The aim of this study was to compare the results, in terms of temperature, colour change and morphology, of two different laser wavelengths with two different concentrations of hydrogen peroxide (HP). The lasers used were KTP (potassium-titanyl-phosphate) laser (λ = 532 nm (PD = 1.98 W/cm2)) and Er:YAG laser (λ = 2940 nm (PD = 2.54 W/cm2)). The bleaching gels used were PolaOffice 35% HP gel and PolaOffice+ 6% HP gel (SDI, Australia). Thirty-six extracted human teeth were selected and divided into two groups. For the 35% HP treatment, 18 teeth were randomly assigned to three subgroups: (1) HP gel without laser irradiation vs. HP gel + KTP laser irradiation; (2) HP gel without laser irradiation vs. HP gel + Er:YAG irradiation; and (3) HP gel + KTP laser irradiation vs. HP gel + Er:YAG irradiation. The same protocol was used for the 6% HP bleaching treatment. The bleaching results were analysed by a spectrophotometer, the thermal elevation by K thermocouples and the enamel surface by a scanning electron microscope (SEM). The Kruskal-Wallis test and the Mann-Whitney test were performed, and the data were analysed using the software StatView and the free Web statistics tool BiostaTGV. The thermal elevation of the Er:YAG groups was higher than KTP, while only the group 35% HP gel vs. 35% HP gel + Er:YAG showed significant colour differences (p < 0.05). SEM photographs showed slight enamel surface morphologic alterations after bleaching treatment. The Er:YAG laser may improve the bleaching results of 35% HP even if it increases the gel temperature, when compared to the KTP laser.
Keywords: Bleaching; Er:YAG; KTP; Laser; Whitening.