Influence of Bruxism during Sleep on Stomatognathic System.

Nocturnal tooth contact such as bruxism has been considered to be one of the major factors of temporo-mandibular disorders (TMD). However, little information has been reported regarding mandibular movements during bruxing, because of the limitation of the measuring method. The purpose of this study was to investigate the influence of bruxism on the stomatognathic system. A new device for measuring nocturnal mandibular movements was developed using a PIN photodiode sensor, which was integrated with the polysomnography including both masseter and anterior temporal EMG. The maximum error of the system was revealed to be less than 0.2 mm. One episode was defined depending upon EMG activities above 5% MVC, and mandibular movement for each episode was classified into 3 patterns (Clenching, Grinding, and Mixed). Nine subjects were selected for the study. Two of them reported bruxing habits and one subject had some symptoms of TMD. Mandibular movement was analyzed only for these three subjects. Frequency and duration of the episode were 3.8-10.9 and 47.8-174.9 sec per hour, respectively. The values of two bruxism patients was high, comparing to the other seven subjects. Clenching pattern during "Mixed movement" was most frequently observed for all three subjects, and EMG activities during clenching were stronger than those during grinding. These findings suggested that tooth clenching during sleep may be harmful to the stomatognathic system, rather than other mandibular movements.