Current Concepts on the Management of Tooth Wear: Complex Restorative Care Cannot Be Cure Upon the Physical Properties of Three Compos- Part 2

Current concepts on the IN BRIEF • Provides an overview of the available restorations commonly used for the PRACTICE management of tooth wear: management of pathological tooth wear. • Illustrates some of the techniques currently used to restore worn dentitions. • Stresses the role of contingency planning, part 4. An overview of the as often the quantity and quality of available tooth tissue has already been severely compromised by the process of restorative techniques and dental wear. materials commonly applied for the management of tooth wear

S. B. Mehta,1 S. Banerji,2 B. J. Millar3 and J.-M. Suarez-Feito4 VERIFIABLE CPD PAPER

This final article of the four part series on the current concepts of tooth wear will provide the reader with an evaluation of the data available in the contemporary literature with regards to the survival analysis of differing restorative materials, and their respective methods of application to treat tooth wear. It is vital that the dental operator is familiar with the role of differing materials which may be used to restore the worn dentition, some of which may prove to be more suitable for the management of particular patterns of tooth wear than others. The active management of tooth wear unfortunately commits the patient to a lifelong need for considerable maintenance, and it is imperative that this is understood from the outset.

RESTORATIVE MATERIALS/ 1 RESTORATIONS COMMONLY According to Poyser et al. the position USED IN THE MANAGEMENT within the dental arch of each worn tooth OF TOOTH WEAR and the quantity of remaining tooth tissue will determine the most appropriate A number of materials/restorations are form of restoration. While conventional commonly used for the treatment of restorations have been used historically, cases presenting with tooth wear (TW). such as conventional cast gold onlays, partial and full veneer crowns or metallo- ceramic crowns, with advances in adhesive Fig. 1 Gingival enamel ‘ring’, commonly seen among worn teeth, which is vital to the CURRENT CONCEPTS ON dentistry a number of other options have successful outcome of resin-retained/resin THE MANAGEMENT OF become available, including: bonded restorations TOOTH WEAR • Direct composite resin restorations 1. Assessment, treatment planning and • Indirect composite resin restorations (rather than relying solely on dentine bond- strategies for the prevention and the • Cast adhesive alloys (metal palatal ing), and concomitantly help to control mar- passive management of tooth wear veneers and metal adhesive onlays) ginal microleakage. The exact reason for the 2. Active restorative care 1: the management of localised tooth wear • Adhesive ceramic restorations. presence of the gingival ring of enamel is 3. Active restorative care 2: unclear, but the neutralising effect of the the management of generalised tooth wear These will be considered in more detail presence of gingival crevicular fluid is 4. An overview of the restorative techniques below. thought to play an important role. It has and dental materials commonly applied for also been suggested that the presence of the management of tooth wear Direct composite resin restorations plaque at the gingival margin may act as Composite resin has been used for the res- a barrier to prevent the diffusion of erosive 1,2General Dental Practitioner and Senior Clinical Teach- er, Department of Primary Dental Care, King’s College toration of anterior teeth for the past 30 acidic substrates. London Dental Institute, Bessemer Road, London, SE5 years. The use of resin composite to treat Direct composite resin when used in the 9RW; 3*Professor, Consultant in Restorative Dentistry, Department of Primary Dental Care, King’s College cases of tooth wear was first described by management of cases of tooth wear offers London Dental Institute, Bessemer Road, London, SE5 Bevenius et al.2 the advantages of:4 4 9RW; Section of Periodontology, Faculty of Dentistry 3 and Medicine, University of Oviedo, Oviedo, Spain According to Briggs et al. a rim of enamel • An acceptable aesthetic outcome *Correspondence to: Professor Brian J. Millar is usually present at the gingival margins • A non-invasive procedure Email: [email protected] of severely eroded teeth. The latter, com- • May be used as a diagnostic tool Refereed Paper monly termed the ‘gingival ring’, as shown • Well tolerated by pulpal tissues Accepted 14 November 2011 DOI: 10.1038/sj.bdj.2012.137 by Figure 1, will improve the predictability • Minimally abrasive to ©British Dental Journal 2012; 212: 169-177 of bonding hard tissue to resin composites antagonistic surfaces

