Bleaching Gels Used After 1 Week of Mixing: Efficacy, Hydrogen Peroxide Penetration, and Physical-chemical Properties.

OBJECTIVES: 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. METHODS AND MATERIALS: 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). RESULTS: 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. CONCLUSIONS: 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.

Application Tip and Concentration of a Self-mixing Bleach: Hydrogen Peroxide Inside the Pulp Chamber, Color Change, and Amount of Bleaching Gel Used.

PURPOSE: The objective of this study was to evaluate if the application method (tip with brush or tip without brush) and hydrogen peroxide (HP) concentration (6% or 35% self-mixing) of in-office bleaching gel influences the penetration of HP into the pulp chamber, color change, and the amount of bleaching gel used. METHODS: Forty healthy premolars were randomly divided into the following five groups (n=8): no treatment; HP6% using a tip with a brush, HP6% using a tip without a brush, HP35% using a tip with a brush, and HP35% using a tip without a brush. After treatments, the HP concentration (µg/mL) within the pulp chamber was determined using UV-Vis spectrophotometry. The color change (ΔEab, ΔE00, and ΔWID) was evaluated using a digital spectrophotometer. The amount of gel used (g) in each group was measured using a precision analytical balance. Data from each test were submitted to parametric tests (α=0.05). RESULTS: The tip with a brush resulted in a lower amount of HP inside the pulp chamber and less gel used when compared with the tip without a brush, regardless of HP concentration (p<0.05). However, regarding the tip used, although no significant difference was observed when HP35% was used (p>0.05), a higher whitening effect was observed when the 6% HP was applied without a brush as opposed to with a tip brush (p<0.05). CONCLUSIONS: The use of a tip with a brush, regardless of the in-office bleaching gel concentration (6% or 35% self-mixing), presented a lower penetration and lower volume of spent gel when compared to a tip without brush. However, the whitening effect depended on the concentration of HP used.