrom deep undercuts or in thin sections particularlybetween teeth.

The impressions should be rinsed under runningwater to remove mucus and/or blood and spray dis-infected with aqueous 0.5% chlorhexidine solutionor immersed in 1% sodium hypochlorite solution for10 minutes. Following decontamination, the impres-sions should be washed in running water and thensealed in a clear polythene bag that allows the labo-ratory technician to inspect them prior to casting themodels.

These models may be used for the diagnostic stage(see Chapter 24) or may be constructed after otherrestorative work has been done.

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Secondary (Working) Impressions

All other dental treatment should usually be com-pleted prior to the secondary impression stage. Thismight include:

� Extraction of unsavable teeth� Scale and polish and oral hygiene instruction� Restorations� Other periodontal therapy� Mouth preparation for the denture

The design for the partial denture may require thepreparation of the teeth for rest seats and/or modify-ing the shape of the teeth in other ways, e.g. grinding,to allow the chosen path of insertion.

Special tray

A secondary impression is taken in a specially con-structed spaced tray and is only necessary for the archin which a denture will be constructed. The specialtray is usually made of acrylic thus allowing it to beeasily modified by reduction or addition to the bor-ders. The tray should be tried in the mouth and ex-amined to ensure it is short of the tissue reflection byapproximately 2 mm if alginate is to be used. Thisspace allows the impression material to flow aroundthe borders and be moulded by the tissues. There isno need to spend time accurately defining the bor-der extension in those areas of the mouth not relatedto the fit of the denture; for example, with free-endsaddles the anterior labial sulcus depth is of no conse-quence. However, the areas immediately adjacent tothe saddles require special attention.

The tray should be constructed with spacers con-tacting the teeth or tissues in at least three positions,avoiding teeth with rest seat preparations, to ensurecorrect relocation of the tray and an even thickness ofimpression material. In the case of a standard impres-sion technique for a lower arch with free-end saddles,the spacers should contact the ridge towards the pos-terior aspect of the tray.

The most commonly used impression material forpartially edentulous mouths is alginate. It is suffi-ciently accurate, when supported by an evenly spacedtray, for the construction of cobalt–chromium frame-works. However, it does have some limitations:

� Tearing on removal from severe undercuts� Poor dimensional stability due to syneresis� Rapid setting reaction at higher temperatures – the

material in contact with the tissues therefore setsfirst, which may give rise to stresses within thematerial if the tray is moved during setting

The likelihood of tearing can be reduced by block-ing out approximal areas provided they are not es-sential to the overall impression. Soft carding waxis a suitable material since it is easy to apply andto remove. If it is necessary to reproduce severeundercuts, then an elastomeric impression materialshould be chosen, i.e. polyether or silicone. Thepolyethers are stiffer than other elastomers and maytherefore be difficult to withdraw from severe under-cuts. Both materials are expensive, relative to algi-nate, and therefore not frequently used in impres-sions requiring large quantities of material. Theyare, however, more dimensionally stable and shouldbe considered when the impression cannot be castwithin 30 minutes of removal from the mouth (seeChapter 17).

Free-end saddlesOpinions vary regarding the best impression tech-nique for the lower arch with extensive free-end sad-dles. The single-stage elastic impression produces acast which represents the hard and soft tissues at rest(mucostatic). It has been argued that a functional rela-tionship should exist between the various supportingstructures so that both the teeth and the mucosa arecompressed equally. To achieve this and to controlthe load applied to both teeth and ridges there aretwo main approaches:

� Reduce the load� Distribute the load between teeth and residual

ridges

The load can be reduced by leaving a tooth off thesaddles and/or by using narrow teeth.

Distribution of load is more complex and includessuch methods as stress breaking and various combi-nations of the position of rests and clasps. Mucocom-pressive impression techniques attempt to distributethe load by reproducing the tissues covering the ridgeas they are under load.

Free-end saddle rock (downward movement of thesaddle under load) can occur if the denture is con-structed using a mucostatic impression when there isdisplaceable mucosa overlying the edentulous ridge.When load is applied to the occlusal surface ofthe artificial teeth, part of the force is transmittedthrough the denture base and displaces the underlyingmucosa. The degree of movement of the saddle willdepend on the load applied and the condition of thetissues underneath it.

Although it is possible to use a dual-impressiontechnique comprising a first-stage mucocompres-sive impression of the saddle areas with an overall

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25. Partial Dentures – Clinical Procedures 275

alginate final impression, this is a cumbersome proce-dure. An easier and more effective way is to constructthe metal framework on a cast from a mucostaticimpression and then to obtain mucocompressive im-pressions of the saddle areas in order to modify theseareas of the cast. This is known as the altered casttechnique.

Procedure for the altered cast technique1 Working impression in alginate taken in evenly

spaced special tray2 Construction of cobalt–chromium framework

with the addition of close-fitting saddles3 Clinical trial of the metal framework4 Border trimming of the saddles using greenstick

tracing compound – or other suitable material5 Zinc oxide–eugenol paste (or elastomer or impres-

sion wax) impression of the saddle areas ensuringthat the metal framework is held firmly in positionon the teeth whilst the material sets; no direct loadis applied to the saddle areas – this ensures the fitof the framework is not disturbed

6 In the laboratory the free-end saddles are cut awayfrom the original working cast and the denture thenseated in place; the cast is made good by pouringgypsum into the saddle areas

7 The saddle areas are processed onto the metalframework using the altered working cast

This technique has the advantage that it should avoidfree-end saddle rock occurring with a new denture.However, it requires additional clinical and labo-ratory stages, which it can be argued, are not al-ways necessary. An alternative approach is to com-plete construction of the partial denture on theoriginal working cast and to assess the fit in themouth.


There may be sufficient remaining natural teeth to al-low the working models to be mounted on the artic-ulator in centric occlusion simply by placing them to-gether by hand. Their relationship should be checkedagainst that of the natural teeth and, if they are inaccord, guidelines can be marked across upper andlower teeth to inform the technician of this relation-ship.

If there are too few teeth to provide a stable andprecise relationship but there are some natural teeththat contact and form an appropriate occlusal verti-cal dimension in centric occlusion, then an occlusal

registration using shellac-based wax rims is required.One or two rims may be necessary depending uponthe number of teeth remaining. Here the rim(s) sim-ply aid the registration of the horizontal relationshiparound the existing teeth.

The wax rim(s) can be trimmed vertically until justout of contact either with each other or the opposingteeth and a layer of bite registration material placedon them. The patient is asked to close his back teethtogether and the occlusion registered.

If, however, the natural teeth do not give an in-dication of either the vertical or horizontal relation-ship then the reference position for the constructionof the dentures will be centric relation. The regis-tration procedure resembles that used in the com-plete denture technique that will be discussed inChapter 26.

Sometimes it is more convenient to register the oc-clusion after the construction of the metal frameworkwith wax rims attached to the framework. For exam-ple, in cases of lower free-end saddles. This has theadvantage that the framework will ensure proper lo-cation and support for the rims. However, if there aresections of the framework that have an occlusal rela-tionship, e.g. the occlusal aspects of rest seats, thenocclusal registration and articulation will be essentialfor the construction of the casting. If the metal frame-work is not constructed to an accurate occlusal recordin the first place, much grinding may be necessary attry-in.

Try-In of the Wax/Metal Partial Denture

First check that the design constructed by the labora-tory conforms to the prescription and that the fit onthe model is satisfactory.

The try-in procedures will be determined bywhether it is a wax or metal try-in. If a wax try-in thenthe artificial teeth will have been set-up. The checkprocedure in this case should include:

� Fit and adaptation� Retention and stability� Occlusion� Occlusal vertical dimension� Tooth position and aesthetics

First examine the mouth and occlusion without thedenture as a reminder of the relationship. An appre-ciation of the retention and stability of the denturecan be gained at this stage by checking the general fitof the base and adaptation to the supporting tissues.A comparison should be made of the occlusion with

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and without the denture in place to ensure that thenatural teeth still come together – unless, of course,the partial denture(s) has been specifically designed tomodify the horizontal and vertical occlusal relation-ships. Tooth position should be assessed in relationto both stability of the prosthesis and aesthetics. Fi-nally, the dentist should check the shade of the arti-ficial teeth against the natural teeth before allowingthe patient to inspect them. The patient’s opinion isobviously important but, if possible, try to persuadehim/her to look at the mouth in a mirror at a realisticviewing distance, i.e. 2 or 3 feet away. Many patientshold a mirror very close to the face and mouth ratherthan from the distance others normally see them.When both dentist and patient are satisfied with thetrial procedures the wax try-in can be returned to thelaboratory.

For a metal try-in, first check the general fit by en-suring that the rests fit snugly into the prepared seatsand that the denture can be inserted and removed withrelative ease. It is most important to check that themetalwork does not interfere with the occlusion. Forthis reason it is common to inspect the metal frame-work before the addition of the artificial teeth or sad-dles. If the patient is to receive partial dentures inboth upper and lower arches then the sequence is asfollows:

� Check the occlusion of the natural teeth� Seat one framework in the mouth and reassess the

occlusion – if the natural teeth do not contact re-duce the metal accordingly

� Take out the first framework and seat the otherand repeat the occlusal examination

� When satisfied that both frameworks are individu-ally satisfactory, examine the occlusion with bothin place. Once again adjust the metal accordingly

Note. It is usually appropriate to limit grinding to themetal framework but on occasions reduction of theopposing tooth structure may be warranted to gainsufficient space to accommodate a sufficient thicknessof metal.

If the upper anterior teeth are to be backed with anextension of the metal framework to give them addi-tional protection, then it is important that a wax trialof tooth position is assessed to establish the correcttooth position and hence the appropriate position ofthe metal backing.

When the metal try-in has been performed, teethcan be added, either in the laboratory or at thechairside (if small in number) and a further try-in completed. On this occasion occlusal discrepan-

cies should, if the previous visit was performed ade-quately, be due only to the artificial teeth or wax andcan be dealt with accordingly. When satisfied withthe occlusion and aesthetics the try-in is sent to thelaboratory for processing.

Insertion of Dentures

When the processed dentures are returned from thelaboratory the acrylic components should be checkedfor surface imperfections such as sharp ridges or ‘pim-ples’. The denture should then be inserted without un-due pressure until firmly seated. Once again a check ismade of fit in relation to adaptation and the extensionof the borders. The fitting surface can be checked us-ing a pressure indicating paste to ensure even contactover the entire surface.

If the partial denture has a metal framework, theadaptation of the rests to the teeth and the generalfit of the metalwork should be inspected as duringthe try-in visit. If the denture does not appear to befully seated then, if the metal try-in was performedproperly, it should only be the acrylic component thatrequires attention. Ensure that acrylic ‘flash’ has notextruded under the rests or the metal contact areasadjacent to the natural teeth.

If the design of the lower denture includes a free-end saddle, the denture should be examined for down-ward movement of the saddle under load. This is doneby resting the fingers of one hand on the anteriorframework while applying pressure to the saddle withthe index finger of the other hand. If a free-end saddlerock is evident, it will be determined by movement ofthe anterior framework away from the teeth. In thiscase the fitting surface of the free-end saddle(s) willrequire modification. This can be done using either achairside or laboratory reline.

Chairside reline

A chairside reline can be completed using one of theself-curing polymers marketed for use in the mouth(e.g. Tokuso Rebase). The technique is as follows:

1 Having checked for correct extension, the fittingsurface of the saddles and the borders are cleanedand dried – they can be roughened if the resin isnot ‘fresh’

2 Bonding agent, if supplied, is painted sparingly onthe area to be relined

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25. Partial Dentures – Clinical Procedures 277

3 By following the manufacturer’s instructions, a mixof the material is applied to the saddle areas andthe denture inserted in the mouth

4 The framework is held firmly in place, with no di-rect load being applied to the saddles

5 After 2 or 3 minutes the denture is removed whilstthe polymer is still rubbery to check that it has notflowed into undercut areas and that there are noimperfections

6 Excess can be trimmed away with a sharp knifeand the denture returned to the mouth for a furtherperiod to allow curing

7 When rigid, the borders are trimmed and polished8 A final check is made of the occlusion

Such a reline should last many months and has the ad-vantage that it is completed with the patient present.A period without the denture is therefore avoided.It is also suitable for making during domicillaryvisits.

Laboratory reline

A laboratory reline requires impressions of the sad-dles, which can be completed using zinc oxide–eugenol paste, elastomers or impression wax. It maybe necessary to reduce undercuts to prevent fractureof the stone model when the denture is removed andalso to grind a thickness from the fitting surface tomake more space available for the impression mate-rial. As before, the fitting relationship of the metalframework to the natural teeth must be maintainedby ensuring that the occlusal rests are correctly seatedthroughout the impression. Readjustment of the oc-clusion must be anticipated when the relined dentureis fitted.

If a reline at the fit stage of denture constructionis a planned procedure, sufficient space to accommo-date the impression material can be predetermined byusing metal foil 1 mm thick over the saddles prior toadding the acrylic resin in the laboratory.

Completion of the insertion stage

When the fit of the denture is considered satisfactory,it should be examined for an even and simultane-ous occlusion and adjusted, if necessary, to allow free

movement between centric occlusion and centric re-lation.

When satisfied with all aspects of the denture thepatient is shown how to insert and remove it from themouth without damaging either the tissues or suscep-tible components such as clasps.

Finally, the patient should be given advice and guid-ance on denture wearing, especially if a first-timewearer, and instructions on cleaning both the dentureand the natural teeth. Verbal communication shouldbe reinforced by giving the patient a sheet of writ-ten instructions. Simple guidelines on cleaning are asfollows:

Unless your denture(s) and remaining natural teethand gums are kept really clean, there will be an in-creasing amount of tooth decay and gum disease. Toprevent this you should

� Clean your teeth and rinse your denture(s) aftereach meal

� Pay particular attention to cleaning the teeth nextto the denture

� Avoid in-between meals snacks, especially sweetand sticky foods.

When brushing your partial denture, handle it care-fully to avoid bending or breaking any of the parts.The intricate design of a partial denture makes it sus-ceptible to plaque build-up and a routine of brush-ing using a soft toothbrush and soap and water andsoaking in a denture cleanser every night will ensuremaximum cleanliness.

Review

A week after the insertion, the patient should be re-viewed. Any problems to do with comfort and func-tion should be discussed and the denture supportingarea examined for ulceration or erythema. It may benecessary to ease the denture in such areas.

The occlusion should be rechecked with articulat-ing paper and adjusted if the displacement of the den-ture bearing areas has resulted in uneven contact.

Continuing care should be arranged and the patienttold about the importance of maintenance of the den-ture and surrounding tissues and the need for regularrecall to check for caries and periodontal disease.

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Chapter 26Removable Prosthodontics: Complete Dentures

Whilst the number of edentulous individuals is decreasing as more people retain their teeth into old age,the provision of complete dentures remains an important aspect of restorative dentistry. It is still much moreof an art than a science and the skilled operator exercising a judgement based on experience and artistrywill have greater success. This chapter considers the design and construction of complete dentures togetherwith overdentures.

Introduction

When the natural teeth are lost, there is a correspond-ing reduction in the alveolar bone resulting in loss ofsupport for the perioral muscles and tissues. Com-plete dentures are necessary to restore and preservethe facial appearance and masticatory function andthey play a major role in the physical and mental well-being of the individual. The loss of all the natural teethand the construction of complete dentures can be con-sidered as the final phase of restorative treatment andshould, where possible, be the product of a plannedtransition from the natural dentition. This transitionperiod would normally include a period when par-tial dentures are worn and would allow the individ-ual to adapt to and master the techniques of wearingprostheses that should encourage ready adaptation tocomplete dentures.

Functional Aspects of Complete Dentures

Retention

Retention may be defined as the resistance of a den-ture to dislodgement (usually directly away from theridge) and in complete dentures depends on two in-teracting factors. These are:

� Muscular forces� Physical forces

Muscular control is very important for complete den-tures, especially in the lower arch. If the shape of thepolished surfaces of the denture is in harmony withthe oral musculature so that the muscles when func-tioning tend to seat the dentures rather than dislodge

them, retention will be enhanced and the patient’s ac-quisition and development of the necessary control-ling skills will be easier.

Physical forces depend upon:

� Adhesion – the force of attraction between dis-similar molecules in close contact (acrylic–saliva–mucosa)

� Cohesion – the force of attraction between likemolecules (saliva–saliva)

Both are influenced by the nature, quantity, surfacetension and viscosity of saliva as well as the accuracyof fit of the prosthesis. A thin saliva film provides thebest retentive force. For optimum retention denturesmust be correctly extended and closely adapted to thetissues.

The flanges of a denture must be adequately ex-tended and correctly shaped to produce the borderseal and to provide resistance to the ingress of airthat would otherwise destroy the physical forces.The magnitude of physical retention is also relatedto the area covered by the denture and it is there-fore important to utilise the maximum available(Fig. 26.1).

Support

Support provides the resistance to the compressiveforces of chewing, swallowing, clenching etc. Thepressure on the underlying mucosa and bone is re-duced as the support area is increased, even thoughthere is evidence that individuals with well supporteddentures can chew with higher forces, so again themaximum possible area should be used. Close adap-tation of the impression surface of the denture ensuresan even distribution of load to the tissues.

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26. Complete Dentures 279

Fig. 26.1 The fitting surface of two lower dentures.The lower picture shows a denture that is grosslyunderextended in both lingual and buccal sulci. The upperpicture shows one that is correctly extended.

Stability

This may be defined as the resistance of a denture todisplacement (mainly in a lateral direction) by func-tional forces. The degree of stability depends uponthe shape and consistency of the ridges and palate foran upper denture and the relationship of the denturebase to the underlying bone. Flat ridges readily allowlateral movement of the dentures. Maximum stabilityis gained when the ridges have pronounced contoursand where there is little displaceable overlying softtissue (Fig. 26.2).

Construction of Complete Dentures –Clinical Stages

The construction of complete dentures by con-ventional techniques involves the following clinicalstages:

Fig. 26.2 Types of alveolar ridge. The models on the leftshow ridges that are pronounced and will give goodsupport to the dentures whilst those on the right showconsiderable resorption. A denture made for such a flatlower ridge will require considerable adaptation by thepatient in order to stabilise and control it.

� Assessment of the patient, treatment planning andpreliminary impressions

� Final impressions� Recording jaw relationships and choice of artificial

teeth� Checking trial dentures� Inserting and reviewing the dentures

Assessment of the patient

An assessment of the patient will include a past den-tal history and medical history taken in a calm andrelaxed atmosphere. This background information ispossibly more important with complete dentures thanwith any other aspect of dental treatment. A greatdeal can be ascertained about the individual’s expec-tations and their motivation for seeking treatmentthat can have a direct bearing on the eventual suc-cess or otherwise of dentures. Sometimes, especiallywith those with no previous denture wearing experi-ence, the level of expectation for both aesthetics andfunction from dentures can be unreasonably high.

The history of experience of wearing dentures isparticularly valuable since it is likely that the indi-vidual who has worn the same set of dentures suc-cessfully for a reasonable length of time will morereadily adapt to new dentures than will the individ-ual for whom a series of unsuccessful dentures hasbeen made. Time spent at this early stage will helpelicit whether it is the design and construction of

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previous dentures that is at fault or if the personalityand mental attitude of the patient are the overridingfactors. It will also help develop a closer rapport withthe patient and help the dentist gain a greater under-standing of the prosthetic requirements.

Medical historyA thorough medical history should include knowl-edge of any drugs being taken since their relationshipto certain oral symptoms is well recognised. It is alsoimportant to recognise that the elderly tend to sufferfrom multiple pathology and a patient may be tak-ing several drugs. A complaint of a dry mouth maywell be associated with atropinic or tricyclic drugsand can have important consequences for successfuldenture wearing. There are few medical conditionsthat contraindicate the construction of complete den-tures though several, e.g. stroke, Parkinsonism anddebilitating disease, may severely reduce the patient’sadaptive capacity and chances of success.

ExaminationAn examination of the patient should include an ex-traoral inspection that effectively begins when theindividual enters the room. Information on mobil-ity, communication and general demeanour can berapidly ascertained. Attention should be paid to theface, particularly lip posture at rest and during func-tion, and possible habits associated with denturewearing such as lifting the lower denture with thetongue. The intraoral examination should includea thorough screening of all the tissues for pathol-ogy and a more detailed assessment of the denturebearing tissues. The dentist has an important rolein the early detection of oral neoplasia, particularlycarcinoma. Palpation of the alveolar ridges will de-termine their consistency and elicit the presence ofpainful areas. Denture construction should be de-layed if pathology is present until such time as theoral tissues are returned to an appropriate healthystate.

The patient’s dentures should be inspected first outof the mouth for cleanliness, general shape, tooth po-sition and occlusal relationships and tooth wear. Theycan then be examined individually intraorally for fit,border extension, tooth position in relation to thetongue, cheeks and lips and aesthetics before mak-ing a general assessment of stability and retention.With both dentures in place, horizontal and verticalocclusal relationships and freeway space can be deter-mined. This examination will identify design features

that can either be reproduced in the new dentures orbe modified to create improvements.

Other investigations that may be necessary includeradiographs that may reveal the presence of retainedroots, buried teeth and other rarer pathology suchas cysts, blood screening for deficiency states andsmears or culture to confirm the presence of Candidaalbicans.

