Influence of Bleaching Gel Peroxide Concentration on Color and Penetration through the Tooth Structure
1,3,4Department of Restorative Dentistry, Institute of Science and Technology, Séo Paulo State University-UNESP, Sao Jose dos Campos, Séo Paulo, Brazil
2Department of Restorative Dentistry, Taubaté University, Taubaté, Séo Paulo, Brazil
Corresponding Author: Carlos RG Torres, Department of Restorative Dentistry, Institute of Science and Technology, Sao Paulo State University-UNESP, Séo José dos Campos, Séo Paulo, Brazil, Phone: +55 12 3947 9376, e-mail: email@example.com
How to cite this article: Torres CRG, Zanatta RF, Godoy MMM, et al. Influence of Bleaching Gel Peroxide Concentration on Color and Penetration through the Tooth Structure. J Contemp Dent Pract 2021;22(5):479–483.
Source of support: Coordination for the Improvement of Higher Education Personnel (CAPES)
Conflict of interest: None
Aim and objective: The purpose of this study was to assess the effect of hydrogen peroxide concentration on the bleaching efficacy and penetration through the tooth structure.
Materials and methods: One hundred enamel/dentin specimens with cylindrical shape were obtained from bovine incisors. The surfaces were polished and the size standardized. They were divided into five groups (n = 20), following the concentration of hydrogen peroxide in the bleaching gels: 20, 25, 30, 35, and 40% (w/w). The specimens were placed over artificial pulpal chambers containing acetate buffer solution and bleached for 30 minutes (three applications of 10 minutes each). Aliquots of the acetate solution were collected, and the peroxide concentration was measured by an analytic spectrophotometer. The color of the samples was analyzed using a colorimetric spectrophotometer at the baseline and 7 days after the bleaching procedure. The color difference was calculated using the ∆Eab formula. The data were analyzed by one-way ANOVA and Tukey’s test (p <0.05).
Results: The peroxide concentrations of 20–30% showed smaller bleaching effect than the higher concentrations (p = 0.001). The peroxide penetration was significantly higher (p = 0.001) for the more concentrated gels (35 and 40%).
Conclusion: The higher peroxide concentrations enhance the bleaching efficacy, but also increased the peroxide penetration through the tooth structure.
Clinical significance: In-office bleaching gels with higher concentrations of hydrogen peroxide (35 and 40%) present superior whitening efficacy. Nevertheless, they might also intensify the negative biological effects on the pulpal tissue, since they exhibit increased penetration potential.
Keywords: Bleaching, Color, Concentration, Peroxide.
Dental bleaching is a highly effective technique for the treatment of discolored teeth.1 The whitening effect is promoted by hydrogen peroxide, which is a small molecule with a strong oxidizing effect, capable of forming reactive free radicals that oxidize chromophore molecules inside the dental hard tissues by means of a redox processes.2,3
Different from the at-home technique, the in-office procedure uses bleaching gels with high hydrogen peroxide concentrations, generally around 35% (w/w), in order to promote a faster whitening outcome with reduced number of applications.4 In the highly competitive dental materials market, new bleaching gel formulations are often launched by manufacturers, and they use different approaches to attract the dentist attention to their brands. The first one is to increase peroxide concentrations, claiming to intensify the bleaching result and reduce the time required for the treatment. The second is to reduce the concentration, claiming to diminish the level of sensitivity during and after the treatment, as well the negative effects on the pulp. In both cases, the marketing intention is to make their products more attractive to the dentists, even sometimes without a clear scientific evidence supporting those claims.
The hydrogen peroxide concentration of mostly the currently available products varies between 20 and 40%. However, it has not yet completely demonstrated whether the higher concentrated gels are really more effective. This is due to the fact that other ingredients in the formulation of the bleaching gel can modulate the whitening outcome,5,6 besides the peroxide concentration per se, such as the pH,7 viscosity,8 kind of thickener,9 humectant and pH adjuster10 or presence of surfactants.11 Therefore, a study testing the variation of peroxide concentration in the same bleaching gel formulation, in a dose–response analysis, could help to confirm or not this hypothesis.
