Study of the area of bioelectric activity of the masseter muscle group in patients with intact dentitions

Aim. To determine normative values of the area under the curve of bioelectric activity of masseter and temporal muscles in patients with intact dentitions and physiological occlusion.

Materials and methods. Thirty-four patients (14 men and 20 women) aged 18–44 years with intact dentitions in the absence of third molars were examined. Electromyographic study was performed using a 4-channel "Synapsis" electromyograph by surface electromyography method. Bioelectric activity of masseter muscles (m. masseter) and temporal muscles (m. temporalis) was recorded bilaterally during three functional tests: relative physiological rest (10 seconds), maximum voluntary clenching (10 seconds), and arbitrary chewing of an almond kernel. The area under the electromyographic signal curve was analyzed as an integral indicator of muscle activity.

Results. At rest, the mean values of bioelectric activity area were 25.2–27.7 μV×ms for all studied muscles without significant differences between them. During maximum clenching, a significant increase was recorded: for temporal muscles up to 318.4–326.8 μV×ms, for masseter muscles up to 533.4–572.1 μV×ms with masseter/temporalis ratio coefficient from 1.63 to 1.79. During arbitrary chewing, the activity area was  227.2–227.9 μV×ms for temporal muscles and 359.9–370.9 μV×ms for masseter muscles (coefficient 1.57–1.63). The activity area during maximum clenching exceeded the indicators during chewing by an average of 1.5 times.

Conclusion. Reference values of bioelectric activity area of masticatory muscles in individuals with intact dentitions have been established. A regular predominance of masseter muscles over temporal muscles during functional loads was revealed, due to anatomical and physiological features and the nature of occlusal contacts. The obtained data can serve as a normative basis for diagnosing functional disorders of the masticatory apparatus and monitoring the effectiveness of prosthetic treatment.

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