Clinicians notice that patients sometimes do not show the same amount of satisfaction with the result of dental treatment as therapists would expect so the goal of this study was to examine the extent to which patients perceive a difference for tooth whitening. The study was designed as a double blind, placebo-controlled randomized trial. The subjects were 60 students of dental medicine, aged 19 to 28 years (75% women) randomly assigned to an experimental (N =30) and control group (N = 30). Frontal teeth of both jaws of the experimental group were bleached with whitening gel (Signal Lamp Easy Plus Professional Fast signal set signal, Unilever, Argentina)during 30 minutes, and control group was subjected to the same gel process without the active substance. Before and one week after the procedure all subjects answered psychometric instruments of quality of life Oral Health Impact Profile (OHIP), Psychosocial impact of dental aesthetics questionnaire (PIDAQ) and Orofacial Esthetic Scale (OES). The color of the upper right incisors was determined before and after the procedure by calibrated digital spectrophotometer to all the subject (SpectroShade Handy Dental Type 713000, MHT, Verona, Italy). Using the CIE L.a.b. formula, chromaticity, translucency and brightness were determinate. Color and chromatic change was significantly higher in the active compared to the placebo group (3.8±1.5 vs. 1.7±1.5 i -3.2±1.5 vs. 0.0±1.1; p<0.001). Subjects whose teeth were bleached reported significantly increased OES and decrease of psychological (PI) and social influence (SI) in PIDAQ, orofacial appearance (OFI) and psychosocial impact (PSU) of OHIP. In the control group there was no objective change of color but the subject also reported increase of OES and decrease of OFA, PI and dental self-esteem. SI is the only dimension that is significantly lower in the active compared to the control group (-2.0±3.4 vs. 0.4±2.6; p=0.036). In conclusion, it seems that people cannot detect the color change due to teeth whitening, and the placebo effect has a significant importance.