¹⁹F MAS-NMR and solution chemical characterization of the reactions of fluoride with hydroxyapatite and powdered enamel

Abstract

Solution chemical and 19F magic angle spinning-nuclear magnetic resonance (MAS-NMR) methods have been utilized to study the effects of fluoride dose, fluoridating pH, and mineral surface area on the dynamics of fluoride reactivity with hydroxyapatite and powdered human dental enamel in vitro. Both solution chemical fluoride uptake and NMR measurements demonstrated that the reaction products of ionic fluoride with apatite include mixtures of FAP, FHAP, and CaF2, with increased amounts of CaF2 promoted by increased F concentration or decreased pH. NMR analysis showed FAP or FHAP as a reaction product of fluoride uptake under all conditions, regardless of whether CaF2 was formed, unambiguously demonstrating fluorite as an additive rather than substitute form of F reactivity. pH stat measurements demonstrated the release of OH- during F reactivity with apatites corresponding to ion exchange formation of FAP/FHAP or dissolution/reprecipitation formation of CaF2. Phosphate release into solution accompanied fluoride uptake under all conditions, including regions where ion exchange predominated. Whereas powdered dental enamel demonstrated fluoride uptake behavior similar to that of synthetic apatite, the resulting reaction products differed as analyzed by 19F MAS-NMR.

Effect of a Surface-Active Cation on Fluoride/Enamel Interactions in vitro

“…4), it is likely that such a fluoride deposition was in the form of firmly, probably apatitically bound fluoride. Such a conclusion is in agreement with the data re ported by McCann and Bullock [1955] and White et al [1988].…”

Calcium Fluoride Formation on Sound Enamel Using Fluoride Solutions with and without Lactate

“…The majority of the F in this investigation was retained as FAP or fluorhydroxyapatite (FHAP). This supports the results obtained by White et al [1988] and White and Nancollas [1990] who used nucle ar magnetic resonance techniques to demonstrate that the main reaction products after topical F treatment of enam el were FAP or FHAP. regardless of whether CaF^ was formed as an intermediate reaction product.…”

Structure of Artificial Enamel Lesions after Topical Applications of High-Concentration Sodium Fluoride Solution in vitro

“…As to the reason for the structural evolution, it is generally accept ed that an acidic environment is advantageous to the forma tion of CaF2 according to the following equation [Fischer et al. 1954;Duschner and Uchtmann, 1988;White et al, 1988], Ca5(P 0 4)j0H+F ----5CaF; + 3POi +011 Since the F concentration was higher, the reaction de scribed by the equation became violent. Thus, the original structure of AEL in the CL was completely damaged.…”