Purpose: To evaluate the effect of different in-office and at-home bleaching agents, applied for different periods on enamel susceptibility to erosion and brushing abrasion, in order to help dentists provide better treatment recommendations for patients that can minimize potential adverse side effects of tooth whitening treatments. Methods:The following experimental factors were considered: three in-office bleaching treatments;(G1-Opalescence Boost 40% hydrogen peroxide, G2-iBrite Plus 30% hydrogen peroxide, G3-Gel White In-Office Dental Bleaching 16% carbamide peroxide), and three at-home bleaching treatments;(G4-Opalescence PF 20%, G5-Opalescence PF 15%, G6-Opalescence PF 10%); two different frequencies of applications; and two models (erosion only/erosion and abrasion). Two control groups were used; G7 for in-office and G8 for at-home bleaching treatments. Control groups specimen remained in artificial saliva during the period corresponding to bleaching procedures. Study blocks were formed by gluing two enamel slabs together, generating 80 study blocks that were distributed among 8 groups. Each group was bleached with its assigned bleaching agent, then further subdivided into two subgroups where half the slabs were subjected to another cycle of bleaching treatment. The blocks of each bleached group and corresponding control groups were then subjected to a one-day cycling model. Cycling consisted of citric acid erosive challenges and toothbrushing abrasion, where only one side of the blocks was brushed. Artificial saliva was used to remineralize the specimens after erosive and abrasive challenges, and as storage media between bleaching treatments. After each erosion/abrasion cycle, surface loss (in micrometers) was determined by noncontact profilometry. Data were analyzed using ANOVA (α=0.05).Results: Bleaching did not increase enamel susceptibility to erosion or abrasion regardless of the bleaching gel concentration or frequency of application. Bleaching gels containing fluoride, calcium or potassium nitrate might have offered protection against enamel erosion and abrasion. Toothbrushing abrasion was the single most important factor contributing to tooth wear regardless of bleaching. Although it may not be of clinical significance, in-office bleaching caused more surface loss than at-home bleaching.