Relationship between masseter muscle electromyographic activities and the position of the mandible

Objective To investigate the changes in electromyographic activities of the temporal and masseter muscles at different positions of the mandible.Methods Twenty orthodontic patients with Angle Class II malocclusion and mandibular retrusion(ANB6°) aged 10-14 years were enrolled in this study.All the patients were treated with Forsus fixed functional appliance combined with MBT straight-wire appliance.The electromyographic activities of the temporal(T) and masseter(M) muscles before,during and after functional treatment were evaluated by assessing the average integrated electromyogram(EMG) and T/M ratio at clenching status in different mandibular positions. Results After functional forward positioning of the mandible,the electromyographic activities of the temporal and masseter muscles decreased and T/M ratio increased significance at the clenching status(P0.05).Conclusion The appliance insertion and activation is associated with a decreased EMG activity of the temporal and masseter muscles, and the T/M ratio is correlated to the position of the mandible.