A Finite Element Analysis Of TMJ Under The Effect Of Force At Different Part Of Mandible.

Being the exposed part of the body, the mandible is easy to be hurt. It is important to understand the trauma mechanism of mandible and TMJ. The traditional methods, such as human body research,animal experiment, and model experiment,are complicated and hard to be carried out in controlled conditions. With the development of mathematical model technique and computer analog technique, finite element analysis (FEA) shows its superiority.In this paper, we reviewed the past researches of TMJ injury, the development of method of biomechanics analysis, and the FEM model for TMJ reconstruction.By using the thin-layer CT scanning (1mm),3D/WATS thin-layer MR scanning (1mm) and Matlab software, we established a 3D finite element model of TMJ which included the whole dentulous mandible. The model could simulate five kinds of the mandibular position: closed mouth, 1cm, 2cm, 3cm,and 4cm opened mouth.Secondarily, the mechanic analysis was carried out on the basis of the FEM model.The stress variation in articular disk and articular cartilage was studied while instantaneous force was added to the left angle of mandible. METHODS: Instantaneous force of 1000N was applied to the left angle of mandible,with the direction perpendicular to the frankfort plane. The distribution of Von Mises stress (equivalent stress, abbreviated EQV stress) and its maximum value were measured to observe the mechanic variation in the articular disk and articular cartilage. RESULTS:(1) The maximum values of EQV were rather low when the mouth was closed. (2) In different mandibular position of opened mouth, the maximum EQV were mostly located on the posterior band of the articular disc, and the anterior oblique surface of articular cartilage. (3) The maximum EQV of articular disc were always higher on the left side than the right side. But the value distribution differed in the articular cartilage, which was higher on the left side in three mandibular positions of closed mouth, 1cm and 4cm opened mouth, and higher on the right side in two positions of 2cm and 3cm opened mouth. (4) The locations of the maximum EQV were symmetrical in the both side of the articular disk and articular cartilage.The stress variation in articular disk and articular cartilage was studied while instantaneous force was added to the mandibular mentis. METHODS: Instantaneous force of 1000N was applied to the mandibular mentis in the saggital plane in three directions, which were perpendicular, 60o oblique , and parallel to the frankfort plane. The distribution of Von Mises stress (equivalent stress, abbreviated EQV stress) and its maximum value were measured to observe the mechanic variation in the articular disk and articular cartilage. RESULTS:(1) The maximum values of EQV were located on the posterior band of the articular disc, and the anterior oblique surface of articular cartilage in all groups with different force direction and different mandibular position. (2) The direction of the instantaneous force affected the maximum value of EQV in the articular disk and articular cartilage, and the highest value occurred in the group hit by force parallel to the frankfort plane. (3) The maximum values of EQV were rather low when the mouth was closed.The experiment proved that our models could precisely present the real TMJ and mandible, and the results of the study corresponded with the clinical cases. Some problems in the past experiments were solved with the models. It can provide us a new method to study the TMJ biomechanics.