IN-VITRO COMPARISON OF PARAMETERS AFFECTING THE FIXATION STRENGTH OF SAGITTAL SPLIT OSTEOTOMIES

Purpose: The goal of this study was to determine how different paramet ers affect the bending strength of human cadaver mandibles that have u ndergone a sagittal split osteotomy. Materials and Methods: The effect s of screw material (titanium [Ti] vs polylactic acid/polyglycolic aci d [PLA/PGA]), screw configuration (linear vs inverted L-shape), screw diameter (2.0 mm vs 2.7 mm), material into which screws were inserted (human mandible, bovine rib, synthetic polymer), and loading rate (1.0 mm/min vs 10.0 mm/min) were quantified, Also, biomechanical principle s were used to model shear stress and displacement, Variable lever arm s, screw material, screw diameter, screw configuration, distance betwe en screws, and bone properties were all evaluated in this model. Resul ts: Accounting for variable mandible geometries and differentiating be tween deflections (and shear stresses) due to bending and due to torsi on, in vitro mechanical testing revealed that there was a statisticall y significant difference in total shear stress at 3 mm of deflection d epending on screw material (Ti > PLA/PGA), screw diameter, and materia l into which screws are inserted (mandibles > ribs = synthetic polymer ). There was no significant difference in total shear stress depending on screw configuration or strain rate. Conclusion: Total shear stress and deflections are important and more viable parameters than load to assess parameters of clinical importance in osteotomy or fracture fix ation.