Objective: Recently, it was reported that nocturnal rhythmic masticatory muscle activity (RMMA) and swallowing occurred frequently while esophageal pH was decreased due to gastroesophageal reflux. The purpose of this study was to test the hypothesis that the frequency of nocturnal jaw muscle activities excluding twitch or myoclonus increases while esophageal pH is decreased. Methods: Twelve healthy young adult volunteers participated in this study. We measured the masticatory muscle activity (EMG), orofacial movements, and pH in the lower esophagus during sleep by using conventional methods. Using the EMG and audiovisual data, we scored RMMA, short burst, and clenching episodes according to the research criteria of Lavigne et al. We then scored decreased esophageal pH episodes automatically by using esophageal pH data and analysis software. For comparisons within subjects, the paired t-test or Wilcoxon rank sum test was used according to the data distribution. Results: The frequency of jaw muscle activities while esophageal pH was decreased was significantly higher than that while esophageal pH showed a high value. The frequency of RMMA episodes that occurred most frequently, short burst episodes that occurred second most frequently, and clenching episodes during decreased esophageal pH episode was significantly higher than that during time other than the decreased esophageal pH episode. As for the other EMG episodes, there was no significant difference. The decreased esophageal pH episodes included significantly more RMMA and short burst episodes than the other episodes. Conclusion: These results suggest that the majority of nocturnal jaw muscle activities that occurred during sleep are associated with gastroesophageal reflux in healthy young adults.

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