Biomechanical Study Of Mandible And The RIF Of Mandibular Mental Fracture

The treatment of the mandibular fracture will affect the function of chew and lower of facial contour. However, this biomechanical study is to establish the functional model of mandible and evaluate the different rigid internal fixation(RIF) technique of mandibular symphysis fracture.A three-dimensional finite element(3-D FE) method was used to analyze the stress field distribution of integral mandible and a symphysis fractured mandible which was treated with RIF (that is plate-screw technique). The 3-D FE model was loaded by the chewing muscles. However, we developed a physiologically accurate mandibular model. The bite force, strain and the stress shielding were observed. In this work, rigid internal fixation models of mandibular mental fracture with one/two-miniplate and screws were modeled by using ANSYS and Pro/E. The CT images of human mandible were pre-processed and pixels were extracted from the mandibular contours, then the solid model is produced. After constructing the screw and plate models in Pro/E, the models of RIF of mandibular mental fracture were constructed by the finite element software. This method can be used to simulate various mandibular fractures under various RIF techniques, and the stress analysis can direct the clinical treatment.Based on the solid models, the material properties and the element types were defined. The finite element model of integral mandible and the REF for the mandibular symphysis fracture were successfully constructed by using the free mesh.Due to the importance of immediately functional activity of post-operation, the massseter muscle, temporal muscle, medial pterygoid muscle, lateral pterygoid muscle and anterior digastric muscle force vectors were considered. The muscle vectors were loaded as a hank of forces and placed the corresponding dissected position. The fixation restriction was applied to simulate the position of the bite, and the symmetric fixation restrictions were applied on the condylars. The fixation of the plate-screw was considered as the prestress and the appointed displacement is put on the axes direction of screws.In order to get the biomechanical behavior of the integral mandible and REF of symphysis fractured mandible under the functional condition, the biting positions of ICP, INC, MOL-L and MOL-R were selected. The RDF techniques of one and two miniplate(s) to fix the mental fracture were compared in this study. The result indicate that the vons mises stress of mandible was concentrate in the body, mental, upper boundary part of angle, latter boundary part of ramus , condyle of mandible and the alveolus around the bite positions. In the symphysis fractured mandible, the two miniplates and screw fixation is better than the single miniplate and screw fixation, under the condition of the single miniplate fixation and MOL-L and MOL-R biting conditions of the two miniplates fixation, the stress of miniplate-screw system exceeds the yield stress of Titanium 900MPa and can not provide the enough stability of fixation. What's more, in the course of single fixation treatment, the large distortion presented to the screw thread, which may result in failure of the fixation.