Root deformation and root resorption

描述：正畸牙根吸收是一个主要的临床和法医学问题。大约一半的美国人口接受正畸治疗，根据一些估计，90%的患者经历了可检测到的牙根缺失。5%到58%的人经历了严重的(5毫米)损失。机制尚不清楚，但据信破骨细胞是这种遗传学调节的丢失的原因。归根结底，吸收是对牙冠负荷的一种反应。当正畸力叠加在改变的咬合上时，“自然”的牙根变形在幅度、方向、持续时间和频率上都会发生变化。有人提出，这些变形通过两种方式造成根部破坏。首先，当根部弯曲时，凸弯的一侧被拉伸，而另一(凹)侧被压缩。这种拉伸/压缩会损害牙骨质和/或牙本质。第二，牙根弯曲还会在牙骨质-牙本质界面产生剪应力，导致可能的分层。进一步的假设是，正常的生理吸收部位作为应力集中器，加剧了局部的根损伤。反过来，受损的根更容易被吸收。这些现象将通过机械测试、组织学、显微CT的新应用和有限元(FE)计算机模型来检验。 本研究的具体目的是(1)量化牙根疲劳损伤，(2)开发/验证MicroCT损伤评估，(3)将应力梯度与损伤相关联，(4)将牙根形状与应力相关联，以及(5)评估邻近对侧牙根的损伤以确定其是否适合用作对照。 将循环载荷应用于新鲜身体犬(犬)下颌中切牙的冠部。带有牙齿及其周围牙槽骨的块将进行显微CT成像，然后使用传统的基本品红组织学方法检查其损伤情况。将对两种损伤评估进行比较，并将损伤位置与有限元计算的应力梯度结果相关联。这个多学科项目将在两个不同的领域做出贡献--了解正畸相关的牙根吸收的机制，并展示3D MicroCT成像成为钙化组织损伤评估的新“黄金标准”的潜力。

DESCRIPTION: Orthodontic root resorption is a major clinical and medico-legal concern. Approximately half the US population is treated orthodontically, and according to some estimates, 90 percent of patients experience detectable root-loss. Five to 58 percent experience severe (>5mm) loss. The mechanisms remain obscure, but it is believed that osteoclasts are responsible for this genetics-modulated loss. Ultimately, resorption is a response to loads on the crowns of teeth. When orthodontic forces are superimposed on altered occlusion, the "natural" root deformations are changed in magnitude, direction, duration, and frequency. It is proposed that these deformations cause root damage in two ways. First, as the root flexes, the convex bending side is stretched, while the other (concave) side is compressed. This tension- /compression can damage the cementum and/or dentin. Second, root bending also produces shear stresses within the cementum-dentin interface, leading to possible delamination. It is further hypothesized that normal physiological resorption sites act as stress concentrators that intensify local root damage. In turn, the damaged root is more vulnerable to resorption. These phenomena will be examined using mechanical testing, histology, a novel application of microCT, and finite element (FE) computer models. The Specific Aims of this study are to (1) quantify root fatigue damage, (2) develop/validate microCT damage assessment, (3) correlate stress gradients with damage, (4) relate root-shape to stresses, and (5) assess damage in the adjacent contralateral root to determine its suitability for use as control. Cyclic loading will be applied to the crowns of fresh cadaveric canine (dog) mandibular central incisors. Blocks with a tooth and its surrounding alveolar bone will be microCT imaged and then examined for damage using the traditional basic fuchsin histological method. The two damage assessments will be compared and the locations of damage will be correlated with the results of FE calculated stress gradients. This multidisciplinary project will contribute in two disparate areas - understanding the mechanism of orthodontics-associated root resorption, and demonstrating the potential of 3D microCT imaging to become the new "gold standard" of calcified tissue damage assessment.