Tooth surface loss: tools and tips for management

Loss of tooth form and posterior stability

Notwithstanding the aesthetic effects of TSL, particularly when anterior teeth are affected, TSL of posterior teeth leads to loss of the natural tooth anatomy and cuspal form which, in turn, leads to a less stable intercuspal position (ICP). This reduced ‘posterior stability’, together with TSL of anterior teeth and reduced anterior guidance, may lead to a forward postural and functional position with adoption of an edge-edge incisal relationship (pseudo Class III) and subsequent anterior toothwear (Figure 6) owing to lack of posterior disclusion and simultaneous functioning on anterior and posterior teeth. Conceptually, this is distinct to a discrepancy between the retruded contact position (RCP) and ICP and is more related to the lack of stability of the existing ICP. This presentation may be seen even with relatively mild wear and may be managed with intervention only to anterior teeth to restore incisal guidance. However, anterior restorations will be more prone to failure without a concurrent increase in posterior stability. Retention of direct composite in situations where anterior teeth require mainly or only incisal build-up may prove problematic, particularly with a background of attritive TSL – in such cases restoration of incisal edges and subsequent placement of adhesive (gold) palatal veneers to ‘protect’ the composite may prove helpful31 (Figure 7). Opinions vary regarding the relative importance of providing posterior stability and also the most appropriate restorative material to achieve this, as aptly demonstrated during recent interactive treatment planning discussions at the British Society of Prosthodontics (BSSPD) sessions at the Second Pan Dental Society Conference. However, it is this author's view that, in many cases of TSL where there is a need to restore posterior teeth, the durable restoration of two pairs of occluding molars (typically all four first molars) through provision of adhesive gold onlays with minimal preparation (see below) has much to commend it, either in isolation or as part of a broader treatment plan.

Dento-alveolar compensation and short teeth

When teeth lose tooth structure, the ‘space’ of lost tooth tissue is rarely left owing to dento-alveolar compensation that typically occurs in conjunction with progressive TSL.32^,33 Thus teeth may have short clinical crown heights and require restoration yet still be in functional contact with the opposing dentition; here problems present related to retention of any restoration and also related to maintaining pulpal health: the conventional method of obtaining space, ie removal of tooth structure with preparation, is likely to be injurious to the pulp or could even expose the pulp.

Methods to create space

Where TSL is localized to anterior teeth, space for restoration is typically required palatally and incisally. In such situations, it is often suggested that equilibration of the occlusion with RCP and ICP coincident will allow this space to be created. However, this approach entails removal of further tooth structure, which is difficult to justify in a patient whose presenting problem is that of loss of tooth structure. It is difficult to obtain stability in the newly established ICP, and the amount of space created is rarely sufficient to enable restoration: such an approach, therefore, seems hard to recommend. A more appropriate method for obtaining space is to undertake localized axial tooth movement utilizing the ‘Dahl concept’. The Dahl concept has been reviewed in depth elsewhere34^,35 and has evolved from the use of a removable appliance (Figure 8) to the use of direct or indirect restorations.

Use of direct composite to provide axial tooth movement is straightforward in most cases of anterior TSL. It is important that anterior teeth are built up not to recreate natural anatomy but with a more prominent cingulum to provide a flat ‘centric stop’ such that functional forces are directed axially. The use of a diagnostic wax-up and duplication of this to use as a matrix to ‘preview’ the intended outcome with a provisional material (Figure 9) and guide placement of composite is invaluable. A detailed guide of this technique using translucent stents and an ‘every other tooth’ technique has been previously published in this journal.36 Opaque silicone putty is readily and conveniently available and can also be used as a matrix, but in this case it is important to note that the resin-composite will need to be polymerized through the tooth structure with subsequent attenuation of the light intensity. If such a technique is adopted, a high power curing light is essential, as is further curing of the composite following removal of the matrix (Figure 10). An alternative to the ‘every other tooth’ technique is to use sections of metal matrix strip interproximally, embedded in the silicone (Figure 11): finishing and polishing is, however, more difficult in such cases.