• Being easy to repair and adjust • Cost-effective material • Restorations may be applied within a single visit.4

The disadvantages of direct resin composite restorations for the above purpose a b include:4 • Polymerisation shrinkage, which Fig. 2 Clinical case 1. Tooth wear has been restored by the ‘freehand’ application of resin composite, with zero tooth reduction. a) Pre-operative case of mild attrition that has just may culminate in marginal leakage started to involve the dentine layer. Intervention advised to prevent further wear, in particular and staining differential wear. b) The post-operative view at 12 years • Accelerated wear rate (when compared to metals/ceramics) and possible inadequate wear resistance for posterior use5 • Bulk fracture(s) • Discoloration • Need for optimal moisture control • Need for good quality/quantity of dental enamel a b • Complexity of application, particularly for palatal veneers. Limited control over occlusal and inter-proximal contours.

Briggs et al.3 have described the use of direct composite resin restorations as an intermediate restorative option among c d cases with tooth wear (‘intermediate composite restoration’; ICR). The use of an ICR with complementary routine preven- tative measures to manage ‘at risk sites’ (to reduce long term catastrophic damage, particularly where future sporadic bursts of aggressive wear may take place with changes in lifestyle or personal circum- e f stances), has been an advocated approach.3 Fig. 3 Clinical case 2. The direct application of resin composite to treat a case of tooth wear, It has been proposed that an ICR would with the aid of a silicone matrix derived from a diagnostic wax up. Figures show pre-op (a and b), a diagnostic model (c), palatal putty matrix (d), and restored teeth with Gradia Direct help to protect vulnerable teeth during the (GC) (e and f) so called ‘danger years’. However, it has also been argued that the placement of intermediate composite resin restorations will undoubtedly com- • Use of a customised polyvinylsiloxane aesthetically acceptable and occlusally mit the patient to long-term restorative (PVS) matrix stable/functional restorations). For cases maintenance care, which may ultimately • Use of a customised vacuum formed of anterior maxillary wear, where a re- culminate in the need for subtractive, matrix. organised approach is adopted, it has been conventional indirect restorations.6 suggested that composite resin is added While a number of different restorative The application of direct composite resin initially to the cingular areas of the max- placement techniques have been described ‘freehand’ has the potential to offer excel- illary canines, and the mandible subse- in the literature, it is generally accepted lent aesthetic results, as shown by clinical quently manipulated into its retruded arc that resin composite restorations when case 1, Figure 2. of closure (before curing). The patient is applied to areas of high loading should With the use of the freehand tech- then guided to close into the uncured resin placed be in the thickness range of 1.5- nique restorations may be placed within until the desired space is achieved to place 2.0 mm.1 The techniques for applying this a single visit, without the need for tak- material to restore the remaining anterior material directly can be considered under ing impressions. However, this method teeth.7 The remaining teeth are then ‘built three broad categories, hence: of material application is considerably up’ by the incremental application of • Freehand application dependent on operator skill (to achieve resin composite using the occlusal stops

a b c Figs 4a-c The use of a transparent silicone index to facilitate the application of resin composite to treat a case of lower anterior tooth wear

