Hypermobility of the articular heads of the temporomandibular joint: pathology or variant of the norm?

Introduction: Among the large contingent of patients with TMJ dysfunctions, there are persons with hypermobility of the joint heads of the lower jaw. Moreover, at present, the question of the frequency of occurrence of hypermobility of articular heads of the TMJ is not reflected. The aim of the work is to find out the frequency of occurrence of hypermobility of articular head among a healthy population and to evaluate the clinical, radiological, and electromyographic characteristics of the muscular-articular complex in these individuals.

Material And Methods: Surveys were conducted for 476 students aged 19 to 25 years. For people with revealed articular hypermobility of the articular heads, chewing and temporal muscle electromyography, TMJ aiming zonography in a lateral projection with open and closed mouth were performed with an assessment of the correspondence of the articular fossa of the temporal bone to the size of the articular head, the location of the articular heads relative to the apex of the articular tubercle.

Results: Of the examined 476 students, 95 people (20%) revealed hypermobility of the articular heads of TMJ. According to the results of clinical, functional and radiological studies of TMJ, we identified three degrees of hypermobility: light, moderately expressed, significant. With light to moderate degree of hypermobility, electromyography of the temporal and chewing muscles and TMJ zonography did not reveal a difference in performance compared to healthy ones. Most of the examined did not note functional discomfort from the joints. With a significant degree of hypermobility of the articular heads, electromyography of the temporal and chewing muscles revealed a lack of synergism in their work. On TMJ zonograms with an open mouth, the articular heads extended anteriorly beyond the tops of the articular tubercles almost under their outer base.

Conclusions: It has been established that hypermobility of the joint heads of the TMJ, which does not cause signs of pathology in the form of masticatory function disorders, discoordination of the masticatory muscles and uncontrolled displacements of the lower jaw, the presence of a pain symptom should be considered as a variant of norm.