Academic literature on the topic 'Gonion mandible'

碩士<br>高雄醫學大學<br>牙醫學研究所<br>89<br>Mandibular prognathism due to excessive growth of mandible, varies in facial characteristics and incidences amoung the different ethnic proups. People who are seeking management of mandibular prognathism are usually disturbed by prominent lower third of the face, poor chewing function and psychological factors. In Taiwan, the high incidences and more severely dentofacial deformity in mandibular prognathism was noted and the problem could only be solved by combined orthodontic treatment and surgery. The purpose of this study was to investigate the changes in gonial region and the factors contributing to skeletal stability in mandibular prognathism treated by modified intraoral vertical ramus osteotomy. Thirty-two patients( 9 males and 23 females ), treated for absolute mandibular prognathism by modified intraoral vertical ramus osteotomy, were evaluated cephalometrically at least two-years postoperatively. A set of three standardized lateral cephalograms were obtained from each subject, i.e., preoperative (A), immediately postoperative (B1) and two-years postoperatively (B6). Some cephalometric landmarks were used for evaluating the positional and angular change postoperatively. The results showed that (1). In stability, during the postoperative period, the Me moved forward with 1.9mm in 22 patients( group I ) whose mean setback of Me was 13.96mm, and the relapse was 13.61%. In other group, the Me moved backward with 2.46mm in 10 patients( group II ) whose mean setback of Me was 11.31mm, and the backward instability rate was 21.75%( 2.46/11.31). (2). The Go moved backward with 1.35mm and upward with 1.90mm in group I, the gonial angle increased for 3.69°, and angle between palatal plane and mandibular plane was increased for 5.00°; In group II, the Go moved backward with 1.85mm and upward with 3.32mm , the gonial angle increased for 4.06°, and angle between palatal plane and mandibular plane was increased for 5.22°. Both in group I and II, there was a tread for clockwise rotation of mandibular corpus. The length of pterygomasseteric sling was mild increased due to the backward movement of Go. (3). The displacement of condylar process( forward or backward ) didn’t influence the stability, but the condyle could not return to its original position completely. The position of condyle may be controlled by bone remodeling. (4). The results of multiple regression showed that the postoperative stability was only correlated with amount of mandibular setback, and rotation of mandibualr corpus and amount of displacement of condyle could not influence the stability. The amount of Go backward movement depends on two factors, one is the position of osteotomy site in distal segment, and the other is the position of osteotomy site in distal segment immediately postoperative. The more horizontal distance between Go and osteotomy site, the less tread of posterior movement of Go postoperatively. When the distal segment setback to ideal position of occlusion and the osteotomy site was behind to Go, the more distance between osteotomy site and Go, the more tread of posterior movement of Go postoperatively. But when the osteotomy site was before to Go, we found that the horizontal position of Go postoperatively was unchanged nearly. The pterygomasseteric sling could be lengthened and distorted under the limitation and it has potential to recover the original length and position if the stretch was larger then the upper limitation. In our study, there was no relationship between the stability and positional change of Go postoperatively. But in group II, we found the distance between the Rp and osteotomy site was larger then amount of mandibular setback. We suspected that the backward movement of Me was caused by loosening the pterygomasseteric sling or other else. It needs more study cases for further examination.