Effects of Enzymatic Activation of Bleaching Gels on Hydrogen Peroxide Degradation Rates, Bleaching Effectiveness, and Cytotoxicity

Abstract

SUMMARY Objectives: The aim of this study was to evaluate the effect of horseradish peroxidase (HRP) on the release of free radicals, bleaching effectiveness, and indirect cytotoxicity of a 35% hydrogen peroxide (HP) bleaching gel. Methods and Materials: First, HP degradation rates and free radical release were evaluated for 35% HP in contact or not with HRP (10 mg/mL). The bleaching gel associated or not with HRP was then applied (3 × 15 minutes) to enamel/dentin discs adapted to artificial pulp chambers, and the culture medium in contact with dentin surfaces (extract) was collected and exposed to cultured odontoblast-like cells. Membrane damage and viability of cells as well as oxidative stress were evaluated. Residual HP/free radical diffusion was quantified, and bleaching effectiveness (ΔE) was assessed. Unbleached discs served as negative controls. Results: The addition of HRP to the 35% HP bleaching gel enhanced the release of free radicals in comparison with plain HP gel. The 35% HP-mediated cytotoxicity significantly decreased with HRP in the bleaching gel and was associated with reduced HP/free radical diffusion through the enamel/dentin discs. ΔE values increased every bleaching session for HRP-containing gel relative to positive control, accelerating the whitening outcome. Conclusion: The enzymatic activation of a 35% HP bleaching gel with HRP accelerated HP degradation mediated by intensification of free radical release. This effect optimized whitening outcome as well as minimized residual HP and free radical diffusion through enamel and dentin, decreasing the harmful effects on odontoblast-like cells.

Polymeric biomaterials maintained the esthetic efficacy and reduced the cytotoxicity of in‐office dental bleaching

“…Previous studies, in which chemical catalyzers were added to a bleaching gel with 35% H 2 O 2 , and it was applied on enamel for 45 min (three sequential applications lasting 15 min each), these also reduced the cytotoxic effects caused by the traditional in-office protocol. [12][13][14] Nevertheless, these adverse effects were greater than those observed in the present research, in which the combination of SNan and PPol was used on enamel before application of the bleaching. In spite of this and the important esthetic result obtained in this study when the biomaterials were incorporated into the inoffice bleaching procedure, it is possible to consider that the transamelodentinal diffusion of H 2 O 2 and consequent cytotoxicity of the bleaching protocols tested still remained high after a single bleaching session of 45 min (three applications lasting 15 min each).…”

“…This could be explained by the fact that the HRP enzyme incorporated into the polymeric primer had high potential as a catalyst, 42,43 acting as an oxidase for potentiating oxidationreduction reactions. 15 In a previous study, Ortecho-Zuta et al 13 Li et al 44 demonstrated that black tea has polyphenolic compounds in its structure, and that these chromophores participated in the sedimentation of color on the organic substrate of teeth. 19,45 Therefore, the enamel/dentin discs used in the present research were exposed to black tea prior to the bleaching treatments, as has been done in various previous studies in this field.…”

“…Then, 100 μl of the carboxy-H 2 DCFDA (Invitrogen) probe was applied in each well and the plate was kept in an incubator (Thermo Fisher Scientific, RCO3000T-5-VBC, Asheville, NC) for 45 min. 13 After this, in each group, the excitation and emission of fluorescence was evaluated at 492 and 527 nm (Synergy H1; Biotek, Winooski, VT), respectively. In the negative control group (G1), the H 2 O 2 was substituted by ultra-pure water (Invitrogen), and the values obtained from readouts of the fluorescence was normalized by the negative control group.…”

“…On conclusion of performing the protocols lasting 45 min, established in this study, the products were removed from the enamel surface, which was carefully washed with deionized water. Then, the discs were again kept in an environment with 100% humidity for 72 h. 13 The delta E (ΔE) values were obtained before and 72 h after bleaching, by applying the follow- (after bleaching) whiteness index was calculated according to: DWI = WI after bleaching -Wibaseline. 29 The values for perceptibility (PT) and acceptability (AT) thresholds were adopted as 50:50%, ΔE were 1.2 (PT) and 2.7 (AT) 30 and ΔWI were 0.72 (PT) and 2.60 (AT).…”

Cytotoxic effects of hydrogen peroxide on periodontal cells

“…[1][2][3][4][5][6] While generally regarded as a safe agent for these applications, H 2 O 2 has a strong oxidant potential. Its effects in teeth and pulpal tissues have been well studied; [22][23][24][25][26][27] The results of our study showed, for the first time, that, in both the osteoblast and gingival fibroblast cell lines tested, exposure to a 0.05-µg/ml solution of H 2 O 2 (10-fold lower than the reportedly safe concentration of 0.68 µg/ml) elicited a cell-viability decrease of up to 50% (P<0.05), thus rejecting the first two null hypotheses. This effect was more pronounced with longer incubation times.…”