Previous studies showed that the use of highly concentrated hydrogen peroxide gels produces whitening effect with minimal or no negative effect over the physical properties of the enamel surface.4,12-14 However, due to its low molecular weight, the peroxide can diffuse through the intercrystalline spaces of enamel and inside the dentin tubules, reaching the pulpal chamber and starting an inflammatory process, which increases tooth sensitivity potential.2,15,16 When the amount of peroxide reaching the pulp chamber is excessive, the cells release large amounts of several inflammatory mediators into the tissue and consequently induce an inflammatory response.17,18 This response is nonspecific and may be intense, with vascular dilation and exudation of cells, such as macrophages, which are responsible for the degradation of the extracellular matrix.19 A direct correlation between the peroxide concentration in the bleaching gel and its diffusion through the enamel and dentin is expected,20 although this was not observed in all studies.6 Since a higher quantity of molecules reaching the pulpal tissue can exceed the antioxidant capacity of the pulp cells and consequently lead to their damage, this issue is clinically relevant and deserves further investigation. Due to the effect of the various components in the formulation, a previous study showed that even gels with similar peroxide content can show different penetration rates, impairing the understanding of the real correlation between peroxide concentration and the pulpal penetration.21
Thus, this study aimed to evaluate the influence of hydrogen peroxide concentration on the bleaching efficacy and peroxide penetration through enamel and dentin. The null hypotheses tested were that peroxide concentration does not influence the bleaching effect or the penetration.
MATERIALS AND METHODS
This in vitro study was conducted in the Institute of Science and Technology of Séo José dos Campos (Sao Paulo State University—UNESP, Brazil). One hundred bovine incisors, freshly extracted and intact, were kept in 0.1% thymol solution at 5°C until use. A diamond trephine mill was used to cut specimen with 6 mm of diameter, from the central area of the buccal surface of the crowns, including enamel and dentin tissues, as previously described.16,20
The thickness of the specimens was standardized in 2 mm (1 mm enamel and 1 mm dentin) using a P1200 silicon carbide (SiC) abrasive paper disk (FEPA-P, Struers, Ballerup, Denmark) and a dedicated specimen holder. For that, the specimen was attached to the holder and the desired enamel thickness adjusted based on DEJ. The excess was removed, and the surface was ground flat, using a polishing machine (DP-10, Panambra, Séo Paulo, SP, Brazil). Then, the specimen was reversed inside the holder and the dentin surface was flattened until reaching 1 mm thickness. The enamel surface was polished with a sequence of water-cooled SiC abrasive disks (P2400 and P4000 grit), applied for 20 seconds each. The enamel surfaces were analyzed with a stereomicroscope to verify the absence of cracks or defects. The smear layer on the dentin side was removed by the application of 37% phosphoric acid gel for 15 seconds, followed by copious washing with water. The specimens were immersed in 2 mL of distilled water inside Eppendorf tubes until required.
Baseline Color Assessment
The baseline color of all specimens was assessed with a spectrophotometer for colorimetric analysis by reflectance (CM-2600d, Konica Minolta, Osaka, Japan). The baseline light reflectance was assessed in standard conditions, with the device adjusted to small area view (SAV) of 3 mm, specular component included, observer angle of 2°, standard D65 illuminant, and 100% UV included. A standard ceramic white background (CERAM, Lucideon, Staffordshire, UK) was placed under the specimen during the color measurement.11 Between the specimen and the background, an optical contact was provided using polyethylene glycol 400 (Labsynth, Sao Paulo, SP, Brasil).1 Three consecutive measures were taken from each specimen, and the values were later averaged. The color measurements were quantified in terms of the L*, a*, b* (CIELAB) coordinates.2
After the initial color measurements, the enamel/dentin specimens were distributed into five groups (n = 20), according to the concentration of hydrogen peroxide present in the bleaching gels: 20, 25, 30, 35, and 40% (w/w). These concentrations were chosen for being the most commonly available in commercial products, allowing a dose–response analysis.
