Objective: To study the histology and ultrastructure of the tidemark in the adult condylar cartilage and their significance.
Methods: After 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.
Results: In 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.
Conclusions: In 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.