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The synthesis of Mn‐containing hydroxyapatite (HA) samples was carried out by precipitation from an aqueous solution with and without carbonate at pH 5.8−6.0. Chemical analyses have shown that Mn uptake (about 70%) is proportional to the amount of initially added Mn. The molar Ca/P ratios of the samples (1.53−1.63) indicate the formation of nonstoichiometric HA, with the higher values being obtained for the carbonated samples. Powder X‐ray diffraction (XRD) and IR spectroscopy have shown well‐defined patterns with structural data characteristic of HA. The calculated lattice constants were found to be similar to those known for HA, without any effect of the varying Mn content. High temperature treatment of selected samples was studied by XRD and IR and showed that the apatite structure is stable up to 400 °C for all samples. At 600 °C samples with low carbonate content transform partially, and at 800 °C completely, to β‐Ca3(PO4)2, while for samples with higher carbonate content (3.5−6.0%) the apatite structure is stable up to 800 °C, and a colour change to blue occurs. EPR spectroscopy reveals that manganese is divalent in all precipitated samples and present in a cubic impurity phase. After heating above 600 °C it is partially oxidized to MnV in the samples with high carbonate content and enters the HA lattice as the blue MnO43− ion. In the carbonate‐poor solids Mn2+ seems to partly occupy the Ca2+ sites in β‐Ca3(PO4)2 when sintered at temperatures above 400 °C. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The present study describes the detailed changes in carbonate distribution throughout the different stages of development in human and bovine enamel, from early formation to maturation. Twenty-two human maxillary and mandibular deciduous anterior teeth and 46 bovine teeth were studied. The major mineral ions, calcium and phosphorus, were also analyzed to facilitate comparison of carbonate content with progressing mineralization. The results showed that as enamel matured and mineral concentration increased, carbonate concentration decreased. The observed decrease in percent carbonate per weight enamel mineral may be due to dilution by an influx of relatively carbonate-free mineral, and could, in part, explain the observed increase in crystallinity of enamel mineral as the tissue matures.

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