The effects of relative food item size on optimal tooth cusp sharpness during brittle food item processing

Abstract

Teeth are often assumed to be optimal for their function, which allows researchers to derive dietary signatures from tooth shape. Most tooth shape analyses normalize for tooth size, potentially masking the relationship between relative food item size and tooth shape. Here, we model how relative food item size may affect optimal tooth cusp radius of curvature (RoC) during the fracture of brittle food items using a parametric finite-element (FE) model of a four-cusped molar. Morphospaces were created for four different food item sizes by altering cusp RoCs to determine whether optimal tooth shape changed as food item size changed. The morphospaces were also used to investigate whether variation in efficiency metrics (i.e. stresses, energy and optimality) changed as food item size changed. We found that optimal tooth shape changed as food item size changed, but that all optimal morphologies were similar, with one dull cusp that promoted high stresses in the food item and three cusps that acted to stabilize the food item. There were also positive relationships between food item size and the coefficients of variation for stresses in food item and optimality, and negative relationships between food item size and the coefficients of variation for stresses in the enamel and strain energy absorbed by the food item. These results suggest that relative food item size may play a role in selecting for optimal tooth shape, and the magnitude of these selective forces may change depending on food item size and which efficiency metric is being selected.

Finite element modeling of occlusal variation in durophagous tooth systems

“…Compared with larger prey items, smaller prey generate loads that show a more pronounced change in both maximum strain energy and first principal strain as tooth models go from concave to flat. FE models of 4-cusped bunodont teeth loaded by brittle spheres of varying sizes showed a similar pattern of size-mediated variation in strain (Berthaume et al, 2014). Similarly, hemispherical tooth models worn flat were able to achieve a higher load to critical failure when loaded by flat surfaces than by rounded surfaces (Keown et al, 2012).…”

“…In addition to resisting tooth failure, hominid tooth morphology was also influenced by the ability to break food items (Berthaume et al, 2011). A mix of different cusp morphologies on the same tooth, as opposed to all sharp or all blunt for instance, takes these opposing evolutionary pressures into account to optimize bunodont tooth function: creating high stress in prey objects while minimizing stresses in the tooth enamel (Berthaume et al, 2013(Berthaume et al, , 2014.…”

Food mechanical properties and dietary ecology

“…To process these foods, force, energy and/or stress needs to be spread over a larger portion of the food item, creating an isostress condition, as this allows more cells to burst open per chew than if the force, energy, or stress was concentrated. This isostress condition is most efficiently accomplished through blunter/duller teeth (Evans and Sanson, ; Freeman and Lemen, ; Berthaume et al, ; Berthaume, ).…”

“…Once we gain a better understanding of how food items both interact with teeth and breakdown during mastication, which can be done in an experimental or theoretical approach [e.g., (Brainerd et al, ; Berthaume et al, ; Müller et al, )], we can better conclude what mechanical property data should be gathered in the first place. Building on these empirical findings, we can make better links between diet and both craniomandibular and dental morphology.…”

“…There are size dependent, and therefore non‐mechanical, properties of diet, that are important in feeding biomechanics. For example, the force needed to access a food item has been hypothesized to be linked to bite force, enamel thickness, and stresses and strain experienced by the craniofacial complex during mastication, and relative food item size has been related to gape angle, food item placement, stretch of the masticatory muscles, and possibly tooth morphology (Dumont and Herrel, ; Martin, ; Herrel et al, ; Taylor and Vinyard, ; Dumont et al, ; Eng et al, ; Lawn et al, ; Santana et al, ; Daegling et al, ; Strait et al, ; Berthaume et al, ; Smith et al, ). But as non‐mechanical properties are system dependent [e.g., puncture resistance (Norconk and Conklin‐Brittain, )], how should they be measured?…”