Restorative Dentistry 3: Replacing Teeth PDF

Summary

This textbook chapter, part of a larger text on restorative dentistry, examines treatment planning for patients with missing teeth. It covers various options for tooth replacement, including bridges and dentures. It also discusses considerations for patients' age, oral health, and medical conditions.

Full Transcript

273 Chapter 7 Restorative dentistry 3: replacing teeth Treatment planning for patients with missing teeth 274 Bridges 278 Bridges—​design 282 Bridges—​practical stages 284 Bridge failures 286 Resin-​bonded bridges 288 Removable partial dentures—​principles 292 Removable partial dentures—​component...

273 Chapter 7 Restorative dentistry 3: replacing teeth Treatment planning for patients with missing teeth 274 Bridges 278 Bridges—​design 282 Bridges—​practical stages 284 Bridge failures 286 Resin-​bonded bridges 288 Removable partial dentures—​principles 292 Removable partial dentures—​components 294 Removable partial dentures—​design 298 Removable partial dentures—​clinical stages 300 Immediate complete dentures 302 Complete dentures—​principles 304 Complete dentures—​impressions 306 Complete dentures—​recording the occlusion 308 Complete dentures—​trial insertion 310 Complete dentures—​fitting 312 Denture maintenance 314 Cleaning dentures 316 Denture problems and complaints 318 Candida and dentures 320 Denture copying 322 Overdentures 324 Dentistry and the older patient 326 Age changes 328 Dental care for the elderly 330 Relevant pages in other chapters OcclusionI, % p. 234; acrylic and other denture materials, % Denture materials—​ acrylic resins, p. 680; casting alloys, % p. 670; impression ma- terials % p. 666. Further reading D. W. Bartlett 2004 Clinical Problem Solving in Prosthodontics, Churchill Livingstone. D. Ricketts & D. W. Bartlett 2011 Advanced Operative Dentistry: A Practical Approach, Churchill Livingstone. G. A. Zarb et al. 2013 Prosthodontic Treatment for Edentulous Patients: Complete Dentures and Implant-​ supported Prostheses, Elsevier. 274 Chapter 7 Restorative dentistry 3: replacing teeth Treatment planning for patients with missing teeth Solutions for missing teeth will vary depending on the number, their loca- tion and function, and the patient’s wishes. A minimally invasive approach is preferable where possible. Twenty-​one or more is considered the minimum number of teeth consistent with a functioning dentition but this may vary depending on the patient’s age, pattern of tooth loss, and incisal relation- ship. Replacement of missing teeth, therefore, isn’t always necessary. The Adult Dental Health Survey in 2009 showed that 86% of dentate adults had 21 or more natural teeth but this proportion d significantly as age i.1 In 2009, 6% of adults aged 16yrs or over were edentulous compared with 37% in 1968. These edentulous patients are also in the older age groups. For those with insufficient teeth for satisfactory function and aesthetics, fixed or removable prosthodontic solutions will be needed. The use of bonding techniques and implants can help minimize unnecessary destruc- tion of valuable tooth tissue. Indications for the replacement of missing teeth i masticatory efficiency. Improve speech. Preserve or improve health of the oral cavity by preventing unwanted tooth movements (vertical/​rotational/​tipping/​drifting).2 Improve distribution of occlusal loads. Space maintenance. Restore aesthetics. Prepare patient for complete dentures. Treatment planning for the replacement of missing teeth History Active listening in order to clarify the patient’s aims and expected outcomes is essential. It is important to enquire about previous denture history (just because a patient is not wearing a denture does not mean that they have not had one) and assess the reasons for failure or success. PMH Medical factors can impact upon availability for Rx and ability to cope with dentures. Some drugs may d salivary flow. Social history Other considerations may affect Rx, e.g. transport arrangements. Clinical examination EO and IO examinations, including a thorough assess- ment of any pathology, remaining teeth, existing restorations, periodontium, and edentulous areas (ridge form and extent, compressibility of mucosa). Assess tongue size, tonicity of the lips, and the volume and viscosity of saliva. An evaluation of any current dentures: what to copy and what to correct. Some patients present with a collection of unsuccessful dentures! 1 Health and Social Care Information Centre (M http://​www.hscic.gov.uk). 2 H. L. Craddock et al. 2007 J Prosthodont 16 485. Treatment planning for patients with missing teeth 275 Special investigations Radiographs/​ sensibility testing (especially of po- tential bridge abutments). Mounted study models and wax-up in partly dentate cases. Diagnoses These are then listed and will allow appropriate Rx planning after considering the Rx options. If pre-​existing denture problems are diagnosed, some could be addressed via modifications to the existing dentures prior to embarking on the construction of replacement prostheses. Options for the replacement of missing teeth No replacement First consider whether benefits of replacing missing teeth (improved mastication, speech, occlusal stability, and aesthetics) outweigh disadvantages (i oral stagnation, tooth preparation, cost). If not, then re- placement is C/​I. An occlusion with the second premolar to the second premolar present in each jaw (shortened dental arch) is usually functionally adequate. Bridges (% Bridges, p. 278.) These have the advantage that they are fixed. Resin-​bonded cantilever design is minimally invasive. Conventional bridges can have good appearance, but are destructive of tooth tissue, moderately expensive, and require lengthy clinical time. Implant-​supported prostheses These can be fixed or removable and have the advantage of avoiding preparation of natural teeth but involve surgical pro- cedures and are expensive. They help maintain supporting bone and have a high level of predictability if carefully planned and carried out. Removable partial dentures (% Removable partial dentures—​ principles, p. 292.) These can be minimally invasive as only minor (or no) tooth prep- aration is required but i plaque accumulation/​changes in composition. Damage to soft tissues and remaining teeth is exacerbated by poor denture design and/​or lack of patient care. Can be a good option when there are multiple edentulous areas or as a training/​interim appliance prior to F/​F. Can be used to replace missing soft tissue and aesthetics can be very good but patients often dislike removable prostheses. Complete immediate dentures These are indicated for patients who have already mastered wearing a partial denture and whose remaining teeth have a poor prognosis. Complete dentures These require patient compliance as well as good clin- ical and technical management for success. They can replace hard and soft tissue, but patients tend to dislike them and successful denture control can be difficult for patients to master. In the older, partially dentate patient it is important to assess whether the patient is likely to retain some functional teeth for the remainder of their lifespan. If this is improbable, some advocate providing F/​F dentures while the patient is still young enough to adapt. Orthodontic space closure This is an option that is seldom used but may be appropriate, particularly in the imbricated dentition. 276 Chapter 7 Restorative dentistry 3: replacing teeth Treatment planning If replacement is indicated: consider fixed or re- movable prosthesis. A number of factors affect this decision (Table 7.1). These factors need to be favourable if expensive and complex bridge-​ work is required. Removable prostheses are indicated if general or local factors are less than ideal. Always consider implants or shortened dental arch therapy. Treatment options These must be clearly explained to the patient with the advantages and disadvantages of each. This is essential in the management of expectations and to allow informed consent. Initial treatment Relief of pain and any emergency Rx including temporary modification of existing dentures, if indicated. Unless immediate dentures are planned, extract any teeth with hopeless prognosis. Consider extraction of teeth with poor prognosis. OHI and periodontal Rx. Preliminary design of partial denture. Carry out restorations required. Modify design if necessary and commence prosthetic Rx (% Removable partial dentures—​clinical stages, p. 300). Removal of pathological abnormalities (e.g. retained roots), and pre-​ prosthetic surgery, if required. Carry out definitive prosthetic Rx. Table 7.1 Fixed or removable prosthesis? General Local Patient’s motivation/​condition OH and periodontal health Age Number of missing teeth Health Position of missing teeth Occupation Occlusion Cost Condition of potential abutments Length of span Degree of resorption TREATMENT PLANNING FOR PATIENTS WITH MISSING TEETH 277 278 Chapter 7 Restorative dentistry 3: replacing teeth Bridges Definitions Bridge (fixed partial denture) A prosthetic appliance that is definitively at- tached to remaining teeth and replaces a missing tooth or teeth. Abutment A tooth which provides attachment and support for a bridge. Retainer The part of the fixed prosthesis that is cemented or bonded to an abutment tooth in order to provide retention. In the case of an implant, this may be screw or cement retained. Pontic The artificial tooth that is suspended from the abutments. Connector The component that joins the pontic to the retainer. May be rigid or non-​rigid. Saddle The area of edentulous ridge over which the pontic will lie. Units Number of units = number of pontics + number of retainers. Retention Prevents removal of the restoration along the path of insertion or vertical direction of the preparation. Support The ability of the abutment teeth to bear the occlusal load on the restoration. Resistance The features of tooth preparation that enhance the stability of a restoration and resists dislodgement along an axis other than the path of placement. Types of bridge Fixed–​fixed The pontic is anchored to the retainers with rigid connectors at either end of the edentulous span. Both abutments provide retention and support. Both preparations must have at least one common path of inser- tion to allow the prosthesis to be fully seated. Fixed–​movable The pontic is anchored rigidly to the major retainer at one end of the span and via a movable joint to the minor retainer at the other end (Fig. 7.1). The major abutment provides retention and support while the minor abutment provides support only. This design allows some inde- pendent movement of the minor abutment and has the advantage that the preparations need not be parallel. Direct–​cantilever Pontic is anchored at one end of the edentulous span only. Spring cantilever A tooth-​retained, mucosal-​supported bridge. The retainer and pontic are remote from each other and connected by a metal bar which runs along the palate. Usually an upper incisor is replaced from the pre- molars or a molar. It is useful where there is an anterior diastema or if the posterior teeth are heavily restored; however, they are often poorly toler- ated. These are rarely used now. Minimal or no preparation resin-​bonded bridges Retained by resin composite (% Resin-​bonded bridges, p. 288). May be adhered by glass ionomer adhe- sives when considered for temporary purposes. Compound/​hybrid Combination of more than one of the types listed. Bridges 279 Fig. 7.1 Fixed movable bridge replacing the lower left first permanent molar. Removable Can be used to describe screw-​retained implant bridges and removable partial dentures. Can be removed by dentist for maintenance. Types of retainers Full coverage crown. Three-​quarter crown. Onlay. Inlay. All of these restorations have been used as retainers in conventional bridgework. They are listed in order from most retentive to least retentive. Wherever possible, one of the first two should be used, as the failure rate of the last three is much higher. Post crowns should be avoided if possible, and onlays or inlays should only ever be used as minor retainers in fixed–​ movable bridges. It is ideal to aim for equal retention on abutments unless deliberately trying to ‘build in’ a failure point. 