Pre-prosthetic preparation of the mouth

ExtractionsRetained root fragments are the most common ra-diographic finding but, as with unerupted teeth, theirremoval should not be automatic. Surgical removalcan involve the loss of a great deal of bone, whichmay already be in short supply, and could result in areduction of the useful denture bearing foundation.Removal of roots or teeth should normally thereforebe limited to those that are:

� Incompletely covered by bone� Associated with periapical infection� Showing signs of cystic change around the crown� Associated with pain or discomfort

Modifications to the alveolar ridgeThe success of complete dentures may be improvedby surgical modification to the alveolar ridge. Theprocedures that might be used are:

� Reduction of bulbous maxillary tuberosity� Smoothing of irregular bony prominences� Removal of flabby ridge� Ridge augmentation� Implants

Treatment plan and prognosis

Having considered all the available information itmay well be that the dentist will consider that hecannot improve upon the existing dentures. Also, ifit has not been possible to determine the cause of acomplaint, it is unwise to offer to make new denturessince faults (if they exist) may be perpetuated andthe chances of success reduced. In either case, consid-eration should be given to referring the patient to aspecialist. Certainly, in these circumstances, the firstoption on the treatment plan could be to explain mat-ters carefully to the patient with suitable reassurance,but to offer no treatment.

Other treatments, depending on the clinical find-ings, could include:

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� Relining/rebasing or other adjustments to an ex-isting denture

� Construction of new dentures using either a con-ventional or a duplication technique

The prognosis for successful treatment is dependenton a number of factors including the patient’s age,adaptability, demeanour, previous denture experienceand the anatomy of the mouth.

Preliminary impressions

Preliminary impressions can be taken using eithermetal stock trays or plastic disposable trays. A highviscosity, irreversible hydrocolloid (alginate) or im-pression compound is the material of choice.

CoverageEach impression should cover the entire denture-bearing area and should achieve the closest possiblecontact with the mucosa.

ExtensionThe upper impression should extend to the functionaldepth of the labial and buccal sulci, including thetuberosities and hamular notches, and posteriorly tothe junction of the hard and soft palate. The lowershould extend to the functional depth of the lingual,labial and buccal sulci and cover the retromolar padsposteriorly. Only limited accuracy is needed at thisstage since this will be an essential component of thefinal impression.

Final impressions

Special traysSpecial trays are required to ensure that the final(secondary or working) impressions can be achievedwith accuracy of detail and borders moulded to thefunctional width and depth of the sulci. Stock traysare manufactured to average sizes and therefore arelikely to be less than ideal for any individual. Al-though modification of stock trays is possible, theresultant impression is still unlikely to be extendedcorrectly.

Self-curing acrylic is most commonly used for spe-cial tray construction. It has the advantages of beingrelatively inexpensive, simple to shape and is rigid inmodest thickness. The upper tray should have a smallhandle placed in the midline of the anterior region,sloping forwards at an angle of 45◦. This configura-tion avoids interference with the lip. On the lower,

the handle is vertical and two finger rests are placed,one in each of the second premolar regions. This en-ables the index fingers to support the tray withoutinterfering with the borders of the impression.

Special trays can be divided into two types, close-fitting or spaced.

Close fittingAs the term implies, no spacing is used. Zinc oxide–eugenol paste is usually the material of choice in thistype of tray, although other materials such as siliconeperfecting pastes may be used. These materials are ac-curate in thin film but require adequate support, espe-cially at the borders. Correct tray extension is there-fore important and can best be achieved by checkingthat the borders are slightly short (1–2 mm) of thefunctional depth of the sulci and then using green-stick tracing compound (or other suitable material)to establish the optimum extension. This techniquewill define not only the depth of the sulcus but alsoits width. This combination can be used for upperand lower impressions provided there are no oppos-ing bony undercuts.

It has the advantage that the materials are stablewhen set and less susceptible to distortion than algi-nate. No adhesive is necessary for zinc oxide–eugenolbut the tray must be clean and dry.

SpacedAlginate and plaster of Paris impressions requirespaced trays. The spacers ensure an even thick-ness of the impression material for maximum accu-racy. Alginate is specifically indicated when oppos-ing substantial undercuts exist that could prevent thewithdrawal of a close-fitting tray and a non-elasticmaterial.

The tray can be constructed with ‘built-in’ stops,that contact the mucosa, or greenstick tracing com-pound can be added at the chairside. This should becompleted before checking the border extension sincethe stops will effectively lift the tray away from thetissues and it may then appear underextended.

The tray borders should only extend to within1–2 mm of the full depth of the sulcus to leave roomfor the impression material to flow around them andfill the remaining space. This avoids the common er-ror found with alginate impressions of displacing thetissues and thus overextension.

Adhesive specific to alginate is more efficient thandepending solely on holes drilled in the trays for reten-tion. No adhesive is required for plaster impressionsbut the tray must be clean and dry.

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Objectives of final impressionsThe objectives of the final impression are to definethe support area for the denture to achieve optimumretention and stability.

The flabby upper ridgeThe combination of a complete upper denture op-posing natural lower anterior teeth may result in thedestruction of the maxillary alveolar ridge oppositethe natural teeth and its replacement with fibrous tis-sue. Conventional impression techniques will tend todisplace this type of ridge which needs to be recordedin its ‘rest’ position. To minimise displacement a lowviscosity alginate or plaster of Paris can be used. Analternative is to take a two-stage impression using azinc oxide–eugenol paste in a close-fitting tray thatcovers only the firm part of the ridge and then filling inthe anterior region with a fluid mix of plaster of Paris.

Jaw relationships

Jaw relationships are recorded using occlusal rims;these consist of a base and a rim. A variety of ma-terials may be used for constructing the bases, but arigid material such as shellac or acrylic is preferred,to avoid distortion. Rims are invariably made of wax,either performed or fashioned from sheets.

Objectives of occlusal rimsOcclusal rims are used to transfer morphological in-formation about the eventual polished surfaces andocclusal surfaces of the dentures from the patientto the laboratory, to enable the technician to pro-ceed to the wax trial denture stage. In essence, theyprovide the technician with details of precisely wherein relation to the denture-bearing areas, the artificialteeth and supporting material should be located. Oc-clusal rims should record the following information:

� Aesthetics and arch form� Jaw relationships

Aesthetics and arch formThe upper rim should be adjusted to the required in-cisal level with the appropriate lip support. This de-pends on the length of the lip and the age of the pa-tient and although the average visibilities of the cen-tral incisors to the upper lip line (at rest and withoutsmiling) are often quoted as:

� Young person: 2 mm below lip� Middle age: 1–1.5 mm below lip� Old age: 0–2 mm above lip

Fig. 26.3 Occlusal registration for complete dentures. Theupper rim shows the registration of the occlusal plane, theintercanine distance, incisal length and tip position andmidline. The rims are sealed in centric relation by ZOEpaste.

There can be considerable individual variation andthese measurements should therefore only be used asa guide.

The labial surfaces of the upper anterior teeth givesupport to the upper lip and provide facial contour.Frequently, the artificial incisors may be incorrectlysited in a more lingual position than their naturalcounterparts. The incisive papilla is an importantlandmark that can be used as a guide when trim-ming the labial face of the rim. Studies have shownthat the incisal edges of the upper central incisorteeth lie approximately 8–10 mm anterior to the cen-tre of the incisive papilla when the dental base re-lationship is class I. This structure is affected verylittle by resorption and remains fairly constant inposition.

The upper rim should be trimmed parallel to the in-terpupillary line. The ala-tragal line (passing throughthe tragus of the ear near the external auditory mea-tus and the ala at the base of the nose) can be usedas a guide in the anterio–posterior plane. The cen-tre line is marked on the labial face of the rim; thisusually corresponds with the centre of the philtrum(Fig. 26.3).

Correct arch form is achieved by trimming the buc-cal and palatal surfaces so that the rim lies within theneutral zone, i.e. it lies between the opposing forcesof the lips/cheeks and tongue which ensures stability.The tongue should not be cramped and therefore thelower rim should be trimmed from the lingual aspectuntil the tongue can lie in its normal resting positionwithout dislodging the rim.

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Registration of jaw relationshipsThe objective is to record the jaw relationship at thechosen occlusal vertical dimension with the mandiblein its most superior, posterior position (centric jawrelation/centric relation, Chapter 8). With completedentures centric occlusion is constructed to be coin-cident with centric relation.

The height of the lower occlusal rim must be ad-justed so that, with the patient in the upright posi-tion and the mandible at rest, there is a space of ap-proximately 3 mm between the rims. This separationis called the freeway space (interocclusal clearance).This is achieved by assessing the rest vertical dimen-sion with the patient sitting upright with the headsupported so that the tissues are in their normal rela-tionships. Direct measurement is usually made witheither a Willis gauge or marker dots (on the skin) anddividers. The weight of the lower denture (or occlusalrim) can affect the rest position of the mandible, andthe lower rim should therefore be in situ during theassessment. The occlusal vertical dimension is then as-sessed with the two rims in contact and wax removedfrom the height of the lower until there is sufficientfreeway space.

In the elderly it is usually wiser to accept a slightlylarger than average freeway space, especially if olddentures with a reduced occlusal vertical dimension,resulting from a combination of alveolar resorptionand tooth wear, have been worn for many years.

When the rims have been adjusted to their finalshape and size, centric jaw relation can be recorded.This can be achieved using a variety of techniquesbut the objective is to ensure that the rims contactsimultaneously on both sides and therefore that thereis even pressure. This can be ensured by removing 1–1.5 mm of wax from the anterior and posterior partsof the lower rim leaving pillars of wax in the premolarareas to maintain the occlusal vertical dimension.

The patient is manipulated into the retruded arcof closure with both occlusal rims in the mouth. Lo-cating lines can be scored through both rims in thepremolar areas to serve as a guide. V-shaped notchesare cut into the upper rim in the molar regions and it isthen returned to the mouth. Mounds of a recordingmedium, such as plaster of Paris (Gypsogum), soft-ened wax or an occlusal registration paste, are placedon the lower rim, which is then placed in the mouth.The patient is guided again into the retruded arc sothat the rims contact evenly and the mandible is sup-ported whilst the material sets. Both rims can then beremoved from the mouth while sealed together (Fig.26.3).

The guidelines are checked to ensure that they cor-respond, and finally sticky wax is run over the rimsand recording medium to reinforce the areas prior todespatch to the laboratory for the fabrication of trialdentures.

Choice of teethThe prescription to the technician should include themould size and shade, together with the make andmaterial to be used for the anterior and posteriorteeth. Anatomical or non-anatomical (cuspless) post-erior teeth should be considered with non-anatomicalusually being reserved for those with:

� Atrophic alveolar ridges� The elderly� Difficulty in consistently returning to the centric

jaw relation (e.g. Parkinsonism)� Existing dentures with very worn teeth that have

permitted unrestricted jaw movements

The size, shape and arrangement of anterior teethhave a significant influence on facial appearance andthe psychological importance of the face and teethcannot be over exaggerated. The choice of toothmould is difficult when no natural teeth or pre-extraction records are available. There is little ev-idence to support the much-publicised theories ofmatching tooth mould to face form or that femaleshave rounded teeth and males square, rugged teeth.In general, the size and mould of the artificial teethshould be chosen to fill the space available in the inter-canine region of the upper occlusal rim.

Individuals often request small, light coloured teetharranged symmetrically to create a youthful appear-ance but this can result in a typical ‘denture wear-ers’ look’ not reflecting their biological age. There is,however, much that can be done to achieve a naturalappearance including setting the teeth irregularly andusing darker shades to more appropriately match thepatient’s age.

Articulation

In the laboratory, the type of articulator appropriateto the chosen posterior teeth should be used. An aver-age condylar path (average movement) or adjustablearticulator is necessary for setting up cusped teeth toensure a balanced articulation. This type of articu-lator simulates protrusive and lateral movements ofthe jaw and working and balancing side contacts cantherefore be assessed.

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A simple hinge articulator should only be used forsetting up cuspless teeth using either metal templatesof a sphero-ellipsoidal nature (Boyles plates) or theteeth set to a flat occlusal plane with posterior bal-ancing ramps to maintain a three point contact ratherthan full balanced articulation.

Trial dentures

The wax try-in denture should be returned to theclinic together with the articulator. This allows theclinician to assess the dentures on the articulator priorto examining them in the mouth. The assessment onthe articulator should include tooth position, archshape, extension of the wax work into the sulci andacross the retromolar pads and the posterior aspect ofthe palate. It should also include the occlusion and thegeneral standard of the wax contouring and surfacefinish.

The objective of the intraoral inspection is to checkthe information recorded on the occlusal rims and tocorrect any errors before processing the dentures. Thewax try-ins should therefore be checked for retention,ensuring that maximum coverage has been achieved,and that the borders are suitably extended. The jawrelationships can then be assessed first in the hori-zontal plane and then the vertical dimension. Withthe patient sitting upright, the head supported andthe mandible in the retruded position, the occlusionshould be even and simultaneous without interferenceor deviation.

If the occlusion is obviously incorrect then, follow-ing an assessment of the occlusal vertical dimensionand freeway space, the lower posterior teeth shouldbe removed and the wax rim re-established prior to anew occlusal registration.

When the dentist is satisfied with all aspects of thetry-in the patient should inspect the trial dentures infront of a mirror. It may be helpful if the patient’s part-ner also takes part in this exercise to ensure agreementon the appearance of the teeth.

Finally the extension of the posterior border ofthe upper trial base is checked. This should nor-mally be placed at the junction of the movingtissues of the soft palate and the fixed tissues an-teriorly and should extend laterally over the hamu-lar notches. The Cupid’s bow shape gives an effec-tive seal and is achieved by carving into the surfaceof the working model using, for example, a Lecroncarver. The shape is carved deeper at the posterioredge with a gradual taper anteriorly to account forthe reduced thickness of the submucosa. This carving

Fig. 26.4 Post dam outlined on model.

can be performed after the patient has left the surgery(Fig. 26.4).

Processing

The procedures used to flask, pack and process heat-cured acrylic can result in dimensional changes andare commonly known as the laboratory processingerrors. These can cause occlusal disharmony and anincrease in the occlusal vertical dimension which willneed to be eliminated at the fitting stage. The mostlikely causes are:

� Dimensional change of the wax during flasking� Excessive packing pressure resulting in the teeth

being forced into the plaster� Incorrect alignment or badly fitting sections of the

two halves of the metal flask� Excessive flash either because the acrylic resin

dough was too rubbery when packed or insuff-icient packing pressure was used

� Thermal and polymerising changes in the acrylicresin

If the dentures have been processed using the splitcast technique they can be remounted on the origi-nal articulator. Usually the incisal guidance pin willnot be in contact with the incisal guidance table andequilibration of the artificial teeth will be necessary.This involves first correcting the centric occlusion atthe defined occlusal vertical dimension and then de-veloping balanced articulation.

Insertion of the dentures

Prior to inserting the processed dentures they shouldbe inspected to ensure that the fitting (impression)

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surfaces are free of imperfections, such as acrylicpearls or sharp ridges. If present, these should betrimmed and smoothed. Excessive, opposing under-cuts should have been assessed at an earlier stage and,if appropriate, blocked out prior to processing but itmay be necessary to remove minor undercuts to allowthe dentures to be inserted.

The dentures should be assessed individually in themouth for fit, stability and comfort before examiningthem in combination. If there are signs of discomfort,pressure disclosing pastes in spray form can be usedto determine local areas of pressure that can then betrimmed and smoothed accordingly.

On closure the teeth should meet evenly and simul-taneously without interference or lateral deviation.Minor adjustments to the occlusion can be performedat the chairside using thin articulating paper to markthe teeth and appropriately sized burs or stones. Theaim should be for a positive, even occlusion withevidence of some lateral and protrusive movementwithout interference. If a more major occlusal erroris evident, this should be corrected using laboratoryfacilities.

Check recordA thin layer of warmed, toughened wax is applied tothe lower posterior teeth and the mandible closed inthe retruded relationship ensuring that closure of themandible is stopped before tooth contact occurs toprevent premature contact and lateral or protrusiveslide. This pre-centric record allows the technician toremount the dentures on the articulator and to carryout the necessary modifications to the occlusion.

When satisfied with all aspects of the dentures thepatient is given information and guidance on wear-ing dentures and instructions on keeping them clean.Follow-up visits are made, as necessary, to ensure thatthe new dentures are comfortable and successful.

Duplication Technique (Copy Dentures)

The duplication technique can be used to constructnew complete (or partial) dentures if suitable existingdentures are available. The dentures are duplicated(copied) and these duplicates then form the frame-work for the new set. A variety of techniques is avail-able but all have the same objective with a numberof the techniques being very similar, only differing inthe materials used.

The existing dentures need to have been worn suc-cessfully to warrant duplication although (rarely) the‘best of a bad bunch’ can be chosen for a patient

who has had many dentures constructed by a vari-ety of dentists in order to make controlled modifica-tions without damaging the set that they prefer. Thecommon indications for duplicating dentures are:

� The elderly who may have a reduced adaptive ca-pacity that restricts the use of conventional con-struction techniques

� Others with reduced adaptive capacity (e.g. strokeand Parkinsonism patients)

� Immediate dentures – to reproduce the originaltooth position

� Dissatisfied patients – in order to modify the mostacceptable dentures

� Special features – to copy the shape of an exist-ing denture that may have unusual design featuressuch as flange plumping in cases of seventh nervefacial palsy

� Spare dentures – for those who require an extraset to avoid embarrassment

Advantages of the duplication technique include:

� Exact reproduction of tooth position and contourof the polished surfaces

� Ability to incorporate controlled modifications� The minimisation of problems of adaptation� Clinical attendances are reduced

The most commonly used techniques can be per-formed at the chairside although laboratory methodsare available. The objective of them all is to take im-pressions of the existing dentures in order to be able topour duplicates in self-curing acrylic which are thenused to record the impressions of the mouth and jawrelationships. The duplicates (copies) are obtained atthe chairside by taking impressions of both surfacesof each denture with alginate or silicone putty eitherin pairs of disposable plastic trays or in a plastic soapdish which has had a window cut in the side to allowspace for the sprues. The sprues, which are attachedto the heels of the dentures, permit the duplicates tobe poured using a fluid mix of self-curing acrylic. Thisis usually carried out in the laboratory under an ex-traction hood, for health and safety reasons.

The acrylic duplicates can be modified to correctunder/over extension and used as ‘special trays’ inorder to obtain final impressions and also to recordthe jaw relationships by placing a suitable registra-tion material between the teeth. The contours of thepolished surfaces should be carefully guarded, unlessthere is reason for change, in order to preserve theoverall shape of the final dentures. It should be ap-preciated that the self-cure duplicates are only usedas templates for the processing of the heat-cured

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acrylic dentures and are not incorporated into the fi-nal prostheses.

Immediate Dentures

An immediate denture is one that is constructed priorto the extraction of the natural teeth and inserted intothe mouth immediately after their removal.

The benefits to the patients are that they are neverwithout teeth and therefore the soft tissue profile ismaintained; the dentures assist mastication and hencenutrition; adaptation is enhanced and the develop-ment of abnormal muscle behaviour is avoided bymaintaining normal function. Benefits to the dentistinclude the use of the existing dentition for recordingjaw relationships and for choosing shade and mouldof artificial teeth; tooth position can be reproducedor controlled modifications made as desired.

Disadvantages of immediate dentures include theextra clinical visits that are necessary for after careand eventual replacement of the dentures. It is notpossible to check the aesthetics of the teeth to be re-placed as there can be no try-in stage. If it is not pos-sible to extract the teeth without resorting to surgi-cal techniques cast trimming to simulate the residualridge may be unsatisfactory.

Due to the improvements in adult oral health itis now relatively uncommon to have to provide im-mediate dentures replacing most of the natural teeth.However, depending on the number of teeth remain-ing various options for tooth replacement should beconsidered:

1 Extract posterior teeth, allow the ridges to heal forat least 3 months and construct immediate den-tures to replace the anterior teeth. The advantagesof this are that the healed posterior ridges extendthe life of the prostheses and it is an economic pro-cedure requiring the minimum number of patientvisits – it may, however, allow the possibility oflateral tongue spread

2 The first procedure can be modified to either ex-tract the posterior teeth and allow the ridges toheal, construct partial dentures and then add theremaining teeth to these dentures as an immediateprocedure. Alternatively, extract the posterior teethand fit immediate partial dentures and then add theremaining teeth to these dentures as an immediateprocedure

Both modifications attempt to bring about a suc-cessful transition to complete dentures; however,

the number of extra visits may be unrealistic. Also,a high level of motivation is required to wear sim-ple acrylic partial dentures replacing only posteriorteeth.

3 Extract all the remaining anterior and posteriorteeth and fit immediate dentures. This has the ad-vantage of completing the extractions at one oper-ation which may be important, for example, priorto cardiac surgery but can result in rapid loss of fitof the dentures caused by widespread alveolar re-sorption which necessitates frequent maintenancevisits

Whenever practicable, flanged immediate denturesshould be used since they give superior retention, in-crease the life of the dentures, add strength to thedenture base, allow for repositioning of the artificialteeth, protect extraction sockets and aid healing. Theycan also be used when marked periodontal pocketingis present which would preclude the use of the open-face (gum-fitted) design and they support the use oftemporary lining materials which is helpful during themaintenance phase.

Principles of Overdentures

The term overdenture describes a prosthesis that de-rives support from one or more abutment teeth orroots by completely enclosing them beneath its fit-ting surface. Complete overdentures are more com-mon than partial overdentures.

Rationale for overdentures

The maintenance of alveolar bone is probably thestrongest argument for the retention of teeth or rootsas overdenture abutments:

� The mandibular ridge is particularly susceptible topost-extraction change; maxillary and mandibularalveolar resorption rates are approximately in theratio 1:4

� Clinical experience confirms that alveolar bone ismaintained whilst healthy teeth or roots remain

� Retention of a number of abutments maintains apositive ridge form with a greater height and vol-ume of bone. The denture is therefore more stableand retention should also be improved

The success or failure of a prosthesis is dependentupon the integration of sensory feedback and mo-tor response and the masticatory system relies on

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feedback from receptors in temporomandibularjoints, ligaments, muscles, mucosa and periodontaltissues. The loss of teeth decreases the level of propri-oceptive information.

