Light-activated bleaching: Effects on surface mineral change on enamel

Abstract

Aim: This study evaluated the in vitro effect of 35% hydrogenperoxide (HP) on surface enamel change when activated withdifferent light curing units (LCUs).Materials and methods: Enamel blocks (4 × 4 × 2 mm) wereobtained from bovine incisors. The initial microhardness of theenamel was determined for each specimen. After this enamelblocks were randomly divided into four groups (n = 10) andtreated 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 witha Quartz Tungsten-Halogen (QTH); and HP + Light EmittingDiode, 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 surfacemineral change was calculated according to the baseline andpost-treatment microhardness values. Additionally, six samplesfrom each group were randomly selected and prepared forscanning electron microscopy (SEM) characterization. The datawere analyzed using an analysis of variance (ANOVA) to detectdifferences between the three time periods, and an ANOVA andTukey's test with a confidence level of 95%.Results: There was no significant difference between theinitial hardness values and hardness values after treatment inany of the groups or time periods (p > 0.05). No major surfacealterations were detected with SEM when comparing controlgroups to those undergoing bleaching treatments. Conclusion: The use of 35% HP in combination to QTH orLED light curing units LCU does not have detrimental effect onthe enamel surface topography or in the mineral content, whencompared with unbleached enamel or enamel submitted to 35%HP treatment alone.