ascertained initially as a reference guide. This technique does, however, require the operator to be very familiar with average mesio-distal tooth widths and relative tooth proportions respectively. The use of a stable, rigid ‘polyvinylsiloxane – PVS matrix guide’ formed from a b the palatal or lingual aspect a diagnostic wax up (or a duplicate cast of a wax up), where the desired occlusal prescription and aesthetic form have been established indirectly has the potential for providing excellent results by facilitating the use of an incremental build up technique, which in turn will allow aesthetic layering and c d the application of increments to permit Figs 5a-e The use of a sectioned optimal light polymerisation, as depicted thermoplastic template where a ‘labial by clinical case 2, Figure 3. The accuracy of window’ has been cut away to permit resin the wax up and a well adapted matrix are, application to manage a case of multiple diastemata however, critical to a successful outcome. With the advent of clear or transparent silicones such as Memosil (Heraeus Kulzer, Newbury, Bucks, UK), it is possible e to ensure that adequate quantities of material are applied onto worn palatal surfaces (without the inclusion of major voids) The use of a ‘vacuum formed matrix length retained by the means of custom- and subsequently light cured (through the guide’ has been well described by Daoudi ised wedges trimmed so that they do not matrix), which is an obvious drawback and Radford.8 They suggest that a dupli- interfere with the placement of the matrix. associated with the use of non-transparent cate cast poured in dental stone is formed Resin is applied into the matrix (follow- materials. The lack of rigidity offered by from a diagnostic wax up, and a vacuum ing the appropriate conditioning of the available transparent silicones can make formed transparent matrix is formed in a affected teeth for the purposes of adhesive the accurate positioning of such indices material of choice. Mizrahi9 has advocated bonding) and firmly seated into place and difficult, which may culminate in the need that the matrix should be formed from a resin light cured. for copious adjustments. Furthermore, the rigid material (to permit accurate seating) The management of interproximal removal of ‘flash’ from the material may and be of approximately 1 mm in thick- excess, and the inability to apply resin prove challenging (by virtue of its trans- ness. The matrix should be extended over incrementally or indeed in layers, are parent nature), which will also increase sound teeth that do not require restora- obvious drawbacks with this approach. the need for further alteration of the resin tion to provide positioning stops for the Other commonly encountered prob- composite restorations post light-curing. matrix to remain in place when resin is lems with the use of a vacuum formed For further details on how to fabricate and applied. Small relief holes can be cut into guide include: apply a PVS matrix guide the reader is the matrix to avoid air entrapment.8 • Sensitivity that may occur during the referred to an article by Nixon et al. from To avoid bonding of resin material curing process due to heat build up 2008.7 Figure 4 provides an example of a to interproximal surfaces, Daoudi and • Poorly fitting matrices transparent silicone index to treat a case of Radford8 have described the interproxi- • Overfilling of matrices, which will lower anterior tooth wear by the applica- mal placement of wedge shaped cellulose culminate in gross excess tion of resin composite. acetate strips of approximately 4 mm in • Air entrapment.

