Remodeling simulation of human bone structures

骨骼具有适应机械环境的结构（沃尔夫定律）。然而，应用于骨的物理和生物条件的复杂性阻止了我们研究骨结构如何在多种载荷条件下提供足够的耐久性的机制。为了挑战这个问题，我们将人类下颌骨的内部结构与通过模拟骨重塑方法产生的那些结构进行了比较，我们在先前的研究中成功地使用了模拟骨重塑方法来再现人类股骨颈的二维结构（Tezuka，K等人，2005，J Bone Miner Metabol 23，1-7）。一个由大约150万个元素组成的三维下颌骨模型是从一个14岁女性骨囊肿的连续计算机断层扫描（CT）图像中构建的。从CT图像预测肌肉的位置和方向，以及它们的力。我们模拟了各种咬合条件，如门齿，左/右组（LG+RG），或左/右磨牙（LM+RM）咬，通过限制相应的牙齿在成角度的平面的运动。有限元法（FEM）分析和重塑模拟一个接一个地进行，并且重复直到获得适应于每个载荷条件的内部结构。结果，LM+RM咬合条件产生的结构显示出与真实的下颌骨最高程度的相似性。然而，其他条件下产生的结构也显示出与真实的下颌骨的结构的显著相似性，这表明下颌骨的结构已经形成以提供足够的耐久性以适应各种咬合条件。骨细胞如何结合联合收割机从各种条件下的输入，并产生一个单一的结构与耐久性变化的机械环境的精确机制仍然是未知的，然而，计算机辅助方法将是一个强大的工具，让我们进一步了解这样的复杂问题。

Bone has a structure adapted to the mechanical environment (Wolff's law). However, the complexity of both physical and biological conditions applied to bone have prevented us from investigating the mechanism as to how bone structure can provide enough durability to multiple loading conditions. To challenge this problem, we performed a comparison of the internal structure of human mandible with those structures generated by a simulated bone remodeling method that we used successfully in a previous study to reproduce the 2-dimensional structure of the human femoral neck (Tezuka, K et al., 2005, J Bone Miner Metabol 23, 1-7). A 3-dimensional mandible bone model consisting of approximately 1.5 million elements was constructed from sequential computer tomography (CT) images of a 14-year-old female with a bone cyst. The locations and directions of muscles, and their forces were predicted from the CT images. We emulated various biting conditions, such as incisor, left/right group (LG+RG), or left/right molar (LM+RM) biting, by restricting the movement of the corresponding teeth in angled planes. Finite element method (FEM) analysis and remodeling simulation were performed one after the other, and repeated until the internal structure adapted to each loading condition was obtained. As a result, the LM+RM biting condition generated structures showing the highest degree of similarity with the real mandible. However, structures generated by other conditions also showed significant similarity with that of real mandible, suggesting that the structure of mandible has been formed to provide enough durability to various biting conditions. The precise mechanism as to how the bone cells combine the input from various conditions and generate a single structure with durability to varying mechanical environment is still unknown, however, computer-aided methodology will be a powerful tool to give us further insight into such complex problems.