Biochemical reports on temporomandibular joint (TMJ) composition at physiological and pathological conditions have been rather scarce when compared to those of morphological studies. The present investigation was intended to characterize cross-links and types of collagen in TMJ disc, which is thought to be one of the most important elements in maintaining the structure, strength and smooth function of the joint.
Amino acid analyses of human and porcine TMJ discs ascertained that collagen was the majority among the tissue components. Reducible cross-links were analyzed by radiochromatography after reducing with [3H]-NaBH4 and characteristic patterns were obtained in reducible cross-links of porcine and human samples, respectively. In porcine discs, relatively large amounts of reducible cross-links such as dihydroxylysinonorleucine, hydroxylysinonorleucine and histidinohydroxymerodesmosine were detected. Age-related decrease in all of the reducible cross-links was observed. Human discs contained less amount of reducible crosslinks than porcine samples. However, one reducible component related to hexitollysine, which is desig-nated Al, was abundant in human discs.
Non-reducible cross-links, pyridinoline and histidinoalanine in TMJ discs, were determined with an amino acid analyzer after hydrolysis. The former was detected in all tissue samples examined and was found to decrease with aging. The latter, which is considered to be a cross-link between collagen and related proteins, was detected in aged samples especially in perforated disc but not found in younger samples.
Collagen type analysis by gel electrohorcsis revealed that both procine and human TMJ discs consisted almost exclusively of type I, however, porcine sample contained a trace amount of type III collagen.