References

Davies S, Gray R. What is occlusion?. Br Dent J. 2001; 191:235-245
Milosevic A. Occlusion: 2. Occlusal splints, analysis and adjustment. Dent Update. 2003; 30:416-422
Davies S, Gray R, Whitehead S. Good practice in advanced restorative dentistry. Br Dent J. 2001; 191:421-434
Eliyas S, Martin N. The management of anterior tooth wear using gold palatal veneers in canine guidance. Br Dent J. 2013; 214:291-297
Wassell R, Naru A, Steele J, Nohl F. Applied Occlusion 2nd edn. Quintessentials of Dental Practice – 29, Prosthodontics – 5.London: Quintessence Publishing; 2008
Wassell R, Steele J, Welsh G. Considerations when planning occlusal rehabilitation: a review of the literature. Int Dent J. 1998; 48:571-581
Summitt J, Robbins J, Hilton T, Schwartyz R. Fundamentals of Operative Dentistry A Contemporary Approach, 3rd edn. London: Quintessence Books; 2006
Arnold M. Bruxism and the occlusion. Dent Clin North Am. 1981; 25:395-407
Muts E, van Pelt H, Edelhoff D Tooth wear: a systemtic review of the treatment options. J Prosthet Dent. 2014; 112:752-759
Gulamali A, Hemmings K, Tredwin C Survival analysis of direct composite Dahl restorations provided to manage localised anterior tooth wear (ten year follow-up). Br Dent J. 2011; 211
Milosevic A, Burnside G. The survival of direct composite restorations in the management of severe tooth wear including attrition and erosion. A prospective 8-year study. J Dent. 2016; 44:13-19
Brunthaler A, Konig F, Lucas T, Sperr W, Schedle A. Longevity of direct resin composite restorations in posterior teeth. Clin Oral Invest. 2003; 7:63-70
McCabe J. Applied Dental Materials, 7th edn. Oxford: Blackwell Publications; 1990
Bartlett D, Sundaram G. An up to 3 year randomized clinical study comparing indirect and direct resin composite used to restore worn posterior teeth. Int J Prosthodont. 2006; 19:613-617
Banerji S, Mehta SB, Ho CK. Practical Procedures in Aestheric Dentistry.Oxford: Wiley-Blackwell; 2017
Murray M, Brunton P, Osborne-Smith K, Wilson N. Canine risers: indications and techniques for their use. Eur J Prosthodont Restor Dent. 2001; 9:137-140
The Glossary of Prosthodontic Terms 9th edn, GPT-9, The Academy of Prosthodontics Foundation. J Prosthet Dent. 2017; 117:e1-e105
Celar A, Tamaki K, Nitsche S, Schneider B. Guided versus unguided mandibular movement for duplicating intraoral eccentric tooth contacts in the articulator. J Prosthet Dent. 1999; 81:14-22
Tamaki K, Celar A, Beyrer S, Aoki H. Reproduction of excursive tooth contact in an articulator with computerized axiography data. J Prosthet Dent. 1997; 78:373-378
Koyano K, Tsukiyama Y, Kuwatsuru R. Rehabilitation of occlusion – science or art?. J Oral Rehab. 2012; 39:513-521
Berry D, Poole D. Attrition: possible mechanisms of compensation. J Oral Rehab. 1976; 30:201-206
Loomans B, Opdam N, Attin T, Bartlett D, Edelhoff D, Frankenberger R, Benic G, Ramseyer S, Wetselaar P, Sterenborg B, Hickel R, Pallesen U, Mehta SB, Banerji S, Lussi A, Wilson N. Severe Tooth Wear: European Consensus Statement on Management Guidelines. J Adhes Dent. 2017; 19:111-119
UK Adult Dental Health Survey 2009.: The Health and Social Care Information Centre; 2011
Wilson P, Banerjee A. Recording the retruded contact position: a review of the clinical techniques. Br Dent J. 2004; 196:395-402
Mehta SB, Banerji S, Millar BJ, Saures-Fieto JM. Current concepts in tooth wear management. Part 3 Active restorative care 2: The management of generalised tooth wear. Br Dent J. 2012; 212:121-127
Capp N. Occlusion and splint therapy: Chapter 3 Tooth Surface Loss.London: BDJ Books; 2000
Mehta SB, Banerji S, Millar BJ, Saures-Fieto JM. Current concepts in tooth wear management. Part 4. An overview of the restorative techniques and materials commonly applied for the management of tooth wear. Br Dent J. 2012; 212:169-177
Rosenstiel S, Land M, Fujimoto J. Contemporary Fixed Prosthodontics, 5th edn. Oxford: Elsevier; 2016
Celenza F. The centric position: replacement and character. J Prosthet Dent. 1973; 30:591-598
Saunders W, Saunders E. Prevalence of per-radicular periodontitis associated with crowned teeth in an adult Scottish subpopulation. Br Dent J. 1998; 185:137-140
Edlehoff D, Sorenssen J. Tooth structure removal associated with various preparation designs for anterior teeth. J Prosthet Dent. 2002; 87:503-509
Dahl B, Krungstad O, Karlsen K. An alternative treatment of cases with advanced localised attrition. J Oral Rehab. 1975; 2:209-214
Dahl B, Krungstad O. Long term observations of an increased occlusal face height obtained by a combined orthodontic/prosthetic approach. J Oral Rehab. 1985; 12:173-170
Poyser N, Porter R, Briggs P, Chana H, Kelleher M. The Dahl concept: past, present and future. Br Dent J. 2005; 198:669-676
Hemmings K, Darbar U, Vaughn S. Tooth wear treated with direct composite at an increased vertical dimension: results at 30 months. J Prosthet Dent. 2000; 83:287-293
Ibbetson RJ, Setchell DJ. Treatment of the worn dentition: 2. Dent Update. 1989; 16:300-307
Gerasimidou O, Watson T, Millar B. Effect of placing intentionally high restorations: randomized clinical trial. J Dent. 2016; 45:26-31
Ibbetson R. Clinical considerations for adhesive bridgework. Dent Update. 2004; 31:254-260
Djemal S, Setchell D, King P, Wickens J. Long-term survival characteristics of 832 resin-retained bridges and splints provided in a post-graduate teaching hospital between 1978 and 1993. J Oral Rehabil. 1999; 26:302-320
Banerji S, Mehta SB, Kamran T, Kalakonda M, Millar BJ. A multi-centred clinical audit to describe the efficacy of direct supra-coronal splinting – a minimally invasive approach to the management of cracked tooth syndrome. J Dent. 2014; 42:862-887