Sensory feedback can be considered under twoheadings that relate to research studies:

� Tactile sensitivity discrimination (the discrimina-tion of differences in thickness of objects placedbetween the teeth). Little difference has been re-ported between natural teeth, conventional com-plete dentures and overdentures; it is possible thatmuscle spindles play the major role

� Minimal load thresholds (the discrimination ofvarying levels of force). Overdentures give im-proved discriminatory ability at both higher andlower biting force levels. This may prevent exces-sive loads being applied and hence maintain loadsdirected to the alveolar bone within physiologicallimits

There may be some psychological benefit gained froman overdenture. By retaining some of the teeth itmay prevent the feeling of total loss of natural teethand perhaps make eventual transition to conven-tional complete dentures more acceptable. Mastica-tory performance is enhanced since the overdenturewearer has a functional advantage over those withconventional dentures. There is scientific evidencethat overdentures allow the food to be chewed moreeffectively.

Indications for overdentures

� Complete denture opposing natural teeth – pre-vents overloading of mucosa caused by highmasticatory forces and retards rate of alveolar re-sorption thus enhancing long-term success of theprosthesis

� Cleft palate and surgical defects – if the defect isextensive, it may be impossible to provide a satis-factory conventional denture if teeth are lost

� Extreme wear of natural teeth – see Chapter 27� Hypodontia – often a substantial number of per-

manent teeth absent� Poor prognosis for conventional complete den-

tures – degree of bone loss in edentulous areasand unfavourable muscle attachments may indi-cate potential problems

� Doubtful partial denture abutment – overeruptedor periodontally involved teeth may not be satis-factory as conventional partial denture abutments

Patient selection

Overdentures should be considered whenever the lossof teeth is anticipated. There are few general healthcontraindications except for severe debilitating ill-ness, mental handicap, history of bacterial endocardi-tis and some candidates for cardiac surgery. Youth orold age is not a contraindication in itself and over-dentures should be constructed when clinically indi-cated. It is important to inform potential patients ofthe number of visits and time required since this willbe greater than, for example, for a clearance and con-ventional dentures. The ability to attain and maintaina high standard of oral hygiene is essential.

Abutment selection

The choice of abutment is dictated by the numberand location of remaining teeth. Bi-lateral abutmentssymmetrically located are ideal. Canines are the mostoften used teeth with premolars the next favourite(the second premolar being preferred in the maxillasince it is commonly single rooted). Maxillary incisorsare satisfactory but mandibular incisors are the leastacceptable and the use of molars may be limited byendodontic considerations. Adjacent abutments aremore difficult to clean and can make the maintenanceof gingival health a problem.

Dental examination

The clinical examination should include charting ofcaries and defective restorations, assessment of gin-gival condition, periodontal pocket depth and toothmobility and periapical radiographic survey of possi-ble abutments and study models.

A high level of caries activity is undesirable sincethere is a possibility of recurrence in unprotectedabutment teeth or adjacent to margins of copings.Root caries precludes the use of a tooth.

Teeth with a less than ideal periodontal conditionmay have to be accepted. However, the abutmentshould have minimal mobility and adequate bonesupport (half the root length surrounded by bone).An improved crown/root ratio, achieved by reduc-tion of the clinical crown in the doming procedure,will enhance likely success. If positive retention, in theform of root face attachments, is envisaged the abut-ment tooth will be subjected to considerably greaterforces. Substantial bone support for the root is there-fore essential. Active gingival and periodontal diseaseshould be eliminated prior to further treatment.

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When considering endodontic therapy, radio-graphic evaluation is essential although root canaltherapy may be unnecessary in cases of severe wearwhen the root canal may be obliterated by secondarydentine. Single-rooted teeth are preferred for ease ofroot filling and the possible use of the canal for postretention if copings on the abutments are envisaged.

Treatment plan

There are several methods of progressing to completeoverdentures.

Immediate complete overdenturesThe treatment sequence might include periodontaltherapy and endodontics prior to preliminary and fi-nal impressions and recording the jaw relationship.

At the try-in of the trial set-up, a decision is takenon the position of the artificial teeth to replace thosebeing extracted or reduced as abutments, and on theprovision of a flange. Similar criteria are used as forthe normal immediate denture procedure, i.e. the ap-pearance of the natural teeth to be copied or is theposition of the artificial teeth relative to their naturalpredecessors to be altered to modify the aesthetics?Although desirable, it may not be possible to use afull flange because of bony undercuts adjacent to theabutments.

On completion of the denture the chosen teethare prepared as overdenture abutments to producea smooth dome shape with the highest point approx-imately 2 mm above gingival level. A glass ionomerrestoration is placed in the entrance to the root canal.Other teeth are then extracted and the denture fitted.

At the first review visit, one day after the extrac-tions, the root faces and restorations are polished. Theoverdenture is adapted to the abutments by addingself-curing acrylic to the depressions in the dentureover the root faces. Excess acrylic is allowed to es-cape via small vent holes drilled through the denturebase whilst the denture is retained in position by lightocclusal pressure.

Further review appointments will be necessary dur-ing the socket healing and ridge remodelling period.After approximately 6 months the root face can beassessed for possible coverage with copings.

Conversion of existing partial denture tocomplete overdentureExisting partial dentures can be utilised and convertedto complete overdentures using either a laboratorybased technique or a chairside method.

Laboratory method1 Dome-shaped preparation of endodontically

treated abutment teeth2 Impression with partial denture in situ (plus im-

pression of other arch and occlusal record)3 In the laboratory – artificial teeth positioned over

domed root faces and flange added4 Converted dentures fitted

This method has the advantage that the converteddenture has been made in the laboratory and the dis-advantage that the patient will be without a dentureduring construction.

Chairside method1 Endodontic treatment of abutment teeth2 Impression with denture in situ (leave denture in

impression)3 Dome-shaped preparation of abutment teeth4 Tooth coloured self-curing acrylic is placed in the

abutment teeth indentations of the impression andthe impression (with the denture still included) ispositioned carefully in the mouth

5 When polymerisation is complete, the flange isadded with hard chairside reline material

This method has the advantage that the patient is notwithout the denture but has the disadvantages thata lengthy appointment is necessary and the additionsmay be weaker and more prone to fracture.

Treatment of abutment teeth

There are several ways in which abutment teeth canbe used in association with overdentures:

� Domed with access sealed with glass ionomercement

� Gold coping on root face with post� Gold thimble on vital tooth� Attachment fitted to the coping

The selection may often be a personal preference butthe essential difference between the systems is the re-tention of the denture and the extent to which lat-eral forces are transmitted to the abutment teeth. Thedome transmits the least force whilst the attachmenttransmits the most.

Domed root faceThis is the simplest method. The teeth will normallybe root filled and the access sealed with glass ionomercement to provide a fluoride reservoir to assist theprevention of recurrent caries. The level of the domein relation to the gingival tissue may vary according

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(a)

(b)

(c)

Fig. 26.5 Overdenture abutments: (a) Diagram of root face coping and post; (b) clinical case with gold copings on 31|13and glass ionomer cement in |2; (c) stud attachments on 3|3.

to the restorative state of the tooth. Whilst the ideallevel is 2 mm above the soft tissue, pre-existing deeprestorations may cause the removal of more tissue. Inany event the root face should not be sub-gingival. Ifthis occurs, a coping should be used.

Gold copingsDome shapeThis will provide some protection to the root facefrom recurrent caries together with some additionalresistance to lateral displacement of the denture. It isthe most common and usually uses the root canal forretention on a cast post; therefore, endodontic treat-ment is necessary. The profile of the coping may flator raised as a stud (Fig. 26.5) and deficiencies causedby previous caries/restorations can be occluded. Theplacement of the copings should be delayed, if possi-ble, for approximately 6 months after the overdentureis fitted to allow the gingivae to reach a realistic level.

Thimble shapeThis is designed to protect the dentine overlying avital pulp. It offers more retention and stability to thedenture but greater stress is placed on the root and

the extra height creates a less favourable crown/rootratio. Because of its size it intrudes further into thedenture base.

AttachmentsThese increase the retention of the denture greatly butincreased stresses are transmitted on insertion and re-moval of denture and during function. Therefore theabutment roots require excellent periodontal support.Good maintenance is essential and time consuming,and the laboratory costs are greatly increased oversimple castings.

They are very useful when the denture foundationis unfavourable as in a cleft palate or a flat lowerridge or when displacing forces may be high, e.g. acomplete overdenture opposed by natural teeth. Inpatients who cannot tolerate a conventional denturepalate, attachments can overcome the loss of retentionwhere palatal coverage has to be reduced.

There are three basic types of attachments:

� Stud attachments� Bar attachments� Magnets

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The male portion of the stud attachment is usually onthe root and the female portion in the denture (Fig.26.5c). The space required is approximately midwaybetween a dome shape and thimble coping; space isalso required in the denture base to accommodate thefemale portion. Examples of this type are the Rother-mann Eccentric, Dalla Bonna 604 and the Kurer PressStud system.

The bar attachment consists of a rigid bar attachedto abutment teeth and a sleeve in the overdenture. Thebar splints the abutments and distributes stress be-tween them. Substantial loads can, however, be gen-erated with this system. Plaque control is difficultand maintenance of attachments complicated. TheDolder bar and Ackerman bar are examples of thistype.

The magnet system involves a magnet being sol-dered to a root face coping and a corresponding fer-romagnetic block being processed into the denturebase.

Clinical appraisal

Good oral hygiene is the single most important factorthat influences the continued health of the supportingtissues. With inadequate oral hygiene wearing over-dentures can cause:

� Periodontal damage – either gingival hypertrophyor retraction of the gingival tissue with loss of bonysupport. There is a specially high risk if attach-ments are used

� Caries of the root face

Preventive measures and continuing care

Patients should be on a structured continuing careprogramme to provide regular inspection and main-tenance of the denture and abutments.

Effective plaque control of the root faces is essen-tial using a fluoride toothpaste. Topical fluoride gelmay also be useful, both applied directly to the rootface and into the depressions in the fitting surface ofthe denture that overly the abutments. The patientmust also adopt an efficient denture cleansing pro-gramme using hypochlorite solution (see later sectionon ‘Keeping dentures clean’).

Gingival recession is a possible problem and thismay indicate reshaping of the dome preparation andmodifying the fit of the dentures using self-curingacrylic resin chairside reline material and carry outperiodontal treatment as appropriate.

Recurrent caries of the root face may be removedthus modifying its shape or a gold coping might beprovided.

Alveolar resorption occurs mainly distal to theabutments following which stability of the denturewill deteriorate. This will require correction eitherwith a conventional reline technique or with a chair-side reline material.

Advice for New Denture Wearers

A patient receiving new dentures should be givenguidance as to the difficulties that may be encounteredand advice on a cleaning and maintenance regime.Since patients tend to forget verbal information givenat the chairside, written instructions to take home andread at leisure are helpful. There are many denture-cleansing agents on the market but the followingguidelines are suggested:

Getting used to complete denturesThe best results from your new dentures can onlybe achieved with practice and patience. It may takeseveral weeks for you to become fully accustomed tothe dentures. Do not be discouraged by friends orrelatives who tell you how easy it was for them.

To begin with, the dentures may cause an increaseof saliva in your mouth. This should return to normalin a few days. Eat mainly soft foods for the first fewdays and don’t take large bites.

Cut your food into small portions and try tochew with your back teeth on alternate sides.Some people with new dentures find that suckingboiled sweets helps them to get accustomed to thedentures.

When to wear your denturesYou may wear your dentures during the day and nightfor the first week to help you get used to them morequickly. From then on you should leave them out atnight, in a container of water or recommended clean-ing agent. Your mouth needs a rest if it is to remainhealthy.

Keeping your dentures cleanEnsure that your dentures are kept really clean. Rinsethem after each meal and brush all of the surfacesmorning and night with a soft toothbrush and soapand water.

Use the commercially produced cleanser ‘Dentu-ral’ regularly. Follow the instructions on the containercarefully. If your denture has any metal components,

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the ‘dentural’ will not cause any damage provided youuse only the short (half-hour) cleaning period. Rinseyour dentures well after using ‘dentural’.

The comfort of your mouthNew dentures sometimes cause areas of soreness.These may be relieved by leaving the dentures out of

your mouth for 24 hours. If the trouble persists, anadjustment will be necessary. However, if it has beennecessary to leave the dentures out, ensure that theyare worn for 12 hours immediately prior to visitingthe dentist for an adjustment. This will help in locat-ing the exact cause of the trouble.

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Section VProblems


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Chapter 27Tooth Surface Loss

The loss of enamel and dentine caused by means other than caries and trauma has become more significantas teeth are retained for longer and people’s dietary habits change.

The aetiology is often complex as can be the treatment. Prevention of the condition by education andintervention by the dentist is important.

Tooth surface loss, also called tooth wear, refers tothe interrelated effects of attrition, abrasion and ero-sion.

� Attrition is the loss of enamel and dentine resultingfrom tooth to tooth contact

� Abrasion involves an abrasive agent between oragainst the tooth surface

� Erosion involves a chemical agent

The principal causes or predisposing factors are:

� Developmental anomalies� Malocclusion� Posterior tooth loss� Parafunctions and habits� Restorative materials� Diet� Systemic disease� Natural wear and tear

Aetiology and Clinical Features

Developmental anomalies

Localised enamel hypoplasia is never a serious prob-lem since isolated zones of surface loss will not usuallydisturb occlusal stability.

However, the more difficult conditions are thoseof amelogenesis imperfecta and dentinogenesis imper-fecta. These are part of a range of pathology, includ-ing osteogenesis imperfecta, that are manifestationsof disturbances in the formation of calcified tissues.These disturbances are genetic in origin and are oftenseen as familial traits.

In amelogenesis imperfecta, the enamel matrix for-mation is disturbed with normal calcification of what

does form. The extent of the disorder varies fromlocalised areas of pitting, to a very thin shell ofenamel. The enamel is hard but may be deposited infine lamellations as well as in normal prismatic struc-ture in other areas.

The teeth are poor aesthetically and vulnerable tocaries and attrition in affected areas.

Dentinogenesis imperfecta (Fig. 27.1) is uncom-mon and is due to defective odontoblastic activity.The dentine is soft with the deeper layer having fewtubules and incomplete calcification. Also, the pulpchamber becomes obliterated.

Clinically, the weak bond of the enamel to the den-tine results in enamel loss, even though the enamelitself is usually normal. The colour of the teeth is ab-normal, being brownish and the roots may be stunted.Because of the obliteration of the root canals, apicalinfection may occur.

Malocclusion

Certain malocclusions, particularly involving the an-terior teeth, may bring the teeth into abnormal func-tional contacts. Those that create the most problemsare an edge-to-edge incisor relationship and an un-favourable Angle’s Class II division 2 incisor relation-ship. The latter case may involve close apposition ofthe palatal surfaces and tips of the upper incisors withthe labial surfaces of the lower incisors. Also, gingi-val trauma may result from the deep overbite. Surfaceloss can be dramatic (Fig. 27.2) if the malocclusionremains untreated.

Posterior tooth loss

If several posterior teeth are lost, mastication is likelyto be effected on the remaining anterior teeth. These

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296 V. Problems

Fig. 27.1 Dentinogenesis imperfecta.

teeth are not well suited to grinding movements andrapid surface loss can result. This type of problem ismore common in geographic areas where the level ofdental care and awareness has been inadequate, andis usually coupled with non-provision of, or refusalto wear, dentures.

Even with partial dentures present, there is a greattendency to use the natural teeth, and part of theeducation of the patient at the fitting stage of thedentures should be to stress the need to use themeffectively.

Cases exhibit progressive loss of incisor andcanine crown length and when this becomes un-sightly the patient is prompted to seek treatment (seeFig. 18.5).

Fig. 27.2 Severe surface loss and periodontal traumacaused by a long-standing Angle’s Class II division 2malocclusion. Management of such a case would requirepre-restorative orthodontics.

Fig. 27.3 The typical flat occlusal plane of a bruxist.

Parafunctions and habits

Bruxism (Chapter 28) is the most dangerous para-function, with enamel and dentine loss. Again, theincisor length loss is what prompts the request fortreatment, but prevention, in the form of an occlusalsplint, should be applied as soon as the surface loss isnoted (Fig. 27.3).

The exposed dentine may be sensitive, but since theattrition is usually coupled with secondary dentineformation and the retreat of the pulp, it is more oftensymptomless. The obliteration of the root canals bysecondary dentine can lead to apical infection andthe use of apical radiographs in the diagnostic phaseis important. Root canal therapy would be indicatedbefore the canals become obstructed.

Habits, such as nail biting, pipe smoking, hair gripopening and so on, can cause abnormal wear patterns,particularly of an isolated nature.

Tooth brush abrasion may be caused by incorrectbrushing technique, seen particularly at the cervicalmargin of the buccal surfaces of the left side in a righthanded person (or vice versa). It is accompanied bygingival recession and loss of exposed cementum (Fig.27.4). It has been proposed that the occlusion maycause cervical stresses leading to dentine fatigue andbreakdown rather than brushing and this is referredto as abfraction.

Restorative materials

Conventional large particle composites and unglazeddental ceramics can remove enamel quite successfullyduring normal function, with their effect greatly ac-celerated by parafunction. Again, correct treatmentplanning, or early intervention, is the best course.

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27. Tooth Surface Loss 297

Fig. 27.4 Tooth brush abrasion.

Coarse particle composites should be avoided forlarge restorations. If a ceramic occlusal surface hasbeen prescribed (in spite of the advice given in Chap-ter 14), this should be reglazed following adjustments,rather than ‘polished’.

Diet

High consumption of acidic food and drinks suchas citrus fruits, cola, lemonade, alcopops and some‘sports drinks’ removes surface enamel; even wine andtea are incriminated. Cola is a particular hazard asit contains phosphoric acid, citric acid and carbonicacid. The labial aspects are usually affected, unlessdrinking is via a straw, in which case the palatal as-pects of the upper incisors may dissolve. The worstcases are ‘diet freaks’ who eat large amounts of citrusfruit and brush their teeth immediately afterwards.The acid removes the mineral and the brushing re-moves whatever matrix is left – thus acceleratingthe process. The dentine is less mineralised than theenamel and this is removed first leaving a saucerised

Fig. 27.5 Saucerisation of the incisal edges is a sign oferosion.

Fig. 27.6 Labial erosion of the upper incisors and canineswith exposure of dentine. The patient was obsessed with afresh fruit diet and tooth brushing. There is loss of muchenamel with absence of lamellae, with the dentine showingthrough and consequent sensitivity.

appearance (Fig. 27.5). Another modern habit is tosip cans of fruit drinks throughout the day; this sim-ply drips acid continuously onto the tooth surface. Aswith carbohydrate intake and caries it is the frequencyof exposure rather than the volume.

The surface enamel looses its lamellated appear-ance and will have a high amorphous gloss. Even-tually, dentine will be exposed in the eroded areas,particularly bucco-cervically and occlusally. Becausethe erosion causes a more rapid enamel loss than thatcaused by attrition alone, secondary dentine does notform quickly enough to prevent sensitivity (Fig. 27.6).

Another diagnostic sign of acid erosion is ‘lipping’at the cervical margin of the crown where enamelocclusally to the lip has been removed, whilst thatbelow the lip has not (Fig. 27.7).

Fig. 27.7 Erosion of the buccal surface showing lipping.

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298 V. Problems

Prevention via dietary advice is the best approach,and patients could be advised to rinse with fresh wa-ter after eating fruit, rather than brushing. A reduc-tion in intake of fruit and acidic drinks should alsobe advised and particular effort be made in advisingparents about their childrens’ diet.

Systemic disease

Childhood diseases may interfere with the enamelmineralisation of developing teeth and these mayerupt with bands or localised zones of hypominerali-sation. These areas will be weak and, if in functionalrelationship with opposing teeth, will be lost fairlyrapidly. The zones or bands will be chalky white andrough; they will be more prone to staining than theadjacent enamel.

In the adult, the most common systemic problemaffecting the tooth surface is gastric reflux. Due tocardiac sphincter problems, or even very acidic in-digestible meals, gastric secretions are forced up theoesophagus and into the mouth. These secretions arehighly demineralising and the areas most commonlyaffected will be the palatal surfaces of the upper teeth.Occlusal surface loss also occurs leading to existingrestorations being left above the level of the surround-ing tooth.

This is a classic feature of erosion in the absence ofocclusal forces, where the affected tooth surface hasno occlusal contact.

Prolonged vomiting may also create the same pic-ture, and is one hazard of pregnancy. In addition, thedisorders of bullimia and anorexia nervosa are ac-companied by vomiting.

Natural wear and tear

Teeth are kept longer by a population of increasingaverage age. It is therefore inevitable that teeth simplywear out.

Indications for Treatment

Cases with tooth surface loss will require restorativetreatment if there is:

� Associated pathology, e.g. caries, apical infection� Sensitivity� Loss of occlusal stability and function� Deterioration in aesthetics

Principles of Treatment

Where there is a clear external aetiological agent, thisshould be eliminated prior to restorative work. Elimi-nation of habits, dietary advice for acid erosion, med-ical referral for gastric reflux and occlusal splints forbruxism fall under this heading.

Provision of partial dentures to provide poste-rior support prior to the consideration of advancedrestorations for worn anterior teeth is essential. Acomplicated treatment plan will fail if the patient willnot wear the dentures!

The severe malocclusions mentioned above willrequire orthodontic correction or simply extrac-tions. The correction of unfavourable relationshipsby crowns has limitations due to the position of theroots.

Patients with progressing anterior surface loss, par-ticularly male, may only be concerned that the con-dition does not worsen. Timely provision of partialdentures coupled with glass ionomer cement restora-tion of incisal edge ‘saucers’ may well be sufficient inmany cases.

