Evaluation of the mandibular ramus fracture line after sagittal split ramus osteotomy using 3-dimensional computed tomography.

ABSTRACT

PURPOSE: The true fracture line on the mandibular ramus after sagittal split ramus osteotomy cannot be observed using conventional x-ray techniques such as an orthopantomography. The aim of this study was to observe the fracture lines on the mandibular ramus after sagittal split ramus osteotomy by 3-dimensional computed tomography. PATIENTS AND METHODS: The subjects of this study were 30 patients with mandibular prognathism (7 men and 23 women). Their ages ranged from 17 to 45 years (mean age, 24 years). Osteotomy was performed by 3 techniques--the short medial cut, the lateral cut at the mandibular angle, and the connected cut. Sixty mandibular splits were evaluated by 3-dimensional computed tomography 1 to 2 weeks postoperatively. RESULTS: The mandibular ramus was fractured at 3 sites--the lingual surface, the posterior border, and the buccal surface. No fracture lines through the mandibular canal were observed. In relation to the 3 types of lateral bone cut end (A, lingual surface; B, inferior border; C, buccal surface) and the 3 fracture sites, 36 of the 37 lingual surface fractures were type A, 12 of the 14 posterior border fractures were type B, and 9 of the 9 buccal surface fractures were type C. CONCLUSION: A desirable splitting pattern occurred when a short lingual cut just above the lingula and a lateral bone cut of the mandibular angle were made, extending to the inside through the inferior border of the mandible. These observations also proved that the split patterns of the mandibular ramus could be controlled by the position of the lateral bone cut end.