Fatigue of Restorative Ceramics

牙科陶瓷由于其美观， 外观、耐磨性、隔热性和生物相容性。不幸的是，牙科陶瓷 与牙科合金相比，它很脆。这种抗断裂性的缺乏损害了它们的强度， 可靠性，导致预期寿命缩短。咬合负荷的大小很少超过324 N 有限元模型预测这些载荷在人体中产生22至87 MPa的应力， 臼齿牙冠传统牙科陶瓷可承受11.6 MPa（铝瓷）至240 MPa（Dicor） 在单次循环失效之前的应力。尽管有这种安全边际，但在使用后，失效率高达30%（Dicor）。 已经报道了七年的体内试验。循环疲劳载荷显然对最大应力有影响 疲劳破坏是牙科陶瓷研究人员所关心的问题。疲劳失效 当初始裂纹在亚临界裂纹扩展（SCG）后达到临界应力强度时，陶瓷发生断裂。 本项目的总体目标是开发更简单的牙科陶瓷SCG测量方法， 通过以下具体方法，开发更准确的全瓷修复体寿命预测方法 目的：（1）建立一种精确的应力-寿命-失效概率（S-N-P）模型， 在最小数量的标准几何样本上进行循环疲劳测量。 (2)提出了一种确定应力腐蚀和循环应力腐蚀各自贡献的方法， 对于给定的陶瓷和应力函数，降解为SCG。(3)验证假体寿命的准确性 使用有限元软件结合时变可靠性软件进行预测。(4)到 确定疲劳强度分布与单次循环强度分布的关系。(5)到 确定通过表面重塑的裂纹愈合是否影响疲劳寿命。具体目标1-4将 研究两种牙科陶瓷：一种表现出恒定的断裂韧性，另一种表现出 断裂韧性对缺陷尺寸的依赖性（R曲线行为）。一种裂纹愈合的瓷器 行为将在具体目标5中进行分析。

Dental ceramics have become increasingly prolific as restorative materials because of their esthetic appearance, wear resistance, thermal insulation, and biocompatibility. Unfortunately, dental ceramics are brittle in comparison to dental alloys. This lack of fracture resistance compromises their strength and reliability, resulting in decreased lifetime expectancy. The magnitude of occlusal load rarely exceeds 324 N in humans, and finite element models have predicted these loads to induce stresses of 22 to 87 MPa in molar crowns. Traditional dental ceramics can withstand 11.6 MPa (aluminous porcelains) to 240 MPa (Dicor) of stress before single-cycle failure. In spite of this margin of safety, failure rates as high at 30% (Dicor) after seven years in vivo have been reported. Cyclic fatigue loading clearly has an impact on the maximum stress that can be withstood, and fatigue failure is rightfully a concern of dental ceramic researchers. Fatigue failure of ceramics occurs when initial flaws reach a critical stress intensity following subcritical crack growth (SCG). The overall goals of this project are to develop easier methods of measuring SCG for dental ceramics and to develop more accurate methods for predicting all-ceramic prothesis lifetimes through the following specific aims: (1) To develop a method for constructing accurate S-N-P (stress-lifetime-failure probability) models for dental ceramics from cyclic fatigue measurements on a minimum number of standard geometry specimens. (2) To develop a method for determining the individual contributions of stress corrosion and cyclic degradation to SCG for a given ceramic and stress function. (3) To verify the accuracy of prosthesis lifetimes predicted using finite element software in conjunction with time-dependent reliability software. (4) To determine how the distribution of fatigue strength relates to the distribution of single-cycle strength. (5) To determine whether crack healing through surface remodeling affects fatigue lifetime. Specific Aims 1-4 will investigate two dental ceramics: one that exhibits constant fracture toughness and one that exhibits dependence of fracture toughness on flaw size (R-curve behavior). A porcelain that exhibits crack healing behavior will be analyzed in Specific Aim 5.