Effect of Strontium in Combination with Fluoride on Demineralization

Abstract

Enamel demineralisation – particularly in the form of dental caries – is one of the most common endemic diseases worldwide. Therefore, several agents (e.g., fluoride and strontium) were explored in order to test their effects on the demineralisation and remineralisation process. Previous studies have proposed a synergistic effect of fluoride and strontium on demineralisation as well as fluoride uptake. However other studies have questioned this synergy.

This study aims to investigate the effect of strontium in combination with fluoride on the demineralisation process and fluoride uptake by hydroxyapatite discs at pH 4. To achieve these aims, various techniques were used in combination including, fluorine magic-angle spinning, nuclear magnetic resonance spectroscopy (19F MAS-NMR) to determine fluoride substitution in hydroxyapatite. In addition, solution analysis was carried out using real-time (Ca2+ and F-) ion-selective electrodes (ISE) and inductively coupled plasma optical emission spectrometry (ICP-OES) for Ca, Sr, and P.

Compressed hydroxyapatite circular discs were investigated as model analogs of enamel. Ten discs were allocated into four groups based on the incorporation and concentration of Sr, F, Sr+F (or not, for the control group) in the demineralisation solution into which they were placed. Each disc was demineralised for 24 h under 37±0.5 °C, and Ca2+ ISE and F- ISE were used. Subsequently, the experimental solutions were analysed by ICP-OES, and 19F MAS-NMR used to analyse the disc samples. In summary, our study demonstrates a concentration-dependent synergistic action of strontium in combination with fluoride in retarding the dissolution rate of hydroxyapatite discs compared to each ion alone. Further, it showed an antagonistic effect on fluoride uptake compared to fluoride alone.