Color Change and H₂O₂ Enamel/Dentin Diffusion after Carbamide Peroxide Protocols

Objective: To evaluate the enamel color change and the transenamel/transdentinal H₂O₂ diffusion after application of carbamide peroxide (CP) gel in different protocols. Methods: Enamel/dentin discs adapted to artificial pulp chambers were placed in wells containing 1 mL of acetate buffer. The following groups (n=10) were established: G1: control (no treatment); G2: 3 applications of a 35% H₂O₂ gel for 15 minutes (positive control); G3 and G4: 3 or 1 applications of 37% CP gel for 20 minutes, respectively; G5 and G6: 3 or 1 applications of 37% CP gel for 10 minutes, respectively. Immediately after the bleaching procedures, 100μL of the acetate buffer solution was collected and transferred to a glass tube containing 200μL of leuco crystal violet and 50μL of horseradish peroxidase, producing a blue solution. The optical density of the blue solutions was determined by spectrophotometer and converted into micrograms of H₂O₂ (ANOVA/Tukey;a=0.05). Before and after the bleaching procedures, the tooth color was assessed according to the CIELab system using a spectrophotometer (Kruskal-Wallis/Mann-Whitney;a=0.05). Results: Concerning H₂O₂ diffusion, there was no significant difference between the positive control (G2) and G3. For G4, G5 and G6, the amount of H₂O₂ that diffused across enamel and dentin was significantly lower when compared to G2 and G3, with no statistical difference among them. Regarding color change, only G2 and G3 presented a significant color change when compared to control group (G1), with no significant difference between them (p>0.05). For those groups, a lighter and brighter enamel was observed.  Conclusion: The bleaching protocol using a 37% CP gel applied 3 times for 20 minutes each application promoted a significant tooth bleaching. In spite of the lower amount of transenamel/transdentinal diffusion of H₂O₂, the reduction of frequency and application time of the 37% CP gel caused no tooth bleaching