Effects on gastric mucosa induced by dental bleaching--an experimental study with 6% hydrogen peroxide in rats

Assessment of Oxygen Expansion during Internal Bleaching with Enamel and Dentin: A Comparative In Vitro Study

Internal bleaching is a conservative, non-invasive, and simple treatment that is frequently performed in daily clinical practice. The present in vitro study analyzes the oxygen expansion of different bleaching agents resulting from the oxidation reaction when interacting with enamel and dentin. Enamel and dentin were crushed separately until obtaining a fine powder with particles of an approximate size between 0.06 and 0.2 mm. Each enamel and dentin sample were mixed with 37% carbamide peroxide (CP 37%), 30% hydrogen peroxide (HP 30%), sodium perborate (SP) combined with HP 30% (HP 30% + SP) and SP with distilled water (SP). A total of 280 1 mm diameter glass tubes were used with 70 for each bleaching agent (30 for powdered enamel evaluation, 30 for powdered dentin evaluation, and 10 controls). The bleaching agents were placed in the prepared tubes immediately after mixing the components. As expansion occurred, the oil inside the tube was displaced, through which the resulting expansion was evaluated and measured for 10 days. A significant expansion was observed that varied in magnitude according to the bleaching agent and the tooth structure used. Student's t test and Welch's ANOVA were used to analyze the data obtained. The highest mean expansion of both enamel and dentin was observed with 30% HP (66.6 mm for enamel, 94.5 mm for dentin) followed by HP 30% + SP (48.6 mm for enamel, 52.7 mm for dentin), CP 37% (38.4 mm for enamel, 52.6 mm for dentin) and finally SP with water (12.7 mm for enamel, 4.4 mm for dentin). It was observed that the expansion in the SP group with enamel was significantly lower than in the rest of the groups, while that registered for HP 30% was significantly higher. (p < 0.001). The results with dentin were similar, with a significantly lower expansion for SP and higher for HP 30% (p < 0.001). The oxygen expansion observed as a result of the interaction between bleaching agents and dental tissues could contribute to improving our understanding of bleaching and its results. These results suggest that bleaching agents react with the organic component of the tooth structure.

Novel in-office peroxide-free tooth-whitening gels: bleaching effectiveness, enamel surface alterations, and cell viability

To evaluate the bleaching ability, the effect on enamel surface and cytotoxicity of novel tooth-whitening formulations containing papain, ficin, or bromelain. Forty bovine dental discs (6 cm ×4 cm) were pigmentated and randomly allocated into the following groups (n = 10): Group 1, 20 wt% carbamide peroxide (control); group 2, 1% papain-based whitening; group 3, 1% ficin-based whitening; and group 4, 1% bromelain-based whitening. The whitening gels were prepared and applied on the enamel three times per day once a week, for 4 weeks. Color measurement was obtained by CIEDE2000. Enamel Knoop microhardness and roughness were evaluated. The WST-1 assay was used to evaluate the cell viability of mouse fibroblast cells (L929). Data were statistically analyzed by one-way analysis of variance (ANOVA) and Student Newman Keuls's post hoc test at α = 0.05 significance level. Bromelain, ficin-based, and carbamide peroxide bleaching gels showed a similar color change (p < 0.001). Higher enamel hardness decrease and higher enamel roughness were caused by the carbamide peroxide (p < 0.05). The experimental whitening gels did not affect cell viability. Tooth bleaching gels containing bromelain, papain, or ficin have substantial clinical potential to be used in the development of peroxide-free tooth whitening gels.

Cytotoxic Effects of Zoom® Whitening Product in Human Fibroblasts

Tooth whitening procedures are increasing; however, side effects can occur, such as damage to pulp cells, by the whitening products. This study aims to assess the cellular effects promoted by a whitening product, namely, the oxidative stress fostered by the active agent hydrogen peroxide, with and without photoactivation. Additionally, if cellular recovery occurred, we intended to determine the time point where cells recover from the tooth whitening induced damage. Human fibroblasts were exposed to hydrogen peroxide, Zoom^®, Zoom^® + irradiation, and irradiation alone. The following analysis was performed: metabolic activity evaluation by the MTT assay; cell viability, mitochondrial membrane potential, peroxides production, superoxide radical production, and reduced glutathione expression by flow cytometry. We determined the IC₅₀ value for all groups, and a dose-dependent cytotoxic effect was verified. At the times analyzed, hydrogen peroxide groups showed no metabolic activity recovery while a cell recovery was observed after 24 h (Zoom^®) and 48 h (Zoom^® + irradiation). Cell death was seen in hydrogen peroxide and Zoom^® + irradiation groups, mainly by apoptosis, and the irradiation had a cytotoxic effect per se. This in vitro study supports that whitening products with moderate hydrogen peroxide (HP) concentration have a temporary effect on cells, allowing a cellular recovery.