The bleaching gels tested were prepared in our laboratory, immediately before starting the application, as previously described by Torres et al.16 It was produced by the mixture of two solutions. One contained 50% hydrogen peroxide (w/w) associated with an acrylic thickener in acidic pH, while the other was an alkaline solution responsible for the gel formation. The solutions were mixed at 3:1 ratio by volume, using a 1000 μL automatic micropipettes (Labmate Soft, HTL, Warsaw, Poland). The final pH of all tested gels was 6.7, checked by a benchtop pH meter (DM-22, Digimed, Séo Paulo, Brazil), previously calibrated with buffer solutions 6.86 and 4.01. The peroxide concentration on each gel was checked by titration using sodium permanganate.2
Hydrogen Peroxide Penetration
After initial color measurements, the specimens were placed inside an artificial pulpal chamber device to measure the diffusion of hydrogen peroxide, as described in previous works.2,16,20 A constant volume (20 μL) of acetate buffer (pH 4.5) was placed inside the chamber, aiming to collect and stabilize the hydrogen peroxide that penetrated the tooth structure.16 The specimens were positioned inside the device, with the dentin touching the liquid simulating the pulpal fluid, while the surface was tightly sealed using a perforated lid and a rubber O-ring, allowing the penetration of peroxide only by diffusion through enamel and dentin.16
The gel was applied over the enamel with 2-mm-thick layer for 10 minutes and stirred every 2 minutes to displace the oxygen bubbles produced. After this time, the gel was aspirated with a vacuum cannula and reapplied two more times, with a total application time of 30 minutes. To allow the peroxide penetration through enamel/dentin, the specimens were kept inside a sealed box with 100% relative humidity for 2 hours.16,20
After this time, the chambers were opened and 5 μL of acetate buffer was collected from each one. The hydrogen peroxide concentration was quantified by the spectrophotometric method proposed by Bauminger22 and modified by Hannig et al.,23 as fully described in previous studies.2,16
Final Color Assessment
After the bleaching procedure, the specimens were kept in artificial saliva for 7 days to obtain color stability and to allow hydration.2 The final color was evaluated the same way used for baseline. The color change was calculated using the total color difference formula: ∆E = [(∆L)2 + (∆a)2 + (∆b)2]½.2
Color and penetration data were checked for normality assumption using the Kolmogorov–Smirnov test. Then, one-way ANOVA and Tukey’s test were performed, with a significance level of 5%.
The Kolmogorov–Smirnov test showed normal distribution for color and peroxide penetration (d >0.05). ANOVA showed significant differences among the groups regarding the peroxide penetration (p = 0.0001), and Tukey’s test revealed that the 35 and 40% concentration promoted higher peroxide penetration than 20 and 25% (Table 1). Regarding color change (∆E), ANOVA also showed significant differences among the groups (p = 0.0001). Tukey’s test showed that the more concentrated gels (35 and 40%) presented higher ∆E values compared to the other concentrations tested (Table 1). In relation to the color coordinates, the L* values increased, the b* values reduced, and the a* values showed small and nonsignificant changes, indicating that the bleaching treatment turned the teeth more luminous and less yellow for all groups.
