Meeting Abstract
Domestic pigs and their wild relatives are true omnivores, and are convergent in their craniodental morphology with other omnivores such as hominin primates. Prior attempts to characterize food-tooth interactions and jaw movements associated with mastication have been limited to those aspects of the oral apparatus that are externally visible (with videography) and/or to 2D movements of oral structures (with monoplanar videofluoroscopy). Here, we used XROMM, a 3D technique that combines CT-based morphology with biplanar videofluoroscopy, to measure tooth displacements during mastication and to examine the relative movement of opposing teeth during occlusion. We found that relative motions of the premolars contained a distinct, and somewhat unexpected, anteroposterior component within the transverse trajectory of the power stroke. Furthermore, the occlusal movements responsible for food reduction occur in the larger context of jaw movements at the posterior temporomandibular joints (TMJ). Despite a relatively mobile omnivore-type TMJ, we observed that the pig TMJ moved detectably in only 3 of 6 possible degrees of freedom during mastication: 2 rotations, pitch and yaw, and 1 translation, protraction-retraction. Jaw depression (pitch) was coupled to jaw protraction, and asymmetrical yaw produced the observed alternating left-right chewing cycles. The integration of tooth, joint, and rigid body jaw movements elucidated the kinematic underpinnings of the occlusal power stroke, a key aspect of mammalian mastication. XROMM also allowed us to determine how hypothetical kinematics inferred from tooth and TMJ structure compare with actual kinematics in the context of naturalistic feeding behaviors.
