An In Vitro Biomechanical Evaluation of Fixation Techniques for Sagittal Split Ramus Osteotomy: Mandibular Advancement and Setback

Abstract

Statement of the Problem: This comparative study was an analysis of a mandibular stability following bilateral sagittal split ramus osteotomies for mandibular setback with monocortical titanuim plate fixation or bicortical screw fixation. Materials and Methods: A total of 57 patients with skeletal Class III malocclusion who underwent sagittal split osteotomies and mandibular setback were included in this study. Of these patients, 29 patients were osteosynthesized monocortically with titanium plate, and 28 patients were osteosynthesized bicortically with positioning screws. Method of Data Analysis: This retrospective study utilized cephalometric radiographs, which were taken preoperatively, and 1 week, and 1 year postoperatively. Cephalometric parameters – gonial angle (GA), mandiblular plane angle (MPA), SNB, upper facial height ratio (U/F) were measured. Postoperative changes in the mandibular shape were analyzed by Wilcoxon signed-rank test to determine the stability of fixation methods. Results: The postoperative changes in gonial angle and mandibular plane angle tended to increase in both monocortical (changes in GA: 2.20, MPA: 1.19) and bicortical fixation group (changes in GA: 2.18, MPA: 1.17). In addition, the upper facial height ratio showed decrease in both monocortical ( 0.64) and bicortical fixation group ( 0.25). However, SNB showed decrease in monocortical fixation group ( 0.62), and increase in bicortical fixation group (0.30). In statistical analysis, there was no significant difference in postoperative changes in gonial angle, mandibular plane angle, SNB, upper facial height ratio in both patient groups. Conclusion: These findings suggested there was no significant difference in postoperative changes in mandibular shape in both monocortical and bicortical fixation group after sagittal split ramus osteotomy. It was concluded that monocortical osteosysnthesis using miniplate could be used to obtain stable postoperative changes after mandibular setback.