|Groups||Hydrogen peroxide penetration||Color change (∆E)|
|Mean||SD||Homogeneous sets||Mean||SD||Homogeneous sets|
The possibility of obtaining quicker bleaching is the main marketing appeal and explains the increasing popularity of the in-office bleaching technique.6,21 However, to reach the desired results, high concentrations of hydrogen peroxide gels are frequently used, which is correlated with the higher levels of sensitivity in relation to the at-home technique.24
It is well known that the free radicals are responsible for the oxidation of chromophores on the organic components of the tooth and color change.25 A study showed that the amount of free radicals in a peroxide solution is proportional to its concentration.25 It is therefore expected that the higher concentrated gels would produce higher bleaching effect. In the current study, the results showed that peroxide concentration is directly proportional to the bleaching effect (Table 1), allowing to reject the first null hypothesis. Similar results were observed in in vitro studies.1,4,25-29 Borges et al. showed that 20% hydrogen peroxide gel produced a significantly smaller color change than a 35% hydrogen peroxide gel, but without differences on the effect over the enamel surface microhardness.4 Sulieman et al. analyzed the number of applications necessary for previously stained teeth to the shade C4 reach the shade B1. The number of applications increased exponentially as the peroxide concentration decreased, requiring one application for 35%, 2 for 25%, 4 for 15%, 7 for 10%, and 12 for 5%. However, some in vitro studies failed to provide correlation between the concentration and the bleaching effect.30-32 A clinical trial has also shown a correlation between the bleaching effect and the peroxide concentration,33 although another did not confirm this effect.34 Reis et al. compared similar gel formulations containing different peroxide concentrations (20 and 35% w/w). After two bleaching sessions, the more concentrated gel produced higher bleaching, although both products resulted in similar levels of tooth sensitivity.33
Despite the effectiveness of the in-office dental bleaching procedure, around 70% of the patients that undergo this treatment reported dental sensitivity, from mild to severe.5,24,35,36 This can be explained by the rapid peroxide penetration into the pupal chamber, leading to an oxidative stress surpassing the antioxidant inherent capacity of the tissue,37 which can result in inflammation,38 small histological changes39 or, in extreme situations, to necrosis of the pulp.40 The penetration occurs due to the low molecular weight of the hydrogen peroxide molecule and the porosity of the enamel and dentin tissues. Although the penetration is essential to produce the desired bleaching effect, it is also responsible for the irritative effects on the pulp, and a balance between the two aspects must be reached. Some manufacturers created less concentrated gel in an empiric attempt to reduce the negative effects of the highly concentrated products, wishing to keep the effectiveness.5,6 According to the results of the current study, it is expected that peroxide reduction in the gel formulations will also reduce the effectiveness of the treatment.
Many in vitro studies showed that the amount and speed of pulpal penetration are directly proportional to the hydrogen peroxide concentration in the bleaching gel,20,26-28,31,32,39,41-43 which is in agreement with the results of the current study (Table 1), allowing to reject the second null hypothesis. The researches also showed the increase in cytotoxicity,26 lymphocyte-like cell activation and expression of interleukin,44 enzymatic inhibition,45 formation of tertiary dentin,32,39,46 and dental permeability,47 and that the peroxide concentration of the bleaching gel is higher. The higher peroxide penetration observed in the current study can explain the higher levels of sensitivity observed on some clinical trials for the more concentrated gels.34,48
After applying the peroxide gel over the enamel surface, a certain amount will penetrate the tooth, while the rest will remain stable or suffer decomposition. A study showed that after the bleaching procedure, a small reduction of peroxide concentration occurs inside the gel layer applied over the tooth, indicating minor degradation and penetration rates.21 A study showed that the diffusion phenomena during dental bleaching are determined by the chemical affinity of the peroxide molecule with the organic components of the tissues.49 The peroxide can easily and quickly penetrate the enamel due to its low organic content (2% by volume). From those peroxide molecules that actually entered the enamel, around 63% accumulate at the DEJ, due to its high organic content, reacting and attaching to the organic components of the dentin (38% by volume). Only, the remaining 37% is able to diffuse through the dentin tubules and to reach the pulpal chamber. That creates a concentration gradient of peroxide inside the tooth during its diffusion dynamics.49 Therefore, not all peroxide molecules inside the bleaching gel actually penetrate the tooth, and from those that penetrated, just a small part really reaches the pulp. That explains the very low peroxide concentrations into the pulpal chamber observed in this study as well in others,6,21,42 below 10 μg/L, while a 35% hydrogen peroxide gel (w/w) has a concentration of 388500 μg/L.