Application of desensitising agents for patientswith dentine sensitivity of occlusal surfaces may notbe successful. There seems to be a difference betweenthe response of a relatively localised zone of cervi-cal dentine and the larger area of occlusal exposeddentine. This is particularly true of acid erosion caseswhere the dentinal tubules will be opened by dem-ineralisation.

Localised hypomineralised areas of enamel can besuccessfully restored with acid-etch-retained compos-ite and larger areas with aesthetic problems will re-quire veneers or crowns.

In relation to posterior teeth there has been achange in approach in recent years. Figure 27.8 showsthe upper arch of a young adult with extensive dis-ruption of the occlusion (Fig. 27.9). The mainstay ofmanagement for many years of such a case was multi-ple crowns accompanied by an increase in vertical di-mension to accommodate them in the occlusion (Fig.27.10).

This approach is technically demanding for boththe dentist and the technician and requires the patientto be fastidious with oral hygiene and diet control.The long-term maintenance of patients with multi-ple crowns can be demanding with recurrent cariesand pulp disease being risks. Furthermore, nothinglasts forever and the replacement of 10- or 12-year-old crowns can be more challenging and problematicthan the original provision.

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Fig. 27.8 Posterior surface loss in a young adult. Theincisors were the only teeth relatively unaffected.

Fig. 27.9 The buccal occlusion of the case shown inFig. 27.8.

Fig. 27.10 The restoration of the case shown in Fig. 27.8.The vertical dimension was increased to accommodate thecrowns because the surface loss had reduced the crownheight and further tissue reduction would have beendangerous.

The provision of 28 crowns is also horrendouslyexpensive!

The preferred treatment for many cases of poste-rior tooth surface loss is now the provision of acidetch retained composite ‘onlays’. The composite willbe retained by being attached to the ‘halo’ or lip ofenamel that usually remains at the cervical region ofthe damaged teeth and this can be supplemented bydentine bonding agents. In comparison with multiplecrowns, this treatment is relatively simple to performand the composite can be easily be repaired or re-placed in the event of damage. The remaining toothwill not be usually compromised. The technique iswell within the skills of a general dentist and spe-cialist training is not needed. It is therefore very costeffective.

The building of the composite can be done free-hand but more accuracy will be achieved by using anocclusal mould made from a pre-operative diagnos-tic waxing (Fig. 27.11). When the diagnostic waxingis complete, it should be duplicated into stone and avacuum formed transparent mould made. This mouldcan be used to shape the composite occlusal surfacesand alternate teeth should be build up to ensure thatseparation of the contact areas is achieved.

The consequences for the occlusion are interesting.The posterior surface loss is usually accompanied bycompensatory alveolar bone growth and this main-tains face height, or occlusal vertical dimension, inspite of the wear. Restoration of the worn areas willintrude into the freeway space and it used to be con-sidered that this needed to be planned in detail and

Fig. 27.11 Diagnostic waxing for a wear case. The waxedmodel can be duplicated in stone and a thermoformed vinylmould made to be a matrix for the composite additions.

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300 V. Problems

(a) (b)

Fig. 27.12 Upper incisors with the surface loss caused by dietary erosion.

the patient’s tolerance of such intrusion be checkedby means of an occlusal splint.

It is now recognised that worn teeth can be built upby several millimetres without causing disturbance tothe neuromusculature and that subsequently there arechanges in tooth position by intrusion and extrusionof teeth.

These changes can be used in changing the occlu-sion prior to treatment and this technique was firstreported by Dahl. Many versions of the principle canbe applied to simple treatment. Figure 27.12 shows acase with both labial and palatal surface loss of theupper incisors caused by acid erosion. Restoration ofthese by crowns would require much removal of theremaining tooth tissue. However, the Dahl principlecan be applied to increase the vertical dimension bythe application of composite to the palatal surfacesof the incisors (Fig. 27.13), which leads to intrusion

of these teeth accompanied by extrusion (or over-eruption) of the posterior teeth (Fig. 27.14). By thismethod, space is created for restoration of the wornsurfaces without destructive tooth preparation. (Thesame effects can be created by an occlusal splint withpartial occlusal coverage.) The incisors were then re-stored by crowns but an alternative method whichreduces the amount of tooth reduction is to placepairs of palatal and labial veneers, sandwiching theremaining tooth tissue between them.

It is more difficult to restore worn anterior teethwhen posterior teeth have been lost. Here posteriorocclusal stability needs to be provided by dentureswhich in turn will need to increase the vertical di-mension to create space for the restorations. Withoutthe posterior support, any new restorations of the an-terior teeth would be subjected to occlusal stressesand would break. Again, anterior restorations in these

(a) (b)

Fig. 27.13 (a) Composite applied to the palatal surfaces of the incisors shown in Fig. 27.12; (b) the composite hasincreased the vertical dimension and the posterior teeth have been taken out of occlusion.

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Fig. 27.14 Four months later there has been intrusion ofthe incisors and extrusion of the posterior teeth and theposterior teeth are in occlusion. The incisors may now berestored without removing tooth tissue on their palatalaspects.

cases should be acid-etch-retained composites and notcomplex crowns whose failure would lead to loss ofthe teeth.

Whether the posterior occlusion is restored by den-tures or composite build-ups, the restoration of the

Tooth Surface Loss – Summary

There are many ways that tissue may be lost from tooth surfaces without caries being involved and preven-tion of surface loss is essential by education of the public. Also, early recognition of the problem by thedentist allows the provision of the appropriate interceptive treatment.

Removal of the aetiological agent(s) is important following which the emphasis is now on simple treatmentthat does not compromise the remaining tooth substance and the provision of restorations that can bereplaced easily when they are lost, without the risk of losing the teeth.

anterior teeth needs to be done carefully and sequen-tially.

The lower incisor tip is the starting point for de-termining the new incisal guidance. Its new posi-tion should be in line with the long axis of thetooth to maintain it in muscle balance. The heightof the tip, determined from the new occlusal plane,in turn dictates the position of the cingulum cen-tric stops on the upper incisors. The remainder ofthe incisor crowns can be shaped empirically to pro-vide overbite and overjet consistent with the dentalbase relationship and, if known, the patient’s previousappearance.

Overdentures

These are the treatment of choice for the older patientwith a number of missing teeth in addition to surfaceloss. The principles of treatment were described inChapter 26.

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Chapter 28Temporomandibular Dysfunction

This topic is very controversial. The number of therapies proposed to treat the condition probably reflectsthe lack of a fundamental scientific understanding of its aetiology and pathology. Much confusion is causedby the inclusion of several different conditions under the one heading.

In spite of this, there is a body of moderate opinion that is in basic agreement; this chapter presents thismainstream approach.

General Features

Pathology in the temporomandibular joints (TMJs)and muscles of mastication together with disturbanceof their neural control may lead to incoordination orrestriction of mandibular movement and pain.

Whilst the principal outcome of this is pain in themuscles of mastication, which may be reported asheadache or even toothache, the underlying patholo-gies that give rise to this are complex and varied. Theprimary cause may be within the joints themselves,leading to movement problems or, more commonly,a relatively simple, but poorly understood, muscleproblem.

The most straightforward aspect of this wide rangeof pathology is that affecting the TMJs. This includes:

� Derangement of the joint� Inflammation of the joint� Degenerative disease� Extrinsic trauma� Growth disorders

Detailed description of the last four conditions is out-side the scope of this book and the reader is referred totexts on oral pathology and surgery for this. However,the conditions must be included in the differential di-agnosis of temporomandibular dysfunction.

Derangement of the joint has already been men-tioned in Chapter 8 and may involve the articular discbeing out of phase with the condylar head or simplytrapped permanently out of place. This is consideredfurther later.

The muscle problem, temporomandibular dys-function (TMD) also termed muscle dysfunction

syndrome, craniofacial dysfunction or temporo-mandibular joint/muscle dysfunction syndrome, ischaracterised by one or more of the following, in-dependent of other oral pathology.

� Incoordination of mandibular movement� Pain in the muscles of mastication� Restriction of movement

The disorder may or may not be accompanied by jointderangement or may have been preceded by painlessclicking of the TMJ.

It is important to note the proviso that the condi-tion is independent of other oral pathology. That is,it is a primary condition (see later).

Aetiology

The neuromuscular control of mandibular movementis extremely complex and was outlined in Chap-ter 8. There are various irregularities of tooth re-lationships, some caused by dentists, which werediscussed in Chapters 8, 14 and 18. These includepre-centric prematurities, working and non-workinginterferences, tilting, overeruption, missing teeth,malocclusions and, sometimes, faulty restorations.

There is a central nervous system function, referredto as the ‘adaptive capacity’, that is able to compen-sate for hard tissue irregularities by controlling mus-cle function. This CNS centre is able to modify controlof mandibular movement to take account of all theirregularities mentioned above. Probably the mostimportant oral function affected is swallowing whichinvolves the learnt position of centric occlusion.

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28. Temporomandibular Dysfunction 303

The closure of the mandible into centric occlusionis performed on a preferred arc of closure that avoidsany pre-centric prematurities. Being able to reach cen-tric occlusion without touching interferences is partlylearnt and partly reflex behaviour and, in the normalsubject, is easily reproduced. Further, man has thecapacity to adapt to and use many extremes of mal-occlusion quite successfully for functional purposes.Indeed, this adaptation can be quite rapid in the pres-ence of, say of a newly restored occlusal surface whose‘strangeness’ disappears after a few days.

However, several things may interfere with muscleand joint coordination, which may have more lastingeffects:

� Trauma, such as prolonged opening, wide yawn-ing, or tough foods

� Pernicious habits such as nail biting� Parafunctional clenching or grinding – bruxism� ‘Correction’ of gross malocclusion by posture� Extensive restorations or dentures of incorrect oc-

clusal contour� Independent oral pathology� Emotional stress – anxiety, worry, major life event� Psychiatric illness

The effects of trauma as an aetiological agent are verybasic and can be understood clearly. Nail biting re-quires the mandible to be advanced to edge-to-edgeincisal contact and maintained in that position fornibbling. The masticatory apparatus is not well suitedto this function, and fatigue and spasm may developin the lateral pterygoid and masseter muscles.

Bruxism consists of continued parafunctionalmovements, which again cause the muscles to tire.

The moderate to gross Class II division 1 maloc-clusion causes problems in the achievement of a con-ventional oral seal and also, to compensate for theaesthetic problems of a chinless profile, subjects oftenposture forward continuously. This again fatigues themuscles.

A faulty occlusal surface may induce an abnormalpattern of chewing, either because of avoidance orbecause of awareness of a problem, and incoordina-tion results. It is assumed that the adaptive capacityis exceeded in these cases.

Independent oral pathology is a major heading inthe differential diagnosis of TMD. The true syndromeoccurs in the absence of such pathology, but some-times similar muscle pain is induced by other disor-ders. These include carious teeth, pulpal conditions,apical pathology, split-roots – the list is very long. The

aetiology is simply based on avoiding a painful or un-comfortable contact during function or parafunction.

The neuromuscular coordination is lost because anew pattern of movement is being attempted and jointclicking and muscle tenderness may be the results.Treatment to remove the pathology will usually in-duce the muscle pain to resolve with no active occlusaltherapy.

Emotional stress, worry, anxiety-based disorders orpsychiatric disorders are considered to be major fac-tors in the aetiology. These factors are recognised tobe of importance in other conditions such as duode-nal ulcer, low back pain and migraine, and TMD fallsinto the group of stress related pathology. Why somepeople get ulcers while others get facial pain is notclear but it would seem that susceptible patients areat risk of certain conditions.

The influence of the psychological factors wouldappear to be the interference with central functions.Again, the neural control of mastication is affectedleading to incoordination. Psychological problemsare complex and it is not for dental surgeons to playthe amateur psychiatrist! However, some understand-ing is necessary.

Surveys have indicated that 40% of the populationmay have TMD during their lives. Classically, thereis an acute episode in late teens that clears quickly,followed by a more chronic recurrence in middle age.Women and men are affected equally but in manyclinical studies there are as many as seven times morewomen than men attending for treatment. This find-ing is likely to be influenced by the fact that womenseek medical advice more frequently than men.

Clinical Features

The principal symptoms are masticatory muscle painor spasm that builds to a peak of pain that then de-clines over a period of several months or even years.The disorder has no physical signs and is solely re-ported by the patient on the basis of symptoms.Whilst palpation of the muscles will result in reportedtenderness and there may be limitation of opening, allthese are reliant on the patient’s response.

Pain around the face and head will cause patient’sconcern and may be exaggerated by focused atten-tion, misconception and fear. An account of the painpicture based on the information, seen in Fig. 2.1,may be valuable for diagnosis. As was mentionedabove, the condition affects susceptible patients andsuch patients may be treatment seekers, exaggerating

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304 V. Problems

their symptoms for attention. The superimpositionof anxiety may reduce the pain threshold of theindividual.

Bilateral palpation of each pair of masticatory mus-cles in turn is required to build up a picture of theseverity of the disorder but subjectively this can bedone by careful questioning. The extent of sleep loss,inability to chew and pain on opening will all con-tribute to an understanding of the extent of the prob-lem; this in turn will give a guide to the possible suc-cess of treatment.

Temporomandibular joints

The acute muscle symptoms may have been precededby painless clicking and locking of the mandible orbe accompanied by clicking in the TMJs. Other TMJpathology may provoke muscle pain but this, al-though the same as that of TMD, is a secondary aspectof another primary pathology.

The classic TMJ click occurs on opening and/orclosing with tooth separation of about 1–2 mm that iscaused by the articular disc becoming displaced fromthe head of the condyle and then catching up eitherfrom posterior or anterior. The disc can become per-manently displaced but this may be found in the ab-sence of any symptoms at all. The click can be felt bypalpation of the joints or heard via a stethoscope.

Failure of the relocation of the disc–condylar com-plex during opening can result in locking of themandible at mid-opening. The disc is trapped ante-riorly on or beyond the eminence. This again canbe painless and patients may become used to reliev-ing the problem themselves. However, once lockingis accompanied by pain, the patient will usually seektreatment.

If treatment is not sought and the condition doesnot resolve, then progress of the disorder may con-tinue with painful function, permanent displacementof the disc and eventually osteoarthritis. However,locking will usually have disappeared to be replacedby the pain from the joint in all functional positions.

The diagnosis of disc displacement is notoriouslydifficult to confirm since conventional radiographsare often normal. There may be pain in the joints,functional difficulty and there will often be occlusalderangement associated with the displacement. Withthe discs being displaced anterior to the condylarheads, the condylar heads can position themselvesfurther superiorly. On closure the teeth at the pos-terior ends of the arches will touch only with the ap-pearance of an anterior and partial lateral open bite.

The teeth no longer in contact in centric occlusionmay have non-contacting wear facets which revealthat they used to be in contact.

Joint derangement may also cause speech problemsbecause the anterior teeth no longer occupy the sameposition. To confirm the pathology, an MRI scan isrequired.

Muscle pain, spasm or tenderness plus limitationof opening can occur without joint disturbance, butthe reverse is unlikely.

Management

This is perhaps one of the most controversial areas ofdentistry and the multitude of treatments that are usedprobably reflects the difficulty of accurate diagnosisand the low level of understanding of the pathologyof the disorder.

The other complicating factor in the assessment oftreatment methods is the self-limiting nature of thedisease. There is definitely a peak of pain and dys-function and then resolution, and much treatment islikely to be applied in the declining phase of the dis-ease, thereby showing favourable results.

Broadly, conservative treatment may be categorisedas follows:

� Reassurance and explanation of the condition� Basic physiotherapy� Occlusal therapy� Systemic therapy

Of these, probably the third and fourth are mutu-ally exclusive, with individual practitioners having astrong preference for using one or the other. A bal-anced view would be that there is a place for all ofthese possibilities in the treatment of the condition,but the difficulty is to define the exact type of pa-tient and syndrome which would benefit from eachtherapy.

There is some evidence to suggest that personal-ity type or susceptibility to psychological disease mayhave a bearing on the success of treatment. Some pa-tients may be treatment seekers and would not besatisfied with reassurance only. Others with a highpsychological morbidity might be better treated withsystemic antidepressants rather than local occlusaltherapy.

There is a high level of placebo response reportedin several studies and the confidence of the operatorin his favoured therapy also influences the outcome.

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Reassurance and explanation

This is of fundamental importance, particularly inthose patients who are in severe pain, may have lostsleep and find it difficult to eat. They need a simpleexplanation of the condition that will allay their fearsthat their condition is serious or even sinister.

An explanation based on the analogy of the pulledmuscle or sprained ankle seems readily acceptable tomost patients. The particular muscles involved can bedemonstrated, and headache from the temporals orneckache from the sterno-mastoid or posterior bellyof the digastric is easily explained. Clicking of theTMJs can also be compared with common clicking inother joints.

The relationship of the condition to anxiety orstress can be discussed, particularly if the patient ad-mits to clenching or grinding during the day.

Basic physiotherapy

This is to rest the affected muscles, ease spasm by theapplication of moist heat or cold (as in sports injurytherapy) and the use of appliances, again to rest orsupport the affected parts.

Patients should be advised to avoid wide opening,to let their jaw ‘hang loose’ to relax the muscles, andtake a soft diet. An insulated hot water bottle is prob-ably the most readily available way of applying heatto the muscles, though there are commercially avail-able ‘heat packs’ which are very useful.

Having relieved muscle spasm, the jaws should begently and steadily restored to normal function, eitherby positive exercise or by increasing the normality ofthe diet.

The exercises could be called neuromuscular re-training and one of the more popular is making sym-metrical opening and closing movements from a cen-tral starting position. However, if these cause pain orfatigue they should be restricted. Indeed the use ofexercises before the pain has been relieved by rest canbe positively harmful.

The most common physiotherapeutic appliance isthe occlusal splint which will be considered next.

Occlusal splint

In the early descriptions of TMD and its management,irregularities of the occlusion were incriminated asthe principal aetiological agents. This led to the useof occlusal equilibration (Chapter 14) as a primarytreatment. In the ensuing years, the role of stress and

psychological problems became evident and the oc-clusion was relegated to a secondary role.

The purpose of the occlusal splint is to rest themasticatory muscles and allow the musculature toplace the mandible into whatever position is desiredwithout being influenced by the teeth. The precisionof centric occlusion requires the mandible to alwaysreach this position for swallowing and this may notbe the most ‘comfortable’ position for the muscleswith their neuromuscular incoordination. The splintshould introduce freedom of movement and alsobalance and stability to the mandible in its closedposition.

A further function is to increase the muscle lengthwhich thereby reduces the power that can be gener-ated by the muscles.

Many designs have been advocated and these in-clude upper splints, lower splints, soft splints, hardsplints, part occlusal coverage splints, total occlusalcoverage splints, smooth splints, indented splints. Thereader who would like to pursue this myriad of tech-niques is referred to the bibliography to complete hisconfusion!

All designs seem to have moderate to good successrates and, because of the particular history of TMD,Solberg has suggested that the occlusal splint is ‘thegold-plated placebo’. The confidence of the operatorin his splint could be very important in inducing a pos-itive response from the patient. There are very highplacebo responses in many studies, some of the orderof 45%. Suggestion and cognitive awareness comple-ment the placebo effect. Cognitive awareness in thiscontext is the reminder of there being something tobe avoided by the presence of the splint.

This writer has his own favourite, which works inhis hands, and intends to describe this in detail to-gether with his justification for using it.

The type and features are as follows:

� Lower – this is less obtrusive than an upper andseems better tolerated

� Hard – accurate adjustment is possible togetherwith exact stability on closure

� Smooth – allows freedom for the musculature totake the mandible to a range of stable positions

Again, the explanation of the function of the splint tothe patient is crucial to its success.

The splint is basically acrylic and can be made ei-ther in the laboratory on an articulated mounting,or from a vacuum-formed plate that has cold-curingacrylic added at the chairside. The former is expen-sive of laboratory time and the latter is expensive of

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306 V. Problems

(b)

(a)

Incisal guidance no centric contact

Canine guidance no centric contact

Supporting cusp contacts

Buccal

SC

Splint

Fig. 28.1 (a) Transverse section of a splint in the molar region. The upper supporting cusp meets the splint on a flat plateau,(b) Ideal occlusal contacts shown diagramatically.

chairside time. The final features of each should bethe same:

� The base must be stable on the lower teeth, beretentive and not rock

� The supporting cusps of the upper canines, pre-molars and molars should meet the splint with

even contact on flat plateaux in any position fromcentric relation to centric occlusion and slightlyanterior to that (long centric) (Fig. 28.1a). Thisfreedom of movement and evenness of contactshould extend about 1 mm in each lateral direc-tion. The patient should be able to slide smoothly

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Fig. 28.2 Lower occlusal splint.

on the splint by about 1-mm radius from centricocclusion

� There should be no incisal contact in long cen-tric. This allows freedom in the arc of closure (Fig.28.1b)

Variations in this design are the incorporation of ca-nine guidance and incisal guidance by a raised planeanteriorly providing posterior disclusion. However,no real advantage as been found for this.

The occlusal contacts should be checked carefullywith articulating paper (Fig. 28.2).

The splint should be worn full-time, particularlyduring eating and only removed for cleaning. Itshould be reviewed at 1 week and the occlusal con-tacts checked again, and then at 4–6 weekly intervals.

The resolution of the muscle pain is likely, providedit is not severe and long standing, within 2–3 months.The superimposition of an internal derangement ofthe joint may require consideration after the muscularpain has diminished (see later).

Following relief of symptoms, a decision must bemade as to when the splint can be discarded. Initially,the splint should be reduced to night wearing only for4 weeks to judge response. If pain does not recur, thenthe splint can be left out altogether, followed again byreview (Fig. 28.3). Many patients then keep the splintto hand for any recurrence of symptoms.

