The use of oxidizing agents for tooth whitening is widely used in dental practice. However, the effect of this procedure on the adhesion of biomaterials is not totally understood. In order to study the behavior of adhesives with the surface of bleached enamel, we used healthy teeth extracted for orthodontic indication (n = 20). The crowns of the specimens were divided in three equivalent areas. One of these areas was treated with H2O2 35% (Opalescence Xtra Ultradent ). Another area with carbamide peroxide 10% (Platinum Daytime Colgate ). The third area served as control. As a positive control H2O2 35% (Fluka) was used. The adhesion technique was realized with Adper Scotch Bond (3M ) whose primer was labeled with Rhodamine B (1 mg / ml). 100 μm thick sections were obtained of each specimen, which were observed and photographed in a confocal laser scanning microscope. The images were morphometrically analyzed. It was noted that in the enamel bleached with H2O 35% or carbamide peroxide10% the depth of penetration, characterized by a red fluorescence in prismatic and interprismatic enamel was significantly lower than in the control specimens. These observations allow us to infer that the tooth whitening produces morphological changes that alter the penetration of adhesive biomaterials and that the lack of tensile strength could be due to a mechanical effect and not only due a failure in the polymerization of adhesive by the presence of oxidants radicals.