Manda Marianthi, Galanis Christos, Georgiopoulos Vasilis, Provatidis Christofer, Koidis Petros
Department of Fixed Prosthesis and Implant Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece.
J Prosthet Dent. 2009 Jan;101(1):54-65. doi: 10.1016/S0022-3913(08)60292-9.
Increased technical failure has been reported for cross-arch fixed partial dentures (FPDs), particularly for cantilever units with minimum osseous support.
The purpose of this study was to investigate the effect of severely reduced bone support on the stress field developed within the connectors for 3 types of cross-arch FPDs.
Six digital parametric models were developed, derived from a 3-dimensional (3-D) initial model. The latter simulated a human mandible, dentate bilaterally to second premolars, with normal height of alveolar bone. In the initial model, the teeth were prepared and splinted with a cross-arch FPD bilaterally with one of the following: no cantilever, 1-unit cantilever, or 2-unit cantilever. All structures were obtained from computed tomography (CT)-scan images or constructed in 3-D computer-aided design (CAD) and reverse engineering environments. A 3-D finite element analysis (3-D FEA) was performed.
The reduction of the alveolar bone in the no-cantilever FPD model caused a greater increase of stress in the region of connectors among the splinted teeth in comparison to the 1- and 2-unit cantilever FPD model. The stress state within the connectors of the cantilever segment remained constant. The connectors proximal to the retaining abutment demonstrated the highest stress values, independent of the osseous support. The stress values in the region of the same connectors in the 2-unit cantilever restoration were almost double, compared to the 1-unit cantilever model. Decreasing the osseous level in the 1- and 2-unit cantilever FPD models caused milder stress distribution and magnitude in the region of connectors among the splinted teeth.
The stress field developed within the connectors of the cantilever segment is independent of the osseous level. The stress field within the connectors among splinted teeth depends on the osseous support and both the presence and length of the cantilever segment. Furthermore, this study indicates that adding a cantilever segment has a positive effect on the stress behavior of the splinted teeth connectors in situations of reduced osseous support.
据报道，跨牙弓固定局部义齿（FPD）的技术失败率有所增加，特别是对于骨支持最少的悬臂单元。
本研究的目的是调查严重减少的骨支持对3种类型跨牙弓FPD连接体内部产生的应力场的影响。
从三维（3-D）初始模型衍生出6个数字参数模型。初始模型模拟了一个人类下颌骨，双侧牙齿到第二前磨牙，牙槽骨高度正常。在初始模型中，对牙齿进行预备，并双侧用以下一种情况的跨牙弓FPD进行夹板固定：无悬臂、1单元悬臂或2单元悬臂。所有结构均从计算机断层扫描（CT）图像中获取，或在3-D计算机辅助设计（CAD）和逆向工程环境中构建。进行三维有限元分析（3-D FEA）。
与1单元和2单元悬臂FPD模型相比，无悬臂FPD模型中牙槽骨的减少导致夹板固定牙齿之间连接体区域的应力增加更大。悬臂段连接体内部的应力状态保持不变。靠近固位基牙的连接体显示出最高应力值，与骨支持无关。与1单元悬臂模型相比，2单元悬臂修复体中相同连接体区域的应力值几乎翻倍。在1单元和2单元悬臂FPD模型中降低骨水平会导致夹板固定牙齿之间连接体区域的应力分布和大小更缓和。
悬臂段连接体内部产生的应力场与骨水平无关。夹板固定牙齿之间连接体内部的应力场取决于骨支持以及悬臂段的存在和长度。此外，本研究表明，在骨支持减少的情况下，增加悬臂段对夹板固定牙齿连接体的应力行为有积极影响。