Bruxism may also be managed by such a splint,though it should be heat cured for strength, and anupper one is usually more durable. Nights-only wear-ing is quite successful as this is when most parafunc-tion occurs. Recent work has suggested that bruxismis an inherited trait and whilst a splint will protectthe teeth from damage and may change the parafunc-tional pattern, the overall condition cannot be ‘cured’.

Other splint types can be equally successful and alower full coverage soft splint is popular. This has the

Fig. 28.3 Flow chart showing the progress oftemporomandibular dysfunction with treatment.

advantage that occlusal adjustment is not requiredand it is easily replaced if it splits.

Occlusal aspects

The vast majority of people have occlusal irregulari-ties but few of these people suffer from TMD. Indeed,in those patients who suffer from TMD the occlusaldisharmonies will have been present for some yearsprior to the commencement of the disorder, and inmany patients once the muscular pain has been re-solved and whatever has predisposed them to the con-dition has been resolved, they return to adapting tothe disharmonies.

Certainly, occlusal equilibration should never beused as the primary treatment, since the musculaturewill be provoked by the periods of opening requiredfor the therapy and CR is not likely to be reproduciblewith muscle pain and incoordination present.

If the pain is resolved by the use of the splint,then some workers consider this to be diagnostic ofocclusal disharmonies being a primary aetiological

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308 V. Problems

agent. The complexity of the disorder, though, doesnot lend itself to such simple assumptions. A compar-ative study of equilibration versus feigned equilibra-tion showed better resolution in the latter group!

Correction of major occlusal disharmonies is possi-bly of long-term value. This would include orthodon-tic correction of instanding incisors or the extractionof overerupted wisdom teeth. There is some evidenceto support the correction of a lateral deviation on clo-sure into CO.

However, the presence of postero-anterior slidesfrom CR to CO on closure is so common, that thesereally cannot be classed as aetiological agents intheir own right. It may be that they become signif-icant when the syndrome has developed, and theirreversible elimination by a splint helps the syndrometo resolve. But after this, they appear to return to theirprevious level of insignificance.

Provision of restorationsAn incorrect occlusal surface can clearly initiateavoidance and then muscle pain that is similar to thatof TMD. In these cases the muscle pain is secondaryto the primary agent, the poor restoration, whose cor-rection would be likely to eliminate it.

This approach can be used in mild cases, but inothers the muscle pain must be resolved first, beforerestorative therapy is commenced. This is again re-lated to the likelihood of provoking the muscles bytreatment and the difficulty in obtaining reproducibleocclusal contact positions whilst the muscle pain ispresent.

The occlusal splint is without doubt appropriatehere and is almost certain to succeed. Following this,re-restoration can be started.

Simple restoration replacement should be straight-forward, but more extensive restorations can presentdifficulties. Alongside this, one can consider the prob-lems of providing restorative therapy in general forresolved TMD patients.

The dangers are that the provision of prolongedtreatment could restart the syndrome by fatiguing themuscles, and then that the new restorations could alsorestart it.

The patient must also understand these dangers sothat the operator is not held liable for the recurrenceof the disorder.

Restorative therapy should be kept to the minimumpossible and performed over short visits. An intrao-ral prop should be used to give a firm platform onwhich to stabilise the muscles. If there is any signof the syndrome during treatment, treatment should

be suspended immediately. It may be necessary toreimplement the splint therapy and restabilise thecondition.

Systemic therapy

Some systemic therapy may be used to accompanythe occlusal splint. This could be analgesics (solubleaspirin or non-steroidal anti-inflammatory drugs canbe very effective), or muscle relaxants. The most com-mon muscle relaxant for TMD is diazepam but thisshould only be used for 2 or 3 days and then in verylow doses, about 4 mg at night. The tranquilliser ef-fect and the possibility of dependence is then verylow.

The major use of systemic therapy is to counter-act the central aetiological agents of stress and anxi-ety by prescribing antidepressants. The proponents ofthis approach argue that occlusal disharmonies maybe present but they always have been and that whathas happened is a neuromuscular problem inducedby interference with neural pathways. Various antide-pressants have been used and good success rates havebeen reported. However, these are not substantiallybetter than the rates for splint therapy.

The average dental surgeon, if he or she believes inthis approach, should make the diagnosis and then re-fer the case to a medical practitioner for prescription.Whilst lower doses of antidepressants are effective,possibly by virtue of their action in reducing muscletone, the side effects of the therapy must be monitoredand appropriate training is necessary to do this.

Other therapies

Outside the mainstream of conventional and reason-ably well-substantiated therapy are other approaches.These are based on empirical theories and obser-vations and may be related to chiropractic andosteopathy. A relationship of the occlusion to thebiomechanics and balance of the vertebral columnhas been proposed, particularly to the skull position.Treatment aims here appear to be directed at correct-ing occlusal anomalies to reposition the skull and ver-tebral column. This is claimed to relieve headache andlow back pain. The occlusal therapy may be accom-panied by therapy from a cranial osteopath.

None of this has any scientific substantiation and itmust be remembered that these patients are suscepti-ble individuals, perhaps with sub-clinical psychiatricproblems, who may be vulnerable to suggestion.

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Internal Derangement of the TMJ

The articular disc may simply be out of phase withthe condylar movement or may be permanently dis-placed. In addition, there may be derangement of thearticular surfaces, either from trauma or from chronicinflammation.

The simplest form of derangement is the clickcaused by the out of phase disc catching up with thecondyle, and if this is painless, no treatment is usuallynecessary.

If the clicking is accompanied by muscle pain, thenthis is stabilised first, and the result may be a pain-less click. Again, no active treatment for the residualclick is necessary. The only problem is that the elasticfibres posterior to the disc, which bring it back fromprotrusion, can become stretched, leaving a prolapseddisc.

However, if the joint pain persists after splint ther-apy, together with limitation of opening and jointsounds, then further treatment will be necessary. Thisis also true of locking, which can occur withoutclicking.

Further treatment must be done upon the basis ofan accurate diagnosis and to do this MRI scans of

Temporomandibular Dysfunction – Summary

The condition remains a controversial area because of the difficulties of defining and diagnosing the syn-drome and the large number of treatments, including placebo, which have reasonable success rates.

Simple, reversible, non-invasive therapies are recommended as the first option with the more difficultprocedures and systemic drug therapy held in reserve for those who do not respond to the first approach.

There is clearly a small group of patients who show little response to all forms of treatment, and whoeventually get better by themselves!

the TMJs are necessary. These will reveal whether thedisc is displaced or whether there are arthritic or otherchanges in the joint.

Simple conservative therapy has some success inreleasing the displaced disc back to its normal posi-tion. This is done with a repositioning splint, which isvery similar to the muscle stabilising splint describedearlier, but has positive tooth-guiding planes forclosure.

The path of closure is anterior to that normally em-ployed, and the maximum contact position is forwardalso. Thus, the condyles are advanced and pulleddownwards in the fossae. The splint should be madefrom a wax record which reproduces the position ofthe mandible on closure just before the click occurs.The splint must be worn continuously and should notbe used in the presence of muscle pain, which will bemade worse by the abnormal forward posture.

Success rates for repositioning splint therapy arevariable and this type of therapy should be reservedfor those cases which have remained insoluble fromthe muscle stabilisation splint.

The internal derangements resulting from traumaor osteoarthritic change require surgical manage-ment.

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Chapter 29Management of Failure in the RestoredDentition 1: Fixed Restorations

We all have failures! But it is essential to learn from them and not make the same mistake again. This bookhas tried to give a practical, common-sense approach to many aspects of restorative dentistry, and to followits advice, the authors believe, would reduce the incidence of failures. The management of failures is amajor challenge because of the damage already done. This chapter and the next deal with the problems.

Failure of restorations may be caused by the den-tist, the patient, continuing pathology, inadequaciesin materials and a combination of all four!

The dentist may be responsible for:

� Treatment planning errors� Technical errors

The treatment plan must be tailored to fit the pa-tient and be based on an accurate diagnosis of thepathologies present (Chapter 4). It must also fit thedentist’s skills and facilities. For instance, a treatmentplan based on the skills and experience of a specialistand his supporting team is likely to be quite beyondthe reach of the average general practitioner and his.

Poor treatment planning, then, is a major problem,often compounded by technical errors. Simple plans,made up of easy stages are always best, no matter howskilled the operator. Unreasonable demands on tech-nical expertise that does not exist, and patient moti-vation and awareness that is half-hearted, are recipesfor disaster!

It would be boring world if everything was perfect,and thankfully a lot of less than perfect dentistry re-quires no treatment, other than regular observation.

The questions to be answered in the affirmative be-fore embarking on re-restoration are:

� Is there any active pathology in the area of theproblem?

� Are there any symptoms?� Is there an aesthetic problem that disturbs the

patient?� Is there a functional problem?

If the answer is ‘yes’ to any of these, then action is re-quired; but there are many examples of imperfection,where nothing should be done.

Examples for Masterly Inactivity

The ditched, corroded amalgam restoration

Do not replace such a restoration unless there is ev-idence of recurrent caries, either clinically or radio-graphically, or there are symptoms of microleakage(see Fig. 3.4).

The under- or overfilled root canal

Do not interfere unless there are clinical or radio-graphic signs of an enlarging apical area, or symp-toms. If you do decide to interfere, be certain thatthere is some glimmer of hope that you can do better!Is the canal apical to the short filling obstructed, forexample?

Intracoronal Restorations

‘Cracked tooth syndrome’

This condition can cause considerable difficulty in di-agnosis. There is a hairline, vertical fracture extendingfrom the base of a large cavity, either to the root fur-cation or down the root. The patient will complainof vague symptoms, perhaps mainly on biting, thatare often poorly localised. Radiographs will usuallyshow no abnormality. Diagnosis may be assisted byusing a device that places pressure on individual teethduring biting. A small piece of rubber attached to ahand instrument works well and the patient will saywhich tooth feels uncomfortable on biting.

The affected tooth will usually have a large MODamalgam present, again possibly with no apparentdefects. Removal of the amalgam will reveal a deep

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29. Failures in Fixed Restorations 311

occlusal floor and a flat plastic should be gently turnedwithin the cavity to attempt to open the buccal wallfrom the lingual. A crack in the floor may then berevealed.

The prognosis for the tooth is poor, though symp-toms may be relieved by placing an acid-etched com-posite restoration. The cusps will be held together,thus preventing the flexure stimulating the periodon-tium. However, the fracture line is vulnerable to in-fection, which may occur at time.

Dentine pins

Pins in the periodontal ligament or pulp are a com-plication that can be unavoidable, due to the blindnature of their insertion. The misplacement of thepinhole should be diagnosed as soon as it has beendrilled, either because the resistance to cutting wassuddenly lost or because blood appeared in thehole.

The hole should not be used, but filled with calciumhydroxide. However, if a pin has been inadvertentlyplaced in such a hole, then pulpal or periodontal in-fection can occur. Treatment of the pulpal infectionmight require root canal therapy, whilst the periodon-tal infection may require raising a flap, cutting theexcess pin away and smoothing it flush with the root.

If the pin is superficial, then a crown preparationcould cover it as a method of sealing. If the pin is in-accessible, then extraction could be the only solution.

Beware of interpreting the two-dimensional radio-graph incorrectly. A correctly placed pin may be su-perimposed on the pulp shadow.

Post Crowns

These are particularly vulnerable to operator errorduring preparation. The root morphology is un-known and unseen, and it is easy to be misled by anapparently large root face which tapers dramaticallyin the alveolus.

The side of the post hole may be perforated duringpreparation, or the root may be weakened leading tovertical fracture during preparation, cementation orlater function. Posts may fracture in the canal.

Lateral perforation

Large, parallel-sided posts are prone to this compli-cation and particular teeth are also vulnerable. The

upper lateral incisor being small and angulated dis-tally and palatally is a particular trap, as are rootswith mesial and distal concavities (see later).

Teeth that can be either two rooted or single rooted,such as upper premolars, also give rise to problems,simply because the root morphology is unseen.

Perhaps the best advice is to avoid posts in teethwhich are known to be variable in morphology, andconstruct pinned cores instead (see Chapter 11).

The differential diagnosis for a post crowned tooththat is giving problems must always include the pos-sibility of a perforation, and a second radiographicview can be helpful (Fig. 29.1). This will also showthe position of the perforation as labial or palatal byparallax.

The management of the lateral perforation dependsupon its site and size, and the restorability and prog-nosis of the tooth as a whole. A carious, short-rootedtooth is better extracted, rather than embarking upondifficult treatment. Also, if a perforation can be pos-itively diagnosed as palatally placed, then the toothshould be extracted.

Having decided upon trying to save the tooth, thefirst decision is whether to remove the offending post,or leave it in situ. A small-rooted tooth may not sur-vive the stress involved in withdrawing a post, and athreaded post can stress the root excessively on beingunscrewed.

If the post can be removed (or if the perforationhas been observed at preparation), then the post holeshould be re-established in the correct line (Fig. 29.2),an impression taken and the new post fitted at the timeof surgical exposure of the perforation.

The perforation should be isolated so that ce-ment does not enter the bone, and the post cementedwith polycarboxylate cement. An acrylic provisionalcrown should be placed as well. The perforation iscleaned and retention provided around it by a smallround bur. Mineral trioxide aggregate (MTA) is thenplaced to seal the perforation (Fig. 29.2).

This procedure may be complicated by the wedge-shaped nature of the perforation, which may be longin the long axis of the tooth and whose walls can bevery thin.

If the original post cannot be removed, then sur-gical repair may be attempted by removing the postmaterial that is outside the root profile, and cutting achannel around its end. This is then sealed with MTA.

A small perforation, noticed at the time of prepara-tion, may be packed with MTA from within the canal,the post made in the correct line, cemented as usual,and reviewed radiographically periodically.

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312 V. Problems

(a) (b) (c)

Fig. 29.1 Periapical radiographs of the |12 region: (a) suggests that the post is in the correct line of the canal; (b) taken toshow the |2, reveals the post off-line; (c) taken for the |3, reveals a palatal perforation of |1. Unfortunately, the originaldiagnosis had been made using ‘(a)’ only, and the patient had been treated for temporomandibular dysfunction. The centralincisor was later extracted.

Fig. 29.2 A post crown with a lateral perforation has beenremoved, and the canal re-established in the correct line. Anew post was constructed and cemented at apical surgeryand the perforation sealed.

Two cautionary tales

A diagnostic disaster 1The case illustrated in Fig. 29.3 had a post crownconstructed on the upper left lateral incisor some 8years previously. The tooth had given problems sub-sequently, and an apicectomy was performed. Thisdid not resolve the problem and the patient, havingmoved home, consulted a new practitioner.

He said that the previous apicectomy had failed,and the operation should be repeated. He providedthe root seal shown in Fig. 29.3a.

The tooth still gave trouble, and a further housemove brought the patient yet another adviser. Thehospital practitioner who saw her advised that thesecond apicectomy had failed, and that the operationshould be repeated.

He also tested the vitality of the crowned central in-cisor and the crowned lower incisor (Fig. 29.3b) withice and concluded that they were non-vital (Ceramicis a good insulator!). He advised that both these teethshould be apicected also, in spite of the absence ofany apical pathology.

After a 9-month wait, the three apicectomies weredone by a further practitioner, as a day case. He pro-vided the surgical results shown in Figs. 29.3c and d.

The upper lateral still did not recover, and the pa-tient was seen by the author. Surgical investigation

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(a)

(c) (d)

(b)

Fig. 29.3 (a) The post crown on the lateral incisor had given trouble since it had been fitted, and the tooth had beenapicected twice previously, with no benefit. There is no apical pathology present on the crowned |1, (b) The lower centralincisor had a badly fitting crown on it, but no apical pathology. The practitioner prescribed a further apicectomy for 2|, andbecause of negative pulp tests on 1| and |1, apicectomies were prescribed for these as well, (c) and (d) The results of theapical surgery. (c) The upper lateral incisor continued to be painful, (d) The operator has failed to identify the apex of |1 andhas deposited amalgam in bone. The tooth was subsequently found to be vital.

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314 V. Problems

(b)

(a) (c)

Perforation

Root profile

Crown profile

Fig. 29.4 (a) The radiograph shows thepost in |5 to be slightly off-line, but notdramatically so. However, the root profileof single rooted upper premolars tends tohave concavities (b), which cannot beseen. The large crown profile gives a falsesense of security, but a perforation hasoccurred ((c), arrowed).

of the strong possibility of a lateral perforation bythe off-line post was done, a perforation found andrepaired, and the tooth settled.

The lower incisor turned out to be vital, was rootfilled and post crowned, and the large mass of mis-placed amalgam left under review.

The patient pressed a successful claim for dam-ages, and all teeth were still present and symptomless4 years later.

A diagnostic disaster 2The upper second premolar illustrated in Fig. 29.4had given trouble since the post crown had beenfitted. Acute inflammation developed such that thewhole quadrant was painful with all the teeth beingtender.

The patient attended a Sunday morning emergencyservice and, for some reason, the dentist diagnosedacute apical infection of the two perfectly sound in-cisors of the upper left side. These were ‘opened todrain’ and the patient attended hospital the next day.

The vital pulps, still present in the incisors, wereextirpated and the teeth root filled later. The patientelected to have the perforated premolar extracted. Nolegal action resulted.

This case illustrates firstly, the danger of makingposts on roots with unseen concavities, and secondly,the need to have the fullest information available be-fore a committed diagnosis is made. In the face ofseven tender teeth in a quadrant and no radiographs,the prescription of analgesics and antibiotics is a safercourse of action.

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(a) (b)

Fig. 29.5 Check for root fracture when a post crown has been lost. (a) The root face appears normal; (b) the flat plastic istwisted gently in the canal and the fracture (arrowed) has opened.

Vertical fracture

Complete vertical fracture is often the consequenceof a blow or jar to a post crown which knocks it out.Short, or ill fitting, posts are particularly vulnerable.Diagnosis may not be obvious, but root integrity mustbe checked before recementing the crown. A small flatplastic instrument should be inserted into the posthole, and turned gently to open any fracture line(Fig. 29.5). Excessive force is not necessary andshould be avoided. In the event of a vertical fracture,the tooth is unsavable.

Incomplete fracture is very difficult to diagnose. Itis an occasional finding during apical surgery, and allroots with posts should be inspected carefully at thetime of surgery.

The crack, or cracks, may have been caused byover-zealous preparation with large twist drills, or bya later blow. They can remain stable for some time,but in some cases tissue fluid leaks through and initi-ates corrosion, either of the post or of a metallic rootfilling.

The corrosion products open the fracture line, in-fection supervenes, and the tooth gives symptoms.The tooth is unsavable, but diagnosis may not bemade until surgery is attempted, at which time astained root is revealed (Fig. 29.6).

Vertical fractures may also be caused by tapered,threaded posts upon insertion. These are dangerousand should not be used.

Fractured post

This is a particular complication of cast posts or smallposts of all types. A blow, or a jar during eating,shears the post at a casting defect. The root should be

checked for vertical fracture, and if intact, removal ofthe fragment performed.

A special kit (Masserann, Micro-Mega) is recom-mended (Fig. 29.7). This is a series of cutting tubes(trepans) that are designed to cut an annulus around

Fig. 29.6 A partly fractured root which has allowed tissuefluid to reach the metal post, and corrosion has resulted.This was found at apicectomy and the tooth was laterextracted.

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316 V. Problems

Fig. 29.7 A Masserann trepan. The cutting tube removescement or dentine from around the object in the canal,which is thereby released.

the fragment, thus releasing it. Direct and straightaccess is required to the fragment and the choiceof diameter of trepan used is important. It shouldbe only fractionally larger than the fragment so thatthe minimum of dentine is removed. Assuming thatthe root filling remains intact the tooth can then bere-restored.

Fixed Prosthodontics

High standards of treatment planning and construc-tion coupled with the joint efforts of the patient andthe dentist in a continuing care programme oughtto result in bridgework that has a minimum life ex-pectancy of 10 years. Faults in treatment planning,such as the use of dubious teeth as abutments, faultsin construction, such as poorly fitting margins, or in-adequate oral hygiene by the patient may all reducethis dramatically.

Possible sources of failure are:

� Cementation failure� Recurrent caries� Non-vitality and apical pathology� Periodontal disease� Incorrect occlusion� Fractured ceramic� Wear and tear

Cementation failure

This may be due to poor stability of preparations,differential biomechanical loading of abutments orfatigue of the cement. In multi-retainer conventionalbridgework, it can be very difficult to diagnose, since

it may be partial, with the crown apparently still se-cure. The patient may report vague symptoms thatwill relate initially to dentine stimulation by mi-croleakage and then to carious attack. These symp-toms may not be specific to one tooth, and in a mul-tiple unit restoration, this can be perplexing.

Radiographs will not reveal anything at the earlystage, unless there is a deficient crown margin.

Applying displacing pressure to the restoration mayreveal looseness or tell-tale bubbles at the cervicalmargin. This can be helpful in single crowns or onone side of a pontic, but multiple retainers may besupporting the failed one.

Unfortunately, the diagnosis can only be made withconfidence when the crown is fully unseated, by whichtime caries could have destroyed most of the prepa-ration (Fig. 29.8).

All this points to choosing luting agents of thehighest possible resistance to dissolution and fittingbridges with the best possible marginal adaptationand retention.

Once cementation failure has been diagnosed ona bridge, the whole restoration must be removedwithout damage (see later), the integrity of the

Fig. 29.8 Cementation failure. Radiograph of a bridgeretainer whose connection with the bridge has beendestroyed by slow caries. The pulp has disappeared also.

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abutments checked and the bridge recemented if theabutments are satisfactory.

