Clinical Study of Soft Tissue Profile Changes Associated with Sagittal Split Ramus Osteotomy of the Prognathic Mandible : Prediction of Soft Tissue Profile Following Orthognatic Surgery

Dentofacial deformities result from abnormal growth of facial bones. The purpose of orthognatic surgery is to improve functions and esthetics. If the improvement in esthetics is not sufficient, the patient may not be satisfied with the results of treatment. This study was prompted by the realization of a need for more substantial data from which a reliable, predictive format could be developed to aid in treatment planning for prognathic patients. Forty patients treated surgically for mandibular prognathism were selected from the files of the First Department of Oral Surgery, Kyushu Dental College Hospital. In all of the cases selected, surgery had involved sagittal split ramus osteotomy and orthodontic treatment had been performed pre- and postoperatively. Four sets of lateral radiographic cephalometric films were taken for reference : Just before surgery, 1 month, 3 months and 6 months after surgery. The effect of treatment was posterior movement of soft and hard tissues of the lower third of the face. Further, a trend toward relapse consisting mainly of anterior displacement persisted until 6 months after surgery. Prediction of the postoperative position of soft tissues was evaluated by stepwise multiple regression analysis. Then, a multiple regression equation which showed a coefficient of determination over 0.9 with as few variables as possible and with significance below 0.01 on F-test was determined as a predicting equation. Furthermore, residual standard deviation of all multiple regression equations were less than 2.0 mm. Nevertheless, cases with open bite and high or low tension of the lower lip showed major predictive error. Prediction of the postoperative soft tissue profile following orthognathic surgery is possible with sufficient precision for clinical use using these multiple regression equations.