Muscle activity with the mandibular lip bumper.

This prospective study was designed to measure muscle activity with lip bumper treatment. Surface electromyography was used to measure upper and lower lip activity with and without the appliance in place. Measurements were taken on a sample of 25 adolescent patients (age range, 10 to 17 years) before and after 12 months of lip bumper treatment. Recordings included a closed lip rest position, swallowing of water, and speech of the words "church," "phone," and "pop." Insertion of the lip bumper at the pretreatment recording resulted in significantly increased activity of the upper and lower lips at rest (P <.001) and while swallowing (P <.05), whereas the response for speech was variable. Pretreatment and posttreatment muscle activity measurements of the lower lip were compared to determine whether 12 months of treatment with the appliance resulted in muscle adaptation. The initial increase of muscle activity with insertion of the appliance for the closed lip rest position and for swallowing was not followed by a decrease during the treatment period. There were significant differences in muscle activity when comparing the "new" equilibrium introduced by the lip bumper to the "old" pretreatment equilibrium without the appliance. Although it was shown that the insertion of the appliance had a significant influence on muscle activity of the lips, the results of this study did not indicate adaptation of the lower lip to the appliance over the treatment period.