TABLE 1. Mean microhardness values and standard deviations for each bleaching agent at the different time intervals.

Bleaching agent	Baseline	Time interval 21 days	14 days post-treatment
Control	334.7 ± 51.7 Ba	322.6 ± 75.9 ABa	339.5 ± 44.3 Aa
Day White	2Z 268.0 ± 78.1 Bab	297.0 ± 32.0 ABab	330.8 ± 23.0 Aab
Platinum	258.7 ± 111.5 Bb	274.4 ± 39.3 ABb	308.4 ± 55.1 Ab

Values followed by same capital letters horizontally and same small letters vertically are not significantly different by ANOVA and Tukey test (p<0.05).