School of Oral Health Sciences Faculty of Health Sciences

University of the Witwatersrand

DEPARTMENT OF PROSTHODONTICS

CLINICAL PROCEDURES FOR COMPLETE DENTURE CONSTRUCTION (v.6)

1. PROCEDURE FOR THE VISIT: HISTORY AND EXAMINATION Note: All procedures must be explained to the patient in advance. Objective: To arrive at a diagnosis, treatment plan, and plan of treatment. Requirements S examination set S prosthetics set which should include a Willis gauge, figure-of-eight callipers, and

dividers S kidney dish S cup of water for patient, bib and bib chain S student’s instrument set At the first visit, the procedures for taking and recording the history, examination, diagnosis, prognosis, treatment plan, and plan of treatment are carried out. On completion, present the patient to your Supervisor, and obtain approval for the plan of treatment. Record as much detail as possible in the patient’s file, and obtain a signature from the Supervisor before continuing any further or before dismissing the patient. Always use the chair allocated to you. On entering the clinic, prepare the unit, chair, bracket table and working surface to receive your patient. The tumbler stand should have a clean cup of water. The bracket table should be covered with paper towel, and have a denture bowl filled with cold water and a kidney dish on it. Your working surface must be covered with clean paper sheets, and a paper bib should be prepared, with a bib chain, for your patient. The instruments required should be all be ready at your chair before the appointment begins, placed in a suitable container. This clean and neat presentation of your equipment allows your patient to sense your hygienic approach, and feel comfortable with having you work in their mouth. This mode of professional conduct relates to all stages of treatment. At this point you are ready to receive your first patient. If you have arrived late your patient may be seated already. If you are ready ahead of your patient (which you should be) then call him or her from the waiting room and escort your patient to your chair. Seat your patient comfortably and introduce yourself as the person who will be attending to their treatment. Your courteous approach has a considerable effect on the success of your treatment.

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The receptionist will have given the patient their white treatment card. The patient's personal details are recorded on the front of the card. Make a quick assessment of your patient's ability to respond to your conversation and to answer your questions so that you speak to them at an appropriate level, i.e. avoid scientific terminology and dental jargon. To assist you in your assessment, read all the information which has been entered on the patient's card, and enter any missing details (e.g. telephone numbers, year of birth, etc.). History Taking, Examination & Recording the Information Purpose The purpose of taking a history is to discover the reason why the patient is seeking treatment. The history will expose the patient's previous history of, and present attitude to, dental treatment. The examination of the patient's mouth allows you to collect data that will assist you to make a diagnosis of the nature of the patient's problem. The diagnosis is an essential first step in establishing a treatment plan for the patient. All useful information will be recorded on the appropriate form in the patient’s file. If you do not understand the reasons for the standard questions or examination, please consult your supervisor, lecture notes or textbooks. Do not fill out the forms as a blind ritual; you must understand why this information is required. 1. Main Complaint(s) These are the patient's complaints about their existing dentures or absence of dentures or their oral problems. It is best to record the patient's own words (e.g. "I can't eat with the old teeth"). Do not record what you think is wrong, nor ignore a complaint which you think is false; for example a patient may say: "These teeth don't feel right", when he actually means: "I don't like the appearance". Always record these complaints as they are presented to you. 2. History of the main complaint The patient may have had one or all of their complaints for some time, and this is useful information in helping assess their attitude, which may vary from one of fortitude for having put up with their problems for so long, to one of frustration and anxiety and anger for having had such complaints for so long before getting treatment. 3. Social History If you know little or nothing about the social context within which your patients live their lives, it will be more difficult for you to understand some of their complaints, or correct some of their habits and misconceptions, all of which will affect your ability to match their expectations of treatment. Apart from that, getting to know your patients is one of the most pleasurable aspects of being a caring health professional. 4. Expectations You can make the most technically correct dentures in the world for your patient, but if you have incorrectly identified their real expectations, or if you haven’t even tried to discover them, your dentures will be a failure. Note “your” dentures – they will never become part of the patient and will always be yours if they fail! So, much of the communication that goes on at this first visit is absolutely vital to the success of complete denture treatment. And listening to / hearing the patient is an important but often neglected part of that communication.

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It has often been said that the first visit is the most important for these reasons – and no actual treatment has yet been carried out. 5. Dental History Patient’s attitudes to dentistry and the dental profession will be influenced by their experiences, and the reasons for their loss of teeth. Tooth loss is debilitating, disabling and depressing. So, note when tooth loss occurred, the reasons for the loss, and the patient’s attitude to that loss. 6. Denture History This covers a number of factors, e.g. the number of years that dentures have or have not been worn since the teeth were extracted; previous use of partial dentures, immediate dentures, or complete dentures and their success or failure; pre-prosthetic surgery performed, etc. The manner in which this information is given to you will again give you insight into the attitude of your patient towards denture wearing, and their expectations. 7. Medical History Only pertinent aspects of the medical history need be recorded. We are obviously not interested in the usual childhood illnesses. Important conditions such as cardiovascular, respiratory, neurological and metabolic disorders are the ones to record. Any aspect of general health which may affect the treatment or the wearing of dentures must be noted. Any drug therapy which affects the oral structures or function may be significant. 8. Habits There are many habits that people adopt that can affect the successful wearing of complete dentures, such as smoking, clenching, cleaning with the wrong materials (such as toothpaste, peroxide), pipe smoking / sucking, nail biting, and leaving the dentures in the mouth for too long. You need to discover any adverse habits in order to explain their adverse effects to the patient, and to continually reinforce the need for change throughout the treatment. 9. Radiographic examination As a tertiary and teaching institution, we routinely take a panelipse radiographic view for our edentulous patients, even though the odds are against discovering anything that may require treatment. Nevertheless, you should note any abnormalities detected, as some may in fact affect your subsequent treatment plan. 10. Extra-oral examination As a dentist your examination and diagnosis is not limited to the inside of the patient’s mouth. There is a whole human being attached to that mouth. Look at the patient’s head, neck and face. Note anything that might affect the mouth, or indicate pathosis, such as asymmetries, scars, lesions, as well as the outward appearance of the mouth. Whilst talking to the patient you will be able to start to assess their current dental appearance, which may well relate to their main complaints. Record clicks or crepitus during jaw opening, closing or protrusion. Deviations on opening or closing may be significant. Pain during jaw movement or restriction of movements may stem from the temporomandibular joints, or from the muscles, or both. Note the details of the symptomatology and palpate the muscles concerned to establish tenderness to pressure or spasm. Ask your supervisor to demonstrate the palpation of the muscles of mastication, if you are uncertain about the sites to palpate.

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11. Intra-oral examination • Examine and record the following for each of the arches: • Ridge shape and size. Classifications can be useful, and many have been proposed; the

earliest one was that of Atwood, in 1971, but this has since been discredited. In 1991 Cawood and Howell proposed another classification, and this has stood the test of rigorous evaluation, and this is what will be used here. Cawood and Howell classified potential denture-bearing bone as follows:

• Class I – dentate • Class II – immediately post extraction • Class III – well rounded ridge form, adequate in height and width • Class IV – knife-edge ridge form, adequate in height, and inadequate in width • Class V – flat ridge form, inadequate in height and width • Class VI – depressed ridge form, with some basal bone loss evident

Of course, you must realise that this is not precise, and there are ridges that will fall between two classes, but the classification is useful to give you an idea of the kinds of problems you may encounter when making the dentures and the problems the patient may encounter when wearing them. For example, a Class III ridge is much easier for both of you to cope with than a Class V.

• Presence of undercuts • Quality of the mucosa: inflamed, firm or flabby, thickness, mobility, attachment to

bone • Position and size of the fraenula, especially if they will interfere with retention • Test the tuberosity sulcus – place a finger buccal to a tuberosity and ask the patient to

move their jaw to the other side. You will feel the influence of the coronoid process. Then remove your finger, retract the cheek and peer into the sulcus and ask the patient to repeat that movement. The idea is to see how narrow that sulcus is likely to be under function. Whilst checking the tuberosity sulcus in this way, at the same time, view the sulcus at the root of the zygoma: you will be surprised as to how shallow it can be in this region. Record your findings, for this will help you with understanding the expected extensions of the flanges of the impressions.

• Check for any bony protuberances and if they create any undercuts: again, this will help you decide if a denture can extend over them or if surgery may be required to reduce undercuts. Bony ridges may also need to be reduced and should be recorded, such as the mylo-hyoid ridge. Check for the mandibular tubercles, especially in Class V and VI ridges, where they mabe higher than the ‘crest’ of the ridge.

• Note the size and activity of the tongue, its position, fraenum, and median sulcus. In particular, note what happens to the tongue when the patient is just asked to open their mouth – does it retract towards the back of the mouth, or does it remain with the tip of the tongue anteriorly? If the former, the patient will need to re-train their tongue to behave as in the latter case. If the tongue naturally retracts to the back of the mouth, this will dislodge all but the most retentive of lower dentures.

• Record the length and tonicity of the lips, presence of lesions, or scar tissue • Classify the skeletal and anterior ridge relationships (Class I, II or III) and note any

discrepancies in size and relationships that may, for example, require teeth to be set in a cross-bite.

• Note oral pathology or other pathology which is not mentioned in the medical history. Do not record normal changes such as the sublingual varicosities seen in elderly patients.

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12. Examination of existing dentures A great deal of useful information can be obtained from a thorough examination of a patient’s existing dentures, and you should record as much of this information as possible. Please note that this evaluation is also how you will evaluate the new dentures as well! 12.1 Extra-oral: with the dentures out of the mouth, record your observations of the

following: • cleanliness of the dentures • presence of wear of both the denture base acrylic and the teeth (occlusal and/or

buccal surfaces) • the arch form and shape of the external surfaces • the incisor relationship • the inter-alveolar distance (IAD) (using the figure-of-eight callipers) at the first

molar and at the incisive papilla • the external appearance of the patient with the dentures in the mouth, at rest and in

occlusion: check the lip support, possible skeletal relationship, and if there appears to be excessive freeway space

12.2 Intra-oral: the following aspects need to be evaluated:

$ Retention: place each denture in turn and test the retention by holding the upper between thumb and first two fingers with the thumb over the flange opposite tooth 11, and the lower between thumb and first finger holding the incisors. Test the resistance to a force applied in the direction away from the tissues as: $ excellent (extremely difficult to dislodge and little or no movement before

dislodgement) $ good (difficult to dislodge but moved away from the tissues slightly before

dislodgment) $ fair (denture was dislodged easily) $ poor (denture offered little or no resistance to dislodgement).

$ Stability: this is tested by estimating the relative force necessary to move the denture, when applying a force in a direction towards the tissues. Two types of force are used, direct and rotary. $ For the upper, place a forefinger just behind the upper incisors and push; then

place your thumb over the first quadrant premolars and forefinger over the second quadrant premolars and apply a rotary force; then place a forefinger over the first quadrant premolars and push; and then place a forefinger over the second quadrant premolars and push.

• For the lower, place a forefinger over the lower incisors and push; then place your thumb over the fourth quadrant premolars and forefinger over the third quadrant premolars and apply a rotary force; then place a forefinger over the fourth quadrant premolars and push; and then place a forefinger over the third quadrant premolars and push.

Assess the resistance to movement as: • excellent (little or no movement on application of strong direct or rotary

force) • good (little or no movement of application of strong rotary force, but moved

and was dislodged when strong direct force was applied to one side or to the front of the denture)

• fair (considerable movement on application of rotary force and was dislodged by moderate direct force)

• poor (a slight force, either rotary or direct, caused the denture to move and become dislodged).

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$ Centric occlusion: place the dentures in the mouth and close the patient into the centric relation position: if you are unsure how to do this, ask your supervisor. Assess the relative occlusion in centric relation as: • excellent (no fault in centric occlusion when the patient closed the jaw in

centric relation) • good (a slight objectionable contact, possibly caused by only one cusp, made

the dentures slide slightly (½ mm. or less) to get into centric occlusion from centric relation. The sliding is not sufficient to tip or dislodge the dentures)

• fair (objectionable occlusal contacts on one side caused the dentures or the lower jaw to move about 1 mm to get the teeth into centric occlusion from the first contact in centric relation)

• poor (a gross error in the occlusal relations which could only be corrected by re-setting the teeth or by rebasing the denture or both).

$ Inter-occlusal (freeway) space: measure this by means of a Willis gauge as explained in the section on jaw relation records. Remember that the actual measurements at the occlusal and resting vertical dimensions are unique to you at the time of recording and therefore irrelevant – what counts is the difference between the two!

$ Arch form: assess conformity or not, to the neutral zone. $ Appearance: assess the amount of lip support, whether the size, colour and shape

of the teeth are acceptable to the patient. If they are not, ask the patient to bring an old photograph, if available, of them smiling. This will be of great value when selecting suitable artificial teeth.

13. Diagnosis This is not just the fact that the patient is edentulous! Record any pathology observed, and summarise the main problems observed for both the patient and their existing dentures. Try to determine how those problems arose – for example, continuing bone resorption causing loss of retention / stability and subsequent soreness; incorrect vertical dimension or centric relation; patient’s original expectations unrealistic, and so on. 14. Prognosis All that you have done up to now will lead you to developing a prognosis. This is the realistic interpretation of your ability to solve all the problems encountered and analysed. This is vital for matching the patient’s expectations with yours, and will enable you to respond realistically to the patient’s needs and demands. Much of this will need to be reinforced during subsequent appointments, especially if changes in habits, or attitudes, are required. 15. Treatment Plan In complete denture Prosthodontics this is fairly simple, and entails detailing any preliminary treatment that may be required, as well as specifying the type of dentures to be made, and summarising the techniques appropriate to that patient. Include planned changes to be made relevant to the existing dentures; planned freeway space changes; and aesthetic requirements such as diastemas. 16. Plan of treatment A plan of treatment sets out just what will be carried out at each visit. This is really useful for both you and the patient. The patient needs to know how many times to come, how long each visit will take, and therefore how long it will be before they receive their new dentures. And you need to know exactly what you want to accomplish at every appointment, so you can be properly prepared. Always over-estimate the number of

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appointments at this stage – you can be more specific later on if necessary, but it’s always nice to be able to say that the dentures will be ready sooner than you thought. It’s very disappointing to be told they will take a lot longer! Treatment Authorisation Your final diagnosis, prognosis, treatment plan and plan of treatment must be dated and signed by your supervisor before you actually commence treatment. At this stage it is your obligation to also ensure that the patient knows how much the treatment will cost, and what their contribution to that cost will be, when and how they will arrange payment. The final prosthesis cannot be delivered until payment is completed. Please consult with your supervisor if your patient reports any difficulties relating to payment, as it is possible to arrange for a reduction or waiver of fees. It is your responsibility to arrange future appointments. Ensure that on completion of your treatment for one patient, another patient is booked to see you. Remember at the end of each visit, check:- $ The patient treatment card – treatment written up & dated by you and signed by your

supervisor. Remember that meticulous record keeping is not only an essential part of clinical practice; it is also a legal requirement!

$ The laboratory card – filled in by you and signed by your supervisor $ Session assessment form – completed by your supervisor in conjunction with you $ Procedure stage form – completed by your supervisor in conjunction with you $ The appointment book – patient's details and treatment stage written on the

appointment sheet by you $ The patient's appointment card – details of next appointment Finally, please give your patient the form with all your details on it, so they will know how to contact you. Note: Please note that at each stage where it is necessary for you to show your work to

your supervisor, you are expected to critically appraise that work first, and not just ask "Is this alright?" This will show your supervisor that you have an understanding of what aspects are acceptable and what may not be acceptable in order to proceed to the next stage. Your correct critical appraisal will positively affect your clinical ranking mark for that session, even if that appraisal recognises faults. This is the same principle we use when assessing your session mark: you are expected to critically appraise your own performance over the whole session first, before discussing with your supervisor (see the document on the BEST system of clinical assessment).