During the phase of tooth movement, the restorations will be subjected to the entire occlusal functional load and some chipping or deterioration of the composite restorations is to be expected, however, following re-establishment of the posterior occlusion, the restorations typically remain serviceable as the definitive restoration, with only simple polishing or minimal refurbishment. It is for this reason that individual restorations rather than splinted restorations are essential. Concerns regarding splaying of anterior teeth are largely unwarranted provided the palatal form is appropriate. These restorations have been shown to have good medium term survival (median survival of ~5years) for both maxillary and mandibular teeth.37–40 When failure does occur, further direct repair is often possible. When a need for more robust restoration arises, ie a full coverage crown, the use of these ‘medium’ term restorations will have made this subsequent treatment easier and will also have enhanced the ‘life cycle’ of the tooth. Given the good survival, it is difficult to recommend full-coverage restorations as part of the initial treatment plan, and in many cases it is wiser to delay the final decision until after the posterior occlusion has re-established. However, in cases where there will be a clear need for subsequent crowns and thus separated restorations are not required, splinted composite restorations are much easier to provide and even more so if a combined indirect/direct technique is used, with the palatal contour formed indirectly and only the labial aspect left to be built up by hand (Figure 12).

Generalized TSL and direct composite

In cases of generalized TSL, where the majority of teeth would best be served by restoration, space is best obtained by increasing the occlusal vertical dimension (OVD) and providing full-arch or full-mouth restoration (see also decreased OVD below). This approach is often very extensive and technically demanding, not to mention potentially costly. The common approach when a full mouth restoration is contemplated is to assume automatically that teeth will require indirect restorations and that these will be full-coverage crowns. It is, however, uncommon for a patient with TSL to require the majority of teeth to be restored with full coverage crowns and, although published case reports of such treatments abound, the wholesale preparation of teeth and removal of further tooth structure in a patient who presents with TSL is unjustified: many such cases can be restored with direct composite alone or in conjunction with adhesive indirect restorations.

Survival of composite ‘reconstructions’ has been shown to be reasonable and, as argued above, for the use of composite anteriorly, future failure can be managed much more easily and the life-cycle of teeth extended:41 a matrix can prove very helpful to establish appropriate contour, particularly of the occlusal aspects of teeth (Figures 13 and 14) in a similar fashion to their use described above for build-up of anterior teeth. Whether considering anterior or posterior teeth, a ‘ring’ of enamel to which to bond gives more predictable bonding – this is often present in patients with TSL, perhaps owing to some protective effect of the gingival crevicular fluid. There is limited but conflicting evidence regarding the use of composite restorations, whether direct or indirect, to restore posterior teeth;41^,42 however, a balance needs to be made between treatment options that have a low ‘cost’ to the tooth (in terms of loss of tooth structure and little iatrogenic harm to pulpal tissues) but high maintenance and those treatment options that may well have better survival, but at the cost of loss of tooth structure owing to the preparation required and potentially catastrophic failure.

If composite restorations are restricted primarily for restoration of axial contours of teeth and for restoration of functional surfaces of premolar teeth (generally not functional surfaces of molars) and are placed as part of a planned treatment, with the occlusal scheme providing good posterior stability (perhaps with indirect onlays – see below) and posterior disclusion on excursive movements (discussed above), then a positive treatment outcome is likely.

Even when there is a need for indirect restoration, the use of direct composite can be invaluable during the provisionalization phase and this ‘stepping-stone’ phase may be extended for the convenience of the patient or dentist to break up what is otherwise extensive treatment (Figure 15). In cases where direct composite will not achieve the treatment aims, extensive preparation of teeth should still be avoided where possible and minimal preparation and adhesive techniques employed.

