EDX-analysis of fluoride precipitation on human enamel

Konstantin Johannes Scholz,Gerlinde Ferstl,Wolfgang Buchalla,Helga Ebensberger,Marianne Federlin,Karl-Anton Hiller

doi:10.1038/s41598-019-49742-5

Abstract

One mechanism of action for the anticaries effect of topical fluoridation is through precipitation of CaF2. In this in vitro study energy-dispersive x-ray spectroscopy (EDX) is used as a semiquantitative method to detect enamel fluoride-precipitation under the influence of acidic and neutral pH-value and absence or presence of a salivary pellicle. Crowns of 30 human caries-free third molars were quartered into four specimens and the enamel surface ground flat and polished. Two specimens each were stored in human saliva (120 minutes pellicle formation). Teeth were randomly allocated into 6 treatment groups: NaF_a (experimental acidic sodium fluoride; 12500 ppmF−, pH 4.75); NaF_n (experimental neutral sodium fluoride; 12500 ppmF−, pH 7.0); GB_a (acidic gel base; 0 ppmF−, pH 4.75); GB_n (neutral gel base; 0 ppmF−, pH 7.0); AmF-NaF_a (experimental acidic amine/sodium fluoride; 12500 ppmF−, pH 4.75); EG_a (acidic amine/sodium fluoride; Elmex Geleé, CP-GABA GmbH; 12500 ppmF−, pH 4.75). Each gel was applied for 60 seconds to one specimen with and one specimen without pellicle. Two specimens served as controls (no gel, without/with pellicle). Atomic percent (At%) of O, F, Na, Mg, P, Ca was measured by EDX. ∆At% and Ca/P-ratios were calculated. EDX could semi-quantify superficial enamel fluoride-precipitation. Only specimens treated with acidic fluoride gels showed fluoride-precipitation, a salivary pellicle tended to decrease At%F.

Highlights

For over 75 years studies confirm the caries-preventive effect of water fluoridation above 1 parts per million on caries prevelance and composition of teeth[1,2,3,4,5]
It is likely that those complexes serve as a pool for release of fluoride ions, which enable an inhibition of demineralization by adsorption on partially demineralized crystals[15]
It has been shown that scanning electron microscopy (SEM) techniques with or without energy-dispersive x-ray spectroscopy (EDX) are suitable methods for characterizing single KOH-soluble precipitates on human dental enamel[12], but these methods are still not widely used for characterization of the enamel surface following topical fluoride application

Summary

Introduction

For over 75 years studies confirm the caries-preventive effect of water fluoridation above 1 parts per million (ppm) on caries prevelance and composition of teeth[1,2,3,4,5]. Deposition of CaF2-like complexes on enamel surfaces following topical fluoridation by high fluoride containing agents with low pH-value has been frequently described[12]. It is not exactly known if it is pure CaF2 or if there were other components in these complexes[13,14]. Previous studies suggest that CaF2-precipitation is enhanced on a clean enamel surface without plaque or pellicle, for high fluoride concentrations, long exposure period and low pH of the fluoride solution or gel[12,18,19]. It has been shown that scanning electron microscopy (SEM) techniques with or without energy-dispersive x-ray spectroscopy (EDX) are suitable methods for characterizing single KOH-soluble precipitates on human dental enamel[12], but these methods are still not widely used for characterization of the enamel surface following topical fluoride application

Results

Discussion

Conclusion