OPTIMIZED STRESS STATES IN CERAMIC-BASED RESTORATIONS

目前，大约90%的固定修复体是超陶瓷材料 修复 最近基于瓷的金属陶瓷修复体 边缘、较薄的金属内冠、树脂粘结、支持种植体，以及 悬臂设计与增加的结构风险相关， 失败 此外，还没有建立可靠的方法， 评估简单生物材料的热收缩相容性状态 或三材料金属-陶瓷条或更复杂的单个单元或 多单元假体。 尽管有许多关于热的研究， 金属陶瓷系统的收缩相容性，还没有模型 开发用于预测临床假体中的残余应力， 组成特性，例如热收缩系数、弹性 模量和粘度值。 此外，还没有研究分析了 潜在破坏性拉伸应力的相对大小或位置 由于临床相关的金属-陶瓷收缩差异 假体设计，以便潜在失效的关键区域可以 鉴定 这项为期五年的研究计划的最初重点将是 建立实用的筛选测试， 从不兼容的系统兼容，并确定关键区域， 热不相容性引起的残余拉应力 假体设计。 此外，潜在的故障机制将 以及加强陶瓷修复体的方法 基于冷却速率变化的分析，热回火 处理和离子交换处理以诱导保护性压缩 警告陶瓷中残余应力分布的应力 在将它们放置在口腔中之前， 四种新型 技术发展将用于拟议的分析： 1)一种用于有限元分析的三维粘弹性单元 2）在液体介质中进行热回火， 改变残余应力分布并减少拉伸应力， 金属-陶瓷和全陶瓷假体的关键风险区域，3） 单、双离子交换强化处理 富钾和富铷的浆料， 温度在短时间内，和4）微型 半导体应变计（标距长度约100 μ）， 与产生光弹性应力的光应力涂层结合 实际尺寸模型的负载假体表面内的图案 或放大模型设计，以验证有限元预测的应力分布 元素分析 拟议的研究将旨在 评估由热收缩引起的瞬态和残余应力状态 不相容性，将实验不相容性数据与 从粘弹性模型中获得的那些，这些模型已经被开发成 预测不相容应力，并开发热处理 协议，以优化由此产生的应力分布在这些 假肢 拟议研究的总体目标是开发 预测模型，分析金属陶瓷的失效风险因素， 基于分析和实验模型的玻璃陶瓷澄清， 并改变残余应力分布， 全瓷和金瓷修复体的安全性， 热处理、回火、离子交换、化学蚀刻和设计 因素

Approximately 90% of the fixed prostheses made today are meta-ceramic restoration. Recent metal-ceramic prostheses that are based on porcelain margins, thinner metal copings, resin bonding, supporting implants, and cantilever designs are associated with an increased risk of structural failure. In addition, no method has yet been established to reliably assess the thermal contraction compatibility status of simple biomaterial or trimaterial metal-ceramic strips or more complex, single-unit or multiple-unit protheses. In spite of numerous studies on the thermal contraction compatibility of metal-ceramic systems, no model has yet been developed to predict residual stresses in clinical prostheses based on constituent properties such as thermal contraction coefficients, elastic moduli, and viscosity values. Furthermore, no study has yet analyzed the relative magnitudes or locations of potentially damaging tensile stresses caused by metal-ceramic contraction differences in clinically relevant prosthesis designs so that critical zones of potential failure can be identified. The initial focus of this five-year research program will be to establish practical screening tests that differentiate thermally compatible from incompatible systems and to identify critical zones of residual tensile stress caused by thermal incompatibility in selected prosthesis designs. In addition, potential failure mechanisms will be investigated as well as methods of strengthening ceramic-based prostheses based on analysis of cooling rate variations, thermal tempering treatment, and ion exchange treatment to induce protective compressive stresses that alert the residual stress profiles in the ceramic structures prior to their placement in the oral cavity. Four novel technological developments will be employed for the analyses proposed: 1) a three-dimensional visco-elastic element for finite element analysis of incompatibility stresses, 2) thermal tempering in liquid media to alter residual stress profiles and to reduce tensile stresses in critical-risk areas of metal-ceramic and all-ceramic prostheses, 3) single and double ion-exchange strengthening treatments based on potassium-enriched and rubidium-enriched slurries that are fired at low temperatures over short time periods, and 4) micro-miniature semiconductor strain gages (gage length approximately 100 mu) in combination with PhotoStress coatings that produce photoelastic stress patterns within the surface of loaded prostheses of actual-size models or enlarged-model designs to validate stress profiles predicted by finite element analysis. The proposed research studies will be designed to assess transient and residual stress states caused by thermal contraction incompatibility, to correlate experimental incompatibility date with those obtained from visco-elastic models that have been developed to predict incompatibility stresses, and to develop thermal processing protocols to optimize the resulting stress distributions in these protheses. The overall objective of the proposed research is to develop a predictive model, to analyze failure risk factors for metal-ceramic and glass-ceramic restorations based on analytical and experimental models, and to alter residual stress distributions that will enhance the margin of safety for all-ceramic and metal-ceramic prostheses by control of thermal processing, tempering, ion exchange, chemical etching, and design factors.