Statement of problem

How processing by computer-aided design and computer-aided manufacturing (CAD-CAM) or traditional chairside fabrication techniques affects the presence of defects and the mechanical properties of interim dental prostheses is unclear.

Purpose

The purpose of this in vitro study was to compare the effects of CAD-CAM versus traditional chairside material processing on the fracture and biomechanical behavior of 4-unit interim prostheses with and without a cantilever.

Material and methods

Two types of 4-unit interim prostheses were fabricated with abutments on the first premolar and first mandibular molar, one from a prefabricated CAD-CAM block and one with a traditional chairside polymer-monomer autopolymerizing acrylic resin (n=10). Both groups were assessed by compressive strength testing and additionally with or without a cantilevered second molar by using a universal testing machine with a 5-kN load cell. A finite element model (FEM) was built by scanning both prosthesis designs. Finite element analysis (FEA) replicated the experimental conditions to evaluate the stress distribution through the prostheses.

Results

Interim fixed prostheses manufactured by CAD-CAM showed significantly higher mean fracture loading values (3126 N to 3136 N) than for conventionally made interim fixed prostheses (1287 N to 1390 N) (P=.001). The presence of a cantilever decreased the fracture loading mean values for CAD-CAM (1954 N to 2649 N), although the cantilever did not influence the traditional prostheses (1268 N to 1634 N). The highest von Mises stresses were recorded by FEA on the occlusal surface, with the cantilever design, and at the transition region (connector) between the prosthetic teeth.

Conclusions

Interim partial prostheses produced by CAD-CAM had a higher strength than those manufactured traditionally. The presence of a cantilever negatively affected the strength of the prostheses, although the structures manufactured by CAD-CAM still revealed high strength and homogenous stress distribution on occlusal loading.

中文翻译：

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带有和不带有悬臂的4单元临时假体的CAD-CAM与传统椅子旁处理的比较：力学，断裂行为和有限元分析

问题陈述

目前尚不清楚通过计算机辅助设计和计算机辅助制造（CAD-CAM）或传统的椅边制造技术进行的处理如何影响缺陷的存在以及临时义齿的机械性能。

目的

这项体外研究的目的是比较CAD-CAM与传统椅边材料处理对带有和不带有悬臂的4单元临时假体的断裂和生物力学行为的影响。

材料与方法

两种类型的4单元临时假体在第一前磨牙和第一下颌磨牙上分别带有基台，一种来自预制的CAD-CAM嵌段，另一种具有传统的椅旁聚合物单体自聚合丙烯酸树脂（n = 10）。两组均通过抗压强度测试进行评估，并通过使用带有5 kN称重传感器的通用测试机在有或没有悬臂第二磨牙的情况下进行评估。通过扫描两种假体设计，建立了有限元模型（FEM）。有限元分析（FEA）复制了实验条件，以评估假体的应力分布。

结果

由CAD-CAM制造的临时固定假体显示出比常规制造的临时固定假体（1287 N至1390 N）更高的平均骨折负荷值（3126 N至3136 N）（P = .001）。悬臂的存在降低了CAD-CAM的骨折负荷平均值（1954 N至2649 N），尽管悬臂不影响传统假体（1268 N至1634 N）。用悬臂设计，在假牙之间的过渡区域（连接器），FEA记录了最高的冯·米塞斯应力。

结论

CAD-CAM生产的中期局部假体比传统的假肢具有更高的强度。悬臂梁的存在对假体的强度产生了负面影响，尽管由CAD-CAM制造的结构在咬合负荷下仍然显示出高强度和均匀的应力分布。