リン酸酸性フッ化アンモニウムのエナメル質におよぼす影響について

The purpose of this study was to evaluate the possibility of clinical use for fluoride topical treatment of a phosphoric acid-acidified ammonium fluoride solution, in which fluoride concentration and pH was similar to a conventional APF solution. Experiments were performed in vitro using a solution of phosphoric acid-acidified NH₄F (9000ppm of F^-, pH 3.4) and APF (Acidulated phosphate fluoride solution, 9000ppm of F^-, pH 3.4).<BR>In the experiments with intact enamel, morphological observation, acid solubility test and fluoride uptake on enamel blocks following topical treatment (for 60 min at 20°C) with fluoride solutions were studied by means of the scanning electron microscope, chemical analysis, and electron probe X-ray microanalysis (Experiment 1). In the experiments with powdered enamel, chemical analysis and identification of reaction products using X-ray diffractometry were carried out in enamel following the application of fluoride solutions (for 25 min at 37°C) (Experiment 2).<BR>In order to observe the relationship between CaF₂ formation and reaction times, enamel powder was treated with fluoride solutions at 37°C for 2, 4, 6 and 10 minutes. CaF₂ in enamel was determined by internal standard technique used X-ray diffraction. Retention of CaF₂ in enamel and fluoride released from enamel into distilled water were determined by X-ray diffractometry and chemical analysis (Experiment 3).<BR>Scanning electron microscopic examination of enamel surfaces treated with NH₄F revealed heavy deposits of crystalline material, whereas after treatment with APF, the deposit was homogeneous material. Acid solubility test proved the aquisition of acid resistance by the enamel. In the electron probe X-ray microanalysis, the fluoride uptake of NH₄F-treated enamel surface was a few times higher than that of APF-treated enamel. X-ray diffractometry showed that CaF₂was formed in the experimental groups, and a large amount of CaF₂ with high crystallinity was formed in NH₄F treated enamel. In NH₄F-treated enamel, about two times more CaF₂ was formed than at the same reaction time in APF-treated enamel. The retention of CaF₂ in enamel treated by washing was higher in NH₄F-treated enamel than in APF-treated enamel because of the large amount of CaF₂ formation with high crystallinity.<BR>Therefore, since phosphoric acid-acidified ammonium fluoride solution (9000ppm of F^-, pH 3.4) produces a large amount of CaF₂ with high crystallinity in enamel, the CaF₂ will effectively a prevent caries as a source of dilute fluoride supply. NH₄F can be expected to have the same effect as APF with a shorter time of application or at a lower concentration.