Microhardness change of human dental enamel due to power bleaching with different gels

Abstract

Aim: Since the introduction of bleaching treatments in the office, different lights have been suggested to accelerate the bleaching reaction. This study aimed to evaluate the microhardness of tooth enamel after office bleaching using different materials. Materials and methods: Thirty-three sound human upper premolars were randomly divided into 3 groups as follows (n=11): Group 1: Whitesmile HP40% gel with R&B LED light source with 3 W power output; Group 2: HP 35% Dr Smile gel with a 980 nm diode laser, 2 W power and continuous wavelength; Group 3: HP 40% Ultra boost gel according to factory instructions. Enamel surface microhardness was measured before and after the bleaching procedure in each group using the Vickers microhardness test. One-way ANOVA and Tukey post hoc tests were used for statistical analysis. We used a SEM microscope to examine the surface of one sample from each group and one sample as a negative control. Results: In group 1, enamel microhardness increased remarkably (p=0.013) whereas in group 2 and group 3 enamel microhardness decreased. Enamel microhardness decreased in group 3 significantly (p=0.00) but its reduction in group 2 was not significant (p=0.833). SEM examination of the enamel surfaces after bleaching revealed erosion and surface porosities in group 1, enamel structure melting, and shallow porosities in group 2, and enamel prism exposure and etching in group 3. Conclusions: Due to the limitations of the present study, power bleaching with HP40% Whitesmile gel with LED Monitex increases microhardness, so it can have better results for treatment in the clinic. Additionally, using Dr Smile gel with a 980 nm diode laser does not reduce surface microhardness.