[Study on enhancement effect and mechanism of the acid resistance of enamel by Fe2+ and F].

PURPOSE

The phase of new substances and the effect on enamel lattice was analysed after ferrous sulfate ,sodium fluoride treatment through X-ray diffraction, in order to explore the mechanism of Fe2+ and F- reinforced enamel acid resistance.

METHODS

Fragments of enamel obtained from fifty molars were ground into powder and randomly divided into four groups: C (control,deionized water); Fe2+ (15 mmol/L FeSO4); F- (1.23% NaF) and Fe2++F- (15 mmol/L FeSO4 and 1.23% NaF). Before exposure to acid, the samples were incubated in one of the experimental solutions for 48 hours. After that, the samples were submitted to six alternating remineralization and demineralization cycles. A complete cycle consisted of the following steps:① demineralization in 5 mL of the beverage (Coca-Cola, pH=2.58) for 5 minutes under gentle agitation;② remineralization in 5 mL of artificial saliva for 1 hour at 37℃. X-ray diffraction was employed to identify precipitates and estimate their lattice constants before enamel power dried at 40℃.

RESULTS

The XRD pattern of the group of ferrous sulfate was not sharper than control while the full width half maximum of peak increased and became more gentle. The enamel crystal grain size and crystallinity decreased. Secondary phase retrieval showed there was new phase formed which was iron phosphate. Diffraction spectrum of ferrous sulfate with fluoride group was similar to fluoride alone, the full width half maximum of peak became sharper and more narrow.The enamel crystal grain crystallinity improved and there was new phase of calcium fluoride formed.

CONCLUSIONS

Fe2+ and F- both had certain influence on the crystal structure of enamel. However, the impact of Fe2+ was concealed when reacted with high concentration F-. Fe2+ may participate in the nucleation of apatite through substitution of calcium in apatite. Acid-resistant enamel surfaces are established due to precipitation of ferric phosphates on the enamel surface, and combination of Fe2+ with PO4(3-) dissolved on enamel surface. F- may participate in the nucleation of apatite through substitution of OH-; at the same time, the calcium fluoride precipitation was established.