Preemptive Use of Piroxicam on Tooth Sensitivity Caused By In-Office Bleaching: A Randomized Clinical Trial

This clinical trial evaluated the effect of preemptive use of the non-steroidal anti-inflammatory drug piroxicam in a single dose 30 min prior to in-office bleaching on the prevention of tooth sensitivity (TS) reported by patients. Fifty patients were submitted to two sessions of in-office tooth bleaching with 35% hydrogen peroxide used for 2 sessions, each consisting of a single 45-min application, with an interval of 7 days between session. Thirty minutes prior to the procedure, the patient randomly received a single dose of piroxicam (200 mg) or placebo in a double-blind, randomized, crossover design. The TS was evaluated using verbal rate (VRS) and visual analog (VAS) scales during the bleaching procedure and at 24 h after each session. The color changes were assessed by the Vita Bleachedguide scale 1 week after each bleaching session. Risk of TS was calculated from the VRS and analyzed by the McNemar test, while the level of TS was analyzed by the Mann-Whitney test. For the VAS, t-tests were used to compare data from the treatments at each assessment time. Data regarding color changes were subjected to Wilcoxon and Mann-Whitney tests (α=0.05). The preemptive administration of piroxicam did not affect the risk and level of TS compared to placebo, irrespective of the assessment time. The treatment sequence did not affect bleaching effectiveness. In conclusion, the administration of a single dose of piroxicam prior to in-office tooth bleaching was unable to significantly reduce the risk and level of TS.

Chronic exposure to 35% carbamide peroxide tooth bleaching agent induces histological and hematological alterations, oxidative stress, and inflammation in mice

Previous studies have demonstrated the side effects of tooth whiteners on the gastric mucosa. However, the impact of dental bleaching products on the liver, kidney, and heart remains obscure. The present study investigated the toxic potential of 35% carbamide peroxide (CPO) containing tooth whitening product (TWP) on the liver, kidney, heart, and stomach of mice, pointing to the role of oxidative stress and inflammation. Mice received 250 or 500 mg/kg body weight CPO-TWP orally for 3 weeks and samples were collected for analyses. Both doses of CPO-TWP induced a significant increase in circulating liver, kidney, and heart function markers. CPO-TWP-administered mice showed several histological alterations and a significant increase in liver, kidney, heart, and stomach lipid peroxidation levels along with diminished glutathione, superoxide dismutase, and catalase. In addition, administration of CPO-TWP provoked anemia, leukocytosis, and a significant increase in circulating levels of pro-inflammatory cytokines. In conclusion, exposure to 35% CPO-TWP induced functional, histological, and hematological alterations, oxidative stress, and inflammation in mice. Therefore, the frequent use of tooth bleaching agents should be monitored very carefully to avoid the application of excess amounts as well as the intake.

Association Between In-Office And At-Home Tooth Bleaching: A Single Blind Randomized Clinical Trial

This controlled randomized clinical trial evaluated the effect of associating at-home and in-office bleaching procedures on tooth sensitivity (TS) and bleaching effectiveness. Forty patients subjected to on session of in-office bleaching with 38% peroxide hydrogen. Subsequently, the patients were randomly allocated to receive a second session of in-office bleaching or to use a tray containing 10% carbamide peroxide delivered during 7 consecutive days. The worst TS score reported during or after each bleaching procedure was recorded using a verbal rating scale and TS risk (score different from 0) was calculated. Color changes were measured 7 days after each in-office session (for patients receiving in-office procedures only) or after the end of at-home bleaching (for the combined protocol), and 6 months after the last procedure for both bleaching protocols. Color was assessed by a spectrophotometer and by color match with the Vita Classical and Bleach guide scales. Statistical analyses were carried out to assess possible differences between the protocols regarding the outcomes and to analyze the effect of time of assessment on color changes. The bleaching protocol did not affect the risk for and the maximum level of TS reported, irrespective of the time of assessment. In the color evaluation, the bleaching protocol also did not affect the ultimate tooth color. In conclusion, after one in-office bleaching session, there was no difference in bleaching effectiveness and TS between performing a second in-office session and associating it with 1-week at-home bleaching.

Hydrogen peroxide promotes gastric motility in the newborn rat

BACKGROUND

When compared with infant formula, human milk enhances gastric emptying in preterm infants. Hydrogen peroxide (H₂O₂) is present in large quantities in human milk that has an antimicrobial role for the mother and infant. In vitro adult rat studies suggest that H₂O₂ facilitates gastric motor contraction. Hypothesizing that H₂O₂ enhances gastric motility, we investigated its effects on the newborn rat stomach tissue.

METHODS

Rat newborn and adult gastric fundic segments, or their smooth muscle cells, were used to evaluate the muscle response to H₂O₂ exposure. Tissue expression of Rho kinase 2 (ROCK-2; Western blot), its catalase activity, and H₂O₂ content (Amplex Red) were measured. H₂O₂ gastric mucosal diffusion was evaluated with Ussing chambers.

RESULTS

In both newborn and adult rats, H₂O₂ induced gastric muscle contraction and this response was attenuated by pre-incubation with the antioxidant melatonin. H₂O₂ passively diffused across the gastric mucosa. Its effect on the muscle was modulated via ROCK-2 activation and inhibited by melatonin.

