Development of the model to calculate the mechanical stress which applied to the region of TMJ during functional jaw movement

对10例正常受试者、10例颞下颌关节（TMJ）内部紊乱患者和10例单侧后牙交叉咬合患者在咀嚼、开合下颌运动和自主握紧时的下颌6自由度运动及合颌肌、开颌肌进行测量，并采集所有受试者的形态学图像数据。将实时时间尺度转换为归一化时间。对其中1例进行头部CT检查，包括颞下颌关节。利用CT图像和医学快速成像有限元模型制作程序在计算机上制作三维有限元模型。利用该模型和各受试者的形态学图像数据，分别建立有限元模型。假设图像上的CT值与骨矿物质密度成正比，每块骨的弹性模量与骨矿物质密度的立方根成正比。力学参数为髁突、下颌窝、关节盘和下颌骨的最大主应力和von Mises应力。上述肌肉的力由力矩平衡方程导出。利用上述数据和模型建立了TMJ机械应力计算模型。我们首次发现咀嚼侧髁突向下颌窝方向的位移大于非咀嚼侧髁突向下颌窝方向的位移，椎间盘位移抑制了咀嚼时髁突的运动和开合颌运动，咀嚼时后牙合侧髁突向下颌窝方向的位移更大。在所有受试者中，使用上述模型计算的结果几乎相同。因此，我们证实了我们计算TMJ机械应力的模型是有效的。

Mandibular movement with 6 degrees of freedom and jaw-closing and opening muscles were taken during mastication, open-close jaw movement and voluntary clenching in 10 normal subjects, 10 patients with temporomandibular joint (TMJ) internal derangement, and 10 patients with unilateral posterior crossbite, Morphological image data were also taken in all subjects. The real time scale was transformed to normalized time. CT of head including TMJ were taken in one of above subjects. 3-D finite element model was made in a computer by using CT images and medical fast imaging finite element model making program. Using this model and morphological image data in each subject, respective finite element model was made. It was assumed that CT values on the image were proportional to the bone mineral density and the elastic moduluses of each bone were proportional to the cube root of the bone mineral density. The mechanical parameters were maximum principal and von Mises stresses on the condylar, mandibular fossa, articular disc and mandible. The forces of aforementioned muscles were derived from the equation of equilibrium of moment. The model to calculate the mechanical stress to TMJ was made by using aforementioned data and model. We revealed for the first time that the displacement of the condyle on the chewing side was greater in the direction of the mandibular fossa than that on the non-chewing side, that disc displacement inhibited the condylar motion during mastication and open-close jaw movement, and that the condyle on the posterior crossbite side moved more in the direction of the mandibular fossa, during mastication. In all subjects, almost same results were calculated by using aforementioned model. Therefore, we confirmed that our model to calculate the mechanical stress to TMJ was valid.