280 Chapter 7 Restorative dentistry 3: replacing teeth Selection of abutment teeth General factors must be taken into account, e.g. caries status and ex- isting restorations. Also, two other considerations specifically relate to bridgework—​retention and support. Assessment of retention Retention offered by a potential abutment tooth depends on clinical crown height and the available surface area. It is im- portant to assess the amount of enamel present for retention for resin-​ bonded bridges. Obviously, larger teeth offer more retention and should be chosen in preference to smaller ones. The teeth of both arches are listed in Table 7.2 in order of the amount of retention offered (if a full coverage restoration is used). Assessment of support Three factors are important: 1. Crown–​root ratio. Ideally should be 2:3 but 1:1 is acceptable. As bone is lost, the lever effect on the supporting tissues is i. 2. Root configuration. Widely splayed roots provide more support than fused ones. 3. Periodontal surface area. Ante’s law, ‘the combined periodontal area of the abutment teeth must be at least as great as that of the teeth being replaced’, has no scientific basis and no longer has a place in contemporary bridgework design. It does not take into account that we are dealing with a biological system—​as the load is i on the abutment teeth, a biofeedback mechanism operates to cause a reduction in this load. The teeth of both arches are listed in Table 7.3 in order of the support offered, assuming that the periodontal tissues are intact. Taper and parallelism For most designs, abutments should be prepared with a common path of insertion. Opposing walls of abutments should have a 6° taper or a total degree of convergence of 12°. Checking parallelism: direct vision, with one eye; survey mirror with parallel lines inscribed. Management of tilted abutments (% Tilted abutments, p. 282). Types of pontic Modified ridge lap This type of pontic should make (minimal) contact with the buccal aspect of the ridge. Gives good aesthetics and is the most popular type. Bullet Makes point contact with the tip of the ridge. Can be used for pos- terior bridgework. Ovate Aims to address the issue of emergence profile in the maxillary an- terior region. Has greater mucosal contact and applies light pressure to the underlying mucosa. Needs a smooth, convex surface to allow flossing. The patient must have excellent OH. The ‘modified ovate pontic’ lies slightly more labial to the ovate pontic, so tends to be used more in aesthetic areas. Bridges 281 Table 7.2 Assessment of retention Greatest l l l l l Poorest Maxilla 6 7 4 5 3 1 2 Mandible 6 7 5 4 3 2 1 Table 7.3 Assessment of support Greatest l l l l l Poorest Maxilla 6 7 3 4 5 1 2 Mandible 6 7 3 5 4 2 1 Hygienic Does not contact saddle, therefore supposedly easy to clean but can still be challenging and may lead to food packing if insufficient clearance. Unaesthetic, therefore limited to molar replacement. Saddle (ridge lap) Extends over ridge buccally and lingually, therefore diffi- cult to clean. Should not be used. 282 Chapter 7 Restorative dentistry 3: replacing teeth Bridges—​design Designing bridges Assess prognosis of all teeth in vicinity to d risk of another tooth requiring extraction in the near future. Assess possible abutment teeth (check restorations, endodontic status, periodontal condition, mobility, and take periapical radiographs). Select design of retainers, e.g. full or partial crown. Full coverage is preferred. Consider pontics and connectors. With this information compile a list of possible bridge designs. Consideration of the advantages and disadvantages of each design combined with a diagnostic wax-​up should help to narrow down the choice. Where possible, try the least destructive alternative first. Specific design problems Periodontally involved abutments First control periodontal disease. Then consider whether a bridge is indicated. A fixed–​fixed type of design is pref- erable to splint teeth together. Consider fibre-​reinforced resin composite fixed partial dentures for this specific indication. Pier abutments This is the central abutment in a complex bridge that sup- ports pontics on either side, which are in turn anchored to the terminal abutments. In this situation, the pier abutment can act as a fulcrum and when one part of the bridge is loaded the retainer at the other end experi- ences an unseating force which can lead to cementation failure. To over- come this a stress-​breaking element must be introduced, e.g. fixed–​movable joint, or avoid pier abutments by simplifying the design. Tilted abutments Occurs most commonly following loss of a molar. There are several approaches if bridgework is planned: Orthodontic Rx to upright abutments. Two-​part bridge, e.g. fixed–​movable. Telescopic crowns—​placement of individual gold shell crowns on abutments, over which the telescopic sleeves of the bridge fit. Precision attachments—​a precision screw and screw tube can be incorporated into a two-​part bridge. After cementation the screw is inserted, which effectively converts the bridge to a fixed–​fixed design. Canines The canine is often the keystone of the arch, and a very difficult tooth to replace. The adjacent teeth are poor in terms of the amount of re- tention and support that they offer and the canine is often subject to enor- mous stresses in lateral excursion (in a canine-​guided occlusion). If a canine is to be replaced with a bridge, the occlusal scheme should be designed to provide group function in lateral excursion—​never canine guidance. Bridges—design 283 284 Chapter 7 Restorative dentistry 3: replacing teeth Bridges—​practical stages As always, a thorough history and examination are required (% Treatment planning for patients with missing teeth, p. 274). It is essential to clarify the patient’s attitude to and expectation of Rx. They must be assessed for ac- tive disease due to poor OH or diet and for pre-​existing TMD. The re- sponse to initial Rx to stabilize active disease should be monitored before embarking on definitive Rx. If bridgework is planned, the following stages are carried out: Diagnostic mounting—​take accurate impressions of both arches, a facebow record, and have the models mounted on a semi-​adjustable articulator. The mounting can be carried out either in ICP (best fit) or in RCP, for which a precentric record will be necessary. If a reorganized approach to reconstruction is being considered, or if the clinical examination has revealed significant occlusal interferences, an RCP mounting should be performed. Carefully examine the occlusion and consider what occlusal consequences the proposed restoration will have. Diagnostic waxing—​in effect, this is a mock-​up of the final restoration on the mounted models. Wax can be added to the teeth to simulate the effect that the restoration will have on the final occlusion and aesthetic result. In the anterior part of the mouth a denture tooth can be used. In addition to assessing aesthetics and occlusion, the diagnostic wax-​ up can serve as a template from which the temporary bridge can be constructed. An impression is taken of the wax-​up in a silicone putty and saved for later. At this stage, the design of the prosthesis must be finalized. Preparations—​before the preparations are carried out, any suspect restorations in the abutment teeth are replaced. Preparations are carried out in accordance with basic principles (see Chapter 6) and care is taken to ensure that a single path of insertion is established. When checking for parallelism, one eye should be kept closed and the use of a large mouth mirror is very helpful. Custom-​made paralleling devices can be used but they are very cumbersome. Temporary bridge—​this is normally constructed using the matrix which has been formed from the diagnostic wax-​up; in this way the temporary bridge should reproduce the aesthetics and occlusion of the final bridge (if the wax-​up was done properly!). The matrix is filled with one of the proprietary temporary crown and bridge resins (e.g. Protemp®) and seated over the preparations. After it has set it is removed, trimmed, polished, and cemented with a temporary cement (e.g. TempBond®). Or a laboratory-​made temporary bridge may be used. The pontic should be contoured so that it is hygienic (e.g. to a modified ridge lap design). Bridges—practical stages 285 Impressions—​an impression is taken using an elastomeric material. Ideally, all of the preparations should be captured on one impression, but this can be very difficult if multiple preparations are involved. If difficulties are encountered in this respect, they can often be overcome by using the transfer coping technique. In this technique, acrylic (DuraLay®) copings are made on dies of the preparations for which a successful impression has been achieved. These are then taken to the mouth and seated on the appropriate tooth, and the impression repeated to capture the other preparations. On removal, the coping will be removed in the impression and the dies can be reseated in the copings and a new model poured around them. CAD/​CAM digital techniques can also be used. Occlusal registration—​under most circumstances the models will be mounted in ICP in the position of best fit, and therefore an occlusal registration will not be necessary. Where numerous preparations have been carried out and it is difficult to locate this position, or where there is a lack of AP