Increased fluoride uptake and acid resistance by CO2 laser-irradiation through topically applied fluoride on human enamel in vitro

Objectives The aim of the current in vitro study was to evaluate the effect of CO2-laser treatment immediately after applying amine fluoride solution on enamel. It was hypothesized that such a treatment would increase enamel fluoride uptake, and reduce dissolution rate and thermal surface alterations. Methods Fluoride uptake was determined in 40 human enamel sections randomly assigned to four groups (n=10), which were either left untreated (1), exposed to a 1% amine fluoride solution for 15 s without irradiation (2), irradiated for 15 s with a continuous-wave carbon dioxide laser (3), or laser-treated for 15 s through the amine fluoride solution applied immediately beforehand (4). Fluoride uptake was determined with an ion selective electrode after acid dissolution of the specimens (surface and subsurface layers). For the determination of acid resistance, another 40 enamel sections were treated according to the above protocol. Acid resistance was determined in surface and subsurface layers by measuring eluted calcium upon 3% lactic acid exposure with atomic absorption spectrometry. Enamel surface alterations after laser irradiation were monitored using scanning electron microscopy. Results Laser irradiation through the fluoride solution led to significantly higher fluoride contents in the surface enamel layer compared to fluoride treatment alone or laser treatment alone (p=0.002). Laser treatment with or without fluoride resulted in an increased acid resistance of enamel specimens. Fewer surface alterations were observed upon SEM examination of specimens irradiated through the amine fluoride solution compared to counterparts treated with laser only. Conclusions CO2 laser light application through an amine fluoride solution may be useful and effective in the prevention of caries.