The use of this method has been suggested to be unsuitable in cases of advanced severe tooth wear.8 To overcome the problem of interproximal excess, Daoudi and Radford8 have described an approach involving the restoration of alternative teeth or ‘every other tooth’ to a b permit the complete establishment of individual tooth anatomy with emphasis on the interproximal areas. It may also be possible to ‘modify’ a thermoplastic template to permit the more accurate placement of resin composite to treat cases of anterior tooth wear.9 Shown in Figure 5 is a case of diastema closure, c d attained by resin application. A thermoplastic template has been formed from a duplicate cast of a diagnostic wax up. Following clinical evaluation of the fit of the template, a labial window has been cut away so that resin has been applied to the aproximal surfaces, initially just short of the inter-proximal contact area. e f The contact areas have been formed subsequently, aided by the placement of a Teflon coated dead soft sectional matrix (Garrison Solutions), which provides control of this key area, and avoids the creation of over- hanging restorations. The use of the clear thermoplastic template permits light curing from a palatal direction. This approach can g h be extended to include the management of the worn dentition, where direct resin composite has been prescribed to treat affected surfaces, as described by Mizrahi in 2004.9 Please note the omission of rubber dam isolation in this case, as the patient was unable to tolerate the presence of a dam. An alternative means of applying a i j vacuum formed matrix to treat cases Figs 6a-j Clinical case 3. Use of a modified vacuum formed template for management of of tooth wear to overcome some of the worn lower anterior teeth problems listed above is shown by clinical case 3, Figure 6 for the management of worn lower anterior teeth. The latter approach, whereby the vertical dimension placed interproximally through slits cut clinical condition is further complicated was increased by 3 mm by the addition of into the template. Resin was inserted into by the diminutive nature of these teeth direct resin composite (Gradia Direct, GC) to the template by means of holes cut into the and often less than optimal visual access. the worn lower anterior teeth (LL1, 2; LR2, template of a suitable size to accommodate Figure 6 depicts an example of a ‘modi- 1). A sectioned 0.5 mm thickness thermo- a resin composite ampoule. Composite resin fied vacuum formed template’, whereby plastic template (Acorn Plastic) was used was applied, after being warmed in a com- warmed resin composite has been injected to apply resin composite, formed from a posite resin warmer, Ena Heat Micerium, into a modified (sectioned) matrix. It is a duplicate cast of an accurately prescribed Italy. The worn teeth were restored on an case of a 79-year-old male patient whose diagnostic wax up, fabricated to provide individual basis. PTFE tape was placed presenting complaint related to the poor an even anterior guidance on protrusion interproximally while etching teeth, to appearance of his lower anterior dentition and canine guided occlusion during lateral prevent resin adhering to undesired areas and poor aesthetics of his partial dentures. and protrusive mandibular movements. interproximally. The existing dentures were The patient has an FWS of 6 mm. It was Metal matrix strips of 0.05 mm thickness modified by the application of a light cured decided to adopt a minimally invasive (Polydentia, Mezzovico, Switzerland) were composite resin (Revotek, GC) to achieve