The level of peroxide penetration and the severity of the damage depend on the thickness of enamel and dentin, which varies among the groups of teeth.39 A study showed that in-office bleaching with 38% hydrogen peroxide can cause irreversible pulpal damage in lower incisors but not in premolars.40 In addition, the presence of cracks and a tooth abrasion can also increase the peroxide penetration.50 However, a clinical trial did not find correlation between the thickness of enamel/dentin layer and the tooth sensitivity.48
However, the levels of penetration and the tooth sensitivity are affected by other aspects of bleaching formulation besides the peroxide concentration. A clinical trial showed that the addition of calcium to the 35% hydrogen peroxide bleaching gel can significantly reduce absolute risk of tooth sensitivity, without affecting the bleaching effect.51 In vitro studies showed that the pulpal peroxide penetration was significantly reduced with the addition of calcium to the hydrogen peroxide gel.6,16 Some studies analyzed bleaching gels with different pHs and concluded that the smaller is the pH, the higher is the peroxide penetration into the pulpal chamber.52,53 Another study showed that chemical activation of bleaching gels can also reduce the pulpal penetration.2
The penetration and cytotoxicity are also increased by exposure to thermal sources41 or light, the existence of restorations,54 and the contact time.21,26 Special protocols were suggested to minimize the negative effects on the pulp, changing the application time and peroxide concentration, aiming to increase the safety and comfort to the patients.27,28,32 Some studies showed that although the penetration of peroxide rises with the contact time with the surface, this increase is not proportional.21,26 The increase in time from 15 to 45 minutes raised the penetration of a 38% hydrogen peroxide gel from 4.7 to 5.7 μg/mL.21
The results of this study cannot be directly transferred to the clinical conditions since the penetration in vivo is affected by the positive pulpal pressure. Although a previous study showed that pulpal pressure does not influence the bleaching outcome,15 the amount of peroxide reaching the pulpal tissue will be certainly affected in vivo.29 Besides the pulpal pressure, the presence of the odontoblastic processes can also interfere with the penetration, partially filling the tubule entrance. It is the first and more affected alive structure during the peroxide penetration.40,45 In addition, the enzymatic breakdown of the hydrogen peroxide by catalase and peroxidase, as part of the defense mechanism of the pulp, will reduce the peroxide concentration in the tissue.55
It was concluded that the higher peroxide concentrations lead to the increase in tooth bleaching effect, but also increase the hydrogen penetration through the dental structure.
1. Caneppele TM, Borges AB, Torres CRG. Effects of dental bleaching on the color, translucency and fluorescence properties of enamel and dentin. Eur J Esthet Dent 2013;8(2):200–212. PMID: 23712341.
2. Torres CRG, Wiegand A, Sener B, et al. Influence of chemical activation of a 35% hydrogen peroxide bleaching gel on its penetration and efficacy-in vitro study. J Dent 2010;38(10):838–846. DOI: 10.1016/j.jdent.2010.07.002.
3. Torres CRG, Guimarées CA, Ribeiro ZEA, et al. Influence of different types and concentrations of chemical catalysts on dental bleaching efficiency. J Contemp Dent Pract 2015;16(11):893–902. DOI: 10.5005/jp-journals-10024-1778.
4. Borges AB, Zanatta RF, Barros ACSM, et al. Effect of hydrogen peroxide concentration on enamel color and microhardness. Oper Dent 2015;40(1):96–101. DOI: 10.2341/13-371-L.
5. Reis A, Dalanhol AP, Cunha TS, et al. Assessment of tooth sensitivity using a desensitizer before light-activated bleaching. Oper Dent 2011;36(1):12–17. DOI: 10.2341/10-148-CR.
6. Mena-Serrano AP, Parreiras SO, Nascimento EMS, et al. Effects of the concentration and composition of in-office bleaching gels on hydrogen peroxide penetration into the pulp chamber. Oper Dent 2015;40(2):E76-E82. DOI: 10.2341/13-352-L.
7. Torres CRG, Crastechini E, Feitosa FA, et al. Influence of pH on the effectiveness of hydrogen peroxide whitening. Oper Dent 2014;39(6):E261–E268. DOI: 10.2341/13-214-L.
8. Kwon SR, Pallavi FNU, Shi Y, et al. Effect of bleaching gel viscosity on tooth whitening efficacy and pulp chamber penetration: an in vitro study. Oper Dent 2018;43(3):326–334. DOI: 10.2341/17-099-L.
