Bilateral supra- and infrahyoid EMG activity during eccentric 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 infrahyoid electromyographic (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- and infrahyoid 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 significantly modified by the type of laterotrusive occlusal scheme.

Influence of laterotrusive occlusal scheme on bilateral masseter EMG activity during clenching and grinding.

This study was designed to determine the effect of the occlusal scheme on masseter EMG activity at different jaw posture tasks. The sample included 30 healthy subjects with natural dentition and bilateral molar support, 15 with bilateral canine guidance, and 15 with bilateral group function. An inclusion criterion was that subjects had to be free of signs and symptoms of any dysfunction of the masticatory system. Bipolar surface electrodes were located on the left and right masseter muscles. EMG activity was recorded during the following jaw posture tasks: A. maximal clenching in the intercuspal position; B. grinding from intercuspal position to edge-to-edge lateral contact position; C. maximal clenching in the edge-to-edge lateral contact position; D. grinding from edge-to-edge lateral contact position to intercuspal position. EMG activity in tasks B, C, and D was lower than in task A (mixed model with unstructured covariance matrix). EMG activity was not significantly different with canine guidance or group function. EMG activity recorded on the nonworking side was higher than the working side during task C, and no different between tasks B or D. On the nonworking side, EMG activity in task B was significantly lower than C and D, and similar between task C and D. On the working side, EMG activity was significantly higher in task D than C and B, and in task B significantly higher than task C. The EMG patterns observed could be of clinical importance in the presence of parafunctional habits, i.e., clenching and/or grinding.