Evaluation of the stability of different patterns of angular fractures by finite element analysis

Angle is a common site for mandibular fractures. Fractures of the mandible are classified as favorable and unfavorable depending on the fracture plane and muscles acting on these fragments. Mini-plate fixation on the external oblique ridge according to biomechanics defined by Champy for both favorable and unfavorable fractures has become a standard treatment protocol for providing rigid internal fixation. The purpose of this study was to evaluate and compare the mechanical stresses of mini plates, screws and cortical and spongious bone of horizontally favorable and unfavorable mandibular angle fractures. 3-dimensional finite element model of a mandible was constructed from the serial axial sections 1 mm apart from an existing 2-D CT image. Horizontally favorable and unfavorable fractures of mandibular angle area were simulated on a computer model and molar bite force of 200N was applied vertically. The mechanical stress values of the mini-plate, screws and bone were evaluated and compared. The stress values of the cortical bone, miniplate and screw system of the favorable fracture model was higher than the unfavorable fracture model. The highest stress values were measured in the proximal segment of the favorable fracture and distal screw of proximal segment. As a result unfavorable fractures did not show any disadvantage regarding the miniplate and screw fixation.