stability in the models, some form of inter-​ occlusal record will be necessary. A popular technique involves the use of transfer copings, and is described in the section on occlusion (% Occlusal records, p. 237). Metal work try-​in—​if a porcelain fused to metal bridge is being constructed, it is advisable to try-​in the metal work before the porcelain is added, particularly for larger span bridges. At this stage the fit of the framework can be evaluated and the occlusion adjusted. On occasions it will be found that one retainer seats fully while the other does not. This can occur if there has been some minor movement of the abutments since the impression was taken. If this is the case the bridge should be sectioned, and hopefully both retainers will then seat. The two parts are then secured in their new position with acrylic resin (DuraLay®) and sent back to the laboratory for soldering. Trial cementation—​the finished bridge is tried in and any necessary adjustments made. The bridge should then be temporarily cemented (with modified TempBond®) for a period of a week or so. The advantage of a trial cementation period is that if any further adjustments are necessary they can be carried out outside the mouth and the restoration repolished and reglazed. The patient is instructed in how to clean the bridge (use of Super Floss® or an interdental brush). Permanent cementation—​after the period of trial cementation, the bridge is re-​evaluated and the patient asked if they are happy with it. If all is well the bridge is removed and cemented with a permanent cement (usually traditional or RMGIC). Follow-​up—​arrangements are made to recall the patient to check that the bridge is still functioning satisfactorily. 286 Chapter 7 Restorative dentistry 3: replacing teeth Bridge failures Patients should be warned about these prior to Rx. Most common reasons for failure Loss of retention. Mechanical failure, e.g. # of casting. Problems with abutment teeth, e.g. 2° caries, periodontal disease, loss of vitality. Management of failures Depending upon type and extent of problem: Keep under review. Adjust or repair in situ. Replace. Replacement Before replacement of a bridge is embarked upon, a careful analysis of the reasons for failure is necessary. Minor problems in an otherwise satisfactory bridge should be repaired if at all possible. Fractured porcelain can be repaired with one of the specialized repair kits available (e.g. CoJet™). 2° caries or marginal deficiencies, if small, can be restored with traditional GIC. Failure may be due to loss of vitality. This is not ne- cessarily an indication for removal of the bridge because RCT can often be carried out through the retainer of the abutment. Removing old bridges To remove intact, try a sharp tap at the cer- vical margin with a chisel or preferably a slide hammer. Orthodontic band-​ removing pliers can also be used but these require a small hole to be cut in the occlusal surface. If only one retainer is loose, support the bridge in position while trying to remove it so that it does not bind. Retainers can be cut through, but this will destroy the bridge. Bridge failures 287 288 Chapter 7 Restorative dentistry 3: replacing teeth Resin-​bonded bridges This technique involves bonding a cast metal framework, carrying the pontic tooth, to abutment teeth using an adhesive resin. This type of bridge is al- most exclusively used for cantilever adhesive bridgework, i.e. one abutment and one pontic (Fig. 7.2). Fixed–​fixed designs have been problematic, with one retainer debonding being a common clinical finding. The resin bonds to the abutment tooth using the acid-​etch technique and to the metal frame- work by either mechanical or chemical means. Fibre-​reinforced bridges are also available. Classification Position Anterior. Posterior. Retention Macromechanical: Perforated (Rochette). Mesh (Klett-​O-​Bond®). Particular (Crystalbond™). Micromechanical: Electrolytically etched (Maryland). Chemically etched. Chemical: Sandblasted. Tin-​plated. Chemical retention to a sandblasted metal surface is now used virtually ex- clusively. A dual-​affinity cement (e.g. Panavia™ 21) is used, which chemically bonds to both enamel and non-​precious alloys. Advantages Less expensive than conventional bridge or cobalt chromium partial denture or implant in the shorter term. Minimal or no tooth preparation required. No LA required as preparation is in enamel. Potential for rebond if debond occurs. Disadvantages Tendency to debond especially if planning and preparation and placement technique is poor. Metal may show through abutments. Creation of a natural emergence profile can be challenging especially in very resorbed ridges. Use of an ovate pontic can be helpful. Indications Short span-​single tooth edentulous space. Sound abutment teeth (or only minimal restoration) and sufficient crown height to ensure sufficient surface area for acid etch bonding. Favourable occlusion. Resin-bonded bridges 289 Fig. 7.2 Adhesive cantilever bridgework replacing missing upper canines. Treatment planning This is as for conventional bridgework. If ortho- dontic Rx is needed to localize space or upright adjacent teeth, it is advisable to retain with a removable retainer for at least 3 months prior to bridge placement. Design The design is usually cantilever. If a fixed–​fixed design is used and there is a debond of one retainer, caries can develop quickly and un- detected under this retainer. Fixed–​fixed design may be used if periodontal splinting is required or retention required following orthodontics. Tooth preparation There is debate as to what is the ‘ideal’ prepar- ation and some advocate no preparation. The need for preparation will be defined by the individual clinical situation. Guidelines for preparation Give a single path of insertion. Provide near-​parallel guiding planes eliminating undercuts, which allow coverage of maximal surface area for bonding. Provide space in occlusion to accommodate bridge. Need at least 0.7mm for wings. i retention, e.g. using a wrap-​around design (covering >180° of tooth circumference) to resist lateral displacement and reduce stress on the cement bond. Mesial and distal grooves enhance resistance form. To prevent gingival displacement a minimal chamfer is recommended. Provide axial loading of the abutments—​prepare cingulum or occlusal rests. A connector height of at least 2mm is required. NB: tooth preparation should usually be confined to enamel, and the frame- work should be designed with maximal coverage (to i surface area available for bonding). 290 Chapter 7 Restorative dentistry 3: replacing teeth Technique Chemical method using Panavia™ 21 Following tooth preparation an elasto- meric impression of the abutment teeth is taken plus an alginate impression of the opposing arch. At the try-​in stage the bridge should be assessed for fit, aesthetics, etc., and then the fitting surface thoroughly cleaned with alcohol (assessment of occlusion may not be possible until after cemen- tation). Contamination of the fitting surface with saliva must be avoided and cementation is best done under a rubber dam. Following etching and washing of the abutment(s), and placement of a dentine adhesive system, the wings of the bridge are coated with Panavia™ 21 and the bridge seated into place and held firmly until set. Use of acetate strips and Super Floss® at this stage will clear most of the excess cement and prevent it adhering to the adjacent teeth. The cement must then be covered with a substance known as OxyGuard®, which prevents O2 inhibition of the surface layer. After 3min the rubber dam is removed and any excess cement removed. Problems Dentine exposed during preparation. Use a dentine adhesive system. Metal shining through abutments. Cut wings away incisally before cementation or use a more opaque cement. May have to consider conventional bridge or placing veneer on labial surface. Debonds. If one flange only, can usually detach other by a sharp tap with a chisel or by using ultrasonic scaler tips. If a persistent problem, consider conventional bridge. The trend is for these bridges to be used for cantilevered bridgework and it is not usual for fixed–​fixed adhesive bridgework to be prescribed due to problems with unilateral debonding. Caries occurring under debonded wings. Remove bridge and repair. Further reading D. S. Thomas, et al. 2017 Article I. A systemic review of the survival and complication rates of resin-​bonded fixed dental prostheses after a mean observation period of at least 5 years. Clin Oral Implants Res 28 11. Resin-bonded bridges 291 292 Chapter 7 Restorative dentistry 3: replacing teeth Removable partial dentures—​principles Definitions Saddle That part of a denture which rests on and covers the edentulous areas and carries the artificial teeth and gumwork. Connector (major and minor) Joins together component parts of a denture. Support Resistance to vertical forces directed towards mucosa. Retainers Components which resist displacement of denture. Indirect retention Resistance to rotation about fulcrum axis by acting on the opposite side to the displacing force. Retention of the denture may be pos- sible through other means as opposed to clasping, such as guide planes. Fulcrum axis Axis around which a tooth-​and mucosa-​borne denture tends to rock when saddles are loaded. Bracing Resistance to lateral movement. Reciprocation The mechanism by which lateral forces generated by a reten- tive clasp passing over a height of contour are counterbalanced by a recip- rocal clasp passing along a reciprocal guiding plane.3 Guide planes Two or more parallel surfaces on abutment teeth used to limit the path of insertion, and improve retention and stability. Survey line This indicates the maximum bulbosity of a tooth in the plane of the path of withdrawal. Free-​end saddle Edentulous area posterior to the natural teeth. Stress-​breaker A device allowing movement between the saddle and the re- taining unit of partial denture. Gum-​stripper A tissue-​borne partial denture which can ‘sink’. Swinglock denture Has a labial retaining bar or flange which is hinged at one side of the mouth and locks at the other.4 Sectional denture Made in two or more sections which are then fixed to- gether with screws or other devices. Classification Kennedy Describes the pattern of tooth loss (Fig. 7.3): I. Bilateral free-​end saddles. II. Unilateral free-​end saddle. III. Unilateral bounded saddle. IV. Single, anterior bilateral bounded saddle. Must cross the midline. Any additional saddles are referred to as modifications (except Class IV), e.g. Class I modification 1 has bilateral free-​end saddles and an anterior saddle. 