Light-activated bleaching: effects on surface mineral change on enamel.

AIM This study evaluated the in vitro effect of 35% hydrogen peroxide (HP) on surface enamel change when activated with different light curing units (LCUs). MATERIALS AND METHODS Enamel blocks (4 × 4 × 2 mm) were obtained from bovine incisors. The initial microhardness of the enamel was determined for each specimen. After this enamel blocks were randomly divided into four groups (n = 10) and treated as follows: Control, no bleaching procedure performed; HP - LCU, application of 35% HP gel without light activation; HP + QTH, application of 35% HP gel and light activation with a Quartz Tungsten-Halogen (QTH); and HP + Light Emitting Diode, application of 35% HP gel and light-activation with a LED. New microhardness measurements were obtained, immediately, 7 and 14 days after treatment. The percentage of surface mineral change was calculated according to the baseline and post-treatment microhardness values. Additionally, six samples from each group were randomly selected and prepared for scanning electron microscopy (SEM) characterization. The data were analyzed using an analysis of variance (ANOVA) to detect differences between the three time periods, and an ANOVA and Tukey's test with a confidence level of 95%. RESULTS There was no significant difference between the initial hardness values and hardness values after treatment in any of the groups or time periods (p > 0.05). No major surface alterations were detected with SEM when comparing control groups to those undergoing bleaching treatments. CONCLUSION The use of 35% HP in combination to QTH or LED light curing units LCU does not have detrimental effect on the enamel surface topography or in the mineral content, when compared with unbleached enamel or enamel submitted to 35% HP treatment alone.