The application of occlusion in clinical practice part 3: practical application of the essential concepts in clinical occlusion

From Volume 46, Issue 2, February 2019 | Pages 100-112

Authors

Subir Banerji

BDS, MClinDent (Prostho), PhD FDSRCPS(Glasg) FCGDent, FDTFEd, BDS, MClinDent (Prostho), PhD, FDSRCPS(Glasg), FCGDent

Articles by Subir Banerji

Email Subir Banerji

Shamir Mehta

Deputy Programme Director MSc Aesthetic Dentistry, King's College London

Articles by Shamir Mehta

Abstract

Abstract: Parts 1 and 2 of this series of articles addressed the clinical assessment of a patient's occlusal scheme and, where indicated, noted the appropriate occlusal records required to permit further evaluations to take place. This article will focus on the clinical application of the principles discussed previously.

CPD/Clinical Relevance: Following the assessment and recording of the static and dynamic intra-occlusal relationships, the application of the outcomes to achieve a long-term functional result is necessary to appreciate the relevance in clinical scenarios of the determinants, and their interaction is described.

Article

Having carried out a clinical assessment of a patient's occlusal scheme and, where indicated, attained the appropriate occlusal records to permit further evaluations to take place (as discussed in Parts 1 and 2), the next stage would logically involve the application of any information gathered to attain a desirable functional (as well as aesthetic) outcome with the proposed treatment plan.

A firm understating of the basic concepts in clinical occlusion (largely based on the guidelines for good occlusal practice)1 inclusive of the concept of the ‘ideal occlusal scheme’,2, 3 as well as acquiring the skills to attain the relevant occlusal records and use of associated apparatus, is important to achieve an optimal outcome during the occlusal rehabilitation of the patient.

Part 3 of this series will aim to appraise the circumstances when it may be appropriate to conform to the patient's existing occlusal scheme as well to consider when a re-organizational approach towards occlusal rehabilitation may be more suitable.

This article will also explore the aspect of patient ‘adaptability’ to occlusal changes. The cumulative gathering of knowledge surrounding this aspect is indeed challenging some of the traditionally maintained concepts in clinical occlusion.

How and when to take the conformative approach to restorative rehabilitation

The conformative approach to the restorative rehabilitation of a dentition would involve the provision of restorations to any of the affected teeth at the ‘pre-existing occlusal scheme, without incurring a change in the occlusal vertical dimension (OVD) and in the existing intercuspal position (ICP)’.4 Within the framework of the primary care setting, it is likely that the majority of the routine restorative treatment being provided will involve taking the conformative approach.5 There are, however, some circumstances where the conformative approach would generally not be indicated. Such circumstances may involve and/or include:3, 6

  • A planned increase in the OVD;
  • For severely malpositioned tooth/teeth with unacceptable function and or aesthetics;
  • Evidence of occlusal dysfunction, including signs of recurrent failure, de-bonding or fracture of existing restorations due to an underlying occlusal cause;
  • Signs of trauma from the occlusion (soft tissue or periodontal); and/or
  • A recurrence of TMJ disorders that may have relapsed following a period of successful occlusal splint therapy.
  • Most experienced practitioners will be all too aware of the consequences of failing to conform to the pre-existing occlusal scheme effectively, which may cumulate in possible deleterious longer-term consequences,5 that are often noticed in hindsight.

    The conformative approach with direct (chairside) restorative materials

    From a practical perspective, when a conformative approach is to be taken, it is imperative to leave sufficient reference points to make sure that the new restorations do indeed conform to the existing occlusal scheme.3

    Accordingly, when planning the making of a direct restoration for a tooth that is not involved with the provision of guidance to the mandible during any dynamic movements, it is appropriate to mark up the pre-operative centric stops in the intercuspal position (ICP) using articulating paper (as described in Part 2). The application of a thin layer of copal varnish prior to the actual process of marking the occlusal contacts with articulating paper will not only help to transfer marks from the paper, but also help to retain their presence for the duration of the procedure.7 Photographic records, video records to observe the dynamic relationship, as well as written records may also prove helpful. Pre-operative stops may be marked up in one colour; upon completion of the restoration, a different colour of articulating paper may be used − the presence of co-incidence between the two sets of markings together with evidence of patent Shimstock foil holding contacts in the intercuspal position (that may be heavier in the case of the posterior dentition), would be supportive of having effectively conformed to the pre-operative occlusal scheme.

