Crowns Revision Tool

8/18/2019 Crowns Revision Tool

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2013

Crowns –

Revision tool An article designed to give dental students an overviewinto the World of Crowns. Useful as a revision andreference tool, this article is intended to be easy to

read for anyone unfamiliar with Crown provision, with

tips and guidance from an existing dental student.

-Chirag Patel------

5th Year Student

(Liverpool

University Dental

Hospital)

As featured on


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With Special thanks to:

Professor Callum Youngson (Head of LiverpoolUniversity Dental School)

Dr Sophie Desmons (Clinical tutor at Liverpool

University Dental School)

Leona Yip (Editor)


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ContentsIntroduction ............................................................................................................................................ 4

Pre-operative assessment .................................................................................................................... 4

Types of Crownii, ,

................................................................................................................................... 8

Full Metal Crowns ............................................................................................................................... 8

Metal Ceramic Crowns ........................................................................................................................ 8

All Ceramic Crowns ............................................................................................................................. 9

Resin Bonded Porcelain Crown ........................................................................................................... 9

Composite Crowns ............................................................................................................................ 10

Post and Core Crowns ....................................................................................................................... 10

Three-quarter Crowns ....................................................................................................................... 10

Occlusion, ,

........................................................................................................................................... 11

Aesthetics, , , ,

........................................................................................................................................ 14

Tooth Preparationiv, ii, , ,

........................................................................................................................ 17

Full Metal Crown Preparation ........................................................................................................... 19

Metal Ceramic Crown aka Porcelain fused to Metal ........................................................................ 19

Anterior tooth preparation ........................................................................................................... 19

Posterior Tooth Preparation ......................................................................................................... 20

All Ceramic Crown ............................................................................................................................. 21

Resin Bonded Porcelain Crown ......................................................................................................... 22

High Strength Porcelain Crowns ....................................................................................................... 23

Posterior tooth preparation guideline: ......................................................................................... 23

Composite Crowns ............................................................................................................................ 23

Trouble shooting ............................................................................................................................... 23

Impressions, ,

........................................................................................................................................ 25

Temporary restorationsii, iv, ,

................................................................................................................. 27

Types of Temporary Crown ............................................................................................................... 27

1) Preformed Crowns: Plastic (Opaque: polycarbonate or acrylic) or Metal (aluminium,

stainless steel or nickel chromium)............................................................................................... 27

2) Matrices: Impression Matrix, Vacuum Formed Matrix, Odus Pella/Strip Crowns ................... 28

3) Direct Syringing ......................................................................................................................... 28

4) Lab made Temporary Crowns ................................................................................................... 29


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Temporary restorations for Resin Bonded Crowns ...................................................................... 29

Try in and Cementation,

...................................................................................................................... 30

Try in procedure: ............................................................................................................................... 30

Cementation of the Crown ............................................................................................................... 31

Choosing a cement ........................................................................................................................ 31

Cementing Procedure ................................................................................................................... 33

References ............................................................................................................................................ 34


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IntroductionA Crown is a type of dental restoration that covers a dental implant, or a tooth that has undergone

moderate to severe destruction by caries or wear. It is essentially a “cap” that covers a tapered

tooth preparation, to restore function and aesthetics. Crowns are fabricated outside of the mouth(Indirect ) and can be made from a number of materials, with choice depending on the clinical

situation and patient requirements. The indirect method of producing a Crown is more expensive

than direct methods of restoration because of the extra time and resources required in production

(often by a dental lab), however it allows for the production of an overall better restoration in terms

of both strength and form.

This revision article aims to give a basic overall understanding of the sequences involved in

producing a Crown, beginning with a pre-operative assessment, to final cementation.

All images, other than those explicitly stated, have been provided courtesy of Liverpool University

Dental Hospital.

Pre-operative assessment i ii iii Crown preparations involve the removal of a large amount of coronal tooth structure and should

only be considered after less destructive alternatives have considered, but are too un-retentive, un-

aesthetic or lacking resistance. It is a given, that in Crown preparation, a small amount of sound

tooth structure is removed, however this is done with the intention of saving the tooth from

subsequent loss of larger quantities of tooth. A full coverage Crown can be indicated if all the axial

walls of a tooth have been affected by caries or wear, and a Three Quarter Crown is indicated if one

of the axial walls of the tooth remains sound.

The decision to restore a tooth with a Crown is further influenced by a number of factors, including

patient expectations, the patient’s oral hygiene and periodontal status, occlusion, and the dentist’s

ability to perform the procedure.

The following factors all need to be factored in before a decision can be made on whether a Crown is

suitable or not.

Patient expectations

-It is very important to gauge an individual’s expectations from the Crown, and compare to one’s

own clinical judgement on what can be achieved realistically. The response will also influenceselection of material, with often a compromise between function and aesthetics.

For example, for an anterior tooth, a Gold Shell Crown would be very retentive and require least

removal of tooth tissue compared with an All Ceramic Crown; however few patients would accept

this aesthetically.

Treatment tolerance and maintenance

-If the patient is unable to open their mouth sufficiently or for long periods of time, this would

impinge on a dentist’s ability to carry out the preparation and take impressions.

-If a patient suffers from parafunction such as bruxism, a Crown lifespan would be significantly

reduced.-A patient must be able to maintain good oral hygiene, for the longevity of the Crown, and


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periodontium.

Justification of tooth removal

-The inevitable removal of sound tooth in a Crown preparation, and therefore weakening of tooth

structure, must be justified by the provision of a Crown that will serve to protect the tooth fromfurther loss of tooth structure, and gain of function.

-Studies have shown that 1-15% of vital teeth become devitalized after Crown preparation, due to

exposure of thousands of dentinal tubules, and this needs to be kept in mind when considering

Crown preparation, as this can lead to periapical pathology later on.

Oral environment

-The oral environment in terms of plaque control, parafunction, caries risk and occlusion need to be

considered for the success of a Crown. Parafunction can be difficult to control, however the other

factors are manageable and once ideal, are key to the success of Crown work.

-Plaque is a primary cause of caries and periodontal disease, and it is important that a patient’s oral

hygiene is stabilized before the provision of any Crown work.-High plaque levels in a patient with Crown restorations increase the risk of caries progression and

tooth loss, especially where there are marginal deficiencies between the tooth and Crown.

Periodontally, plaque can lead to loss of attachment, and gum recession, which would lead to

mobility and an unaesthetic appearance around the margins of the tooth.

-It is the dentist’s responsibility to communicate the importance of good oral hygiene and the direct

influence on the Crown’s success. This information should be followed by oral hygiene instruction

including, tooth brushing advice, flossing techniques, mouthwash advice etc. A tell-show-do method

has proven to be successful in teaching patients how to brush and floss.

-Dietary advice is also important in reducing caries risk. The patient should be taught the link

between sugar attacks and acids with the risk of caries and to limit such exposures. The UK has an

aging population, and root caries within this cohort is likely to be an increasing threat. Root caries isdifficult to deal with, and will cause the failure of even the best Crown restoration.

Occlusion

-An accurate assessment of occlusion in ICP and the guiding teeth in both lateral and protrusive

movements is required in order to understand the stresses that the Crown will undergo. This can be

observed visually, using articulating paper and on study models.

