Research Project Highlight

Molar Enamel in Howler Monkeys

In the field of anthropology, teeth have provided insights into many topics including primate diet, paleobiology, and evolution, due to the fact that they are largely composed of inorganic materials and may remain intact long after an animal is deceased. Previous studies in the Weihs Group have reported that the mechanical properties, chemistry, and microstructure of enamel vary with location within human molars.

This study, which appeared in the January 2010 issue of the American Journal of Physical Anthropology, uses nanoindentation to map the mechanical properties of Alouatta palliata (howler monkey) molar enamel on an axial cross-section of three different molar samples. Variations in mechanical properties were then correlated with changes in microstructure and chemistry using scanning electron microscopy and electron microprobe techniques. Quite surprisingly, the howler monkey enamel showed microstructures, chemical constituents, and magnitudes of mechanical properties that are very similar to those found in humans. However, the howler monkey enamel showed less variation in hardness and Young’s modulus throughout its thickness compared to humans, despite the very different diet of this species. Data such as these are being used to better understand how animals adapt to variations in their diet and hence the loadings on their during mastication.


We have used nanoindentation techniques to characterize the hardness and stiffness of enamel as a function of position on cross-sections of human teeth.

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