Journal of Dental Research, Vol 80, 327-335, Copyright © 2001 by International & American Associations for Dental Research Online Journals
Mass properties of the pig mandible
F. Zhang, G. E. Langenbach, A. G. Hannam and S. W. Herring
Department of Oral Health Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, Canada.
Specification of mass properties is an essential step in the modeling of
jaw dynamics, but obtaining them can be difficult. Here, we used
three-dimensional computed tomography (CT) to estimate jaw mass, mean bone
density, anatomical 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 intervals 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 positive correlation between estimated mean bone
density and age. The mass center was consistently in the midline, near the
last molar. The mean distance between the mass center and geometric center
was small, especially when bone marrow was taken into account (0.58 +/-
0.21 mm), suggesting that mass distribution in the pig jaw is almost
symmetrical with respect to its geometric center. The largest moment of
inertia occurred around each mandible's supero-inferior axis, and the
smallest around its antero-posterior axis. Bone marrow contributed an extra
9% to the moments of inertia in all three axes. Linear relationships were
found between the actual mass and a mass descriptor (product of the
bounding volume and mean bone density), and between the moments of inertia
and moments of inertia descriptors (products of the mass descriptor and two
orthogonal dimensions forming the bounding box). The study suggests that
imaging modalities revealing three-dimensional jaw shape may be adequate
for estimating the bone mass properties in pigs.
