Finite Element Study of Three Different Treatment Designs of a Mandibular Three Implant-Retained Overdenture

Abstract This study compares ball, bar-clip and bar-ball attachment systems for implant-retained mandibular overdentures with three implants. The first implant is placed in the middle of the mandible and the other two are imbedded in the first premolar regions. Linear elastic finite element analysis is used for design analysis. Three dimensional geometry of the mandible is generated from computed tomography. Other parts are modeled using SolidWorks software. The foodstuff is positioned at the right first molar, representing the most frequent masticating situation. To obtain accurate mesh-independent results, finite element models are solved using several mesh grids. They are then validated by means of a detailed convergence analysis. The results demonstrate that the highest von-Mises stress in the bone is always located around the neck of the implant, at its upper threads. Ball and bar-ball attachments transfer the highest and lowest stresses to the bone surrounding the implants, respectively. The lowest stresses in the cortical and cancellous bones are due to bar-ball attachment. Yet, the overdenture gets its maximum movement for this arrangement. Consequently, the use of bar-ball attachment is only recommended for the cases in which stress transferred to peri-implant bone is more important than overdenture stability. Among the three treatment designs, ball attachment seems to exhibit the lowest lateral and overall displacements and hence, better overdenture stability.

摘要：本研究针对三种植体支持式下颌覆盖义齿，对比球附着体、杆卡附着体与杆球附着体三种附着系统的应用效果。其中，第一枚种植体植入下颌骨正中，剩余两枚植入第一前磨牙区域。本研究采用线弹性有限元分析开展设计分析：通过计算机断层扫描（Computed Tomography，CT）获取下颌骨的三维几何模型，其余部件通过SolidWorks软件进行建模。将食物载荷模型置于右侧第一磨牙处，以模拟临床最常见的咀嚼工况。为得到与网格无关的精准分析结果，本研究采用多组网格划分方案对有限元模型进行求解，并通过详细的收敛性分析完成模型验证。研究结果表明，骨组织内的最高冯·米塞斯应力（von-Mises Stress）始终分布于种植体颈部及其上部螺纹周围。球附着体与杆球附着体分别向种植体周围骨组织传递最高与最低的应力。皮质骨与松质骨内的最低应力均由杆球附着体产生，但此时覆盖义齿的位移量达到最大值。因此，仅当种植体周围骨组织所受应力比覆盖义齿稳定性更为关键时，方可推荐使用杆球附着体。在三种治疗设计方案中，球附着体的侧向与整体位移均为最低，故覆盖义齿稳定性更佳。