ANATOMIC AND DIRECTIONAL VARIATION IN THE MECHANICAL-PROPERTIES OF THE MANDIBULAR CONDYLE IN PIGS

Stereologic studies of trabecular architecture suggest that the pig ma ndibular 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 mecha nical properties of 22 pig mandibular condyles in three loading direct ions at a mean strain rate of 0.14 (+/- 0.12)% s(-1). A total of 91 re ctangular beam specimens (averaging 9.0 mm x 6.0 mm x 5.0 mm) was test ed. For each specimen, 5 or 6 non-destructive tests were performed bef ore compressive failure. Strain in both longitudinal and transverse di rections 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), specim en length of 9 mm, and cross-sectional area of 30.25 mm(2). Generally, modulus of elasticity (E) and ultimate stress (sigma(u)) in the anter ior 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 (0.8 1 g/cm(3)) were seen in the anterior inferior/middle region under supe ro-inferior loading. The lowest values (0.94 GPa for E, 2.38 MPa for s igma(u), and 0.52 g/cm(3) for rho) were found in the inferior/posterio r 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 pa rticularly strong and stiff.