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Background: Biomechanical stability in patients in whom mandibular prognathism was corrected with different fixation methods during bilateral sagittal split osteotomy (BSSO) surgery remains controversial and needs to be clarified., Methods: A three-dimensional (3D) finite element (FE) model of the mandible was developed to simulate the biomechanical responses of osteo-synthesis screws and the stability of different screw-placement arrangements in BSSO. Six types of fixation methods for the osseous segments were simulated with two or three screws in different placement arrangements to avoid injury to the inferior alveolar nerve., Results: A triangular configuration of the screw position across the nerve presented less stress loading than the linear configuration, and hence provided better stability as the preferred fixation method for BSSO of the mandible. When the screws were aligned in a linear setting, the stress values were 4 times higher, implying a less stable fixation. Neither two nor three screws applied at the superior border appeared to be better at exploiting the increased thickness of the cortical bone encountered in this region., Conclusions: According to the 3D-FE analysis, the configuration with three screws inserted in a triangular shape across the inferior alveolar nerve (Type 4) demonstrates the best rigidity among six screw-placement configurations. Three 2.3-mm diameter bi-cortical screws were considered a sufficient fixation tool after BSSO of the mandible., ((c) 2008 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.)