Department of Dental Materials Science, Tokyo Dental College, Tokyo, Japan.
Oral Health Science Center, Tokyo Dental College, Tokyo, Japan.
J Biomed Mater Res B Appl Biomater. 2020 Oct;108(7):2799-2806. doi: 10.1002/jbm.b.34609. Epub 2020 Mar 19.
The coronoid process provides attachment to temporalis and masseter muscles, and thus plays an important role in mastication. Tendons connect muscles and bones, mediating the transmission of functional loads to bones. Thus, tendon-bone entheses govern mechanical stress in bones. The preferential orientation of biological apatite (BAp) crystallites, the main mineral component in bones, is an important index for bone quality and function, and is largely influenced by locally applied stress. In this study, we analyzed BAp orientation, Young's modulus, and bone mineral density (BMD) at different sites in the human coronoid process. No differences in BMD were found among the analyzed sites, but BAp crystal orientation was observed to differ. BAp crystallites showed a uni-directional orientation in the mesiodistal direction at the coronoid process apex, but were oriented in the direction vertical to the occlusal plane at other sites. Young's modulus tended to vary according to the BAp orientation. At the apex, a tendon form with characteristics different from those at other sites, including the presence of a fibrocartilaginous layer that may act as a stretching brake to control stress concentration, was observed. These findings suggest that the functional pressure of the temporalis muscle affects bone quality and strength.
冠状突为颞肌和咬肌提供附着点，在咀嚼中起重要作用。肌腱连接肌肉和骨骼，介导功能负荷传递至骨骼。因此，肌腱-骨附着点控制骨骼的机械应力。生物磷灰石（BAp）晶体的优先取向是骨骼质量和功能的重要指标，主要受局部施加的应力影响。在这项研究中，我们分析了人冠状突不同部位的 BAp 取向、杨氏模量和骨密度（BMD）。分析部位的 BMD 无差异，但观察到 BAp 晶体取向不同。BAp 晶体在冠状突顶点呈沿近远中方向的单方向取向，但在其他部位则沿垂直于咬合面的方向取向。杨氏模量似乎随 BAp 取向而变化。在顶点处，观察到一种与其他部位不同的肌腱形态，包括存在纤维软骨层，可能起到拉伸制动器的作用，以控制应力集中。这些发现表明颞肌的功能压力影响骨骼的质量和强度。