3 M https://​www.academyofprosthodontics.org/​_​Library/​ap_​articles_​download/​GPT9.pdf. 4 M. Chan et al. 1998 Dent Update 25 80. Removable partial dentures—principles 293 Kennedy Class I Kennedy Class II Kennedy Class III Kennedy Class IV Fig. 7.3 Kennedy classification. Craddock Describes the denture type: Tooth-​borne. Mucosa-​borne. Mucosa-​ and tooth-​borne. Acrylic versus metal dentures Approximately 75% of the dentures provided in the UK have an acrylic connector and base. Although metal bases are generally preferred because the greater strength of metal permits a more hygienic design, an acrylic base is indicated for: Temporary replacement, e.g. following trauma or in children. Where there is inadequate support from the remaining teeth for a tooth-​borne denture. When additions to the denture are likely in the near future. However, where financial constraints C/​I a metal base, attention to the fol- lowing may avoid the production of a gum-​stripper: Wide mucosal coverage to provide maximum support. Keep base clear of the gingival margins wherever possible. No interdental extensions of acrylic. Point contact and wide embrasures between natural and artificial teeth. Labial flanges for extra retention and bracing. Additional support from wrought SS rests. 294 Chapter 7 Restorative dentistry 3: replacing teeth Removable partial dentures—​components Saddles These can be made entirely of acrylic or have a sub-​framework of metal overlaid by acrylic. Rests These are an extension of the denture onto a tooth to provide support &/​or prevent over-​eruption. Occlusal rests are used on posterior teeth (usually over either the mesial or distal marginal ridge and fossa) and cingulum rests on anterior teeth. Rests may be wrought or cast; the latter is preferred for strength and fit. Clasps These provide direct retention by engaging the undercut portion of a tooth (Fig. 7.4 and Fig. 7.5). The action of a clasp must be resisted either by a non-​retentive clasp arm above the maximum bulbosity of the tooth or by a reciprocal connector. Clasps can be classified by their position (occlusally approaching or gingivally approaching) or by their construction and material. A minimum length of 14mm is generally advocated for cobalt–​ chrome clasps to prevent rapid distortion. Cast Cast (cobalt–​chrome) clasps are stiff, easily distorted, and liable to #. However, provided they are limited to undercuts of 0.25mm, the advan- tage of being able to cast them as an integral part of a denture framework offsets these drawbacks. Wrought Wrought clasps are usually attached by insertion into the acrylic of a saddle. SS is the most commonly used alloy, but gold clasps are more flexible and easily adjusted (and distorted). The stiffer the wire, the smaller the undercut that can be engaged. This can be offset by reducing the diameter of the wire to i flexibility (but i the likelihood of #) or by i the length of the clasp arm (e.g. gingivally ap- proaching clasp). Cast cobalt–​chrome can be too stiff for occlusally ap- proaching clasps on premolar teeth. The actual design used depends upon: Depth of undercut: 0.25mm—​cast cobalt–​chrome; 0.5mm—​SS wire; 7mm between floor of mouth and gingival margin to give 3mm clearance from gingivae. Does not contribute to indirect retention. Usually cast. C/​I if incisors are retroclined. If insufficient space can use sublingual bar. Sublingual bar lies horizontally in anterior lingual sulcus, but opinions differ as to patient tolerance. More rigid than lingual bar. Lingual plate is well tolerated and provides good support, bracing, and indirect retention if used in conjunction with rests but covers gingival margins. Can be made of cast metal or acrylic. Continuous clasp is really a bar which runs along the cingulum of the lower anterior teeth and is usually used in conjunction with a lingual bar. Poorly tolerated. Dental bar is similar to continuous clasp, but of i cross-​sectional area and without lingual bar. Useful for teeth with long clinical crowns. Provides support and indirect retention. May not be well tolerated. Buccal/​labial bar is indicated when the lower incisors are retroclined. Fig. 7.4 and Fig. 7.5 show the two most commonly used types of clasp. Removable partial dentures—components 297 298 Chapter 7 Restorative dentistry 3: replacing teeth Removable partial dentures—​design P/​P design is carried out after assessment of the patient and with reference to any previous dentures. A set of accurately articulated study models is essential. Surveying Objectives: Establish path of insertion. Define those undercuts which may be used to retain the denture. Define those undercuts which require blocking out prior to finish. If the path of insertion is at 90° to the occlusal plane, insertion of the denture will be straightforward; however, where the teeth are tilted or few under- cuts exist, an angled path of insertion may be advantageous. Whether this provides more resistance to displacement during function is controversial. A survey line can then be marked on the teeth to indicate their maximum bulbosity in the plane of the path of withdrawal. This is done using a dental surveyor. Design Outline saddles. Usually straightforward. If less than half a tooth width or if in doubt of the need to replace a missing tooth, omit. Plan support. Support can be tooth only, mucosa only, or both. Tooth-​ borne support (occlusal and cingulum rests) should be used wherever possible, as teeth are better able to withstand occlusal loading and support will not be compromised following resorption. Tooth and mucosa support are inevitable with large or free-​end saddles and where plate designs are used. Tissue-​only support should be utilized when no suitable teeth are available, and is less damaging in the upper than the lower arch, because of the palatal vault. Need to assess the role of the denture, length of the saddles, the amount of support required (? denture opposed by natural or artificial teeth), and the potential of remaining teeth to provide support (root area in bone), before a final decision is made. Obtain retention. Retention can be: Direct. E.g. clasps, guide planes, soft tissue undercuts, or precision attachments. Of these, clasps are the most commonly used. The best arrangement is to use three clasps as far away from each other as possible. Guide planes help to establish a precise path of insertion and withdrawal. Need be only 2–​3mm in length, reducing reliance on clasps. Composite resin can be added to abutment teeth to maximize undercuts. Indirect. This is derived by placing components so as to resist ‘rocking’ of the denture around direct retainers, e.g. by the position of clasps and rests and the type of connector. Particularly important with free-​ end and large anterior saddles. Assess bracing required. Bracing is provided by the connector, maximum saddle extension, and the reciprocal arms of clasps. Elimination of occlusal interferences d need for bracing. Choose connector. After consideration of earlier listed points. Is there space in the occlusion to accommodate the chosen connector? Where possible, the connector should be cut away from the gingival margins. Reassess. ? As simple as possible. ? Aesthetic. Removable partial dentures—design 299 Instructions to technician. Should include written details and diagram. Where some confusion may arise over the precise position of a component, it may be helpful to mark this directly on the cast. CAD programs are now available for design, communication, and production of prostheses. Some design problems The lower bilateral free-​end saddle (Class I) This presents a particular problem because of a lack of tooth support and retention distally, small saddle area compared to force applied, and distal leverage on abutment tooth in func- tion (which i with resorption). Possible solutions include: Maximize indirect retention by placing rests and clasps on mesial aspect of the abutment tooth and using lingual plate design. Using a muco-​compressive impression of saddle area to d displacement in function—​the altered cast technique. Use fewer, smaller teeth and maximize base extension. RPI system for distal abutment teeth—​mesial Rest, distal guiding Plate, and mid-​buccal I bar. During function the saddle moves tissue-​ward and rotates around the mesial rest. The plate and I bar are constructed in such a way as to disengage from the tooth and avoid potentially harmful loading. Stress-​breaker design (advantages more theoretical than practical). Use precision attachments (beware of overloading abutments). Class IV Can sometimes avoid unsightly clasps anteriorly by the use of: A flange engaging a labial alveolar undercut. Avoiding distal facing clasps. A mesial-​facing clasp will engage more as the anterior saddle tries to drop/​rotate out. A rotational path of insertion5 utilizing rigid minor connectors that are rotated into proximal undercuts anteriorly. Interproximal undercuts, which may allow minimal display of clasps—​ ‘hidden clasps’ (Fig. 7.6). An acrylic spoon denture held in place by the tongue. Multiple bounded saddles A horseshoe design, which utilizes guide planes for retention, may be indicated. Fig. 7.6 Sectional partial denture (Implant bar retained). 5 T. W. Chow et al. 1988 Br Dent J 164 180. 300 Chapter 7 Restorative dentistry 3: replacing teeth Removable partial dentures—​clinical stages Assessment and treatment plan. % Treatment planning for patients with missing teeth, p. 274. Take first impressions. These are usually taken using alginate in a stock tray. For free-​end saddles modify the tray first with compound or silicone putty. Record occlusion. If ICP is obvious, the occlusion can be recorded conventionally (% Occlusal examination, p. 236) at the same visit as first impressions. If ICP is not obvious, wax record blocks will be required and a separate visit. Where there are no teeth in occlusal contact, the steps involved are the same as for recording the occlusion for F/​F (% Complete dentures—​recording the occlusion, p. 308). If there is an occlusal stop, but insufficient standing teeth to produce a stable relationship of the casts, the procedure is as follows: Determine the occlusal vertical dimension (OVD) and mark the position of two index teeth with pencil. Define the occlusal plane using the record block on which this is easiest, e.g. tooth to tooth in a bounded saddle, tooth to retromolar pad in a free-​end saddle. Check the record blocks in the mouth, using the mark on the index teeth as a guide, and adjust blocks if necessary. Record occlusion with bite-​recording paste. Check the relationship of the index teeth on the articulated casts corresponds to that in the mouth. Mounted casts are surveyed and denture designed (% Occlusal considerations for restorative procedures, p. 236). Tooth preparation may be required to: Accommodate rest seats. Rests need to be >1mm for strength, therefore if insufficient room in occlusion to accommodate this bulk, tooth reduction is required. Establish guide planes. Accommodate clasp arms passing over contact points. Modify unfavourable survey line, e.g. d bulbosity. i