Objectives: The objective of the present study was to evaluate the mechanical stress in reconstruction plates and the screw-plate-bone-interface used in bridging a mandibular angle defect by means of the finite element method (FEM). The influence of plate geometry as well as the configuration and the diameter of the screws on the mechanical stress distribution was to be determined at the same time and used as the basis for developing suggestions to optimize the design of the reconstruction plates. Methods: Based on the geometrical data of a human mandible, an angle defect bridged by a titanium reconstruction plate was generated and exposed to chewing force. The reconstruction plate was tightly fixed with M2.7 titanium screws. Plate design, screw configuration and screw diameter were varied. The mechanical stress was calculated according to von Mises stress hypothesis. Results: In the osteosynthesis system with a standard reconstruction plate, the result of the finite element analysis revealed strains resulting from in the simulated functional stresses which far exceed the tensile strengths of the components (1365 MPa reconstruction plate, 175 MPa osteosynthesis screw). Possible clinical consequences could be a fatigue fracture of the plate itself, gradual loosening of the osteosynthesis screws and irreversible damage to the bone. The stress is already reduced to less than half by increasing the nominal diameter of the screw threads to 4.5mm (525 MPa reconstruction plate, 199 MPa osteosynthesis screw. Conclusion: Maximizing the interface between the bone and the reconstruction plate also had a very favorable effect. In consequence of the large interface and a triangular or square configuration of the screws, the stresses could be once more substantially reduced, the plate could be made thinner and thus better adapted to the geometry of the mandible.

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