Objective: To determine the susceptibility of teeth to darken after bleaching with 35% hydrogen peroxide and 16% carbamide peroxide. Method and Materials: Thirty-eight premolars were covered with varnish and the mesiobuccal facets polished up to 0.04 µm, leaving a flat surface. Thirty-six of these premolars were then randomly assigned to 3 groups and the shade of the polished surfaces recorded using a Vita shade guide set in a value disposition. According to the manufacturers' instructions, 12 samples were bleached with 35% hydrogen peroxide (in-office group) and 12 samples with 16% carbamide peroxide (at-home group). The 12 samples in the control group were not bleached. Two days later, the shades of the bleached teeth were recorded; all samples were immersed in silver nitrate 50% for 4 hours, rinsed, and fixed (using a dithioxamide solution) for 24 hours. Polished surfaces were cleaned and the samples' shade recorded and analyzed using ANOVA. The remaining 2 premolars were bleached the same as those in the test group and analyzed using atomic force microscopy. Results: The mean shade values were 6.2, 3.7, and 10.9 for in-office samples; 8.8, 1.7, and 6.1 for at-home samples; and 7.8 and 9.4 for the control group. After pigmentation, the at-home group had a lighter shade than the in-office group (P = .001). Atomic force microscopy showed no significant surface differences. Conclusion: While all the samples were susceptible to pigmentation, this tendency was greater following application of 35% hydrogen peroxide. Keywords: atomic force microscopy, at-home bleaching, in-office bleaching, peroxide, pigmentation, tooth bleaching