Meeting Abstract

P3-38   -   On the implications of an unfused mandibular symphysis for the biomechanics of chewing in rats McParland, ED*; Mitchell, JK; Laurence-Chasen, JD; Afolabi, O; Aspinwall, LC; Takahashi, K; Ross, CF; Gidmark, NJ; Knox College, Galesburg, IL; Knox College, Galesburg, IL; University of Chicago, Chicago, IL; Knox College, Galesburg, IL; Knox College, Galesburg, IL; University of Chicago, Chicago, IL; University of Chicago, Chicago, IL; Knox College, Galesburg, IL edmcparland@knox.edu

Chewing involves complex, 6-degree-of-freedom motions in mammals to break down food. Most mammals studied to date chew on one side (termed the “working side”) of the mouth at a time, though muscles are still active on the opposite (“balancing”) side. These species (e.g., pigs and monkeys) have a single lower jaw bone, where the mandibular symphysis fuses the left and right sides. Rats have an unfused mandibular symphysis which could impact the kinematics and biomechanics of chewing, since the left and right hemimandibles can move at least partially independently. We used XROMM to reconstruct 3D motions of both hemimandibles and the skull in rats. Preliminary analysis of 355 chews from 3 individuals shows some similarities to mammals with a fused symphysis. Consistent with other mammals, the mandibular condyle translates anteriorly (4 mm) as the mouth opens (15 degrees). Contrary to motions in pigs and monkeys, we observed small and unpredictable yaw of the condyles. We observed 3-5 degrees of yaw between hemimandibles at the mandibular symphysis, which is not possible in taxa with a fused symphysis. Whereas pigs and monkeys employ a lateral translation of the tooth for the power stroke during occlusion, anterior translation of the lower molar is larger and more patterned than mediolateral tooth translation in our rats. We also observed mirrored translations along the mediolateral axis: left and right molars translate medially in synchrony, and then translate laterally in synchrony. These results suggest that in rats, the power stroke consists of mostly anterior/posterior grinding that may not employ a working/balancing side chewing pattern.