Anatomic and directional variation in the mechanical properties of the mandibular condyle in pigs.

Stereologic studies of trabecular architecture suggest that the pig mandibular condyle is strongest when loaded supero-inferiorly, and that stress is concentrated in the antero-inferior region (Teng and Herring, 1995). To test these hypotheses, we investigated the uni-axial mechanical properties of 22 pig mandibular condyles in three loading directions at a mean strain rate of 0.14 (+/- 0.12)% s-1. A total of 91 rectangular beam specimens (averaging 9.0 mm x 6.0 mm x 5.0 mm) was tested. For each specimen, 5 or 6 non-destructive tests were performed before compressive failure. Strain in both longitudinal and transverse directions was measured by foil strain gauges on the central part of the specimen. Data were normalized at a strain rate of 0.1% s-1, specimen length of 9 mm, and cross-sectional area of 30.25 mm2. Generally, modulus of elasticity (E) and ultimate stress (sigma u) in the anterior regions of the condyle were greater than those in the posterior. E, sigma u, and Poisson's ratio (upsilon) were significantly different among the test directions, but ultimate strain (epsilon u) was not. The highest values of E (4.04 GPa), sigma u (14.97 MPa), and rho (0.81 g/cm3) were seen in the anterior inferior/middle region under supero-inferior loading. The lowest values (0.94 GPa for E, 2.38 MPa for sigma u, and 0.52 g/cm3 for rho) were found in the inferior/posterior region in medio-lateral loading. Although the mechanical properties of the condyle vary depending upon location, these results verify that the condyle is strongest and stiffest under compressive loads in the supero-inferior direction, and that the anterior-inferior region is particularly strong and stiff.