The following is a fictitious case history, as an example of the type of information that needs to be recorded.

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A Fictitious Case History Patient: Male factory worker, 55 years old, denture wearer. Social history: Married - 4 children. Wife also a denture wearer. Expectations: Expects dentures to be the same as natural teeth. Aesthetics important Main complaint: Complains of looseness of lower denture, particularly when

speaking, and occasional soreness when chewing hard foods. Unhappy with the appearance

History of main complaint: Always had some trouble with this denture but worse in last

year. Denture history: Early loss of teeth due to caries – remaining teeth extracted 6 years

ago. Only had one set of dentures previously. Was edentulous for some time before wearing denture.

Medical history: NAD (No abnormality detected) Habits: Wears dentures at night. Radiographic examination: NAD Examination of patient: Extra oral: NAD Intra oral: Well preserved upper alveolar ridge. Active floor of mouth, redness

of lower ridge mucosa, and lower ridge resorbed posteriorly. Examination of denture: Extra oral: Arch form poor, posterior acrylic teeth show signs of wear; tight

incisal contact. Inter-alveolar distance 18mm at incisive papilla. Intra oral: Upper retentive. Lower denture lifts up when tongue protruded.

Lack of lip support both upper and lower. Arch form does not correspond to neutral zone. Freeway space 5mm. Teeth a little small. Occlusal contact mostly on anterior teeth. Discrepancy of 3mm between CO and CR positions.

Diagnosis: unrealistic expectations denture stomatitis on lower ridge

loss of vertical dimension due to wear of acrylic teeth poor centric occlusion position

poor arch form poor aesthetics

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Prognosis: Maxilla: prognosis good because minimal amount of resorption. Mandible: prognosis poor because of resorption posteriorly Generally: patient’s expectations need to be modified Treatment Plan: 1. Treat denture stomatitis and correct habits. 2. Construct new dentures with correctly extended bases, especially lower, correct arch

form, improved aesthetics. 3. Recall at regular intervals. Plan of treatment: Visit 1. Oral hygiene instruction including advice on altering denture habits. Treatment

of denture stomatitis by incorporating anti-fungal agent in tissue conditioner 2. Continued treatment of stomatitis. Check on patient's adaptation to changed

habits 3. Primary impressions and re-new tissue conditioner 4. Secondary impressions when mucosa is normal 5. Jaw registration. Re-new conditioner if necessary 6. First try-in.

7. Second try-in 8. Final try-in 9. Chairside re-mount, grind in occlusion, place denture 10. Recall

11. Further recalls as necessary.

P Notes «

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2. PROCEDURE FOR PRIMARY IMPRESSIONS Definition An impression is the negative record of the tissues of the oral cavity which constitute the basal seat of the denture. An impression is made in a plastic material which hardens or sets while in contact with the tissues. Objectives To obtain primary impressions so that study models and special trays can be made. The idea is to obtain a negative record of the entire denture bearing surface, to define fully the perimeters of the sulcus and to obtain details of certain superficial anatomical features. The impression is taken in order to make a positive cast or model of the tissues. These models can then be used for diagnostic purposes and/or to allow for construction of a custom-made or special tray which is used to make a more accurate secondary impression. Requirements this manual

examination set and prosthetics set kidney dish cup of water for patient, and bib periphery wax bowl and spatula irreversible hydrocolloid (alginate) impression material: use the chromogenic

alginate if available marking sticks hot water student’s instrument set Step 1: Arrival and preparation of the patient The patient must be seated upright with the head rest offering support so that the head, neck and torso are in line. Fasten the bib on the patient using the bib chain, and move the bracket table to a position accessible to you, and adjust the unit light to shine on the patient's mouth. Adjust the chair height so that the patient's mouth is at a comfortable level for you to work. For the lower impression, you will stand to the front and to the right of the patient, and the chair will need to be raised so that the patient’s mouth is at a level just below that of your shoulder. For the upper impression, you will stand behind and to the right of the patient. This time, the chair should be positioned so that the patient's mouth is at your elbow level. It may be necessary to tilt the chair back slightly for an upper impression – do not tilt the head, tilt the chair. The above positions (and subsequent descriptions) apply to right-handed operators: if you are left-handed, please reverse the descriptions! Step 2: Selection of trays There are three basic aids in selecting a stock tray: 1. Observe the width and develop a mental picture of the arch form and size.

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2. Use the old dentures if available – the fitting surface will give an indication of the arch form and tray size required.

3. Using a set of dividers: a) Lower: open the dividers and place the tips so that they rest on the lingual surfaces

of the retromolar pads. Select a tray which has the correct arch form and correlates to the divider measurement.

b) Upper: open the dividers and place the tips in the buccal sulcus alongside the maxillary tuberosities. Compare this dimension with the flanges of the trays available. Select a tray which has the correct arch form and correlates with the divider measurement.

Once you have selected stock trays which you believe are correct for the patient, place each tray in turn over the appropriate ridges and assess their suitability for taking the primary impression: a) Checking the lower tray:

S Stand in the position described earlier for taking the lower impression S Grasp the tray handle in the right hand, having wet the tray first by dipping it into

the water in the denture bowl on the bracket table (wetting the tray helps to lubricate the mouth and makes the procedure more comfortable for your patient)

S Retract the (patient’s) right corner of the mouth with your left hand or with a mouth mirror held in that hand

S Rotate the tray so that the handle points towards the patient's left and retract the left corner of the mouth with the buccal flange of the tray.

S Rotate the tray into the mouth. Position the tray carefully in the mouth over the ridge. The tray must be capable of recording the entire alveolar ridge, without appearing to impinge on the ridge, or excessively on the sulcus.

b) Checking the upper tray

S Stand in the position described for taking upper impressions S Wet the tray in the bowl of water S Retract the (patient’s) left corner of the mouth with your left hand or with a mouth

mirror held in that hand S Hold the tray so that the handle points away from the patient and to the right S Slip the right corner of the tray into the mouth and rotate the tray towards the left,

so that the left corner also enters the oral cavity S Position the tray over the ridge and align the midline of the tray with the maxillary

labial fraenum. Check the tray for correlation with arch form. Once again it must be capable of recording the entire alveolar ridge, without appearing to impinge on the ridge, or excessively on the sulcus.

If in doubt as to the size of the tray, try to use the smallest appropriate tray, not the largest. Obtain approval from your supervisor before proceeding.

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Step 3: Preparing the trays Upper tray Periphery wax is to be used to adjust the stock trays so that they will adapt more closely to the patient’s anatomy. The wax must be soft enough to be displaced by pressure or by the muscle actions of the patient. The wax can be softened over (not in!) a flame, or in hot water. If you have softened the wax using hot water, be sure to dry the wax before placing on the (also dry) tray, otherwise it will not stick. Place four stops in the dry tray at canine and molar regions. Use selective pressure to ensure that most of the border of the tray is short of the shallowest sulcus, and that the tray is stabilised on the ridge. If part of the tray border extends into the sulcus, add more wax to the stop in that region to lift the border away from the sulcus and re-seat the tray with less pressure. If part of the tray border is too far from the shallowest part of the sulcus (usually the case in the tuberosity region, add softened (and dried) periphery wax to the border, place the tray in the mouth, and border-mould by moving the cheeks or lips, until the wax border is now just short of the shallowest sulcus. You must carry out these movements, as you want to pull the lips and cheeks down to record the shallowest part of the sulcus. If part of the tray is too far away from the tissues in a horizontal direction (usually the case in the premaxilla), then add wax to the inside of the flange of the tray. It is often necessary, and kinder to the patient, to also add periphery wax to the posterior border of the tray in order to try to prevent excess impression material impinging too much on the soft palate, thereby setting off the gag reflex. Lower tray The principles for placing wax stops and assessing the border extensions are the same as in the upper, except for two areas, the buccal shelf and the lingual flange posterior to the pre-mylohyoid fossa, and including the retro-mylohyoid fossa. For the buccal shelf area, it is sometimes necessary to add some periphery wax, both to prevent the tray impinging on the tissues, and also to provide the correct extension laterally to the external oblique ridge. For the posterior lingual flange and retro-mylohyoid fossa, this area must always be recorded in periphery wax, as the tray extension will be inadequate to support the impression material, because of the force and nature of the tongue movements in this area. Place the softened and dried periphery wax on the border of the tray from the region of the pre-mylohyoid fossa, and just inside the border of the tray, especially at the region of the retro-mylohyoid fossa. Border-moulding is carried out by requesting the patient to first lift the tongue gently as the tray is inserted, then to protrude the tongue quite forcibly, and then to push the tip alternately into each cheek and then into the anterior palate (they will have to close their mouth slightly for this last action). These actions are quick, and take very little time. Check carefully that the periphery wax has in fact been moulded by these actions - it should have taken on the characteristic S-shaped curve of this region.

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Ask your supervisor to check the trays before making the impression. Do not proceed until this has been done. Step 4: Impression taking Spray alginate adhesive onto the tray: do this by first placing a paper towel behind the tray, and holding it over the sink. Allow the adhesive to dry before placing the alginate. It should feel tacky but not be liquid. Upper To mix the alginate, obtain the correct amount of water in the measure provided. Consult your supervisor as to the number of scoops of alginate to use, which will determine the amount of water used. Place this water in an alginate mixing bowl. Note this should be done first: the order is water first then the alginate powder! The water must not be above room temperature. Warm water will decrease the setting time of the material, which will make it set before you can complete the impression. If you wish to have a longer working time e.g. on a hot day, use iced water for mixing. Shake the powder in the closed container. Open the container and scoop up the powder in the measure provided. Level off the excess with a clean, dry spatula. Do not condense the powder as a low water/powder ratio will result in too thick a mix. As each scoop is measured out the powder is tapped into the water. Use the broad alginate / plaster spatula to mix the alginate until a smooth homogenous mix results. Use a chromogenic alginate, and mix until the colour changes from purple to pink. Load the tray level with the border. With a finger, scoop the alginate from the posterior border of the tray, and use this alginate to load the vault of the palate, and the tuberosity sulcus on each side (you will need to scoop more alginate from the bowl). If the patient has a fairly prominent premaxilla, you can also add some to the labial aspect of the anterior ridge. The mixing spatula, or a wooden tongue depressor, may also be used for this purpose. Do this before the chromogenic alginate changes colour again. Then place the tray, preferably straight up towards the palate, or slightly anteriorly first. Never place the tray posteriorly first (as in an orthodontic impression). Place the tray so that the wax stops contact the ridge with a slight “puddling” action, holding the lips and cheeks away as far as is possible. Then pull the lips and cheeks down and then up, to “push” the alginate into the sulcus. Then request the patient to make muscle movements as follows:

S Pull upper lip down as far as possible (to record the extent and width of the anterior sulcus)

S Open wide, then smile broadly (to record the extent and width of the buccal sulcus)

S Close jaw and move from side to side (to record the influence of the coronoid process on the width of the tuberosity sulcus)

S Relax Remove the impression when the alginate has set fully. Immediately ask the patient to rinse out. See to the patient's comfort before inspecting the impression. If the impression is acceptable, rinse the impression thoroughly under running tap water, cover with a damp paper towel and set aside with the impression surface facing downwards, so that water does not pool on the impression, thereby potentially causing distortion.

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Lower Mix chromogenic alginate and mix until the colour changes from purple to pink. Load the tray level with the border. When placing the tray, ask the patient to gently lift the tongue first, and then gently extend it forwards as you place the tray to the stops. Place the anterior part of the tray first, as the patient lifts the tongue, then the posterior part as the patient moves the tongue forwards. The patient may then gently protrude the tongue, but keep the tip just behind or just resting on, the tray handle. This allows the posterior part of the tongue to arch upwards thus allowing the alginate to record the lingual sulcus. Then pull the lips and cheeks up and then down, to “push” the alginate into the sulcus. Then request movements as follows:

S Make “oo” shape (not sound!) with lips S Open wide S Smile S Place the tongue gently into each cheek and the palate (not nearly as strongly as

when adjusting for the periphery wax) S Relax, keeping the tongue forwards

Remove the impression when set, and proceed as per the upper. Step 5: Evaluation of the impressions Evaluate the impressions to ensure that

$ The stops are all showing, indicating that the tray has been fully seated $ The sulcus has been recorded evenly $ There are no voids in the impression which will affect the construction of special

trays. If the impression is satisfactory, check with your supervisor, and proceed to mark the extension of the special trays with a marking stick on the alginate, with the help of your supervisor. The purpose of this important step is to ensure that the special tray has the correct extension, according to the anatomy of the patient, and according to how this has been recorded in the primary impression. This is because some areas of the primary impression may be a little too over-extended, and this can be adjusted for by comparing the impression directly with the situation in the mouth. In this way, the marking pencil line will be recorded on the primary models, and the dental technician will reproduce the correct anatomical contours clinically determined rather than arbitrarily determined in the laboratory. Upper: first mark the border to allow for the frena, checking in the mouth for their full action and attachment relative to the crest of the ridge. Mark the impression to allow for their full action. Then mark the full extent of the sulcus in the tuberosity areas, extending the mark to the hamular notches. Then check in the mouth for the action of the sulcus in the root of zygoma area, and mark the tray extension on the impression. Lastly, assess the anterior impression borders for the amount of overextension, and mark where the tray should extend to. Then finally just join up all these marks, and you will have as near perfectly extended a special tray as you can get – always provided that the technician follows these lines of course.

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Lower: once again, first test and then mark for the action of the frena. Then mark the full extension of the buccal shelf, extending this posteriorly to allow for the masseter notch, and then half way up the retro-molar pad. Now try to identify the mylohyoid ridge, and mark it, or where you judge it to be. Finally check the remaining border extensions and mark where you feel the tray should extend to, and then once again, join up the lines. Step 6: Disinfection Rinse the impressions thoroughly under running tap water, and disinfect them before transporting them to the laboratory. Remember to transport them wrapped in wet paper towels, upside down (tray on top). Step 7: Record keeping Record the procedure in the patient's file, sign the file, and obtain the signature of your supervisor. Make out a laboratory card, and request the appropriate type of special tray for your patient, and again obtain the signature of your supervisor. Make the next appointment with your patient. The type of special tray will depend on a number of factors, but the following is a general guide: Cawood and Howell Class III and most Class IVs: spaced tray, upper and lower Cawood and Howell Class V and VI: upper: spaced, lower: close-fitting Upper anterior flabby ridge: window tray with posterior handles, spaced Lower flabby ridge: spaced over the ridge, close fitting elsewhere, with spacer left in place. Then discuss the clinical mark with your supervisor. You should first assess yourself, and suggest the mark you deem most appropriate to your performance, and reach consensus with your supervisor (who nevertheless will be the final arbiter!). Step 8: Clean up Thoroughly clean up the clinical area, leaving it as you would expect to find it. Step 9: Marking the models Unfortunately no matter how well we mark the impressions, the line still does not appear to be that clear on the model, and so it is necessary to re-mark the models before they are finally sent for the special trays to be made. Once again, it would be best to do this in the presence of your supervisor, and you should make every effort to do so as soon as possible after the models have fully set. We recognise that this may not always be possible, and as the models must go to the lab as soon as possible, if your supervisor is not available, please consult the laboratory manager, Mr Gert Kruger.

