Abstract
Occlusal splints are commonly used for treatment of sleep bruxism. However, there is no clear consensus on the mechanics of action and the best design of occlusal splint. One possible reason is due to the extremely dificulty in measuring and analyzing jaw movements during sleep. In this study, the six-degree-of-freedom jaw tracking system for sleep study constructed with the jaw tracking device using intra-oral sensors, an ambulatory polysomnograph and an AV monitor was employed to record jaw movements during sleep and analyze vertical component of resting jaw position at the incisal point in the supine position. We then examined the association between the vertical positions and the frequencies of sleep bruxism events. Twelve healthy adult subjects (7 males, 5 females; mean age 25.5 ± 5.7 years) without sleep disorder or stomatognathic dysfunction and with individual normal occlusion were participated in this study. Their jaw movements during sleep were recorded for two nights. To avoid the inclusion of the first night effect, the data from the second night were used for analysis. Since all participants got excellent sleep, the inluence of this system on sleep was a minimum. The mean vertical jaw position was 2.9-6.0 mm. Although vertical jaw position was not affected by sleep stages, there were significantly more epochs with a vertical jaw position of 2.5-5.0 mm in stage 1 (P<0.05) and significantly more epochs with a vertical jaw position of 2.5-5.0 mm or ≥ 5.0 mm than those with < 1.0 mm or 1.0-2.5 mm in stage REM, 2, 3&4 (P<0.05). Epochs with a vertical jaw position of ≥ 2.5 mm accounted for 84.2 ± 16.3% of all epochs. There was a negative correlation between mean vertical jaw position and frequency of sleep bruxism (R2 = 0.705, P<0.05). The results suggest that humans maintain vertical jaw opening during sleep throughout the night and the vertical jaw position can be used as a certain reference value to decide the occlusal thickness of splint for treatment of sleep bruxism.