-An ideal occlusion would be canine guided on lateral excursion, in the absence of non-working side

interferences

-Nearly all anterior teeth are involved in guidance on protrusion.

-Posterior teeth undergo the greatest amount of occlusal stress

-Decision of the material of the Crown is influenced directly by the occlusion

Periodontal health

-Teeth with attachment loss can be Crowned, and it is only in cases where the disease is

unstable/uncontrolled that a Crown be contraindicated.

-A Crown with poor margins can compromise the health of the periodontal tissues, especially if

meticulous oral hygiene isn’t maintained.

-Ideally, all Crown margins should be placed supragingivally, to avoid the problems associated with

gingival recession, however, in cases where subgingival preparations are indicated, it is important

the margins are as smooth as possible.

-Subgingival preparations should lie within the depth of the gingival sulcus, and should never

encroach onto the biologic width of the periodontium. The biologic width is an approximately 2mm

of distance established by the supracrestal connective tissue and the junctional epithelium. If a


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Crown margin encroaches on the biologic width, it causes inflammation, which may lead to

attachment loss, apical gingival migration and pocket formation.

Endodontic status

-In a vital tooth with no pulpal involvement, a Crown can be planned without endodontic treatment,

but a note kept in mind that there is a risk of devitalisation after tooth preparation.-In a Non-vital tooth, or pulpally involved tooth, endodontic treatment should be carried, to remove

infection, prior to Crown placement.

-In a tooth that already contains a root filling, where there is still pathology, a decision needs to be

made on whether to re-endo or not. The success rate of re-endo treatment is low, however, there is

an increased chance of success if referred to a specialist.

Tooth structure

-Caries extent and existing restorations should be assessed, because the Crown needs to rest on a

sound margin of tooth and over a strong enough preparation or core.

-Frequently, the tooth to be Crowned has an existing restoration. All previously placed materials

should be removed, unless it has been recently placed and you are sure it is retained to sound tooth.If >50% of coronal tooth structure remains after caries and restoration removal, and no more

increase in strength is required, then a bonded compomer or resin ionomer base may be used to

restore the tooth to the required preparation form. If


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where treatment is beyond one’s scope of experience, knowledge and skill.

Treatment planning

-Even after the above considerations, a degree of flexibility should be kept within one’s mindset,

because of complications or other needs that may arise, for example, the need for endodontic

treatment, a lack of improvement in oral hygiene, caries that extends deeper than initially thoughtetc. The patient should also be aware of such possibilities.


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Types of Crown ii, iv, v Full coverage Crowns

Full Metal Crowns

Metal Ceramic Crowns All Ceramic Crowns

Composite Crowns

-Superior retention and resistance compared to Three Quarter Crowns and Veneers

-Good cosmetics achieved with MCC’s, ACC’s and Composite Crowns

-Should only be considered once less destructive alternatives have been considered

-Used where all axial surfaces have caries or have been previously restored

-“Tie” together tooth surfaces, for strength and support

Full Metal Crowns

-These are Crowns cast entirely in metal, and can be made from a number ofdifferent alloys (mixtures of metal). They can be made in thin sections, whilst

still maintaining their properties in strength, and therefore tooth preparations

are less destructive than MCC’s and ACC’s.

-FMC’s can have a hardness similar to enamel, and are used in situations where

occlusal loading is high, for example posterior teeth

-Occlusal and interproximal tooth contacts can be achieved easier with FMC’s and so it’s use is

indicated in cases where this would be difficult to achieve with other materials

-Using dissimilar metals adjacent to each other can cause adverse reactions, and so if a patient has

existing successful metal FMC’s then it could be wise to use the same again.

-Aesthetically, FMC’s do not match the cosmetics of a normal tooth, and patient preference could be

a major factor in the decision to provide one or not.

Metal Ceramic Crowns-These are Crowns consisting of a Metal “coping/cap” with a Ceramic layer

fused over it

-Combines the strength of a metal substructure, with the better aesthetic

properties of porcelain

-Greater strength than some ACC’s due to the metal substructure

-Very destructive preparation, to accommodate for the thickness of the Metal

AND overlying Ceramic, however less so than an ACC.

-MCC’s can be made with entire Porcelain coverage or partial coverage: Metalocclusally and lingual/palatally. The advantage of the latter is that a less

destructive tooth preparation is required, with retention and resistance form

maximised. Metal occlusal contacts are also easier create and adjust, and

cause less opposing tooth damage compared to Porcelain.

-Used on posterior teeth where aesthetics are important, and FMC’s are contraindicated for any

other reason

-If there is insufficient space anteriorly for an ACC, due to the thickness of the Ceramic, an MCC

could be indicated

-If a visible ACC repeatedly fails due to occlusal stress, an MCC could be indicated

Contraindications-If there is a risk of excessive opposing tooth wear. In such cases, the opposing tooth could be


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ground down and provided with a composite, or the patient could be provided with a night time

occlusal splint.

-In a young patient, where risk of pulpal damage during preparation is high. In such cases, a Dentine

Bonded Ceramic Crown may be a viable option.

All Ceramic Crowns-An All Ceramic Crown is, as the name suggests, made entirely from ceramic, and can produce the

excellent aesthetic results compared to other Crowns.

-These Crowns are made via a number of different techniques, and are

classified under traditional Porcelain Jacket Crowns, Dentine Bonded Crowns

and those with strengthened cores.

-ACC’s are relatively weak restorations, being brittle in thin sections,

so therefore are usually restricted to anterior restorations where

occlusal forces are usually lower and aesthetics are important.

-Apart from the Dentine Bonded kind, preparation’s for ACC’s are the

most destructive compared to other Crown preparations, soalternatives should be considered first.

-Due to the aesthetic nature of ACC’s they can be used to mask

severely discoloured anterior teeth and existing post and core

substructures. In existing Post and Core restorations where there is a risk of trauma, an ACC is

preferred over an MCC, because stresses are more likely fracture the Porcelain, rather than being

transferred to the Post Core leading to root fracture.

Contraindications

-Edge to edge occlusion, due to risk of fracture under occlusal loading.

-Where opposing teeth occlude in the cervical fifth of the palatal surface.

-Where ideal preparation form cannot be achieved to support the porcelain.

Resin Bonded Porcelain Crown-Although these can classified under the ACC group of

restorations, it is worth a separate entity, because of the

differences in properties and tooth preparation.

-RBPC’s are a comparatively recent addition to a dentist’s

armamentarium, and have been described as a full-coverage

ceramic restoration, which is bonded to the underlying tooth

using a resin composite based material. The bond interface lies

between a micromechanically retentive ceramic fitting surface

and a dentine bonding system.

-RBPC preparation is less destructive than other All Ceramic preparations, which causes less pulpal

irritation and adheres to the concept of being a conservative as possible. With this however, comes

the difficulty in production by the lab, and in fabricating a temporary restoration, which is important

for pulpal protection.

-As with other ACC’s the manufactured RBPC’s are weak until bonded to the underlying tooth,

especially because DBC’s are thinner in section.

