FROM SERUM TO THE MINERAL PHASE - THE ROLE OF THE ODONTOBLAST IN CALCIUM-TRANSPORT AND MINERAL FORMATION

Dentin may be considered as a calcified connective tissue and is in it s composition as well as in its mode of formation closely related to b one. Dentin is formed by two simultaneous processes in which the odont oblasts are instrumental: the formation of the proteinaceous dentin ma trix, and mineral crystal formation in this matrix. As part of this, t he odontoblasts actively transport Ca2+ ions towards the site of miner al formation. The cells maintain a delicate intracellular Ca2+ ion bal ance by the concerted action of transmembraneous transport mechanisms, including Ca-ATPase, Nac/Ca2+ exchangers and calcium channels of the L-type, and possibly intracellular Ca2+-binding proteins. The net effe ct of this is a maintenance of a cytoplasmic sub-micromolar Ca2+ activ ity and an extracellular accumulation of Ca2+ ions at the mineralizati on front. In addition to the major matrix constituent, collagen, non-c ollagenous macromolecules, such as dentin phosphoprotein (phosphophory n), dentin sialoprotein, and proteoglycan, are synthesized by the odon toblasts and deposited in the matrix. Such polyanionic macromolecules are presumably responsible for the extracellular induction of hydroxya patite crystals, but may also function to inhibit mineral growth and t o regulate crystal size. Accordingly, it can be concluded that dentino genesis comprises an interplay between several factors in the tissue, cellular as well as extracellular.