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

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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.