Properties of the Temporomandibular Joint in Growing Pigs

A subset of temporomandibular joint (TMJ) disorders is attributed to joint degeneration. The pig has been considered the preferred in vivo model for the evaluation of potential therapies for TMJ disorders, and practical considerations such as cost and husbandry issues have favored the use of young, skeletally immature animals. However, the effect of growth on the biochemical and biomechanical properties of the TMJ disk and articulating cartilage has not been examined. The present study investigates the effect of age on the biochemical and biomechanical properties of healthy porcine TMJs at 3, 6, and 9 months of age. DNA, hydroxyproline, and glycosaminoglycan (GAG) content were determined and the disks and condyles were tested in uniaxial unconfined stress relaxation compression from 10% to 30% strain. TMJ disks were further assessed with a tensile test to failure technique, which included the ability to test multiple samples from the same region of an individual disk to minimize the intraspecimen variation. No differences in biochemical properties for the disk or compressive properties at 30% stress relaxation in the disk and condylar cartilage were found. In tension, no differences were observed for peak stress and tensile modulus. The collagen content of the condyle was higher at 9 months than 3 months (p < 0.05), and the GAG content was higher at 9 months than 6 months (p < 0.05). There was a trend of increased compressive instantaneous modulus with age. As such, age-matched controls for growing pigs are probably appropriate for most parameters measured.