    In the event of the centric stops being positioned on the restorative material, it is imperative to ensure that an adequate thickness of material is present at the aforementioned location so as to avoid premature failure. Furthermore, the occlusal contacts formed on the restoration should be of the pin-point variety as opposed to the broad-rubbing form, which may otherwise inadvertently serve to provide occlusal contact during excursive movements of the mandible. As part of the final verification of the completed restoration, the absence of any occlusal interference should also be ascertained.

    Where the affected tooth is involved with the provision of mandibular guidance and the use of a plastic restorative material has been selected to restore the occluding aspect of the tooth that provides this function, the situation is somewhat more complicated. With the use of plastic based materials, it may be acceptable to retain this feature amongst anterior teeth, as the level of occlusal loading is likely to be significantly lower than with the case further posteriorly in the oral cavity (assuming that an appropriate dimension of restorative material can be placed in the areas of functional loading).8 Indeed, there is good evidence to support the role of direct resin composite restoration for the functional-aesthetic rehabilitation of anterior teeth that have been significantly affected by the condition of tooth wear (TW), where guiding contacts will likely be provided by the restorative material (inclusive of cases treated by placing the restorative material in a supra-occlusal location); however, minor failures are to be expected.9, 10, 11

    Further caution should be applied in the case of a posterior tooth, as the occlusal loading will be higher, with the heightened risk of fracture or premature wear. Most experienced practitioners will of course be aware of the relatively lower tensile strength offered by silver amalgam, as well as the risk of bulk fracture as a common cause of failure of direct posterior resin composite restorations, especially associated amongst patients who may display a tendency towards parafunctional jaw clenching and grinding habits and where micro-filled type materials may have been prescribed to fabricate the restorations.12, 13, 14 A choice therefore needs to be made in relation to the retention of this feature in the post-treatment scenario.

    If the decision has been taken to retain the role of the occluding surface with guidance, pre-operative centric stops together with the dynamic occlusal contacts should be identified and marked up using articulating paper, as described in Part 2 of this series. A pre-operative silicone index/key can be prepared of the occluding surface of the tooth either prior to carrying out any tooth preparation, or following a mock-up protocol (as described below in relation to the canine rise restoration − where the patient's jaw crudely serves as a form of articulator in trialling differing occlusal prescriptions) or from a diagnostic wax-up. The information provided by the silicone key can be used to help guide the application of resin composite in a manner that will aid the transfer of the occlusal prescription and thus copy the occlusal anatomy into the definitive restoration. Final adjustments may be made intra-orally to ensure that the correct functional form is ultimately attained. Patients should, however, be advised of the heightened risks of mechanical failure, as considerable stresses will be incurred by the dental material in this location. The use of a silicone key fabricated prior to the removal of a large discoloured, with perhaps some marginal leakage yet functionally sound, anterior composite restoration may be useful to copy the functional prescription in the replacement restoration and therefore conforming to the existing occlusal scheme.

    In some cases, the decision may be taken to lower the mechanical burden on the material by eliminating the role of the occluding surface in providing mandibular guidance (maintaining the centric stop only). This must, however, be undertaken with caution as it may result in the tooth being visibly shorter in height than from its pre-operative status. The latter may not only have possible aesthetic implications, but also include the prospect of transferring the guiding contact onto another surface in the patient's oral cavity, which may prove less favourable. The actual effect of adjusting away the guiding contact can be determined using a set of diagnostic casts mounted in centric relation (as discussed in Part 2), whereby selective grinding can be performed on a set of dental casts.

    Should the above circumstances prove unacceptable, a decision may be taken to prescribe an indirect dental material/restoration that offers superior mechanical properties (ensuring that valid informed consent is attained), or to consider the addition of dental material (circumstances permitting) at another location in the patient's mouth, so as effectively to ‘lift’ the affected tooth out of providing mandibular guidance. In doing so, this would aim to shift this burden of responsibility to another tooth (Figures 1 and 2).

    Figure 1. Minimally prepped adhesive gold onlay restorations opposing each other in the molar region.
    Figure 2. The canine tooth is providing guidance in lateral excursion to disclude the onlays shown in Figure 1, therefore limiting the lateral forces on these restorations during function.

    Indeed, the approach of providing a ‘canine rise/Stuart lift restoration’15, 16 is one frequently prescribed by the authors and can prove very helpful in dealing with patients who present with recurrently failing class IV restorations at their central maxillary incisor teeth, where the loss of canine guidance as a result of tooth wear may have culminated in the former teeth becoming involved as a working side or non-working side interference, and has been described in further detail below, as well as for the overall management of patients presenting with TW.15

    The canine rise restoration

    This form of restoration acts by altering the cuspal incline of the canine teeth so as to provide a canine-guided occlusion, whilst retaining the occlusal vertical dimension constant. ‘The prescription of a riser restoration is however, not advocated for use on teeth that do not display signs of wear’.

    As part of the process of providing a canine-rise restoration, a complete occlusal assessment, as described in Part 1 of this series, should be carried out. The placement of the riser restoration will result in an alteration to the aesthetic zone. Thus, in order to help gain informed consent, a mock-up of the riser restoration should be undertaken, achieved by simply drying the canine tooth and placing resin composite (without any bonding) on the canine, thereby allowing the patient to visualize the aesthetic outcome.