retention, e.g. by the addition of resin composite to create undercuts. Consider crowning teeth with a poor long-​term prognosis prior to denture construction. Record second impressions using a special tray. Alginate is the most commonly used material, but elastomers are preferable. It is helpful to have a wax try-​in before the framework is made. This enables you to confirm the tooth position so that the retentive elements for the acrylic are placed appropriately. Removable partial dentures—clinical stages 301 Try-​in of framework: Check extension, adaptation, and position of clasp, and rests. If casting does not fit, use of correcting fluid may reveal which areas to relieve. Check upper and lower separately for OVD and occlusion, and then together. Major faults: repeat second impressions. Minor faults: adjust at finish. Re-​record occlusion, if required. Select tooth mould and shade. Altered cast technique, if required. Try-​in of waxed denture on framework: Check position of denture teeth. Check flange extensions/​thickness. Check OVD and occlusion. Check aesthetics with patient and only proceed when patient is satisfied. Prescribe post-​dam relief areas and management of undercuts. Finish. Once any fitting surface roughness is eliminated, the dentures are tried in separately, adjusting undercuts and contacts as required. The extension, occlusion, and articulation are then adjusted if necessary. Give the patient written and verbal instructions, and a further appointment. Rebasing P/​P Acrylic mucosa-​borne dentures can be rebased at the chair-​side with self-​cure materials, but difficulty may be experienced in re- moving the denture in the presence of undercuts, and the materials are generally inferior to the original denture base. Alternatively, P/​P can be rebased in the laboratory by means of a technique similar to that used for F/​F (% Rebasing, p. 314). Alternatively, make a new denture. For cast metal dentures an impression can be recorded of the saddle area using an elastomer or ZOE, while holding the denture by the framework. In all cases care must be taken to avoid the introduction of occlusal errors, e.g. i OVD. 302 Chapter 7 Restorative dentistry 3: replacing teeth Immediate complete dentures When the remaining teeth have a poor prognosis, the transition from the partly dentate to edentulous state must be managed carefully. Patients must be warned about the effects of resorption and the need for early rebasing/​ replacement. Rx planning must be thorough. Rx alternatives for partial denture wearer A gradual transition towards being edentulous via additions to a transitional P/​P can i the chances of successful adaptation to F/​F especially for the older patient. Immediate complete denture. This has the advantage that the form and position of the natural teeth can be copied and is said to promote better healing and reduce resorption, but frequent adjustments and early replacement are necessary. Overdenture (% Overdentures, p. 324); may retain alveolar bone. Rx alternatives for patients with no previous denture experience Provide a partial denture and allow the patient to adapt before progressing to an immediate complete denture—​the best solution. Extract the majority of posterior teeth leaving sufficient only to maintain OVD and occlusal relationship, and then make immediate complete dentures when resorption has slowed. Extraction of the remaining teeth and provision of a denture after healing has occurred (post-​immediate denture). Avoid if possible as considerable guesswork is involved in the subsequent denture and the chances of the patient coping successfully are d. Types of immediate complete denture Flanged. Either full or part (extended 1mm beyond maximum bulbosity of ridge). Open face. No flange, artificial teeth sit over (or just into) the socket of the natural predecessor. Flanged dentures are preferable as they afford better retention and make subsequent rebasing easier. However, where a deep labial undercut exists into which it would be impossible to extend a flange, the choice is either surgical reduction or an open-​face denture. Most patients choose the latter. Clinical procedures 1° impressions (as for P/​P, % Removable partial dentures—​clinical stages, p. 300). 2° impressions in alginate or silicone. Recording occlusion. Where there are sufficient posterior teeth remaining, a hand articulation should suffice, and this can be taken at the same visit as impressions are recorded. Otherwise, record blocks will be required. Try-​in. This will be limited to those teeth that are already missing. Check fit, extension, and stability, etc. In addition, need to prescribe: Type of flange required. Any proposed changes in position of anterior artificial teeth compared to natural teeth. Immediate complete dentures 303 Extraction of remaining teeth as atraumatically as possible. Finish. Repeated removal and insertion of the denture should be avoided, therefore adjustments should be limited to making the patient comfortable. They should be instructed not to remove the denture before the review appointment in 24h. Review. The fitting and occlusal surfaces are adjusted as required. If dentures are unretentive they will require temporary reline (% Denture problems and complaints, p. 318). Recall. Regular inspection of immediate dentures is important as rapid bone resorption means that they will require rebasing early. However, this should be deferred, if feasible, for at least 3 months after the extractions. A possible regimen is 1 week, 1 month, 3 months, 6 months, and then yearly. Laboratory procedures These are similar to F/​F except that the plaster teeth are removed and the cast trimmed to mimic the changes that will occur in the hard and soft tissues following extraction, before final processing. Surgical procedures See % The extraction of teeth, p. 383 and % Minor pre-​prosthetic surgery, p. 426. Problems Denture unretentive. Use a temporary reline material (replaced regularly) to tide patient over initial 3 months and then reline with heat-​cure acrylic. Gross occlusal error. Adjust occlusal surface of one denture until even contact attained. This denture can then be replaced after initial resorption has occurred. 304 Chapter 7 Restorative dentistry 3: replacing teeth Complete dentures—​principles Retention The resistance of a denture to displacement. It is dependent upon (i) peripheral seal, (ii) contact area between denture and tissues, (iii) close fit, and (iv) viscosity/​volume of saliva. Neuromuscular control has more to do with stability than retention. Stability The ability of a denture to resist displacing forces during func- tion. Influenced by forces acting on polished and occlusal surfaces, as well as the form of the supporting tissues. Neutral zone The area where the muscular displacing forces are in balance. Ways to optimize retention and stability Maximum extension of denture base (as far as the surrounding musculature will allow). The upper denture should extend distally over the tuberosities and onto the compressible tissue just anterior to the vibrating line on the palate. The lower denture should extend the full depth and width of the lingual pouch, and halfway across the retromolar pad. NB: over-​extension will result in a denture that is easily displaced in function. As close an adaptation of denture base to mucosa as possible, to maximize the surface tension effects of saliva. Placement of the teeth in the neutral zone. More important in −/​F. The better retention of F/​− often allows some latitude in this respect. Correct shape of the polished surfaces so that muscle action tends to re-​seat the denture. A good border seal. This is achieved by ensuring that the flanges fill the entire sulcus width and by placing a post-​dam on compressible tissue. Balanced occlusion free from interfering contacts. Common denture faults Lack of freeway space (FWS). Failure to reproduce closely enough the features of previous successful dentures. Occlusal errors. Incorrect adaptation and extension. Complete dentures—principles 305 306 Chapter 7 Restorative dentistry 3: replacing teeth Complete dentures—​impressions 2 Tissues must be healthy before final impressions are recorded. If neces- sary, use tissue conditioner in present F/​F (% Tissue conditioners, p. 314). Classically, two sets of impressions are recorded of the edentulous mouth. The purpose of the first is to record sufficient information for a special tray to be made in which to record the second or master impression. Preliminary impressions These are recorded using an (edentulous) stock tray and alginate, elastomer (both preferable for undercut or flabby ridges), or impression compound. A line should be marked on the impression to indicate to the technician the desired extension of the special tray. In the upper, the posterior limit should be the hamular notches and the vibrating line, and in the lower the retromolar pads. Special trays These can be made in self-​cure or light-​cure acrylic. The space left for the impression depends upon the material to be used: ZOE = 0.5mm; elastomer = 0.5–​1.5mm (depending on viscosity); alginate = 3mm. For trays with >1mm space use greenstick stops clinically to aid positioning. Master impressions These aim to record the maximum denture-​bearing area, and to develop an effective border seal, the functional width and depth of the sulcus. The special tray should be modified by reducing any over-​extension and the peripheries adapted by the addition of greenstick tracing compound. Non-​ perforated trays ensure that a peripheral seal with the upper tray can be demonstrated before taking the impression. However, a perforated tray reduces the compression of tissue leading to a more mucostatic impres- sion. Gently manipulate the patient’s soft tissues and ask them to slightly protrude their tongue to imitate functional movements. Muco-​compressive versus muco-​static A muco-​ compressive impression technique is sometimes advocated to give a wider distribution of loading during function and to compensate for the differing compressibility of the denture-​bearing area, thus preventing # due to flexion. ZOE or compos- ition is used. However, dentures made by this method are less well retained at rest, which is the greater proportion of time. Alginate is said to be more muco-​static. Tissue adaptation following a period of use probably reduces the clinical difference between the two techniques. Special techniques Neutral zone impression technique This is used for recording the neutral zone in patients with limited natural retention for −/​F. Record second impressions and occlusion. A fully extended acrylic baseplate is made on the lower cast, with wire loops added which do not extend above the occlusal plane. The upper trial denture or record block is inserted. Tissue conditioner is placed on the baseplate and around loops, and inserted. Ask patient