The purpose of this study was to investigate changes in lip-closing force, tongue pressure, and buccinator pressure before and after orthognathic surgery, and to compare these changes between skeletal Class II and Class III female patients.

Thirty-six female patients who underwent orthognathic surgery at Kyushu Dental University Hospital were enrolled. Patients were divided into two groups (Group A: skeletal Class II; Group B: skeletal Class III), and ten females with normal occlusion served as the control group. Lip-closing force, tongue pressure, and buccinator pressure were measured one day before surgery, and at three months and one year postoperatively. Maximum values were analyzed using the Mann–Whitney U test and Wilcoxon signed-rank sum test.

Lip-closing force, tongue pressure, and buccinator pressure significantly increased one year after surgery in both groups (p < 0.05), although a tendency toward reduction was observed at 3 months, except for lip-closing force in Group A.

The change rates for lip-closing force and buccinator pressure tended to be higher in Group A, whereas tongue pressure tended to increase more in Group B. However, a significant difference was observed only in lip-closing force (p < 0.05).

Orthognathic surgery significantly improves perioral muscle function as well as facial esthetics. Significant improvements were observed in lip-closing force, tongue pressure, and buccinator pressure at 1 year postoperatively. Moreover, the increase in lip-closing force was significantly greater in Class II patients than in Class III patients.