    The technique described here relates to the placement of resin composite in a direct manner to restore a worn maxillary canine. Resin composite has the merits of being aesthetic, as well as allowing for contingency planning, should the patient be unable to tolerate the restoration. Adjustments can also be made readily, or the restoration removed with no significant harm being incurred. Resin composite is also a relatively inexpensive material. If the patient can tolerate the restoration, a more robust restorative material in the longer term can be considered.4, 15

    The appropriate shade of resin composite is then chosen. The centric stop on the canine tooth should be identified and marked using articulating paper. Following isolation, the enamel tissues should be cleaned using air abrasion or a slurry of oil-free pumice and the tooth prepared to receive a resin-bonded restoration. For a severely worn canine tooth, a dentine shade of resin composite may be required along with the enamel shade, taking great care only to add material superior (incisal) to the marked centric stop. The inadvertent placement of composite resin on or inferior (gingival) to the centric stop will culminate in an increase in the patient's occlusal vertical dimension.

    The efficacy of the completed restoration placed should be carefully evaluated; ideally it should provide canine guidance, which can be verified by asking the patient to demonstrate a lateral excursive movement. The centric stop should be coincident to the one pre-operatively, with no change in the OVD. The guidance should result in disclusion on both the working and non-working side. Articulating paper can be used to aid the verification process. The ramp provided should harmonize with the residual occlusion, otherwise displacement and/or mobility of the canine teeth may result.

    The conformative approach with indirect restorative techniques

    This occurs when providing indirect restorations affecting the occlusal surfaces that will be designed to conform to the existing occlusal scheme. Also, in the case of a single unit posterior crown/onlay, where the affected tooth is neither involved in providing any form of mandibular guidance during any lateral excursive or protrusive movements and does not carry the first point of contact in centric relation (CR) − the retruded contact position (RCP). Also, following the process of completing the tooth preparation, the use of hand-held casts to fabricate the restoration would be deemed sufficient; in this case, an intercuspal (ICP) record may be taken (if required), as discussed in Part 2.5 Upon the process of try- in and fitting of the definitive restoration, it is important to verify that the centric stops pre-and post-cementation are co-incident, with the presence of patent holding contacts elucidated, using a section of appropriately supported Shimstock foil (analogous to the processes as described above for a direct restoration).

    In the case of providing a limited number of multiple posterior restorations (three units or less − inclusive of dental bridgework) where the teeth will not be involved in providing mandibular guidance (such as for a patient displaying a canine-guided occlusal scheme), it would be sensible to attain a facebow record as well as an ICP record so as to enable the use of either an average value articulator5 or a semi-adjustable articulator, where average values may be applied to programme the device, as described in Part 2. This will hopefully provide the dental technician with further information on how best to develop the anatomical form of the restorations in relation to features such as the; cusp height, cusp angles and the placement of the cusp tips and grooves, as described in Part 1.

    When preparing multiple teeth (three or less), in order to maintain reference points it may be sensible to prepare a single tooth and obtain an ICP record immediately following the preparation, by interposing a dimensionally stable registration medium (as an appropriate form of PVS bite registration material or a cold-cured acrylic) between the opposing occluding surfaces in the intercuspal position. As the subsequent teeth are prepared, the first record is positioned and the recording process is repeated. Following the final preparation, the individual records are positioned and can be incorporated in an overall ICP registration. Confirmatory Shimstock holds can also be recorded from the other teeth. These records can then be used to mount the working cast against the opposing pre-mounted study cast. In the case of a single unit anterior crown that will not be involved in providing mandibular guidance during any dynamic movements, and/or in the case of the guidance being readily established from the adjacent teeth, the protocol as for a single unit crown as described above would be applicable.

    However, were it established that the given anterior tooth does indeed have a critical role in providing guidance, and there is the desire to preserve/‘copy’ this function into the definitive indirect restoration then, accordingly, a set of accurate pre-operative study casts should be fabricated, a facebow record taken and, if necessary, a record of the intercuspal position also attained.

    Using the above records, the diagnostic/pre-definitive restoration casts can be suitably mounted on a semi-adjustable articulator in the intercuspal position. A customized incisal guidance table (also sometimes referred to as an anterior guidance table, or incisal bite table) should then be fabricated.3 The latter has been defined as a device ‘used for transferring to an articulator the contacts of anterior teeth when determining their influence on border movements of the mandible’, and can be used to copy the occlusal prescription and features of the guiding surfaces, thereby preserving the desired dynamic occlusal scheme.17 The technical stages involved with the fabrication of the latter device in summary (Figures 3, 4, 5 and 6) include:3

  • The mounting of a set of pre-definitive restoration casts onto a semi-adjustable articulator;
  • Followed by the act of raising the incisal pin of the articulator by approximately 1.5 to 2 mm;
  • The tip of the incisal pin should be lightly coated in petroleum jelly (to act as a separator);
  • An appropriate quantity of cold-cured acrylic should be mixed according to the manufacturer's instructions and, when at the ‘doughy’ stage, the material should be transferred to the incisal guidance table. There are a variety of cold-cured acrylic materials that can be used for this purpose;
  • Whilst the acrylic material is still setting, the tip of the incisal pin should be transcribed through the material by moving the upper member of the articulator backwards and from side-to-side, thereby guiding the incisors through simulated excursive and protrusive movements; in this way, a record will have been made of the articulator during dynamic movements;
  • Once set, it is important to verify that the incisal pin has formed a patent contact with the registration material (thereby ensuring that the ICP has been maintained) − this can be checked using a section of suitably supported Shimstock articulating foil;
  • The table can be carefully trimmed to remove any excess, without compromising the record, concomitantly permitting optimal visualization of the movements of the tip of the pin whilst making sure it remains in contact with the acrylic based table;
  • The working cast can now be mounted against the antagonistic pre-existing cast (using an intercuspal record if necessary);
  • The customized incisal guidance table can then be used to fabricate the definitive restoration, applying the record of the pre-restorative envelope of mandibular movement to determine the desirable crown height, length and anatomy of the guiding surfaces. In an analogous manner, it is important to ensure that the incisal pin remains in contact with the guidance table in the appropriate manner, which can be verified using Shimstock foil as well as GHM articulating paper.
  • Figure 3. In this case, the upper left canine tooth is to be replaced with a metal ceramic implant-supported crown with the same canine guidance as present on the diagnostic crown. The figure shows the anterior customized guidance table has been constructed using the cast of the diagnostic crown for the canine guidance.
    Figure 4. The upper working cast and the newly fabricated crown are shown here as for the case in Figure 3 and the canine guidance has been maintained as per prescription using the anterior customized guidance table.
    Figure 5. Close-up of an anterior customized guidance table showing the pattern of the indentation.
    Figure 6. Close-up of an anterior customized guidance table with the articulator pin in contact during right lateral excursion of the mandible.

