Prevention of Enamel Demineralization With a Novel Fluoride Strip: Enamel Surface Composition and Depth Profile

Objectives: This study aims to assess the use of a low concentration (1450 ppm) fluoride strip as an effective fluoride delivery system against enamel demineralization. The enamel surface composition and depth profile after fluoride strip treatment were also investigated.
Methods: Enamel surfaces after different application times of fluoride strips or toothpaste treatments were analyzed using X-ray photoelectron spectroscopy and depth profiling and scanning electron microscopy. In vitro enamel demineralization was assayed using a pH cycling model. The dissolution of calcium ions from the specimens that had been treated for different lengths of time was quantified using ion chromatography.
Results: After 24-hr fluoride-strip treatment, the enamel was covered with a CaF₂ layer which showed a granular morphology of 1 μm in size. Below the CaF₂ layer was a region of mixed fluorapatite and CaF₂. Fluoride infiltrated extensively in enamel to produce highly fluorinated fluorohydroxyapatite (FHAP). In comparison, low-fluoride-level FHAP and carbonate-containing hydroxyapatite were formed on the enamel specimen exposed to toothpaste. Compared with toothpaste treatments, the treatments with the fluoride strip as short as 1 hr significantly inhibited enamel demineralization and longer treatments increased this effect substantially.
Conclusions: The fluoride strip is effective for topical fluoride delivery and inhibits in vitro demineralization of enamel by forming CaF₂ and fluoride-containing apatites at the enamel surface.