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.

Effect of Daily Usage Time of 4% Hydrogen Peroxide on the Efficacy and Bleaching-induced Tooth Sensitivity: A Single-blind Randomized Clinical Trial.

OBJECTIVE: Compare the risk/intensity of tooth sensitivity (TS) and color change of a 30-minute vs. the recommended 120-minute application time of 4% hydrogen peroxide (HP) for at-home bleaching. METHODS: A single-blind, parallel, randomized clinical trial was conducted with 92 adult patients with caries and restoration-free anterior teeth A2 or darker, randomly allocated to two groups. Bleaching trays containing 4% HP were used for three-weeks. A four-week regimen was also offered to the patients for the 30-min group after the end of the 3-week protocol. The color change was assessed with the Vita Classical (VITA Zahnfabrik, Bad Säckingen, Germany) and Vita Bleachedguide shade guides (VITA Zahnfabrik) and the Vita Easyshade spectrophotometer (VITA Zahnfabrik) at baseline, weekly, and 30 days after the bleaching. The absolute risk and the intensity of TS were assessed daily using the 0-10 visual analogue scale (VAS) and 5-point Numerical Rating Scale (NRS) scale, and patient satisfaction was recorded with a Likert 0-7 scale. Risk of TS (Fisher's test), intensity of TS in NRS scale (Mann-Whitney test), VAS scale (t-test), and a color change (t-test) were compared. RESULTS: The 30-minute group saw color change of around 1 SGU inferior to the 120-minute group in all-time assessments (p<0.05). After an extra week of bleaching, mean color change was similar (p>0.05). Patient satisfaction was high for both groups (p>0.05). CONCLUSIONS: A four-week protocol of at-home dental bleaching with 4% HP for 30 minutes/day whitened teeth similarly to the 120 minutes/day protocol, with low intensity of dental sensitivity and high patient satisfaction.