9. do Carmo Públio J, Zeczkowski M, Burga-Sánchez J, et al. Influence of different thickeners in at-home tooth bleaching: a randomized clinical trial study. Clin Oral Investig 2019;23(5):2187–2198. DOI: 10.1007/s00784-018-2613-9.
10. Ito Y, Otsuki M, Tagami J. Effect of pH conditioners on tooth bleaching. Clin Exp Dent Res 2019;5(3):212–218. DOI: 10.1002/cre2.172.
11. Caneppele TMF, Torres CRG. Influence of surfactants on the effectiveness of bleaching gels. Clin Oral Investig 2011;15(1):57–64. DOI: 10.1007/s00784-009-0358-1.
12. Magalhées JG, Marimoto ARK, Torres CRG, et al. Microhardness change of enamel due to bleaching with in-office bleaching gels of different acidity. Acta Odontol Scand 2012;70(2):122–126. DOI: 10.3109/00016357.2011.600704.
13. Borges AB, Guimaraes CA, Bresciani E, et al. Effect of incorporation of remineralizing agents into bleaching gels on the microhardness of bovine enamel in situ. J Contemp Dent Pract 2014;15(2):195–201. DOI: 10.5005/jp-journals-10024-1514.
14. Jurema ALB, de Souza MY, Torres CRG, et al. Effect of pH on whitening efficacy of 35% hydrogen peroxide and enamel microhardness. J Esthet Restor Dent 2018;30(2):E39–E44. DOI: 10.1111/jerd.12367.
15. Borges AB, Batista GR, Arantes PT, et al. Influence of simulated pulpal pressure on efficacy of bleaching gels. J Contemp Dent Pract 2014;15(4):407–412. DOI: 10.5005/jp-journals-10024-1553.
16. Torres CRG, Zanatta RF, Silva TJ, et al. Effect of calcium and fluoride addition to hydrogen peroxide bleaching gel on tooth diffusion, color, and microhardness. Oper Dent 2019;44(4):424–432. DOI: 10.2341/18-113-L.
17. Lima LF, Alencar AHG, Decurcio DA, et al. Effect of dental bleaching on pulp oxygen saturation in maxillary central incisors - a randomized clinical trial. J Appl Oral Sci 2019;27(7):e20180442. DOI: 10.1590/1678-7757-2018-0442.
18. Kina JF, Huck C, Riehl H, et al. Response of human pulps after professionally applied vital tooth bleaching. Int Endod J 2010;43(7):572–580. DOI: 10.1111/j.1365-2591.2010.01713.x.
19. Vaz MM, Lopes LG, Cardoso PC, et al. Inflammatory response of human dental pulp to at-home and in-office tooth bleaching. J Appl Oral Sci 2016;24(5):509–517. DOI: 10.1590/1678-775720160137.
20. Torres CRG, Souza CS, Borges AB, et al. Influence of concentration and activation on hydrogen peroxide diffusion through dental tissues in vitro. Sci World J 2013:193241. DOI: 10.1155/2013/193241.
21. Marson FC, Gonçalves RS, Silva CO, et al. Penetration of hydrogen peroxide and degradation rate of different bleaching products. Oper Dent 2015;40(1):72–79. DOI: 10.2341/13-270-L.
22. Bauminger BB. Micro method for manual analysis of true glucose in plasma without deproteinization. J Clin Pathol 1974;27(12):1015–1017. DOI: 10.1136/jcp.27.12.1015.
23. Hannig C, Zech R, Henze E, et al. Determination of peroxides in saliva-kinetics of peroxide release into saliva during home-bleaching with whitestrips and vivastyle. Arch Oral Biol 2003;48(8):559–566. DOI: 10.1016/s0003-9969(03)00102-x.
24. Tay LY, Kose C, Loguercio AD, et al. Assessing the effect of a desensitizing agent used before in-office tooth bleaching. J Am Dent Assoc 2009;140(10):1245–1251. DOI: 10.14219/jada.archive.2009.0047.