to swallow, purse lips and say ‘Ooh’ and ‘Eee’. The impression is removed and trimmed down until it can be fitted onto the articulator to replace the lower occlusal rim. Complete dentures—impressions 307 A mould of the impression is made into which wax is poured. The wax is cut away so that each denture tooth can be positioned within the zone recorded to make the trial denture. The polished surfaces should replicate the impression. Flabby (displaceable) ridge Classically occurs under a F/​− opposed by nat- ural lower teeth. If mild, then an impression recorded with alginate or elastomer in a tray perforated over the flabby area may suffice. For more severe cases a two-​stage technique is required, using a special tray with a window cut out over the flabby tissue. First, an impression is recorded in the tray with ZOE and the paste trimmed away from the flabby area. This is then re-​seated and low-​viscosity elastomer or impression plaster placed into the window to complete the impression. NB: combination type cases should have the dentures constructed on a semi-​adjustable articulator to minimize occlusal displacing forces. Functional impression Tissue conditioner is placed inside the patient’s existing denture. After several days of wear a functional impression is produced. Common impression problems and faults A feather edge indicates under-​extension. This can be corrected by the addition of greenstick to the tray and repeating. Tray border shows through impression material. Reduce tray in the area of over-​extension and repeat the impression. Air blows. If small, can be filled in with a little soft wax. If large, retake the impression, or if using silicones or ZOE the impression may be added to. Tray not centred. Often partially due to using too much material so that it is difficult to see what is where. Remember to line up the tray handle with the patient’s nose (except for ex-​boxers). Retching. A calm and confident manner is necessary for successful impressions. Gain the patient’s confidence by attempting the lower first and use a fast-​setting, viscous material. Distraction techniques may help, e.g. wriggling the toes on the left foot and the fingers of the right hand at the same time (the patient, not the operator). Patient with dry mouth: ZOE is C/​I; use elastomer instead. Areas where tray shows through in otherwise good impression. Can be overcome by prescribing a tin-​foil relief when dentures are being processed. 308 Chapter 7 Restorative dentistry 3: replacing teeth Complete dentures—​recording the occlusion When recording the occlusion with wax rims mounted on rigid acrylic or shellac bases, the aim is to provide the technician with information for con- structing trial dentures. As head posture can affect FWS, position the patient so that the Frankfort plane is horizontal. A wax trimmer and a heat source are required to adjust the rims. Check fit of bases. If poor, can either repeat second impressions, or take a ZOE or low-​viscosity elastomer impression with the base and proceed. Adjust upper rim to give adequate lip support. Trim occlusal plane of upper rim. Position of the occlusal plane. This should be placed so that ~1–​2mm (d with age) of tooth are visible below the patient’s upper lip at rest. The occlusal plane should lie midway between the ridges parallel to the inter-​pupillary and the ala-​tragal lines. At rest, the tongue should rise just above the lower occlusal plane posteriorly. Centre lines, canine lines, and smile line should be marked. Trim lower record block to obtain correct lip support and bucco-​lingual position of posterior teeth. Adjust lower rim so that it meets upper evenly in RCP, with 2–​4mm of FWS: Vertical dimension. The FWS is the space between the occlusal surfaces of the teeth when the mandible is in the rest position. In the majority of patients it is 2–​4mm. The OVD for an edentulous patient can therefore be determined by measuring their resting face height and subtracting a FWS. Resting face height is assessed using: A Willis gauge, to measure the distance between the base of nose and the underside of the chin. Is only accurate to ±1mm. Spring dividers, to measure the distance between a dot placed on both the chin and the tip of the patient’s nose. This method is less popular with patients and is C/​I for those with a beard. The patient’s appearance and speech. Mark the centre lines. Locate rims in RCP, e.g. with bite-​recording paste: Horizontal jaw relationship. Record the more reproducible RCP. In the natural dentition, ICP is ~1mm forward of RCP; some prosthetists advise adjusting the finished dentures to allow the patient to slide comfortably between the two positions. Prescribe mould and shade of artificial teeth for try-​in. Consider using a facebow registration to mount the maxillary cast on the articulator. Complete dentures—recording the occlusion 309 Position of the anterior and posterior teeth Ideally, the artificial teeth should lie in the space occupied by the natural denti- tion. The extent to which it is possible to compensate for a Class II or III mal- occlusion depends upon the retention afforded by the ridges. In the natural dentition the upper incisors lie ~10mm anterior to the posterior border of the incisive papilla. With resorption this comes to lie on the ridge crest, there- fore the artificial teeth should be placed labial and buccal to the ridge, to give adequate lip support and a nasolabial angle of ~90°. Posterior teeth should be narrow to i masticatory efficiency. Low-​ cusped teeth are preferred, but cuspless teeth are useful for patients with poor natural retention or a ‘wandering’ ICP. When considering the colour, mould, and arrangement of the anterior teeth, the patient’s age, facial ap- pearance, and most importantly their opinion, must be considered. If you disagree about the suitability of their choice, document it. Type of articulator to be used for setting up the teeth Most textbooks advocate semi-​adjustable or average value articulators for F/​F dentures. However, most dentures are made on simple hinge articula- tors to the satisfaction of the majority of patients, probably because they are able to adapt to the occlusion that results. An average value type is the preferred method. It will give some degree of balanced articulation which can then be refined in the mouth and will help avoid the introduction of occlusal interferences. Common pitfalls Inaccuracies caused by poorly fitting bases. Rims contacting prematurely posteriorly and flipping-​up anteriorly, or vice versa. Failure to provide adequate FWS. This is less likely to occur if the rest position is recorded with only one denture or rim in position. Attempting to correct too much when replacing old worn dentures and exceeding the adaptive capacity of the patient. 310 Chapter 7 Restorative dentistry 3: replacing teeth Complete dentures—​trial insertion Trial dentures are constructed by setting-​up the prescribed teeth in wax on acrylic or shellac bases. Both the dentist and patient must be satisfied before the dentures are processed in acrylic. Clinical procedures Check the trial dentures On and off the articulator. Comparison with the patient’s existing dentures is helpful to see if the features to be copied or modified have been successfully incorporated. Singly in the mouth. To check extension, stability, and the position of the teeth relative to the soft tissues. Together in mouth. Examine vertical dimension, occlusion, aesthetics, and phonetics (‘S’ sound will be affected by i or d FWS). Seek the patient’s opinion Some advocate getting patients to sign an accept- ance slip before going to finish. Prepare post-​dam This should be placed just anterior to the vibrating line on the palate, which can be assessed by asking patient to say ‘Aah’. The degree of compressibility of the tissues is assessed and the depth of the post-​dam cut accordingly (usually ~1mm). The post-​dam is recorded by marking the master impression with indelible pen and prepared on the upper cast with a wax knife in the shape of a Cupid’s bow. Complete prescription to the technician This should include: Any changes in posterior tooth position or anterior tooth arrangement. For fibrous undercuts >4mm and bony undercuts >2mm, decide whether they are to be plastered out or the flange thickened for adjustment at finish. Tin-​foiling for relief of hard or nodular areas, if required. Gingival colour and contour. Denture base material. This is usually heat-​cure acrylic; however, metal bases are indicated for patients with a history of fractured dentures. Identification marker, which is preferably legible. Common problems and possible solutions Over-​extension of flanges. Reduce. Under-​extension of flanges. Try a temporary wax addition to flange first, to check effect of extending it. If this is satisfactory a new impression is required. Teeth outside neutral zone. Remove offending teeth and replace with wax which can be trimmed until correct. Incorrect OVD. If too small, can i by adding wax to the occlusal surfaces of teeth, but if too large, will need to replace lower teeth with wax and re-​record OVD. Occlusal discrepancy or anterior open bite or posterior open bite. Replace lower posterior teeth with wax and re-​record OVD. Complete dentures—trial insertion 311 Too little of upper anterior teeth visible. Reset anterior teeth to correct position and ask the laboratory to adjust occlusal plane accordingly. Too much of upper anterior teeth showing. The effect of reducing the length of the incisors can be judged by colouring the incisal region with a black wax pencil and then indicating desired change in position to lab. Inadequate lip support. An i in support can be assessed by adding wax to the labial aspect of the upper try-​in. A new try-​in will be required if large errors are being corrected or if any doubt still exists about the occlusion. 