Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA; Materials Science and Engineering Department, Idaho National Laboratory, Idaho Falls, ID, USA.
Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA; Physical and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA, USA.
Acta Biomater. 2024 Apr 1;178:208-220. doi: 10.1016/j.actbio.2024.02.038. Epub 2024 Feb 28.
The enamel of mammalian teeth is a highly mineralized tissue that must endure a lifetime of cyclic contact and is inspiring the development of next-generation engineering materials. Attempts to implement enamel-inspired structures in synthetic materials have had limited success, largely due to the absence of a detailed understanding of its microstructure. The present work used synchrotron phase-contrast microCT imaging to evaluate the three-dimensional microstructure of enamel from four mammals including Lion, Gray Wolf, Snow Leopard, and Black Bear. Quantitative results of image analysis revealed that the decussation pattern of enamel consists of discrete diazone (D) and parazone (P) bands of rods organized with stacking arrangement of D+/P/D-/P in all mammals evaluated; the D+ and D- refer to distinct diazone bands with juxtaposed rod orientations from the reference plane. Furthermore, the rod orientations in the bands can be described in terms of two principal angles, defined here as the pitch and yaw. While the pitch angle increases from the outer enamel to a maximum (up to ≈ 40°) near the dentin enamel junction, minimal spatial variations are observed in yaw across the enamel thickness. There are clear differences in the decussation parameters of enamel across species that are interpreted here with respect to the structural demands placed on their teeth. The rod pitch and band width of enamel are identified as important design parameters and appear to be correlated with the bite force quotient of the four mammals evaluated. STATEMENT OF SIGNIFICANCE: The multi-functionality of tooth enamel requires both hardness and resistance to fracture, properties that are generally mutually exclusive. Ubiquitous to all mammalian teeth, the enamel is expected to have undergone adaptations in microstructure to accommodate the differences in diet, body size and bite force across animals. For the first time, we compare the complex three-dimensional microstructure of enamel from teeth of multiple mammalian species using synchrotron micro-computed tomography. The findings provide new understanding of the "design" of mammalian enamel microstructures, as well as how specific parameters associated with the decussation of rods appear to be engineered to modulate its fracture resistance.
哺乳动物牙齿的釉质是一种高度矿化的组织，必须承受一生的周期性接触，这激发了下一代工程材料的发展。在合成材料中尝试实施受釉质启发的结构的尝试取得了有限的成功，这主要是由于缺乏对其微观结构的详细了解。本工作使用同步辐射相衬 microCT 成像来评估包括狮子、灰狼、雪豹和黑熊在内的四种哺乳动物的釉质的三维微观结构。图像分析的定量结果表明，釉质的交错模式由离散的牙本质带（D）和副牙本质带（P）组成，这些带中的棒以 D+/P/D-/P 的堆叠方式排列；D+和 D-是指从参考平面看具有相邻棒取向的不同牙本质带。此外，带中的棒取向可以用两个主角度来描述，这里定义为节距和偏航角。虽然节距角从外釉质增加到最大值（在靠近牙本质釉质交界处可达约 40°），但在釉质厚度内观察到偏航角的空间变化很小。不同物种的釉质交错参数有明显差异，这些差异被解释为对其牙齿结构要求的差异。釉质的棒节距和带宽被确定为重要的设计参数，并且似乎与评估的四种哺乳动物的咬合力商相关。
牙齿釉质的多功能性需要硬度和抗断裂性，这两种性质通常是相互排斥的。所有哺乳动物牙齿中都普遍存在的釉质，预计其微观结构已经适应了不同动物的饮食、体型和咬合力的差异。我们首次使用同步加速器微计算机断层扫描比较了来自多种哺乳动物牙齿的复杂三维釉质微观结构。这些发现提供了对哺乳动物釉质微观结构“设计”的新理解，以及与棒的交错相关的特定参数如何被设计来调节其抗断裂性。
