Background and purpose: Prevention of dental caries is one of the primary goals in dentistry. Application of fluoride decreased dental demineralization but the preventive ability of this fluoride is limited. Nowadays different investigations into dental erosion focused on the preventive effect of laser irradiation. The purpose of this applied study was to assess the effect of diode laser (λ = 810nm) and CO2 laser treatment in combination with NaF 2.26% varnish on deciduous enamel microhardness.

Materials and methods: Seventy-two human mandibular deciduous incisors were polished and randomly allocated to the following treatments (n = 12): (1) NaF varnish (2.26% F); (2) NaF varnish + diode laser; (3) NaF varnish + CO2 laser; (4) CO2 laser; (5) diode laser; (6) control group (no treatment). Enamel alterations were determined using Vickers surface microhardness (VMH) testing after treatment and after erosion challenge. For the formation of artificial caries, the samples were immersed in hydrochloric acid, and then enamel alterations were determined again. The mean VMH were tested using analysis of variance and Tukey test.

Results: All treatments except CO₂ laser improved the hardening of enamel surface (P<0.05) and increased the resistance of samples against demineralization. The NaF + diode laser group had significantly higher surface microhardness value than the other groups (P<0.05). There were no significant differences between diode laser, NaF and CO₂ laser + NaF groups in surface microhardness.

Conclusion: The surface microhardness was the highest when both laser and fluoride were applied. Therefore, the effect appears to be synergistic; also, diode laser compared with CO2 laser was more effective in improving the hardening of enamel surface.