The Effect of Various Fluoride Products on Dentine Lesions during pH-Cycling

This study compared the effect of topically applied fluoride products on dentine lesions in an in vitro experiment. Demineralized bovine dentine specimens were treated once with either SDF solution (35,400 ppm F), NaF varnish (22,600 ppm F), TiF4 solution (9,200 ppm F), SnF2 gel (1,000 ppm F), no treatment (control), or preserved as baseline lesions. After the application and subsequent removal of the fluoride products, the specimens were subjected to pH-cycling. Calcium loss and uptake in the de- and remineralization buffers were assessed daily. Fluoride release into the buffers was analyzed on days 1, 2, 3, 5, 8, and 13. After the pH-cycling period, mineral distribution throughout the lesion depth was analyzed using transversal microradiography (TMR). X-ray energy-dispersive spectroscopy (EDS) examined the deposition of silver, titanium, and tin after application of SDF, TiF4, and SnF2, respectively. Overall, calcium loss and uptake analysis in the de- and remineralization buffers revealed that the SDF product was the most effective in inhibiting lesion progression, followed by the TiF4, NaF, and SnF2 products. Fluoride analysis disclosed a steep reduction of the amount of fluoride released into de- and remineralization buffers with time. The fluoride effects on de- and remineralization continued beyond the days that fluoride was released into the buffers. TMR analysis showed significant remineralization in the outer zone of the dentine lesions for all fluoride products, with SDF giving hypermineralization in this zone. In the inner zone, lesions developed in all fluoride groups, with the smallest in the SDF group. EDS showed silver and titanium deposition in depth up to 85 μm and 8 μm, respectively, while no tin deposition was observed. The silver in the dentine lesions did not contribute significantly to the density of the TMR profiles in the SDF group. In conclusion, all topical fluoride products protected the dentine lesions against lesion progression, but at different degrees. SDF showed a superior effect in protection against further demineralization and enhancement of remineralization. This was probably attributed to its fluoride concentration that was the highest among the fluoride products.