Other Advantages:

-Good fracture resistance vs other ACC’s

-Excellent aesthetics

-Can facilitate for situations of large preparation taper, because retention lies to a larger extent in

the bond strength

RBPC image from:

http://www.mkvasant.co.uk/

dental-publication-

croydon.html


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-Luting material is insoluble in liquid

-No marginal gaps, as these are filled with the luting material

Disadvantages

-Fluid isolation is essential with the dentine bonding systems, and this can be difficult to achieve,

especially where margins are subgingival-The luting procedure is more time consuming, and highly technique sensitive

-There is a lack of longitudinal data on effectiveness

Composite Crowns-These are Crowns made from composite systems with reinforced fibres

-Currently, not widely used, however the potential for future use is considerable due to decreased

lab costs, good aesthetics and less wear to opposing teeth

-Do not chip as easily as Porcelains

-Greater wear rate and future staining due to abrasion removing protective surface

Post and Core Crowns-These are Crowns placed on a core with an attached pre-fabricated or

custom Post that goes into the pulp chamber and root canal of an

endodontically filled tooth for the purposes of increased retention

where it cannot be achieved by other means.

-Previous thought, was that the inclusion of a post would strengthen a

root filled tooth, however studies have failed to prove this, and rather

there is a risk of root fracture as occlusal forces would be directed down

the long axis of the post.

Three-quarter Crowns-Three quarter Crowns are used where the one wall of a tooth

remains intact and healthy, hence

covering three of the axial walls and occlusal surface instead of full

coverage.

-A conservative option, however technically challenging.

Post and Core Image

from:

http://dentistatrajkot.com/Default.aspx?ql=1472

¾ Crown image from:

http://www.toothiq.com/denta

l-

information/page.aspx?id=a13e

ea02-f12b-4ea0-a7d9-


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Occlusion vi, vii, viii -An understanding of occlusion is important to the success of Crown provision, and you should carry

out a pre-operative examination of a patient’s occlusion as a matter of routine.

-Before we carry on, it is important to get a grasp with some basic principles and terminology relatedto occlusion:

ICP (aka Centric Occlusion and Maximum Intercuspation) – The position of the mandible, when the

maxillary and mandibular teeth are at their most interdigitated.

-Generally this is the position in which restorations are made

RCP (aka Centric Relation) – The reproducible position of the mandible independent of tooth-tooth

contact(s) when the mandible is closing in terminal hinge axis

-There are a few situations in which a Crown will need to be adjusted to conform in RCP too and

these include:

-When altering a patient’s OVD

-When ICP is not stable-Where you need to habituate the mandible distally

-Where deflective contacts in RCP exist and need to be removed. A deflective contact is any contact

that diverts the mandible from the normal path of closure into ICP

-When restoring anterior teeth, and movement into RCP results in heavy anterior forces against

teeth to be prepared

-If RCP is a considerable factor, casts mounted in RCP and mounted on a semi-adjustable articulator

can be used to further assess occlusion and allow for trial adjusting

Terminal Hinge Axis (aka Retruded Axis)- The most retruded position of the mandible, determined

by the TMJ, not tooth contact. The mandible moves in a purely rotational movement in this

position.

Working Side (aka Rotating/ Functional side)- The side to which the mandible moves during a

functional movement, i.e. if the mandible moves to the right, the right side is the working side, and

the left is the non-working side.

Non- working Side (aka Balancing side)- The side opposite to the working side during lateral

excursion.

Functioning Cusps- These are the Palatal Cusps of the maxillary teeth and Buccal cusps of the

mandibular teeth which occlude with opposing fossae, marginal ridges and cusp slopes.

Non-functioning/Balancing Cusps- These are the Buccal Cusps of the maxillary teeth and Lingual

cusps of the mandibular teeth.

Guidance- The contacting teeth when a patient slides their mandible slides laterally or antero-

posteriorly from ICP are guiding teeth. The path that the mandible takes is determined partly by the

teeth in contact, and hence they provide “Guidance”.

-When a patient slides their mandible to the side they are about to chew on, this side becomes the

“working side” and the opposite side becomes the “non-working side”

-“Canine guidance” is when only the upper and lower canines on the working side are in contact

during lateral excursion, causing all of the posterior teeth to disclude. For restorative purpose

canine guidance is the ideal.-“Group function” is when several pairs of teeth are in contact on lateral movement to the working


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side, usually being premolars or premolars and canines

-Incisors and canines usually provide guidance on protrusive movement

-Guidance teeth undergo non-axial (lateral or antero-posterior) forces on excursion and if a guiding

tooth is to be Crowned, there is an increased risk of fracture or decementation, particularly if the

loads are heavy. Considering the guiding teeth before preparation is essential, and will alsoinfluence your choice of material. If the guiding teeth needing to be Crowned are strong enough,

then the same guidance pattern can be re-established, however if it is felt that occlusal stresses are

too high, then guidance can be moved onto other teeth. Changing guidance can be achieved by

altering the occlusion slightly, for example if Crowning a guiding canine tooth; the Crown can be

adjusted out of occlusion transferring the role to the premolars instead.

Interference- Interferences are any teeth that hinder smooth guidance of the mandible into ICP. A

“Working side interference” is an interfering tooth/teeth on the same side that the mandible is

moving to. A “Non-Working side interference” involves a tooth on the side that the mandible is

moving away from in this sense. Generally it is best to remove working and non-working side

interferences before a tooth is prepared.

Now that the terminology and basic principles have been outlined, we can further discuss and look

into the clinical applications

Occlusal RecordsInitial Occlusal examination

-An initial examination with regards to ICP, RCP and tooth relation in guidance is essential before any

tooth preparation.

ICP- to assess reproduceability and contacts to be re-established

RCP- to assess if any deflective contacts are present

Guidance- if the Crown’s to be prepared are guiding teeth, this will affect choice of material andwhether guidance needs to be altered. Mark teeth with different coloured articulating paper under

different excursions for an extra visual guide.

-TMJ dysfunction – Palpate the muscles of mastication for tenderness

-Feel for any clicking or crepitus

-Assess mandibular movements, keeping an eye for any deviation

-Individual teeth – assess mobility, wear, caries

-A more detailed initial examination may be needed if there are specific occlusal problems or a

history of Temporomandibular Dysfunction

-It is useful at this stage to take impressions for upper and low hand held study casts, for further

examination where there is an unimpeded view of occlusion. Study casts can also confirm whetherthere is a stable ICP, and if there is not, the possibility of inter-occlusal records would need to be

considered. Study cast impressions can be done in Alginate with stock trays, with an emphasis on

impression quality in the occlusal areas rather than the peripheries and depths of the sulci. It is

important to note that simple Study Casts do not provide any information of excursion or RCP, and if

this is required, Articulate Study Casts are indicated.

Articulated Study Casts (Semi-adjustable articulator)

-Indications:

-Where you need to ensure correct guidance against your restoration, especially where multiple

Crowns are being prepared.

