EMG-CHARACTERISTICS OF MASTICATORY MUSCLES IN SUBJECTS WITH BRUXISM
Authors: Smaglyuk L.V. , Liakhovska A.V. , Smaglyuk V.I. , Trofymenko M.V. 
Published: April 2022

Today, bruxism is a fairly common phenomenon. Bruxism is often defined as the parafunctional activity of the masticatory and facial muscles. Parafunction is called increased inappropriate activity, tension or even spasm of the masticatory and facial muscles, as well as the muscles of the tongue. However, the peculiarity of the work of masticatory muscles during the day in patients with signs of bruxism remains insufficiently studied.
The aim of our study was to determine the features of EMG-activity of masticatory muscles in patients with bruxism.
Materials and methods of research. We performed a clinical examination and superficial electromyography (EMG) of the masticatory muscles in 13 subjects aged 25 to 43 years. There were 7 women (53.8%), 6 men (46.2%). All examined subjects were somatically healthy, had no bad habits and defects of the dental arches. The mean age of the subjects was 32.5 ± 5.4 years. In the sample of patients, there were clinical signs of bruxism such as pathological abrasion of the hard tissues of the teeth; point dentin exposure; cracks in tooth enamel; hyperesthesia; pain or feeling of tension and discomfort in the masticatory muscles. All patients were performed superficial electromyography of the anterior temporal and masseter muscles using a 4-channel computerized electromyograph, according to the recommendations by Ferrario V., Sforza C. Electrical biopotentials of masticatory muscles were registered in tests lasting 10 s each: maximum bilateral teeth clenching, clenching of teeth on the left side; clenching of teeth on the right side. The data obtained during the EMG were processed using Synapsis software from Neurotech. We analyzed the indicators of maximum amplitude, mean amplitude (μV) of each muscle in every test. For objective evaluation of the results, we performed electromyography of masticatory muscles of 15 subjects comparable in age and sex without clinical signs of bruxism (control group, mean age was 33.4 ± 6.1 years).
Research results. We determined the characteristics of EMG-activity of masticatory muscles in the control group in the test of bilateral maximum teeth clenching: symmetrical activity of masseter and temporal muscles on the left and right sides (p> 0.05), the value of maximum amplitude of contractions did not exceed 1200 μV. It was found higher EMG-activity of the masseter and temporal muscles on a working side, compared to a balancing one in the test of unilateral teeth clenching, that was statistically confirmed (p<0,05).
In patients with bruxism, the EMG-activity of the masticatory muscles differed from the control group. Thus, the maximum amplitude of muscle contractions in all tests was significantly higher (p <0.05) among people with bruxism. EMG-activity of masseter muscles in the majority of cases (10 subjects – 76.9%) was greater than the temporal. In tests of unilateral teeth clenching, the EMG-activity of the temporal and masseter muscles was slightly higher on the working side, but the difference with the indicators on the balancing side was not statistically confirmed (p> 0.05). We found the peculiarity of the EMG-activity of the masticatory muscles in subjects with bruxism: the presence of pathological rhythmic peaks of activity in the resting phase. Differences in the indicators of EMG-activity between the subjects with bruxism and control group were evaluated using analyses of Student’s paired t-test. The hypotheses were verified at the level of significance p<0,05.
Conclusions. Bruxism is a complex problem of the whole human body, characterized by neuromuscular activity. In our study, some features of EMG-activity of masticatory muscles were studied and established. Patients with clinical signs of bruxism had significantly higher values of maximum, mean amplitude, which are 2.3-3.5 times higher than normal. In most cases, the EMG-activity of the masseter muscles was higher than the temporal. Presence of pathological rhythmic peaks of activity in the resting phase was found. In the future, it is planned to study individual changes in EMG-activity of masticatory muscles in patients with bruxism at different stages of total dental rehabilitation.