Objective: To observe the effect of 10% carbamide peroxide bleaching agent on the enamel, dentin, and cementum of human teeth. Method and Materials: Teeth were treated with one of two 10% carbamide peroxide bleaching agents (3M Zaris, 3M Espe; Nite White Excel, Discus Dental) for 2 hours/day for 7 or 14 days. Treated teeth and 10 additional nontreated teeth were immersed in 50% silver nitrate solution. The prepared surface was then viewed under a confocal laser scanning microscope, photomicrographs were taken, and the degree of penetration of silver nitrate into the structure of bleached teeth was determined. Results: No penetration was seen in enamel of any group, and statistical analysis showed a significant difference in the degree of penetration only between treated and nontreated groups of dentin and cementum (P .05). No significant difference was seen between 7 and 14 days. Conclusion: Although the effect was not significant, further investigation is needed to determine the effect of long-term treatment of carbamide peroxide on human tooth substance. Schlagwörter: carbamide peroxide, cementum, dentin, enamel, penetration, silver nitrate