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2.1 Alternative procedure for primary impressions The use of compound There are many situations when this procedure is most useful. For example, if you cannot find a stock tray that conforms to the shape of the alveolar arches, or if the resorption pattern of the ridge is such that you cannot locate the wax stops adequately. The use of impression compound will then allow a recording of the edentulous area without having to make constant alterations to the stock trays. Step 1 Chose (preferably non-perforated) stock trays in the usual manner. Pre-heat brown impression compound to the appropriate temperature in the compo bath. Use one cake for the lower and one to one-and-a-half cakes for the upper. Step 2 Upper Once the compound has softened, mould it into a round ball and place on the impression tray, moulding it to the general contours of the tray in such a way that it covers the palate as well as the borders of the tray. Seat the tray, whilst observing the compound as it is extruded into the sulcus. Border-mould by manipulating the patient’s lips and cheeks quite vigorously. When firm, remove from the mouth and chill. Now evaluate the extension of the impression by returning it to the mouth and assessing the relationship of the border to the sulcus. The objective is to ensure that the compound is at the shallowest part of the functional sulcus. Identify any areas that require correction; if over-extended, for each area, soften using a hand-held flame, then temper in hot water, and return to the mouth for further border moulding. Areas of under-extension are added to using green stick compound in the same manner. Lower Mould the softened compound into a sausage-shape and place into the tray, once again moulding it to the general contours of the tray, and especially the posterior lingual sulcus and the retro-mylohyoid fossa area. Place in the mouth using the same actions described previously when using periphery wax. When firm, remove from the mouth and check and adjust in the same manner as for the upper. Step 3: Evaluation of the impressions Check with your supervisor, and proceed to mark the extension for the special trays with a marking stick on the alginate, with the help of your supervisor. Although you will have border-moulded the impressions, the fact is, compound is still a very stiff material, and

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there will inevitably be some over-extension, though perhaps not as much as with alginate. Nevertheless, check in the mouth in the same way as before (Step 5 above) and mark the impression for the extension of the special trays. Then proceed as per steps 6 to 8 of the procedure for an alginate impression. Step 4: Optional technique: alginate wash The purpose of this technique is to save time on the necessary border moulding of the compound impression, so as to record the sulcus in alginate only. Trim the borders of the compound with a clean, sharp Stanley-knife blade, by removing sufficient compound in length and width, such that the borders will be just short of the shallowest sulcus. Evaluate with your Supervisor before proceeding further. Step 5 Spray with alginate adhesive and dry. Place alginate in the impression and proceed as per steps 4 to 8 of the procedure for an alginate impression.

P Notes «

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3. PROCEDURES FOR FINAL IMPRESSIONS Definition A final impression (also called a secondary impression) is an impression that records the entire area to be covered by the denture base and that provides for intimate tissue contact and border (peripheral) seal to prevent the ingress of air between the denture base and soft tissue. It is used for making the master cast or model used in fabricating the denture. Objectives $ The bases should extend over the maximum amount of supporting tissue without

overly displacing the musculature or free mucosa. $ Maximal reproduction of detail with minimal distortion of the impression material. Special (or Custom) Trays Definition An individual tray made for the patient in order to obtain a highly accurate final impression. Rationale for the use of a special tray $ It is custom-made for the patient. $ Allows an even thickness of impression material, particularly at the peripheries. $ Facilitates the use of less viscous impression materials. $ Permits alteration of the tray by removal or addition of material. Requirements for specials trays $ Should be rigid to prevent distortion of the impression during the procedure and

transportation to the laboratory $ Should allow for full movement of the tongue, cheeks and lips without interference

from the handles or tray borders. $ Should support the final impression material so that the height and width of the

functional sulcus are recorded. NOTE: In order to use the surgery time to maximum efficiency, you should be properly

prepared before your arrival in the surgery. The laboratory work of the previous stage (i.e. the special trays) should have been completed and signed on the laboratory card by the technician in charge. If you have constructed the primary models and special trays yourself, allow your supervisor to assess the laboratory work before proceeding with the treatment. This will contribute to your Session Mark in your clinical assessment.

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3.1 THE FINAL IMPRESSION USING A SPACED SPECIAL TRAY Instruments and Materials Required this manual examination set and prosthetics set kidney dish cup of water for patient, bib, and bib chain green stick compound Bunsen burner, and hand-held flame

Zinc-oxide-eugenol impression paste Vaseline compo bath with hot water

student’s instrument set which should include a Stanley knife with a clean, non-rusty blade

Arrival and preparation of the patient The patient should be seated in your dental chair in the position described in the section on Primary Impressions. Step 1: Evaluation of the spaced special tray Evaluate the special trays on the models. Models and trays should conform to the following guidelines: Primary Models - poured in 1:1 mixture of plaster and stone

$ base to be 12mm in height $ land 2mm in width and trimmed flush with deepest part of sulcus $ no scratch marks on alveolar ridge $ model once trimmed should conform to shape of the arch $ base parallel with alveolar ridge $ base parallel to an average plane of the ridge in cases of uneven resorption $ no porosities $ A line for the extension of the special trays should be clearly visible, either as

picked up from the primary impression, or subsequently outlined. Upper Spaced Special Tray

$ must be clean and smooth i.e. no sharp, rough edges, but not polished $ even thickness of material (2-3mm) particularly at the peripheries, which should

be rounded $ one handle to be placed anteriorly, angled at no more than 45E; as a guide, its

dimensions to be 15mm long by 15mm wide, and 3mm thick $ has relief holes in the palate, one anteriorly below the incisive papilla, and one

on each side of the palate, in the second molar region $ stops should not have sharp edges but should be clearly defined, and should wrap

over the ridge crest $ periphery conforms to line picked up from the impression or to line drawn on the

model by the student, under supervision, if the line from the impression is not clearly visible.

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Lower Spaced Special Tray $ must be clean and smooth i.e. no sharp, rough edges, but not polished $ even thickness of material (2-3mm) particularly at the peripheries, which should

be rounded $ 3 small handles to be placed, one over each first molar area, and one anteriorly,

which is angled at no more than 45E and slightly curved; as a guide, posterior handle dimensions to be 7mm high by 15mm long by 5mm wide; the anterior handle to be 15mm long, 15mm wide, 3mm thick

$ stops should not have sharp edges but should be clearly defined, and should wrap over the ridge crest

$ periphery conforms to line picked up from the impression or to line drawn on the model by the student, under supervision, if the line from the impression is not clearly visible

$ lingual flange not to be extended beyond the mylohyoid ridge and the retro-molar pad

The trays should allow for adequate impression material at the peripheries yet provide sufficient support for the material. Reduce obviously over-extended trays, and smooth out irregularities. Adjust the stops if they have sharp edges. Step 2: Intra-oral evaluation of the trays Observe the patient’s anatomy and form a mental picture of the optimal extension of the tray, befor evaluating the special tray in the mouth. Holding the tray with one hand, retract and manipulate the cheeks, and ask the patient to perform normal movements, to see whether the periphery of the tray is just short of the functional sulcus. Posteriorly, the upper tray should extend just past the border of the hard and soft palate (seen by locating the vibrating – “ah”-line). Ask the patient to protrude the tongue just past the lower lip to see whether the lower lingual flange allows this movement without the tray being dislodged Step 3: Adjusting the tray Over-extended areas of the tray must be adjusted by grinding away the acrylic. Under-extended areas of the tray should be built up by using green-stick compound. There are two ways to use this material. 1. Soften the outer part by twirling it in a flame quickly, so that the inner core of the stick

remains firm. Then ‘paint’ the softened outer part onto the tray. To add more, use a different piece of greenstick, because the inner core rapidly softens.

2. Twirl the stick over (not in) the flame slowly, so that the entire stick becomes soft and then add that softened part to the tray.

Once the greenstick has been added, soften it so that it is even and glossy, using a hand-held flame. You must then temper it (i.e. dip in hot water), so as not to burn the patient’s tissues. This water must be at the working temperature of green stick, which is 51ºC or 125ºF. Place the tray in the mouth and perform the appropriate vigorous border-moulding. After removal from the mouth the greenstick should be chilled in cold water to harden it completely. Vigorous movements are required, because as the greenstick is very stiff, you do not want to over-extend, because impression material will still be placed over it.

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Check that the green stick has been displaced by the tissues – it will have a dull appearance and be smooth. Check in the mouth as to its conformity to the functional sulcus. If it has reproduced the functional sulcus, take a sharp and clean Stanley knife and reduce it by 1-2mm. Greenstick should always be applied to the inside of the posterior border of the maxillary tray. It assists in the formation of the posterior palatal seal by lifting the soft palate, which is very important for a successful denture. It also minimises the flow of impression material on to the soft palate and throat, and allows better patient comfort during the impression taking. Green stick should always be used to record the posterior lingual sulcus and its extension into the retromylohyoid fossa. As the vertical extension of the tray should be to the mylohyoid ridge, the green stick is placed inside this extension, and a little extra is placed in the region of the retromylohyoid fossa, as this would have been blocked out on the primary model in order to construct the special tray. Use the same sequence of actions for border moulding as when using periphery wax for the primary impression. Once it has reproduced the functional sulcus, take a sharp and clean Stanley knife and reduce it by 1-2mm. Obtain permission from your supervisor before continuing to the next stage. Step 4: The final impression Upper The upper final impression is made using zinc-oxide and eugenol impression paste if no severe undercuts are present. If the undercut is severe the upper final impression can be made using a regular bodied elastomer, or a suitably mixed (i.e. with a extra water) dust-free alginate. Zinc oxide eugenol paste is a very sticky material. You should smear a thin layer of petroleum jelly (Vaseline) on the patient's lips and chin (beard and moustache, too) before you start to mix, and wipe any excess off with a tissue. This makes it easier to clean the patient's face if any paste adheres to the skin. Make sure the special tray is dry. Squeeze out equal lengths of zinc oxide impression paste (about 10 cm) on a mixing pad ensuring an even diameter of material as it emerges from the tube. Mix using the narrow (preferably flexible) spatula in your kit. An evenly coloured smooth mix should be formed. While you are loading the tray, instruct the patient to rinse their mouth. Load the tray by judging to have placed a little more than the space made available; do not load the tray as if it were a primary impression. Place the tray by using a gentle but firm “puddling” action, to ensure that the tray is placed to its stops whilst holding the lips and cheeks away as far as is possible. Then pull the lips and cheeks down and then up, to “push” the impression paste into the sulcus. Then ask the patient to produce the same sequence of gentle functional muscle movements as for the final stage of the primary impression. After a minimum of 4 to 5 minutes, allow air into the vestibules and gently remove the tray in the line of least resistance. If retention is so great that the impression won't move, ask the patient to puff the cheeks with air and attempt removal of the tray again. If you still have difficulty, use water from the triplex syringe, applying it along the periphery. Do not touch the periphery with your fingers when removing a retentive impression.

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See to the comfort of the patient as a priority, after removal of the impression. Allow them to have a thorough mouth rinse, as ZOE paste does not taste pleasant. Clean the patient’s face if necessary, using orange solvent. While assessing the impression, handle it with great care. Check it carefully for pressure points, voids, folds or any aberration which does not conform to a normal anatomical contour. Assess the peripheral extensions very closely. If the impression has faults it may be necessary to retake it. The increased area of the upper compared with the lower generally militates against making any correction to the impression, but it may be possible to correct some defects by using another layer of paste. Do not ever just try to correct defects by adding small isolated amounts of paste: this will distort the impression. Lower The lower final impression is usually made in two stages. Squeeze out even lengths of impression paste (about 6cm) onto a mixing pad. Ensure that the diameter of the lengths extruded is the same. Dry the lower special tray. Protect the patient's lips (and/or beard) with a little Vaseline. Mix the paste, load the tray so that an even amount of material covers but does not fill the tray (remember that the spacer was only one layer of wax), and convey to the mouth. Use the same method, and request the patient to produce a sequence of border moulding movements that are functional, involving no gross movements, exactly as described for the final stage of the alginate primary impression. Remove the tray when set, and immediately ask the patient to rinse out. See to the patient's comfort before inspecting the impression. Clean the patient’s face if necessary, using orange solvent. Rinse the impression thoroughly under running tap water. Inspect the impression carefully. Sometimes, if the entire periphery is correct but only the stops remain, it may not be necessary to take the final wash impression. If this is the case, gently and carefully grind the stops to reduce them a little, and accept the impression. Normally, though, there are other aspects of the impression that are not quite right, in which case further adjustments are needed, as well as a wash impression. Reduce any parts of the tray exposed due to excessive pressure or over-extension. Remove the stops showing through the impression. Clean the impression surface and use orange solvent to remove a thin layer over the crest of the ridge. Wash this off, and repeat the impression procedure using another, thinner, layer of impression paste, again using a sequence of border moulding movements that are functional,. Step 5: Decide on the type of trial base Discuss with your supervisor which type of base you are going to use, acrylic or wax, and which jaw relation procedure you are going to use (i.e. if you are going to set the upper anterior teeth at the chairside). Use a wax base if you feel you will have a small inter-alveolar distance (15mm or less), if you feel comfortable with the extension of your final impressions, or to save your patients a small additional laboratory fee. Use an acrylic base if you want to be certain of having good retention especially of the upper, if you’re not certain of the peripheral extension of the lower, and may want to use the base to take another final impression, if you want the

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finished denture to look more attractive (as the base will be made of clear acrylic), and if the patient does not mind paying a little extra on the lab fee (if they are paying). If you intend to use the alternative jaw relations procedure (see section 4.2) then select the tooth mould and shade at this appointment, as per step 12 of section 4. Step 6: Record keeping Record the procedure in the patient's file, sign the file, and obtain the signature of your supervisor. Write your instructions on the laboratory card, and again obtain the signature of your supervisor. Make the next appointment with your patient. Then discuss the clinical mark with your supervisor. You should first assess yourself, and suggest the mark you deem most appropriate to your performance, and reach consensus with your supervisor (who will still be the final arbiter!). Step 7: Disinfection Rinse the impressions thoroughly under running tap water, and disinfect them before transporting them to the laboratory. Handle the impressions with the utmost care while boxing and casting them in the laboratory. Step 8: Cleaning up Thoroughly clean up the clinical area, leaving it as you would expect to find it.

3.2 THE MANDIBULAR FINAL IMPRESSION USING A CLOSE-FITTING

SPECIAL TRAY The procedure described above allows for some degree of functional recording of the supporting areas of the impression by using stops that create a space between the tray and the mucosa. These are ground out in the lower as they are not placed in primary support areas. In the upper they are usually adjusted for at the final delivery stage. However, not all mouths have ridges that can enable stops to be placed, and alternative procedures must be used. Essentially there are two options, the use of a full spacer and full border moulding, and the use of a close-fitting special tray. The former (described in the next section) is useful for lower flabby ridges; the latter (described here) is used for resorbed (“flat”) lower ridges (Cawood and Howell Class V and VI and occasionally some Class IV ridges if the cres of the ridge is not too sharp. This is not an easy impression to take, and, as with many prosthodontic procedures, there is often no substitute for experience when making these impressions. In many cases, though, a functional impression reline may still be required once the dentures are finished.

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Step 1: Evaluation of the close-fitting special tray Evaluate the special trays on the models. Models and trays should conform to the following guidelines: Primary Models – see Step 1, section 3.1 above Lower Close Fitting Special Tray $ must be clean and smooth i.e. no sharp, rough edges, but not polished $ even thickness of material (2-3mm) particularly at the peripheries, which should be

rounded $ 3 small handles to be placed, one over each first molar area, and one anteriorly, which

is angled at no more than 45E; as a guide, posterior handle dimensions to be 7mm high by 15mm long by 3m thick; the anterior handle to be 15mm long, 15mm wide, 3mm thick, and long enough so that the impression surface of the tray will be horizontal when placed on the bench and resting on the anterior handle and the posterior edges (to assist with boxing the impressions)

$ periphery conforms to line picked up from the impression or to line drawn on the model by the student, under supervision, if the line from the impression is not clearly visible.