312 Chapter 7 Restorative dentistry 3: replacing teeth Complete dentures—​fitting Some adjustment of completed dentures is inevitable following processing. On average, a 0.5mm i in height occurs and a slight shift in tooth contact posteriorly. The main steps are: Adjustment of fitting surface First, smooth any roughness and if necessary gradually reduce the bulk of the flanges in areas of undercut until the denture can be easily inserted without compromising retention. Check occlusion The vertical dimension of the dentures is maintained by contact between the upper palatal and lower buccal cusps, therefore adjustment of these should be avoided if possible. Get patient to occlude and check contact with articulating paper. If contact uneven, or heavy contacts seen, adjust the fossae. For cusped teeth only, place articulating paper between occlusal surfaces and ask patient to make small lateral movements and adjust buccal upper and lower lingual (‘BULL’ rule) cusps only to remove any interferences. Remove any interferences to protrusive movements. Balancing contacts are desirable, but not essential unless they can be established easily by minor adjustments to working side contacts. Some authorities suggest providing even occlusal contact only at the time of fitting, allowing the patient to adapt to their new dentures before trying to achieve balanced articulation. Advice to the patient Verbal and written instructions should be given. Most patients take some time to adapt to their new dentures. During this time a softer diet is advisable. If pain is experienced, the patient should try to continue wearing their dentures and return for adjustment as soon as possible so that affected areas can easily be seen. If this is not possible, they should stop wearing the dentures until 24h prior to the next visit. Although patients should be encouraged not to wear their dentures at night, adaptation may be speeded up if they are worn full-​time for the first 1–​2 weeks. When the dentures are not being worn they should be stored in water to prevent them drying out and warping. Plastic denture boxes are cheap, and safer than a glass of water at the bedside. Cleaning (% Cleaning dentures, p. 316). Complete dentures—fitting 313 Review The patient should be seen 1–​2 weeks after fitting to ease the dentures and adjust the occlusion. Localization of the cause of any irritation due to a flaw on the fitting surface can be helped by: Pressure relief cream which is painted onto the fitting surface of the denture. Indelible pencil, or denture fixative powder mixed with zinc oxide, which is applied carefully to the area thought to be responsible and the denture inserted. On removal, the mark will have been transferred to the adjacent mucosa and should correspond with the damaged area. If there is no obvious cause relating to the fitting surface remember that occlusal faults can cause displacement and mucosal trauma, and an excessive OVD is a common cause of generalized soreness under −/​F (% Denture problems and complaints, p. 318). Stress the importance of regular review to all patients with dentures. 314 Chapter 7 Restorative dentistry 3: replacing teeth Denture maintenance 2 Review patients with F/​F annually. Regular maintenance will help prevent damage due to ill-​fitting dentures and will i the likelihood of early detection of oral pathology. Problems caused by lack of aftercare of F/​F As a result of resorption all dentures become progressively ill-​fitting, l loss of retention and stability. Movement of dentures in function may result in: Resorption. Predisposition to candidal infection. Denture irritation hyperplasia (% Problems in denture wearers, p. 426). Inflammatory papillary hyperplasia of the palate. All of these are exacerbated by wear of the occlusal surfaces. Rebasing The terms ‘rebasing’ and ‘relining’ are commonly used interchangeably. Strictly speaking, relining is replacement of the fitting surface (e.g. with a temporary material) and rebasing is replacement of most or all of the denture base. Rebasing is indicated where the only feature of F/​F that requires im- provement is the fitting surface; otherwise consider replacement F/​F using the copy method. For rebasing, the material of choice is heat-​cure acrylic (% Denture materials—​rebasing, p. 682), but this necessitates the patient being without their dentures while the addition is being made. Self-​cure acrylic applied at the chair-​side appears attractive, but its properties are inferior. For a heat-​cure rebase, a wash impression (ZOE or low-​viscosity elastomer) must be recorded inside the denture. Technique To avoid an i in OVD, record the impression for one denture at a time. Check occlusion and adjust if required. Note OVD. Remove undercuts from fitting surface. Correct extension and place post-​dam in greenstick. Apply impression material and insert in mouth. Get patient to close into contact with opposing denture. Check OVD and occlusion. Remove and examine impression; if unsatisfactory (or if in doubt) repeat. An alternative method for inflamed tissues is to record a functional impres- sion (% Functional impression, p. 307) over several days with a tissue con- ditioner (e.g. Visco-​gel®), in which case the resulting impression needs to be cast immediately. Denture maintenance 315 Tissue conditioners (e.g. Coe-​Comfort™, Visco-​gel set®) These are r0esilient materials which give a more even distribution of loading and thus promote tissue recovery. They are particularly useful where ill-​ fitting dentures have caused trauma, as it is important to allow the tissues to recover before impressions for replacement dentures or a rebase are taken. Technique Relieve any areas of pressure on the fitting surface and re- duce any over-​extension. A minimum thickness of 2mm is required and the material should not be left for >1 week. Repeated applications may be necessary. Tissue conditioners can also be used after pre-​prosthetic surgery. They become less soft with time therefore they should be replaced at least weekly. For patients who have very atrophic ridges and who struggle with denture wearing, a definitive soft lining aimed at distributing stresses more evenly to the denture bearing area may be helpful, e.g. GC reline™ or Permasoft®. GC reline™ may also be used to engage bony undercuts. Soft linings These are indicated for: Older patients with a thin atrophic mucosa. Usually for −/​F. Following prosthetic surgery. To utilize soft tissue undercuts for i retention, e.g. following hemimaxillectomy, clefts. It is wise to make a new denture first in acrylic and adjust the occlusion, before placing soft lining. A minimum thickness of 2mm is required, which may significantly weaken a lower denture necessitating placement of a metal strengthener on the lingual aspect. No material is ideal and soft linings are best avoided (% Soft liners, p. 682). 316 Chapter 7 Restorative dentistry 3: replacing teeth Cleaning dentures When new dentures are fitted, the importance of regular, thorough cleaning, especially of fitting surfaces, with soap, water, and a brush to prevent the build-​up of plaque, stain, and calculus should be emphasized. Unfortunately, few patients are sufficiently diligent, due in part to being con- ditioned by advertising, to expect to use a denture cleaner. Advise patients to clean their dentures over a basin of water to act as a safety net (Table 7.5). Practical tips Hypochlorite solutions are effective for acrylic den- tures when used overnight, but if used with hot water are liable to cause bleaching, therefore warn patient.6 The peroxide cleaners are popular but are ineffective if used for only 15–​30min as the manufacturers advise. See Table 7.6. Table 7.5 Cleaning dentures—​formulations Formulation Active ingredients Problems Powder Abrasives, e.g. calcium Abrasion carbonate Paste Abrasives + eugenol Abrasion + crazing (Dentu-​creme®) Abrasive + phenol oil Abrasion + sensitivity Hypochlorite Sodium hypochlorite Can corrode metal (Dentural®) Effervescent Dissolves to give alkaline Doubts about (Steradent®) peroxide solution effectiveness Dilute acids 3–​5% hydrochloric acid or Can corrode metal (Denclen®) 5–​10% phosphoric acid Enzymatic Proteolytic enzymes Not widely available Table 7.6 Cleaning dentures—​peroxide cleaners Avoid Use Visco-​gel® Acids, alkaline peroxide Hypochlorite Molloplast® Acids, alkaline peroxide Hypochlorite Coe-​Comfort™ Hypochlorite, alkaline peroxide Soap + water Metal denture Hypochlorite Alkaline peroxide Any denture Household bleach 6 C. A. Crawford et al. 1986 J Dent 14 258. CLEANING DENTURES 317 318 Chapter 7 Restorative dentistry 3: replacing teeth Denture problems and complaints The most common complaints are of pain and/​or looseness, which can be due to denture errors or patient factors. The latter should be foreseen and the patient warned in advance of the limitations of dentures. Unless the cause is immediately obvious, e.g. a flaw on the fitting surface, a systematic examination of the fitting and the polished and occlusal surfaces (including the jaw relationship) should be carried out. Pain This can be due to a variety of causes, including roughness of the fit- ting surface, errors in the occlusion, lack of FWS, a bruxing habit, a retained root, or other pathology. Forward or lateral displacement of a denture due to a premature contact can lead to inflammation of the ridge on the lingual or lateral aspect, respectively. With continued resorption, bony ridges be- come prominent and the mental foramina is exposed, which can lead to localized areas of specific pain. Pain from an individual tooth on P/​P Excessive load and/​or traumatic occlusion. Leverage due to unstable denture. Clasp arm too tight. Looseness This more commonly affects the lower than the upper den- ture (Table 7.7). Burning mouth This can be due to (i) local causes, e.g. i OVD or sensitivity to acrylic monomer, or be unrelated to the denture (e.g. irritant mouth washes, candidiasis); or (ii) systemic causes, e.g. the menopause, deficiency states, cancerophobia, or xerostomia. Cheek biting Check first that teeth are in the neutral zone. If satisfac- tory, d buccal ‘overjet’, i.e. reduce buccal surface of lower molars (provided there is a normal bucco-​lingual relationship). Speech See Table 7.8. Retching Map out extent of sensitive area on palate using a ball-​ended instrument and firm pressure, and check extension of denture. Palateless dentures may be a solution, but their retention is poor. Training dentures. These can take the form of a simple palate to which teeth are added incrementally, starting with the incisors. Hypnosis. Implants (% Introduction to implantology, p. 361) and a fixed prosthesis. Denture problems and complaints 319 Table 7.7 Denture faults—​looseness Denture faults Patient factors Incorrect peripheral extension Inadequate volume of saliva Teeth not in neutral zone Poor ridge form Unbalanced articulation d adaptive skills, e.g. elderly patient Polished surfaces unsatisfactory Table 7.8 Denture faults—​speech Patient’s complaint Possible cause Difficulty with f, v Incisors too far palatally Difficulty with d, s, t Alteration of palatal contour Incorrect overjet and overbite An s becomes th Incisors too far palatally Palate too thick Whistling Palate vault too high behind incisors Clicking teeth OVD Inadequate FWS Lack of retention The grossly resorbed lower ridge Resorption is progressive with time, which is a good argument for avoiding rendering young patients eden- tulous. The mandible resorbs more quickly than the maxilla, which exacer- bates the problem of retention for −/​F. Management is dependent upon the severity of the problem and the patient’s biological age. Minimizing destabilizing forces upon the lower denture, e.g. Maximum extension of denture base. d number and width of teeth. i FWS. Lowering occlusal plane. Neutral zone impression technique (% Special techniques, p. 306). Surgery (% Problems in denture wearers, p. 426). Implants (% Introduction to implantology, p. 361). Recurrent fracture Apart from carelessness, this is usually caused by occlusal faults or fatigue of the acrylic due to continual stressing by small forces. Flexing of the denture can occur with flabby ridges, palatal tori, and following resorption. Notching of a denture, e.g. relief for a prominent fraenum, can also predispose to #. Rx depends upon the aetiology, but in some cases provision of a metal plate or a cast-​metal strengthener may be necessary. 