Minimal preparation and adhesive indirect restoration

In many patients with TSL the use of adhesive restorations can overcome a number of issues including:

In situations where it is simply too difficult to achieve full correct contour with direct composite restoration of posterior teeth, provision of an indirect composite can overcome these problems, although often minimal preparation is helpful to aid accurate seating of the restoration and/or achieve a margin that is amenable to finishing. Similarly, ceramic restorations may be etched with hydrofluoric acid, silane-treated and bonded with resin-based luting cement and used as an alternative aesthetic adhesive onlay (Figure 16). Both these techniques are particularly suited to restoration of premolars, although the improved aesthetics and durability of porcelain is somewhat offset by the slightly greater bulk of material required and greater difficulties in repair and maintenance when failure does occur. Similarly, the use of ceramic in thin sections with minimal preparation may be appropriate for anterior teeth requiring full-coverage crowns as an alternative to ‘traditional’ crowns (Figure 17). Such resin-bonded crowns (RBCs) have good survival and excellent aesthetics.43^,44 In cases where there is concern regarding the amount of force that these restorations may be subjected to, for example TSL due to attrition/bruxism, then a reasonable compromise is to use stronger more durable crowns, for example porcelain fused to metal crowns with metal guiding surfaces, but to restrict these to canines and use RBCs for incisors, ensuring shared guidance on protrusion. There is scant evidence regarding their suitability for use on posterior teeth and thus they should be used posteriorly with caution, although the author has used RBCs successfully on premolars with good results in patients where posterior stability is good and attrition/bruxism is not a factor.

A convenient and conservative means by which to provide durable posterior stability is through the use of adhesive gold onlays to restore molars with minimal preparation45^,46(Figure 18). A variety of methods have been employed to bond gold alloys to tooth structure, whether for molars or for anterior palatal veneers, as described above: the simplest of these is alumina-blasting, however, heat-treatment to produce an oxide layer provides a more effective solution.47^,48 Whichever technique is employed, it is important that a bi-functional resin is used (for example Panavia F, Kuraray, Osaka, Japan).49

Decreased OVD and gross wear

If the rate of TSL is such that it progresses quicker than dento-alveolar compensation occurs, then a decrease in the OVD may be seen. The relevance of this in dentate patients is debatable; such a presentation may lead to a more extensive treatment plan entailing full-mouth or full-arch reconstruction at an increased OVD, but traditional arguments relating to tolerance (or otherwise) of such an increase are likely to be of little relevance in mostly/fully dentate patients where any restoration is all tooth supported.50^,51 However, the situation in partially dentate patients who will require mucosal supported tooth replacement is frequently very different. In many cases, a lack of opposing units with TSL on those few teeth that do occlude leads to a lack of stable posterior support, which may in turn give the appearance of a decreased OVD, usually with a more cranial and forward habitual/functional position and consequent anterior TSL, sometimes termed a ‘collapsed’ occlusion.52 In many of these cases, the RCP is at an appropriate OVD but is simply unstable, and what appears to be a problem relating to lack of space to restore anterior teeth is, in fact, a problem of a lack of posterior support with space available anteriorly (Figure 19). Where RCP contacts do not exist to guide determination of OVD, and where TSL is gross and uncompensated (Figure 20), basic principles for provision of removable prostheses should be followed. In a few cases, patients may present with multiple retained teeth, but with these not being suitable for restoration, even with remedial treatment, in such cases an overdenture is often the only treatment option, even if this entails further reduction of the clinical crowns (Figure 21): where such reduction of clinical crowns would be excessive, then an overlay/onlay denture may be more appropriate.53 Such options may also be the modality of choice where economics or time constraints do not allow consideration of complex and extensive treatment plans.

Adjunctive treatments

Surgical crown lengthening may be required where conventional full-coverage indirect restorations are planned but insufficient tooth structure is present to retain a crown, but can be obtained through moving the entire attachment apparatus apically (which requires bone removal in conjunction with gingivectomy or an apically repositioned flap). Similarly, such procedures may be helpful to improve aesthetics and increase the length of incisors in an apical rather than incisal direction.54 Another technique to allow restoration of teeth with insufficient coronal tooth structure to retain a crown is to place a post-retained core. This obviously will entail elective endodontic treatment and this decision should not be made lightly, nor without thought to the subsequent functional forces that will be placed on the then-compromised tooth. It is important to note that elective endodontic treatment itself (with subsequent post-retained core crown) will not create space, but is simply to manage the problem of insufficient coronal tooth structure. In many cases where TSL is extensive to the degree that this is a considered treatment option, other methods of gaining space will also be required.