stable occlusal contacts, while the definitive occluding surfaces among patients with however, only in recent times have mate- dentures were being constructed. parafunctional tooth grinding/clenching rial formulations been introduced into the The above technique of ‘injection habits. A failure rate of 28% was deter- marketplace which possess the desired moulding’ has the potential to permit the mined over an observation period of three mechanical properties and aesthetic val- application of resin in incremental layers, years. Failures among posterior teeth may ues to provide an alternative to the use of whereby a cone of dentine shade could be accounted for by the fact that mate- dental ceramics. be applied centrally before applying the rial is commonly inadvertently applied to Most contemporary indirect compos- desired enamel shade of appropriate resin certain areas in thin sections, which may ite resin products are based on hybrid with the template then in situ. fracture, flex, crack or chip.1 The choice of resins which offer a superior level of Direct composite resin restorations are resin (hybrid versus micro-filled) may also fracture resistance when compared to frequently used as ‘medium term restora- be influential to prognostic outcome, as a micro-filled resins. Indirect resin resto- tions’ for cases of TSL, often before the study by Schmidlin et al.14 has reported a rations offer two primary advantages application of conventional restorations very favourable outcome for the role of over direct counterparts, hence a reduced (especially where there is a need to cre- direct hybrid composite resin restorations level of polymerisation shrinkage (as this ate space inter-occlusally by controlled to treat posterior segmental wear over a takes place extra-orally) and the ability tooth movement), hence in a ‘diagnostic’ medium term evaluation period. to apply further treatment after the initial manner.3 The use of resin composite for It is important to note the conclusions curing phase. the latter application will help with the of a long term study which has compared According to Wendt17 the hardness and design of the correct horizontal and verti- the survival of direct and indirect restora- wear resistance of certain composite resins cal occlusal scheme, thereby simplifying tions for the treatment of advanced tooth can in theory be further enhanced by dry the fabrication of longer term definitive wear.15 Over a ten-year assessment period, heating ‘post-light curing’. Specifically, the restorations which are often made from a survival rate of 62.0% was reported for properties of hardness and abrasion resist- more costly materials such as cast gold direct resin bonded composite restorations ance could hypothetically be increased by alloys, as discussed in further detail below. (RBCs) and 74.5% for indirect convention- up to 60 to 70% by dry heating at a tem- A number of studies have evaluated the ally retained restorations respectively. Bulk perature of 125°C (258°F) for a period of efficacy of resin composite to treat wear fracture was noted as the most common five minutes after first light curing.17 A of the anterior dentition. A success rate of mode of failure for RBCs, which were slow rate of heating has also been pos- 86% for labial direct composite veneers readily addressed conservatively by either tulated to cause continued or ‘extended’ was reported over a period of three years repair or replacement, while failures for polymerisation, culminating in a greater by Welbury in 1991.10 Hemmings et al. elu- the indirect category of restorations were molecular size as well as annealing of cidated a success rate of 90% with direct generally of a catastrophic nature, fre- polymer chains, which has been suggested resin composite restorations placed in quently involving the complete loss of res- to reduce the potential for residual strain maxillary anterior teeth (at an increased torations, which often required subsequent formation within the polymer matrix and vertical dimension), with a mean follow up root canal therapy or indeed extraction. a concomitantly increased ability to flex period of 30 months.11 Similar results have Interestingly, a promising survival rate of with the tissue when an occlusal load is published by Redman et al.12 and Poyser 78% was described for RBCs placed in the applied (a feature which ceramics do not et al.1 over a similar evaluation periods anterior region. display, and is indeed thought to account (two to five years). Interestingly, the study In conclusion, direct resin restorations for their increased level of brittleness).18 by Poyser et al.1 involved the application may serve as acceptable medium term (or Alternative approaches to heat treat- of direct resin composite restorations to intermediate) definitive restorations par- ment include the application of a slower worn mandibular anterior teeth to increase ticularly for the management of anterior rate of polymerisation (which has been the anterior occlusal vertical dimension tooth wear. However, patients must be suggested to improve the potential for a between 0.5 and 5.0 mm. advised of the need for potential regular greater level of movement of molecular The study by Hemmings et al.11 reported need for polishing, repair and occasional chains and thereby increase the potential a higher success rate for hybrid resins ver- replacement respectively. Their use for the for energising activation sites) and the sus microfilled composites, possibly related management of worn posterior teeth how- elimination of internal porosities within to a slightly superior rigidity offered by the ever requires careful consideration. the resin matrix (which may occur during former variety, making them less vulner- The use of glass fibre re-enforced com- conventional light curing).18 It is thought able to flexure and fracture upon tensile posite resins as described in a case report that oxygen entrapment in the resin may loading; the primary cause of failure was by Akar and Dundar16 or the development lead to partial polymerisation (due to the bulk fracture. of composites with better wear resistance well documented ‘air inhibition effect’), Data for the prognosis of direct resin and minimal/no shrinkage may hold a thus curing can be carried out in a cham- composite restorations to manage worn future promising potential. ber where normal environmental oxygen posterior teeth are very limited. Bartlett is exchanged for a non-reactive gas such and Sundaram13 reported a relatively poor Indirect composite resin restorations as nitrogen or argon.18 prognosis of direct composite resin restora- The use of indirect composite resin restora- However, medium (five years19) and long tions when used to restore worn posterior tions was first described in the mid-1970s; term (11 years20) clinical comparison studies

