Evaluation of stress distribution in resorbable screw fixation system: three-dimensional finite element analysis of mandibular setback surgery with bilateral sagittal split ramus osteotomy.

The purpose of this study was to evaluate the stress distribution of resorbable screw (RS) and cortical/cancellous bone in the mandibular setback surgery with bilateral sagittal split ramus osteotomy (BSSRO) according to fixation geometry and number of RSs using three-dimensional finite element analysis. Three-dimensional virtual models of the mandible and bicortical RS (INION CPS System; diameter, 2.5 mm; length, 12 mm [Inion Ltd, Tampere, Finland]) were constructed by Mimics (Materialise, Ann Arbor, MI) using three-dimensional computed tomography DICOM data with 0.5-mm-thickness cut. After 8-mm setback BSSRO was performed, fixation between the proximal and distal segments of the mandible was done with bicortical RS. Fixation options were classified into 3RL (3 RSs with linear configuration at the retromolar area), 2R1A (2 RSs at the retromolar area and 1 RS at the mandibular angle area), 2R1B (2 RSs at the retromolar area and 1 RS at the mandibular body area), and 3R1A (3 RSs at the retromolar area and 1 RS at the mandibular angle area). After applying the occlusal load of 132 N on the lower first molar, stress distributions of the RSs and cortical/cancellous bone in each option were analyzed by ANSYS program (ANSYS Inc, Canonsburg, PA). Maximum stress concentration was found at the anterior RS fixation in the retromolar area in all options. Although 3R1A fixation showed more even distribution of stress concentration than other fixation options, 2R1A fixation was comparable with 3R1A fixation in view of yield stress in RSs. In terms of fixation geometry and number of RSs, both 2R1A and 3R1A fixation configurations might provide proper stress distribution in BSSRO.