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，应用于骨骼的物理和生物条件的复杂性使我们无法研究骨骼结构如何在多种载荷条件下提供足够的耐久性的机制。为了挑战这一问题，我们将人类下颌骨的内部结构与我们在之前的研究中成功复制人类股骨颈二维结构的模拟骨重塑方法产生的结构进行了比较（Tezuka, K et al., 2005, J bone Miner metabolism 23,1 -7）。通过对一名14岁女性骨囊肿患者的连续计算机断层扫描（CT）图像，建立了一个由大约150万个元素组成的三维下颌骨模型。根据CT图像预测肌肉的位置和方向，以及它们的力量。我们通过限制相应牙齿在角度平面上的运动来模拟各种咬合条件，如门牙、左/右组（LG+RG）或左/右磨牙（LM+RM）的咬合。依次进行有限元分析和重塑模拟，反复进行，直到得到适应每种加载条件的内部结构。因此，LM+RM咬合条件生成的结构与真实下颌骨的相似度最高。但在其他条件下生成的结构也与真实下颌骨具有显著的相似性，说明下颌骨的结构已经形成，能够在各种咬合条件下提供足够的耐久性。骨细胞如何结合各种条件的输入并产生具有不同机械环境耐久性的单一结构的确切机制仍然未知，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些复杂的问题。

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.