Examination of Close-open Jaw Movement Trajectories During Sleep Bruxism

Objectives: Excessive dental attrition is the most common sign of sleep bruxism (SB). However, since dental attrition is a cumulative process of both functional and parafunctional activities, its status is not predictive of ongoing SB. The purpose of this study was to investigate characteristics of jaw movement pattern during SB.
Methods: We recorded jaw movement, biological signals (respiration, EEG, EOG, ECG and EMG) and audio-visual of 8 adult healthy volunteers (23.8+/-2.2 yrs old) for two night with a six-degree-of-freedom measurement system of jaw movements during sleep. This system consists of the electromagnetic jaw tracking device with intra-oral sensor, an ambulatory polysomnograph, and AV Monitor. The masseter muscle activity was quantified in terms of the subject’s 100% maximal voluntary clenching (MVC) level. SB events were detected when elevations of masseter EMG activity above 5%MVC level then classified due to their EMG and jaw movement pattern. Finally, close-open jaw movement cycle (CO-cycle) associated with teeth grinding during detected SB event was selected based on jaw movement in the cranio-caudal direction. We investigated jaw movement patterns of CO-cycle.
Results: Among 231 detected SB events (28.9±11.4 event/night), 121 SB events (15.6±6.5 event/night) contained 371 CO-cycles. Based on mesiolateral displacement of the jaw, CO-cycles were divided into chopper type (123cycles, 33.2%, lateral displacement: 0.81±0.70 mm) and excursion type (248cycles, 66.8%, lateral displacement: 3.42±1.68 mm). In excursion type, excessive excursive jaw movements past the canine edge-to-edge position were found not only during medial excursion (28cycles, 7.5%) but also during lateral excursion (15cycles, 4.1%).
Conclusions: SB with the excessive excursive movement could put repeated excessive frictional pressure on teeth surface. As a result of this study, it was suggested that recording and analyzing of both biosignals and jaw movements during sleep could be essential to clarify the relationship between dental attrition and ongoing SB.