The fracture behaviour of human and pig molar cusps.

Masticatory efficiency depends upon the ability of the molar cusps to apply concentrated bite forces to food particles and simultaneously to withstand the dental stresses that may cause enamel fracture. This study investigated how low-crowned molar cusps in omnivorous mammals, specifically humans, Homo sapiens, and pigs, Sus scrofa, resist fracture under compressive load. A uniaxial compressive load was applied to individual molar cusps with a materials testing machine. The progressive loading and deformation of the cusps were recorded for interrupted and continuous tests. In interrupted tests, the appearance of progressive cusp fracture was recorded. Stiffness and fracture stresses were calculated from continuous test results. Pig cusps responded to both interrupted and continuous loads with greater deformation; progressive crumbling of the cusp tip resulted in new occlusal contacts on enamel lophs. Conversely, human cusps showed minimal breakage before failure. Continuous compressive tests demonstrated the greater stiffness of human cusps, as well as the capacity to sustain higher cusp tip stresses. The greater stiffness and high fracture resistance of human cusps may be attributed to the thickness of enamel. Test results reflected fundamentally different means of crown stress management that correspond with phylogenetic differences in masticatory function.