Dose-Responsive Fluoride Uptake into Enamel Erosive Lesions Monitored by DSIMS

Objective: Evaluation of Dynamic Secondary Ion Mass Spectrometry (DSIMS) as a novel analytical technique to study fluoride penetration into human enamel containing artificial erosive lesions. Methods: Erosive lesions were prepared from human enamel by immersion in 1.0% citric acid, pH3.8 for 5min. Specimens were subsequently treated for 2min with agitated 1:3 w/w dentifrice:deionised water slurries. The experimental dentifrices contained fluoride (as NaF) concentrations of 0ppm, 25ppm, 100ppm, 250ppm, 1000ppm. Treated specimens were vertically sectioned and the fluoride concentration in the first few microns of their surface determined using SIMS in depth profiling mode. The remaining half of each specimen was employed to generate DSIMS images of the cross-sections. Results: Depth profiles of the enamel surface showed that fluoride uptake into the enamel was proportional to the fluoride concentration in the dentifrice. Validation of the surface fluoride concentrations was also obtained using X-ray Photoelectron Spectroscopy (XPS) analysis. DSIMS cross-sectional imaging also showed that the trend in surface fluoride concentration was maintained through the enamel to a depth of approximately 45ìm. Conclusion: This study provides a validated basis for the use of DSIMS as a powerful selective technique for monitoring fluoride uptake into human enamel erosive lesions from sodium fluoride containing dentifrice formulations. Fluoride uptake from formulation-matched dentifrices has been shown to be dose dependent.