-If OVD is being increased-Where occlusion is going to be reorganised because of removal of so many occlusal contacts, and


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RCP will be the new reference

-Where Working and Non-Working Occlusal interferences are being removed

-Where jaw position is being stabilized by an

Occlusal splint

-Where an Occlusal splint is being prescribed to

protect the Crown/Crowns from bruxism

-To accurately position the casts to a patient’s

anatomy in terms of condylar hinge axis and jaw

relation, a Facebow record can be taken alongside an

Inter-Occlusal record. There are a number of systems

on the market to create a Facebow record and they

all work to allow the technician to mount Study Casts

and mimic excursions around to hinge axis as close

as possible. Inter-Occlusal records are achieved by

getting a patient to bite on silicone or wax, leaving a record of intercuspation. It has been shownthat Inter-Occlusal records, in many cases, reduce the accuracy of mounting of the casts. Inter-

Occlusal records should not be used in single tooth restoration cases where a patient has stable ICP,

but rather where casts are unstable and teeth to be Crowned will be key for support. A good Inter-

occlusal record captures the tooth cusp tips, and not fissures or soft tissue.

Replicating tooth guidance

-Where teeth to be prepared are involved in guidance, in both protrusive and lateral excursions, a

record of tooth guidance may be needed. This is so the technician can replicate the existing form of

the tooth/teeth, in order to re-establish occlusion after preparations.-Making a record of these excursions is particularly important where the tooth or teeth to be

prepared are alone in guiding excursions.

-Where numerous teeth are to be Crowned, guidance can be lost altogether, if a record beforehand

is not taken.

-The two most effective methods to overcome this technical difficulties are:

-The “Crown about method”. Where alternate teeth are prepared, hence maintaining some tooth

surface for guidance

-The Custom Incisal Guidance Table – Copies protrusion and lateral excursion by placing a mound of

putty on the Incisal Guidance Table of an Articulator, and moving the STUDY casts (and pin) in the

full range of protrusion and lateral excursions. Once the putty has set, a permanent record of

excursion is made, which is later used for guiding the WORKING casts.


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Aesthetics ix, x, xi, xii, xiii

-Aesthetics is the branch of philosophy, which deals with the nature of art, beauty and taste, with

the creation and appreciation of such subjects. When dealing with shade, shape and form of

restorations, the decision on whether they are visually pleasing or not, is very subjective to apatient’s own opinion. For this reason, it is important to gauge a patient’s demands before the

outset of any treatment. The ideals of patient then need to be weighed up against tooth removal

and potential damage to the pulp and periodontium, with consideration to a dentist’s scope of skills.

Where demands are unrealistic, it is important to communicate this with the patient beforehand,

making a decision based on existing knowledge and experience. Due to the subjective nature of

aesthetics, clinical experience will play a major role in being able to judge visual outcome, and it is

better to undervalue on the scale of realistic possibility, rather than promise over-realistic outcomes.

-Currently, the most aesthetically pleasing Crowns, which have been studied over an extensive

period of time, are those containing Porcelain. In most cases, this comes at the cost of tooth tissue,

because a thicker Crown shell needs to be made for strength, in particular Metal Ceramic Crowns,

which have the most destructive preparations. As stated previously, a more destructive preparationis more likely to cause pulpal damage, and a decision needs to be made on whether to sacrifice long-

term pulp health for aesthetics, or lose aesthetic quality for pulp health.

-Here is a table of what is generally accepted as aesthetically pleasing types of Crown:

All Porcelain

-Conventional Porcelain Jacket Crown

-High Strength PJC

-Dentine Bonded Crown/ Full Coverage

Porcelain Veneer

-Difficulty masking underlying staining due to

thickness

-Temporisation difficult

-Labial Porcelain Veneer -Difficulty masking underlying staining due tothickness

-Temporisation difficult

-Porcelain Onlay

All Composite (Crowns, Veneers, Onlay) -little evidence on stability and longevity

Metal- Ceramic Crown/

Ceramo-Metal Crown

-Most destructive

Composite Bonded to metal Crown

Three Quarter Crown/

Partial Coverage Crown

-After a judgement has been made as to what is achievable in relation to patient demands, there are

ways to help a patient visualise what the restorations may

look like. Time spent showing the patient aesthetic

possibilities at this stage is invaluable in saving future

disappointment.

1. Diagnostic Wax Ups- Created by the lab, these are

study casts, with the potential restoration “waxed

up” to get an idea of form


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2. Composite additions- Composite can be added to the patients teeth, without etching or

application of a bonding agent to show the patient form and shade

3.

Black ink- Can be applied on teeth to mimic the effect of tooth reductions4. Computer generated restorations- Software can be used to generate computer images for a

patient to see, and can be edited to patients preferences whilst in consultation

5. Photographs of previous restorations- Can show a patient the possibilities and limitation if

similar cases are used

6.

Temporary restorations- Gives the patient a feel of the form and shape of the restoration in

relation to their other teeth and facial features before a final restoration is placed

Restoration Margins

-The margins of the restoration can supra or sub-gingival (up to 1mm).

-Where the tooth margin cannot be seen, there is good reason to place the margins supra-gingivally.

Finishing and maintenance is easier with supra-gingival preparations, and there is lower risk ofdamaging periodontal health.

-Where Crown margins will cause an aesthetic problem, preparations can be placed up to 1mm sub-

gingivally. However, caution must be taken where there are prominent roots or thin gingival

coverage, because there is a risk of recession.

-If preparations need to go further than 1mm subgingivally to because of insufficient preparation

height (and therefore retention), Crown lengthening is an option to avoid encroaching into the

biological width of the periodontium.

-In terms of metal or porcelain at the margins, there are arguments stating that metal produces the

most predictable marginal seal. However, in certain areas, where aesthetics are of utmost

importance, a porcelain margin on a shoulder finish line will produce the best results. It is also

worth noting that even a metal margin placed subgingivally can show through the gingival tissue,affecting aesthetics, especially where tissue is thin.

Shade

-Shade matching is another aspect of aesthetics that is very subjective, and a good example where

patient involvement is important. Because of the subjective nature, there are a number of systems

on the market to help make a decision on the shade, with the most common being shade guides,

where a patient’s teeth are compared to common shades used in Crown manufacture.

-Difficulties arise in shade matching, because teeth are non-uniform in colour, have defects, unique

features, are semi-translucent and appear different shades in different lighting conditions.

-Colour can be described by Hue, Value and Chroma. Hue is the name of the colour, for example

red, blue, green. Value is the lightness or darkness of a colour, a high value indicating something islight and a low value, dark. Chroma is the amount of saturation of a particular hue, for example red

with a high chroma would a deeper more intense red, than red with a low value chroma.

-Vita 3D Master and Ivoclar Chromoscope

are two examples of shade guides based on

Hue, with Value and Chroma subdivisions.