    Following the fabrication of a guidance table, the diagnostic cast is replaced with the working cast and the ICP mounting is confirmed. The guidance table now enables the technician to replicate the functional aspects to be replicated into the new restorations.

    Finally, when planning the making of multiple indirect posterior teeth restorations, which may also be involved in providing mandibular guidance (with group function), it would be appropriate to attain a facebow record, a record of the ICP following the process to completing the preparations, as well as lateral and protrusive records (as described in Part 2), to permit the setting of the location of the superior and medial walls of the articulator crudely to simulate the fossa anatomy, as per the records attained. However, concerns with the accuracy of the taking of lateral and protrusive records have been expressed in the literature, with one study reporting duplicity at the level of the articulator to occur amongst approximately 73% of intra-oral protrusive and 81% of intra-oral laterotrusive articulator contacts for up to 4 mm of movement, with another study documenting concerns with the limits to the ability of the articulator to reproduce excursive tooth contacts.18, 19

    Indeed, the risk of further errors and inconsistences likely to be introduced, during the process of the mounting of dental cast and the programming of the articulator, has resulted in some debate concerning the actual merits of using a sophisticated adjustable articulator over that of a more simplistic design (in relation to the final clinical/functional outcome).20

    The management of a posterior tooth carrying the first point of contact in CR − the RCP

    When the mandible is closed in the retruded arc of closure the first point of tooth contact is referred to as the Retruded Contact Position (RCP). A clinical decision will have to be made as to whether to replicate this contact on the indirect restoration. Consideration needs to be given to the material choice in these circumstances so as to optimize the load-bearing capacity of the material if this contact was to be replicated. If it has been decided that this contact will be replicated in the restoration then, prior to the reduction of the tooth, the upper and lower dental casts for the patient are mounted onto a semi-adjustable articulator using a facebow and retruded (CR) arc of closure records. The pin of the articulator is loosened and the RCP is identified. Starting from this position, an anterior guidance table is fabricated as described earlier. The teeth are brought forward into contact in the intercuspal position, and then the lateral movements are made in order to fabricate the guidance table. Once this has been achieved, the working cast can be mounted onto the articulator and the indirect cast restoration fabricated using the prescription as outlined by the customized guidance table.

    How and when to adopt a re-organized approach towards restorative rehabilitation

    According to Eliyas and Martin, a re-organized approach ‘requires the restoration of worn teeth in centric relation (CR) with an increase in OVD’.4 The re-organized approach to the restorative rehabilitation is therefore most likely to be prescribed for patients:

  • Where the existing ICP is unstable and/or undesirable;
  • With the loss of multiple tooth units;
  • With failing (often) heavily-restored dentitions, where mechanical failure is a likely feature, and amongst those presenting with TW, where restorative intervention is indicated;
  • Indeed, in the case of the worn dentition, given that dento-alveolar compensation often follows the loss of coronal tissue in order to maintain the functional merits of the masticatory system21 (thereby maintaining antagonistic units in contact), seldom will there be the required inter-occlusal clearance in the intercuspal position to accommodate a dental material which would be placed at/on the worn tooth/tooth surfaces in order to restore the presenting pathology. Consequently, there would be a need to provide the desired inter-occlusal clearance. The latter may be achieved by either:
  • Placing the restoration in a ‘supra-occlusal position’ (often using minimally invasive techniques), involving either a planned increase in the OVD, and/or by adopting a re-organized approach (utilizing any space that may be present between RCP and ICP), as discussed further below, or
  • By undertaking ‘subtractive’ tooth preparation(s), so as to create the required space (which in the case of a worn dentition may also require pre-restorative procedures such a crown lengthening).
  • Whilst the second approach may permit the application of a conformative protocol, in general it is not advocated as the initial mode of treatment,22 especially given the recent advances in adhesive dentistry, clinical occlusion, available dental materials and, of course, the established biological consequences of undertaking invasive tooth preparations (especially amongst teeth that have sustained, in some cases, severe loss of tooth tissue). A conformative approach is therefore unlikely to be taken in the case of undertaking restorative rehabilitation of a worn dentition unless:

