The Study On EMG Of Masseter And Anterior Temporalis During Mandibular Movement In Skeletal Angle Ⅲ Malocclusion In Mixed Detition

[Objective] To investigate the electromyographic(EMG) activities of anterior temprolis and masseter muscle during various mandibular movement in skeletal Class Illmalocclusion in mixed dentition. [Methods] 38 children with skeletal Class III malocclusion in mixed dentition were selected as a sample group, other 40 children with normal occlusion were selected as a control group. Using four-channel electromyograph with surface electrode to record the EMG activities of bilateral masseters and anterior bundles of temporal muscles during various mandibular movement. [ Results] (1)normal control group:when mandibular is in its rest position, there is mild activity in masseter and temporal is,-when maximal clenching and mandibular is in protraction movement, the EMG activity of masseter is higher than anterior temporal is;when mandibular is in retraction movement, the EMG activity of anterior temporal is higher than masseter and the EMG activities of ipsilateral masseter and contralateral anterior temporal muscle show higher potentials in right and left movements. (2) Angle III group: when mandibular is in its rest position, there is also mild activity in masseter and temporalis; when maximal clenching the EMG activity of anterior temporalis is higher than masseter; whenmandibular is in protraction movement and retraction movement, the EMG activity of masseter is higher than anterior temporalis; The EMG activities of ipsilateral masseter and contralateral anterior bundle of temporal muscle showed higher potentials in right and left movements of Angle EH group. (3) Compared between the normal control group and Angle III group: When mandibular is in its rest position , there are no different activities of EMG in two group. The EMG activities of masseters and anterior bundles of temporal muscles in Angle III group were lower than those in the normal group in both maximal clenching and left mastication. Compared with those in the normal group, the EMG activities of masseters in Angle III group were lower at protruded mandibular position but higher at retruded mandibular position. [Conclusion] There are significantly different activities of EMG in and anterior bundles of temporal muscles muscles in Angle III malocclusion in mixed detition and the normal group.