Aging and Fatigue Crack Growth in Dentin

描述（由申请人提供）：牙齿断裂导致的修复失败是终身口腔健康的主要障碍之一。本研究的总体假设是牙本质的疲劳裂纹生长阻力随着年龄的增长而降低，从而促进了修复牙的断裂。我们的初步研究表明，修复牙齿的牙本质经常存在疲劳裂纹，牙本质的疲劳特性是小管取向和患者年龄的函数。尽管牙本质的结构会随着年龄的增长而发生明显的变化，并且老年人更容易发生牙齿断裂，但衰老对牙本质疲劳特性的影响仍然未知。随着部分牙齿和全牙齿老年人的增加，衰老在修复牙齿失效中的作用变得越来越重要。我们建议将牙本质的疲劳裂纹扩展特性量化为患者年龄、性别和牙本质小管方向的函数，区分在什么年龄发生最有害的变化，并确定裂纹扩展阻力降低的基本机制。疲劳裂纹的萌生和扩展将在人类牙本质标本中进行评估，这些牙本质标本是由拔掉的初磨牙的冠状牙本质制备的。裂纹萌生和循环裂纹扩展的机制将使用数字图像相关的新应用进行表征，并根据患者的年龄和性别进行评估。牙本质的结构和化学变化也将使用分析显微技术进行评估。研究结果将提供对牙本质疲劳裂纹扩展特性的基本理解，使详细的结构-性能关系的发展成为可能。基于定量结果和对作用机制的理解，我们期望确定现有牙齿骨折修复治疗的关键方面以及治疗老年牙齿人口的新方法的潜在需求。该结果有望支持临床技术的发展，以阻止牙齿结构中的裂纹，包括机械和化学修复方法。希望我们的发现将有助于确定增强牙齿组织抗疲劳能力的方法，而不考虑年龄。这些成就将减少与牙齿断裂有关的修复失败的发生率，从而节省数十亿美元的医疗保健费用，并减少人类的痛苦。

DESCRIPTION (provided by applicant): Restoration failures resulting from tooth fracture are one of the primary obstacles to lifelong oral health. The overall hypothesis of our study is that the fracture of restored teeth is fostered by a reduction in the fatigue crack growth resistance of dentin with age. Our preliminary studies have shown that fatigue cracks are often present in the dentin of restored teeth and that the fatigue properties of dentin are a function of both the tubule orientation and patient age. Despite distinct changes in the structure of dentin with age, and identification that tooth fractures occur more frequently in seniors, the influence of aging on the fatigue properties of dentin has remained unknown. With the increase in partially and full dentate seniors, the role of aging on restored tooth failures has become increasingly important. We propose to quantify the fatigue crack growth properties of dentin as a function of patient age, gender and dentin tubule orientation, distinguish at what age the most detrimental changes take place, and identify, the fundamental mechanisms responsible for reduction in crack growth resistance. Fatigue crack initiation axnd growth will be evaluated in human dentin specimens prepared from the coronal dentin of extracted virgin molars. The mechanisms of crack initiation and cyclic crack extension will be characterized using a novel application of digital image correlation and evaluated in terms of the patient's age and gender. Changes in the structure and chemistry of dentin will also be evaluated using analytical microscopic techniques. Results of the investigation will provide a fundamental understanding of the fatigue crack growth properties of dentin that enable development of detailed structure-property relationships. Based on both quantitative results and an understanding of contributing mechanisms, we expect to identify the critical aspects of existing restorative treatments on tooth fracture and the potential need for new approaches in treatment of the aging dentate population. The results are expected to support development of clinical techniques for arresting cracks in tooth structure that involve both mechanical and chemical approaches to repair. Hopefully our findings will help identify approaches for strengthening the fatigue resistance of tooth tissues, regardless of age. These achievements should reduce the incidence of restorative failures associated with tooth fracture, resulting in billions of dollars in savings of health care costs, as well as a reduction in human suffering.