Evaluation of the effect of mandibular length and height on the sagittal split ramus osteotomy rigid internal fixation techniques: A finite element analysis

Purpose: A major concern after mandibular advancement with sagittal split ramus osteotomy surgery is postoperative stability and relapse. Currently, there is no consensus on the ideal fixation technique, or how prognosis is affected by mandibular height and length. The aim of the present study was to assess stress distribution on the fixation units and the bone after sagittal split ramus osteotomy and determine the contributions of different mandibular body heights and lengths. Materials and methods: Sagittal split ramus osteotomy and mandibular advancement were simulated in different height/length models prior to fixation using a miniplate, hybrid, or inverted L system using finite element analysis. The greatest and least amount of stress was generated using the miniplate, and inverted L system, respectively. Results: The highest tension and compression in the bone was measured in the miniplate system. While the inverted L system generated less stress in the fixation units than the hybrid system, the hybrid system caused less stress in the bone and lower displacement values compared to other systems. An increase in length, and a decrease in height, both promoted stress, however, the difference was greatest in the former. Conclusion: Based on our results, when sagittal split ramus osteotomy is planned for a rather long or thin mandible, using the hybrid system for fixation is recommended.