-Electronic devices have been created to

judge shades of teeth, however their

effectiveness has not been fully evaluated,

therefore it is useful to use these as

reference alongside your own judgement

-Devices with magnification and colour

corrected lighting are useful tools in


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assessing surface detail as well as shade

-The following is a scheme for shade determination from the BDJ 2002; 192: 443-450 - Crowns and

other extra-coronal restorations: Aesthetic control:

A scheme for shade determination1. Determine the shade at the start of an appointment, before eye fatigue and tooth

dehydration with resultant shade change occurs (especially after use of rubber dam)

2. Use natural light (not direct sunlight) or a colour-corrected artificial eye source

3. Drape the patient with a neutral coloured cover if clothing is bright, and have the patient

remove brightly coloured make-up

4. Assess the value by squinting. The reduced amount of light entering the eye may allow to

better distinguish degrees of lightness and darkness

5. Glance between shade tabs rapidly (no more than 5 seconds each viewing). Gazing at a soft

blue colour in between attempts is said to reduce blue fatigue- which can result in

accentuated yellow-orange sensitivity6. Choose the dominant hue and chroma within the value range chosen. The canines have a

high chroma and may be useful to assess hue.

7. Compare the selected tabs under different condition e.g wet vs dry, different lip positions,

artificial and natural light from different angles etc

8. Select a shade which is higher in value (lighter) if in doubt. Surface stains can reduce these

dimensions, but not easily increase them

9. Assess for colour characterisation such as stained imbrication lines, white spots, neck

colouration, incisal edge translucency and halo effect (a thin opaque line sometimes seen

within a translucent incisal). Simple diagrams are invaluable.

10. Determine surface lustre

-The above scheme provides good guidance in a methodical approach to shade determination,

however, the results of the restoration will only be as good as your communication with the dental

laboratory. It is important that all the information obtained is communicated clearly, and clarity can

be emphasised by the use of diagrams, photos, two-way communication methods and even visits to

the dental lab if necessary.

-In cases where shade matching and detail has been a difficulty, trial placement of restorations can

be done, and this would be done, before the final surface glaze has been implemented.

Cementation during this trial period would involve the use of modified Zinc oxide and eugenol based

cements, because removal could be a great difficult otherwise. Pigmented luting cements to alter

porcelain shades slightly can also be used in such cases.


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Tooth Preparation iv, ii, xiv, xv, xvi

-Tooth preparation considers a balance of all the factors mentioned in the pre-operative assessment,

with the ultimate goal of producing a preparation that has maximal height and minimum taper for

optimal resistance and retention form. Retention form is the preparation’s ability to resist verticaldisplacement forces, and resistance form is the ability to resist rotation about the vertical axis.

-There are seven key principles of preparation, as outlined by Herbert Shillingberg that determine

the shape and form of preparations.

Seven Key Principles:1. Conservation of tooth structure – To maintain pulp health and tooth strength

2. Retention Form- To prevent the Crown dislodging

3. Resistance Form- To prevent rotational displacement along any of the Crown’s path of

insertion, including long axis

4.

Structural Durability- To provide sufficient space for the material of Crown, in order to

prevent fracture, distortion or perforation5. Marginal Integrity- To implement a finish line that accommodates a robust margin, and

allowing close adaptation to prevent microleakage

6. Periodontium Preservation- To place the margin so that it is accessible for optimal oral

hygiene, and avoid recession

7.

Aesthetics- To create sufficient space for an aesthetically pleasing restoration, in particular

where Veneers are indicated

-These principles should be adhered to, however, quite often; compromises need to be made

between them, because of a patient’s individual requirements. For example, conservation of tooth

structure; this is sacrificed where a Metal-Ceramic Crown is used, because an adequate thickness of

material needs to be made. In such cases, if preparations are too minimal, Crown’s may end upbeing excessively bulky and therefore unaesthetic.

Tooth preparations vary, with regards to-

-Amount of tooth removed- Most for Metal-Ceramic Crowns, Least in Resin Bonded Porcelain

Crowns

-Margin position- Supragingival is ideal; however aesthetic importance may depict the position of

the margin. Subgingival preparations are indicated where metal margins are visible such as: Anterior

teeth and MCC Crown preparations with a bevelled shoulder

-Accessory retention components- Grooves, Boxes

-Degree of Taper- 6 degrees of taper ideally, apart from in Resin Bonded Porcelain Crown

preparations, where around 20 degrees is preferable, and also in High Strength Porcelain Crowns.


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-Margin Finish-

Shoulder Bevelled

Shoulder

Heavy Chamfer Chamfer

Images from: http://www.excel-dental.com/dentallab/tooth_preparation.htm

Metal Ceramic Crown,

All Ceramic/ Porcelain

Jacket Crown

Buccal of Metal

Ceramic Crown

High Strength

Porcelain Crowns,

Buccal of Metal

Ceramic Crowns

Full Metal Crowns,

Palatal/Lingual of

MCC’s, Resin Bonded

Crowns

TIPS to consider:

-Hold the bur parallel to the path of insertion at all times, to prevent undercut and create the correct

taper

-Assess for undercuts using one eye only whilst directing the mirror adjacent to the tooth

-Slightly under-prep, then smooth and refine the preparation, inevitably you will then get the

desired reduction amount

-Complete smoothing is not essential, as it poses a threat to pulp health due to overheating,

especially where a water coolant is not used. However, it is important to remove any irregularities,

sharp lines and corners

-It is helpful to know the exact diameters of the burs used during production of depth grooves,

because they can be used as a measurement tool

Diamond Crown and

Bridge bur kit at LUDH

(from left to right): Long

Needle Diamond Bur,

Short Needle Diamond

Bur, Straight Shoulder Bur,

Straight Chamfer Bur,

Rugby Bur, Tapered

Chamfer Bur


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2. Using a Fissure Bur, carry out a 2.0mm occlusal reduction, using depth grooves as a guide to

reduction. Occlusal reduction is not necessary if there is already a minimum of 2mm occlusal

space in ICP

1.

Now remove 1.2mm of tooth from the facial surface, using a

Shoulder bur via a 2 (or 3)planar reduction to achieve adequate reduction and avoid

pulp. This involves creating two plane depth grooves- gingival

and incisally, followed by smoothing.

-Facial reduction is carried around and stopped 1.0mm away

from the proximal contacts

-If bevelled shoulder is chosen (0.3mm using flame shaped

diamond bur), a subgingival preparation would be needed to

hide the metal lining it

2. Remove 0.5mm from the lingual concavity using a “Rugby

ball” Diamond Bur.

3.

Then remove 0.5mm from the lingual surface, creating achamfer, using a Tapered Chamfer bur

4. Reduce interproximal areas initially using a Long Needle

Diamond bur, then finish using a Tapered Chamfer diamond

bur

-This leaves a preparation with a “winged appearance”. The

primary reason for wings, is to preserve tooth structure, and

it’s secondary effect is that it provides resistance to rotation

-A winged preparation is not essential, and can be removed by blending

the chamfer margin with the shoulder margin using a Tapered Chamfer

Bur.

5.

Smooth sharp lines, corners and irregularities with a Finishing DiamondBur

Posterior Tooth Preparation-Usually involves Maxillary Premolars and First Molars, and mandibular Second Premolars as these

are often visible

-Other posterior teeth may require MCC for appearance if patient wishes so too-Occlusal full ceramic coverage- involves extensive tooth removal and threatens opposing teeth as

dental porcelain is 40x more abrasive than gold to tooth enamel

1. Take two initial Silicone putty indexes- for the provision of a temporary Crown after

preparation, and to use as a reference for how much tooth has been removed. If the existing

tooth contour is incorrect, an index can be made from diagnostic wax up

2. Using a Fissure Bur, carry out a 1.0mm occlusal reduction (if occlusal metal) or 1.5mm

occlusal reduction (if occlusal porcelain), using depth grooves as a guide to reduction.

