THE MECHANICAL SIGNIFICANCE OF THE OCCLUSAL GEOMETRY OF GREAT APE MOLARS IN FOOD BREAKDOWN

Analyses of dental function are an essential component of the study of human evolution. However, with few exceptions, they have utilized the traditional analogizing method of comparative anatomy, and have assum ed rather than demonstrated that proposed adaptive characters confer a performance benefit Since food reduction is a mechanical process, it is appropriate to measure performance using mechanical parameters, spe cifically the ability of a given morphology to induce failure in food particle by either of the two major regimes: crush and shear, correspo nding to simple stresses (tensile and compressive) and shear stress, r espectively. We apply finite elements stress analysis to model the rel ationship between the angulation of the intercuspal occlusal surfaces in a ''puncture crushing'' mode of mastication. On the basis of morpho logical data acquired from sectioned great ape molars, we have predict ed the nature, magnitude and distribution of stress in a standard food particle by models representing each morphotype. Results indicate tha t the blunt-cusped molars of Homo, the gradually-sloping supporting (b uccal) cusps but high-angled guiding (lingual) cusps of the lower mola rs of Pan, and the high angled occlusal surfaces of Gorilla are all mo re likely to fracture small food particles by shear, white the gradual ly sloping occlusal surfaces of Pongo molars are more likely to break them down by ''crush''. Mechanisms of food failure induced by molars o f Pan and Homo will vary according to the orientation of the tooth-foo d contacting surfaces, which in turn will vary according to the size o f the food particle. These genera may be able to break food down eithe r by shear or by ''crush''. (C) 1996 Academic Press Limited