Recurrent caries

This is potentially serious, since once the preparationdentine is reached, caries can spread rapidly. It will berevealed at routine maintenance visits, either by clini-cal or radiographic observation. Provided it is limitedto the immediate area of the margin, the caries can beremoved and the area restored with glass ionomercement. A more extensive zone of caries, and partic-ularly any that runs some way out of sight under aretainer, will necessitate the removal of the crown.

It is interesting to note how patients’ habits and dietmay change. A stable mouth with low caries rate atthe time of treatment planning may exhibit increasedcaries activity if the patient changes to a high-refinedcarbohydrate diet. This may be provoked by stress –sugary tea as a stress relief mechanism, or changes inworking pattern – sucking sweets as a way of passinglong journeys.

These factors need to be considered within the con-tinuing care programme.

Non-vitality and apical pathology

Teeth that have suffered carious attack and are thensubjected to pins and core placement followed bycrown preparation will have had their pulps consid-erably insulted. It is not surprising that a small pro-portion of crowns and bridge retainers become non-vital, often without symptoms. Teeth that have beentraumatised may also succumb. Symptomless non-vitality is difficult to diagnose without there beingapical pathology to reveal it. Hence the need for ra-diographic review of the apices of crowned teeth, aswell as those that have been root filled.

The management of such cases is by root filling thetooth through an access cavity in the crown. If this isimpossible then apical surgery should be consideredand failing this, the tooth should be extracted aftersectioning it from the bridge.

Periodontal disease

Assuming that the bridge was made on a sound peri-odontium, i.e. one that was stable and free of inflam-mation, then prevention is better than cure! Whilstevery patient should be instructed to use Superflossat least twice a day, it is quite surprising to notehow this slips to twice a week and even less. The

result of lack of diligence in plaque removal will bemarginal inflammation, particularly in the embrasureareas. Regular reinforcement of oral hygiene instruc-tion with periodic visits to the hygienist will alwaysbe necessary.

Periodontal breakdown accounts for a surprisinglysmall number of bridge failures. This reflects the op-eration of the biofeedback occlusal load modificationmechanism as well as the resilience of the periodontalligament. Rotational forces are potentially the mostdamaging and these may be caused by an incorrectocclusion, usually on a cantilever design in lateralexcursions.

Breakdown may be manifested by pain on biting,tenderness to percussion and mobility. Group func-tion should be established by equilibration of thebridge or the bridge remade to a fixed–fixed design.

Incorrect occlusion

This may give the patient the feeling that the teeth donot meet evenly, or worse, induce muscle pain similarto that experienced in temporomandibular dysfunc-tion. Changes in overjet may make the patient feel asthough the teeth are ‘cramped’.

The occlusion should be examined first with ar-ticulating paper and shimstock, as described inChapter 14. If the discrepancies are seen clearly andare not large, simple equilibration can be successful.Where there is any doubt about the errors, a diagnos-tic centric relation mounting should be done to permitclear examination of the occlusal contacts.

A trial equilibration can be carried out on the ar-ticulation, and, if successful, repeated on the patient.If the discrepancies are too large, then the bridge willrequire remaking (see later).

If the bridge appears to have induced muscle pain,then this condition must be stabilised first by fitting asplint and under no circumstances should there be anyirreversible adjustments made to the bridge. When thepain has been resolved, a detailed examination of thebridge can be made with a view to accurate diagnosis.

Fractured ceramic

The most likely causes of this are incorrect metal sub-frame design so that the ceramic is not supported orinsufficient occlusal clearance leading to the ceramicbeing too thin.

Small areas may be repaired using a propri-etary silane coupling agent and a composite mate-rial (Fig. 29.9). The disadvantage of this is that the

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318 V. Problems

Fig. 29.9 Repair of fractured ceramic by composite on abridge retainer.

composite is less durable than the ceramic and maydeteriorate in time. Replacing the lost material witha ceramic veneer is a useful technique if a standardveneer preparation can be done on the fractured com-ponent (Fig. 29.10).

Wear and tear

Long-term durability of bridge components is vari-able, even without the supervention of the pathol-ogy mentioned above. The most vulnerable aspectof a well-made bridge is the ceramic. The materialabsorbs water and undergoes static fatigue as wellas losing surface stain and becoming lighter. Beforethe advent of shoulder ceramic, a dark line at the

gingival margin was an inevitable consequence of gin-gival recession.

Changes in colour that affect aesthetics can only beimproved by replacing the whole prosthesis.

Management of the failed bridge

A bridge may be a candidate for replacement if:

� There is recurrent caries� There is cementation failure� One or more abutments show active pulpal or

apical pathology� One or more retainers show bad marginal

adaptation� The aesthetics are unacceptable� The function is unacceptable

Limited recurrent caries might be amenable to localexcavation and restoration, and a single pulpally in-volved tooth in an otherwise acceptable bridge, couldbe root filled through the retainer.

In other cases, particularly where several of the re-placement criteria are fulfilled, removal of the bridgeis the only satisfactory solution. Because the basiccondition of the abutments is hidden by the retainers,the patient must be clearly informed that no guaran-tees can be given about the eventual re-restoration.They must understand that if the abutment teethprove unsatisfactory, a partial denture could be theend result.

The sequence for management is:

1 Preoperative diagnostic mounting2 Provisional replacement constructed, usually a par-

tial denture

(a) (b)

Fig. 29.10 (a) The incisal edge of the bridge retainer on |2 had fractured. A veneer preparation has been done on theremaining crown. (b) A ceramic veneer has been cemented with dual-affinity resin-retained bridge cement.

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Fig. 29.11 A proprietary crown remover being used todislodge a retainer. The device has a spring loading systemthat delivers a jolt through the hook. In order to apply thejolt, the retainer should have a prominent or open margin.There is a risk of tooth fracture if too large a force is used.

3 Remove the bridge4 Section bridge into individual retainers for use as

provisional crowns; fit denture5 Inspect and assess each abutment tooth – vitality,

restorability, prognosis6 Stabilise abutment teeth as appropriate – e.g. RCT,

pinned cores7 Plan new bridge (or alternative replacement)8 Construct new bridge

Perhaps the most difficult stage is the removal of theold bridge. Since it may be desirable to use the retain-ers as individual provisional crowns, removal shouldcreate the least damage possible. There is, of course,the very real danger of damaging the abutment teethas well.

Gentle prising, by placing a Mitchell’s trimmer orchisel at each retainer margin in turn, should be triedfirst. Then, if no movement results, mechanical shockcan be applied to each retainer in an attempt to breakthe lute seal. Ultrasonic scalers can be successful, butthe hammer blows of proprietary crown removers aremore common. These are particularly unpleasant forthe patient, and can fracture teeth underneath thebridge if not used with extreme care (Fig. 29.11).

A recent innovation are WAMkeys (Mirage DentalProducts); Fig. 29.12. The instrument is intended tolever the crown off the preparation by being insertedin the cement layer between the occlusal surface of thepreparation and the inner aspect of the crown. Thelocation of this is by guesswork and the speculativecutting of a narrow horizontal hole in the crown. Thisis deepened until it reaches the centre of the toothpreparation. The appropriately sized WAMkey is

(a)

(b)

Fig. 29.12 WAMkeys.

inserted into the cavity and rotated by a quarter turn.The crown should lift off.

If finally no movement is seen after a few minutesthe last resort is to cut each retainer with the air tur-bine. This technique, whilst destroying the bridge, atleast means that the abutments escape with minimaldamage.

A vertical cut should be made on the buccal as-pect of each retainer, through the metal/ceramic only,using the appearance of the luting agent as a guideto depth. Special burs are available to do this. Careshould be taken not to cut dentine, since this leavesgrooves that may dictate an unfavourable path of in-sertion for the new bridge. A cut across the occlusalsurface may also be necessary for the retainer to bereleased.

To construct the provisional restorations, tempo-rary crown forms may be used or, alternatively, thepreoperative mounting can be used as the templatefor polymer-based provisionals.

The failed bridge shown in Fig. 29.13 presentsseveral problems for its replacement and the

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320 V. Problems

(a)

(c) (d)

(b)

Fig. 29.13 (a) This bridge replacing |3 is cantilevered from |456, which is probably one retainer too many, (b) Theradiograph shows that the premolar crowns have poor margins and short root fillings. There is an apical area on the |4, anda second root which has not been filled. The buccal root canals of |6 have not been filled, (c) The underlying teeth showingrecurrent caries, and inadequate preparations on the premolars, (d) The bridge has been sectioned into individualprovisional crowns to allow the root canal therapy to be redone, and a denture tooth has been acid etched to the |2.Following the root therapy, the bridge was remade from |45, with the |6 being restored with a separate crown.

patient needs to understand these properly before anyattempt is made to start treatment. The radiographsshow inadequate root fillings, all of which need tobe replaced, and the state of the preparations of theabutments cannot be determined until the bridge isremoved. The replacement of this bridge took severalmonths.

The Obsessive Patient

This is a failure, or series of failures waiting to hap-pen! Feinmann and Harris have coined the term ‘OralDysaesthesia’ for patients who have an unnaturalconcern about their dentitions. The term ‘phantombite’ is also used.

Dentists and plastic surgeons are very vulnerable tothe demands of perfection seeking individuals, and indentistry, whilst sometimes reasons for treatment canbe found, no organic disorder will usually be found tounderlie the request for treatment. (This is the third

time this warning has been written in this book – itbears repeating!)

Such patients may complain about the aestheticsof their teeth or the arrangement of their ‘bite’. In thewriter’s experience, many are women in their thirties,with apparently stable family backgrounds.

Other patients, particularly in the older age groups,complain of pain for which no organic pathologycan be found. Some also give impossible patholo-gies as their diagnosis; e.g. a patient believed thatmicroleakage around a crown lead to air entering thenervous system and causing paralysis of the left sideat night!

The dentist can easily be tempted by the history toundertake replacement of the dubious amalgam, pro-vide crowns or even extract perfectly healthy teeth.

Unless a pathological process is diagnosed, nooperative treatment should be performed. This willbe doomed to failure, and the patient will continue todemand more and more until the dentist calls a halt.The patient will then leave in a distressed state.

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Recognition of the problem is the key to avoidingit. Beware of the patient who asks numerous techni-cal questions, offers a history of unsatisfactory careelsewhere or who is overbearingly demanding aboutthe standards of care required.

Medico-Legal Aspects of Failures

Every patient with a failed restoration is a potentiallitigant, but fortunately the vast majority of patientsare loyal to their professional advisers. By discussingpossible problems as they are foreseen during treat-ment, the patient is taken into the dentist’s confidence,and if the worst happens, the patient is expecting ittoo! The patient then sympathises with the dentist.

The ability of the dentist to communicate effec-tively is a major factor in avoiding litigation.

When discussing failures with the patient, it is im-portant to put the problem in the context of the gen-eral difficulty of the technical aspects of dentistry.Explanations about the variation in tooth form, tech-nique sensitive materials and so on, often gain thepatient’s sympathy and understanding.

However, this is not to suggest that deceiving thepatient is appropriate. It is very necessary to explainexactly what is wrong and what needs to be done toput it right, without apportioning blame. If the pa-tient continues to express dissatisfaction with previ-ous care, it is best to be non-committal and supportiveof the previous dentist if at all possible.

The courts do not expect every dentist to have spe-cialist skills and to be successful in every case. Theyrequire that the treatment provided is of a reasonablestandard appropriate to the dentist’s training and ex-perience, and has been delivered in a careful manner.

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Chapter 30Management of Failure in the RestoredDentition 2: Dentures

Management of Denture Problems

Although the possibilities for complaints about den-tures are numerous, the more common denture prob-lems are:

� Pain/discomfort� Looseness/loss of fit� Inability to chew efficiently� Appearance� Speech� Retching� Broken dentures� Burning mouth

Pain/discomfort

Important information necessary for diagnosisand treatment planning includes: site, duration, ag-gravating/relieving factors.

Pain/discomfort may be related to:

� Extension of the borders� Condition of the fitting (impression) surface� Extension of the base� Anatomy of the denture bearing tissue� Occlusal errors� Occlusal vertical dimension

Overextension of the border usually causes localisedpain and is most common in the early period follow-ing the provision of a new denture. It may be possibleto detect the offending area by looking for deflectionof the tissues in the sulci when the denture is inserted,otherwise pressure indicating paste or spray can beused.

The fitting surface of a new denture should be ex-amined for sharp ridges or acrylic resin pearls which,if present, should be trimmed and smoothed. Under-cuts may need to be reduced or eliminated to allowthe dentures to be inserted atraumatically. With thepassage of time and alveolar resorption the adapta-tion of the fitting surface to the tissues may deterio-rate and result in localised pressure spots. These canbe identified with pressure indicating paste/spray and

relieved but other treatment; e.g. relining might alsobe considered.

In the lower arch, a complaint of generalised dis-comfort may result from an underextended basetransmitting high pressure to the reduced area of sup-porting tissue. The remedy is to correctly extend thebase and, of course, to optimise other design factorssuch as occlusion and occlusal vertical dimension.

Localised pain may be caused by anatomic featuressuch as a narrow, sharp mandibular ridge and grossalveolar atrophy resulting in the superficial position-ing of the mental foramen. The complaint is normallyof sharp pain on pressure and, if the mental nerve isinvolved, of a shooting pain along its distribution intothe lower lip.

If the occlusion is not even and simultaneous thenexcessive pressure will be transmitted to the under-lying tissues on the side of the premature contacts.A locked occlusion will not permit lateral excur-sions without resulting in movement (dragging) of theentire denture base over the tissues (commonly thelower). This can be more obvious when new dentureswith anatomic teeth replace an old set with a veryworn occlusion which permitted unrestricted lateralmovements.

Errors in the occlusal vertical dimension can leadto symptoms from the denture bearing tissues or themasticatory apparatus. Lack of freeway space maycause excessive loading of the tissues and resultantgeneralised discomfort. It might also lead to pain inthe muscles of mastication. Excessive freeway spaceis unlikely to result in painful ridges but may causesymptoms in the musculature.

Looseness/loss of fit

A most important factor in looseness of a denture isthe time scale. If the complaint is made at the inser-tion stage of a new denture the dentist should firstbe satisfied that the design features and standard oftechnology are adequate, i.e. border and base exten-sion, adaptation of the base to the tissues, posteriorpalatal seal etc. The patient should then be reassuredthat all is well and that their muscular control of

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30. Problems with dentures 323

the denture(s) with habituation will enhance denturewearing. On occasions the patient may be advised touse a denture fixative to give added confidence in thisearly phase.

Inevitably the alveolar ridges will resorb with time,with the mandible losing ridge height and width atapproximately four times the rate of the maxilla, andthe denture base will no longer ‘fit’ the tissues. It may,however, be some time before the patient complains oflooseness because during the period of gradual ridgeloss (s)he has learnt control of the dentures. Indeed,some patients can control and manipulate old den-tures that, in the view of the dentist, are well pasttheir useful life.

If the looseness can be attributed to the fit-ting surface of the denture whilst other design fac-tors are satisfactory, a reline/rebase can correct thedeficiency.

Inability to chew efficiently

The complaint of lack of chewing efficiency may bedue to worn teeth on an old denture or the use of non-anatomic teeth on a new denture. Excessive grindingof new teeth to correct occlusal errors will also spoilthe shape of the teeth and limit their capacity to re-duce foodstuffs.

Occasionally patients may find difficulty chewingif the occlusal vertical dimension is outside their tol-erance limit. A poor occlusion, for example, whenthe number of teeth contacting is reduced, may alsocontribute to chewing difficulties.

Aesthetics

A complaint of poor appearance relating to denturesusually occurs either immediately the dentures are fit-ted or following gradual deterioration of the condi-tion of the dentures, some years later. If the wax trialstage has been correctly carried out the patient shouldhave had adequate time to examine and approve theappearance and therefore the finished dentures shouldbe satisfactory. It is possible, though unlikely, thatthe teeth have moved or other errors have occurredduring the flasking and processing procedures. Occa-sionally the dissatisfaction arises because the patientreceives an unfavourable comment about their newteeth from a relative or friend. Whatever the reason,a patient unhappy with the appearance of the teeth isunlikely to persevere with the dentures.

Factors which may detract from the appearanceinclude:

� Unsatisfactory tooth shade, contour or size� Labio/lingual tooth position leading to incorrect

lip support� Too much/too little length of crown visible – lip

coverage� Poor contour of gingival margins� Errors in the occlusal vertical dimension

New dentures can greatly enhance the appearance butthere are limitations and some patient’s expectationsmay be unrealistic. For example, dentures cannot re-verse the ageing process and they cannot eradicate thenormal lines and creases in the skin.

Old dentures may have poor aesthetics because ofworn or stained teeth and because of loss of lip sup-port as the dentures ‘settle’ in the mouth followinglong-term alveolar resorption. Bleaching due to overenthusiastic or incorrect use of cleaning agents willalso deleteriously affect both the denture base poly-mer and the teeth.

Speech

A new denture may cause a change in the speech pat-terns although, with adaptation, these usually disap-pear within a few days. If persistent, it is probably be-cause the shape of the polished surfaces and/or toothposition on the dentures has been changed beyondthe adaptive capacity of the individual. In this case,the shape should be compared to the previous dentureand, if necessary, consideration given to repositioningthe incisors and/or modifying the palatal contours ac-cordingly. The most common complaints relate to the‘S’ sound which is dependent on the correct relation-ship of the tip of the tongue and the palatal aspect ofthe upper anterior teeth.

Recurrent fracture of dentures

There are two mechanisms to describe the way den-tures can break:

� Impact fracture� Fatigue fracture

An impact fracture occurs due to a high, short-actingforce impacting on the denture such as can occurif the denture is dropped onto a hard surface. Thistype of fracture can occur at any time in the life ofa denture. A fatigue fracture is the result of numer-ous, relatively low magnitude, repeated forces be-ing applied which eventually cause a small crack,commonly in the midline, which then progresses bycrack propagation to ultimate failure. Failure by this

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324 V. Problems

mechanism is common after a period of wear of sev-eral years.

Midline fatigue fracture is usually associated withone or a number of the following:

� Median diastema� Large fraenal notch� Absence of labial flange� Wedging action of very worn occlusion� Inherent weakness following previous repair

It will occur more readily in those with the ability tochew or clench using heavy masticatory loads and inthose with bruxism.

A majority of the midline fractures can be avoidedby the application of established prosthodontic prin-ciples during denture construction. For example, evenand adequate bulk of denture base material cured toachieve optimum polymerisation and free of porosity;relief of incompressible tissue in the centre of the hardpalate; addition of labial flange to increase rigidity ofdenture base; even and balanced occlusion to reducewedging effect and locking of occlusion. Reduction ofstress concentrators such as notches and diastema toa minimum would also help prevent these fractures.If notches are to be incorporated, a rounded notchis preferred to a sharp one. Consideration should begiven to the use of either a high impact acrylic resindenture base material or a metal (cobalt–chromium)base.

Retching

A few patients have great difficulty coping with a for-eign body in the mouth resulting in retching. Some,those with extreme difficulties, may retch even whenan examination mirror is placed between the lips.Most, however, can tolerate instrumentation or a den-ture in the mouth for varying lengths of time. In theextreme cases there are strong psychological over-tones which cannot be overcome simply; however, inothers, the design and fit of dentures is the predispos-ing factor.

The most common cause of retching related todentures is posterior overextension of the upper orlower denture. The soft palate and posterior ar-eas of the tongue are sensitive to contact causingthe protective retching reaction. Thickness of thebases is also relevant as besides encroaching on thetissues it may also lead to tongue cramping. Oc-casionally, a normally extended or underextendedpoorly fitting upper denture will cause retching whenit drops and contacts the posterior region of the

tongue. The management (modification) of the den-tures will depend on the diagnosis and may well in-clude guidance on the wearing of dentures as well asreassurance.

Burning mouth

A complaint of burning or tingling associated with theoral tissues or lips is referred to as the burning mouthsyndrome. It is most common in women who are over50 years of age. Diagnosis is by a process of elimina-tion since there are numerous potential causative fac-tors. A detailed history and examination will lead to aprovisional diagnosis in most cases but it can be verydifficult, even with the aid of special tests, to reach adefinitive diagnosis in a few cases. Timing and modeof onset should help define if the complaint is relatedto the provision of a new prosthesis.

Local factors such as denture design (e.g. incorrectocclusal vertical dimension, excessive loading of thesupporting tissues, tooth position causing lip/tongueirritation etc.) should be assessed and eliminated. Ex-cessive residual monomer content (more than 1%)due to incomplete curing of the polymethylmethacry-late can lead to chemical irritation with a new orrecently relined/rebased denture. This can only beconfirmed by chemical analysis of the denture baseusing, for example, gas chromatography but if sus-pected the practitioner could request the laboratoryto re-process the denture. Other contributory factorsinclude denture-induced stomatitis, a dry mouth (notethe variety of causes including pharmacotherapy) andsmoking.

Systemic factors include deficiencies that are onlyevident following blood screening tests for iron, folicacid and the vitamin B complex. Investigations mightinclude: serum iron, serum folate, serum vitamin B12,red cell folate as well as the haemoglobin. Anxi-ety and depression (and their associated pharma-cotherapy) should be borne in mind. Close liaisonwith the general medical practitioner is obviouslyimportant.

Denture Relines

A reline can be described as the addition of mate-rial to the existing fitting surface of a denture base.The reline procedure can utilise a permanent or tem-porary material which could be either hard or softand which could be applied at the chairside or in thelaboratory.