Reduce groove depth if the tooth is not in occlusion

3. Reduce the functional cusps of the tooth by an additional 0.5mm, angled at 45 degrees,

producing the functional cusp bevel. This is essential to prevent thin casting and fracture ofthe functional cusp of the Crown


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4. Now remove 1.2mm of tooth from the facial surface, using a

Shoulder bur via a 2 planar

reduction to achieve adequate reduction and avoid pulp. This

involves creating two facial plane depth grooves- gingival and

occlusal, followed by smoothing.

-Facial reduction is carried around and stopped 1.0mm awayfrom the proximal contacts

-If bevelled shoulder (0.3mm using flame shaped diamond bur) is

chosen, a subgingival preparation would be needed to hide the

metal lining it

5.

Using a Tapered Chamfer bur remove 0.5mm lingually/palatally

with 2 planar reduction,

leaving a chamfer margin

-Finishing line initially just above gingival level, and then finished

off to at gingival level or slightly below

6.

Reduce interproximal areas initially using a Long Needle Diamondbur, then finish using a Tapered Chamfer diamond bur

-This leaves a preparation with a “winged appearance”. The primary reason for wings, is to

preserve tooth structure, and it’s secondary effect is that it provides resistance to rotation

-A winged preparation is not essential, and can be removed by blending the chamfer margin

with the shoulder margin using a Tapered Chamfer Bur-Winged prep or blend in

7.

Smooth sharp lines, corners and irregularities with a Finishing Diamond Bur

All Ceramic Crown-Capable of producing best aesthetics of all Crowns

-More susceptible to fracture due to brittleness

-Make as long preparations as possible to give maximum support for

porcelain

-Overshortened preparations- stress concentrates in labiogingival areasproducing “half -moon” fractures

-Best suited for incisors, due to risk of fracture posteriorly

-Avoid in edge-to-edge occlusion

-Should not be used where opposing teeth occlude in the cervical fifth of

the lingual surface

1.

Take two initial Silicone putty indexes- for the provision of a

temporary Crown after preparation, and to use as a reference for

how much tooth has been removed. If the existing tooth contour

is incorrect, an index can be made from diagnostic wax up

2.

Using a Fissure Bur, carry out a 2.0mm occlusal reduction, usingdepth grooves as a guide to reduction. Occlusal reduction is not


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necessary if there is already a minimum of 2mm occlusal space in ICP

-The reduction should be inclined linguogingivally to prevent shearing

3. Now remove 1.2mm of tooth from the facial surface, using a Shoulder bur via a 2 (or 3)

planar reduction to achieve adequate reduction and avoid pulp. This involves creating two

plane depth grooves- gingival and incisally, followed by smoothing.

4.

Remove 1.0mm from the lingual concavity using a “Rugby ball” Diamond Bur. 5. Then remove 1.0mm from the lingual surface, creating a shoulder, using a Shoulder bur

6. Reduce interproximal areas initially using a Long Needle Diamond bur, then

finish using a Shoulder bur, merging the labial and lingual finish lines

7.


Resin Bonded Porcelain Crown-Excellent aesthetics

-Relatively conservative of tooth tissue

-Strength comes largely from the resin bond rather than an underlying core of material

-Ideal for younger patients with large pulps

-May not be suitable for areas of high occlusal load and where there is parafunction due to thin

porcelain, and therefore reserved for anterior teeth

1.

Take two initial Silicone putty indexes- for the provision of a temporary Crown after

preparation, and to use as a reference for how much tooth

has been removed.

2.

Using a Fissure Bur, carry out a 2.0mm occlusal reduction,

using depth grooves as a guide to reduction. Occlusal

reduction is not necessary if there is already a minimum of

2mm occlusal space in ICP

3. Now remove 0.5mm of tooth from the facial surface, using a

Tapered Chamfer bur via a 2 (or 3) planar reduction to

achieve adequate reduction and avoid pulp. This involves

creating two plane depth grooves- gingival and incisally,followed by smoothing and production of a chamfer.

4. Remove 0.5mm from the lingual concavity using a “Rugby

ball” Diamond Bur.

5. Then remove 0.5mm from the lingual surface, creating a

chamfer, using a Chamfer bur

6.

Reduce interproximal areas initially using a Long Needle

Diamond bur, then finish using a Chamfer bur, merging the

labial and lingual finish lines

7.



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High Strength Porcelain Crowns-Have no metal substructure, however utilize high strength ceramics for robustness

-Usually used on posterior teeth

-Relatively destructive preparation

-Degree of taper is greater than for a traditionally cemented Crown

Posterior tooth preparation guideline:

1.

Take an initial Silicone putty index- for the provision of a temporary Crown after

preparation, and to use as a reference for how much tooth has been removed.

2. Using a Shoulder bur, carry out a 2.0mm occlusal reduction using depth grooves as a guide

to reduction (reduce groove depth if the tooth is not in occlusion)

3. Reduce the functional cusps of the tooth by an additional 0.5mm,

angled at 45 degrees, producing the functional cusp bevel.4.

Now remove 0.8-1.0mm of tooth from the facial surface, using a

Shoulder bur via a 2 planar reduction to achieve adequate

reduction and avoid pulp. This involves creating two facial plane

depth grooves- gingival and occlusal, followed by smoothing.

-In this case, create a greater taper than traditional Crown preps

5. Using a Shoulder bur remove 0.8-1.0mm lingually/palatally with 2

planar reduction, leaving a shoulder margin

-Finishing line initially just above gingival level, and then finished

off to at gingival level or slightly below

-Can use a heavy chamfer, depending on company to produce

HSPC6. Reduce interproximal areas initially using a Long Needle Diamond

bur, then finish using a Shoulder bur, merging the labial and

lingual finish lines

7.

Smooth sharp lines, corners and irregularities with a Finishing

Diamond Bur

Composite Crowns-Indications have not yet been fully researched

-Preparation is the same as for High Strength Porcelain Crowns

Trouble shootingMy preparation has ended up too tapered, what should I do?

-You could straighten the axial walls up by further preparing from the base, however this risks pulpal

health and is destructive. Another option is to add accessory retention features such as grooves and

boxes, however once again this is further destructive.

-The best option here may be to use a resin cement to aid retention

My preparation has ended up too short, what should I do?

-3mm is the minimum preparation height, disregarding other factors such as cement used, occlusal

loads, type of Crown.

-If the preparation has become too short for the clinical situation, you may consider addingretention features such as grooves and boxes; once again this is further destructive.


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-Consider the use of a Composite Resin Cement

-Consider Crown lengthening surgery, to extend the margins further down the tooth and therefore

increasing preparation height


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Impressions xvii, xviii, xix

- The impression stage of the appointment is just as crucial as the tooth preparation stage, and any

flaws in the impression sent to the lab, has a potential to produce an ill-fitting Crown. Therefore it is

important to be able to produce well defined impressions, and identify where impressions need tobe retaken. Retaking impressions, is both time consuming, costly, and can be unpleasant for the

patient, and therefore the ability to consistently produce good impressions is important.

