Effect of light activation on tooth whitening efficacy and hydrogen peroxide penetration: an in vitro study.

Objectives: To determine the effect of light activation on tooth whitening efficacy and hydrogen peroxide penetration into the pulp cavity and correlate tooth color change with penetration levels.
Methods: Extracted human canines (40) were randomized into four groups, Group A: placebo gel, Group B, placebo gel with light activation, Group C: 40% hydrogen peroxide gel, and Group D: 40% hydrogen peroxide gel with light activation. Treatment was performed three times, at 1-week intervals. Hydrogen peroxide penetration (HPP) was estimated spectrophotometrically and specimen color measured using the Vita Easy Shade Compact at baseline, after whitening, 1-h, 1-day, 1-, 4-, 8-, 12-, 16-, 20-, and 24-week post-whitening. Color change was measured per Commission Internationale de l'Eclairage methodology. ANCOVA was performed to compare color change and HPP level among the four groups. Partial nonparametric correlations between color change and HPP levels were performed with rank transformations. Tests of hypotheses were two-sided with alpha level of 0.05.
Results: Greater HPP was observed in Groups C and D compared to Groups A and B (p<0.001). Highest overall color change (ΔE*ab) values after treatment were observed in Group D and remained higher than Groups A-C (p<0.01). Changes in lightness and in the yellow-blue dimension (ΔL* and Δb*) were higher in Groups C and D compared to Groups A and B from post-whitening until 24 weeks (p<0.05). HPP levels were not correlated to color change (p>0.05).
Conclusions: Light activation enhanced whitening efficacy without affecting hydrogen peroxide penetration levels.
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