$ lingual flange not to be extended beyond the mylohyoid ridge and the retro-molar pad: ask the patient to protrude the tongue just past the lower lip to see whether the lower lingual flange allows this movement without the tray being dislodged.

Step 2: Assessment of retention Place the tray in the mouth and test whether you can feel any retention. Judge whether any lack of retention may be due to under- or over-extension, and in which areas. The peripheral extension of the tray can also be assessed by taking an alginate wash impression. It is therefore taken before you make any alterations to the tray. The tray should allow for adequate impression material at the peripheries yet provide sufficient support for the material. Mix a half-measure of alginate to a slightly wetter mix than normal (by adding more water but no more than one third extra). Apply this to the tray (no adhesive) and insert it into your patient's mouth. Seat the tray completely. Ask the patient to execute all the movements indicated in the section on primary impressions for border moulding. When the alginate has set, remove the tray carefully. Assess for overextension and under-extension. In overextended areas, the acrylic will show through the roll of alginate and should be reduced as necessary. In under-extended areas the roll of alginate will be deeper than 2mm, and thus the tray will not support the impression material. The tray must be extended by the addition of greenstick and border moulding. Greenstick should always be used to record the posterior lingual sulcus and its extension into the retromylohyoid fossa. As the vertical extension of the tray should be to the mylohyoid ridge, the green stick is placed inside this extension, and a little extra is placed in the region of the retromylohyoid fossa, as this would have been blocked out on the primary model in order to construct the special tray. Use the same sequence of actions for vigorous border moulding as when using periphery wax for the primary impression.

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Step 3: Creating space for the impression paste Reduce the entire fitting surface and periphery of the (border moulded) tray by 1 to 1.5 mm with the exception of the buccal shelves and the retro-molar pads. To do this, it is helpful to use a bur to make notches of the correct depth which you wish to trim on the periphery of the tray. The intervening material can then be ground away, and the periphery reduced evenly. Similarly, grooves of the correct depth can be cut on the fitting surface, to guide you when reducing the tray material. Remove 2 to 3 mm of tray material if there are deep undercuts. Step 4: The final impression The impression is taken with zinc-oxide and eugenol paste, unless there are contraindications to this which your supervisor will point out. Ensure the patient’s lower face and facial hair is still protected with a thin layer of Vaseline. Squeeze out even lengths of impression paste (about 6cm) onto a mixing pad. Ensure that the diameter of the lengths extruded is the same. Dry the lower special tray. Mix the paste, and load the tray so that an even amount of material covers but does not fill the tray (remember that only 1- 1.5mm of space has been burred away).While you are loading the tray, instruct the patient to rinse their mouth. In cases of rapid salivation, place two packs of gauze sublingually on each side and remove just before inserting the impression. Insert the tray carefully, without dragging the impression paste on the lips and position the tray over the ridge. Ask the patient to raise the tongue over the tray. Gently seat the tray with the lip and cheeks lightly retracted. Watch the surplus impression paste oozing over the periphery of the tray. Release the retracted lip and cheeks and ask the patient to relax the tongue by keeping it forwards, just behind the anterior handle of the tray. Once the tray is seated, hold it absolutely still with an even grip under the chin and on the finger rests. After 30 seconds, ask the patient to lick the upper lip gently and then to gently point the tongue into the cheek first on one side, then the other, then to lift it gently into the palate, and finally to protrude the tongue until it touches the tray handle. Remind the patient to hold the tongue there until the impression material has set. Note that these movements are more passive than those described in the section on primary impressions, and for border-moulding with greenstick, because of the less viscous nature of the impression paste. After a minimum of 4 to 5 minutes, remove the tray carefully, allowing air into the buccal sulcus and asking the patient to raise the tongue. See to your patient’s comfort immediately after removing the impression, and allow him/her to rinse out immediately. If the impression is not acceptable, reduce any parts of the tray exposed due to excessive pressure or over-extension. Clean the impression surface, and repeat the impression procedure above using another, thinner, layer of impression paste, again using a sequence of border moulding movements as before. If the error in the impression cannot be corrected with a wash, all the ZOE paste must be removed, and the impression retaken. On successful completion of both impressions, clean the patient's mouth and face of all your materials. Use orange solvent to remove any set impression paste.

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Steps 5 to 8 These are the same as in section 3.1 above 3.3 THE MANDIBULAR FINAL IMPRESSION using a SPACED SPECIAL TRAY

WITHOUT STOPS

In this tray, a spacer of one or two thicknesses of wax is used, to create a space over the areas of denture bearing mucosa that are flabby, but short of the sulcus, and not including the buccal shelves. Any border moulding is carried using green stick compound, with the spacer still in place. Perforations are usually also placed in the tray over the areas of flabby tissue, once the border extensions have been done, and the spacer is removed. It is often possible to take this impression in one stage, as the contact of the tray with the primary support areas ensures that no pressure will be exerted over the flabby ridge tissues. If, however, excessive areas of tray material show through the paste impression, then a wash will again be required, with another layer of impression paste.

3.4 THE UPPER FLABBY RIDGE The presence of an upper flabby ridge presents a particular challenge to impression taking. The aim is, fairly obviously, to produce an impression that records the denture fitting area in such a way as to produce no distortion of the flabby area. This in effect means that a muco-displacive technique must be used for the primary and secondary support areas, and a completely muco-static technique for the flabby part of the ridge. This is accomplished by using a particular type of special tray, and by taking the impression in two stages. The special tray is constructed so that over the flabby ridge, it is completely cut away to form a window, leaving a thin anterior section for the labial sulcus. It therefore has handles similar to those used in lower special trays, only over the molar regions on each side. The borders of the tray are adjusted in the normal manner, and the impression is taken in zinc-oxide eugenol (ZOE) impression paste. A layer of wax can be placed over the window to help contain the impression paste but this is not always necessary. The impression is then inspected and the edges of the paste around the edges of the window are cleaned and cut away with a scalpel. The impression (if satisfactory) is then replaced in the mouth, and now the flabby ridge area can be recorded without any displacement, by literally painting on impression plaster, layer by layer, whilst holding the tray in place under slight finger pressure. This plaster is extended onto the external surfaces of the tray for retention. The patient is usually placed in the supine position, and it is useful to place a small ‘wall’ behind the posterior border of the window to catch any excess plaster. When the plaster is set, the whole impression is removed: be sure that the impression plaster is retained on the special tray and add sticky wax to its edges if necessary. Also be sure that the impression plaster has not extended onto the impression surface of the ZOE paste, but has only recorded the flabby ridge area.

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3.5 ONE-VISIT PROCEDURES FOR FINAL IMPRESSIONS

There is no doubt that the use of special trays ensures the correct extension of the denture bases as accurately as possible; but they require an extra clinical visit, and incur additional laboratory costs. Many mouths, however, have adequate ridges, and many patients are previous and expert denture wearers (and, it must be said, many dentures are successfully worn by patients when even very poor impressions have been made). In fact, it is likely that the majority of denture wearers would benefit from the cost saving aspects of obtaining a final impression in one visit, and would not be disadvantaged by such a technique. This does not mean, though, that an alginate impression taken in a standard stock tray, with no use of stops or peripheral extension modifications, is the answer. It is not. Although many impressions are made in such a manner, it is not considered anything other than malpractice to do so, as there are cost-effective alternatives that sacrifice none of the principles of impression taking. Two such techniques are recommended.

3.5.1 A ONE-VISIT PROCEDURE USING THE DOUBLE ALGINATE TECHNIQUE

To obtain an accurate final impression in one visit, a primary impression is adjusted in such a way as to make it a suitable “tray” for a thin alginate wash. Step 1 Make an alginate primary impression in the normal manner. It is most important that the stops are clearly visible, because alginate is an elastic material and will easily distort under pressure, so that when the tray is replaced in the mouth with the final wash impression, it must be held without pressure, against the stops. Step 2 With a sharp knife, trim off all excess material, taking care not to touch the peripheries. Replace in the mouth and assess the degree of over-extension of the alginate into the sulcus. Carefully trim the frenal areas, and the height and width of the borders so that they are 2mm short of the functional sulcus. Step 3 Use a dust-free alginate (such as Blueprint) that is preferably a different colour from that used for the first impression. Add up to, but no more than, one third extra water to a single scoop of powder. Place in the impression and take the impression in same manner as for a final impression. It is not necessary to use an alginate adhesive, as if this final wash impression is inadequate, it can be removed, and re-taken. There is one problem with this type of impression, and that is, that it is not possible to box the impression in the normal manner, so the model has to be poured in two stages, similar to the technique for primary impressions. However, because this is a final impression, it is critical that the height and width of the border be reproduced accurately. Therefore care

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must be taken with the first pour of plaster, to include both the height and width of the border extensions, and to include small mounds of plaster for mechanical retention of the base. The first pour should set in 100% humidity for no more than 60 minutes, before the second pour is made.

3.5.2 A ONE-VISIT PROCEDURE USING COMPOUND WITH A ZOE PASTE In this technique, a compound primary impression is border moulded is such a way as to convert it into the equivalent of a close-fitting special tray. Because compound is used, there must be no undercuts, and the mucosa must be firm. Step 1 Make a compound primary impression with a stock tray that errs on the side of being too short at the peripheries. This is because extensive border-moulding of the borders of the impression is necessary in this technique, so there should be no interference from the tray. Deficiencies are made up by additions of green stick compound. Step 2 It is now necessary to border-mould each section of the compound border in such a way that it conforms to the height of the functional sulcus. This requires that each quadrant be softened with a hand-held flame, tempered in the compo bath at the working temperature of the compound (to avoid burning the patient), and then returned to the mouth for functional border moulding. Great care must be taken to avoid over-extensions, because of the stiffer nature of compound impression material. Step 3 Once the borders have been adequately adjusted to the height of the functional sulcus, 1-2mm is removed from the height and width of the compo borders with a clean and sharp knife. The tray is then checked in the mouth to ensure that it is just short of the functional sulcus and conforms in every way to the requirements for the border of an acrylic special tray. Step 4 The impression is then taken in the same manner as for a close-fitting special tray, using ZOE paste.

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4. PROCEDURES FOR RECORDING THE POSTERIOR PALATAL SEAL, JAW RELATIONS, AND FOR SELECTING ARTIFICIAL TEETH

Definition Jaw relation records are made to establish the vertical and horizontal relationships of the jaws to each other. Objective To record the relationship of the mandible to the maxillae when the mandible has moved along its terminal hinge pathway, to an acceptable vertical height, so that the centric occlusion position is coincident with the centric relation position. In addition at this visit, the posterior palatal seal (post dam) will be defined and the mould and shade of the artificial teeth will be selected together with the patient. Materials used for the base There are two alternatives for the trial base material: (1) a clear acrylic base, and (2) a wax base, reinforced palatally and lingually with wire. You will start off using a wax base because it is generally considered easier to adjust and manipulate, especially if the final impression should be over-extended. However, with experience, you will find that an acrylic base will allow you to be able to use a base whose retention you have already ensured, so towards the end of your course, you should use such a base. What you then use once qualified is up to you, but at least you will have experienced both. Requirements this manual examination set and prosthetics set kidney dish cup of water for patient, bib and bib chain pink modelling wax marking stick Alminax Vaseline Fox plate Willis gauge student’s instrumentation set Step 1: Seating the patient Seat the patient comfortably in an upright position with the head erect and supported. Postural position and emotional state affect the mandibular rest position, so make the patient feel comfortable and relaxed before starting treatment. The chair should be raised so that the patient's mouth is at a comfortable height for you to work i.e. at a little above elbow height. You should not have to stoop or twist your back while working at the chairside.

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Step 2: Evaluating the laboratory work Evaluate the final models, wax bases and occlusion rims: they should conform to the following guidelines: Final Models

• as primary models BUT land 2-3mm occlusal to deepest part of sulcus, indicating that impression has been boxed.

Occlusion rims

• occlusal rim should conform to the shape of the expected tooth arch, not the crest of the alveolar ridge, but should also conform to the neutral zone

• width of occlusal rim: anteriorly 5mm premolar area 8mm molar area 10mm

• labially upper rim should be 8mm anterior to the centre of the incisive papilla • height of upper occlusal rim: 8mm from the crest of the alveolar ridge anteriorly,

less posteriorly • height of lower occlusal rim: level with base of retromolar pad, slightly higher

anteriorly, parallel to the ridge, • length of occlusal rims: to the distal of the first molars only.

Wax base:

• good tissue detail present on the fitting surface of the wax • wire strengtheners in the palate and lingual flange • accurate reproduction of the sulcus depth and width in wax, with adequate relief for

the frena • no blackened, pitted areas or presence of fingerprints indicating a thin or stretched

area due to overheating • no instability, that is rocking or movement on the cast • no areas of excess material beyond the land of the model • no air bubbles trapped in wax • no wax residues on fitting area

Acrylic base:

• correctly trimmed and finished without damage to peripheries • clear acrylic, polished except where occlusion rims attached • fitting surface clean and free of surface blebs, pimples, etc

Step 3: Intra-oral evaluation of fit Wax base: Evaluate the fit of the wax bases. They should extend to the full depth and width of the sulcus as recorded by the final impression. If they do, but there is no retention, proceed to Step 4. If after adding a posterior palatal seal the base is still not retentive, the peripheries must be carefully adjusted by reducing the height and/or the width until the base is self-retentive. Record these alterations and, with the assistance of your supervisor, alter the models accordingly, by adding plaster where necessary. This is necessary because you cannot expect the dental technician to do this, and so therefore your final base will be over-extended.

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Acrylic base: The fitting surface of each base must first be assessed separately. In the upper, place a thin layer of pressure indicating material over the posterior border, midpalatal suture area, the inner surface of the tuberosity flange, and the areas where the stops were placed. Seat the base (on its own) and exert pressure on the occlusal rim, on both sides of the arch. Remove the base and relieve any areas of excessive pressure. If the patient experienced any discomfort, place pressure-indicating material over the indicated area and repeat. Now examine the periphery of the denture for any under- or over- extension. Over-extended areas can be detected visually or by use of pressure indicating paste. Under-extended areas will be obvious by their contribution to a lack of retention because of loss of peripheral seal. These areas can be corrected by the addition of green stick – if retention is improved then the green stick can be replaced with self- curing acrylic after pouring a suitable model. The lower denture is then placed by itself, but with a layer of pressure indicating material over the entire fitting surface and periphery. Once again, check for, and adjust, areas of excessive pressure or incorrect peripheral extension. Step 4: Posterior palatal seal (post dam) The objective of the posterior seal is to produce a physiological displacement of the tissues at the posterior border of the denture. This is determined by palpation and by identifying the vibrating line. First palpate in the region of the expected posterior border of the denture near the fovea palatinae in the mid line, and identify the attachment of the muscles of the soft palate to the posterior nasal spine of the hard palate. Mark this with a small dot using a marking stick. Now ask the patient to say “ah” in order to identify the vibrating line of the soft palate and place another small dot there. If you find this hard to identify, place a series of dots posterior to the first one, ask the patient to say “ah” again and find the most posterior dot that does not move. Now connect this dot with the hamular notch on each side, and this line will become the posterior border of the denture. Ask your supervisor to check this before proceeding. Wax base: Place the base in the mouth to pick up the mark of the marking stick, and place on the model, to transfer this mark to the model. Define the mark on the model, and trim the base so that it does not extend beyond this line. Wet the model and scrape the model along this line using an Ash No.5 (preferably) or a Le Cron carver. Do not scrape the model excessively – at the most 1.5mm. Now you must judge the amount of displacement the tissues in the area anterior to this line can tolerate. You must use your judgment to reproduce the shape and amount of displacement required to produce a seal. So go back to the mouth, and with the end of the handle of a mouth mirror, palpate the tissues. You will probably find that the mid-line raphe is not displaceable because of the very thin layer of mucosa over the bone, with no sub-mucosal layer, but the area between that and the tuberosities has much glandular tissue in the sub-mucosa. So the postdam becomes an area of displacement, very shallow at first towards the anterior, and gradually deepening to the posterior border. Creating an area in this manner allows for the displacement of the tissues of the palate before the vibrating line is reached, and also means that if the base is made slightly too long, it can be shortened without affecting the seal, as there will still be a displacement of the tissues.