CONCLUSION

H₂O₂, at a concentration similar to that of human milk, promotes gastric motility in the rat. To the extent that the present findings can be clinically extrapolated, the human milk H₂O₂ content may enhance gastric emptying in neonates.

Impact of Microabrasion on the Effectiveness of Tooth Bleaching

The aim of the present study was to evaluate the effect of prior microabrasion on the teeth color change and tooth bleaching effectiveness. Eight sound molars were mesio-distally sectioned and the halves were randomly allocated to receive enamel microabrasion or non-abrasion (control) in one of surfaces (buccal or lingual), while the remaining surface received the other treatment. The tooth color on baseline was evaluated by spectrophotometer (CieL*a*b system). After the microabrasion procedure, the tooth color was measured again. Following, the specimens were bleached with 35% hydrogen peroxide for two sessions with one-week interval. The color was re-evaluated 7 days after each section and 30 days after the second session. The effect of enamel microabrasion on color changes was evaluated by paired T-test. Deltas L*, a*, b*, and E were calculated and data submitted to 2-way repeated measure ANOVA followed by Tukey`s test. Paired T-test was also used to assess possible differences on the ultimate color achieved after tooth bleaching. Enamel microabrasion reduced the lightness and increased the redness of specimens. Specimens that received microabrasion presented higher values of ∆L* than control after each bleaching procedure; and higher ∆a* after the 2nd bleaching session. However, the prior enamel microabrasion did not affect the ultimate values of color parameters. Despite enamel microabrasion have modified the tooth color, this procedure did not affect the ultimate results achieved with tooth bleaching using a high-concentrated hydrogen peroxide.

In-office tooth bleaching with 38% hydrogen peroxide promotes moderate/severe pulp inflammation and production of ll-1β, TNF-β, GPX, FGF-2 and osteocalcin in rats

OBJECTIVES

To study the intensity of inflammatory infiltrate and production of interleukin-1β (ll-1β), tumor necrosis factor-β (TNF-β), fibroblast growth factor-2 (FGF-2), glutathione peroxidase (GPX), and osteocalcin in response to in-office tooth bleaching in rats.

MATERIAL AND METHODS

Twenty male Wistar rats were randomized into four groups (n=5) according to the received treatment (tooth bleaching or no treatment - control) and the period of euthanasia after treatment (24 h or 10 days). We performed tooth bleaching using a 38% hydrogen peroxide gel on maxillary and mandibular incisors. After euthanasia, incisors (20 per group) were processed for histological analysis, immunohistochemistry staining of ll-1β, TNF-β, FGF-2 and GPX and osteocalcin by immunofluorescence. We analyzed data using the Mann-Whitney and Kruskal-Wallis/Dunn tests (p<0.05).

RESULTS

The bleached groups presented statistically significant differences regarding the pulp inflammation stage compared with the control groups. Bleached teeth showed moderate/severe inflammatory infiltrate and control groups presented absent inflammatory cells or a negligible number of mononuclear cells (p<0.001) at two times (24 h and 10 days). There was strong staining for ll-1β, TNF-β, and GPX in bleached groups at 24 h and strong staining for ll-1β, TNF-β, GPX and FGF-2 at 10 days. After 10 days of tooth bleaching, the bleached group showed a statistically superior amount of osteocalcin than the other groups (p<0.01).

CONCLUSIONS

Tooth bleaching with 38% hydrogen peroxide causes severe pulp inflammation, but characteristics of tissue repair after 10 days.

Preemptive Use of Naproxen on Tooth Sensitivity Caused by In-Office Bleaching: A Triple-Blind, Crossover, Randomized Clinical Trial

Objectives:

A triple-blind, randomized, crossover clinical trial evaluated prior use of nonsteroidal anti-inflammatory naproxen on sensitivity reported by patients undergoing in-office tooth bleaching.

Methods and Materials:

Fifty patients were subjected to two sessions of in-office tooth bleaching with 35% hydrogen peroxide in a single application of 40 minutes for two sessions, with an interval of seven days between applications. One hour prior to the procedure, each patient randomly received a single dose of naproxen (500 mg) or placebo. The patient's sensitivity level was evaluated during and immediately after the bleaching using two scales (verbal and visual analog); the verbal scale only was repeated after 24 hours. The effectiveness of the bleaching procedures was evaluated with the Bleachedguide scale. Relative risk to sensitivity was calculated and adjusted by session, while comparison of overall risk was performed by the McNemar test. Data on the sensitivity level for both scales and shade were subjected to the Friedman, Wilcoxon, and Mann-Whitney tests (α=0.05).

Results:

The use of naproxen only decreased the absolute risk and intensity of tooth sensitivity reported immediately after the second session. On the other hand, no measurable effect was observed during or 24 hours after either session. The sequence of drug administration did not affect the bleaching effectiveness.

Conclusions:

Preemptive use of naproxen only reduced tooth sensitivity reported by patients immediately after the second session of bleaching.