Table 3.

Comparison of microhardness at the enamel surface among the groups

Type of post bleaching surface treatment	Enamel Surface
	Mean	SD	Pairwise comparisons
Group 1 (Fluoride)	446.58	53.32	a
Group 2 (Fractional CO2 laser)	429.04	29.04	a
Group 3 (Nanohydroxyapatite)	470.20	53.82	a
Group 4 (Control)	387.70	21.25	b
P-value	0.000*

^*Statistically significant difference at P<0.05.

Different letters indicate significant differences at P<0.05.