[A long-term study on dentofacial changes after sagittal splitting osteotomies in skeletal Class III malocclusions]

The purpose of this study is to clarify the long-term dentofacial changes after sagittal splitting ramus osteotomy in skeletal Class III patients, and to study the factors involved to find its countermeasures. For this purpose we used the radiographic cephalograms in 16 patients (13 females and 3 males) observed for more than five years after surgery. We measured the postoperative changes in the position of Pogonion and the inclination of maxillary and mandibular incisors. The results were as follows: 1. Pogonion was retruded 9.3 mm on the average by surgery. In the period from the removal of intermaxillary fixation to one year postoperatively Pogonion slipped forwardly and upwardly (average; anteriorly 1.0 mm, superiorly 0.8 mm). In the period from one year postoperatively to the time of the final observation Pogonion slipped to a downward direction. 2. No correlation was found between the amounts of vertical displacement by surgery and postoperative vertical changes of Pogonion. On the other hand, a high correlation was found between the amounts of mandibular setback and the forward displacement of Pogonion. 3. Mandibular incisors were tipped labially by preoperative orthodontic treatments, then maxillary and mandibular incisors moved lingually during intermaxillary fixation. After release of intermaxillary fixation, maxillary incisors moved labially in a small distance. After one year maxillary incisors were inclined slightly in the lingual direction. It is obvious that the position of the mandible and the incisor inclination tend to change even after one year. Because the postoperative changes were small in quantity, we supposed they were mostly caused by occlusal changes. Clinically, occlusal relationship in the incisor area, i.e., overjet and overbite, was maintained to be normal. It was considered that the changes of incisal inclination after release of intermaxillary fixation were of a compensatory or adaptational response to a positional change of the mandible.