-At Liverpool University Dental Hospital, the One Stage Heavy and light impression technique is

utilized, using addition silicones. These silicones have excellent dimensional stability and are

thought to have relatively good handling characteristics.

Technique guidelines:

1)

Choose an appropriately sized stock tray by trying in the patient’s mouth

-If the tray is under-extended, it can be adapted by the addition of a stiff material (i.e impression

compound)

-If the stock tray cannot be adapted, a special tray would be indicated

-Metal trays are preferable, because they are rigid and reduce the risk of distortions. Recoil is aproblem that occurs more commonly in plastic stock trays, whereby the walls of the tray flex

outward during occlusal pressure, followed by an inward flexion, producing impressions that are

undersized bucco-lingually

2) Retract the gingiva around the Crown preparation, so that the finish line can be recorded

accurately. The most common method is the “two cord

technique”, where a thin cord is wrapped around the tooth

and placed into the sulcus followed by a thick cord, which

is removed just before the impression is taken.

Sometimes, the cords are impregnated with solutions to

prevent haemorrhage i.e. adrenaline and ferric sulphat.Other methods include:

-Electrosurgery- controlled tissue removal using an electric current through a tip

-Rotary curettage- involves removal of epithelial tissue within the sulcus using a diamond chamfer

bur

3) Block out large embrasures using ribbon wax, to prevent the impression locking into the

patients mouth

4)

Dry the tray and apply adhesive evenly. Blow dry the adhesive lightly to encourageevaporation of the adhesive’s solvent.

-This stage can be done before tooth preparation to allow solvent evaporation and production of a

good bond strength

5) Syringe the wash material (i.e. light bodied silicone) into the sulcus, and over the tooth

preparation

-Remember to remove the thick retraction cord beforehand

-Ensure there are no air bubbles or voids by ensuring the nozzle is not removed from a continuous

stream of material

-Work from the most difficult aspect of the tooth to access and around to the easiest

6) Load the tray with a heavy bodied addition silicone material (i.e. Express 2 Penta) and take

the impression-This should be done before the light bodied silicone sets in the One stage technique


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7) Use excess of material to monitor setting, and remove

once set

-Bear in mind the warmth of the mouth will encourage setting

faster than externally


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Temporary restorations ii, iv, xx, xxi -Temporary Crowns are made for the period of time between tooth preparation and fitting the final

restoration. The only scenario in which a temporary restoration would not be essential, is when

making a Resin bonded Crown where space maintenance and aesthetics are important, becausethere is no or minimal dentinal exposure.

-The functions of temporary restorations are summarized below:

-Tooth vitality protection: Traditional Crown preparations expose thousands of dentinal tubules,

which can lead to sensitivity and pulp death. Therefore it is important to provide a protective

covering over these tubules in the interim.

-Prevention of tooth movement: Without the provision of a temporary Crown, there is a risk of

drifting and over-eruption of the teeth in the long term, therefore disturbing the existing occlusion

-Maintenance of function: Allows the patient to masticate and speak normally

-Aesthetics: Especially important in anterior teeth, where it is important for the patient to have an

acceptable appearance. However, a diagnostic wax-up or computer imaging may be sufficient in

some cases to show the final appearance.-Diagnostic purpose: For the patient to assess function and appearance of a Crown before a

permanent Crown is cemented in place. This is especially important where there are plans to

change the existing aesthetics or occlusion (i.e. increasing OVD or changing guidance surfaces). In

cases where Crown lengthening has been planned, you should provide a temporary restoration for a

minimum of 6 months before a definitive restoration, to allow stabilisation of the periodontium.

Types of Temporary Crown-There are a number of different methods to temporise a Crown preparation, and a major factor

influencing the choice of material is the length of time between tooth preparation and cementation

of the final Crown. Generally, a laboratory made temporary Crown will last longer than a chair sideCrown, and can be tailored to the patient’s needs aesthetically, however the additional cost of

manufacture needs to be balanced against the pros of doing so.

1) Preformed Crowns: Plastic (Opaque: polycarbonate or acrylic) or Metal

(aluminium, stainless steel or nickel chromium)-Non-Custom: These come in a variety of different sizes and the dentist needs to

pick according to the most appropriate marginal, proximal and occlusal fit.

-Plastic preformed Crowns are indicated for anterior teeth and metal Crowns for

the posterior

-Colour matching is needed when choosing an opaque plastic Crown (i.e. Direct-a-

Crown), as the outer shell is retained, differing from a Strip Crown matrix (mentioned later).

1) Once a preformed Crown of appropriate size has been selected, the margins are adjusted for a

closer fit and a small hole placed incisally on the lingual/palatal surface for excess flow, using a high

speed bur.

2) The tooth prepared is coated with petroleum jelly and the Crown is filled with a material such as

Trim plus (polymethyl methacrylate/PMMA) or Integrity (chemical cured composite), and placed

over the preparation.

3) Excess is trimmed away from the margins during the gel phase of the material using a sharp

bladed instrument such as a carver

4) Remove the Crown and adjust occlusal surfaces and any excess using steel or tungsten carbide

burs and soflex discs5) Fill the preparation impression area with a small amount of temporary cement material, and


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position back on the preparation. Remove excess from the margins.

6) Once set, further adjust the Crown margins using steel or tungsten carbide burs and soflex discs

7) Check occlusion using articulating paper

-As these Crowns are not custom-fitted, it is likely that considerable adjustments will need to be

made. For long term temporisation, or multiple Crown cases, lab made preformed Crowns can be

requested and these are usually made in acrylic, or poly-methyl methacrylate.

Temporary cement materials:

-Temp bond – commonly used, however may soften preparations with a composite core. If a

preparation is very retentive, a small amount of modifier can be added so removal is possible.

-Temp bond NE (non-eugenol) – used where there is a composite core or a patient has a eugenol

allergy

-Zinc Polycarboxylate (i.e. Poly-F) – Where preparations may be unretentive and there is a risk of the

temporary Crown falling off

2) Matrices: Impression Matrix, Vacuum Formed Matrix, Odus Pella/Strip Crowns-A matrix is a mould made in the shape of existing teeth or from a diagnostic wax up, and is used to

help fabricate a temporary Crown.

-Impression matrix: a quick and easy way of producing a matrix, frequently involving the use a

polyvinysiloxane to take an impression of the teeth before tooth preparation. The matrix duplicates

the existing tooth form back onto the Crown preparation, utilizing a self-curing composite such as

Integrity.

-Vacuum Formed Matrix: Made of a clear vinyl sheet that is pulled over a

stone cast or

diagnostic wax up, duplicating the form of the existing dentition. Due to the

flexibility of the vinyl sheet, distortions may occur on seating. A benefit of this

type of matrix is that a light cured resin may be used, and set through the clear

material.

-Odus Pella/Strip Crowns: These are clear, Crown shaped matrices, made of

cellulose acetate, and

come in a variety of different sizes. The procedure for creating a temporary

restoration using Strip Crowns is the same as for Preformed Crowns, except the

clear outer shell is removed before adjusting and light cured composite may be

used.

