Electromyographic activity during awake tooth grinding tasks at different jaw posture in the sagittal plane.

OBJECTIVE The goal of this study was to evaluate the electromyographic (EMG) activity of the anterior temporalis, suprahyoid, infrahyoid and trapezius muscles during tooth grinding at different jaw posture tasks. MATERIALS AND METHODS Participants were 30 healthy subjects with natural dentition, bilateral molar support and incisive protrusive guidance. Bipolar surface electrodes were located on the right side of the subject. EMG recordings were performed in the following tasks: (A) Eccentric grinding from intercuspal position to protrusive edge-to-edge contact position; (B) concentric grinding from protrusive edge-to-edge contact position to intercuspal position; (C) eccentric grinding from intercuspal position to the maximum voluntary retrusive position; and (D) concentric grinding from the maximum voluntary retrusive position to intercuspal position. The results were analyzed statistically by Friedman test and Wilcoxon signed rank-sum test. RESULTS EMG activity in the anterior temporalis and infrahyoid muscles was significantly higher during task C than the other tasks. EMG activity in the suprahyoid muscles was significantly higher during task C than task D. EMG activity in the trapezius muscle was significantly higher during task C than tasks A and B. CONCLUSIONS The higher EMG activity recorded in task C could become important when its frequency, duration and magnitude are enough to exceed the adaptation capability of the individual.