Effects of 10% carbamide peroxide on the subsurface hardness of enamel

The purpose of this in vitro stuily was to determine the effects of two 10% carbamide peroxide bleaching solutions on the hardness of enamel from the stirface to the dentinoenamel junction. Fifteen anterior teeth were sectioned faciolingualiy. and their roots were removed. Half of each crown was bleached and half served as its own control. Specimens were bleached with two convtterically available 10% carbamide peroxide solutiorts (Proxigel and Gly-Oxide) for 241-hourperiods. A visible color change occurred. Teeth were embedded in acrylic resin rings, sanded with progressively finer silicon carbide papers, and polished. The polishing process removed ttpproximatelv 800 µm of the cut tooth surface. Specimens were tested with a microhardness tester and a Knoop diamond under a 35-g load; measurements were taken along the cut stirface from the outer enamel surface to the dentinoenamel junction. Matching depths from control and test specimens were compared. For teeth treated with Gly-Oxide, no statistically significant changes in enamel hardness were evident at any depth. For teeth treated with Proxigei, no significant changes in hardness were evident at 50 µm or deeper. A statistically significant decrease in hardness was noted in the outer 25 µm of the enamel surface. It is unknown whether this decrease would have an effect clinically because the remineralizing effects of saliva should resolve any surface change.