Sleep bruxism is defined as a stereotyped movement disorder occurring during sleep. It is characterized by three types of jaw movements: clenching, grinding and tapping. Most of the previous studies have focused on EMG activities of the masticatory muscles, while very few have reported jaw movements during sleep. The purpose of this study was to measure and analyze jaw movement during sleep bruxism. We developed a novel jaw-tracking device with six degrees of freedom using a pair of intra-oral sensors which can be used during sleep. We then constructed a six-degree-of-freedom measurement system of jaw movements during sleep which consisted of the developed jaw-tracking device and an ambulatory polysomnograph that records jaw movements, EEG, EOG, ECG and EMG. A healthy 41-year-old male volunteer with no signs and symptoms of stomatognathic dysfunction was examined for an entire night's sleep using this system. A total of 19 bruxism events (4.8 events/hour) was detected based on the masseter EMG activities above 5%MVC. Mean duration and mean peak activity of the masseter EMG were 3.4±1.5 sec and 31.3±18.6 %MVC, respectively. The masseter EMG activity and jaw movement patterns during these bruxism events were used to classify bruxism types independently. On evaluation of the EMG activities, one clenching-type event and 18 grinding-type events were observed. On the other hand, six clenching-type events, one grinding-type event, seven tapping-type events and five combination-type events were found on evaluation of the jaw movement record. Masseter EMG activities above 5%MVC were observed during bruxism events not only at and around the centric jaw position but also at the eccentric jaw position, contrary to our assumption. These findings indicate the validity of the jaw movement analysis for the evaluation and diagnosis of sleep bruxism.

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It has been said that the dentists are working in hard circumstances especially about their working posture. But to conclude that the work is heavy, we must know the precise data of the posture movement. So, we developed a wireless accelerometer which can be used in the dental work. The object of this study is to examine the applicability of the device and to measure and analyze the posture of the dentists in work.
The 2 axis accelerometer was put on the ear of the dentist. The digital signal was sent to a portable Bluetooth transmitter with a battery power supply in a pocket of the subjects. By the Bluetooth protocol signal the data was transmitted to a computer wirelessly. Five dentists were the candidates of this project and the pitching and rolling movements of their head posture were measured while they were working in dental treatment and in desk work.
The device showed enough applicability in the dental work. The data of the posture were analyzed as time distribution of the inclination angle. In dental work the posture showed wider distribution than the posture in desk work (standard deviation of the pitching 16.7°, 8.6° and the rolling, 14.7°, 5.6°, respectively). The distribution of the pitching movement showed ventral bent of the neck in dental work. This showed postural difference between in dental work and desk work. The data will be an evidence of the hard work condition of the dentists.

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