Biomechanical Evaluation of Mandibular Symphysis Fracture Plating Technique

Objectives: To establish a precise 3-demensional model (3-D FEM) to evaluate the stress distribution of the mandible and the biomechanical behavior of different rigid internal fixation technique for symphysis fracture. Methods: The CT images of healthy male were used to modeling. The FEA models of mandible and plate-screw fixation system were established by ANSYS and Pro/E. The mandible model was divided into an external cortical and internal trabecular layer based on the CT scan. The mandibular fracture was located in symphysis region and one or two 4-hole, 2.4-mm titanium miniplates fixed with moncortical screws, were evaluated. The material characteristics of different structures were assigned based on the literature. Meshing was performed with Solid 92 finite elements. Three static tasks were simulated by perpendicular restrains, which involved clenching in the intercuspal position (ICP); incical clenching (INC); and right unilateral molar clenching (RMOL). Nine pairs of masticatory muscles (superficial and deep masseter; anterior, middle, and posterior temporalis; medial pterygoid; superior and inferior lateral pterygoid; and anterior digastric) assumed to be directly attached to bone with multiple force vectors. The condyle was fixed in all three spatial directions to represent the reaction force at the TMJ. Results: The finial model consisted of more than 230 000 elements with 375000 nodes. The deformation of mandible were focus in clenching area (maximal Von Mises stress=66.667MPa) and condyle (maximal Von Mises stress=26.667 MPa) in RMOL. When one-miniplate were used, the stress in miniplate was up to 4023 MPa (in RMOL), which was beyond the yield point (900 MPa).Conclusions: The FE analysis can play an important role in the study of mechanics of mandibular fracture with some limitations. The two-miniplate fixation technique can provide more stability for symphysis fracture especially under the unilateral biting condition.