Changes in the chemical composition of the bovine temporomandibular joint disc with age.

The bovine temporomandibular joint disc is a fibrocartilaginous structure composed largely of collagen and proteoglycans. Little is known about changes in its composition accompanying growth and maturation. Discs were collected from immature foetuses (3-5 months), mature foetuses (6-8 months, adolescents (18 months), young adults (2-3 yr) and mature adults (over 4 yr), dissected free of fibrous attachments, and separated into outer and inner tissues. For the outer tissues the major findings were that: (1) water content in postnatal specimens was less than in prenatal specimens: (2) collagen content (relative to tissue dry weight) increased up to adolescence with little change thereafter; (3) total glycosaminoglycan, chondroitin sulphate and hyaluronic acid contents decreased during foetal development and then remained relatively constant, and (4) dermatan sulphate (the major glycosaminoglycan at all ages) decreased at maturity while keratan sulphate increased slightly. Results for the inner tissues were similar except that: (1) total glycosaminoglycan content was much higher in postnatal animals; (2) chondroitin sulphate was the major glycosaminoglycan after birth; and (3) keratan sulphate, which was barely detectable in the foetal specimens, increased rapidly after birth. Evidence was also obtained for changes in the copolymeric nature of galactosaminoglycans in the inner tissue. These findings, especially the different pattern of age-related changes in outer (presumably non-compressed) and inner (presumably compressed) tissue, suggest that the disc has the capacity to continually modify its composition in response to the mechanical stresses placed on it.