H2O2 gel bleaching induces cytotoxicity and pain conduction in dental pulp stem cells via intracellular reactive oxygen species on enamel/dentin disc

Background Bleaching is widely accepted for improving the appearance of discolored teeth; however, patient compliance is affected by bleaching-related complications, especially bleaching sensitivity. This study aimed to investigate the role of reactive oxygen species (ROS) in cytotoxicity and pain conduction activated by experimental tooth bleaching. Methods Dental pulp stem cells with or without N-acetyl-L-cysteine (NAC), an ROS scavenger, were cultured on the dentin side of the enamel/dentin disc. Subsequently, 15% (90 min) and 40% (30 min) bleaching gels were painted on the enamel surface. Cell viability, intracellular ROS, Ca2+, adenosine triphosphate (ATP), and extracellular ATP levels were evaluated using the Cell Counting Kit-8 assay, 2’,7’-dichlorodihydrofluorescein diacetate, CellROX, fura-3AM fluorescence assay, and ATP measurement kit. The rat incisor model was used to evaluate in vivo effects after 0, 1, 3, 7, and 30 days of bleaching. Changes in gene and protein expression of interleukin 6 (IL-6), tumor necrosis factor-alpha (TNFα), transient receptor potential ankyrin 1 (TRPA1), and Pannexin1 (PANX1) in dental pulp stem cells and pulp tissue were detected through RT-PCR, western blotting, and immunofluorescence. Results The bleaching gel suppressed dental pulp stem cell viability and extracellular ATP levels and increased intracellular ROS, Ca2+, and intracellular ATP levels. The mRNA and protein expression of IL-6, TNFα, TRPA1, and PANX1 were up-regulated in vitro and in vivo. Furthermore, the 40% gel had a stronger effect than the 15% gel, and NAC ameliorated the gel effects. Conclusions Our findings suggest that bleaching gels induce cytotoxicity and pain conduction in dental pulp stem cells via intracellular ROS, which may provide a potential therapeutic target for alleviating tooth bleaching nociception.

TRPA1 triggers hyperalgesia and inflammation after tooth bleaching

Hyperalgesia has become a major problem restricting the clinical application of tooth bleaching. We hypothesized that transient receptor potential ankyrin 1 (TRPA1), a pain conduction tunnel, plays a role in tooth hyperalgesia and inflammation after bleaching. Dental pulp stem cells were seeded on the dentin side of the disc, which was cut from the premolar buccal tissue, with 15% (90 min) or 40% (3 × 15 min) bleaching gel applied on the enamel side, and treated with or without a TRPA1 inhibitor. The bleaching gel stimulated intracellular reactive oxygen species, Ca2+, ATP, and extracellular ATP in a dose-dependent manner, and increased the mRNA and protein levels of hyperalgesia (TRPA1 and PANX1) and inflammation (TNFα and IL6) factors. This increment was adversely affected by TRPA1 inhibitor. In animal study, the protein levels of TRPA1 (P = 0.0006), PANX1 (P < 0.0001), and proliferation factors [PCNA (P < 0.0001) and Caspase 3 (P = 0.0066)] increased significantly after treated rat incisors with 15% and 40% bleaching gels as detected by immunohistochemistry. These results show that TRPA1 plays a critical role in sensitivity and inflammation after tooth bleaching, providing a solid foundation for further research on reducing the complications of tooth bleaching.

Efeito da aplicação prévia ou adição de dessensibilizantes em géis de peróxido de hidrogênio no esmalte clareado

This in vitro study evaluated the effect of 35% hydrogen peroxide (35HP) gels with different desensitizing agents on color, microhardness and roughness of bleached enamel. Forty enamel-dentin specimens (6x6x2 mm2) were obtained from twenty human molars. After color measurement with a spectrophotometer, the specimens were randomized into four groups (n= 10): 35HPw- 35HP without desensitizing agent; 35HPCa- 35HP with calcium; 35HPK- 35HP with 0.5% potassium nitrate; 35HPTFa- 35HPw + topical application of 5% potassium nitrate and 2% sodium fluoride (TFa). Specimens were evaluated for color (∆Eab* and ∆E00), Vickers microhardness (VHN) and, superficial and volumetric roughness (Ra and Sa, µm) using a 3D non-contact profilometer before and 1-week after bleaching. Data were analyzed by ANOVA and Tukey tests (p< 0.05). Both treatment groups promoted a significant whitening effect and there was no difference between them for any color parameters evaluated. All groups reduced significantly the VHN, but the 35HPK showed a reduction significantly major than the other groups. 35HPCa and 35HP+TFa did not avoid the of Ra and Sa increasing. It can be concluded that 35HP bleaching gels with different desensitizing agents did not affect the whitening efficacy. However, all treatments decreased the microhardness, the addition of calcium into 35HP gel and the application of TFa before bleaching did not revert the enamel roughness under in vitro conditions.