25. Kawamoto K, Tsujimoto Y. Effects of the hydroxyl radical and hydrogen peroxide on tooth bleaching. J Endod 2004;30(1):45–50. DOI: 10.1097/00004770-200401000-00010.
26. Soares DG, Ribeiro APD, da Silveira Vargas F, et al. Efficacy and cytotoxicity of a bleaching gel after short application times on dental enamel. Clin Oral Investig 2013;17(8):1901–1909. DOI: 10.1007/s00784-012-0883-1.
27. Soares DG, Basso FG, Pontes ECV, et al. Effective tooth-bleaching protocols capable of reducing H2O2 diffusion through enamel and dentine. J Dent 2014;42(3):351–358. DOI: 10.1016/j.jdent.2013.09.001.
28. Soares DG, Basso FG, Hebling J, et al. Concentrations of and application protocols for hydrogen peroxide bleaching gels: effects on pulp cell viability and whitening efficacy. J Dent 2014;42(2):185–198. DOI: 10.1016/j.jdent.2013.10.021.
29. Sulieman M, Addy M, MacDonald E, et al. The effect of hydrogen peroxide concentration on the outcome of tooth whitening: an in vitro study. J Dent 2004;32(4):295–299. DOI: 10.1016/j.jdent.2004.01.003.
30. Dietschi D, Rossier S, Krejci I. In vitro colorimetric evaluation of the efficacy of various bleaching methods and products. Quintessence Int 2006;37(7):515–526. PMID: 16841599.
31. Almeida LCAG, Soares DG, Gallinari MO, et al. Color alteration, hydrogen peroxide diffusion, and cytotoxicity caused by in-office bleaching protocols. Clin Oral Investig 2015;19(3):673–680. DOI: 10.1007/s00784-014-1285-3.
32. Barbosa JG, Benetti F, de Oliveira Gallinari M, et al. Bleaching gel mixed with MI Paste Plus reduces penetration of H2O2 and damage to pulp tissue and maintains bleaching effectiveness. Clin Oral Investig 2020;24(3):1299–1309. DOI: 10.1007/s00784-019-03009-5.
33. Reis A, Kossatz S, Martins GC, et al. Efficacy of and effect on tooth sensitivity of in-office bleaching gel concentrations: a randomized clinical trial. Oper Dent 2013;38(4):386–393. DOI: 10.2341/12-140-C.
34. Gonçalves MLL, da Silva Tavares AC, da Mota ACC, et al. In-office tooth bleaching for adolescents using hydrogen peroxide-based gels. Braz Dent J 2017;28(6):720–725. DOI: 10.1590/0103-6440201701516.
35. Rezende M, Loguercio AD, Kossatz S, et al. Predictive factors on the efficacy and risk/intensity of tooth sensitivity of dental bleaching: a multi regression and logistic analysis. J Dent 2016;45:1–6. DOI: 10.1016/j.jdent.2015.11.003.
36. Alomari Q, El Daraa E. A randomized clinical trial of in-office dental bleaching with or without light activation. J Contemp Dent Pract 2010;11(1):E017–E024. DOI: 10.5005/jcdp-11-1-17.
37. Coldebella CR, Ribeiro APD, Sacono NT, et al. Indirect cytotoxicity of a 35% hydrogen peroxide bleaching gel on cultured odontoblast-like cells. Braz Dent J 2009;20(4):267–274. DOI: 10.1590/s0103-64402009000400001.
38. Markowitz K. Pretty painful: why does tooth bleaching hurt? Med Hypotheses 2010;74(5):835–840. DOI: 10.1016/j.mehy.2009.11.044.
39. Cintra LTA, Benetti F, Ferreira LL, et al. Penetration capacity, color alteration and biological response of two in-office bleaching protocols. Braz Dent J 2016;27(2):169–175. DOI: 10.1590/0103-6440201600329.
40. Costa CAS, Riehl H, Kina JF, et al. Human pulp responses to in-office tooth bleaching. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109(4):e59–e64. DOI: 10.1016/j.tripleo.2009.12.002.