respectively on the performance of indirect composite resins have shown that the clinical performance of indirect resin restorations to not be significantly superior when compared to direct materials (where criteria such as occlusal wear, fracture or secondary caries have been assessed).20 However, a b the wear resistance on aproximal surfaces has been described to be improved by the application of heat treatment.21,22 According to Kilpatrick and Mahoney,4 the advantages of indirect composite resin restorations when used in the management of cases of TW include: • Improved control over occlusal c d contour and vertical dimension, when compared to direct restorations, particularly in the case of a larger number of multiple restorations • Perhaps less time involved chairside • Can be added to and repaired relatively simply intra-orally • Aesthetically superior to cast metal e f restorations • Less abrasive than indirect ceramic restorations • Superior strength and wear resistance when compared to direct materials • Polymerisation shrinkage negated intra-orally, other than at the level of the resin luting agent. g

Fig. 7 Clinical case 4. Pre-operative views (a and b); indirect composite palatal veneers made The disadvantages include: on articulated casts (c) were bonded to upper 321/123 to increase OVD, protect the eroded • Inferior marginal fit (versus metal surface from further wear, reduce the palatal dentine sensitivity, restore the aesthetics (d), and ceramic)4 provide a ‘bonded Lucia jig’ effect and encourage mandibular repositioning from CO to CR. • Restorations may be bulky These were bonded on and left for four months for the occlusion to stabilise at increased OVD. Posterior contact was formed (though combination of intrusion, extrusion and • Require at least two appointments mandibular repositioning). Lower labial indirect veneers were also fabricated and bonded on. • Laboratory costs A further four months allowed the occlusion to stabilise (e). Then to complete the aesthetics • May require the removal of hard tissue a labial set of composite veneers were placed (f and g). This case was completed without any tooth reduction, in a completely additive manner. undercuts • Cementation line may require masking with direct materials • Wear and leakage of the resin based the variety of ‘fixed Dahl appliances’. not necessarily displaying signs of tooth luting agent A three year retrospective study by wear, the results of a study by Bartlett and • Possible inadequate wear resistance Redman et al.12 where 73 cases of localised Sundaram13 have provided less promising for posterior use. anterior maxillary tooth wear were treated levels of clinical performance, where indi- by the application of Artglass (an indirect cusp coverage (micro-filled) composite In 2002, a promising short to medium rect ceromer), a very favourable outcome resin restorations were used to treat cases term success rate of 96% was reported was reported, although a high incidence of posterior tooth wear among patients by Gow and Hemmings,23 where 75 teeth of minor wear was described to occur on with tooth wear. A failure rate of 21% displaying signs of palatal TW had been these restorations. over an evaluation period of three years restored with indirect resin composite While the application of indirect com- was described by the latter group; fracture palatal veneers (Artglass), over an obser- posite restorations with cuspal coverage and complete loss were the most common vation period of two years. Thirteen cases on posterior teeth has been reported to be modes of failure. The authors concluded required minor repairs, which were readily very successful, with an ‘excellent level that the use of resin composites (of either achieved intra-orally with the use of direct of clinical performance’ over an evalua- direct or indirect variety) to restore worn materials. Many of the latter cases were of tion period of 30 months24 among teeth posterior teeth should be contraindicated,