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When completed, lubricate the posterior palatal seal area on the model with liquid soap, soften the posterior border of the wax base by holding above the flame of the Bunsen burner, and adapt it to the adjusted model by pressing into the scraped-away and lubricated area. If necessary, add wax to the base to obtain a good adaptation. Acrylic base: Place the base in the mouth to assess the extension of the base to the line marked by the indelible marking stick. If it extends beyond the line, trim the base; if it is short of the line, add green stick to extend the base to the line. Soften green stick compound, and apply a line of compound to the posterior border of the base, from hamular notch to hamular notch, not extending the base any further, but onto the fitting surface of the posterior border. Temper in hot water at the correct working temperature, place in the mouth, and press firmly on the occlusal rims. Test the retention of the base. Remove from the mouth, and assess: the compound should have a dull appearance, and its shape will have been dictated by the amount of displaceable tissues along the vibrating line. If satisfactory, trim back to the vibrating line, if it has extended beyond this. Leave this in place throughout the jaw registration procedure; it will be replaced with self-cure acrylic in the laboratory by pouring a model, removing the green stick, and replacing with acrylic. The master model will then be cut back in this area, and built up again if necessary (not usually). Step 5: Tissue support Place the upper base in the mouth and evaluate the tissue support provided by the labial and buccal surfaces of the occlusal rim. It is often stated that the philtrum of the upper lip should be at a right angle to the columella of the nose, but this varies with ethnicity and is also related to the shape and tonicity of the patient's lips. If the lip appears unnatural, bulky or stretched, reduce the amount of wax on the labial surface of the occlusal rim. Conversely, if the lip appears wrinkled or fallen in, add wax to the labial surface until the lip looks natural and supported. Beware of an appearance that shows the lip to be bulky but convex. This is often due to insufficient lip support at the lower third of the rim, because the angulation of the rim is incorrect. Do not be tempted to remove wax from the periphery without being sure that the angulation of the rim mimics that of the teeth. If the modiolus needs lifting, add wax buccally. Do not proceed to the next stage until the tissue support is correct, as this will be the guide for placing the anterior teeth (of course the very best procedure is to place the anterior teeth at the chairside). Step 6: Incisal height Scribe a line on the occlusal rim to record the incisal edge position: it will be no more than 1mm below the resting lip position, but can be much higher, especially in older patients, and those with a high smiling line. Ask the patient to smile as broadly as possible. This will give you an indication of the amount of room for the teeth, and enable you to estimate the position of the incisal edges of the upper teeth. Scribe another line which will follow this high smile (or lip) line.

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Remove the base and trim the excess wax to the scribed line of the incisal edges. This must be horizontal when viewed from the front of the patient with the patient’s head upright, i.e. with Frankfort Plane parallel to the floor, and should appear to be parallel with the upper lip, although often compromises have to be made. Step 7: Occlusal plane and position of neutrality Replace the base in the mouth and use a Fox plate to check and adjust the levels of the occlusal plane when viewed from the side, using the ala-tragus line (Camper's plane - centre of tragus to centre of ala) as a guide. Remember that this is a guide only, and not fixed. When viewed from the front, the anterior occlusal plane should appear horizontal. Older text-books will advocate the use of the inter-pupillary line but there is absolutely no evidence that this bears any relationship to the occlusal plane. If the ala-tragal line gives the appearance that the occlusal plane is too steep or too flat when viewed from all angles, use your judgement (and that of your supervisor) to adjust it accordingly. Another guide is to ask the patient to close the mandible in a retruded position, and assess if the plane is approximately parallel to the lower ridge. When adjusting the rim, you can either use a heated wax knife, drawn flat across the rim, or a paint scraper. The latter is easier, but it takes experience to get it to the best temperature. Ideally, the wax of the occlusal rim should only melt once you use pressure against the paint scraper, so heat the scraper first, then place it blade down, at an angle to the work surface, so that the handle rests against the back, at a 45° angle. Then press the rim against the scraper, using selective pressure to take more or less wax away. Once you (and your supervisor) are happy with the level and orientation of the rim, scribe a line that will indicate the centre line of the teeth. Once again, you may read in older text-books that this should be coincident with the centre of the face, and see pictures of clinicians using dental floss to try to find out just where this is. But the clinical evidence is that more than 80% of dentate patients have a centre line coincident with the centre of the mouth, not the face, so rather use that as your guide. Also record the corners of the mouth, to assist in the selection of the artificial teeth. As you gain more experience, you will find that a far easier way of verifying the correct position of the anterior teeth, is by setting them up at the chairside. Senior students should attempt this. Place the lower base in the mouth, and assess the lower occlusal rim. Its height should extend from the corners of the mouth to no more than half-way up the retro-molar pads, and parallel to the lower ridge. Some clinicians advocate that the occlusal plane should rather be determined by these guides, especially the height as being at the corner of the mouth, and that the upper rim should then be trimmed to the lower. This has some logic, as it relates the occlusal plane to the lower ridge. In some of your cases, you should try this, but in reality experienced clinicians naturally seek an occlusal plane that does this, whether using the upper or the lower. If the lower wax rim extends beyond the position of the first molars, trim it away entirely, as it will impinge on the posterior borders of the upper rim. Then adjust and trim the rim bucco-lingually into a position of neutrality between the tongue and cheeks. If using acrylic bases, be sure that the posterior extension of the lower base does not interfere with the posterior extension of the upper base.

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Step 8: Terminal hinge movements Practise with your patient the movements required of the mandible, to obtain a pure hinge action, indicating that the mandible has moved along the terminal hinge pathway. There is a variety of methods to do this, the most satisfactory being with a gentle guidance from the operator, holding the lower base in position (you may find it useful to make a small ‘step’ on either side of the base at about the premolar area to help you locate your finger tips to be sure that the lower base does not move). Patients who have difficulty allowing for the required amount of muscle relaxation may find it useful to place the tip of their tongue in contact with the posterior border of the upper base, or in contact with a small bead of wax placed on this posterior border. Interestingly, asking the patient to push their top jaw forward can have the effect of retruding the mandible! Step 9: Vertical dimensions

Resting vertical dimension (Resting facial height)

With only the upper base in the mouth, measure the facial height of the patient at the rest position. The measurement is made by using a Willis Gauge in a manner that will produce consistent results for you. The measurement will not be the same for all clinicians but will be unique to you. Now place the lower record block in position and add or remove wax from the occlusal rim of the lower until the facial height at rest with the one base in position is equal to the height with both occlusal rims in contact. This contact should be after the jaw closes along the terminal hinge pathway. The addition or removal of wax from the rim of the lower should be done such that even contact is maintained between the upper and lower occlusal rims throughout. You may find it necessary to reduce the lower rim excessively (but evenly), and then add a softened rim of wax onto which the patient can close, again to the position where you judge the resting (or occlusal) vertical dimension to be. If you do this, remember to soften the wax correctly (slowly and evenly with no cracking), and to place a thin layer of Vaseline over it before placing in the patient’s mouth. Occlusal vertical dimension (Occlusal facial height)

The occlusal vertical dimension is normally 3mm less than the resting facial height (unless you have determined it to be different, such as when using previous dentures as a guide). This is the inter-occlusal clearance or freeway space, which is present in dentate subjects when the jaw is at rest. To reproduce the freeway space in the edentulous patient it is necessary to reduce the lower occlusal rim by 3mm. Now if both the trial bases are positioned in the mouth and the patient is asked to reproduce the rest position, there should be a gap between the rims of the upper and lower trial bases. This is the freeway space or inter-occlusal clearance. Test the proposed vertical height of occlusion in the following way: 1. Measure the difference between the resting vertical dimension and occlusal vertical

dimension – the freeway space. This measurement (the difference) will be the same for all operators. When using the Willis gauge, keep the gauge in position without moving the upper part that contacts the patient at the naso-labial fold, when measuring the resting and the occlusal vertical dimensions.

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2. Assess the patient's appearance: note the profile and peri-oral muscular activity, especially that of mentalis. Note the change in profile and peri-oral muscular activity between the resting position and the occlusal position. This is probably the best way of determining that you have sufficient inter-occlusal space.

3. Compare with the previous denture if available by measuring the inter-alveolar distance

with a figure-of-eight gauge. Do not decrease the free-way space by more than 3-4mm if the patient previously had a freeway space greater than that, as they will not be able to adapt to such a large change.

Step 10: Horizontal relationships and jaw relation recording Remove a block of a further ±3 mm of wax from the first premolar area posteriorly, leaving only an anterior segment to maintain the accepted vertical height of occlusion. Do NOT just remove wax to make a ‘step’ in the posterior region: remove wax all the way back. Cut two key-ways on each side into the opposite posterior segments of the upper occlusal rim. These key-ways should have vertical walls anteriorly, and should have divergent vee-shapes on each side; the vertical anterior wall prevents anterior movement of the lower, and the divergent vee-shapes prevent lateral movement. Place the upper base in the mouth. Place paper towels around the Bunsen burner, and thoroughly soften a strip of Alminax above and then in the flame until it is floppy and dripping on both sides (do not allow wax to drip into or on the Bunsen!). Never soften Alminax in hot water (forms a scum and does not soften properly) and never use a wax knife (does not soften evenly). Place a small elongated pyramid of wax onto each posterior segment on the lower occlusal rim where you removed wax, so that it just protrudes above the height of the rim. Lightly lubricate (use Vaseline) this pyramid of wax, place in the mouth and, guiding the mandible into a retruded position, ask the patient to close slowly until the anterior record blocks touch. Guide the patient up and down along this terminal hinge pathway repeatedly for five or six movements as the wax cools and hardens. In this way you will be assured of a repeatable action into and out of centric relation position. Remove from the mouth and immediately seal the edges of the Alminax, without affecting the recorded surface indentations. Cool thoroughly under a stream of cold water. Step 11: Assess the recording Outside the mouth, place the two record blocks together. Reject the record just made if: 1. The posterior flanges of the bases are touching. 2. The grey wax extends onto the surface of the pink wax. 3. The occlusal rims are not well localised against each other. Return the bases to the mouth. Reject the jaw registration if: 1. On repeated closure the grey wax record fails to correspond to the key-ways. 2. On closing together there is any perceptible shift of either base 3. On further assessment the vertical height of occlusion is incorrect.

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Measure the inter-alveolar distance (IAD) on the record blocks when held together, at the incisive papilla and at the first molar region, using a figure-of-eight gauge. Compare these figures with any planned IAD changes you may have recorded as part of your treatment plan. Record these IADs in the patient's file and on the laboratory card. Note: If the inter-alveolar distance is 10-12mm, then the occlusal plane will be at a

vertical height that will compromise the setting of the teeth, simply because there is insufficient room for them. In this case, the occlusal plane must be placed mid-way between the upper and lower ridges, but maintaining the plane parallel to that indicated by the upper occlusal rim.

Step 12: Tooth selection Shade selection: the colour of tooth substance is basically yellow. The addition of red tones makes them warmer, and the addition of blue makes them cooler. In order to produce a life-like appearance, the teeth selected should have warmer tones. The colour of natural teeth is due to the underlying dentine shining through the translucent enamel. As more secondary dentine is laid down with advancing years, the shade darkens. Using the shade guide, select one or two shades you believe would suit your patient. Use natural light wherever possible, and examine the chosen shades close to the patient's lips. The shade should be appropriate for their complexion and suit their age. Discuss your choice of shade with your patient. Listen to his or her views on shade preference, and should this differ from your selection, be prepared to alter your selection within reason. After all, beauty is in the eye of the beholder – and it is the patient who will be wearing the dentures, not you. The mould – size and shape – of the teeth: there are some guidelines that have been suggested in the literature (and followed slavishly by the tooth manufacturers) concerning the selection of tooth size and shape, but they have mostly been conjecture. The most commonly heard one is that there is a correlation between the shape of the upper central incisors and the shape of the inverted face: it has been shown, however, that there is absolutely no scientific basis for this assertion. But you will find that as you gain experience you will rely less on guidelines, and more on your experience and the patient's requests and input about their desired appearance with the new dentures. And don’t forget that you did ask them to bring in a photograph of themselves smiling (when (because?) they had their own teeth), so if this is available, you will understand how useful it can be. So, choose a mould size suited to the arch size, mouth size, overall characteristics of the patient, and/or related to the previous denture. Preferably, choose two moulds which you believe would be suitable for the patient, and then allow the patient to make the final choice. If they are obviously unhappy with the choices recommended, you may have to accede to their request (which is often for smaller, whiter teeth). Together with your supervisor, decide on the occlusal scheme you are going to use. In 3rd year you will use cusped articulation, and probably also in 4th year; however in 5th year we recommend using a lingualised occlusion. Record the mould and shade, and the occlusal scheme to be used on the patient's file as well as on the laboratory card.

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Step 13: Record keeping Record the procedure in the patient's file, sign the file, and obtain the signature of your supervisor. Make out a laboratory card, and again obtain the signature of your supervisor. Make the next appointment with your patient. Then discuss the clinical mark with your Supervisor. You should first assess yourself, and suggest the mark you deem most appropriate to your performance, and reach consensus with your supervisor. Step 14: Disinfection The record blocks (wax bases and occlusion rims) and the master casts must be disinfected in the surgery, before transport to the laboratory. The artificial tooth shade guides must be disinfected if they have been in contact with the patient’s saliva, or touched with your contaminated gloves. Step 15: Clean up Thoroughly clean up the clinical area, leaving it as you would expect to find it. Note re. difficulty recording consistent centric relation position: Some patients find it extremely difficult to allow themselves to be manipulated into a consistent closing pathway. If this is the case, try to make the recording at the most distal horizontal position of the mandible to the maxillae. Then, do not add posterior teeth to the lower trial base, but rather make the lower trial base with the six anterior teeth and another record block for the posteriors. At the next appointment you will be able to verify the position of the anterior teeth, and re-record centric.

4.1 ADDITIONAL PROCEDURES: SEMI-ADJUSTABLE ARTICULATOR When a semi-adjustable articulator is used, then after step 12, a face-bow recording is made. Protrusive bites are not made at this stage, as they often tend to distort the Alminax indices. Therefore set the articulator to average values for the next stage. Use of the Spring Bow Step 1: Patient information The first step is to explain to the patient just what it is you are going to be doing, as this is quite awkward for the patient, and they need to understand their role in the procedure, in particular to help stabilise the upper base. Step 2: Placing the bite fork The bite fork is used to secure the upper base, but also to help ensure that the occlusal plane orientation is also transferred to the articulator. For this reason, the prongs of the fork are used on to the outside of the rim, and not as a locating wax bite on the occlusal surface of the rim as in a dentate patient. Do not use the bite fork in that manner.

