In vitro comparison of fixation methods used in sagittal split osteotomy with a major advancement and counterclockwise rotation

The aim of this study was to compare the mechanical characteristics of five commonly used fixation methods for sagittal split osteotomy with a major advancement and counterclockwise rotation with a model that mimics the human mandible. Twenty-five virtually osteotomised and 3-dimensionally printed hemimandibles were fixed with an 8mm gap at the upper border and a 12mm gap at the lower border of the osteotomy. The following fixation methods were used: Group 1: a single miniplate, group 2: two miniplates, group 3: three bicortical screws in the upper border, group 4: three bicortical screws in an inverted L configuration, group 5: a single miniplate and a bicortical screw. A mechanical test using vertical linear loading at 1 mm/min velocity on a universal testing machine was carried out. The forces needed to displace the distal segment from 1-5 mm were recorded. The difference between groups was statistically significant for all displacement levels. Group 1 showed the minimum, group 5 showed the maximum resistance in almost all displacement values and there was a trend for higher to lower resistance values towards groups 5 to 1. Fixation methods that used one bicortical screw and a miniplate or three bicortical screws showed higher load resistance against displacement.