Table 2b. Variations in colorimetric measurements (L*a*b*±SD) of darker teeth at three time intervals. Means with same superscripts in a column within the same group are not significantly different at P<0.05 .

L*	Opalescence Oh	Treswhite Supreme	Hollywood Smiles
Before Bleaching	61.5A±3.2	62.9a±2.8	60.7X±3.4
After Bleaching	79.5B±3.3	77.2b±2.7	70.2Y±3.3
After Staining	67.3C±3.2	65.5a±5.1	63.0X±2.5
a*	Opalescence Oh	Treswhite Supreme	Hollywood Smiles
Before Bleaching	24.4A±3.7	21.8a±4.2	22.6X±2.8
After Bleaching	8.4B±3.7	7.6b±2.6	6.7Y±2.4
After Staining	13.6C±2.3	11.5c±3.1	10.1Z±2.6
b*	Opalescence Oh	Treswhite Supreme	Hollywood Smiles
Before Bleaching	40.1A±1.8	34.4a±6.5	33.6X±4.2
After Bleaching	13.4B±4.7	13.7b±4.5	21.3Y±4.5
After Staining	13.8B±2.8	12.3b±2.3	21.6Y±3.6