Objective

Clasps of removable partial dentures (RPDs) often suffer from plastic deformation and failure by fatigue; a common complication of RPDs. A new technology for processing metal frameworks for dental prostheses based on laser-sintering, which allows for precise fabrication of clasp geometry, has been recently developed. This study sought to propose a novel method for designing circumferential clasps for laser-sintered RPDs to avoid plastic deformation or fatigue failure.

Methods

An analytical model for designing clasps with semicircular cross-sections was derived based on mechanics. The Euler–Bernoulli elastic curved beam theory and Castigliano’s energy method were used to relate the stress and undercut with the clasp length, cross-sectional radius, alloy properties, tooth type, and retention force. Finite element analysis (FEA) was conducted on a case study and the resultant tensile stress and undercut were compared with the analytical model predictions. Pull-out experiments were conducted on laser-sintered cobalt–chromium (Co–Cr) dental prostheses to validate the analytical model results.

Results

The proposed circumferential clasp design model yields results in good agreement with FEA and experiments. The results indicate that Co–Cr circumferential clasps in molars that are 13 mm long engaging undercuts of 0.25 mm should have a cross-section radius of 1.2 mm to provide a retention of 10 N and to avoid plastic deformation or fatigue failure. However, shorter circumferential clasps such as those in premolars present high stresses and cannot avoid plastic deformation or fatigue failure.

Significance

Laser-sintered Co–Cr circumferential clasps in molars are safe, whereas they are susceptible to failure in premolars.

中文翻译：

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设计用于激光烧结可摘局部义齿的环扣的分析模型

客观的

可摘局部义齿（RPD）的扣环经常遭受塑性变形和疲劳破坏。RPD的常见并发症。最近开发了一种新的技术，该技术用于基于激光烧结的牙科义齿金属框架的加工，该技术可精确制造扣环的几何形状。这项研究试图提出一种新颖的方法来设计激光烧结RPD的周向搭扣，以避免塑性变形或疲劳破坏。

方法

基于力学原理，推导了半圆形扣设计的解析模型。用Euler-Bernoulli弹性弯曲梁理论和Castigliano的能量方法将应力和底切与扣环长度，横截面半径，合金性能，齿类型和保持力相关联。在案例研究中进行了有限元分析（FEA），并将由此产生的拉伸应力和底切与分析模型的预测值进行了比较。在激光烧结钴铬（Co-Cr）牙修复体上进行拉出实验，以验证分析模型的结果。

结果

所提出的周向扣设计模型产生的结果与有限元分析和实验结果吻合良好。结果表明，在臼齿中长13 mm的0.25 mm底切槽中的Co-Cr环向扣，其横截面半径应为1.2 mm，以提供10 N的固位力，并避免塑性变形或疲劳破坏。但是，较短的周向扣环（例如前磨牙中的环扣）呈现高应力，无法避免塑性变形或疲劳破坏。

意义

臼齿中的激光烧结Co-Cr环向扣是安全的，而它们在前臼齿中容易损坏。