Temporomandibular disorders. Part 6: related irreversible restorative interventions

Localized occlusal adjustment

A localized occlusal interference may occur iatrogenically following placement of a non-conformative restoration, or due to tooth movement secondary to trauma, loss of periodontal support, or loss of an adjacent or opposing tooth. Most patients rapidly adapt to localized occlusal interferences and no lasting symptoms are reported.^1,2 However, if changes to the articulatory system are outside a patient's adaptive capacity, the patient is likely to return with discomfort. A double-blind randomized controlled trial demonstrated that patients with a history of TMD were significantly more likely to have signs of TMD after placement of a small composite occlusal interference compared with a control group; patients with no history of TMD given the same interference were no different from controls.³ These results show the influence of adaptive capacity, highlighting that there is a group of patients predisposed to TMD who are less able to tolerate changes to their occlusion.

If TMD symptoms begin soon after the introduction of an occlusal interference, it would be warranted to adjust this interference. The occlusion, in this case, may be a precipitating or perpetuating factor in a patient who has a predisposition to TMD.⁴ This is a relatively simple procedure, but nonetheless should only be considered following a thorough history and a systematic occlusal assessment to identify the interference: this will be either a new deflective contact, around which the patient has to deviate, or a working/non-working side interference. This approach should only be considered where the diagnosis is certain and a maximum of two teeth require adjustment. Articulated study models and mock adjustments are not always required (Figure 1).

A case should be considered more akin to an equilibration in situations where: more than two teeth need adjusting to remove the interference; the temporal relationship between TMD onset and the creation of the interference is lacking; or the adjustment involves an intercuspal position contact (thereby reducing the occlusal vertical dimension, or rendering a tooth non-functional). Equilibrations require additional steps, training and experience. As with many concepts in dentistry, the boundary between localized occlusal adjustment and occlusal equilibration can be blurred, and if there is any doubt, there should be a low threshold for considering an adjustment as an equilibration with careful consideration and additional planning.

Occlusal equilibration

Occlusal equilibration is defined as the modification of the occlusal form of the teeth with the intent of equalizing occlusal stress, producing simultaneous occlusal contacts or harmonizing cuspal relations.⁵ Its role in the management of TMD has been debated for decades with many studies being of low quality. Effects shown range from complete resolution of symptoms with equilibration, to placebo/mock equilibration providing relief for the majority of patients.^6,7 A Cochrane systematic review⁸ found no compelling evidence for occlusal equilibration in the routine management of TMD. Although the review only included three studies, these findings were corroborated by Tsukiyama et al⁹ whose study used more inclusive criteria to allow pooling of results from eleven studies with a wider range of methodology.

The lack of evidence for a benefit from occlusal equilibration is not equivalent to evidence of no benefit, but given the invasive and irreversible nature of this treatment, extreme caution needs to be exercised when considering this approach. A thorough history and examination of the masticatory system is of course required, as well as an exhaustive attempt at all conservative and appliance-based therapies. This will certainly include the construction, adjustment and monitoring of a well-made stabilization splint.

The ‘classic’ indication for an occlusal equilibration is a patient who achieves control of their TMD symptoms with a stabilization splint, but upon weaning, has return of symptoms. This indication is logical, but entirely anecdotal, and relies upon the assumption that the reason for symptomatic relief was purely due to creation of a removable ideal occlusion and not any of the other mechanisms by which the stabilization splint may be having an effect (see Part 4 of this series).¹⁰

Patients who are most definitely not candidates for occlusal equilibration are those who present with the complaint of a long-standing, ill-defined dissatisfaction with the way their teeth meet. The term ‘phantom bite’¹¹ was first used to describe such patients who often have a history of multiple interventions by various clinicians in the pursuit of a solution. Several other terms have since been used, including occlusal hyperawareness, occlusal hypervigilance and occlusal dysaesthesia. The aetiology of this phenomenon is unclear, but is probably a combination of psychopathological influences, neuroplasticity, phantom phenomena and changes in proprioceptive stimuli and their transmission.¹² Hypervigilance¹³ is a known behaviour in chronic pain where an individual is exceedingly aware of the sensory experience associated with a part of their body. This is fundamentally a psychological state of altered perception and, therefore, any physical intervention is doomed to failure.

