Effect of smear layer removal on bleaching of human teeth in vitro

The purpose of this study was to evaluate objectively in vitro the effectiv eness of bleaching artificially discolored teeth with or without the smear layer present using sodium perborate mixed with sterile water or 35% hydrog en peroxide (H2O2). Seventy fully developed maxillary anterior teeth were a rtificially stained with human hemoglobin and separated into one control an d four experimental groups. After the smear layer was removed on half the e xperimental teeth and left intact on the other half, all of the teeth were bleached intracoronally with sodium perborate and 35% H2O2 or sodium perbor ate plus water. The bleaching agents were applied twice over a 6-day period . The changes in tooth shade were objectively analyzed using a SP78 sphere spectrophotometer at 1, 30, and 60 days postbleaching. The presence or abse nce of the smear layer did not significantly influence the outcome of bleac hing (p > 0.05). The teeth bleached with sodium perborate and 35% H2O2 were significantly lighter than the teeth bleached with sodium perborate and st erile water (p < 0.0001) at each experimental period. Based on the findings of this study, it is not advantageous to remove the smear layer before int racoronal bleaching.