FAILURE OF DENTAL PORCELAIN

近2300万克朗和400万座桥梁交付给美国 患者每年，其中大部分是部分或完全由 瓷或其它脆性陶瓷。不幸的是，由于 瓷破裂需要更换许多瓷套 仅在短期服务后，目前限制了应用程序 全陶瓷装饰。增加全陶瓷涂层的使用 由于上级生物相容性和更令人愉悦 美观，但由于灾难性骨折， 限制其使用。本提案研究的目标是定义和 用断裂法表征牙科陶瓷的失效机制 力学模型系统 牙科陶瓷的实验室测试一直使用静态 单载荷试验方法。这些静态测试确定了 可以承受的最大应力，但不能有效预测 在临床条件下，假体通常会受到 在失效发生之前，进行多次亚临界载荷循环。牙科陶瓷和 玻璃在潮湿的环境下会发生化学静态疲劳， 环境温度，但以前曾假设这些 材料不经受机械疲劳。然而，白色（1993年）使用 断裂力学方法与尖锐压痕技术， 证明牙科陶瓷对机械的敏感性 疲劳，但无法使用尖锐的 压痕技术因此，牙齿的敏感性 陶瓷的机械疲劳，以及可能的相互作用 必须研究循环机械和静态化学疲劳， 确定导致临床失败的失效机制。 一个断裂力学方法使用一种新的压痕技术是合适的 脆性粗晶材料的疲劳特性，如 牙科瓷器材料缩进多次， 显微镜检查或进一步测试。实验将测试 假设：（1）牙科陶瓷易受机械 疲劳，（2）机械疲劳、化学疲劳及其交互作用 降低牙科陶瓷的强度，（3）所有的疲劳损伤， 累积，（4）裂纹可能由临界压力引发， 小于静态失效所需的压力，（5） 裂纹扩展随加载过程中的压力变化而变化， 卸载周期 结果将定义和量化故障机制。这些知识 失效机制的研究对于确定最佳材料至关重要， 加工和强化技术，是至关重要的 开发用于体内应用的新材料。百特陶瓷 材料将大大减少病人的痛苦和医疗保健 通过减少骨折假体的更换来降低成本， 全瓷修复体的更多应用。

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.