Electromyographic changes resulting from orthodontic correction of Class III malocclusion

This study measured the electromyographic (EMG) amplitudes of the interference pattern (IP) and the integrated EMG (IEMG) of the masseter and temporal muscles in 10 children with Class III malocclusion before, during, and after treatment with a myofunctional appliance (the monobloc), and compared the EMG values with those obtained from 10 children with Class I occlusion. The results showed that before treatment the mean amplitude values of IP were significantly higher in the Class III than in the Class I group. The mean amplitude values for IP activity in both muscles decreased during and after treatment; however, mean values of the IEMG activity did not show significant change for either muscle. These results are attributed to changes in the length of the muscle fibres as well as to neural modifications. This study demonstrates a non-invasive method that can be used to study the functional effects of orthodontic treatment.