Electromyographic analysis of the temporalis and masseter muscles in children and adolescents with unilateral temporomandibular joint ankylosis at different stages of comprehensive rehabilitation

Relevance. Patients with unilateral temporomandibular joint (TMJ) ankylosis have marked functional and anatomical disturbances that adversely affect quality of life and social adaptation. This condition requires complex, multistage rehabilitation. After surgery on the affected side, the unaffected, non-operated joint bears the main functional load for a prolonged period. Long-standing mandibular biomechanical imbalance leads to secondary changes in the masseter and temporalis muscles, including hypertrophy or atrophy. However, the functional status of the masticatory muscles in these patients remains insufficiently studied.

Materials and methods. The study included 65 patients aged 7–18 years with unilateral TMJ ankylosis who were undergoing different stages of comprehensive rehabilitation, including removal of ankylotic masses, placement and removal of a distraction device, mandibular ramus bone grafting, and total TMJ replacement. The patients were divided into two age groups: 7–12 years (n = 25) and 13–18 years (n = 40). All patients underwent electromyographic (EMG) assessment of the temporalis and masseter muscles using a four-channel Synapsis electromyograph (Neurotech, Russia). The mean amplitude of bioelectrical activity (μV) during maximum voluntary clenching was recorded. Values on the affected side were compared with those on the contralateral side and with age-matched reference values. Statistical analysis was performed using the Mann–Whitney U test and Pearson’s chi-square test.

Results. All patients showed an imbalance in the bioelectrical activity of the masticatory muscles. In the 7–12-year age group, the amplitude of masseter muscle bioelectrical activity on the affected side was 43.5% lower than the age-matched reference value, whereas temporalis muscle activity was reduced by 23.3%. On the contralateral side, masseter and temporalis muscle activity exceeded the reference values by 25.7% and 34.4%, respectively. In the 13–18-year age group, masseter muscle activity on the affected side was reduced by 12.5%, whereas on the contralateral side it exceeded the reference value by 63%. Temporalis muscle activity exceeded the reference value by 16.7% on the affected side and by 82% on the contralateral side.

Conclusion. A statistically significant decrease in the electrical activity of the masseter and temporalis muscles was observed on the affected side. The main functional load was redistributed to the masseter and temporalis muscles on the contralateral side and, in the 13–18year age group, also to the temporalis muscle on the affected side. Increased muscle activity on the contralateral side in adolescents may indicate the development of compensatory mechanisms in response to unilateral TMJ ankylosis.

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