ハイドロキシアパタイトのフッ化物化に及ぼす各種イオンの影響

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It is said that the fluoride-containing dental cements are effective for strengthening the dental hard tissues and preventing the occurrence of recurrent caries. This is due to the expective mechanism that the fluoride ion released from the cements will react with hydroxyapatite (HAp) to form fluorapatite (FAp) and calcium or other fluorides. Although some constituents other than fluoride ion may be also released from the cements, their behaviors have not been well defined in association with FAp formation. Therefore, the present study was scheduled to investigate the potential effects of those ions on fluoride ion uptake by HAp and on FAp formation. Synthetic HAp was stirred in the prepared fluoride solution with or without other ions for 24 hours at 37℃, and the quantitative determinations of the fluoride ion uptake and the FAp formation were made by ion meter with fluoride electrode and ESR, respectively. All the experiments were carried out under a fixed condition where the concentration of the fluoride ion was 100ppm and the pH of the solution was 6.0. Both the fluoride ion uptake and FAp formation were inhibited when Zn^<2+> or Sr^<2+> was added to the fluoride solution. It is probably because these ions might have preferentially reacted with HAp to form stable compounds. The presence of Al^<3+>, Ca^<2+> or RCOO^- in the fluoride solution significantly increased the apparent uptake of fluoride ion but decreased the FAp formation. It means that the fluoridization of HAp into FAp was inhibited by the preferential fluoride formation with these ions. If such fluorides are formed in cooperation with HAp, however, they may be effective as the long term sources of fluoride ion even though the initial FAp formation is not marked. The FAp formation was significantly decreased by adding low concentration of PO^<3->_4 in the fluoride solution, while it was increased by higher concentration of PO^<3->_4. It is well known that PO^<3->_4 will easily substitute for CO^<2->_3 in HAp and improve the crystallinity of HAp. The well-crystallized HAp would be less fluoridized. It is also known that dicalcium phosphate dihydrate (DCPD) will be formed from HAp in phosphoric solution and it will be easily fluoridized into FAp. The difference of FAp formation by the concentration of PO^<3->_4 might have come from the interaction of these inhibiting and accelerating effects, and the results showed that the former effect would be valid for the lower concentration of PO^<3->_4 and the latter for the higher concentration of PO^<3->_4. It was found, however, that once HAp was pretreated by PO^<3->_4 the transformation of HAp into FAp was inhibited by the earlier shell formation of FAp from DCPD surrounding HAp crystal. It is concluded from these results that Ca^<2+>, Al^<3+>, PO^<3->_4 and RCOO^- released from fluoride-containing dental cements may be favorable and Zn^<2+> and Sr^<2+> unfavorable for the FAp formation.
九州歯科学会の論文
1986-02-25

著者

河喜多伸一
九州歯科大学保存学第1講座

ハイドロキシアパタイトのフッ化物化に及ぼす各種イオンの影響

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