Associations Between Upper Lip Activity and Incisor Position

Background: Muscle activity in the upper lip may influence the positions of the upper and lower incisors.

Objective: To determine the associations between muscle activity in the upper lip and the inclinations of the incisors, overjet and overbite.

Methods: Forty-five subjects (29 girls, 16 boys), between 11 and 15 years of age with predominantly Class I malocclusion, were used. The inclinations of the incisors, overjet and overbite were measured on lateral cephalometric radiographs. Bipolar electrodes were placed on the upper lip to record the activity in orbicularis oris muscle at rest, during maximal clenching, chewing hazelnuts and swallowing. Correlation coefficients between the cephalometric variables and the electromyographic (EMG) activity in the upper lip were calculated.

Results: There was no gender difference in the EMG activity in the upper lip. There were no statistically significant associations between the EMG activities in the upper lip and the inclinations of the incisors, overjet and overbite.

Conclusions: The positions of the incisors do not appear to be influenced by muscle activity in the upper lip.