方丝弓矫治器三维有限元力学模型的建立

A primary construction of the 3D finite element model for fixed edgewise appliance

目的:以有限元方法建立方丝弓矫治器的力学分析数字模型。方法:采用powerSHAPE3040造型软件,在已有的下颌三维数字模型基础上,划出托槽槽沟中心平面(H)、颊面牙体长轴和托槽中心,以其为基准,构建下颌左侧牙列槽沟为0.018in(1in=2.54cm)的托槽模型。这些托槽在各牙位的槽底厚度相同,托槽槽沟在同一H平面。然后据此托槽和H平面构建出0.016in×0.022in的平直方丝模型。再用ANSYS分析系统将这些三维模型转化为三维有限元模型。牙、牙周膜、牙槽骨和托槽以4点四面体单元划分,弓丝以10点四面体单元划分。结果:获得下颌牙列及其托槽和平直方丝的三维有限元模型。该托槽槽底带有转矩,所建平直方丝在H平面上与托槽槽沟均匀接触,因此初始状态彼此无作用力。结论:该模型初步建立了用三维有限元法对固定矫治技术进行全牙列分析的平台。

PURPOSE:To construct a three-dimensional finite element model (3D-FEM) of the fixed appliance for mechanical analysis. METHODS: The figures of the brackets and the edgewise wire were constructed at the platform of powerSHAPE3040, based on a male's figures of mandibular dentition and alveolar bone. First, the bracket slot center plane (H plane) was lined, which was 4.3mm under the mesial buccal cusp of the 2nd molar and parallel to the XY plane. The point that each tooth's axis of buccal surface (line A) crossed the H plane was at the bracket's center (point O). Second, on the basis of H plane, line A, and point O, 0.018 inch×0.025 inch brackets were constructed on the teeth. All the slots were on the H plane.Then, according to the brackets' slots, plane f was gotten, which went through every slot smoothly and was perpendicular to the XY plane. At the base of slots' basal wall and gingival wall, the 0.016 inch×0.022 inch wire was constructed on the plane f. The figures of edgewise wire, teeth, alveolar bone, and brackets were transferred to ANSYS5.5 system in the IGES format. The teeth, periodontal membrane (PDM), alveolar bone, and brackets were broken down to 4-node tetrahedron element. The 10-node tetrahedron element was chosen to make the model of edgewise wire. RESULTS: The 3D-FEM of the brackets with teeth, PDM, alveolar, and the edgewise wire about the mandible were obtained. This kind of bracket was torqued slot bracket, which is similar to the preadjusted appliance. The edgewise wire was not as same as catenary curve or parabola completely. There were inset and offset on the wire following the dentition model. When the plain edgewise wire was inserted in the brackets, there was no force between the wire and brackets. If the wire was deformed as designed, the action could be analyzed. CONCLUSION: 3D mechanical analysis about the fixed appliance could be done on the model.