下颌后牙固定桥支持骨组织应力的三维有限元法分析Ⅲ.不同类型固定桥桥体下皮质骨应力的分析比较

Three-dimensional Finite Element Stress Analysis of Supporting Bone of Mandibular Posterior Fixed Bridge Part Ⅲ. Comparative Analysis with Stress of the Cortical Bone Beneath Different Pontics of Fixed Bridge

目的 :比较下颌后牙固定桥不同类型桥体下皮质骨的应力分布情况。方法 :设计临床上常用的 3种类型桥体 :改良鞍式、改良盖嵴式和盖嵴式桥体 ,其与桥体下粘膜接触的面积比分别约为 1∶2 / 3∶1/ 3。用三维有限元法计算出 2种载荷的桥体下皮质骨单元的最大主应力 (εmax)和最小主应力 (εmin)值。结果 :3种桥体下皮质骨的应力分布规律相似 ,但接触面积较大者其皮质骨应力较小 ,应力最大值分别相差约 5 %～ 7%。结论 :不同组织接触面积的桥体 ,对桥体下骨组织应力的影响不大。

Objective: To analysis stress of the cortical bone beneath different pontics of mandibular posterior fixed bridge by using three dimentional finite element method. Methods: According to the measured data, the characters of all components of fixed bridge and the supporting tissues, and the principals of finite element, the three dimentional finite element model was developed on the basis of an adult mandible. The model consisted of 1363 nodes and 1134 elements after the fixed bridge was placed. Three different pontics were designed. Young's mudulus and Poisson's ratio were obtained from the literature for each type of tissue or materials in the model. The surfaces of pontic next to the mucosa beneath the pontic consisted of nine elements and the contact area were respectively reduced 1/3. It was assumed all materials in the model were homogeneous, isotropic and linearly elastic. One vertical load of 20 kg and one horizontal load of 20 kg were applied respectively on the occlusal surface of the abutments and the pontics of three different fixed bridge. Three dimentional finite element stress analysis was used to calculate the ε\-\{max\} and the ε\-\{min\} of the cortical bone beneath pontics of fixed bridge. Results: Under the vertical loading, the cortical bone beneath the pontics appeared compressive stresses, the stress values of the cortical bone beneath the pontics were respectively 0 211～ 0 119 (ε\-\{max\}, kg/mm\+2), 0 355～ 0 201 (ε\-\{min\}), 0 224～ 0 125 (ε\-\{max\}), 0 375～ 0 215 (ε\-\{min\}), 0 239～ 0 133 (ε\-\{max\}), 0 395～ 0 228 (ε\-\{min\}) Under the horizontal loading, the cortical bone beneath the pontics exhibited tensile stresses and compressive stresses. The stress values of the cortical bone beneath the pontics were respectively 0 004～0 283 (ε\-\{max\},kg/mm\+2), 0 249～ 0 009 (ε\-\{min\}), \ 0 0042～0 301 (ε\-\{max\}),\ 0 264～ 0 0095 (ε\-\{min\}), 0 0045～0 322 (ε\-\{max\}), 0 281～ 0 0101 (ε\-\{min\}). The stress in the cortical bone beneath the pontics increased when the area of contact was reduced, the stress values changed in 5%～7%, but the rules of stress distribution of three different pontics were similar. Conclusion: Stress values in the cortical bone beneath three pontics are small, and the change of stress in the cortical bone beneath the different pontics of mandibular posterior fixed bridge is small too.