Internal fixation of short bilateral sagittal split osteotomy of the mandibular ramus: A mechanical evaluation

Abstract

This study evaluated in vitro three internal fixation methods for short bilateral sagittal split osteotomy (BSSO) of the mandibular ramus using polyurethane replicas. After simulating an 8-mm mandible advancement with a counterclockwise rotation of 6° to the occlusal plane, the short BSSO was fixed bilaterally by using: (i) three linear bicortical screws; (ii) one miniplate with four monocortical screws and one bicortical screw (hybrid system); and (iii) two miniplates with eight monocortical screws. The load was measured on the central incisors or first molars bilaterally at the displacements of 1, 3, 5, and 7 mm. The data were analyzed using one-way analysis of variance (ANOVA) with Tukey's post hoc test. In addition, a linear regression analysis with dummy variables was performed for each combination of displacement and loading point. There were no statistically significant differences in the loads applied to both central incisors and first molars bilaterally among fixation methods at 1-mm displacement. However, the necessary load was larger for the two miniplates method for 3-, 5-, and 7-mm displacements. Considering the biomechanical aspects and the cost benefit related to the fixation materials, using three linear bicortical screws or a hybrid system may be more favorable than employing two miniplates with eight monocortical screws.

Keywords: bone screw; internal fixation device; orthognathic surgery; osteotomy.