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Purpose: The use of different H2O2 concentrations for in-office bleaching has been questioned. Thus, theaim of this study was to evaluate the efficiency of laser bleaching on color changes and surface roughnessof bovine enamel with different peroxide concentrations. Materials and methods: Forty eight bovine incisors cleaned and labial surface polished up to #1200. Halfof them were artificially stained with black tea and divided into three subgroups and bleached according tothe concentration of H2O2 (15%, 25% and 35% ) (n=8). Specimens were bleached with laser hybrid system(DMC Whitening Lase II, Sao Paulo, Brazil). CIE Lab color system was used to evaluate color using VitaEasyshade Spectrophotometer (Ivoclar Vivadent, Liechtenstien). The remaining specimens were used forsurface roughness evaluation following bleaching. The enamel roughness (Ra) values were measured by StylusProfilometer (Suf-Corder SE 1200, Tokyo, Japan) and Atomic force microscopy (AA3000,Bosten,USA)before and after bleaching. Data were analyzed with Paired sample T-test to evaluate color changes andRa values at each concentration. ANOVA and Tukey test were used to evaluate the difference between thegroups with different bleaching agent concentrations. All tests were computed at 5% significance level. Results: Significant increases in degree of lightness (L*) values observed following bleaching at all concentrations.Different concentrations of peroxide produced significantly different Ra values. Bleachingwith 35% agent produced significantly higher L* value than 15% but similar to 25%. Exposing enamel tohigh peroxide concentration (25% and 35%) significantly increased Ra value in comparison to unbleachedenamel.Conclusion: Color changes and surface roughness of bovine enamel were influenced by hydrogen peroxideconcentrations of DMC laser bleaching system.

Tooth bleaching --- Hydrogen peroxide --- DMC Laser --- Bovine