Mineralization of biological tissue is both strictly regulated and unique to each mineralized tissue. For each tissue, the mineral crystal in question is hydroxyapatite. The mechanisms of mineralization of bone and dentine share close similarities whereby an unmineralized matrix, osteoid or predentine, is calcified by a combination of matrix vesicle-mediated mineralization and heterogenous mineralization. Enamel is mineralized purely by heterogenous mineralization. However, for all three tissues, a number of tissue-specific proteins and proteoglycans tightly regulate mineralization by inhibiting mineralization processes or by guiding mineral deposition. Such proteins, and the cells that synthesize them, are therefore crucial in controlling the rate of mineralization, allowing ordered growth of the mineral crystals and preventing premature crystal fusion.
