Fatigue of Restorative Ceramics

描述(申请人提供)：牙科陶瓷作为修复材料因其美观的外观、耐磨性、隔热和生物兼容性而变得越来越多。不幸的是，与牙科合金相比，牙科陶瓷是易碎的。这种抗裂性的缺乏降低了它们的强度和可靠性，导致寿命缩短。在人类中，咬合载荷的大小很少超过324N，有限元模型预测这些载荷会在磨牙牙冠中产生22到87兆帕的应力。传统牙科陶瓷可以承受11.6 Mpa(铝瓷)到240 Mpa(二分贝)的应力，然后才会发生单周破坏。尽管存在这种安全边际，但已有报道称，体内试验七年后的失败率高达30%(DICOR)。循环疲劳载荷明显影响了可承受的最大应力，疲劳失效理所当然地成为牙科陶瓷研究人员关注的问题。在亚临界裂纹扩展(SCG)后，当初始缺陷达到临界应力强度时，陶瓷就会发生疲劳破坏。本项目的总体目标是开发更简单的测量牙科陶瓷应力应力的方法，并通过以下具体目标开发更准确的全瓷修复体寿命预测方法：(1)开发一种方法，通过在最少数量的标准几何试件上的循环疲劳测量来构建牙科陶瓷的精确的S-N-P(应力-寿命-失效概率)模型。(2)发展一种确定应力腐蚀和循环退化对给定陶瓷和应力函数的应力腐蚀和循环退化的单独贡献的方法。(3)验证有限元软件结合时变可靠性软件预测假体寿命的准确性。(4)确定疲劳强度分布与单周强度分布之间的关系。(5)确定裂纹表面重塑修复是否影响疲劳寿命。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与缺陷大小的依赖关系(R曲线行为)。出现裂纹愈合行为的瓷器将在特定的目标5中进行分析。

DESCRIPTION (provided by applicant): 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 prosthesis 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). Porcelain that exhibits crack healing behavior will be analyzed in Specific Aim 5.