41. Bowles WH, Ugwuneri Z. Pulp chamber penetration by hydrogen peroxide following vital bleaching procedures. J Endod 1987;13(8):375–377. DOI: 10.1016/S0099-2399(87)80196-6.
42. Benetti AR, Valera MC, Mancini MNG, et al. In vitro penetration of bleaching agents into the pulp chamber. Int Endod J 2004;37(2):120–124. DOI: 10.1111/j.0143-2885.2004.00761.x.
43. Hanks CT, Fat JC, Wataha JC, et al. Cytotoxicity and dentin permeability of carbamide peroxide and hydrogen peroxide vital bleaching materials, in vitro. J Dent Res 1993;72(5):931–938. DOI: 10.1177/00220345930720051501.
44. Benetti F, Gomes-Filho JE, Ferreira LL, et al. Concentration-dependent effect of bleaching agents on the immunolabelling of interleukin-6, interleukin-17 and CD5-positive cells in the dental pulp. Int Endod J 2018;51(7):789–799. DOI: 10.1111/iej.12891.
45. Bowles WH, Thompson LR. Vital bleaching: the effects of heat and hydrogen peroxide on pulpal enzymes. J Endod 1986;12(3):108–112. DOI: 10.1016/S0099-2399(86)80300-4.
46. Cintra LTA, Benetti F, Ferreira LL, et al. Evaluation of an experimental rat model for comparative studies of bleaching agents. J Appl Oral Sci 2016;24(1):95–104. DOI: 10.1590/1678-775720150393.
47. Berger SB, Tabchoury CPM, Ambrosano GMB, et al. Hydrogen peroxide penetration into the pulp chamber and dental permeability after bleaching. Gen Dent 2013;61(3):e21–e25.
48. Moncada G, Sepúlveda D, Elphick K, et al. Effects of light activation, agent concentration, and tooth thickness on dental sensitivity after bleaching. Oper Dent 2013;38(5):467–476. DOI: 10.2341/12-335-C.
49. Ubaldini ALM, Baesso ML, Medina Neto A, et al. Hydrogen peroxide diffusion dynamics in dental tissues. J Dent Res 2013;92(7):661–665. DOI: 10.1177/0022034513488893.
50. Briso ALF, Lima APB, Gonçalves RS, et al. Transenamel and transdentinal penetration of hydrogen peroxide applied to cracked or microabrasioned enamel. Oper Dent 2014;39(2):166–173. DOI: 10.2341/13-014-L.
51. Kossatz S, Martins G, Loguercio AD, et al. Tooth sensitivity and bleaching effectiveness associated with use of a calcium-containing in-office bleaching gel. J Am Dent Assoc 2012;143(12):e81–e87. DOI: 10.14219/jada.archive.2012.0075.
52. Acuña ED, Parreiras SO, Favoreto MW, et al. In-office bleaching with a commercial 40% hydrogen peroxide gel modified to have different pHs: color change, surface morphology, and penetration of hydrogen peroxide into the pulp chamber. J Esthet Restor Dent 2019;1–6. DOI: 10.1111/jerd.12453.
53. Balladares L, Alegría-Acevedo LF, Montenegro-Arana A, et al. Effects of pH and application technique of in-office bleaching gels on hydrogen peroxide penetration into the pulp chamber. Oper Dent 2019;44(6):659–667. DOI: 10.2341/18-148-L.
54. Camargo SEA, Valera MC, Camargo CHR, et al. Penetration of 38% hydrogen peroxide into the pulp chamber in bovine and human teeth submitted to office bleach technique. J Endod 2007;33(9):1074–1077. DOI: 10.1016/j.joen.2007.04.014.
55. Benetti F, Gomes-Filho JE, Ferreira LL, et al. Hydrogen peroxide induces cell proliferation and apoptosis in pulp of rats after dental bleaching in vivo: effects of the dental bleaching in pulp. Arch Oral Biol 2017;81(6):103–109. DOI: 10.1016/j.archoralbio.2017.04.013.
© The Author(s). 2021 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and non-commercial reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.