EMG activity of the orbicularis oris and mentalis muscles in children with malocclusion, incompetent lips and atypical swallowing--part I.

The function and the level of activity of the orbicularis oris (upper and lower), and of the mentalis muscles were verified electromyographically in resting position and in several movements and carried out in 18 children aged 8-12 years, divided into three groups: one with normal occlusion, and two with Class II division 1, with atypical swallowing and/or incompetent lips, who had received no orthodontic treatment. It was observed that, in a resting position with the lips separated, there was no activity in any of the muscles. When there was a contact of the lips, action potentials were recorded in the muscles studied, in those individuals with incompetent lips. In the movements of sucking either through a straw or a pacifier and the thumb, there were no differences among the groups. The incompetent lips group presented very marked muscle activity of the lower orbicularis oris and mentalis in the movement of sucking a lollipop. In deglutition of saliva, the orbicularis oris presented slight activity, and the mentalis, moderate. In deglutition of water, the mentalis presented very marked activity, whereas, the upper and lower orbicularis oris presented moderate and marked activities, respectively.