| 0886 Carbonated Apatite Solubility Behavior: Lattice Fluoride and Crystallinity Effects | ||
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G. YAN1, K. MORIBE1, M. OTSUKA1, D.D. HESLOP1, A.A. BAIG2, and W.I. HIGUCHI1, 1University of Utah, Salt Lake City, USA, 2The Procter and Gamble Company, Mason, OH, USA Objectives: Previous studies have shown that the solubility behavior of carbonated apatites (CAPs) of moderate to high crystallinity not containing lattice fluoride may be described by the concept of metastable equilibrium solubility (MES) with an appropriate surface complex governing the MES behavior. The purpose of the present study was to examine the hypothesis that CAPs with incorporated lattice fluoride may exhibit the MES behavior and that, when “swamping” solution fluoride is present, the surface complex with the fluorapatite (FAP) stoichiometry (Ca10(PO4)6F2) may govern the MES behavior. Methods: CAPs were synthesized at 85 oC by a precipitation method yielding preparations having two different carbonate levels (3% and 5%) and incorporated fluoride levels from 0 to 2x104 ppm. X-ray diffraction experiments and Rietveld analysis were conducted to obtain the crystallite microstrain and the unit cell parameters. The acetate buffer MES solution media were prepared at two solution fluoride levels (0.2 ppm and 2.0 ppm) and at two pHs (5.0 and 5.7). The CAP MES distributions were determined after 48-hour equilibration at 30 oC. Results: The a unit cell parameter values of the CAPs were found to decrease as the incorporated fluoride levels increased, this being consistent with the fluoride being incorporated into the crystal lattice. Employing the MES distribution superposition method, it was found that the surface complex possessing the FAP stoichiometry accounted for the MES behavior of all experiments with high precision. In addition, the mean pKFAP [the value of –log(aca10aPO46aF2) at 50% CAP dissolved, where a is the ion activity] correlated well with the crystallite microstrain parameter. Conclusions: In the present studies, CAPs with lattice-incorporated fluoride exhibited MES behavior with the governing surface complex possessing the FAP stoichiometry. The magnitude of the MES correlates well with the crystallite microstrain parameters. Supported by NIDCR Grant DE 06569. | ||
| Seq #100 - Enamel and Dentin: Surface Properties and Crystal Formation I 10:15 AM-11:30 AM, Thursday, 11 March 2004 Hawaii Convention Center Exhibit Hall 1-2 | ||
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