Zusammenfassung

Electromyographic (EMG) investigations about the activities of the muscles have been the focus of attention for many years. In the field of orthodontics, investigators, among other things, tried to evaluate correlation between EMG activity, occlusal relationships and craniofacial morphology to analyze the effect of muscular activity, as an etiological factor in malocclusion. The purpose of the present investigation is to analyze the effect of EMG activity of temporal and masseter muscles quantitatively in skeletal class III malocclusion. 26 patients (9 to If years old), with class III malocclusion were selected and their EMG activity of temporal and masseter muscles in rest position, centric occlusion, clenching, mastication and swallowing were compared with 20 normal children at the same age range. Then the statistical correlation between 13 cephalometric parameters and EMG activities were analyzed and then the regression analysis was performed and the results were as follows:1- The mean amplitude of masseter and temporal muscles activity in rest position, centric occlusion, mastication, and clenching in class III samples were greater than normal group (PO.05).2- The mean duration of masseter and temporal muscles activity in rest position and centric occlusion in class III samples were more than normal group (PO.05).3- According to regression analysis, a linear correlation was observed between ANB angle and temporal muscle activity in rest and centric occlusion that was not observed in other cases.The findings of this study showed that difference in temporal muscle activity in class III malocclusion, in comparison with the normal group, is correlated with skeletal morphology of the face, but according to other investigations it is not ture for the masseter muscle.