This guide will assist you in clinical stages of removable partial denture construction. You will, benefit by following the approaches suggested in this document. It must be understood however, that there may be necessary modification required through situations which are without your control. Such modification should always be discussed with and agreed by your clinical teacher.
Selection of stock tray. Modification of the tray with impression compound or autopolymerising acrylic as appropriate.
Normally a high viscosity alginate should be used as this will compensate for the lack of fit of the stock tray. A thin layer of adhesive should be applied to the tray before starting to mix the alginate.
It is essential at this and subsequent stages to indicate precisely what is required for the next appointment. The prescription on the laboratory card must be clear and comprehensive. If there is
any possibility of confusion it is essential to discuss the case personally with the technician involved. All casts at this stage should be poured in dental stone and the type and material of individual trays indicated.
If the laboratory card is not completed and dated, work will not be available for the next appointment.
The design of a partial denture should be determined before master impressions are recorded.In this respect casts where there are opposing natural teeth in contact, casts must be mounted on
an articulator and surveyed to produce the desired design. In many cases where there are sufficient teeth, casts can be placed in occlusion by hand prior to mounting.In other situations it will be unnecessary to construct occlusal rims to register the jaw relationship of the patient.
The sequence therefore is as follows:-
• Pour preliminary casts.
• Survey initially to vertical path of insertion.
• In very few cases a second survey will be necessary to a modified path of insertion.
• Mount casts on articulator.
• Produce design for removable partial denture.
The provisional design produced should be discussed with your clinical teacher before the patient's next appointment. At this stage a decision should be made on the need for possible tooth preparation or modification. This may indicate that the following may be necessary:-
• Rest seat preparation to provide sufficient space and a horizontal surface for any support component.
• Modification of tooth contour, by grinding or the addition of light-cured composite resin, to improve the action of clasp arms or the occlusal relationship.
The proposed design should be drawn on the laboratory card and also transferred to the study cast which should be retained for reference until the trial stage has been completed. The design prescription must be clear and comprehensive.
If surgical, conservative or periodontal treatment is indicated this must be completed before recording master impressions This is because the type of denture required may influence the overall treatment plan, e.g. rest seats incorporated into Class II restorations, full veneer crowns contoured to provide undercut areas for retention, or tooth extraction as a result of over eruption.
Normally the second visit will be for master impressions if the preliminary casts have already been mounted and a design determined. In cases where the preliminary casts could not be mounted however, the second visit will be devoted to recording the jaw relationship of the patient prior to mounting casts on the articulator and developing a design.
Recording Jaw Relationships
If an occlusal stop is present in the mouth you must determine whether the associated intercuspal position is acceptable. If there is horizontal (antero-posterior or lateral) deviation of the mandible after the initial occlusal contact, it may be necessary to correct the deflective occlusal contact by tooth modification, extraction or (rarely) orthodontic treatment. If there is loss of vertical dimension of occlusion (OVD) the appropriate increase will have to be determined by adjusting
occlusal rims in relation to the rest vertical dimension (RVD).
For the purpose of jaw relationships and their registration partially dentate patients can be divided into two categories:-
· Patients without an occlusal stop to indicate the correct intercuspal position or vertical dimension of occlusion.
· Patients with occlusal contact in the intercuspal position.
In the first category the OVD is determined by establishing the RVD and modifying the occlusal rims until the OVD is some 2-4mm short of the RVD, this distance indicating the amount of interocclusal clearance. The horizontal jaw relationship recorded should be the retruded contact position.
- Occlusal rims (and wax trial dentures) should only be placed in the mouth long enough to carry out a particular clinical procedure. On removal they should be chilled in a bowl of cold water to avoid distortion
- In the mouth the fit and extension of the rim should be checked and modified if necessary to produce acceptable stability.
- The upper occlusal rim should be adjusted so that the occlusal plane is correct in relation to the remaining upper natural teeth. If there is an anterior saddle the rim must indicate the correct incisal level and degree of lip support. Removal of wax from the palatal aspect of this rim might be necessary in order to allow closure of the mandible into the tooth position whilst retaining the incisal level.
