Ultrastructural organic-inorganic relationships in calcified tissues: cartilage and bone vs. enamel.

Close organic-inorganic relationships exist in all calcified tissues, the inorganic substance being linked to crystal ghosts (CGs). These are organic, crystal-like structures present in areas of initial calcification. In cartilage and bone, they form aggregates with the same morphology and distribution as the calcification nodules; in enamel, they consist of long filament- and ribbon-like structures, having the same arrangement as untreated crystals. CGs of cartilage and bone are acidic structures with histochemical properties of proteoglycans; CGs of enamel probably correspond to enamelins. The close morphologic similarity between CGs and crystals suggests that the former have a role in the formation of the latter.