Abstract
Purpose: Rhythmic Masticatory Muscle Activity (RMMA) is rhythmic jaw movements similar to mastication approximately at 1 Hz during sleep, and it accounts for a large part of sleep bruxism. The purpose of this study was to clarify characteristic of EMG bursts of RMMA in bruxers.
Methods: Thirty bruxers who fitted the clinical diagnostic criteria of ICSD-2 of AASM participated in this study. EMG activities of the right masseter muscle were recorded during sleep at home by means of an ultraminiature electromyogram measurement system. After selecting RMMA with the threshold of amplitude of 20% MVC, we analyzed only phasic bursts whose maximum amplitude was more than 20% MVC.
Results: The mean value of the number of phasic bursts in RMMA per hour of sleep for each subject was 19.4. The mean value of the number of phasic bursts in RMMA per episode was 6.1. The total subjects' mean value of the mean values of duration of phasic bursts for each subject was 0.72 sec. Bursts with durations of 0.4-0.5sec were the most frequent of all phasic bursts that composed RMMA and the peak of distribution of burst durations shifted to the left with broad right foot. EMG bursts with maximum amplitudes of 20-30% of MVC were the most frequent of all phasic bursts in RMMA and distribution of maximum amplitudes of the bursts showed broad foot toward the right. In 80% of the subjects, the mean values of maximum amplitude of phasic bursts for each subject were less than 50% MVC.
Conclusion: This study clarified that the distributions of duration and amplitude of phasic bursts that composed RMMA with the threshold of amplitude of 20% MVC have each mode. On the other hand, it was also demonstrated that the distributions have wide ranges and variety of RMMA phasic bursts was suggested.