  • In the presence of localized TW, whereby the required inter-occlusal clearance is available in the intercuspal position (as in the case of the affected tooth involved having no antagonistic contact, as may be seen with an ‘open bite,’ or where the rate of wear exceeds that of the rate of dento-alveolar compensation), and the presenting ICP is considered to be otherwise stable;
  • In the case of localized TW, where the placement of a restoration in supra-occlusion is not indicated due to unfavourable circumstances, or a failure to gain consent, resulting in the need for a subtractive approach (assuming the tooth is not involved as the first point of contact in CR); or
  • In the case of generalized TW, where space is not present as a result of the lack of discrepancy between RCP and ICP and a physiological freeway space of 2−4 mm is maintained.
  • Indeed, given the scale of TW affecting western populations, 23 it is worthwhile considering the protocol for undertaking the re-organized approach for the restorative rehabilitation of a patient with TW. This protocol can be equally well applied to other circumstances where an analogous approach is advocated. In general, the process would involve (Figures 711):

  • The attainment of a set of accurate diagnostic casts, a centric relation record and lateral and/or protrusive records (as described in Part 2) so as to permit the mounting of the casts on a semi-adjustable articulator, which may then be programmed accordingly.
  • The scale of the difference between RCP and ICP will now also become readily apparent from the mounted casts. For some patients, the space between these positions may be sufficient to allow restorative intervention. Indeed, in patients with severe TW (often presenting with the loss of posterior cusp tips and a wearing/failing anterior guidance), there is the tendency for the condyle to slide forward gradually anteriorly. Thus, locating CR can give the effect of ‘distalizing the mandible’ − the resultant space that may be gained can prove invaluable.24
  • However, in other cases, there will be a need to plan an increase in the OVD (undertaken by raising the pin on the articulator). The level of opening is determined by what would be required to meet the needs of the dental material to perform optimally, as well as to fulfil the functional needs and meet the aesthetic requirements of the patient (whilst respecting the limitations of the functional envelope). It has been suggested that the increase in vertical height can be up to 20−25 mm (taken between fixed reference points between antagonistic anterior teeth) in dentate patients, where the condyles remain in the desired position when recording CR − displaying rotation movement only around the terminal hinge axis.4
  • Having determined the occlusal prescription (as well as establishing the aesthetic prescription),15 a diagnostic wax-up may be prepared accordingly, so as to fulfil the aesthetic requirements and to provide the ideal occlusal scheme, as discussed in Part 1 − in summary providing a mutually protective occlusion or a canine occlusal scheme.
  • It is then important to verify the patient's acceptance of the planned occlusal scheme. Where possible this should be accomplished by using a minimally invasive approach, that would allow the ease of adjustment and, in the ideal, full reversal.25 Historically, in the case of patient's requiring a full mouth reconstructing (displaying generalized TW) the latter has been accomplished by the use of an occlusal stabilization splint (Figures 12 and 13), which would provide a temporary, removable ideal occlusal scheme (at the desired OVD).26
  • Compliance with splint therapy can, however, be problematic. Consequently, there has now been a move towards the use of adhesively retained restorations so as to ‘test drive’ the occlusal scheme that can be placed with minimal, irreversible tooth tissue loss. The latter is most often accomplished by taking a PVS index of the occluding surfaces of the diagnostic wax-up and using this information to assist/guide the placement of direct resin composite restorations.25, 27
  • With the current advances in digital dentistry, the use of CAD-CAM techniques to plan and ultimately fabricate indirect resin restorations may also provide the clinician with an alternative approach to that of the use of direct restorations. In either case, the occlusal splint or resin-retained restorations can be readily adjusted, either by a process of addition or subtraction of material, until the functional and aesthetic outcomes have been achieved.
  • In the longer term, having established functional stability and aesthetic and functional tolerance, indirect restorations can be predictably provided (that may be more costly and invasive but offer superior aesthetics and mechanical properties), using the conformative approach as described above.27
  • Where the use of conventionally retained crowns/onlays has been planned at the outset (for instance where the use of adhesively retained restorations may not be suitable or the patient has a heavily restored dentition comprising multiple units of existing crown and bridge work), the use of provisional restorations will help to provide a predictable approach (with or without the prior prescription of a full coverage occlusal stabilization splint).
  • Under such circumstances, the diagnostic wax-up can be duplicated. Using the duplicate cast, a vacuum-formed stent/splint can be prepared in the laboratory.
  • Following the process of tooth preparation (which can be further guided using indices made from the wax-up to help provide a precision approach to carrying out tooth reduction), the stent/splint can be used to fabricate custom-direct (chairside-based) provisional restorations using the desired crown and bridge resin. It would be advisable to prepare alternative teeth in order to allow single unit restorations to be provided, with the aim of optimizing the periodontal health by allowing for the practice of good oral hygiene procedures and also to ascertain the true tolerance as detailed below.
  • Alternatively, the dental technician can undertake tooth preparations on the mounted duplicate casts and fabricate custom indirect ‘shell-type’ acrylic-based provisional crowns with the occlusal endpoint incorporated into these restorations. The latter shells can then be relined chairside by the addition of a suitable material.
  • Some clinicians, however, prefer to take an impression following the completion of the preparations. The resultant casts can then be mounted using suitable inter-occlusal records in CR, and custom indirect provisional restorations fabricated in the laboratory so as to meet the occlusal ideals and aesthetic prescription. There are, of course, advantages and disadvantages of each of the options listed above; for further information, kindly refer to a reputable textbook in restorative dentistry/fixed prosthodontics.28
  • In either case, the provisional restorations should be tried-in and adjusted, as necessary, either by the subtraction or addition of direct resin composite, until the appropriate occlusal contacts and aesthetics are developed. The restorations should then be cemented using a provisional cement. The patient should be periodically reviewed for tolerance and adaptation by assessing for:
  • The presence of the desired occlusal scheme at the time of appraisal − with mutual protection, ideally with a canine-guided occlusion (although this may be challenging in the case of a patient with an anterior open bite, incisal edge-to-edge or Class III relationship).2 The ultimate aim, of course, is to achieve posterior disclusion when performing dynamic jaw movements;
  • Whilst it would be optimal to have shared occlusal contact on protrusion between the six pairs of anterior antagonistic teeth, in some cases (such as with lower incisor crowding),2 this may be very challenging to achieve practically. Therefore, whilst guidance in protrusion should be avoided at one single tooth (especially that of a maxillary lateral incisor), some level of compromise may need to be reached;2
  • Recurrent fracture of the provisional restoration(s);
  • Recurrent de-bonding/loosening;
  • Tooth mobility;
  • Discomfort;
  • Endodontic and periodontal complications;
  • Difficulty with mastication and phonetics;
  • Aesthetic outcome.
  • The provisional restorations may therefore require adjustment as described above, until an acceptable prescription is achieved. Following an observation period of approximately 6−8 weeks, with the patient reporting the lack of any symptoms and signs to suggest a functionally and aesthetically acceptable outcome, the features of provisional restorations may be copied using a conformative approach;
  • Impressions should be taken of the provisional restorations in situ and the pre-definitive restoration casts mounted in ICP, concomitantly employing the use of a customized guidance table to copy the dynamic prescription that will have been established by the process of using provisional restorations;
  • When prescribing ceramic-based restorations, these may be tried in at the biscuit stage, so as to allow for some adjustments to be made prior to the final glazing process;
  • The definitive restorations may be cemented initially using a provisional cement to allow a further period of appraisal.
  • Figure 7. This patient has a failing dentition and will undergo full mouth upper and lower rehabilitation with the use of implant-supported crowns.
    Figure 8. The side profile of patient in Figure 7 before commencement of the treatment.
    Figure 9. Full-arch upper and lower metal ceramic crowns supported by implants in the intercuspal postion for patient shown in Figures 7 and 8.
    Figure 10. (a,b). Patient in excursive movements showing posterior disclusion of the crowns.
    Figure 11. Side profile of the patient shown in figures 9-10 at a recall appointment after a few years.
    Figure 12. An upper full hard acrylic occlusal stabilization splint.
    Figure 13. An upper full hard acrylic occlusal stabilization splint in position in the patient's mouth.

