Fluoride penetration from toothpastes into incipient enamel erosive lesions investigated using dynamic secondary ion mass spectrometry

Abstract

Objective: The primary aim of this study was to assess the utility of dynamic secondary ion mass spectrometry (DSIMS) as a convenient and sensitive technique for determining fluoride uptake and distribution into incipient human enamel erosive lesions in vitro. A secondary aim was to correlate the extent of lesion rehardening following treatment with a toothpaste slurry, with relative fluoride uptake determined by DSIMS. The final aim was to compare fluoride uptake by incipient lesions treated with toothpastes containing different sources of fluoride using DSIMS.

Methods: Relative fluoride uptake into the surface and body of enamel erosive lesions was monitored by DSIMS as a function of fluoride concentration in a series of formulation-matched experimental pastes. Fluoride uptake into lesions that had been subjected to treatment with different toothpaste slurries in a single-treatment enamel lesion rehardening model was also determined, and its relationship with regard to the extent of rehardening and also the fluoride source investigated.

Results: Fluoride uptake by incipient erosive lesions treated with toothpastes containing NaF was quantitatively compared by DSIMS and found to be directly proportional to the fluoride concentration over the studied range (0-1400 ppm). Lesion repair observed in a single-treatment lesion rehardening model was positively correlated with the extent of fluoride uptake by the treated lesions. DSIMS was also able to show differences between commercial toothpastes containing different sources of fluoride and their ability to deliver the fluoride into the body of the lesion. The detrimental effect of sodium hexametaphosphate (NaHMP) present in Crest Pro-Health formulations previously reported in the single-treatment lesion rehardening model was also evident from the DSIMS elemental line scans obtained from the lesion cross-sections.

Conclusion: DSIMS has been shown to be a powerful selective technique for quantifying relative fluoride uptake into enamel erosive lesions, and determining the extent and depth of lesion penetration. The relative efficacy of toothpastes containing fluoride from a variety of sources in the single-treatment lesion rehardening study is positively correlated with fluoride uptake and penetration determined by DSIMS.