Abstract
A cariostatic effect of phosphoric acid-acidified ammonium fluoride solution on artificial caries lesion formation was reported previously. The purpose of the present study was to examine the mode of action of this solution on emanel. Intact human enamel was immersed and stirred in three kinds of solution at 37℃ for 1 hour. The three solutions were as follows : (1) phosphoric acidacidified ammmonium fluoride solution - NH_4F group, 900ppmF^-, pH4.5 ; (2) acidulated phosphate fluoride solution - APF group, 900ppmF^-, pH4.5 ; (3) deionized water - control group. Artificial caries lesions were formed with demineralizing solution according to Moreno (1974), consisting of 50 % synthetic hydroxyapatite saturated lactate buffer (pH4.5). Distribution of phosphorus, calcium, and fluoride in enamel were determined with line analysis by EPMA, and state analysis was performed to identify the reaction products in fluoride treated enamel. The enamel surface contained 17.5% F in the NH_4F group, and 14% F in the APF group. The fluoride penetrated deeper into the enamel in the NH_4F group. Only Ca and F were detected in fluoride-treated superflcial enamel by magnified analysis. Ca and F were also detected in the crystal deposits, and a large ammount of calcium fluoride was seen in the NH_4F group and APF group. The state analysis with EPMA showed that the reaction products were calcium fluoride and fluorapatite, and the volume of reaction products was large in the APF group. In state analysis with EPMA, fluorapatite was detected in the caries lesions, and the volume of fluorapatite was high in the fluoride groups. In conclusion, ammonium fluoride solution acted by producing calcium fluoride and fluorapatite on the enamel surface. Then calcium fluoride was released slowly into the demineralizing solution, and reacted with calcium and phosphorus in solution to produce fluorapatite. The greater formation of calcium fluoride and fluorapatite in the NH_4F group and APF group had a higher cariostatic effect than control group.
