TABLE 3. Mean Knoop microhardness values and standard deviations at different distances from enamel surface, before and after bleaching treatment with different agents.

Agent	50 μm	100 μm	150 μm	200 μm
CP10	176.13 (5.10)	184.38 (5.62)	183.69 (3.53)	179.13 (5.51)
CP16	186.09 (6.60)	180.59 (7.76)	170.59 (7.46)	166.80 (6.17)
HP6.5	180.45 (5.94)	186.00 (6.75)	182.15 (5.77)	174.86 (3.48)