Jaw movement trajectories on the horizontal plane in sleep bruxism

This study aimed to investigate the characteristics of jaw movement trajectories in the horizontal plane and the maximal activities of the masseter muscle during grinding events associated with rhythmic masticatory muscle activity (RMMA), as a potential biomarker for the diagnosis of sleep bruxism.

The biological signals and jaw movement data of eight participants were recorded using a custom-developed intraoral sensor, a six-degree-of-freedom magnetic jaw-tracking device, and polysomnography. These recordings were synchronized using Global Positioning System time data. Jaw movement data during grinding events were compared with simulated grinding (lateral excursion) data obtained before sleep, focusing on deviations from the anteroposterior direction in the horizontal plane. Additionally, the timing of the maximal masseter muscle activity was examined.

No sleep disturbances were reported by the participants. During tooth grinding, the jaw movement trajectories of the lateral excursions in the horizontal plane frequently deviated from the simulated grinding trajectories, indicating variability among participants. Notably, the deviations were more pronounced during lateral excursions to the lateral side, with movements diverging both anteriorly and posteriorly from the simulated grinding trajectories. Regarding the masseter muscle activity, greater activity was observed on the balancing side. Peak masseter muscle activity increased when the jaw movement trajectories deviated posteriorly from the simulated grinding trajectory, on both the working and balancing sides.

Excursions deviating posteriorly during RMMAs from the simulated grinding were associated with significantly greater masseter muscle activity than either excursions deviating anteriorly or those along the simulated grinding trajectory.