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Place the upper base with the rim on a flat surface, and slide the bite fork towards it and adjust the arms of the bite fork so that they will be just slightly narrower at their tips, than the buccal surface of the rim. The curvature of the anterior part of the fork must be to your right. Then heat the tips of the arms, and the two points anteriorly. All these parts will penetrate the buccal and labial surfaces of the rim. Slide the fork over the rim so that they do penetrate the wax of the rim, but ensure at the same time, that the horizontal part of the fork remains parallel with the rim. Secure the tips of the arms and the anterior points to the wax of the rim with sticky wax, and cool thoroughly. Insert the upper base into the patient’s mouth. As you view the fork from the front, its horizontal portion should be just that – horizontal and parallel to the occlusal plane and Frankfort plane. Step 3: Preparatory procedures Prepare the spring bow by ensuring that the bite fork assembly is in the correct position with the tightening screws numbered 1 and 2 facing you and no.3 facing right. Also ensure that the occlusal plane indicator is flush with the left side of the face bow. The screws each help orientate the bow in a different plane: screw 1 allows for the bow to be the correct height, as determined by the orbital plane indicator; screw 2 ensures that the bow is centred correctly, in line with the centre-line of the occlusal rim; and screw 3 positions the bow antero-posteriorly according to the patients external auditory meatus, and also horizontally to Frankfort plane (as patient’s ears are usually not parallel to this!). A final preparatory action is to palpate beneath the patient’s left eye, for the infra-orbital notch. You need to know where this is, for when you locate the bow vertically (see below). Step 4: Locating the spring bow Now insert the upper base with the bite fork into the patient’s mouth, and either (and preferably) ask the patient to hold it in place with the forefinger of their right hand, or place the lower base in the mouth and ask the patient to close into your previously recorded jaw relation record. This is to ensure that the upper base does not move during the rest of the procedure. Place the spring bow so that the ear pieces are opposite the patient’s temples, and slide the bite fork assembly onto the extension of the bite fork where tightening screw no.3 is. As you do this, pull the arms of the bow apart and guide them gently into the patient’s external auditory meatus on each side. This is why the bow is called a spring bow, to enable you to pull the arms apart in order to get the ear pieces located. Now swing the orbital plane indicator over and raise or lower the bow (where screw 1 is) so that the indicator is opposite the infra-orbital notch. Now tighten screw 1 gently. Next, slide the bow to the left or right (where screw 2 is) until its centre is in line with the centre-line of the occlusal rim and tighten screw 2 gently. Finally, view the bow from the front, and make it horizontal and parallel to the occlusal plane, and then tighten screw no.3 gently. Check that each aspect of the bow is correctly positioned, and then tighten each of the screws in turn again, as far as you can. Give a final check that nothing untoward happened during this last tightening, and then loosen the screw retaining the bite fork assembly to the bow, and lift the bow away whilst at the same time releasing the arms from the patient’s ears. All this time, the patient is still holding the upper base in place (or biting on the

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bases). Then release the upper base, which will come away attached now to the entire bite fork assembly. Step 5: Record keeping Record the procedure in the patient's file, sign the file, and obtain the signature of your supervisor. Make out a laboratory card, and again obtain the signature of your supervisor. Make the next appointment with your patient. Then discuss the clinical mark with your Supervisor. You should first assess yourself, and suggest the mark you deem most appropriate to your performance, and reach consensus with your supervisor. Step 6: Disinfection The record blocks (wax bases and occlusion rims) and the master casts must be disinfected in the surgery, before transport to the laboratory, as well as the bite fork assembly (wipe down with disinfectant) and the ear pieces must be removed and also disinfected. Step 7: Clean up Thoroughly clean up the clinical area, leaving it as you would expect to find it.

4.2 ADDITIONAL PROCEDURES: USE OF ANTERIOR TEETH AND BIOMETRIC GUIDES FOR DETERMINNG THE OCCLUSAL PLANE

At the final impression stage, you will have already selected the shade and mould of the teeth to be use, and so at the jaw relations stage the occlusal rims will be returned you together with the 6 upper anterior teeth. Proceed as for the first four steps of the procedure as per section 4 above. Step 5: Incisal height and positioning the upper anteriors At this stage it is now necessary to determine the incisal height and to quickly trim the occlusal rim to that height. It is not necessary to trim the rim to conform to any guides, as we will be using biometric guides to determine the height and orientation of the occlusal plane. Once you are satisfied that you have approximately the right height, then trim the labial contour of the rim to approximate the labial surfaces of the teeth. Do this fairly roughly and quickly, until you have a natural appearance to the patient’s lip. Now identify the centre line as usually being the centre of the mouth. Remove a small amount of wax to one side of this line, and now start placing the appropriate central incisor, in the same manner as you have learnt in the laboratory. The great advantage of doing this at the chairside is that you can continually check the appearance by placing the base back in the patient’s mouth. Do not worry about the appearance of the wax at this stage, but obviously try to work neatly. Your supervisor will assist you and show the easiest ways of setting the teeth first.

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Once you are satisfied with the appearance, allow the patient to see the results and to comment on them, and make any further adjustments if necessary. Reassure the patient that they will have a further opportunity at the next visit to comment again and to see the bases with all the teeth present. Step 6: Vertical dimensions Please refer again to Step 9 in section 4. The difference here is that you need to adjust the lower occlusal rim so that it does not interfere with the newly set upper teeth, as you determine the vertical dimension of occlusion (VDO). Do not worry about the orientation of rim, and trim it until there is contact on either side of the arch with the upper rim posteriorly, and with the incisal edges of the upper teeth anteriorly, at your determined VDO. Step 7: Horizontal relationships and jaw relation recording Please also refer to step 10 in section 4. The procedure is exactly the same, except that here, the contact of the upper incisors to the anterior part of the lower rim becomes your guide as to the correct vertical. It is often useful, though, to also place a thin layer of Alminax on the anterior part of the rim to be penetrated by the maxillary incisors. This gives a three part location: the incisor edges anteriorly and the keyways of the upper posteriorly. Assess the recording for reproducibility in the normal manner, decide on the occlusal scheme to be used (see end of step 12 in section 4) and then follow steps 13 to 15 in section 4. Setting the remaining teeth Although this takes place in the laboratory, it is described here so that you understand how it differs from the procedures described in section 4. Mandibular anterior teeth. In general, teeth are located on dentures close to the position occupied by the healthy natural teeth, although occasionally the mandibular incisors are located more towards the tongue to enhance the stability of the denture. The six lower anterior teeth should match the size, shape and colour of the maxillary teeth as recommended by the tooth manufacturers. Horizontal position: the skeletal relationship of the mandible to the maxilla determines how much the upper incisors protrude past the incisal edge of the lower incisors when the lower jaw is occluding at rest. In a Class I relationship the upper incisors protrude very slightly, in a Class II relationship they will protrude more substantially, whereas in a Class III relationship they protrude or at least contact the incisal edge of the upper incisors. In any event, the labial surface of the lower incisors should not protrude beyond the labial sulcus, and a vertical tangent dropped from the labial surface should extenn into but not beyond the sulcus. This horizontal limit applies even in a severe Class II jaw relationship with a large overjet of the maxilla, unless, of course, the patient insists that the aesthetic advantages of protruding incisors are more valuable than the stability of the lower denture.

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Furthermore, an incisor looks more natural if it is tilted horizontally to create the illusion that it has a root imbedded in alveolar bone. Vertical position: The articulator will guide movements of the casts with the average inclinations of both condyles (30o) and of the incisal platform and pin (10o). Therefore, with the lower incisors aligned horizontally within the limits of the labial sulcus, the wax is softened and the lower teeth brought into contact with the incisal edge of the upper incisors as the mandibular cast protrudes with the guiding pin remaining in contact with the anterior platform. The lower canines can be modified on each side in a similar way to provide contact in eccentric movements. In a Class III relationship, the mandibular incisors are raised to the incisal edges of the upper teeth without concern for eccentric movements. Lower posterior teeth and the occlusal plane The following approach to arranging posterior teeth is based on the principles of: 1) full cusp to fossa contact in the most relaxed and retruded (centric relation) position of the mandible; and 2) at least three points of contact involving incisors and molars between the upper and lower dentures as the mandible moves horizontally. The upper anterior teeth have been arranged to satisfy the aesthetic expectations of the patient. The mandibular incisors and canines were arranged to contact the upper teeth and within the limits of the labial sulcus when the articulator moves the lower cast forward. Consequently, we have established the position of the occlusal plain as the incisal edge of the lower anterior teeth. The retromolar pad lies naturally close to the occlusal surface of the molar teeth, and represents the posterior landmark for the height of the occlusal plane when the natural teeth are missing. Therefore, the molar and premolar teeth are arranged bilaterally on the denture base so that their occlusal cusps touch the occlusal plane between the incisal edge of the lower canines and the middle of the retromolar pads. The teeth are arranged vertically to the occlusal plane and horizontally with the central grooves of the molars and premolars aligned with the crest of the residual ridge. Upper posterior teeth The premolars and molars are arranged on the upper occlusal rim to occlude uniformly with the mandibular teeth but with at least a 1mm overjet to minimise the risk of cheek-biting. They can be arranged with a conventional occlusal overjet or in crossbite depending upon the shape and relative position of the residual ridges. The posterior teeth must not be aligned edge-to-edge because the risk of cheek-biting is increased when there is insufficient overjet of the cusps.

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5. TRY-IN PROCEDURES Definition A try-in is a clinical procedure in which the trial dentures are assessed in order to determine any and all changes or adjustments that are required before the dentures are processed and finished. Objectives 1. To evaluate the records taken at the previous visit. 2. To evaluate and modify the position and arrangement of the teeth until the functional

and aesthetic features of the dentition are satisfactory. Requirements this manual examination set and prosthetics set kidney dish cup of water for patient, bib and bib chain pink modelling wax Alminax hand mirror for patient student’s instrumentation set Step 1: Trial denture evaluation Evaluate the trial dentures: they should conform to the following guidelines: • models are articulated correctly and neatly, and they and the articulator are free of

extraneous wax and plaster • teeth are placed where the original teeth were most likely to have been, so that the arch

form should follow the original arch of the teeth, and be in a position of neutrality • on average: - upper anteriors are 8-10mm anterior to the incisive papilla

- incisal inclination is related to the anterior ridge inclination – it is helpful to imagine the roots of the teeth: they must have come from the bone!

- a tangent to the labial surface of the lower incisors passes through the sulcus

- a perpendicular through the buccal cusp of the lower first molar meets the buccal side of the crest of the ridge

• generally only the lower premolars are set directly over the ridge, because of the pattern of resorption

• teeth are set according to compensating curves • external surfaces have the correct contours • wax gingival margins are correctly festooned around the necks of the teeth, there is no

wax on the teeth or occlusal surfaces, and the wax is smooth, with no blackened areas. • there is maximal intercuspal or cusp to fossa contact in centric occlusion If you made the trial bases yourself, have them assessed by your supervisor, as this will contribute to your try-in mark and your session mark.

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Step 2: Assessment on the articulator On the articulator, look at the arch form (size and symmetry). Remove both trial dentures and look at the arch position relative to the residual ridge. Replace the lower denture on the articulator and look at the occlusal plane height and occlusal curves. Replace the upper denture and look at the relationship of the incisors, canines, premolars and molars in the intercuspal position. Look at the aesthetic appeal of the set-up (if carried out by an outside laboratory it is likely to be stereotyped). Measure the IAD with figure-of-eight callipers and compare it with the previous record. Make sure that the trial bases are well finished and free of sharp edges and rough surfaces. Ensure that the flanges extend into the full depth and width of the sulcus. Compare the trial denture with the patient’s denture and determine whether any planned similarities or differences have been attained. If using a lingualised occlusion scheme check to see that the teeth have been set correctly, with the posterior teeth opposite each other, and with the mandibular teeth correctly adjusted for cusp to fossa contact with not contact of buccal cusps. Step 3: Assessment in the mouth Place the upper trial base in the mouth (without the lower) and check the tissue support, occlusal plane, and centre line. Measure the resting facial height. Assess the posterior arch form by viewing the contact of the teeth against the cheek with the mouth half open (they should contact lightly), and when the patient smiles (there should not be an excessive amount of pink wax showing, and there should be a buccal corridor visible). Place the lower trial base in the mouth and check the lip support and occlusal plane, and assess the posterior arch form by viewing the contact of the teeth against the cheek (they should contact lightly). Check the position of the tongue relative to the arch form and the height of the occlusal plane (should coincide with the corners of the mouth). All these indicators assist in determining that the teeth are in the neutral zone. Examine the occlusal contacts when the patient closes with the jaw in a retruded contact (RC) position. Measure the vertical height of occlusion and assess the freeway space. If there is maximum possible intercuspation in the RC position and the vertical height of occlusion is acceptable, go to Step 5. When using a lingualised occlusion, check the appearance of the uppers in terms of their inclination, and that the lower occlusal surfaces have been appropriately adjusted for balance. If using a semi-adjustable articulator, take three protrusive bites (see section 5.1 below) and adjust the articulator settings before proceeding to the next steps.

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Step 4: Jaw relationship If the teeth do not intercuspate evenly or if the vertical dimension of occlusion is unsuitable the jaw registration must be made again. If the freeway space must be reduced, soften a thin strip of Alminax (you can also use pink wax), place over the posterior teeth, and record the jaw registration again at the correct occlusal vertical dimension. If the freeway space must be increased, the jaw relation must be re-taken using Alminax. In order to accommodate the Alminax the lower posterior teeth will have to be removed from the trial denture. Record the jaw registration by using the Alminax in the same manner as in the previous visit. Any corrections in arch form, occlusal plane, centre line etc, should be noted. Step 5: Phonetics Ask the patient to count from 60 to 70, or to use words with “S” sounds. Stand in front of the patient and observe to see that there is clearance of the incisor teeth during the making of these sibilant sounds. Ask the patient to say “fifty-five”. Stand to the side of the patient and make sure that the upper teeth are touching the mucosal border of the lower lip when “F” and “V” are pronounced. Step 6: Appearance The appearance of the new dentures is probably a main concern of the patient, so pay as much attention to the aesthetics as you do to important physiological features, such as the centric relation, vertical dimension of occlusion and the neutral zone. Evaluate the following points carefully: • Ensure that the midline of the teeth coincides with the midline of the mouth, and is not

slanted. Remember that is only a guide, and you and your patient may wish to modify it.

• The maxillary anterior teeth should support the upper lip in such a manner that it looks natural. Avoid a stretched appearance with obliteration of the nasiolabial fold and distortion of the philtrum.

• The modiolus should be correctly supported by the thickness of the buccal flange. • The size, mould and shape of the anterior teeth should harmonise with the patient’s

facial features and age. • Evaluate the degree of maxillary and mandibular tooth display at rest and when the

patient smiles or speaks. • Compare the patient’s appearance with records such as old photographs and models. • Aesthetics may be improved by irregular setting of anterior teeth and judicious

grinding to simulate attrition. Make slight modifications to an even arrangement, consulting with the patient all the time. This is a fun time for both of you, and you will be surprised at how a dull and artificial arrangement of teeth can be improved with relatively minor changes to the arrangement of the anterior teeth. Consider a slight gap behind the upper canines, as the first premolars tend to contrast sharply and easily look artificial.

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• Remove wax from the necks of the teeth so that the tooth is visible and recognisable as an independent component of the whole dentition. Use dental floss between the teeth to remove any excess wax

• Obtain formal acceptance of the appearance from the patient. It is helpful if a member of the family or a close friend is present to assist in the evaluation of the patient’s appearance. Emphasise that changes to tooth colour, size, shape and position cannot be made once the denture has been processed.

