Early and late electromyographic response to treatment with activators.

An EMG analysis of twenty Class II cases treated with activators shows that: 1. During daytime use of activators, the protractor muscles of the mandible are stimulated, while the retractors are inhibited. 2. During nightime use of activators, no functional stimulation can be recorded. The activator appears to be operated mainly by tissue stretching and the accompanying elastic rebound. 3. Before treatment, as well as after the treatment, Class II cases show a balanced EMG pattern during closure in the intercuspal position. 4. A narrow upper arch should be expanded before treatment in order to avoid occlusal interferences and to make it easier for the lower arch to adapt itself to a protruded position.