Fatigue of Restorative Ceramics

描述（由申请人提供）：牙科陶瓷因其美观、耐磨性、绝热性和生物相容性而成为越来越多的修复材料。不幸的是，与牙科合金相比，牙科陶瓷很脆。这种抗断裂性的缺乏降低了它们的强度和可靠性，导致预期寿命缩短。人类咬合负荷的大小很少超过324 N，有限元模型预测这些负荷会在臼齿冠中引起22至87 MPa的应力。传统牙科陶瓷在单次循环失效前可承受11.6 MPa（铝瓷）~ 240 MPa （Dicor）的应力。尽管有这样的安全范围，但据报道，7年后的失败率高达30% （Dicor）。显然，循环疲劳载荷对可承受的最大应力有影响，疲劳失效是牙科陶瓷研究人员关注的问题。陶瓷的疲劳破坏发生在初始裂纹扩展达到临界应力强度后。本项目的总体目标是通过以下具体目标，开发更容易测量牙科陶瓷SCG的方法，并开发更准确的预测全陶瓷假体寿命的方法：(1)开发一种方法，通过对最少数量的标准几何试样进行循环疲劳测量，构建牙科陶瓷精确的S-N-P（应力-寿命-失效概率）模型。(2)开发一种方法来确定给定陶瓷和应力函数的应力腐蚀和循环降解对SCG的单独贡献。(3)验证有限元软件结合时变可靠性软件预测义肢寿命的准确性。(4)确定疲劳强度分布与单周强度分布的关系。(5)通过表面重塑确定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：一种具有恒定的断裂韧性，另一种具有断裂韧性依赖于缺陷尺寸（r曲线行为）。表现出裂纹愈合行为的瓷器将在具体目标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.