according to the results of their randomised castability Ni-Cr alloys; however, the bio- clinical study.13 logical hazard associated with the inha- An interesting approach is to combine lation of alloy dust containing beryllium the application of indirect and direct com- generated during the finishing and polish- posite resins, as shown by the example of ing stages has culminated in a decline in clinical case 4, Figure 7. its use. However, concerns remain over the use of Ni-Cr alloys among patients who Cast adhesive alloys may display hypersensitivity to nickel. Traditionally conventionally retained indi- The advantages of adhesive cast resto- rect restorations fabricated from cast alloys rations when applied to worn occluding have been used to restore worn teeth/tooth surfaces include:4 Fig. 8 This cast gold overlay was used to restore tooth wear on 27 and shows the surfaces where the aesthetic requirements • They may be fabricated in thin post-view at 24 years with no debonds over are not of paramount importance. Smales sections (0.5 mm) that period. and Berekally15 have reported a relatively • Very accurate, predictable fit attainable good long term prognosis for full veneer • Minimal wear of antagonistic surfaces gold crown restorations when used to • Protective of residual tooth structure manage worn posterior teeth. • Suitable for posterior restorations With the advent of chemically active among parafunctional patients resin luting cements containing agents • Placed supra-gingivally, therefore such as 4-META or dimethacrylate conducive to good periodontal health, (whereby phosphate ester groups are incor- and offer simplification of technique porated into the BisGMA resin), such as with regards to tooth preparation and Superbond (Sun Medical, Kyoto Japan) impression making Fig. 9 An example of a Ni-Cr onlay and the Panavia based cements (Kuraray, • Minimal tooth preparation required. Japan) respectively, it has been possible remaining peripheral margins and extend to form a bond between ‘cast adhesive Disadvantages include: up to the incisal edge, so as to optimise restorations’ and the dental hard tissues • May be cosmetically unacceptable due adhesive retention, aid placement and with a high level of predictability. The to the ‘shine through’ of improve resistance to shearing loads.26 latter has reduced the need for aggressive metallic grey Margins may be finished with either a tooth preparations, thereby lessening the • Limited use among anterior teeth knife edge or chamfer finish. The prepara- ‘biological damage’ inflicted upon already which display wear of the incisal edge tion of cingulum rests may also be useful. compromised tooth tissue (which would be • Adhesive cast restorations do not offer The internal surfaces of all metallic resto- necessary to attain adequate retention and the ease of repair intra-orally ration should be sandblasted with 50 µm resistance form to insure longevity with • There is a need for copious, good alumina (in the case of Type III gold alloy conventional indirect restorations). quality enamel to create acceptable restorations, oxidation must be completed Type III gold alloy and alloys based bond interface before sandblasting). The inclusion of a on nickel-chromium (Ni-Cr) are the most • Close proximal contacts with adjacent metal tag or location lug is also helpful commonly used alloys for the fabrication teeth among posterior teeth may pose when cementing in metal palatal veneer of fixed metallic adhesive restorations, as a concern with the application of resin restorations. The latter may be readily shown by clinical cases 2 and 3 in paper 125 bonded onlay restorations (Yap)27 removed with diamond burs and finished and by clinical case 3 above. While Ni-Cr • Difficulty with the placement of with a set of abrasive discs, such as Sof-lex alloys offer improved bond strengths to provisional restorations. discs (3M, ESPE). resin luting agents, and a higher modulus For either form of restoration (veneer or of elasticity (thereby enabling application The terms ‘gold hats’ or ‘gold bonnets’ onlay), while an inter-occlusal clearance in thinner sections, in conjunction with have been used synonymously with that of between 0.5-1.5 mm is required, this more conservative tooth preparation[s] of posterior adhesive onlays.1 The prepara- may be attained (as is the case with any than Type III gold alloys). Type III gold tion of a tooth to receive a metal adhesive other material described in this section) alloys offer easier working properties and onlay should include an occlusal clearance through an ultra-conservative approach, superior polish ability (on account of a of 1.0-1.5 mm with a minimal chamfer whereby restorations are placed in supra- higher relative value of elongation and of 0.7-1.0 mm finish line occlusally.26,27 occlusion, and occlusal contacts estab- lower hardness respectively) and superior Where the restoration is to be fabricated lished by the process of controlled tooth wear characteristics.26 Examples of adhe- from Ni-Cr alloy, a more conservative intrusion and extrusion. With metallic sive onlay restorations fabricated from the preparation can be applied.27 restorations, owing to their high fracture two materials described above are shown For anterior teeth, the preparation resistance, this can be undertaken with in Figures 8 and 9 respectively. to receive a metal palatal veneer (also a higher level of confidence. A success The addition of beryllium has been termed ‘palatal shim(s)’ should include the rate of 89% for metal palatal veneers was described in the literature to improve the removal of any undercuts and cover all reported by Nohl et al.28 where 210 cast