- Any occlusal contact (e.g. with an opposing tooth) should be checked when the patient closes with the upper rim in place. If the occlusion shows a premature contact between a tooth and the opposing occlusal rim, the rim should be adjusted accordingly until the occlusal contact is re-established.
- The lower rim should then be adjusted to produce even contact.
- The lower rim should then be modified so that there is a small space (about 2-3mm) between the occlusal surface of the rim and the opposing teeth or rim with the mandible in the rest position.
- The retruded contact position should be recorded using wax or an occlusal registration material such as Bite Registration Paste. Petroleum jelly should be spread thinly over the opposing wax rim to act as a separating medium.
- The casts should be placed in occlusion using the occlusal rims and checked to determine that the tooth relationship on the casts is the same as in the mouth. If there is a premature contact between the heels of a cast and the opposing block or cast, this should be eliminated prior to mounting.Correct if necessary.
- The rims should be trimmed until the natural occlusal contact is observed.
- The occlusal contact should be checked with the natural teeth when the patient occludes with the upper rim in place. If the vertical dimension of occlusion has been increased as a result of a premature contact between a lower tooth and the occlusal rim, the rim should be reduced until the occlusal contact is re-established.
- The lower rim should be adjusted until there is an even occlusion at the OVD determined by the intercuspal position.
- Locating notches should be cut in the upper rim, petroleum jelly applied as a separating medium and the intercuspal position recorded with the rims in place using wax or registration paste.
- The casts are placed in occlusion using the occlusal rims and checked to ensure that there is no premature contact between the heels of a cast and the opposing rim or cast.
- Shade, material and mould of artificial teeth should be specified.
- If the next stage is the try-in of a metal framework, the design should be drawn on the laboratory card and full instructions given. This should be signed by your clinical teacher. The study casts should be retained as a guide for the technician.
- If the metal denture is restoring lower free-end saddles consider the need for the altered cast technique. If the technique is to be employed request the addition of acrylic trays to the framework in the saddle areas.
- If the anterior teeth require metal backings, a wax trial denture should be requested for the next stage so that the appearance and position of the teeth can be approved before the metal framework is constructed.
· Wax stops should be placed on the fitting surface of the individual trays before modifying the peripheral extension if necessary.
· Any over-extension of the tray should be corrected using a blue stone.
· Any under-extension should be corrected with the addition of self curing acrylic resin (Total). When mandibular free-end saddle areas are present, border moulding of the tray in the retro-mylohyoid areas should be undertaken routinely.
Recording the Impression
· The tray is dried and a thin layer of adhesive is applied to the whole of the inner surfaces of the tray and to an area extending 3mm beyond the periphery of the tray.
· A low viscosity alginate is used to record the impression. In some cases silicone based or rubber based materials may be used.
· If the impression is satisfactory a cast should be poured in either dental stone (for acrylic dentures) or improved dental stone (for cobalt chromium chromium dentures) as soon as possible.
· All individual trays must be retained until treatment is completed.
The laboratory prescription should indicate the material to be used for cast pouring. Bearing in mind that the occlusion has already been determined naturally or by occlusal rims prior to establishing a design, the subsequent stage should be either trial dentures or the production of a metal casting. In the former situation a shade and mould of teeth must be selected.
In cases where registration was undertaken at the SECOND VISIT, this attendance will be for master impressions.
The Metal Framework
· The framework must conform to the original design.
· The framework must fit the master cast. If the fit is unsatisfactory on the cast it will also be unsatisfactory in the mouth.
· All components which are designed to be clear of the gingival margin area should be checked to ensure that the clearance is adequate.
· In the mouth, these aspects should be checked again, remembering that the likelihood of some instability in free end saddle cases may be due to spacing beneath the mesh retention.
· The occlusion is examined to ensure that there are no premature contacts caused by support units. This should be done by visual examination, from comments by the patient and with the use of articulating paper or disclosing wax. Any premature contact should normally be removed at this stage.
Accordingly the casts must be remounted to this relationship and the teeth set for asecond trial.
The Trial Denture
(This may be at the third visit or the fourth visit according to clinical requirements).
This is the last stage at which modifications can be made before the wax is replaced by acrylic. A careful routine must be followed to prevent any mistakes continuing through to the finished dentures.
The dentures should firstly be examined on the mounted casts in respect of :-
• Adaptation of dentures on the casts.
