Evaluation of Ph Levels and the Effect of Violet Led Light in-Office Bleaching Protocol Alone or Associated With 6% H2o2 on Enamel Microhardness

Abstract

This in vitro study evaluated the effect of three different in-office bleaching techniques on bovine enamel microhardness and the pH variation of peroxide agents during the protocols. Methodology: For Knoop microhardness (KNH) analyses, enamel fragments were divided into 3 groups (n=10): LEDv–hybrid violet LED/Laser light (10x2’ LEDv + 10x30” light-off, 2 cycles); HP6%LEDv–6% HP gel + LEDv/Laser (15x1’ LEDv + 15x1’ light-off); HP35%- 35% HP (1x45’). For pH measurements, bovine teeth were divided into 2 groups (n=10): HP35% and HP6%LEDv. KHN was measured at baseline (T0), 24h after bleaching (T1) and after 7 days in artificial saliva (T7). Initial and final bleaching gels pHs were obtained utilizing a pH-meter. KHN was evaluated by the Wald-type permutation statistic, aligned rank transformation statistical test, Wilcoxon and Mann-Whitney tests; pH levels were evaluated by the Welch-James and Wilcoxon tests (p<0.05). Results: HP35% and HP6%LEDv presented a decrease in KHN from T0 to T1, with no difference among them; baselines values were recovered at T7. For LEDv, no significant difference was found between KHN at T1 and T0; at T7 KHN increased in comparison to T0. The initial pH mean was 7.66 for HP35% and 9.28 for HP6%LEDv; the final pH mean was 7.53 and 8.68, respectively. Conclusions: Bleaching with LEDv alone was the only treatment that didn’t reduce enamel microhardness. HP6%LEDv led to a decrease in KHN values similar to the high-concentrated gel. After seven days in artificial saliva, initial KHN was recovered. Although the pH of both gels decreased during the treatment, it remained above the critical value.