抄録
When sagittal split ramus osteotomy is performed for skeletal Class II cases, it is possible to encounter cases in which occlusal stability cannot be gained due to postoperative relapse. One possible causes is that the centric relation and the centric occlusion have not been obtained during surgery. Progressive condylar resorption (PCR) after surgery is another possible cause of relapse. We examined the evaluation of the condylar position after sagittal split ramus osteotomy. We suggest that the risk factors for PCR include a high mandibular plane angle, TMJ condition prior to surgery, and excessive movement or counterclockwise rotation of the distal segment during surgery. It is also reported that the rigid fixation of the condyle, by placing it above and behind during surgery, leads to factors which increase pressure on the bone and accelerate the changes in the bone after surgery. We performed a procedure to reduce pressure on the condyle, by adopting overcorrection and loose fixation such as transosseous wiring during surgery. We then studied the postoperative change of the mandibular joint's position and the skeletal form.
We monitored eight patients consisting of two males and six females who had undergone sagittal split ramus osteotomy for skeletal Class II cases. We adopted transosseous wiring for fixing proximal and distal segments, and used a surgical splint to provide overcorrection; we then performed the intermaxillary fixation for four weeks. We conducted standardized tomography of the mandibular joint prior to surgery, after surgery (within seven days), and three months after surgery. We took lateral cephalograms prior to surgery, after surgery, and ten to twelve months after surgery. We measured a longitudinal change of the condylar position by standardized tomography of the mandibular joint. First, we regarded a straight line connecting the postglenoid process (BNA) and lowest mark of the condylar process as a base line, and then measured the distance from the base line to the high point of the condyle. As there was some difference in cases in terms of actual measurement, we converted the preoperative measuring value to a standard value, and conducted a comparative assessment of the postoperative measuring value based on the standard value.
The head of the mandible position changed approximately 70% downward soon after surgery, however, three months after surgery it recovered up to near the samelevel as that before surgery.
