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Table 4 Color change using WI and WID values, with data from the Vita Easyshade spectrophotometer measurements, for each group of treatment in different time points. The mean, standard deviation, and statistical analysis are displayed

From: The change of teeth color, whiteness variations and its psychosocial and self-perception effects when using low vs. high concentration bleaching gels: a one-year follow-up

Assessment points Whiteness Index values WId values
37.5% Hydrogen Peroxide 6% Hydrogen Peroxide Mann-Whitney test* 37.5% Hydrogen Peroxide 6% Hydrogen Peroxide Mann-Whitney test*
Baseline 32.19 ± 2.88 31.79 ± 3.39 0.479 11.93 ± 6.04 12.23 ± 7.65 0.789
1-wk after bleaching 24.91 ± 2.85 27.63 ± 4.07 0.018 25.44 ± 4.74a 20.12 ± 7.83a 0.011
1-mth after bleaching 24.65 ± 2.94 28.20 ± 3.39 0.001 25.53 ± 6.62a 18.67 ± 6.87a 0.001
6-mths after bleaching 25.53 ± 2.63 29.31 ± 3.78 0.000 24.12 ± 4.80a 16.18 ± 6.86ab 0.000
12-mths after bleaching 24.89 ± 2.69** 27.81 ± 3.31** 0.003 24.26 ± 4.66a 18,96 ± 7.13a 0.003
  1. * for comparison between both groups in each assessment time; ** for comparison between two assessment time (1-month vs 12-month after bleaching) in each group. No significant difference was found (Wilcoxon test; p > 0.05).** for comparison between two assessment time (1-month vs 12-month after bleaching) in each group. No significant difference was found (Student t test for paired sample; p > 0.05)