Another patient group, relevant to TMD, who may benefit from equilibration are those with a deranged occlusion. In such situations, there is a change in the number or distribution of occlusal contacts that is the cause of an aesthetic or functional complaint. Equilibration for correction of an occlusal derangement should be approached with the same caution as any equilibration; it carries the same treatment risks (discussed below) and although the improvement in the occlusal scheme is immediate, it may not always be stable. Janson et al¹⁴ showed an overall relapse rate of 33% in their case series, with higher relapse rates for younger patients. However, their cohort had skeletal anterior open bites (AOB) that had relapsed following orthodontic treatment and a mean age of 21 years. These results may, therefore, not be generalizable.

A variety of factors, related and unrelated to TMD, can cause a deranged occlusion (Table 1) and the clinician should investigate potential non-TMD causes and refer to a medical specialist where appropriate.

The process for undertaking an occlusal equilibration requires:

Examples of occlusal equilibrations undertaken for deranged occlusions due to neuromuscular changes (Figures 3) and TMJ replacement surgery (Figure 4) are presented.

Additive changes to the occlusal scheme

Considering the not inconsequential risks associated with an occlusal equilibration, additive techniques could be considered to achieve some or all of the same goals. These techniques range from the addition of direct resin composite to key teeth, a common example being canine risers (Figure 5),^15,16 to a complete reorganization of the occlusion using direct and/or indirect restorations. A full appraisal of all the various restorative techniques that could be employed and their respective failure and complication rates is outside the scope of this article, but it must be stressed that, as with any restorative treatment, especially if extensive, the maintenance requirements must be considered.

Considering the dearth of evidence for the efficacy of occlusal equilibration in the management of TMD, the evidence for occlusal rehabilitation with fixed restorations is even more scarce and, therefore, to justify the reorganization of a patient's occlusal scheme as a treatment would be a significant leap of faith.^17,18 There are patients who would benefit from a full-mouth reconstruction for prosthodontic reasons who also have a TMD. Following successful conservative treatment of the TMD, this small group should be provided with a prosthodontically ideal occlusion, but with no promise that this will prevent future symptoms. The management of these patients can be extremely difficult due to their reduced adaptive capacity for occlusal change and, therefore, will often involve a pre-treatment appliance and an extended period of provisionalization.¹⁷

Additive techniques can be used for replacement of missing teeth, and there is research to demonstrate an association between reduced posterior support, through missing posterior units, and TMD symptoms.¹⁹ It has been postulated that such patients posture their mandible to gain better masticatory function.²⁰ This theory, however, goes against the large body of evidence that for the majority of patients a shortened dental arch of the anterior teeth and at least four occluding premolar-sized units is no different from an intact dentition for masticatory ability, signs and symptoms of TMD, migration of teeth, periodontal support and oral comfort.^21,22 There may be individual patients for whom this is not the case and who may benefit from the replacement of posterior support, but this decision must be made on its own merits and not with the intention that this will manage a TMD. To reinforce this point, a multi-centre randomized controlled trial of shortened dental arch compared with the provision of precision attachment-retained removable partial dentures to replace missing posterior units, found no significant difference in TMD signs or symptoms between the groups at any recall up to 5 years.²³

Additive and subtractive changes to the occlusal scheme can sometimes be used in combination to achieve a desirable result while minimizing the negative consequences of either treatment in isolation. Each suitable case is likely to be unique and, therefore, there are no guidelines or evidence to guide the clinician and, as such, the patient needs to understand the unpredictable nature of such a plan. This approach has an extremely high level of complexity. Any clinician considering this treatment modality needs to be confident that they fully understand the process, have experience of simpler cases, and thoroughly plan the end result. Figure 6 illustrates a case where a combined approach was taken.

Conclusion

All of the treatment modalities discussed above, no matter how minor, are irreversible in the sense that once completed, it would be impossible to return to the pre-treatment state. This is obviously true of subtractive methods, but also for additive, as even with careful removal of a restorative material the clinician is unlikely to ever be able to recreate a patient's pre-existing static and dynamic contacts to the level of accuracy detectable by the articulatory system, particularly so in patients with hypervigilance.

Owing to the biopsychosocial nature of TMD, the use of an irreversible biological therapy in its management must always be considered a last resort option following an exhaustive attempt at conservative measures. The evidence base does not suggest that occlusion is a significant factor in the general population of TMD sufferers and would not support routine use of any irreversible occlusal therapy. That being said, for a small group of patients where occlusal discrepancies are considered a precipitating or perpetuating factor, occlusal changes could be justified. It is, however, challenging to confidently identify such patients among the crowd, and that is why a second opinion would always be prudent.

Any clinician embarking upon an irreversible restorative intervention in relation to TMD needs to satisfy themselves that they have the appropriate knowledge, training and experience to justify the procedure, undertake the detailed planning required, carry out the clinical stages, and manage the consequences and complications that may arise.