Bilateral supra- and infrahyoid EMG activity duringeccentric jaw clenching and tooth grinding tasks in subjects with canine guidance or group function

This study compares the effect of tooth clenching and grinding on supra- and infrahyoidelectromyographic (EMG) activity during different laterotrusive jaw posture tasks. The study included 30 healthy subjects with natural dentition and bilateral molar support, 15 with bilateral canine guidance and 15 with bilateral group function. Bipolar surface electrodes were located on the left and right supra- andinfrahyoid muscles. EMG activity was recorded during the following tasks: A. eccentric grinding from intercuspal position to the right lateral edge-to-edge contact position; B. clenching in right edge-to-edge lateral contact position; C. concentric grinding from right lateral edge-to-edge contact position to intercuspal position. EMG activity was not significantly different between tasks on the working side, nonworking side, or between both sides, in subjects with canine guidance or group function (Wilcoxon rank-sum test). When comparing EMG activity by occlusal scheme,no significant differences were found either on the working side or the non-working side (Mann-Whitney U test). This result suggests that supra- and infrahyoid EMG activity in its predominant stabilizing role of the hyoid bone is not significantlymodified by the type of laterotrusive occlusal scheme.