Thursday 9:30-9:45, Broadway III/IV
Teeth need to grip, fracture and fragment food particles without being damaged by wear. Though wear features are well-documented microscopically, many basic issues need to be resolved. These include why most wear features are so small and why scratches tend to outnumber pits. Our approach to this is two-fold. The first is based on the material properties of the interacting particles. We produced wear features on highly-polished surfaces of primate molars using particles mounted on a custom nanoindenter tip. We employed both static (‘pit’) and dynamic (‘scratch’) indentation modes, imaging them by AFM. Forces producing microscopic features were low milliNewton in range, agreeing with predictive equations. These forces are tiny compared to masticatory loads, so why are larger features so rarely seen? One reason is the governing brittle-ductile transition (Lucas et al., 2008), but others specific to scratching include contact roughness and its effect on the frictional coefficient. The higher the coefficient, the lower the force to scratch, thus making scratches more likely features than pits. Physiological issues revolve around the need for lateral excursions in chewing, clearly implicated in the literature in scratch production. Reasons for this include the need to increase the probability of fracture of isodiametric food particles and the control of deformation in membrane-like foods.