RESUMO
PURPOSE: The aim of this study was to compare the presurgical and postsurgical electromyographic (EMG) activities of the lips in patients with skeletal Class III treated with combined orthognathic surgery and contrast these data with those obtained from a control group with skeletal Class I. PATIENTS AND METHODS: Ten patients with skeletal Class III underwent the registration of EMG activity before an orthognathic surgical procedure and 4 months after surgery. The results were compared with a control group of 11 healthy patients with skeletal Class I and clinical and EMG lip competence. EMG activity was recorded from the upper orbicularis oris and mentalis muscles during swallowing, lips in contact (LC), and lips apart (LA) using bipolar surface electrodes. The competence condition was assessed by determining the difference in the EMG activity of the mentalis muscle (LC-LA ≤0 for lip competence). RESULTS: Patients with skeletal Class III showed greater EMG activity than the control group before and after surgery. Patients with skeletal Class III showed a significantly greater difference in LC-LA than the control group before surgery for the 2 muscles (P < .05). No significant difference was found between the skeletal Class III group after surgery and the control group for the mentalis muscle (P > .05). CONCLUSIONS: Four months after treatment with orthognathic surgery, patients with skeletal Class III and an initial muscle activity pattern of lip incompetence different from the control group (P < .05) showed EMG values compatible with lip competence. These values were similar to the control group.