Finally, if the patient had previous dentures, compare your trial dentures with those, to ensure that any planned changes have in fact been effected. Step 7: Disinfection The trial bases and mounted master casts must be disinfected before transport to the laboratory. The articulator should be wiped down with surface disinfectant, as you would clean your working surfaces. Step 8: Record keeping and clean up If there has been a problem with the trial denture, book the patient’s next appointment for a re-try, when the procedures described here will be repeated. If the try-in has been satisfactory and the denture is to be processed, book your patient’s next appointment for delivery of the dentures. Ask for the finished dentures to be returned on remount models. Remind the patient, if they have not already paid for the teeth, that they will be required to pay for the treatment before they can receive the dentures. Follow the usual procedures for recording the details in the patient file and on the laboratory card, obtaining the required signatures and marks, and cleaning up the surgery.

5.1 ADDITIONAL PROCEDURES: SEMI-ADJUSTABLE ARTICULATOR When using a semi-adjustable articulator, after step 3 make three protrusive records and adjust the articulator accordingly. Step 1: Protrusive bites The objective of a protrusive bite is to record the spatial relationship of the mandible to the maxillae when the patient has moved the mandible forwards. As this is only a spatial relationship, no tooth contact must occur. This relationship will then be used to set the condylar guidance angles of the articulator. The articulator has a limit of movement in protrusive of 10mm so it is important that patients with Class II jaw relationships in which there is a large overjet, do not protrude more than 8mm. For most patients, a protrusion to an edge-to-edge incisor relationship will not exceed this 8mm limit. Practise this movement with the patient first: they must protrude their jaw as far as this but keeping the upper and lower centre-lines aligned.

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Place the upper base in the patient’s mouth. Soften a sheet of pink wax along is length, softening half of the width. Then fold over the edge twice making these folds round, and cut off from the remainder of the sheet. Place this softened round over the posterior teeth of the lower base, cutting it if too long. Smear a thin layer of Vaseline over the wax, and place in the mouth. Instruct the patient to perform the protrusion you have already rehearsed with them and to close gently into the wax. Tooth indentations are required, but the patient must not bite through the wax. Instruct the patient to stop when the correct position has been achieved, and to remain in that position. Then soften another sheet of wax in precisely the same way, and take another bite, and then another. The reason for making three bites, is that this is a difficult procedure for many patients, and they often move their jaw to one side, or bite too hard, etc. Therefore take the reading of the two which are most consistent. Step 2: Adjusting the articulator Replace both bases on the articulator, and loosen the holding screws for the condylar guidances. Place a protrusive bite on to the lowers and make sure it fits properly. Then manipulate the upper member of the articulator until the upper teeth more or less fit into the bite. Do this gently, so as not to distort the bite. Now, holding the upper member of the articulator, alter the condylar guidance of one side upwards and downwards so that you can see the upper teeth rocking into and out of the indentations on the wax bite. Gradually reduce the movements of the condylar guidance until the upper teeth fit snugly into their indentations and tighten the condylar guidance screw. Repeat for the opposite side and then repeat all this for each of the other bites. Then call your supervisor, and ask the supervisor to independently do this, to verify the readings you obtained. When you are both satisfied with the condylar guidance angles, scribe these into the plaster mounting of the upper model, as the articulator may be used for another case. Calculate the Bennet angle from Hanau’s formula (CGA/8+12) and set this.

P Notes «

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6. THE DELIVERY APPOINTMENT LABORATORY PREPARATION Construction of Remounting Casts In order to facilitate remounting and save chairside time, remounting casts are made as follows: • Wipe the fitting surfaces of the dentures with a thin layer of Vaseline. Eliminate the

undercuts in the fitting surface of the dentures by blocking them out with slightly damp pumice or tissue paper.

• Pour the casts in white plaster and trim the casts, allowing the peripheral borders of the dentures to make a groove in the cast of only 1 mm so that they may be easily removed and replaced.

• Wash out the pumice or tissue paper from the inside of the dentures and from the surfaces of the casts.

Remounting the Upper Denture • This is also done to save chairside time during the delivery appointment. Replace the

upper denture on its remount cast and position it on the metal occlusal plane indicator jig (as if you were mounting the upper bite block on the articulator). Attach the remount cast with white plaster to a clean upper mounting plate on the articulator, with the articulator closed and the incisal pin touching the incisal table.

• After the remounting plaster has set, remove the jig from the lower member of the articulator and replace it with a clean mounting plate.

• Remove the upper denture and store both upper and lower dentures in clean cold water until the insertion appointment.

CLINICAL PROCEDURES Definition The delivery appointment is the last stage in denture fabrication, when the new dentures are inserted for the first time. Objectives 1. Evaluation of the dentures prior to insertion to preclude laboratory errors e.g. cracks,

acrylic bubbles etc. 2. Evaluation of the dentures in the mouth and correction of obvious flaws e.g. painful

pressure points, over-extensions, etc. 3. Evaluation and correction of discrepancies in centric and eccentric jaw relations. 4. Evaluation and correction, if necessary, of phonetic and aesthetic features. 5. Counselling and education of the patient in the use of dentures, in cleaning and

caring for them and their mouth at home, and in the type of problems they may encounter with the new dentures. This is especially important for patients who are receiving complete dentures for the first time.

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Instruments and Materials Required This manual Diagnostic set Pressure indicating material Pink wax and Alminax Kingsley scraper Articulator with upper remount model in place Lower plaster of Paris remount model Plaster bowl, spatula and knife Articulating paper Occlusal indicating wax (Kerr's) Indelible marking stick Small brush with stiff bristles Student’s instrument kit in clean container Hand mirror Step 1: Evaluating the laboratory work If you have carried out the laboratory procedures yourself, ask you supervisor to assess the finished dentures and remount models before proceeding. This will contribute to the assessment of your clinical performance for the session. If you were using wax bases, carefully inspect the tissue-fitting surfaces of the denture, the flanges and the borders, to ensure that all sharp irregularities which may irritate the tissue have been removed. Remove all blemishes with a Kingsley scraper before placing the denture. If you were using acrylic bases, proceed to step 3. Step 2: Evaluation of the fitting surfaces Inspect each denture separately in the mouth to check the retention and stability. The fitting surface of each denture must be assessed separately. In the upper denture, place a thin layer of pressure indicating material over the posterior border, midpalatal suture area, the inner surface of the tuberosity flange, and the areas where the stops were placed. The pressure indicating material is applied with a small, stiff brush. Seat the denture (on its own) and exert pressure on both sides of the arch. Areas of acrylic base which will exert excessive pressure will show through the pressure paste. Remove the denture and relieve any area of excessive pressure. Eliminate the pressure areas with an acrylic trimming bur and remove the pressure-indicating material with gauze. If the patient experienced any discomfort, place pressure-indicating material over the indicated area and repeat. Ease the dentures in deeply undercut areas which cause pain during insertion or removal of the dentures. Now examine the periphery of the denture for any under- or over-extension. Over-extended areas can be detected visually or by use of pressure indicating paste. Under-extended areas will be obvious by their contribution to a lack of retention because of loss of peripheral seal. These areas can be corrected by the addition of green stick – if retention is improved then the green stick can be replaced with self-cure acrylic after pouring a suitable model.

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The lower denture is then placed by itself, but with a layer of pressure indicating material over the entire fitting surface and periphery. Once again, check for, and adjust, areas of excessive pressure or incorrect peripheral extension. Only when the fitting surfaces and peripheral extension are correct, are the dentures placed both together in the mouth, in order to adjust the occlusion. Step 3: Evaluation of the occlusion The occlusion of all complete dentures must be perfected before the patient is allowed to wear them. Because of the inaccuracies inherent in the materials and methods used in the fabrication of dentures, the new dentures will not have a perfect occlusion. Place both dentures, and holding the lower denture in position, assist the patient to “close slowly together and stop just when the teeth touch for the first time”. Avoid the use of the word “bite” or its equivalent in the patient’s own language, as the patient will tend to close into a protrusive position, and not the centric relation you wish to achieve! If the patient seems to experience difficulty in retruding the mandible, ask him/her to touch the back of the palate with the tip of the tongue while closing on the back teeth. If the patient is asked to stop closure at the very first contact, the error in occlusion (i.e. premature tooth contact) may be visible. As the patient closes from the first tooth contact to firm closure, you will feel and see the slide of the dentures caused by the prematurity. Step 4: Correction of the occlusion Check bite We advocate the routine use of a check bite and clinical remounting of the denture because of the movements that take place inside the mouth as a result of any occlusal discrepancies. Usually you will find some interferences, but the bite will not be opened more than 2-3mm. If the bite is opened more than this, the lower teeth may have to be removed (see section on open bites, below). Apply a thin layer of Vaseline to the occlusal surfaces of the upper denture and place it in the mouth. The interocclusal record may be taken in Alminax (preferably) or one layer of pink wax. Warm Alminax in the normal way to soften it thoroughly and cut two thin strips from it. Lute them to the occlusal surfaces of the posterior teeth of the dry lower denture. The wax should be soft throughout so that the patient can close evenly, and not slide on any hardened centre of the wax. Remember; do not ever use a wax knife to soften Alminax! Now place the lower denture in the mouth and record the maxillo-mandibular relationship in centric relation, using the same hand positions and methods as described for the jaw relation and try-in stages, but ensuring that closure is stopped before any teeth make contact. Remove the lower denture from the mouth and cool the wax in cold water. In order to check the accuracy of this record, replace the lower denture with the occlusal registration in the mouth. Ask the patient to close in centric relation at least three times. If the teeth close accurately into the indentations on the interocclusal record, without evidence of premature contacts or sliding, the recording may be considered to be correct.

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Re-mount the lower denture and model to the upper denture, on the articulator, using impression plaster, which sets rapidly. The principles of occlusal adjustment remain the same, but the actual procedures differ depending on the occlusal scheme used. Cusped articulation On the articulator, lift or remove the incisal pin, place articulating paper between the teeth, and gently tap the upper member of the articulator down so that the denture teeth are repeatedly tapped together in centric. To grind in any prematurities adjust using a small pear-shaped acrylic bur until there is even contact on all the posterior teeth. The dentures are now ready to be ground into lateral excursions. Place the articulating paper between the teeth and slide the dentures to right and left lateral positions up to the point where the canines are in tip to tip relationship with each other. In protrusion, the incisors should contact edge-to-edge. The aim of grinding in is to achieve a condition of occlusal balance with simultaneous contact of sufficient teeth in eccentric positions. In lateral excursions all the posterior teeth and canines on the working side should be in simultaneous contact, with only the opposite side posterior teeth in balancing contact. In protrusive excursions in Class I and mild Class II occlusions the anterior teeth are in incisal tip contact, while the buccal and lingual cusps of the posterior teeth are in contact. Consult your notes on occlusion for the details of how to adjust the different cuspal inclines to achieve bilateral contacts without affecting the centric contacts and the vertical height. Lingualised occlusion If the teeth have been arranged correctly at the final try-in stage, then only the lower teeth need to be adjusted. Once again, start with centric, and adjust the lower central fossae so that each upper palatal cusp is in contact with its opposite lower tooth. Then, without touching those contacts, adjust for lateral and protrusive contacts. Consult your occlusion notes for the details. Once the occlusion has been adjusted on the articulator, the dentures are inserted again and the occlusion is refined intra-orally. The procedure described below for adjusting minimal interferences can be followed. Minimal occlusal interferences Slight occlusal interferences may be corrected using articulating paper. Adjust according to the usual rules for adjusting a balanced occlusion. After having refined the occlusion with articulating paper, place green (Kerr’s) articulating wax (shiny side down, and wet the occluding, dull surface) on the lower teeth and ask the patient to chew as if chewing gum. Use a marking pencil or indelible stick to mark any areas of uneven contact and adjust accordingly. Also check where the marks meet the opposing teeth, and adjust upper or lower as appropriate, unless using a lingualised occlusion, in which case only the lower teeth are adjusted.

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Open bites Large interferences (>3mm) must also be corrected by re-articulating the denture by means of a check-bite, but in this case, because the interferences are so great, the lower posteriors must be replaced. So grind down the lowers, or remove them in a bloc by grinding all around them with a fissure bur. Then re-take the bite, using Alminax, as per the procedure for a check bite above. Re-articulate, and send to the lab for new posterior teeth to be processed onto the denture. Once the occlusion has been adjusted satisfactorily after any of the above procedures, the fitting surface of the lower must again be checked with pressure indicating paste, when the patient bites naturally. Step 5: Re-evaluation of aesthetics The aesthetics of the denture should be critically re-evaluated during the grinding-in procedure, as, for example, any trimming of the incisal surfaces to simulate attrition, if desired, is most conveniently carried out at this stage. Step 6: Final polishing Carefully polish the occlusal surfaces of the teeth once all the occlusal corrections have been made. Polish any other areas that have been adjusted until they are smooth, rounded and shiny. Step 7: Patient instructions Written instructions on denture care are available in several official languages. These instructions also inform patients about problems that they may experience with the dentures. You should discuss these facts with your patient so that they are prepared for problems, and are not de-motivated or discouraged by them. Both verbal and written instructions in the patient's own language should be given so that the patient may understand precisely how to clean the dentures, when to leave them out and how to store them. Go over these with the patient first, to be sure that they are understood. Step 8: Record keeping and clean up Follow the usual procedures for recording the details in the patient file and for obtaining the required signatures and marks. Ensure that the dentures have been paid for, or that the patient has made suitable arrangements for payment, before allowing them to leave with their new teeth. Make an appointment to see the patient, preferably within a few days, or at the most one week. Try to impress on the patient the importance of reassessment of the dentures after a short period of use. Retain the articulator and the remount models for the dentures, in case they are needed for a further occlusal adjustment. This will save chairside time if a remount is required at the recall appointment. Clean all your instruments of plaster and other materials. Clean your chair and working area and leave it in the condition you would like to find it when you return.

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7. THE RECALL APPOINTMENT Definitions A recall appointment is scheduled after the dentures have been delivered. It will usually be one week after insertion of the dentures for students' patients. However, in practice the recall is usually scheduled earlier. Denture complaints are common amongst patients with new dentures, especially first-time denture wearers. The causes may range from pain to inability to chew, but are usually settled by simple clinical procedures. In contrast, denture failure occurs when the patient rejects the dentures outright, or demonstrates an inability to use them or to adapt to them, even when a reasonable period for adaptation has passed. Objectives 1. To check for any problems associated with the denture and to reassure the patient who

is having difficulties. 2. To ease any discomfort that the patient is experiencing with their new dentures 3. To reinforce denture hygiene and usage. Step 1: Assessment of the patient When the patient is seated in the chair, ask them how they are managing with the new dentures. Some may complain about a number of problems, and others will say they are fine. Do not be discouraged by the patient's complaints, even if they seem to be numerous or unreasonable to you. Be courteous and sympathetic and listen carefully to what they say. Remember that a new set of dentures requires much adaptation before it is completely comfortable. The patient has attended the surgery for several appointments/weeks, and is likely to be anxious for the treatment to succeed. It is important to be able to diagnose the faults in a set of dentures from the symptoms given by the patient. A few careful questions will usually single out the exact cause of the difficulty. It is common to have a patient condemning the dentures in exaggerated generalisations when the cause of the complaint will probably be localised to an interfering cusp or one or two pressure spots. Step 2: Extra-oral assessment The denture should be examined extra-orally to check the hygiene. If it is clear that the patient has been having difficulties cleaning the dentures, reinforce the instructions given at the previous appointment. Step 3: Intra-oral assessment Even if the patient reports that there are no problems, you should remove the dentures and inspect the oral cavity. Some patients are so adaptable that they have inflamed areas or even ulcers, but think that it is nothing to worry about. If such areas are present, then the

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dentures should be adjusted. You should also check the occlusion in centric relation and in eccentric positions so that there is no potential for further inflammatory lesions. Distinguish between areas caused by over-extension of the base, and areas caused by pressure. For pressure areas, distinguish between those caused by the base itself, and those transmitted to the tissues by imperfections in the occlusion (these latter are the most common). Step 3: Adjustment (see also following section on denture complaints and failures) Adjust areas obviously caused by over-extension of the flanges first. Then check the occlusion with articulating paper and adjust accordingly. Only then use pressure-indicating material to check the fitting surfaces. Step 4: Record keeping and clean up Reinforce care and maintenance instructions with the patient. Follow the usual procedures for recording the details in the patient file and for obtaining the required signatures and marks, and for cleaning up the surgery. Make further recall appointments until no further adjustments are required. Denture Complaints Denture complaints do not necessarily imply denture failure, provided that the dentures are basically satisfactory. Most of the complaints can be enumerated as follows:

1. Pain 2. Appearance 3. Inefficient chewing 4. Poor retention (maxillary denture) 5. Instability (mandibular denture) 6. Clicking teeth 7. Nausea, gagging or retching 8. Discomfort 9. Altered speech 10. Biting cheek & tongue 11. Food under the denture 12. Lower denture cannot be worn

Pain Many factors can cause pain with new dentures: • Improperly trimmed and defective fitting surfaces may cause irritation or even

ulceration. • Peripheral over-extension; encroachment upon a fraenum or muscular attachment;

encroachment on the muco-buccal fold – all may cause pain, inflammation or even ulceration.