    In summary, the above protocol would aim to achieve an outcome whereby RCP and ICP would be co-incident. Hopefully, it will now also be apparent that, in essence, the only clear difference between the conformative approach and the re-organized approach (from the point of technical execution) is that the latter requires some additional stages of planning and design before providing the definitive restorations, by using techniques to conform to the newly prescribed occlusal scheme that would have been determined by the careful use of techniques that permit adjustment by relative ease.3

    In relation to the re-organized occlusal scheme, it is worthwhile noting the observations of Celenza, where it has been shown that, with time, the slide from ICP to RCP will re-establish with a period of 2−12 years (possibly due to the effect of condylar remodelling, neuromuscular adaptation as well as the progressive wear of the restorative materials).29 This may perhaps challenge the need to be ‘absolute’ when trying to restore to a precise mandibular position − hence that of CR. The latter is perhaps further supported by the plethora of possible errors that may occur when trying to locate and record CR accurately (inclusive of impression-taking, casting, taking occlusal records, during the process of mounting the casts as per the records attained and by the limitations of the design of articulator used), whereby the perceived location of CR may in fact be inaccurate.20 Indeed, the capacity of the patient to adapt to the changes implemented perhaps has a very important role24 which, as discussed below, may to some extent challenge many of the traditionally held concepts in relation to clinical occlusion.

    The placement of dental restorations in ‘supra-occlusion’: the ‘Dahl Concept’

    As discussed above, for the majority of patients, tooth wear is accompanied by dento-alveolar compensation.21 The latter is a form of physiological compensatory mechanism that allows occlusal contacts to be maintained despite the process of tooth tissue loss in order to attempt to preserve the efficacy of the masticatory system. It is probable that adaptation at the neuro-muscular level will also allow patients to accept their ‘new’ intercuspal positions.

    The process of dento-alveolar compensation does, however, lead to the loss of the inter-occlusal space (that would otherwise exist due to the loss of tooth tissue), and thereby present a technical challenge from a restorative perspective in relation to the provision of space to accommodate the chosen restorative material.

    Historically, prosthodontic protocols for the restorative management of TW would have involved the need to undertake irreversible tooth reduction in order to create the space required to accommodate conventionally retained crown and onlay restorations/restorative materials. However, it has been well documented that the preparation of teeth to receive full coverage indirect restoration may culminate in not only the irreversible loss of pulp vitality, but also the marked loss of coronal volume.30, 31

    Whilst, in some cases of TW, the required inter-occlusal clearance can be attained by adopting a re-organized approach toward the rehabilitative process (by utilizing the discrepancy between RCP and ICP as discussed above), this approach may, unfortunately, culminate in several teeth (often teeth unaffected/relatively unaffected by TW) being in need of restorations in order to maintain occlusal stability. It will also increase the overall level of complexity of care, as well as the longer-term maintenance requirements and treatment cost. Under such circumstances, where there is a need to avoid subtractive tooth preparations, one possible option can be the placement of restorations in a supra-occlusal position; a concept commonly referred to as the Dahl Concept/Dahl Phenomenon and is now commonly utilized for the restoration of patients presenting with localized TW (Figures 1418).32, 33

    Figure 14. Localized palatal wear of the upper central incisors.
    Figure 15. Patient, as in Figure 14, showing incisal chipping and translucency which were the patient's complaints.
    Figure 16. Direct composite has been placed palatally on the upper central incisors without any tooth tissue removal to make space for the restorations. The anterior guidance in this case is equally shared by the two central incisor teeth.
    Figure 17. Immediately post op the posterior teeth are not in contact.
    Figure 18. The posterior teeth have re-established contact after a period of one month.

