Study on biomechanics of bone remodeling at microscopic level during orthodontic treatment

本研究旨在阐明正畸治疗过程中机械应力与牙槽骨改建之间的因果关系。牙周膜的材料常数是牙齿及其周围组织应力分析中不可缺少的参数。然而，很少有实验确定的值被报道。在这项研究中，我们开发了一台小型压缩和拉伸试验机，以确定PDL的材料常数。在拉伸试验中，应力-应变曲线不显著地依赖于应变率。相反，压缩试验显示曲线对应变率有很大的依赖性。PDL的拉伸和压缩切线模数分别为0.37和0.SY。-.[)0.11和0.079(]sy.-.在准静态条件下，分别为0.017兆帕。压缩试件的泊松比显著低于拉伸试件的泊松比。根据这些材料常数，我们利用从实验正畸治疗的猫科动物的组织切片的形态结构建立的标本特有的二维有限元模型进行了应力分析。结果表明，破骨细胞的出现与PDL内的主应力分布密切相关。大多数破骨细胞出现在压缩应力约为4kpa的特定部位。

The purpose of this study is to clarify the causal relationship between mechanical stress and alveolar bone remodeling during orthodontic treatment. Material constants of the periodontal ligament (PDL) are indispensable parameters for stress analysis of a tooth and the surrounding tissues. However, few experimentally determined values have been reported. In this study, we developed a small compressive and tensile test machine in order to determine the material constants of the PDL.In tension tests, stress-strain curves did not significantly depend on strain rates. In contrast, compressive tests showed great dependence of the curves on strain rates. Tensile and compressive tangent moduli of the PDL were 0.37(]SY.+-。[)0.11 and 0.079(]SY.+-。[)0.017 MPa, respectively, under quasi-static conditions. Poisson's ratio of a compressed PDL specimen was significantly lower than that of a tensile specimen. Based on these material constants, we couducted stress analyzes using specimen-specific 2-D finite-element models which were constructed from morphological structure of tissue sections taken from a cat canine subjected to experimental orthodontic treatment The results clearly demonstrated that there is a close correlation between the appearance of osteoclasts and the principal stress distribution in the PDL.Most osteoclasts appeared at the specific sites where the compressive stress was about 4 kPa.