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A reline is normally prescribed to improve the fitof an existing denture when the looseness is relatedto the fitting (impression) surface of the denture. Thisusually occurs due to alveolar resorption and is there-fore time dependent. The denture should be exam-ined to ensure that it is otherwise satisfactory, i.e. theocclusion, occlusal vertical dimension and aesthetics.Deficiencies in the border extension should be cor-rected using tracing stick impression compound andundercuts removed from the base before the washimpression is taken. The aim is normally to recordmaximum surface detail without disturbing either thevertical dimension or the occlusion and therefore animpression material such as zinc oxide–eugenol pasteor silicone which can be used in thin section is ideal.When recording the impression the borders shouldbe moulded and then the denture brought into oc-clusion with the opposing natural teeth or denturewhilst the material sets. This avoids disturbing theocclusion.

This clinical procedure is the same for both lab-oratory performed hard and soft relines (and for arebase which involves removal and replacement of asignificant proportion of the old base material).

Soft lining

A soft lining may be added as a reline procedure fora patient with a history of mucosal discomfort andchronic soreness provided other predisposing factorshave been eliminated. To be effective a permanentsoft lining should be 2–3 mm thick. The lining actsto absorb part of the force of occlusion, releasing thestored energy as elastic recoil. It also assists in produc-ing an even distribution of functional load over theentire denture-bearing area, avoiding local concentra-tions of stress. It should therefore increase a patient’sability to use a denture comfortably.

The most effective material is heat polymerised sil-icone since this has good elastic properties and re-mains soft. An adhesive is required to ensure an ad-equate bond to the polymethylmethacrylate denturebase material. Plasticised acrylic is an alternative butis less soft than silicone and hardens as the plasticiserleaches out. It does, however, bond chemically to thedenture base.

Autopolymerising silicones and plasticised acrylicsoft linings are available but their properties do notcompare favourably with those of the heat poly-merised materials. They can, however, be used at thechairside and are suitable for domicillary visits if lab-oratory support is not available.

Temporary soft lining, tissue conditioners

These only remain soft for a limited period (days toweeks) and can be used when it is necessary to give thesupporting tissues an opportunity to recover beforefabricating a new denture or permanently relining anexisting one. They may also be used as functionalimpression materials, for immediate denture mainte-nance, cleft palate speech aids and immediate surgi-cal splints. The powder is a higher methacrylate, e.g.polyethylmethacrylate or copolymers, while the liq-uid is usually a mixture of ethyl alcohol as solvent anddibutyl phthalate as plasticiser. The alcohol and es-ter are solvents for the polymer beads, swelling themand allowing the plasticiser to diffuse in and rapidlyforming a gel through a physical process. Althoughinitially very soft and fluid, leaching and evaporationof the compounds leads to hardening of the materialin the mouth.

Repairs

The material most commonly employed in the con-struction of dentures is polymethylmethacrylate. De-spite its popularity, the material, although adequatein satisfying aesthetic demands, is far from ideal infulfilling the mechanical requirements of such appli-ances. This is reflected in the unresolved problem ofdenture fracture and the accompanying costs to effectrepair.

The causes of denture fracture have been discussedearlier. Although repair of a broken denture shouldbe carried out in the laboratory, to achieve maximumstrength, the patient and denture should be exam-ined first clinically. This examination should elicit thecause of the fracture, the health of the oral tissues andthe suitability of the denture.

If relatively new and otherwise satisfactory, thedenture should be sent for a standard repair. How-ever, if the denture is also loose it may be necessaryand appropriate to carry out a reline (or rebase) at thesame time as the repair since this will both strengthenthe base and improve the fit.

The component parts should be assembled andif there is any doubt about their relocation stickywax should be used to hold them together so thatthe denture can be tried in the mouth. This sameprocedure is necessary before a reline impression al-though it may be necessary to reinforce across thefracture line using pieces of wire, old burs or evenmatchsticks.

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326 V. Problems

If the denture is inherently weak due to the design,e.g. no anterior flange on an upper complete dentureor a small lower complete denture with a soft lining,then consideration should be given to modifying thedenture by adding a flange or incorporating a castlingual metal plate. The construction of a new dentureshould be considered.

Fractured metal components may be more difficultto repair. It is not possible to solder new clasps to acobalt–chromium denture framework. It may be pos-sible to construct a new clasp and retain it within theacrylic saddle region.

Causes of Denture Intolerance

An inability to cope with dentures can be due either tofactors related to the design and construction of thedentures or attributed directly to the patient. A closeexamination and assessment of the dentures shouldalways be made before putting the blame for failureelsewhere.

There are many possible causes of denture intoler-ance and often a diagnosis is reached only by a processof elimination. It is important therefore to follow anorderly pattern in the examination of denture and pa-tient. This should always be preceded by a history ofthe complaint(s) relating it to previous denture expe-rience and the age and general health of the patient.

Design faults

Many complaints of intolerance can be related to ex-tension of the bases, the occlusal vertical dimensionor the relationship of the denture to the neutral zone.Overextension or excessive thickness of the bordersis poorly tolerated and, on occasions, can lead to acomplaint of retching. It can, of course, also causediscomfort and looseness. The complaint of retchingis usually related to the posterior lingual extension ofthe lower denture and the posterior palatal extensionof the upper.

Patients are less likely to cope with dentures withreduced (or negative) freeway space than if there isexcessive freeway space. With reduced freeway spacethey may complain of the dentures feeling too bigfor their mouth, teeth clattering or meeting too early,generalised discomfort of the denture bearing tissuesor pain in the muscles of mastication.

A denture that does not conform with the neutralzone is likely to be displaced in function with the pa-tient complaining of looseness.

Design faults leading to poor aesthetics will, with adiscerning patient, lead to rejection of a denture sincegood appearance is probably the strongest motivatingfactor for denture wear.

Adaptive capacity

The capacity of an individual to adapt to change maybe determined by a number of factors including ageand general health. Chronological age is less relevantthan biological age since a sprightly, mentally activeolder person is more likely to be adaptive than a bio-logically old younger individual.

Adaptive capacity will also depend on generalhealth and is reduced in chronic or debilitating con-ditions. The after effects of cerebrovascular accidentscan severely handicap adaptation leading to consid-erable difficulties with dentures.

Even a normally adaptable individual can have dif-ficulty meeting the demands of excessive changes indesign if a new denture differs markedly from the old.For example, an individual having worn the same un-der extended dentures for more than 20 years andhaving become accustomed to the gradual loss of oc-clusal vertical dimension with resultant gross overclo-sure, due to wear of the teeth and alveolar resorption,is perhaps unlikely to adapt to the sudden change to‘textbook’ dentures fully extended and with the aver-age 3 mm of freeway space.

Personality and mental attitude

Most patients cope well with complete dentures evenwhen the dentures are perhaps less than ideal. Thereare, however, some who are fussy and demandingwith a high level of expectation. These individuals canusually be satisfied provided adequate time and ap-propriate expertise is devoted to them. Unfortunately,there are a few who are obsessive and often illogicalin their attitude to denture treatment who cannot besatisfied. These individuals may seek treatment from anumber of different practitioners but continue to findfault with all the prostheses and to place the blameon anyone or anything other than themselves.

Lack of motivation

As has already been stated, most edentulous patientsare strongly motivated to wear dentures to maintainor improve their appearance. Many, of course, alsogain from the improvement in masticatory function.However, there are those who can cope with their

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diet perfectly adequately without teeth and who arenot unduly concerned with their appearance. Theseindividuals may be put under pressure from relativesor health workers to have dentures. In some casesthey have been without teeth or dentures for yearsand it is unlikely that they will put sufficient effortinto wearing dentures to give much chance of success.

Chronic alcohol abuse

Patients with a known history of alcoholism oftendo not tolerate dentures well. They may complain ofretching whenever the dentures are inserted and maynot persevere in order to learn control of the dentures.This link between retching and alcoholism may be dueto the condition of gastritis which is common.

Soft Tissue Pathology Related toWearing Dentures

Traumatic ulceration

This is the most common pathology resulting fromwearing dentures. This can occur during the first fewdays when new dentures are worn usually becauseof areas of overextension, traumatic contact (in rela-tion to undercuts) or irritation from sharp or roughareas of the fitting (impression) surface. Ulcerationcan also occur when a denture becomes loose andill fitting. When the source of irritation is removedthe ulcer should heal within a few days. If it persiststhe area should be further inspected and, if necessary,biopsied.

Denture-induced stomatitis

This occurs mainly in the maxilla and is more com-mon in females. It is a chronic irritation of thedenture-bearing tissues causing the mucosa to appearbright red. Most patients are unaware of its presencesince it is normally asymptomatic. A number of fac-tors are believed to contribute to the condition:

� Candida albicans� Denture wearing habits� Fit of the denture� Excess residual monomer� General health

Candida albicansPoor oral and denture hygiene allows plaque andfood deposits to accumulate with an associated

overgrowth of the mycelial and yeast forms of thefungus on both the tissues and denture base.

Denture wearing habitsWhen dirty dentures are worn day and night the tis-sues are in constant contact with the infected denturebases and the condition will be aggravated.

Fit of the dentureMechanical trauma from rough or ill-fitting denturestends to irritate the tissues and make them more sus-ceptible to candidal infection.

Excess residual monomerIt is possible that the residual monomer will chemi-cally irritate the tissues and increase their susceptibil-ity to infection.

General healthSystemic factors such as deficiencies of the vitaminB complex, iron and folic acid and immunologicaldefects should be borne in mind especially in thoseresistant to normal treatment regimes.

Treatment

The treatment of the condition can be summarisedunder three headings:

� Improved oral hygiene� Modifications to the fit of the denture� Antifungal therapy

Advice should be given on denture hygiene and clean-ing (see Chapter 26) and the patient requested toleave the dentures out during the night. A hypochlo-rite solution is probably the most effective cleaner forplaque removal and for sterilisation of the denturebase. A poorly fitting denture can be modified using ahard or soft chairside lining material (see section onrelines). Antifungal therapy is directed locally usingNystatin tablets (500,000 units) or amphoteracin Blozenges (10 mg) dissolved in the mouth four times aday for up to 2 weeks or by the use of miconazole oralgel (25 mg/mL) which can be smeared on the fittingsurface of the denture.

Other conditions

Angular stomatitis is an inflammatory, and sometimeserosive, condition which occurs in the folds at thecorners of the mouth. It is usually seen in associationwith denture-induced stomatitis and the presence of

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328 V. Problems

Candida albicans should therefore be suspected. Sec-ondary bacterial infection can occur; also, staphylo-coccus aureus is claimed to be a causative organismof the lesion even in the absence of Candida albicans.Inadequate lip support or insufficient occlusal verticaldimension from the dentures may lead to the develop-ment of folds at the corners of the mouth which, dueto saliva moistening them, can be susceptible to in-fection. Initial treatment is based on that prescribedfor denture-induced stomatitis; miconazole oral gelis probably the most effective agent since it is bothantifungal and antibacterial. Modifications may berequired to the dentures to improve lip support andocclusal vertical dimension. If the lesion is resistantto therapy the possibility of an underlying associateddeficiency (e.g. iron, or vitamin B or C) should beinvestigated.

Papillary hyperplasia of the palate is an inflamma-tory lesion which presents as multiple small nodulesof granulation tissue. It usually occurs in the centralportion of the palate and can correspond to the areaunderlying a relief chamber. Causative factors includechronic irritation from the denture and a superim-posed denture-induced stomatitis. Again, treatmentis first aimed at improving the oral hygiene and re-ducing irritation. Surgical treatment is probably onlyrequired in extensive cases or if there is doubt aboutits benign nature.

Denture-induced hyperplasia is an overgrowth ofgranulation tissue usually associated with the bor-ders of ill-fitting dentures. Trauma from the borderscauses recurrent ulceration and healing with resultant

growth of fibrous tissue. This can present as a foldor multiple folds of tissue and is more common inthe lower jaw associated with the buccal and labialborders. Treatment is aimed first at eliminating thesource of irritation by substantially reducing the bor-der of the denture or by persuading the patient not towear the denture (not always acceptable). Temporarylining of the denture may also be appropriate in orderto improve the fit and stability. Since there is an in-flammatory component to this pathological processthese measures should allow a regression in size ofthe lesion due to the resolution of the inflammatoryprocess. The resultant lesion may then be sufficientlysmall to allow routine prosthetic treatment to be con-tinued however more extensive lesions, which wouldinterfere with the construction of dentures, mayrequire surgical excision.

Oral carcinoma

Whilst this pathology is not related to denture wear-ing it is important to remember the role of the dentistin identifying early lesions of the oral mucosa and lips.Discomfort, ulceration and/or loose dentures mightrelate to a soft tissue lesion. As was stated above anyulceration that does not heal quickly should be inves-tigated further.

Regular recall of complete denture wearers is notroutine. After the first review the patient, if satisfied,is discharged. To be able to make an early diagno-sis of silent lesions, a yearly examination should bearranged.

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Bibliography

This lists some current textbooks on the individual princi-pal subjects of restorative dentistry together with selectedpapers. Some of the papers are of considerable historicalsignificance whilst others deal with the ‘state of the art’.

The Patient

TextsBritish National Formulary (2007) BMJ Publishing Group

Ltd, London.Scully C, Cawson R (2004) Medical problems in dentistry,

5th edn. Wright, Oxford.

GuidanceBritish Dental Association (2003) Infection control in den-

tistry. Advice Sheet A12.National Institute for Clinical Excellence (2004) Dental

recall. Clinical guideline 19.

Radiology and Radiography

TextWhaites E (2007) Essentials of dental radiography and

radiology, 4th edn. Churchill Livingstone, Edinburgh.

Guidance and legislationFaculty of General Dental Practitioners (UK) (2005) Selec-

tion criteria in dental radiography, 2nd edn. Faculty ofGeneral Dental Practitioners, London, UK.

Health Protection Agency (2001) Guidelines on radiol-ogy standards in primary dental care. Health ProtectionAgency, London, UK.

Ionising Radiation (Medical Exposure) Regulations (2000)(IRMER).

Anaesthesia, Analgaesia and Sedation

TextsGirdler NM, Hill M (1998) Sedation in dentistry. Wright,

Oxford.Hill CM, Morris PJ (1991) General anaesthesia and sedation

in dentistry. Wright, Oxford.Meechan JG et al. (1998) Pain and anxiety control for

the conscious dental patient. Oxford University Press,Oxford.

Robinson PD, McDonald F (2001) Local analgaesia in den-tistry, 4th edn. Wright, Oxford.

Trauma

TextAndreassen JO, Andreassen FM (2000) Esentials of trau-

matic injuries of the teeth. Munksgaard, Copenhagen.

The Restoration and its Environment

Oral Biology and Pathology

TextsBerkowitz B et al. (2003) Oral anatomy, histology and em-

bryology, 3rd edn. Mosby, St Louis.Kidd EAM (2005) Essentials of dental caries: the disease

and its management, 3rd edn. Oxford University Press,Oxford.

Periodontology

TextLindhe J et al. (2003) Clinical periodontology and implant

dentistry, 4th edn. Blackwell-Munksgaard, Oxford.

PapersHassell TM (ed) (1993) Periodontal tissues – structure

and function, Vol. 3: Periodontology 2000. Munksgaard,Copenhagen.

Lang NP, Karring T (eds) (1994) Proc 1st Europeanworkshop on periodontology. Quintessence Publishing,London.

Lang NP, Karring T (eds) (1997) Proc 2nd Europeanworkshop on periodontology. Quintessence Publishing,London.

World workshop in periodontics (1996) Vol. 1, No 1.American Academy of Periodontology, Chicago.

Occlusion

TextsAsh MM, Ramfjord S (1995) Occlusion, 4th edn. Saunders,

Philadelphia.Kleinberg I (1991) Occlusion: principles and assessment.

Wright, Oxford.

PapersAlexander PC (1965) The periodontium and the canine func-

tion theory. J Prosthet Dent 18:571–577.Bennett NG (1908) A contribution to the study of the move-

ment of the mandible. Trans R Soc Med 1:77–84.Beyron HL (1969) Optimal occlusion. Dent Clin North Am

13:537–542.


330 Bibliography

Celenza FV (1973) The centric position: replacement andcharacter. J Prosthet Dent 30:591–595.

Chasens AI (1990) Controversies in Occlusion. Dent ClinNorth Am 34:111–123.

D’Amico A (1961) Functional occlusion of the natural teethof man. J Prosthet Dent 11:899–915.

Denbo J (1990) Malocclusion. Dent Clin North Am 34:103–109.

Jent T, Lundquist S, Hedegard B (1982) Group function orcanine protection. J Prosthet Dent 18:719–720.

Lauritzen AG, Bodner GH (1961) Variations in locationof arbitrary and true hinge axis points. J Prosthet Dent11:224–229.

Lindhe J, Nyman S (1977) The role of occlusion in peri-odontal disease and the biologic rationale for splinting inthe treatment of periodontitis. Oral Sci Rev 10:11–17.

Posselt U (1957) Movement areas of the mandible. J ProsthetDent 7:375–379.

Schuyler SH (1969) Freedom in centric. Dent Clin N Am13:681–685.

Stuart CE, Stallard H (1960) Principles involved in restoringocclusion to natural teeth. J Prosthet Dent 10:304–313.

Restorative Dental Biomaterials

TextsAnusavice KJ (2003) Phillips’ science of dental materials,

11th edn. Elsevier, Oxford.McCabe JF, Walls A (2007) Applied dental materials, 9th

edn. Blackwell-Munksgaard, Oxford.

PapersChadwick BL et al. (2001) Longevity of dental restorations

– a systematic review. NHS Centre for Reviews and Dis-semination, York.

European Commission (1998) Dental amalgam.Jacobsen PH (1987) Biological and clinical testing of mate-

rials. J Dent 15:266–268.Jacobsen PH (1988) Design and analysis of clinical trials. J

Dent 16:215–218.

Clinical Management and Techniques

Intracoronal Restorations

TextsKidd EAM, Smith BGN (2003) Pickard’s manual of opera-

tive dentistry, 8th edn. Oxford University Press, Oxford.Roulet J-F, Herder S (1991) Bonded ceramic inlays.

Quintessence, Chicago.

PapersBurke FJT, Qualtrough AJE (1993) Aesthetic inlays: com-

posite or ceramic. Br Dent J 176:53–59.Jacobsen PH, Rees JS (1992) Luting agents for ceramic and

polymeric inlays and onlays. Int Dent J 42:145–149.Rees JS, Jacobsen PH (1996) Restoration of teeth with com-

posite resin 1: direct-placement composite. Dent Update23:406–410.

Rees JS, Jacobsen PH (1996) Restoration of teeth with com-posite resin 2: indirect-placement composite. Dent Update24:25–30.

Management of Deep CariesBrannstrom M, Isaacson G, Johnson G (1976) Effect of cal-

cium hydroxide and fluorides on human dentine. ActaOdontol Scand 34:59–66.

Kidd EAM, Joyston-Bechal S, Beighton D (1993) The use ofa caries detector dye during cavity preparation: a micro-biological assessment. Br Dent J 174:245–248.

Oligushi K, Fusayama T (1975) Electron microscope struc-ture of the two layers of carious dentine. J Dent Res54:1019–1026.

Outhwaite WC, Garman TA, Pashley DH (1979) Pins v slotretention in extensive amalgam restorations. J ProsthetDent 41:396–400.

Endodontics

TextsCohen S, Burns RC (2006) Pathways of the pulp, 9th edn.

Mosby, St Louis.Pitt-Ford TR (2004) Harty’s endodontics in clinical practice,

5th edn. Wright, Oxford.

GuidelinesEuropean Society of Endodontics (2006) Consensus report

of the European Society of Endodontology on qualityguidelines for endodontic treatment. Int Endod J 39:921–930.

PapersBonsor SJ et al. (2006) Microbiological evaluation of photo-

activated disinfection in endodontics (an in vivo study). BrDent J 201:114–117.

Saunders WP, Saunders EM (1994) Coronal leakage as acause of failure in root canal therapy: a review. EndodDent Traumatol 10:105–108.

Zehnder M (2006) Root canal irrigants. J Endod 32:389–398.

Crowns

PapersCheung GSP (2005) Fate of vital pulps beneath a metal–

ceramic crown or a bridge retainer. Int Endod J 38:521–530.

Jacobsen PH et al. (2006) The effect of preparation heightand taper on cement lute thickness: a three-dimensionalfinite element analysis. Eur J Prosthodont Rest Dent14:151–157.

Jorgensen KD (1955) The relationship between retentionand convergence angle in cemented veneer crowns. ActaOdont Scand 13:35–40.

McAndrew R, Jacobsen PH (2002) The relationship be-tween crown and post design on root stress – a finite ele-ment study. Eur J Prosthodont Rest Dent 10:9–13.

McLean A (1998) Predictably restoring endodonticallytreated teeth. J Can Dent Assoc 64:782–787.

Nayyar A et al. (1980) An amalgam coronal dowel andcore technique for endodontically treated posterior teeth.J Prosthet Dent 43:511–515.


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Colour and Aesthetics

TextAhmad I (2006) Protocols for predictable aesthetic dental

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Bridgework

TextsRosenstiel SF et al. (2006) Contemporary fixed prosthodon-

tics, 4th edn. Mosby, St Louis.Shillingburg HT et al. (1997) Fundamentals of fixed

prosthodontics, 3rd edn. Quintessence, London.

PapersAnte IH (1926) The fundamental principles of abutments.

Mich State Univ Soc Bull 8:24–28.Eshleman JR et al. (1988) Tooth preparation designs for

resin bonded fixed partial dentures related to enamelthickness. J Prosthet Dent 60:18–22.

Livaditis GJ, Thompson VP (1982) Etched castings: an im-proved retentive mechanism for resin-bonded retainers. JProsthet Dent 47:52–57.

Nyman S, Ericsson I (1982) Capacity of reduced periodontaltissues to support fixed bridgework. J Clin Periodontol9:409–412.

Rochette AL (1973) Attachment of a splint to enamel oflower anterior teeth. J Prosthet Dent 30:418–422.

