AN IN-VITRO COMPARISON OF THE MECHANICAL CHARACTERISTICS OF 3 SAGITTAL RAMUS OSTEOTOMY FIXATION TECHNIQUES

Purpose: The purpose of this in vitro investigation was to compare the mechanical characteristics of three techniques for the rigid internal fixation of simulated sagittal ramus osteotomies in terms of their ab ility to resist vertical loads resembling masticatory forces. Material s and Methods: Fifteen bovine ribs of similar size and shape were subj ected to uniform osteotomies resembling a sagittal ramus osteotomy, Th ey were divided into three groups and fixed with three 2.0-mm bicortic al positional screws in an inverted L-pattern, eight monocortical scre ws and a sagittal strut plate, or a hybrid system using three 2.0-mm b icortical positional screws, five 2.0-mm monocortical screws, and a sa gittal strut plate. The repaired ribs were secured in a jig, subjected to vertically deforming forces, and evaluated for yield load, yield p oint, maximum load, displacement at maximum load, load at 3.0 mm displ acement, and stiffness. The various groups were compared statistically with a Scheffe multiple comparison test. Results: No statistically si gnificant differences existed between the positional screw group and t he hybrid group (P > .05). No statistically significant differences we re noted in yield displacement, yield load, displacement at maximum lo ad, for any of the groups (P > .05), There were differences noted betw een the monocortical strut group and other groups in maximum load, loa d at 3.0 mm displacement, and stiffness (P > .05). Conclusions: The mo nocortically fixed sagittal strut plate offers less resistance to maxi mum load and loads at 3.0 mm displacement and is less stiff than eithe r a three-positional screw system or a hybrid system, No differences e xisted between the three positional screw systems and the hybrid syste m, However, given the low yield loads and yield displacements, these d ifferences may not be clinically important.