-Procedure for using Impression and Vacuum Formed Matrices:

1) The prepared tooth and adjacent teeth are coated with a thin layer of petroleum jelly and the

matrix is filled with a material such as Trim plus (polymethyl methacrylate), Integrity (chemical cured

composite) or Light cured composite (if clear matrix) and placed over the preparation. Care is taken

to avoid air blows, and over/under filling the impressed area

2) Allow the material to set, or command set with light as necessary, and remove the matrix

3) A mould of the temporary Crown should now be formed, and trimmed with stainless steel or

tungsten carbide burs and soflex discs

4) Cement the temporary Crown in place with the temporary cement materials mentioned before

3) Direct Syringing

-This is used in situations where a pre-formed Crown or matrix cannot be made for any reason. A

polyethyl methacrylate such as Trim or Trim II is indicated in such cases because of its handlingproperties and low exothermic reaction.


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Try in and Cementation xxii, xxiii

-This is usually the final stage in Crown provision, during which the final Crown is assessed, and

material is chosen for final cementation in place. It is important to note that once a Crown has been

cemented, removal for modification is impossible without damaging the Crown and/or toothpreparation.

-A systematic approach in Crown assessment is important, so as not to miss any defects or potential

future problems. Prior to the try-in procedure, the temporary Crown (if provided) must be removed

and the preparation cleaned thoroughly from any temporary cement for example, by using an

ultrasonic scaler.

Try in procedure:1) Check the Crown on the die

-Look for obvious defects, such as casting

blebs, which can be removed with a bur-Check occlusion

-Look for any fitting surface defects, marginal

fit, aesthetics and articulation. Keep in mind

any faults that will appear in the mouth too.

-If there are obvious faults in the Crown,

where it is not related to impression defect,

then it may be necessary to get a lab to

remake the Crown

2) Place gauze in the back of the patients mouth, to prevent the patient swallowing

the Crown

3)

Attempt to seat the Crown on the tooth preparation. If the Crown does not seat:-Ensure the preparation is completely clean of any temporary cement material

-Check proximal contacts: if too tight> grind and polish

-Check for over-extended margins > adjust from the axial surface and not the base, using

soflex discs

-Check the internal fitting surface for burnished areas where the preparation has come in

contact with the Crown. Disclosing wax, aerosol spray or light bodied silicone placed in the

fitting surface can help with identification of imperfections, which can then be ground down

with a white stone

-If the Crown still doesn’t fit, and no obvious impression defect can be found, a remake may

be needed

4)

Assess the fully seated Crown:-Proximal contacts: check with floss, if too tight> grind and polish, if open contacts> returnto lab or build up adjacent teeth

-Marginal fit (the gap between the Crown margin and tooth preparation margin): A poormarginal fit could render a tooth more susceptible to cement dissolution, plaque retention

and secondary caries. Data suggests that a marginal gap of 100µm is at the borderline of

acceptability for long term success. If there is an overhanging margin > adjust from the axial

surface until a probe can pass without catching. If there is a deficient margin > the Crown

may need to be remade

- Aesthetics: Check the shade and contours. ACC shades can be altered slightly by usingcoloured luting cements if necessary. MCC contours can be altered by grinding with

diamond burs, and colour adjusted by staining and refiring in the lab.

-Occlusion: Assess by eye, patient feedback, articulating paper and shimstock. Patient


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Cement type Brand Names Main Strengths Main Weaknesses Recommendations

Zinc Phosphate -DEHP Zinc PhosphateCement

-DeTrey Zinc Phosphate

Cement (Dentsply)

-Long clinical history

-Resistant to water dissolution

-Good compressive strength++

-Good film thickness

-Occasional initial sensitivity

-Low tensile strength

-No adhesion

-Not resistant to acid

dissolution

-Use in Metal supported

restorations with mechanically

retentive preparations

-Contraindicated with most

Composite and All Ceramic

Crowns, because of lack of

adhesion

Polycarboxylate -Poly-F Plus Zinc

Polycarboxylate Cement-DEHP Polycarboxylate

Cement

-DeTrey Zinc

Polycarboxylate Cement

-Fluoride ion release

-Low post-op sensitivity-Bonds to tooth and metal

-Good compressive strength+

-Low adhesion

-Low tensile strength-Not resistant to acid

dissolution

-Difficult to obtain low film

thickness


restorations with mechanicallyretentive preparations

-Can be used in mechanically

unretentive temporary Crowns

Conventional GIC -Ketac™ Cem -Fuji 1®


-Adhesion to tooth and metal

-Easy to use

-Occasional initial sensitivity

-Low tensile strength

-Not resistant to acid

dissolution

-Moisture sensitivity




-Use in Crowns with

strengthened cores, and

where mechanically retentive

-Use where moisture control is

adequate

Resin Modified GIC -RelyX™ Luting Cement -RelyX™ Luting Plus

Cement

-Fuji PLUS™

-FujiCEM™


-Adhesion to tooth and metal

-Good compressive strength++

-Easy to use

-Cement expansion

-Moisture sensitivity




-Use in Ceramic Crowns with

strengthened cores, and

where mechanically retentive


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Composite Resins

-Total Etch System

-Self-Etching Primer

System

-Self-Adhesive

Cement System

-Variolink® II

-Calibra®

-C&B Metabond®

-RelyX™ Veneer Cement

-RelyX™ Arc

-Panavia™ F

-RelyX™ Unicem Cement

-High compressive strength+++

-High tensile strength

-Excellent adhesion to tooth

and metal

-Good aesthetics

-Resistant to water and acid

dissolution

-Enhances strength of ceramic

restorations

-Low post op sensitivity

-Limited clinical history

-Variable film thickness

-Potential marginal leakage

due to curing shrinkage

-Difficulty cleaning excess

-Moisture sensitivity with total

etch systems

-Use in Dentine Bonded

Crowns, and conventional

Crowns where preparations

are unretentive

-As a summary, a strong Crown with good retention can be luted with any cement, whereas weak restorations and those with poor retention must be

bonded with strong cements such as composite resins.

Cementing Procedure

1)

Isolate the tooth, using dental dam (where possible) or cotton wool rolls. If the gingivae inhibit seating, retract using gingival retraction cords

2)

Clean the tooth preparation, and dry, but do not desiccate

3)

Mix the cement according to manufacturer’s instructions

4)

Coat the entire fitting surface with a small layer of cement

5)

Seat the Crown quickly, applying finger pressure, and maintain

6)

Excess conventional cement should be removed after complete setting. Composite resin based cements should be removed at the gel phase of set,as it can be difficult to remove later on. –Gold margins should be burnished before the cement sets, as doing this afterwards can crack underlying

cement


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References

i Jacobs DJ, Steele JG, Wassell RW. Crowns and extra-coronal restorations: Considerations whenplanning treatment. British Dental Journal 2002;192:257 –67.

ii Walmsley, et al. Restorative dentistry. 2 ed2007.

iii Valderhaug A, Jokstad, Ambjornsen E, Norheim PW. Assessment of the periapical and clinical status

of Crowned teeth over 25 years. J Dent 1997; 25: 97-105.

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