    It has been reported that, in most cases, following the process of placing a supra-occlusal restoration, re-establishment of occlusal contacts usually occurs within 4−6 months. However, it may sometimes take up to a period of 18−24 months.34

    The actual Dahl concept refers to the relative axial tooth movement that is observed to occur when a localized appliance or localized restoration(s) are placed in supra-occlusion and the occlusion re-establishes full arch contacts over a period of time. The concept is thought to occur through a process of controlled intrusion and extrusion of the dento-alveolar segments. Indeed, it was reported by Dahl and Krungstad33 that the inter-occlusal space created occurs through a process of combined intrusion (40%) and extrusion (60%). It has also been suggested by Hemmings et al that an element of mandibular repositioning involving the condyles may also be occurring concomitantly.35 Other phrases used to describe the latter concept include ‘minor axial tooth movement’, ‘fixed orthodontic intrusion’, ‘localized inter-occlusal space creation’ or ‘relative axial tooth movement’. The same principle may be extended to the controlled movement of posterior teeth to create space.34

    According to a review by Poyser et al, when considering the studies that have assessed the efficacy of the Dahl concept, a success rate of between 94−100% has been reported; furthermore, the level of space creation appears to be consistent, irrespective of age and sex.34 However, it would appear as if careful case selection with the placement of restorations in the supra-occcusal position is of paramount importance when aiming for a successful outcome with the application of this concept.

    Hemmings et al have reported that failures also occur in patients with gross Class III malocclusions, with mandibular facial asymmetry or with a lack of stable occlusal contacts in either ICP or CR.35 The lack of eruptive potential should also be given due consideration. Patients who may display reduced eruptive potential (and may not be suitable for this form of intervention), include those presenting with:

  • Bony ankyloses;
  • Dental implants restorations;
  • Conventional fixed-fixed bridgework; and
  • Those with anterior open bites.
  • The application of the Dahl concept should also be undertaken with great caution amongst patients who may have/had:

  • An active past history of periodontal disease;
  • Temporomandibular disorders;
  • Where endodontically teeth may be involved; and
  • Post-orthodontic treatment (as stability may become compromised).
  • Whilst there is little evidence in literature to suggest that the process of controlled intrusion and extrusion is associated with possible adverse effects, such as pulpal symptoms, periodontal problems, TMJ dysfunction symptoms and apical root resorption,34 the feature of compliance with removable appliances to achieve intra-occlusal clearance (as per the original appliances used) has been identified as a true concern. To overcome the issues related to patient compliance (as well as the aesthetic concerns of the removable prosthesis with visible clasp display), an alternative approach involving the provision of a fixed metal prosthesis cemented in supra-occlusion, with the same occlusal prescription as with the removable appliance, has been proposed.36 With the subsequent establishment of inter-occlusal clearance, the objective of the treatment plan was to replace the casting with conventional indirect castings.

    The removal of the metallic backings may, however, occur at a risk of further compromising an already brittle, worn tooth. Furthermore, the preparation of such teeth to receive conventional restorations may have a negative impact on the pulpal status and the quantity of remaining dental hard tissue. However, as material technology has continued to evolve, it has now become acceptable to use tooth-coloured materials, such as resin composite, on the affected surfaces as a substitute for adhesively retained metal backings. Such composite restorations may be considered to be medium term restorations (particularly where the wear is largely from erosive causes), and may offer a suitable means of restoring (especially the worn anterior dentition) by minimal intervention, concomitantly offering a satisfactory aesthetic outcome with the scope of contingency planning.

    In relation to occlusal planning, as discussed in Part 2, when attempting to treat a number of teeth (such as the anterior maxillary sextant) using the approach of placing restorations in the supra-occlusal position, it would be appropriate to mount a set of diagnostic casts in CR, and fabricate wax-ups to meet the aesthetic needs of the patient, as well as an occlusal end-point which should ideally conform to the mechanical ideal as discussed in Part 1.

    The concept of placing restorations in supra-occlusion is not only limited to the management of the patient presenting with anterior tooth wear. The concept may be equally as well applied to the:

  • Restoration of localized posterior wear, and the restoration of posterior teeth37 (where for instance there may be limited crown height to permit the placement of a restoration requiring occlusal coverage);
  • For the purpose of intruding over-erupted molar teeth when planning the provision of bridge prostheses;
  • For the restoration of edentulous spaces involving the placement of resin-bonded bridgework by minimal intervention,38, 39 as well as;
  • A means of managing the condition of cracked tooth syndrome (especially where there may be some doubt over the precise diagnosis).40
  • Summary and Conclusions

    It is important for the dental practitioner to be aware of the traditional protocols that are recommended when undertaking restorative rehabilitation. When faced with more challenging situations, it is relevant for the clinician to be aware of the nature of the treatment likely to be required and, where this may be beyond the scope of their practice, to consider the option of referral to a colleague.

    Whilst the advances in knowledge (especially in relation to the potential for adaptability in response to planned occlusal changes) are to some extent altering the way in which the subject of clinical occlusion may be pragmatically approached, it is important, when prescribing treatments that may involve the placement of restorations in the supra-occlusal position, that a careful patient assessment is carried out, valid informed consent is gained and the patient is closely monitored post-treatment.