Assessment of the functional state of the masticatory muscles in patients with a skeletal form of distal occlusion

Objective — to conduct a comprehensive assessment of the functional state of the masseter and temporal muscles in patients with the skeletal form of Class II malocclusion, based on the use of modern diagnostic methods. Material and methods. The study included 20 subjects with normal occlusion (NO) and 30 patients with skeletal form of Class II malocclusion (SF-II-M), determined by calculating the TRG in the lateral projection. They ranged in age from 20 to 37 years. The functional state of the masseter and temporal muscles was assessed using electromyography (EMG) and ultrasound (US). The distribution of occlusal contacts was assessed using the T-scan computer occlusion analysis system. Results. According to EMG data, in patients with SF-II-M, the values of bioelectrical activity of the studied muscles were significantly higher than in individuals with NO. The results of studying the thickness of the masticatory and temporal muscles themselves according to ultrasound data showed that in patients with SF-II-M they were thicker compared to those with NO both during physiological rest (RF) and under isometric tension, which was achieved during our study by maximum voluntary closure of teeth (MVC) in habitual occlusion. The study of the echostructure of muscles on echograms allowed us to conclude that in individuals with NO, both at RF and during MVC, hypoechoic areas prevailed. In patients with SF-II-M during MVC a decrease in echogenicity was observed, which was associated with the opening of reserve capillaries that ensure muscle function in conditions of hypertonicity, established on the basis of EMG and clinical examination data. Analysis of occlusion in patients with NO revealed a symmetrical and uniform distribution of occlusal contacts on occlusiograms, while in patients with SF-II-M, a displacement of the main array of occlusal contacts to the left was determined and a single supercontact was noted on the molars on the right. Conclusion. The study revealed that patients with SF-II-M have severe functional and structural changes in the masticatory muscles, based on data obtained using EMG and an author’s method for analyzing echograms in conjunction with computer-assisted occlusion assessment. A comprehensive understanding of the relationships between the components of the dental system will help dentists uncover the pathogenesis of skeletal anomalies, thereby improving the quality of diagnosis and treatment.