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 treat ed 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 followin g parameters: mean cumulative voltage (MCV), mean maximum peak voltage (MMPV), and rotational direction of the differential lissajous EMG (D L-EMG). The ANB angle improved from -1.0 degrees (mean) to 0 degrees. The electromyographic study revealed a decrease in masseter muscle act ivity on both the working (chewing) and balancing sides, with no impro vement in the coordination of bilateral masseter and anterior temporal muscles.