At-Home Bleaching: Color Alteration, Hydrogen Peroxide Diffusion and Cytotoxicity.

This study evaluated the color change, cytotoxicity and hydrogen peroxide (HP) diffusion caused by different home bleaching protocols: 10% carbamide peroxide (CP) for 3 or 1.5 h, 6% hydrogen peroxide for 1.5 h or 45 min. To quantify the peroxide penetration, disks of bovine teeth were placed in artificial pulp chambers (APCs) containing acetate buffer, which was collected for evaluation in a spectrophotometer. For analysis of cytotoxicity, specimens were adapted in APCs containing culture medium, which subsequently was applied on MDPC-23 odontoblast-like cells for 1 h. Cellular metabolism was evaluated by methyl tetrazolium (MTT) assay and the color change of the specimens was analyzed using the CIE L * a * b * system. The data were submitted to ANOVA and Fisher test (α=5%). The treatment with 10% CP for 3 h was the most effective, and 6% HP for 45 min produced the lowest color change. The groups 10% CP for 1.5 h and 6% HP for 45 min had the lowest trans-enamel dentinal HP penetration, and the 6% HP for 1.5 h had the highest. None of the protocols affected cellular metabolism and morphology. In conclusion, reduced peroxide exposure time reduced the bleaching result; higher HP diffusion did not mean higher effectiveness.

Effect of peroxide bleaching on the biaxial flexural strength and modulus of bovine dentin.

OBJECTIVE: This study evaluated the effects of carbamide peroxide and hydrogen peroxide on the biaxial flexural strength and flexural modulus of bovine dentin. MATERIALS AND METHODS: Thirty coronal dentin disks (0.5 mm thick × 6.0 mm diameter) were prepared from bovine teeth. The disks were randomly divided into three groups (n=10): A control group (unbleached), a group bleached with 10% carbamide peroxide (8 h at 37°C), and a group bleached with 38% hydrogen peroxide (three 10 min applications at 37°C). The specimens were tested in a biaxial flexural apparatus held in a universal testing machine at 1.27 mm/min until failure occurred, and the biaxial mechanical properties were calculated. For each test parameter, the data were statistically analyzed by Fisher's PLSD test (predetermined α = 0.05). RESULTS: The group bleached with 38% hydrogen peroxide demonstrated significantly lower flexural strength than the unbleached control group. Hydrogen peroxide treatment resulted in a significantly lower flexural modulus compared with the control group and with carbamide peroxide bleaching. CONCLUSION: Exposure of dentin to hydrogen peroxide significantly reduced both the flexural strength and the flexural modulus compared with the no-treatment control, whereas exposure to carbamide peroxide did not significantly affect either parameter.

Color alteration, hydrogen peroxide diffusion, and cytotoxicity caused by in-office bleaching protocols.

OBJECTIVES: This study evaluated the color alteration, cytotoxicity, and hydrogen peroxide (HP) diffusion associated with different in-office bleaching protocols. MATERIALS AND METHODS: Bovine enamel/dentin disks were subjected to three bleaching sessions with 35 % HP (three 15-min applications), 35 % HP (one 45-min application), or 20 % HP (one 45-min application). The control group was not bleached. Before bleaching, the disks were adapted to artificial pulp chambers positioned in compartments containing 1 ml of acetate buffer or medium, so that the dentin remained in contact with these substances. Immediately after bleaching, the HP that diffused through the disks was stabilized by acetate buffer and was quantified (two-way repeated measures ANOVA/Fisher's protected least significant difference (PLSD) test; α = 5 %). Cells of mouse dental papilla cell-23 (MDPC-23) were incubated in this culture media for 1 h, followed by analysis of cellular metabolism (methyl tetrazolium assay) (one-way ANOVA/Tukey test; α = 5 %) and morphology (scanning electron microscopy). The specimen color alteration (ΔE) was analyzed by reflection spectrophotometry (two-way repeated measures ANOVA/Fisher's PLSD test; α = 5 %). RESULTS: All protocols showed equal effectiveness at the end of the treatment. HP diffusion was significantly higher in the groups bleached with 35 % HP. Reapplication of 35 % HP resulted in increased diffusion only in the first session; however, the decrease in cell metabolism was similar for all studied protocols. CONCLUSION: Despite greater peroxide diffusion in the groups treated with 35 % HP, all protocols showed the same effectiveness and were cytotoxic to MDPC-23 cells. CLINICAL RELEVANCE: Bleaching protocols using high HP concentrations should be avoided because they exert aggressive actions on odontoblast-like cells.