Efficacy and Safety of Bleaching Gels According to Application Protocol

SUMMARY Objectives: This study evaluated bleaching efficacy, enamel microhardness, and roughness of highly concentrated hydrogen peroxide (HP) gels (35%–40%) using different application protocols. Gel decomposition and pH alteration were also analyzed. Methods and Materials: Bovine enamel/dentin specimens were divided into groups according to the bleaching gel—Pola Office Plus (POP–SDI, 37.5% HP), Opalescence Boost (OPB–Ultradent, 40% HP), Whiteness HP (WHP–FGM, 35% HP)— and application protocol—single application (SA) and multiple application (MA) during the in-office session. Deionized water was used in control group (no bleaching). Thus, seven final groups were obtained (n=15/group). Color (CIE L*a*b*), surface microhardness (SMH), and roughness (Ra) were assessed before/after treatments. The pH of gels was measured, and HP concentration was determined with potassium permanganate titration method in different times. Data were submitted to analysis of variance and Tukey tests (5%). Results: All gels presented similar and clinically acceptable bleaching efficacy (ΔE&gt;2.7) for both SA and MA, as well as no significant differences for SMH and Ra comparing the two protocols in the same gel. Peroxide decomposition significantly increased with time, but final gel concentrations were still high after 45 minutes (32.29% POP; 38.45% OPB; and 32.74% WHP). The pH decreased over time (initial - after 45 min) for WHP (6.83±0.07 - 5.81±0.06), but minimal alterations were observed for POP (8.09±0.09 - 7.88±0.07) and OPB (7.82±0.11 - 7.87±0.07). Conclusions: Peroxide decomposition was very low for all gels tested, and pH remained stable for POP and OPB gels. Bleaching protocol did not influence whitening efficacy and hazardous effects over enamel, thus potentially there was no clinical significance. Therefore, for the products tested, there is no evidence for recommending the gel change during the bleaching session.

A Spectrophotometric Study on Light Attenuation Properties of Dental Bleaching Gels: Potential Relevance to Irradiation Parameters

Background: During in-office bleaching, appropriate light sources are applied in order to enhance the activity of the bleaching gels applied onto teeth. For this method to be effective, a high absorption of light within the gel is necessary. Variation in the light attenuation capability of the gel, the duration of application and light activation can contribute towards safety hazards associated with this procedure. Methods: In this study, seven different gels and hydrogen peroxide have been evaluated for their optical properties by means of spectrophotometry (440–1000 nm). The transmitted light spectrum was used to estimate the intensity loss for each gel. The mean intensity decreases observed were statistically analysed using an analysis of variance (ANOVA). Results: The five more-pigmented gels tested indicated a very similar intensity loss of around 80%, whereas the remaining two gels showed significantly less attenuation (predominantly, p < 10−6). Conclusions: Throughout the spectrum of wavelengths examined, and according to the underlying studies evaluated, five of the gels assessed demonstrated an attenuation high enough to possibly avoid overheating of the underlying enamel dentine and pulp. An evaluation of appropriate irradiation parameters is proposed.

Do bleaching gels affect the stability of the masking and caries-arresting effects of caries infiltration—in vitro

Objectives The aim of this study was to evaluate the influence of different bleaching gels on the masking and caries-arresting effects of infiltrated and non-infiltrated stained artificial enamel caries lesions. Materials and methods Bovine enamel specimens (n = 240) with each two sound areas (SI and SC) and each two lesions (DI and DC) were infiltrated (DI and SI), stained (1:1 red wine-coffee mixture,70 days), and randomly distributed in six groups to be bleached with the following materials: 6%HP (HP-6), 16%CP (CP-16), 35%HP (HP-35), 40%HP (HP-40), and no bleaching (NBl,NBl-NBr). Subsequently, specimens were pH-cycled (28 days, 6 × 60 min demineralization/day) and all groups except NBl-NBr were brushed with toothpaste slurry (1.100 ppm, 2×/day, 10 s). Differences in colorimetric values (ΔL, ΔE) and integrated mineral loss (ΔΔZ) between baseline, infiltration, staining, bleaching, and pH cycling were calculated using photographic and transversal microradiographic images. Results At baseline, significant visible color differences between DI and SC were observed (ΔEbaseline = 12.2; p < 0.001; ANCOVA). After infiltration, these differences decreased significantly (ΔEinfiltration = 3.8; p < 0.001). Staining decreased and bleaching increased ΔL values significantly (p ≤ 0.001). No significant difference in ΔΔE was observed between before staining and after bleaching (ΔEbleaching = 4.3; p = 0.308) and between the bleaching agents (p = 1.000; ANCOVA). pH-cycling did not affect colorimetric values (ΔEpH-cycling = 4.0; p = 1.000). For DI, no significant change in ΔZ during in vitro period was observed (p ≥ 0.063; paired t test). Conclusions Under the conditions chosen, the tested materials could satisfactorily bleach infiltrated and non-infiltrated stained enamel. Furthermore, bleaching did not affect the caries-arresting effect of the infiltration. Clinical relevance The present study indicates that bleaching is a viable way to satisfactorily recover the appearance of discolored sound enamel and infiltrated lesions.

Effects of 16% Carbamide Peroxide Bleaching on the Surface Properties of Glazed Glassy Matrix Ceramics

Objective. To determine the influence of the home bleaching agent, Opalescence PF, on the surface roughness and microhardness of glazed glassy matrix CAD-CAM ceramics. Materials and Methods. The 28 sintered leucite- and lithium disilicate-reinforced ceramic specimens (IPS Empress CAD and IPS e.max CAD) were divided into control and bleached groups. The home bleaching agent was applied to specimens of bleached groups for 7 days. The surface roughness and microhardness of all specimens were measured. A scanning electron microscope was used to evaluate the surface properties. The data were statistically analyzed by two-way ANOVA. Results. The control e.max CAD showed the lowest surface roughness values. For both Empress and e.max CAD, surface roughness was significantly higher for the bleached group (p<0.05). No significant differences in microhardness were observed. Conclusions. According to our study, patients should be careful when using home bleaching agents because whitening agents can affect the mechanical properties of full ceramic restorations like e.max CAD and Empress CAD. Ceramic polishing may be required in clinical situations where ceramic restorations are accidentally exposed to bleaching gels.