Mass properties of the pig mandible

Specification of mass properties is an essential step in the modeling of ja w dynamics, but obtaining them can be difficult. Here, we used three-dimens ional computed tomography (CT) to estimate jaw mass, mean bone density, ana tomical locations of the mass and geometric centers, and moments of inertia in the pig jaw. High-resolution CT scans were performed at one-mm slice in tervals on specimens submerged in water. The mean estimated jaw mass was 12 % greater than the mean wet weight, and 33% more than the mean dry weight. Putative bone marrow accounted for an extra 13% of mass. There was a positi ve correlation between estimated mean bone density and age. The mass center was consistently in the midline, near the last. molar. The mean distance b etween the mass center and geometric center was small, especially when bone marrow was taken into account (0.58 +/- 0.21 mm), suggesting that mass dis tribution in the pig jaw is almost symmetrical with respect to its geometri c center. The largest moment of inertia occurred around each mandible's sup eroinferior axis, and the smallest around its anteroposterior axis. Bone ma rrow contributed an extra 9% to the moments of inertia in all three axes. L inear relationships were found between the actual mass and a mass descripto r (product of the bounding volume and mean bone density), and between the m oments of inertia and moments of inertia descriptors (products of the mass descriptor and two orthogonal dimensions forming the bounding box). The stu dy suggests that imaging modalities revealing three-dimensional jaw shape m ay be adequate for estimating the bone mass properties in pigs.