Design Optimization of Denture Prostheses by Fatigue Evaluation System

本课题旨在开发一套基于疲劳抗力评价的义齿设计优化系统，包括可摘义齿和种植义齿。优化修复设计，最大限度地减少临床长期使用中假牙的疲劳断裂和失效。进行了三类调查；1)临床失效义齿和种植义齿的断口分析；2)临床失效义齿和种植义齿的有限元模型力学分析；3)可摘义齿和种植材料的疲劳试验，并研究结果与临床失效义齿的相关性。在研究2中，采用标准化有限元模型分析了可摘义齿和种植义齿的结构部件，如托架、主接头和小接头、卡环、树脂与金属之间的界面区域、种植颈部和种植体上部结构中产生的应力分布。这部分项目表明，临床失效概率与模型显示的最大拉应力密切相关，而义齿部件的几何形状和尺寸不一定是导致失效的原因。结果与研究1的结果进行匹配验证。在研究3中，推广了模型中拉伸峰值应力与临床使用义齿失效概率的因果关系。综合分析结果为建立基于义齿结构抗疲劳性能的义齿设计优化系统提供了可能。详细的分析结果已在下一页发表。现在应该根据本项目所提出的设计优化理论系统地进行义齿设计。

This project was conducted to develop a design optimization system of dental prostheses including removable dentures and implant prostheses based on the evaluation of fatigue resistance. The prosthodontic design was optimized to minimize the fatigue fracture and failures in the long term clinical use of the dentures.Three categories of investigations were conducted ; 1) Fractographic analysis of clinically failed removable dentures and implant prostheses, 2) Mechanical analysis by means of finite element models of clinically failed removable dentures and implant prostheses, and 3) Fatigue tests of the removable denture and implant materials, and subsequent investigation of the correlation of the results with clinically failed dentures. In the study 2, stress distributions created in the structural components of the removable dentures and implant prostheses such as rest, major and minor connectors, clasps, interfacial region between the resin and the metal, implant neck, and implant superstructures, were analyzed by means of standardized finite element models. It was indicated in this part of the project that the clinical failure probability was closely related to the maximum tensile stress shown in the models, while the geometry and dimensions of the denture components did not necessarily cause the failure initiation. The result was confirmed by matching verification with the results shown in the study 1. In the study 3, the cause and effect relations of the tensile peak stress in the models with the failure probability of the clinically used dentures were generalized. The results of this comprehensive analysis suggest possibility of establish the design optimization system of dental prostheses based on the fatigue resistance of the denture structures. Detailed results of the analyses have been published as described in the next page. The prosthodontic design should be now systematically executed in line with the design optimization theory indicated in this project.