Dentin horn angle and enamel thickness interactively control tooth resilience and bite force.

UNLABELLED

Fossil teeth are a primary source for inferring species development via evolutionary adaptation due to their linkage to feeding ecology and well perseverance. The main working tools in such studies are bite force analysis derived from jaw musculature and lever arms and morphogenetic based on enamel thickness and occlusal surface area. Despite progress made, quantitative correlation between predictions and behavior is still lacking. We studied histological sections in varieties of extracted premolar and molar human teeth. Sections corresponding to planes intersecting tips of primary cusps as well as more random planes were considered. The results revealed a unique, conclusive link between cuspal enamel thickness d and dentin horn angle φ, a developmental parameter which contribution to tooth functioning has been overlooked. Naturally led by design principles of corbel arches, we examined the bending stress at the horn apex due to axial cuspal loading. The results show that this d vs. φ relationship produces a constant force causing cusp fracture P, making the latter a viable measure of tooth resilience. A preliminary study on published sections of extinct hominin teeth showed that their d vs. φ behavior is consistent with modern humans albeit with varying P. Scaling BF with P enables direct estimate of bite force from measures of d and φ in fossil teeth, achievable nondestructively from micro-computed tomography scans.

STATEMENT OF SIGNIFICANCE

The correspondence between cuspal enamel thickness and dentin horn angle in the postcanine row is a natural design here revealed for the first time. This correspondence yields constant force causing fracture at the horn apex, P, making the latter a viable measure of tooth resilience. Scaling bite force (BF) with P enables direct estimate of BF. The proposed mechanistic link between bite force and anatomical parameters d and φ, expressed in a simple analytic form, offers direct, development-based expectation for examining evolutionary processes in hominins.