metal palatal veneers and observed over applied in bulk, which may necessitate of application will depend on a plethora a period of 56 months. considerable tooth reduction, and of factors such as the preference of the Type III gold restorations do, however, be associated potentially with operator (and patient), the relative skills require either heat treatment of the fit sur- higher failure rates among patients of the operator, the mechanical demands face (this may be carried out at 400°C for who display signs of wear by required of the restorative material and four minutes in an air furnace) to form parafunctional tooth clenching and undoubtedly the presence of any finan- an active oxide layer, or tin plating of the grinding habits respectively cial constraints. fit surface, to increase the surface energy • Potentially abrasive to the opposing When applied correctly, it would appear to enhance bonding with resin cements. dentition (particularly in the case that most of the materials listed above pro- The combination of sandblasting and tin of feldspathic porcelains); glazed vide relatively high (90%) medium term plating had been described by Wada29 to porcelain has been shown to be 40 prognostic outcomes (with an evaluation maximise resin retention to gold alloys. times more abrasive to antagonistic period of approximately five years). Where Tin plating is thought to produce a rough- surfaces than Type III gold29 possible, however, a reversible, adhesive, ened surface which will not only enable • Difficult to repair intra-orally additive approach should be adopted, as micro-mechanical retention but also • Difficult to adjust discussed further below. chemical adhesion through the formation • Susceptible to degradation wear in of hydrogen bonds with tin-oxide. The acidic environments CONSENT AND CONTINGENCY PLANNING dulling effect of the metallic restoration • Costly. also commonly referred to in the litera- The importance of gaining informed ture as ‘grey-out’ or ‘shine through’ may Magne et al.31 have described an ultra- consent when contemplating the active be partially masked by the use of opaque conservative approach to the management restorative management of a patient resins or by the covering of the labial sur- of worn palatal surfaces with the use of presenting with tooth wear cannot be face with a tooth-coloured veneer. occlusal therapy combining centric rela- over-emphasised. Channa et al.30 undertook a five-year tion and the use of the Dahl principle Such cases often require complex, analysis in 2000 of the clinical performance (with short term direct composite resin extensive, time consuming and finan- of gold adhesive onlays to restore posterior restorations) to create space for palatal cially expensive treatment regimens. It occlusal surfaces. A survival rate of 89% ceramic veneers with the need for minimal is vital that the patient understands the was reported. The prime cause of failure was tooth reduction. eventual restorative outcome, the scope wear of the metal alloy which resulted in A number of other studies such as of occlusal changes being planned, the cement exposure and subsequent de-bond- Aristidis and Dimitris32 have described a limitation of currently available restora- ing. According to Yap,27 resin bonded onlays success rate of 90% over a period of five tive materials and techniques, as well as are most suitable for teeth where at least two years, for the management of TSL with the adaptation required to adjust to a new walls are left intact (especially if there are ceramic restorations. occlusal prescription. no patent interproximal contacts), and more For the case of ceramic onlays, an The risks of intolerance and restorative so for teeth where there is a plan to increase interocclusal clearance of 2.0 mm is failure by means of restoration fracture, the occlusal vertical dimension. Where there required. Preparations should be finished de-bonding, leakage, secondary caries, may be a cosmetic concern with the display occlusally with a shouldered margin. wear, discoloration and the high main- of metal from adhesive onlay, sandblasting Where a metal substructure is used, ideally tenance needs should be discussed at the intra-orally post-cementation may help to the occlusal surface should be fabricated outset. The possibility of initial speech reduce the visible gleam associated with this in metal to not only reduce the need for and masticatory difficulty should also form of the restoration. further inter-occlusal clearance but also be raised, as well as the risks develop- to provide a less abrasive surface; the ing TMJ dysfunction and tooth mobil- Adhesive ceramic restorations application of a metal collar at the margin ity. Where conventional restorations are Ceramic restorations when used in the may also help to reduce the levels of tooth planned, the further loss of tooth tis- management of cases of TSL may provide: reduction in this critical load bearing area. sue and the risks of pulpal damage or • Superior aesthetics (however this is Oh et al.33 have suggested that an iatrogenic pulp tissue exposure should also depends on where the margin occlusal splint should be provided for be explained. is located) nocturnal use (post-restoration placement) As every practitioner will be aware, • Good abrasion resistance for all wear cases treated with ceramics to all restorations will ultimately fail. Often • Lower relative surface free energy protect restorations from parafunctional patients who have parafunctional tooth compared to resin composites, thus less habits associated which may be associated grinding/clenching habits may resume susceptible to staining with premature degradation. activity post-restoration. For the case of • Higher level of gingival tissue Dentine bonded crowns, as discussed in a worn dentition, where the availability tolerance. paper 2,34 may also prove to be useful resto- of dental hard tissue is already compro- rations for the management of wear cases. mised, treatment plans should where possi- However, such restorations are: In summary, the choice of a particu- ble be minimally invasive, thus permitting • Brittle and prone to fracture unless lar material and its respective method contingency options, should they fail. It

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