Bleaching Gels Used After 1 Week of Mixing: Efficacy, Hydrogen Peroxide Penetration, and Physical–chemical Properties
This in vitro study aimed to evaluate the bleaching efficacy (BE), hydrogen peroxide penetration into the pulp chamber (HPP), and physical–chemical properties (concentration, pH, and viscosity) of in-office bleaching gels immediately and after 1 week of mixing. We randomly divided 49 premolars into seven groups: control (no bleaching) and the following in-office bleaching (Opalescence Boost 40%, Total Blanc One Step 35%, and Whiteness HP Blue 35%) applied at two storage times: immediately and after 1 week. We evaluated the BE using a digital spectrophotometer and the HPP through UV-Vis spectroscopy. We measured the initial concentration, pH, and viscosity using titration, a Digital pH meter and Rheometer, respectively. For statistical analysis, we used a twoway analysis of variance and Tukey and Dunnet tests (α=0.05). We observed higher BE and HPP for Opalescence Boost and Total Blanc One Step after 1 week of mixing than for Whiteness HP Blue (p<0.001). We observed a significantly lower initial concentration for Whiteness HP Blue 1 week after mixing compared to immediately (p=0.00001). All bleaching gels showed a decrease in pH after 1 week of mixing (p=0.00003). However, Total Blanc One Step had a lower pH at both evaluation times (p<0.001). Only Opalescence Boost maintained viscosity 1 week after mixing. Opalescence Boost was the only bleaching gel able to keep bleaching efficacy, with the same characteristics of permeability and physical– chemical properties after 1 week of mixing.SUMMARY
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Means of pH during the time of application of the bleaching agents in different experimental groups (*).
Average viscosity (thixotropy in Pa s) according to the two application times in different experimental groups (*). Abbreviations: IM, immediate after mixing; 1S, 1 week after mixing.
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