FAILURE OF DENTAL PORCELAIN

近2300万克朗和400万座桥梁被交付给美国 每年的病人，其中大部分是部分或完全由 瓷器或其他易碎的陶瓷。不幸的是，由于以下原因而失败 瓷器破裂需要更换许多修复体 仅在短期服务后，目前限制了应用 全陶瓷修复体。全瓷修复体的使用量增加 由于卓越的生物兼容性和更令人愉悦的 美观，但由于灾难性骨折，临床失败率很高 限制它们的使用。本提案研究的目标是定义和 用断口表征牙科烤瓷的失效机理 力学模型体系。 牙科瓷器和陶瓷的实验室检测使用了静电 以往采用的是单荷载试验方法。这些静态测试确定 可以容忍但不能用于预测的最大应力 假体通常在临床条件下出现故障 故障发生前的多次亚临界载荷循环。牙科陶瓷和 玻璃在有水分的情况下会发生化学静态疲劳 环境温度，但之前一直认为这些 材料不会发生机械疲劳。然而，怀特(1993)使用 一种采用尖锐压痕技术的断裂力学方法 证明牙科瓷器对机械的敏感性 疲劳，但无法用这种尖锐的现象来表征 压痕技术。因此，牙齿的易感性 陶瓷的机械疲劳，以及它们之间可能的相互作用 循环机械疲劳和静态化学疲劳必须研究 确定导致临床失败的失败机制。 使用一种新的压痕技术的断裂力学方法是合适的 到脆性粗晶材料的疲劳特性，如 牙科瓷器。材料经过多次缩进， 显微镜检查或进一步测试。实验将测试 假说：(1)牙科瓷器易受机械影响 疲劳；(2)机械疲劳、化学疲劳及其相互作用 降低牙科瓷器的强度；(3)所有疲劳损伤都是 累积，(4)裂缝可能是由临界压力引起的， 小于静态破坏所需的压力，(5) 裂纹扩展随载荷过程中压力的变化而变化。 卸货周期。 研究结果将定义和量化失效机制。这一知识 对失效机制的分析是确定最佳材料的关键， 加工和强化技术，这对 用于体内应用的新材料的开发。更好的陶瓷 材料将大大减少患者的痛苦和医疗保健 通过减少骨折假体的更换来降低成本，并将允许 全瓷修复体的更广泛应用。

Almost 23 million crowns and 4 million bridges are delivered to American patients annually, most of which are partly or completely made of porcelain or other brittle ceramics. Unfortunately, failure due to porcelain fracture necessitates the replacement of many restorations after only short periods of service, and currently limits the application of all-ceramic restorations. Increased use of all-ceramic restorations is desirable due to superior biocompatibility and more pleasing esthetics, but high clinical failure rates due to catastrophic fracture limit their use. The goal of this proposal study is to define and characterize the failure mechanism of dental porcelain using a fracture mechanics model system. Laboratory testing of dental porcelains and ceramics has used static single-load test methods in the past. These static tests determine the maximum stresses that can be tolerated, but are not valid for predicting failure in clinical conditions where prostheses are usually subjected to many subcritical load cycles before failure occurs. Dental ceramics and glasses undergo chemical static fatigue in the presence of moisture at ambient temperatures, but it has previously been assumed that these materials do not undergo mechanical fatigue. However, White (1993) used a fracture mechanics approach with a sharp indentation technique to demonstrate the susceptibility of a dental porcelain to mechanical fatigue, but was unable to characterize the phenomenon using that sharp indentation technique. Therefore, the susceptibilities of dental ceramics of mechanical fatigue, and the possible interaction between cyclic mechanical and static chemical fatigue must be investigated to identify failure mechanisms responsible for clinical failure. A fracture mechanics approach using a new indentation technique is suited to the fatigue characterization of brittle coarse grained materials, like dental porcelains. Materials are indented multiple times and microscopically examined of tested further. Experiments will test the hypotheses that: (1) dental porcelain is susceptible to mechanical fatigue, (2) mechanical fatigue, chemical fatigue, and their interaction decrease the strength of dental porcelain, (3) all fatigue damage is cumulative, (4) cracks may be initiated by a critical pressure, much smaller than the pressure necessary for static failure, (5) the rate of crack propagation varies with respect to pressure changes during load- unloading cycles. The results will define and quantify failure mechanisms. This knowledge of failure mechanisms is essential to identify the best materials, processing, and strengthening techniques, and is critical to the development of new materials for in vivo applications. Better ceramic materials will substantially decrease patient suffering and health care costs by reducing the replacement of fractured prostheses, and will allow greater application of all-ceramic prostheses.