Correlating the Performance of Primate Enamel to Variations in its Chemistry, Structure and Properties

牙齿是人类化石记录中最常见的元素，很大程度上是因为它们是人体中最具弹性的结构。灵长类动物牙齿的主要成分之一是牙釉质，这是一种由羟基磷灰石晶体以一种复杂的方式旋转在一起形成所谓的棱镜的复合材料。牙釉质发育和形态的复杂细节提供了丰富的见解，从发育历史的永久标记到功能意义的结构各向异性的记录。然而，我们对牙釉质结构的了解也掩盖了对其物理性质知之甚少的事实。事实上，大多数人认为牙釉质是一种均匀的物质，就像钢或水一样，具有均匀的特性。然而，化学、棱柱附着力和微观孔隙率的变化会导致牙釉质的硬度和刚度发生显著变化，从而影响其在咀嚼过程中的行为。本项目的目的是利用纳米压痕技术记录牙釉质力学性能（硬度和刚度）的变化。这些特性将与人类和其他灵长类动物牙釉质的化学和微观结构的变化相关联。研究将仅限于提取和博物馆臼齿（上颌M1）的两个物种：现代人类和Macaca fascicularis。反过来，这将使我们能够进行各种比较，除了对两个物种的拔牙和博物馆牙齿的上颌M1牙釉质特性进行基本比较之外。本研究项目将重点对新鲜提取的牙齿和博物馆的牙齿进行比较，以验证博物馆样本的机械完整性。该项目还将研究具有生物力学意义的问题，例如，牙釉质在所谓的功能尖和支撑尖上是否不同，老年人的牙齿是否比年轻人的牙齿更坚硬。更好地了解牙釉质的力学特性将为牙齿功能、牙科临床反应、古生物学和进化理论提供丰富的见解。

Correlating the Performance of Primate Enamel to Variations in Its Chemistry, Structure and Properties NSF #0749981 T.P. Weihs and M.F. Teaford Johns Hopkins University Teeth are the most common elements in the human fossil record largely because they are the most resilient structures in the body. One of the major components of primate teeth is enamel, a composite made of hydroxyapatite crystals spun together in a complicated fashion forming what are known as prisms. The intricate details of enamel's development and morphology have provided a wealth of insights, ranging from permanent markers of developmental history to documentation of structural anisotropy of functional significance. However, what we know about enamel's structure also masks an incredible lack of knowledge about its physical properties. In fact, most people think of enamel as a homogeneous substance, like steel or water, with uniform properties. Yet, variations in chemistry, prism adhesion and microscopic porosities can lead to significant variations in the hardness and stiffness of enamel and hence its behavior during mastication. The purpose of this project is to document variations in the mechanical properties (hardness and stiffness) of enamel using nanoindentation techniques. These properties will then be correlated with changes in the chemistry and the microstructure of enamel in humans and other primates. Studies will be limited to extracted and museum molars (maxillary M1) for two species: modern humans and Macaca fascicularis. This will, in turn, allow us to perform a variety of comparisons, in addition to the basic comparisons of the enamel properties of maxillary M1 for extracted and museum teeth of both species. This research project will focus on comparisons of freshly-extracted teeth and museum teeth to verify the mechanical integrity of museum samples. This project will also examine questions of biomechanical significance e.g., do enamel properties differ on so-called functional and support cusps Are the teeth of older individuals stiffer than those of younger individuals A better understanding of the mechanical properties of enamel will yield a wealth of insights into dental function, dental clinical responses, paleobiology, and evolutionary theory.