• Position of artificial teeth with regard to adjacent natural ones.
• The arrangement of anterior teeth.
• Extension and contouring of wax flanges.
In the mouth the trial dentures should be examined in respect of:-
- Adaptation of the dentures.
- Occlusion including the vertical dimension of occlusion.
· Contouring of wax flanges with regard to peripheral extension, shaping of polished surfaces, coverage of gingival margins. Appearance. Modify positions of teeth and incisal edges of anterior teeth to achieve a pleasing result. Ask for patient's comments on appearance. Show the patient the dentures in the mirror and ensure that they are satisfied.
· If, at this stage, the occlusion is incorrect, modifications must be carried out before continuing with the next stages. An increase in occlusal height may be achieved by adding pink wax to the occlusal surfaces of posterior teeth on one of the dentures. A reduction in occlusal height is achieved by replacing the posterior teeth on one denture with wax rims and adjusting these to occlude evenly at the correct vertical dimension. Wax or bite registration paste may be used for the final recording.
If the occlusion has been re-recorded this will indicate a change in the jaw relationship. Accordingly the casts must be remounted to this relationship and the teeth set for asecond trial.
Carefully list and describe any modifications you wish the technician to carry out before finishing
To ensure that interference with insertion of the finished denture will not occur as a result of
inadequately blocked out tooth undercuts the following instructions and procedure must be
• Undercuts are blocked out in wax on the master cast, in respect of vertical path of
• The master cast should be duplicated.
• The denture should be processed on the duplicate cast.
• The processed denture should be fitted back on master cast.
• Examine the dentures and check there are no sharp edges or acrylic 'pearls' on the fitting surface of the saddle areas.
• Insert denture into the mouth. Occasionally the denture cannot be seated because acrylic has been processed into an undercut area on the cast; this is due to inadequate blocking out of the undercuts. If the area of acrylic to be removed is not immediately apparent, use pressure relief cream. Always remove the acrylic by approaching with the bur from the fitting surface.
The seal between denture and tooth in the non-undercut area should never be touched.
• In the mouth, check:-
- Adaptation of components
- Retention and stability
• Occlusal contact is checked by asking for the patient's comments, by visual inspection, and by the use of articulating paper. Articulating paper should be inserted bilaterally and not unilaterally. In the latter instance, the patient may tend to deviate the mandible to the side on which the paper is placed.
• Occlusal adjustment should be continued until both the patient's comments and visual inspection confirm that even contact has been achieved in the chosen jaw position. Attention should be given to occlusal contacts in lateral and protrusive positions. In many cases the dentures will be adjusted so that they conform to the occlusal guidance provided by the remaining natural teeth.
Advice to the Patient
• Insertion and removal of denture. The patient must be taught the correct way to handle the denture. Vulnerable components must be pointed out.
• A printed sheet of instructions is provided for the patient. This will mention in particular aspects such as cleaning/eating/wearing at night/pain/need for regular recall - including recall with the hygienist.
• It is important to discuss these points verbally with the patient first of all. The purpose of the sheet is simply to act as an aide-memoir.
• Finally you should ensure that the patient knows who to contact (i.e. you) in the event of problems arising with the denture. You are responsible for the prosthetic care of the patient which does not end with the insertion of a denture. Where problems arise, an appointment MUST be made to see the patient at your next available opportunity.
The patient should be asked for comments on the first week or fortnight of wearing the dentures.
A history must be taken of any complaint. Subsequent examination must be directed to diagnosing the cause of the complaint before making any adjustments. Whether or not there are any problems reported by the patient, the denture-bearing tissues must be examined and the occlusion must be checked. At times a patient may claim to be perfectly comfortable even though extensive ulceration is present.
Any inflammation of the denture-bearing tissues, which is not related to the peripheral area, is most likely due to occlusal causes. Therefore a careful inspection must be made of occlusal contact in tooth position and excursive movements, and the necessary adjustments made. The impression surface of the denture must not be 'eased' empirically. Should attention of the
impression surface be required, a disclosing material such as pressure indicator paste should be used.
A check must be made on the patient's oral and denture hygiene with the use of disclosing Solution. Steps to reinforce plaque control must taken if appropriate