Light and electron microscopic morphology of the temporomandibular joint in growing and mature crab-eating monkeys (Macaca fascicularis): the condylar calcified cartilage.

In an attempt to show maturational alterations in the calcified cartilage, mandibular condyles of four growing and four adult male monkeys (Macaca fascicularis) were studied using light microscopy as well as transmission and scanning electron microscopy. All specimens were initially fixed by perfusion in the presence of ruthenium red. For examination of the hard tissue surfaces in the scanning electron microscope, uncalcified tissues were removed with sodium hypochlorite. In growing animals, almost the entire hard tissue surface in the joint region of the condyle was formed by calcified cartilage, while in adult animals, calcified cartilage was confined to load-bearing regions. In growing animals, the appearance of the calcified cartilage surface suggested a continuously advancing mineralizing front similar to that seen in the epiphyseal plate. Chondrocytes mostly exhibited a terminal stage of hypertrophy, and seemed to die and get lost through vascular invasion and subsequent endochondral ossification. In adult animals, most of the calcified cartilage surface appeared comparatively stable, and resembled the tidemark of articular cartilage. Chondrocytes were usually small and appeared viable. However, on the adult condyles, there were always circumscribed islands where chondrocytes and the pattern of mineralization resembled those seen in growing animals. In these regions, prominent chondroclastic activity indicated extensive articular remodelling. These observations suggest that at the end of somatic growth, condylar calcified cartilage undergoes considerable maturation from a type reminiscent of hyaline growth cartilage to a type resembling articular cartilage. Concomitantly, chondrocytes appear to change their developmental program, in that they stop enlarging and lose their commitment to death. However, they may be able to retain, or switch back to, a more immature stage, in case there is need for extensive articular remodelling.