Fourier transform infrared microspectroscopic investigation of the maturation of nonstoichiometric apatites in mineralized tissues: a horse dentin study

Fourier transform infrared microspectroscopy (FTIRM) was used to study carbonated apatite/collagen interactions and maturation in horse secondary dentin. Unlike human dentin, this model contains no peritubular material around the odontoblastic processes and is thus quite similar to bone in composition, but not subject to tissue turnover. Crystals close to the mineralization front were very immature, showing high HPO4 and very low CO3 levels. Carbonate ions were located essentially in very labile, reactive environments, probably on the crystal surface. Removal of some of the HPO4 ions from crystals during maturation was linked to an increase in total carbonate content. The CO3 ions in labile environments decreased, probably after incorporation into more organized regions of the lattice. However, this increase of total carbonate content was associated with greater mineral crystallinity, confirming findings in other studies of synthetic apatite maturation in vitro. The good correlation between these results and those of in vitro experiments suggests that crystal maturation is essentially due to physicochemical processes and that the organic matrix controls only crystal size, multiplication, and/or organization.