Electromyographic investigation of chin cup therapy in Class III malocclusion.

Electromyographic activity was evaluated in 20 patients (10 girls and 10 boys, mean age 10 years) with Class III malocclusion who were treated with a chin cup appliance. The posttreatment data were obtained at the end of phase 1 chin cup treatment when the anterior crossbite had been corrected. EMG activity of the masseter and temporal muscles for each subject were studied during unilateral chewing using the following parameters: mean cumulative voltage (MCV), mean maximum peak voltage (MMPV), and rotational direction of the differential lissajous EMG (DL-EMG). The ANB angle improved from -1.0 degree (mean) to 0 degree. The electromyographic study revealed a decrease in masseter muscle activity on both the working (chewing) and balancing sides, with no improvement in the coordination of bilateral masseter and anterior temporal muscles.