OBJECTIVETo study the histology and ultrastructure of the tidemark in the adult condylar cartilage and their significance.

METHODSAfter embedded in paraffin, 50 adult condyles were stained with HE, partly with Van-Gieson and histochemical methods, then observed by light microscope. 3 cases of the tidemark region were observed by transmission electron microscope, another 5 cases were studied by scanning electron microscope.

RESULTSIn the tidemark region, there had shown the presence of the AKP and calcium, absence of the proteoglycan, abundance of the membrane-bound matrix vesicles, crystals of hydroxyapatite and lipid nodule-like substances, which were often observed in the load-bearing areas. The collagen fibrils of the noncalcified cartilage crossed the tidemark gradiently and were continuous with those of the calcified cartilage; a band of horizontal fibrils surrounded the whole tidemark region, which was wider in the load-bearing areas than that in the nonload-bearing areas and which interweaved with the gradient fibrils so as to form a net. Digested with papain, the surface of the tidemark was highly undulating, and a lot of chondrocyte lacunae were seen on the surface, which were surrounded by calcified tissues.

CONCLUSIONSIn the region of the tidemark, physiological calcification takes place and is more active in the load-bearing areas; gradient and horizontal fibrils interweave with each other, which is correlated with the force on the articulation.