Meeting Abstract
Substantial variation in the structural relationships within the masticatory system (i.e., among teeth, joints, and muscles) through the evolutionary history of mammals has greatly influenced the mechanical performance of the system. These changes are typically viewed as evolutionary responses associated to specific pressures; such as the need to generate occlusal force, to resist masticatory stresses, or for delicate motor control. Thus, variation in the musculo-skeletal configuration are expected to reflect adaptations to these competing and varying demands. To evaluate the relative importance of these elements in shaping the evolution of the masticatory system necessitates adequate understanding of how variation in each factor affects the mechanical performance of the system as a whole. Using 3D models of the cranium and mandibles from 69 species of primates, we evaluated how variation in jaw muscles size and position affect bite performance within an ecological and phylogenetic framework. In addition, we modelled the effect of gape angle and condylar translation on muscle strain and muscle moment arms, as well as the effect of the elevation of the jaw joint with respect to the occlusal plane. Our data shows that relative importance of the temporalis and medial pterygoid muscles to produce bite force is affected by phylogeny but the masseter is not. Dietary differences affect the relative importance of the medial pterygoid muscle, suggesting that maybe this muscle is important for motor control to process foods of different mechanical properties. The effect of gape angle on muscle mechanics is complex, depending on the portion of the masticatory muscle (e.g., anterior vs posterior fibers).
