An Efficient Method for Predicting Fracture of Hard Food Source

In this paper we present a fast and reliable method for estimating the bite force required to fracture hard foods. The process involves complementary physical testing and finite element modeling. For physical testing, metal castings of upper or lower teeth are prepared. Metal tooth castings are mounted on a pivoting fixture interfaced to an Instron machine to simulate bite mechanics and thus to fracture hard food specimens. For the finite element model the tooth surfaces are modeled as rigid surface bodies in a nonlinear multi-load step contact analysis, while the food item is modeled as an elastic body. However, because only tooth surface information is needed in the model, we are able to automatically develop the geometry of the tooth surface using a tactile digitizing stylus with stereo lithographic surface profile information directly exported and subsequently imported into the FEA tool. We therefore avoid the need to laser scan tooth geometry which introduces significant “noise” into the surface model representation that must be painstakingly “cleaned” manually using software tools. The physical testing provides the force required to fracture the food item, while the finite element model provides the complete stress and strain state of the food item at the moment of fracture. Using this approach we have simulated the tooth biting mechanics of fossil primates to estimate biting force required to initiate a crack in a hard food source such as a macadamia nut. These analyses are designed to measure how occlusal morphology affects feeding performance, as the bite force needed to initiate a crack may vary according to tooth shape. The bite forces found using this approach will be used as an input for full-skull finite element models of early hominids (extinct fossil relatives of humans). The results of this work will be useful in testing the hypothesis that derived craniodental features in some of these hominids are adaptations for feeding on hard, brittle, seasonally available foods.