Photoelastic analysis of internal screw fixation after sagittal split ramus osteotomy

An experimental study on mechanical behavior and stability of internal screw fixation (ISF) of sagittal split ramus osteotomy has been carried out. A stress freezing method in a three-dimensional photoelastic experiment was used. Four ISF's that utilized different screw placement patterns were used for photoelastic analysis: (1) 3 screw linear pattern placed at 90 degrees to the lateral surface of the model; (2) triangular pattern at 90 degrees to the surface of the model, 2 above and 1 below the mandibular canal; (3) 2 screw linear pattern at 90 degrees, and (4) 3 screw oblique linear pattern at 75, 60 and 45 degrees to the surface of the model. The stress distribution differs markedly according to these 4 methods.