Dental treatment as perceived etiology of temporomandibular disorders

Occlusal disharmony and chronic oro-facial pain: from clinical observation to animal study

BACKGROUND

Occlusion can be viewed as the most sensitive susceptor of the central nervous system in the oro-facial region. Its inalienable relationships to the temporomandibular joint, the muscles, the stomatognathic system and even the central nervous system are self-evident. Almost all the dental treatments inevitably change the occlusion, potentially or actually, locally or extensively, and immediately or gradually.

OBJECTIVE

The objective of this study was to present a narrative literature on occlusal disharmony and chronic oro-facial pain.

METHODS

Literature reviews focusing on clinical studies about the relationship between occlusal disharmony and myofascial oro-facial pain, and related preclinical studies about the animal models of, as well as the peripheral and central mechanisms underlying this condition related to, occlusal disharmony were used as starting point and guidelines to describe the topics mentioned. A search of the PubMed database was performed mainly with the following search terms: "occlusion," "occlusal interference," "occlusal disharmony," "occlusal change," "oro-facial pain" and "myofascial pain."

RESULTS

Relevant literature from the past 70 years until the present day was meticulously studied. The literature review together with three related characteristic clinical cases revealed an intimate association between occlusal disharmony and chronic oro-facial pain, involving pathological changes, extending from the peripheral tissues to the central nervous system. The patients suffered from psychological distress, sleep disturbance and poor life quality.

CONCLUSION

Occlusal disharmony-related oro-facial pain is a clinical problem that deserves attention, although there are no universally accepted clinical protocols. The existing literature provides some constructive suggestions, but further research is needed.

Physical, psychological and socio-demographic predictors related to patients' self-belief of their temporomandibular disorders' aetiology

BACKGROUND

The aetiology of temporomandibular disorders (TMDs) has been widely discussed in literature, but little is known about patients' self-belief of their TMD aetiology.

OBJECTIVE

For six categories of self-believed aetiology of the TMD complaint (viz., occlusal factors, physical trauma, emotional stress, deep pain input, parafunctions and unknown), associations with physical, psychological and socio-demographic predictors were assessed.

METHODS

In this retrospective study, medical records of 328 TMD patients who had visited a clinic for Orofacial Pain and Dental Sleep Medicine were analysed.

RESULTS

The most frequently reported self-believed TMD aetiology was 'unknown' (42.3%). The category 'occlusal factors' was associated with pain worsening with emotion. 'Physical trauma' as self-believed aetiology was associated with TMD dysfunction score. 'Emotional stress' was associated with awake bruxism and age 18-49 years. 'Deep pain input' was associated with TMD dysfunction score, sleep bruxism, and arthritis or joint pain. 'Parafunctions' were associated with sleep bruxism. 'Unknown' was associated with TMD symptoms severity and work disability.

CONCLUSION

For each category of self-believed aetiology of the TMD complaint, different associations with physical, psychological and socio-demographic predictors were identified. This may suggest that individual phenotypes play a role in the patient's belief in the cause of the TMD complaint. Determination of phenotypic risk factors associated with aetiological self-belief might help clinicians to provide better treatment, including counselling, to their patients.

[Electrophysiological monitoring of pain afferent pathway of the trigeminal nerve and its functional plasticity in response to occlusal interference in rats]

OBJECTIVE

To observe the effect of occlusal interference on the afferent pathway of the trigeminal nerve and neuronal excitability in the trigeminal subnucleus caudalis (SPVC) of rats by electrical stimulation of the trigeminal ganglion (TG) and extracellular recordings of SPVC activities.

METHODS

Twenty male Wistar rats were randomly divided into control group and model group (n=10). In the model group, occlusal interference for 30 consecutive days was induced using light-cured flowable resin on the right maxillary molars. During occlusal interference, the pain sensitivity was scored with von Frey Fibers in the masseter. Simultaneous recordings of electrical activities from the SPVC, electrocardiogram, body temperature and electromyogram of the breath muscles of the anesthetized rats were performed, and the responses evoked by electrical stimulation of the TG were analyzed.

RESULTS

Compared with the control rats, the rats in the model group showed significantly increased pain sensitivity scores (P < 0.05) and increased spontaneous discharge frequency of the SPVC (P < 0.05). The amplitude of the SPVC responses induced by electrical stimulation of the TG showed stimulus intensity-dependent changes (P < 0.05), and the amplitude evoked by 4 mA and 8 mA stimulation was similar between the model group and the control group (P>0.05). Train stimulation (0.2 ms, 1 mA, 30 s, 100 Hz) of the TG significantly increased the discharge frequency of the SPVC only in the rats in the model group (P < 0.05).

CONCLUSIONS

The functional activities of the pain afferent pathway of the trigeminal nerve can be electrophysiologically monitored by electrical stimulation of the TG and extracellular recordings of SPVC activities in rats. Occlusal interference can increase the excitability of the neurons in the SPVC and enhance their sensitivities to TG afferent activation, suggesting the neural plasticity of the pain afferent pathway.