• Poor fit of the denture base can cause irregular pressure and pain on the denture bearing area.

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• Unyielding bony prominences such as the root of the zygoma tend to bear more weight than soft areas and may become painful, inflamed or ulcerated.

• Incorrect centric relation. If there is a premature contact in centric relation, the interfering teeth will take the bulk of the occlusal force. This force is directed via a related area of the denture base to the mucosa, and may result in inflammation or ulceration.

• When there is insufficient freeway space (i.e. excessive vertical dimension of occlusion or an “opened bite”) there is a continuous and reflex apposition of the teeth and clenching of the jaw. The resultant pressure may cause pain on the mucosa. There may also be a sensation of tiredness from the muscles.

• If the upper posterior teeth are placed too far buccally, or if the flange is too thick, the coronoid process of the mandible may impinge upon the maxillary denture during lateral excursive movements.

• Pressure on a sharp and thin lower ridge or the mylohyoid ridge. This may have to be treated with a soft lining or by surgery.

• Resorption of the lower ridge being such that the denture exerts pressure over the mental foramen, resulting in neuralgic pain.

• Certain pathological conditions, e.g. atrophic or sensitive mucosa, burning mouth syndrome.

• Pressure on a retained root or unerupted tooth may cause tenderness over that area. Treatment Examine the patient carefully to identify the source of the pain. Discuss your diagnosis with your supervisor and treat accordingly. Appearance Patients who have accepted the appearance of the trial denture and the delivered dentures, may be influenced by negative comments from friends and relatives after they leave the surgery. Usually, the comments are made because the other people are not used to their friend/relative's appearance. Counselling the patient will help them to realise that others will get accustomed to their new appearance. If there has been a laboratory error during processing, or some other error has occurred in denture fabrication, the problems of poor appearance are more difficult to solve. Common aesthetic problems are: • Anterior teeth are the main concern of the patient and if they are of incorrect shape,

colour, size and position, the denture may be rejected. • An “overclosed bite” with excessive freeway will cause the characteristic nose-to chin

approximation. • Inadequately shaped flanges and a narrow arch will cause ‘falling in’ of lips and

cheeks. In other words, the edentulous appearance due to the loss of natural teeth, alveolar resorption and reduced soft tissue tone, has not been corrected.

• Inadequate lip support or excessive lip support.

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Treatment Solving the problem of appearance may be achieved through counselling about adaptation and altered appearance. Often just re-shaping the labial flanges can help, especially if they are very different from the patient’s existing dentures. More serious problems may require additional clinical or laboratory procedures, with which your supervisor will assist you. Inefficient chewing An inability to eat ‘anything’ is a complaint often found in patients who have never worn dentures and who become impatient during the adaptation period. Patients who are accustomed to an old set of dentures may have difficulty controlling the new set while eating. A reported inability to eat meat may be caused by an over closed bite (or excessive freeway space) which reduces muscular efficiency, or incorrect centric relation causing cuspal interferences or prematurities. Treatment Check the centric relation and the eccentric movements of the dentures. If there is an occlusal discrepancy it may be resolved by selective grinding, or by remounting and grinding in the dentures. Check your diagnosis and work out the treatment with your supervisor. Poor retention An inadequate posterior palatal seal is often the cause of looseness in an upper denture. When the mouth is opened, denture over-extension, tight and hypertonic musculature, and encroachment on the buccal space by the dental arch will cause the denture to lose retention. Under-extension with lack of peripheral seal, sparse or excessive, thick or thin saliva, and a thin tight unyielding mucosa, will oppose retention. When coughing or sneezing there is increased pressure in the mouth, coupled with exaggerated muscular activity which will break the seal and cause the denture to dislodge. An incorrectly shaped polished surface will not engage muscular activity that can be put to use in helping retention. Treatment Establish the reason for the lack of retention in the denture. Your supervisor will assist you in your diagnosis and subsequent treatment of the problem. Instability Inexperienced denture wearers are often acutely aware of the instability of the mandibular denture compared to the maxillary denture. There may be no improvement you could make to this, in which case counselling becomes important, to reinforce the counselling you should already have given on explaining how to control the lower dentures. Factors such as chewing evenly on both sides instead of only on one side, and correct positioning of the tongue should be re-explained. Lateral movement of the denture on the basal seat can be caused by cuspal interference during lateral excursion, an under-extended periphery, particularly in the lower lingual area, and a flabby mucosa.

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When a flabby ridge is encountered, especially in the upper anterior region, the denture feels unstable, even if there is sufficient retention, because it moves against the very resilient basal tissues every time occlusal forces are applied. Treatment Depending on the cause of the instability, improvement is not always possible. Discuss with your supervisor whether any denture alterations are required. Remember that there are limitations in the use of dentures compared to natural teeth and also compared to the patient's expectations of false teeth. Clicking Clicking of the teeth may be caused by inadequate closest speaking space, inadequate freeway space, cuspal interferences during eccentric excursions, and poor retention and/or stability of the dentures. Some patients (more often elderly) have a habit of playing with the dentures, which also causes noises. Treatment Establish the cause of the clicking noise, and treat as necessary. Nausea, gagging or retching Denture over-extension onto the soft palate may stimulate a gag reflex directly by continuous contact or indirectly by intermittent contact brought about by the activity of the soft palate or posterior third of the tongue. An under-extended denture (or an unstable denture from occlusal interferences) will lack a posterior seal, will dislodge intermittently, irritate the posterior third of the tongue and thus cause nausea. A palpable and thickened posterior border will also irritate the tongue. Interference with tongue space, as in an excessively large vertical dimension which causes compensatory protrusion of the tongue, or in a narrow arch which forces the tongue to occupy an unnatural position, may also manifest as nausea. Treatment Establish whether there is a physical reason for the gagging and correct it with the help of your supervisor. Psychological causes of retching are more difficult to diagnose and treat. Discomfort This is a complaint found mainly in experienced denture wearers. On examination there is no pain, there is good retention and in all respects the dentures are satisfactory. A comparison of the old dentures with the new ones might reveal an altered tongue space due to a narrower arch which occurs characteristically in the upper denture. Secondly, it might be found that the old dentures have a greater freeway space than the new dentures. A sudden increase in the vertical dimension will cause increased muscle tone, pain on the alveoli and a feeling of tension and tiredness in the muscles. Thirdly, if the occlusal plane has been raised, lowered or altered in the new set up the patient may not adapt to the change.

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Treatment Establish exactly what kind of discomfort the patient has. Consult your supervisor to decide on whether adjustments are necessary to the denture. Once again, do not underestimate the importance of discussion and counselling with your patient. Altered Speech New denture wearers often find difficulty with speech. This disappears quickly as the tongue adapts to an altered environment. Treatment If the speech defect continues indefinitely, a diagnosis must be made, e.g. a palatogram could be done and relevant alterations to the denture base effected. Tooth positioning in relationship to phonetics may also need investigation. Biting the Cheek and Tongue The cheek may be bitten if there is insufficient posterior overjet, if there is excessive freeway space or if the buccal flange does not hold the cheek away from the teeth. If the position of the teeth is not neutral, then either the cheek or the tongue will be bitten, depending on whether the arch is too wide or too narrow. Treatment Establish with your supervisor if adjusting the dentures would help solve the problem. Food under Dentures This complaint usually comes from patients who are not accustomed to dentures and whose musculature cannot yet deal efficiently with the food in the mouth. Incorrectly contoured external surfaces will not help the musculature. If a denture is without retention and dislodges continually, food will naturally tend to collect under it. An efficient peripheral seal will prevent the ingress of food under the denture. Treatment Establish the cause of the problem, and treat as necessary. Difficult Lower Denture Because the mandibular denture is less stable than the maxillary denture, there may be more trauma to the tissues and the denture is also difficult to control. The complaint is particularly found in people who have very flat lower ridges, often in conjunction with high and active sublingual or labial musculature. These patients have a history of wearing a lower denture for a short period and experience difficulty in eating, poor retention and discomfort. The new denture should be examined giving particular attention to a sufficient freeway space: a correctly extended periphery; the correct centric relation and balanced occlusion; and neutrality.

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If a new lower denture is required the following features must be incorporated in the treatment: a new impression with a good peripheral seal; and a well adapted stable base for jaw relation recordings and trial dentures. If the arch form, occlusal plane or balanced occlusion are incorrect, the upper denture will also have these features, so an entirely new set of dentures may have to be made. Denture Failure The most common causes of denture failure are: 1. Insufficient freeway space. If the discrepancy in vertical dimension is too great, the

dentures will have to be re-made with correct vertical dimensions. 2. Incorrect jaw relations. The use of anatomical teeth necessitates cuspal interdigitation

which, if the jaw relations are incorrect, causes the mandible to deviate to an eccentric occlusal position. Small discrepancies can be corrected by remounting and grinding in the dentures. Large discrepancies necessitate remaking one or both dentures.

3. Insufficient tongue space. The teeth should occupy a position of neutrality between the

muscular forces of the tongue, cheeks and lips. If the teeth are set up too far lingually, the tongue will dislodge the lower denture, will be bitten when chewing and will give the sensation of being “crowded in”. In addition, it will influence the rest position.

4. Poor retention. This is usually caused by an under-extended periphery, lack of, or

exaggeration of the posterior palatal seal, peripheral over-extension, ill-fit of the denture due to a faulty or warped impression, teeth set up in non-neutral positions, dislodgement and breaking of the seal from cuspal interference.

5. Patients who have been using one set of dentures for a long time may object to any

alteration in vertical dimension, peripheral shape, tooth position, arch form and articulation.

Should denture failure be diagnosed, the dentures often require remaking, correcting the problem(s) that caused failure.

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8. PROCEDURES FOR THE DUPLICATION OF DENTURES General indications This procedure is useful when a patient requests new dentures, but has been satisfied with an old set for some years. Wear, staining or fractured teeth are usually the main complaints, and if most other aspects such as arch form, jaw relations and stability are found to be acceptable, then there is good reason to duplicate the dentures. This is because the procedure requires fewer visits, is relatively quick and therefore more cost-effective, and does not introduce large changes to which the patient must adapt. This makes it ideally suited for the elderly patient. The changes that are made must be minimal, and this procedure cannot be used to correct large deficiencies in arch form or vertical dimension. Clinical procedures – first visit Make four wax sprues using two sticks of periphery wax moulded together for each one. Attach one sprue to each side of the denture posteriorly, on the polished surface; at the hamular notches on the upper, and at the retromolar pads on the lower. 1. Chose a box tray that is much larger than the denture. Fill with alginate, and press the

denture into this to make an impression of the teeth and polished surfaces. Press the denture in so that the alginate is just short of the periphery of the denture. Whilst the alginate is still unset, smooth over the surface and make is flat as you can. This applies to the inner surface of the lower as well. When set, cut V-shaped grooves in the periphery of the alginate, at least one on each side, and one anteriorly.

2. A laboratory silicone putty is mixed according to the manufacturer's instructions and

loaded onto the fitting surface. Whilst the putty is still soft, bent paper clips are half buried within the material for retention of the plaster support. Quick setting impression plaster is then used to cover the putty and the adjacent (notched) borders of the impressions so that the entire denture is invested. When the plaster has set, the impressions of the fitting and polished surfaces are separated, and the dentures removed, as well as the wax sprues.

3. If the denture has an acceptable vertical height and the teeth allow the denture to be

hand articulated, a jaw registration is not required. However, if the teeth are so worn that the dentures cannot be hand articulated out of the mouth, or if the vertical dimension must be increased by no more than 2-3 mm, then a jaw registration is made, using jaw registration wax. A determination must be made, as to whether this increased vertical dimension requires a change in the position of the occlusal plane (usually by lowering the position of the upper arch) or whether the occlusal plane will divide the new space between the upper and lower arches.

5. The patient is then dismissed, after choosing a suitable tooth shade.

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Laboratory procedures 1. Duplication of the denture in wax The two halves of the investment are carefully reunited, sealed with sticky wax, and molten modelling wax poured into the mould. The modelling wax should be hardened with the addition of some sticky wax, as pure modelling wax is usually too soft for this purpose. When the wax has hardened, the mould is separated, leaving a wax replica of the denture. The half consisting of the silicone impression of the fitting surface, reinforced by the impression plaster, is then trimmed if necessary, in preparation for articulation. The impression of the polished surfaces should not be discarded until an adequate wax replica has been obtained: a plaster model is then poured using these impressions. The two wax replicas on their models are articulated, by hand or with the jaw registration, sealed together, and articulated on an average-value articulator. 2. Setting the teeth The wax teeth are removed alternately, one by one, and replaced with artificial teeth of the correct shape and size. After replacing the anterior teeth, the plaster cast of the denture should be used to evaluate the arrangement, if a true likeness of the old dentures is desired. The completed trial dentures are waxed up in preparation for the next clinical visit. If a new jaw registration was made at an increased vertical dimension, the occlusal plane is set at the position previously determined. Clinical procedures – second visit 1. The trial dentures are evaluated using conventional clinical techniques. It is important

to realise that the trial dentures cannot be repositioned on an articulator after the final impressions are made, so any re-positioning of teeth must be done at this stage.

2. When the trial dentures are satisfactory, the final impressions for the new dentures are

made using zinc oxide-eugenol paste or elastomeric impression materials. The impression technique is identical to that used when the rebasing a denture, and a "closed-mouth" technique can be used to maintain the proper jaw and tooth relationships during the impression procedure.

Laboratory procedures The trial dentures may be immediately flasked but it is generally easier to bead and box and pour a cast for each, to enable final adjustments to be made to the wax work. The dentures are flasked and processed in the conventional way. Clinical procedures – third visit These procedures will be the same as for the delivery of any complete dentures, with the exception that a remount procedure will not have been possible: this is now done at the chairside with a suitable check-bite.

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Advantages of the technique 1. The familiar features of old successful dentures are retained in the new dentures. 2. The new dentures are completed in three visits. 3. It is a technique particularly suited to treatment of elderly patients. 4. It is cost-effective. Disadvantages The final impressions are the weakest point in the technique, as the vertical and horizontal jaw relationships are at risk, and it is generally unsatisfactory to make final impressions in a trial denture, as distortion of the wax may occur. References Owen CP (2006): New dentures from old: a duplication method using “appropriatech”. J Can Dent Assoc. 72:393-397 © C P Owen and Department of Prosthodontics, School of Oral Health Sciences, Faculty of Health Sciences, University of the Witwatersrand. Updated: February 2007 (v.6)