320 Chapter 7 Restorative dentistry 3: replacing teeth Candida and dentures Candida is a common oral commensal. It becomes pathogenic if the en- vironment favours its proliferation (e.g. dentures, i carbohydrate intake, antibiotic alteration of the bacterial flora) or the host’s defences are com- promised (% Oral candidosis (candidiasis), p. 438). Denture stomatitis Also known as denture sore mouth, a misnomer because the condition is usually symptomless. Classically, seen as redness of the palate under a F/​ − denture, with petechial and whitish areas. 90% of cases due to Candida albicans, 9% to other Candida spp., and 65yrs old. This is entirely different from biological age. Two factors are mainly responsible for the i relevance of dentistry for the elderly: an i in the proportion of the elderly in the population and the im- provements in dental health that have resulted in more people keeping their natural teeth for longer. The proportion of edentulous adults in the UK fell from 37% in 1968 to 6% in 2009.12 Challenges Age changes, both physiological and pathological. Disease and drug therapy (see Chapter 13). Delivery of care. Restorative problems Reduced adaptive capacity; therefore if teeth are unlikely to last a lifetime, the transition to at least partial dentures should be made while the patient is able to learn the new skills necessary. Age changes in the denture-​bearing areas, including bone resorption and mucosal atrophy. This leads to reduced masticatory forces and reduced masticatory efficiency. Root caries, which can occur following exposure of root surfaces by gingival recession, in association with changes in diet, d self-​care, and d salivary flow. Details of management are given in % Root caries, p. 25. Prevention of root caries in susceptible patients is possible using a topical fluoride mouthrinse, high fluoride toothpaste, or fluoride-​ containing artificial saliva, e.g. Luborant® or Saliva Orthana®. Tooth wear (% Tooth wear/​tooth surface loss, p. 252) is especially prevalent when partial tooth loss has occurred. Pulpal changes, including sclerosis (% Sclerosed canals, p. 354) and d repair capacity. Reduced manual dexterity, making OH procedures difficult. Epidemiological studies of the periodontal needs of the elderly population are still sparse and some trends may be masked by a high rate of edentulousness. The available evidence suggests that, although older patients develop plaque more quickly, the need for periodontal Rx i up to middle age, and thereafter the majority can be maintained by regular non-​surgical management. 12 Health and Social Care Information Centre 2009 Adult Dental Health Survey: Oral Health in the United Kingdom (M http://​www.hscic.gov.uk). Dentistry and the older patient 327 328 Chapter 7 Restorative dentistry 3: replacing teeth Age changes Age changes are defined as an alteration in the form or function of a tissue or organ as a result of biological activity associated with a minor disturbance of normal cellular turnover. In general d microcirculation, d cellular reproduction, d tissue repair, d metabolic rate, and i fibrosis. Degeneration of elastic and nervous tissue. These result in reduced function of most body systems. Oral Oral soft tissues A d in the thickness of the epithelium, mucosa, and sub-​ mucosa is seen. Taste bud function d. With age, an i occurs in the number and size of Fordyce’s spots (sebaceous glands), lingual varices, and foliate papillae. Recent evidence suggests that stimulated salivary flow rate does not fall purely as a result of age. However, medications, head and neck radiotherapy, or systemic disease can affect salivary output. Dental hard tissues Enamel becomes less permeable with age. Clinically, older teeth appear more brittle, but there is no significant difference be- tween the elastic modulus of dentine in old or young teeth. The rate of 2° dentine formation reduces with age, but still continues. Occlusion of the dentine tubules with calcified material spreads crownwards with age. Tooth wear is an age-​related phenomenon and can be regarded as physiological in many cases. However, excessive and pathological wear can be caused by parafunction, abrasion, erosion (dietary, gastric, or environ- mental), or a combination of these factors (% Tooth wear/​tooth surface loss, p. 252). Dental pulp i fibrosis and d vascularity mean that the defensive capacities of the pulp d with i age, therefore pulp capping is less likely to succeed. Also i 2° dentine and i pulp calcification. Periodontium i fibrosis, d cellularity, d vascularity, and d cell turnover are found with i age. Gingival recession has been previously thought to be an age change but is now known to be a part of periodontitis. Systemic Immune system A d in cell-​mediated response and d in number of circu- lating lymphocytes leads to an i incidence of autoimmune disease as well as a d in the older patient’s defence against infection. Also an i in neoplasia is seen. Steroid Rx for autoimmune disease may complicate dental Rx. Nervous system Ageing involves both a physiological decline in function and dysfunction associated with age-​related disease (e.g. strokes, parkinsonism, trigeminal neuralgia). A d in acuity compounds the problem. Cardiovascular Hypertension and ischaemic heart disease worsen with age. Anaemia is more common in the elderly. In general, the greatest problems arise when a GA is required. Pulmonary system Lung capacity d with age and chronic obstructive airways disease i in prevalence. Endocrine system Diabetes is more common. Age changes 329 Muscles d bulk, slower contractions, and less precision of control occur. This is highly relevant to dentures and function. Nutrition Poverty, impaired mobility, d taste acuity, and d masticatory func- tion can result in nutritional deficiencies in the elderly. These can manifest as changes in the oral mucosa. Mucosal disease, which is more common with i age Oral cancer (% Oral cancer, p. 452). Lichen planus (% Lichen planus, p. 468). Herpes zoster is more common with i age due to a d in T-​cell function. Neuralgia occurs more frequently after an attack in the elderly. Benign mucous membrane pemphigoid (% Mucous membrane pemphigoid, p. 444). Pemphigus (% Pemphigus, p. 442). Candidal infection is seen more frequently in the older age groups due to an i proportion of denture wearers and i immune deficiencies. This list is obviously not exhaustive. 330 Chapter 7 Restorative dentistry 3: replacing teeth Dental care for the elderly General management problems Medical and drug history (see Chapter 13.) It is wise to check any compli- cated medical problems with the patient’s GMP or physician. Unfortunately, many doctors are only familiar with the dental Rx they have personally re- ceived, therefore give details of what is proposed. Communication Communication with the elderly may sometimes require patience and understanding. Older patients may try to cover up deafness, poor eyesight, and lack of comprehension, so it is better to err on the side of over-​stressing an important point or instruction, but avoid sounding pat- ronizing. Active listening and questioning to check understanding is helpful. It is often helpful to enlist the assistance of a relative or friend of the older patient (with the patient’s consent). Oral hygiene OH may be compromised by arthritis &/​or a stroke. Advise an electric toothbrush or modifying the handle of an ordinary toothbrush to make it easier to grip, e.g. with an adhesive bandage or bicycle handlebar grips. Alternatively, self-​cure acrylic can be used to make a custom grip for a toothbrush. Delivery of care Dental practice Consideration should be given to: Access for a wheelchair or Zimmer frame. Dental practices are required to provide reasonable adjustments to ensure Rx is accessible (Equality Act 2010). Timing of appointments; e.g. for a diabetic patient these need to be arranged around meals and drug regimens, and early morning visits are probably C/​I for arthritic patients as it may take them a couple of hours to ‘get going’. Positioning of the patient. Some elderly patients are unhappy to be recumbent in the dental chair. In addition, this position is C/​I for those with cardiovascular or pulmonary disease. Adjust dental chair gradually as rapid movement from a flat to upright position can result in postural hypotension. Domiciliary care An estimated 12–​14% of the elderly population is bed- ridden or housebound to such a degree that they cannot visit their GMP or GDP. Domiciliary care aims to provide care for those patients.13 There is an i demand for domiciliary oral healthcare and guidelines for delivering these services have been published.14 13 D. Lewis & J. Fiske 2011 Dent Update 38 231. 14 British Society for Disability and Oral Health 2009 Guidelines for the Delivery of a Domiciliary Oral Healthcare Service (M http://​www.bsdh.org.uk). Dental care for the elderly 331 Key points Can Rx be carried out successfully? Consider maintenance required by any proposed Rx. Elaborate procedures which fail may leave the patient worse off. The objective is to maintain optimum oral function. Sometimes retention of a few teeth can be disadvantageous. Medical crises (e.g. a period in hospital) can result in a very rapid change in a previously stable oral state (e.g. rapid caries attack, loss of denture-​ wearing skill through lack of use). Avoid sudden changes in occlusion. The shape/​form of dentures should not be changed anteriorly. During restorative work refrain from introducing significant occlusal change. If necessary to extract teeth, do so a few at a time, with additions to existing dentures. Some clinical techniques of particular value in elderly patients Adhesive restorations, e.g. GI for root caries. Acid-​etch bridgework is less destructive to abutments and is therefore more fail-​safe. Gradual tooth loss, with additions to existing P/​P, is less demanding of a d adaptive capacity. Replacement dentures should be made with careful regard to existing appliances. Use of copying techniques again d amount of adaptation required. If recording the occlusion proves difficult, use cuspless teeth or lingualized occlusion. Mark dentures with the patient’s name. Bleaching and bonding and minimally invasive dentistry should be considered.

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