Impact of combined CO2 laser irradiation and fluoride on enamel and dentin biofilm-induced mineral loss.

Abstract

The caries-protective effects of CO2 laser irradiation on dental enamel have been demonstrated using chemical demineralization models. We compared the effect of CO2 laser irradiation, sodium fluoride, or both on biofilm-induced mineral loss (∆Z) and Streptococcus mutans adhesion to enamel and dentin in vitro. Ground, polished bovine enamel, and dentin samples were allocated to four groups (n=12/group): no treatment (C); single 22,600-ppm fluoride (F) varnish (5% NaF) application; single CO2 laser treatment (L) with short pulses (5μs/λ=10.6μm); and laser and subsequent fluoride treatment (LF). Samples were sterilized and submitted to an automated mono-species S. mutans biofilm model. Brain heart infusion plus 5% sucrose medium was provided eight times daily, followed by rinses with artificial saliva. After 10days, bacterial numbers in biofilms were enumerated as colony-forming units/ml (CFU/ml) (n=7/group). ∆Z was assessed using transversal microradiography (n=12/group). Univariate ANOVA with post hoc Tukey honestly-significant-difference test was used for statistical analysis. Bacterial numbers were significantly higher on dentin than enamel (p<0.01/ANOVA). On dentin, LF yielded significantly lower CFUs than other groups (p=0.03/Tukey), while no differences between groups were found for enamel. The lowest ∆Z in enamel was observed for L (mean/SD 2036/1353vol%×μm), which was not only significantly lower than C (9642/2452vol%×μm) and F (7713/1489vol%×μm) (p<0.05) but also not significantly different from LF (3135/2628vol%×μm) (p>0.05). In dentin, only LF (163/227) significantly reduced ∆Z (p<0.05). CO2 laser irradiation did not increase adhesion of S. mutans in vitro. Laser treatment alone protected enamel against biofilm-induced demineralization, while a combined laser-fluoride application was required to protect dentin.