Peroxide gels are effective in changing tooth colour but their effect on restorative materials has been poorly studied. The purpose of this investigation was to assess the impact of a commercially available whitening gel containing hydrogen peroxide and a sodium percarbonate formulation on the surface of restorative materials. A total of 12 subjects participated in a double-blinded crossover study. Each wore an intra-oral appliance containing five bovine enamel blocks restored with amalgam, posterior composite, microfilled composite, glass ionomer cement and porcelain. Appliances were worn continuously for 14 days and whitening products were applied twice daily. After 14 days the appliances were removed and values for roughness (R(a)) were obtained using atomic force microscopy. Mean values of R(a) were assessed between baseline and 14 days, and although minor variations were seen, there were no statistically significant differences detected for any material or any whitening product.