The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

How does food item size affect optimal tooth sharpness?


1Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, 2Department of Anthropology, University of Massachusetts, Amherst, 3Department of Biology, University of Massachusetts, Amherst

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Models of the masticatory process suggest that tooth shape is correlated with the internal material properties of the foods that animals eat, while the size of food items is correlated with tooth size. Here, we investigate the idea that during fracture of a brittle hemisphere with constant material properties, optimal tooth sharpness is constant regardless of food item size.

We utilized finite element analysis (FEA) and a parametric model of a bunodont maxillary molar to test this hypothesis. Tooth sharpness was varied in the buccolingual and mesiodistal directions while all other parameters were held constant. We tested four isometrically-scaled hemispherical food items, in which the radii of the hemispheres were equal to 1/3, 2/3, 3/3 and 4/3 the distance between the cusps. Optimal tooth shape was defined by maximizing the optimality function (tensile stresses in the food item)/ (tensile stresses in the enamel). We developed a morphospace for each hemisphere size using the Taguchi method to randomize tooth sharpness values, and compared the optimal morphologies from each morphospace.

As the size of the hemispheres increased, the hemisphere went from interacting primarily with the valleys between the cusps to interacting with the cusps themselves, fundamentally changing the contact mechanics between the food item and the tooth. This altered the stress distributions in both the hemisphere and the tooth. The results caused us to reject our null hypothesis. It appears instead that optimal tooth sharpness changes as food item size changes, even when food item material properties and shape are held constant.

This work is supported by the National Science Foundation Physical Anthropology HOMINID program (BCS 0725126, 0725147, BCS 0725078, 0725183, and 0725141) and the National Science Foundation Biomesh Grant (DBI 0743460). NSF was not involved in this research.

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