Implants

TextsPalacci P, Ericcson I (2000) Esthetic implant dentistry: soft

and hard tissue management. Quintessence, London.Palmer R (2000) A clinical guide to implants in dentistry.

BDA Books, London.Sclar AG (2003) Soft tissue and esthetic considerations in

implant therapy. Quintessence, London.Sethi A, Kaus T (2005) Practical implant dentistry: diagnos-

tic, surgical, restorative and technical aspects of aestheticand functional harmony. Quintessence, London.

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healing. J Dent Ed 67:932–949.Koka S (1998) The implant–mucosal interface and its role

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the edentulous patient, 4th edn. Blackwell, Oxford.Davenport JC (2000) A clinical guide to removable partial

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Problems

Tooth surface loss

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with advanced localised attrition. J Oral Rehabil 2:209–214.

Milosevic A (1999) Eating disorders and the dentist. Br DentJ 186:109–113.

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Dent J 156:165–170, 205–209.Gray RJM et al. (1995) Temporomandibular disorders: a

clinical approach. British Dental Association, London.Greene CS, Laskin DM (1972) Splint therapy for myofacial

pain dysfunction syndrome: a comparative study. J AmDent Assoc 84:624–628.

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332


Index

Abrasion resistance of materials, 75,77, 78

Adhesion and adhesives, 83–85bond strength testing, 85–86cements, 189clinical applications

cores, 110intracoronal cavities, 88resin-retained bridgework, 216veneers, 181

conditioners, 83physical and chemical properties,

83–85systems, 83

Aesthetics, 88, 175–186colour, 175–177,dentures, 271in crown and bridgework, 158, 171,

224, 227, 232, 233, 234in implants, 250–252

Age changes in dentition, 28, 42Allergy, 8

antibiotics, 127cements, 94

Alloysbridgework, 188–9ceramic bonding, 164–165Alveolar bone, 54resorption, 204–207

Amalgam, 95, 102, 110carving, 105condensation, 105core placement, 113–114corrosion, 18, 81, 259creep, 77, 81, 246mixing, 104physical properties, 76polishing, 105proportioning, 104toxicity, 86

Amelogenesis imperfecta see Toothsurface loss

Anaesthesia, general, 25Analgesia, 124, 257Antibiotics, 126–7

allergy, 127prophylactic, 9systemic, 20, 119, 127

Apical pathology, 53–54, 266abscess, 20cyst, 20, 53

diagnosis, 18–20granuloma, 20, 53infection, 7, 53perforation, 109treatment, 20

Apical surgery, 129–133flap design, 133indications, 129review, 132technique, 130–132through and through, 132

Apprehension, 26–27Articulators, 144–147

see also Occlusion

Bacterial endocarditis, 28Basic Periodontal Examination (BPE),

9–10Biological compatibility of materials,

81Bleaching, 178–179Blood dyscrasias, 27Blood tests, 11Bridgework, conventional, 217–225

See also resin-retained bridgework,implants

abutment tooth assessment, 223aesthetics, 220–221, 224anterior, 234–239biological factors, 217–218cantilever, 210, 317cementation, 233clinical procedures, 226–239connectors, 210, 219, 220contact areas, 222definitions, 210design, 217–221failures, 316–320fitting, 231–233indications, 201–204mechanical factors, 218–220occlusal registration, 229, 230occlusion, 151–152, 153, 222, 232,

233path of insertion, 218, 219, 220,

227, 229pontics, 210, 221, 222precision retainers, 224–225, 238,

239, 289preoperative considerations,

221–224

diagnostic articulation, 222preparations, 227–229problems, 203provisional, 226–228relocalisation, 230–231review, 233spring cantilever, 210stages in construction, 226treatment planning, 201–207try-in, 229, 231–233

Bruxism, 296, 307Burning mouth, 324Burs, 99

Calcium hydroxideliners, 101root canal dressing, 22, 125

Candida albicans, 327–328Cardiovascular conditions, 28Caries, 46–52

aetiology, 15–16, 46–48approximal, 89–90, 91cervical, 92–3coronal, 51deep lesion, management of, 99–104dentine, 48–50diagnosis, 14–16early (white spot) lesion, 49, 51enamel, 49–51excavation, 51–2fissure, 50microorganisms, 46–47, 52occlusal, 89pathology, 44–52progression, 44, 48pulpal response, 50–1rate, 15recurrent, 10, 266remineralization, 44, 51, 91research techniques, 48–49

ground sections, 48microbiopsy, 49microradiography, 49scanning electron microscopy, 49transmission electron microscopy,

49root, 51stabilisation, 19symptoms, 6treatment, 96–99tooth susceptibility, 48


334 Index

Cavity preparationfor amalgam, 85–6, 91–2for composite, 85–6, 88margin finishing, 93preventive resin restoration, 88, 89,

90principles of, 85–6

Cementation, 187–8, 210–11failure, 265–6see also Cements

Cementsbases, 101–102cementation, 172–173, 233liners, 101, 102luting agents, 173physical properties, 76

Cementum, 42, 54Centric occlusions see OcclusionCentric relation see OcclusionCeramics, dental

bonding alloys, 164–165castable, 163colour, 157–9core shine, 182corrosion, 81crowns, 163–165fractured, 267inlays, 92, 106milled, 164strengthening, 163–165veneers, 179–181, 187

Charting, 11dental, 11periodontal, 11

Cleft palate, 225Clinical examination, 9–11Clinical trials of materials, 86Colour, 175–186Colour stability of materials, 81Complete dentures, 278–290

construction, 279–285duplication (copy dentures),

285–286immediate dentures, 286ovedentures, 286–290retention, 278stability, 279support, 278

Compomers, 94, 95Composites, 92–93, 102

adhesion, 88clinical indications, 92, 96, 98,

101colour stability, 77fluoride leach, 88handling, 82, , 83, 99, 103–104inlays, 88, 105–106light curing, 93–94, 88

metal reinforced, 110properties, 76, 77, 80, 81, 92–93,

94, 95technique, 103–104

Consent to treatment, 26Continuing care, 31Corrosion of materials, 18, 81Cracked tooth syndrome, 310–311Creep of materials, 77, 246Cross-infection prevention, 29, 173Crowns, 157–174

cementation, 172–173choice of material, 163–166errors, 165margins, 160–161, 166metal-ceramic, 164–166multiple, 50, 298–299occlusion, 162post, 168–171, 312–314principles of preparation, 158–163provisional, 171root filled teeth, 166–171stability, 159treatment planning, 157—158,

298

Dahl, 300Deep carious lesion, 107–114

diagnosis, 107direct pulp cap, 109indirect pulp cap, 108management, 107–109photo-activated disinfection, 108postoperative assessment, 109pulp assessment, 107restoration, 110–114see also Caries; Root canal

treatmentDentine, 37–39

age changes, 42bonding agents, 79–80caries, 48–50formation, 37–39hypersensitivity, 6mineralization, 38odontoblasts, 38, 36physical properties, 71pins, 111secondary, 38, 42, 44, 49–50sensitivity, 38–39, 44–45structure, 37tertiary, 49–50tubules, 36, 38, 49

Dentinogenesis imperfecta see Toothsurface loss

Dentistabilities, 4, 26facilities, 180

Denture problems, 322–328See also Complete dentures, Partial

denturesaesthetics, 323burning mouth, 324carcinoma, 328denture intolerance, 326–327design faults, 326looseness, 322pain/discomfort, 322recurrent fracture, 323relines, 324–325repairs, 325retching, 324soft lining, 325soft tissue pathology, 327speech problems, 323

Diabetes, 8, 29Diagnosis, 15–21

apical pathology, 18–20caries, 16–17confirmation, 15occlusal disorders, 20periodontal disease, 20, 135–138prosthodontics, 199–209provisional, 18–19pulpal disorders, 17–18restorations, 16root canal treatment, 105–8

Dietanalysis, 15in caries, 15, 47–48in tooth surface loss, 246–7

Dimensional changes of materials, 80,195

Discoloured teeth, 177–178management, 17–181

bleaching, 178–179microabrasion, 178veneers, 179–181

Dislocationof teeth, 23of temporomandibular joint, 253

DMF index, 15Ductility of metals, 75

Enamel, 35–37age changes, 42ameloblasts, 37aprismatic enamel, 37bonding agents, 79–80caries, 47–48early (white spot) lesion, 47–48, 51formation, 37hypoplasia, 177, 178incremental lines, 37ionic exchange, 37matrix, 35, 37


Index 335

physical properties, 71prisms, 35, 36, 41remineralization, 42restorative implications, 41–43structure, 37–39surface, 37, 44

Enamel-dentine junction, 39Epilepsy, 27Examination

clinical, 9–11complete dentures, 280extraoral, 9partial dentures, 263intraoral, 9

Extractions, 31, 138, 184, 280

Facebow, 145Failures in fixed restorations,

310–321cementation failure, 316, 318cracked tooth syndrome, 310dentine pins, 311, 317fixed prosthodontics, 316–320fractured ceramic, 317–318intracoronal restorations, 85, 310management of failed bridge,

318–320medico-legal aspects, 321non-vitality, 317obsessive patient, 320occlusion, 317, 246post crowns, 311–316

fractured posts, 315–316lateral perforation, 311–314Masserann kit, 315–316vertical fracture, 315

recurrent caries, 317WAMkeys, 319wear and tear, 318

Family and social history, 8Fracture toughness of materials,

75Freeway space, 67Full mouth reconstruction, 298–299

Gastric reflux, 247General anaesthesia, 27Gingiva, 53–4Gingival retraction cord, 168, 169Gingivitis, 57–59

acute, 17, 22aetiology, 57chronic marginal, 20clinical features, 57definition, 57epidemiology, 58modifying factors, 58pathogenesis, 58

plaque formation, 57prevention, 58–59

Glass ionomer cement, 93–95, 110adhesion, 88clinical indications for use, 94, 110fluoride leach, 82, 94handling characteristics, 97properties, 71, 88resin-modified, 88, 93–94, 95

Glenoid fossa see Temporomandibularjoint

Goldceramic bonding alloys, 164–165crowns, 161–163inlays, 92, 96, 105properties, 76

Haemophilia, 27Handling characteristics of materials,

82–83amalgam, 104–105composite, 103–104glass ionomer cements, 104mixing, 82setting time, 83working time, 83

Hardness of materials, 76, 78Hepatitis B, 29Hinge axis see OcclusionHistory taking, 5–8

dentures, 263, 279Human immunodeficiency virus

(HIV), 29Hypodontia, 225

Immediate dentures, 286Implants, 240–262

aesthetics, 250–252anatomy, 245basic principles, 240–248bone structure, quantity and quality,

204, 206, 246bone augmentation, 256bone-implant interface, 247cement-retained prosthesis, 242clinical cases, 262clinical review, 258complications, 257–258contraindications, 249–250emergence profile, 206, 253external connection type, 241failure, 243–244guided bone regeneration, 257history, 240immediate placement, 244, 245implant-mucosal interface,

248–249indications, 208, 249

materials, 242osseointegration, 243overdentures, 261, 262peri-implantitis, 258placement techniques, 242–243platform switching type, 241position, 253–255radiographic assessment, 247screw-retained prosthesis, 241soft tissue augmentation, 257survival studies, 261terminology, 240tissue augmentation, 256–257treatment planning

Impression techniques and materials,187–196

addition cured silicones, 188–189assessment, 194classification, 189clinical techniques, 192–194components, 189condensation cured silicones, 188,

189decontamination, 194electrosurgery, 191gingival management, 190–191handling, 192–194materials, 187–190partial dentures, 273–275polyethers, 189polysulphides, 189–190properties, 187requirements, 187special trays, 191, 192, 193, 226,

281syringe, 192

IndicesBPE (CPITN), 9–10DMF, 15oral hygiene, 10

Infrabony pockets, 17, 18INR, 11–12Instrumentation, 112–13

in cavity preparation see Bursfractured, 126

Intracoronal restorations, 91–106,108–114

anterior, 99–100approximal caries, 96–101cavity design and preparation,

91–92, 96–99cavity finishing, 93ceramic inlays, 92, 106choice of material, 92–96composite inlays, 92, 96composite restoration, 92, 96, 99,

103cracked tooth syndrome, 260


336 Index

Intracoronal restorations (cont.)glass ionomer cement restoration,

99, 102gold inlays, 92, 96, 105indications for treatment, 91linings, 101matrices, 102preventive resin restoration, 97stability, 92, 134tunnel prearation, 98

Isolation, 108

Light curingcomposite, 92liners, 102

Lining materialsbases, 101–102liners, 102varnishes, 82

Mandibular guidance see OcclusionMastication

neural control, 72cycle, 73innervation, 67, 68muscles, 64, 144physiology, 71–72

Materials see Restorative materialsMatrices, 102–103

for amalgam, 102–103wedges, 103

Medical historyinfluence on treatment planning,

28–30influence on implants, 249–250influence on periodontal

management, 137, 138taking, 7–8

Medico-legal problems, 313, 321Microabrasion, 178Microleakage, 82, 86Microradiography, 48Model construction, 195Modulus of elasticity, 75–78Mouthrinses, 125

Occlusal management, 143–156analysis, 143–150articulators, 144–146confirmation of articulation, 149deprogrammer, 149equilibration, 152, 154, 222,

307–308equipment, 144–147errors in articulation, 149–150facebows, 145–146partial dentures, 263principles of treatment, 150–156

reconstruction, 150,records, 146–147, 172

copings, 230dynamic, 147

splints, 305–307surface loss, 295–301see also Occlusion;

Temporomandibulardysfunction

Occlusionanalysis, 143–145centric occlusion, 65–66, 128, 144,

146,centric relation, 66–67, 128–9, 144,

146clinical examination, 11, 128, 143,

216–17cusp/fossa relationship, 65–67, 143definition, 62disorders, 163–4

diagnosis, 18see also Temporomandibular

dysfunctionfunctional anatomy, 62–71hinge axis, 65, 130incorrect, 317influence on treatment planning, 30interferences, 143mandibular displacement, 67, 143mandibular guidance, 69–71

condylar, 69tooth, 69

anterior, 66canine, 70, 153group function, 70incisal, 70, 152posterior, 69

muscles of mastication, 64, 144parafunction, 71Posselt’s envelope, 65, 66premature contacts, 68, 69registration, 152, 207–8, 227, 235retruded arc of closure, 67, 143retruded contact position, 67, 143side-shift, 70stability, 134–5, 136, 199see also Occlusal management

Oral hygiene, 8, 20, 24, 25, 30, 31,57, 58, 61, 139

in bridgework, 181, 209indices, 10influence on treatment planning, 30instruction, 22in intracoronal restorations, 91review, 29

Orthodontics, 162–3pre-bridgework, 193, 196

Overdentures, 286–290, 301

Painin apical disorders, 7atypical facial, 7in caries, 7dentures, 270diagnosis, 7evaluation of, 5–7neural mechanisms, 19in periodontal disease, 7in pulpal disorders, 6–7trigeminal neuralgia, 7see also Analgesia

Partial dentures, 263–272, 273–277clasps, 267–269clinical procedures, 273–277connectors, 264, 266, 270, 271crowns, 270design, 142, 264–266, 271diagnosis and treatment planning,

263–264free-end saddle, 274–275

altered cast technique, 275insertion, 276–277materials, 266occlusal registration, 275path of insertion, 265–266preliminary impressions, 273problems,reline, 276–277review, 277RPI system, 272secondary (working) impressions,

274surveying, 264–266, 269try-in, 275–276undercut gauges, 268

Patientaspirations, 3–4influences on treatment planning,

25–26, 123–4, 180motivation, 3, 25–26, 141obsessive, 269previous experience of dentistry,

3, 8Perforation of root

apical, 109lateral, 113repair, 113

Periapical infection, 53–54cyst formation, 54

Periodontal disease, 7, 17, 18, 20,54–57, 56–60, 135–142,199, 266–267

aetiology, 56–7bone loss, 181–2periodontitis, 59

definition, 59clinical features, 59


Index 337

clinical management, 135–139guided tissue regeneration, 140maintenance, 141pathogenesis, 59, 60, 135–137patient factors, 137pocketing, 17, 18surgical techniques, 141susceptibility, 59–60treatment planning, 138–139

Periodontium, 40–42, 56–57cells, 40, 42charting, 9–10diagnosis, 17–18examination, 11fibres, 40gingiva, 53–4ground substance, 40mastication, 72nerves, 40pathology see Periodontal diseaseresponse to movement and load,

41–2and restorations, 60–61vasculature, 40

Photo-activated disinfection (PAD),108, 125

Pins, dentine, 111–113cemented, 111failure, 260friction grip, 111placement, 111–112self-threading, 102–3

Plaque, 43, 44in caries, 178in periodontal disease, 61following tooth loss, 199formation, 43, 54–5index, 10scores, 121–2, 135structure, 43see also Oral hygiene

Polycarboxylate cement, 94Porcelain see CeramicsPost crowns, 149–51

core characteristics, 150failures, 260–5lateral perforation, 260–4in overdentures, 239–40preparation, 150

Precision retainers see BridgeworkPregnancy, 27–8Prosthodontics, general

choice of prosthesis, 201–209deleterious effects, 207replacement of missing teeth,

200–209treatment planning, 200–209

Provisional bridges see Bridgework

Provisional crowns, 151Pulp, 39–40

age changes, 42anatomy, 39assessment in deep caries, 107capping

direct, 109indirect, 108

necrosis, 16, 52pathology

acute pulpitis, 6, 16, 20chronic pulpitis, 6–7, 16diagnosis, 16stabilisation, 20

physiological response, 6response to caries, 52–53testing, 11, 107treatment see Root canal treatment

Pulpal protection, 101–102bases, 101liners, 102principles, 101

Pulpotomy, 101

Radiographsbitewing, 12, 19, 86cone beam CT, 247distortion, 12–13orthopantomogram, 12, 28periapical, 12–13, 17–19review, 31in diagnosis, 30in root canal treatment, 12, 13,

116–117technique, 12–13

Radiotherapy, 27Resin modified glass ionomer cements,

88, 94Resin retained bridgework, 210–216

alloys, 215cementation, 214–215cements and bonding, 215–216debonding, 216design, 211–212history, 210immediate replacement, 214indications, 212tooth preparation, 211–212treatment planning, 212

Restorative materials, 74–87,111

adhesion, 83–85biological compatibility, 86choice, 92, 135, 153clinical testing, 86degradation, 70, 80dimensional changes, 80handling characteristics, 82–83

implants, 242mechanical properties, 74–81partial dentures, 266–267physical properties, 74, 77surface finishing, 83thermal properties, 79–80tooth surface loss, 296–297see also individual materials

Retruded arc of closure see OcclusionRetruded contact position see

OcclusionReview and recall, 31Rheumatic heart disease, 26Risk assessment and prognosis, 31Root canal treatment, 115–134

canal preparation, 118–125access, 118–119apical anatomy, 117high-torque rotary, 123–124instrumentation, 122irrigation, 124orifice enlargement, 119pulp extirpation, 119step-back technique, 123working distance determination,

119–120complications, 127crowns, 151diagnosis, 115disinfectants, 125filling, 121, 126, 259–60filling material, 120–121fractured instrument, 126, 127isolation rubber dam, 118medication, 125open apex, 128outcome, 133perforation, 123, 124, 127,photo-activated disinfection (PAD),

125pre-endodontic preparation,

117–118problems, 124, 126–127radiography, 106, 107recurrent infection, 129

see also apical surgeryreview, 128root canal morphology, 116technical objectives, 115treatment planning, 115–118

Root fracturetraumatic injuries, 21vertical, 264–5

Saliva, 43, 44in caries, 45components, 41influence on materials, 76


338 Index

Sedationinhalation, 27intravenous, 27oral, 27

Shadeguides, 176taking, 176–177

Shortened dental arch, 208–209Smear layer, 84Sorption and solubility of materials,

80Stabilisation, 21–24

of apical pathology, 22of caries, 21definition, 15of gingival conditions, 24of pulpal pathology, 21

Swallowing, 63, 68

Temporomandibular dysfunction, 7,302–309

aetiology, 302–303clinical features, 303–304definition, 302management, 304–308

basic physiotherapy, 304,305

occlusal therapy, 307equilibration, 307restorations, 257splints, 305–307

reassurance, 305systemic therapy, 307

Temporomandibular jointanatomy, 62–64

bones, 62, 63disc, 62, 63ligaments, 63microscopic, 63

arthritis, 304dislocation, 304examination, 144function, 65glenoid fossa, 63internal derangement, 302, 309scan, 309

Thermal properties of materials,79

conductivity and diffusivity,79–80

expansion, 79Tooth loss, consequences, 199–200Toothbrushes, 139

abrasion, 296Toothpastes, 139Tooth surface loss (attrition, abrasion

and erosion), 295–301aetiology, 295, 245–7developmental anomalies, 295

amelogenesis imperfecta, 156,295

dentinogenesis imperfecta, 156,295, 296

diet, 297–298gastric reflux, 298malocclusion, 295

misuse of restorative materials,296–297

parafunctions and habits, 296posterior tooth loss, 295–296systemic disease, 298treatment planning, 298–300

Traumatic injuries, 22–24dislocation and avulsion, 23enamel/dentine, 22enamel/dentine/pulp, 23enamel only, 22root fracture, 23, 264–265

Treatment plangeneral structure, 30–31

Treatment planning, generalprinciples, 4, 25–32

in Prosthodontics, 199–209Trigeminal neuralgia, 7

Veneers, ceramic, 179–181, 187Viscoelasticity of materials, 75Vitality tests, 11, 123

electrical, 11test cavity, 11thermal, 11

Wedges, 103

Xerostomia, 29

Zinc oxide-eugenol cement, 22, 101,111

Zinc polycarboxylate cement, 102


339


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Health & Medicine

Restorative dentistry