Changes in the lip closing force of patients with Class III malocclusion before and after orthognathic surgery

The purpose of this study was to examine the changes in lip pressure before and after orthognathic surgery for skeletal Class III patients. The subject groups were 32 female and 31 male patients diagnosed with mandibular prognathism and/or maxillary retrognathism who underwent orthognathic surgery. Control groups consisted of 20 women and 20 men with normal occlusion without dento-alveolar deformity. Maximum and minimum lip closing force was measured with Lip De Cum (R) for the control groups and subject groups preoperatively and 6 months postoperatively. The difference between the pre- and postoperative values of the groups was examined statistically. The maximum lip closing force in men was significantly larger than that in women in both the preoperative Class III group (p = 0.0330) and the control group (p = 0.0097). The preoperative Class III group was significantly smaller than the control group in maximum lip closing force in both men (p < 0.0001) and women (p < 0.0001). The postoperative maximum lip closing force was significantly larger than the preoperative value in both men (p = 0.0037) and women (p = 0.0273) in the Class III group. This study suggested that the maximum lip closing force increases after orthognathic surgery in Class III patients.