[Tensile mechanics of mandibular condylar cartilage]

To study the biomechanical properties of the mandibular condyle cartilage and determine its functional importance.

Eight condyle specimens of the four pig temporomandibular joints were obtained by autopsy and stored in sealed plastic bags at -20 degrees C. These pigs were healthy, aged 1 year +/- 2 months. In the coronal direction, 300 microns wide, rectangular cartilage-bone specimens were prepared on the right condyles using specified knife. In the sagittal direction, rectangular cartilage-bone specimens with the same width were obtained on the left condyles. Standard rectangular testing specimens were prepared from cartilage-bone specimens in a microtome kept at -20 degrees C (300 microns wide and 250 microns thick). The specimens were inserted in a soft-tissue uniaxial tensile test machine and immersed in a bath of Ringer's solution at room temperature. Preconditioning of the specimens was carried out prior to the uniaxial tensile experiment and the specimens were elongated to failure with the constant strain rate (0.05 mm/s). The resulting mean values were curved fitted with Fung's two-parameter (A, B) exponential stress strain equation using a nonlinear regression program.

The data obtained showed that a typical nonlinear biomechanical behavior of the condyle cartilage. Toe-region and quasi-linear zone were obvious on the experimental stress strain relation curve. Theoretically fitted parameter A and B were 0.47 and 4.13 (coronally) and 0.60 and 4.70 (sagittally). The sagittal specimens showed greater tensile stress (2.92 MPa), tensile stiffness (9.04 MPa), energy absorption (6.02 N.mm) but less tensile strain (37.34%) than that of the coronal specimens (2.15 MPa, 6.55 MPa, 4.91 N.mm, and 41.12%). The differences were statistically significant (P < 0.05).

The mandibular condyle cartilage is a kind of biophasic material which shows nonlinear viscoelastic behavior, anistrophic characteristics in biomechanical function and high ability to resist tensile stress in the longitudinal direction.