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dentin interfaces
International Journal of Adhesion & Adhesives 47 (2013) 141–145
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Influence of hydrogen peroxide-based bleaching agents on the bond strength of resin–enamel/dentin interfaces Victor França Didier a, André Ulisses Dantas Batista a, Robinsom Viégas Montenegro a, Rodrigo Borges Fonseca b, Fabíola Galbiatti de Carvalho c, Silvio de Barros d, Hugo Lemes Carlo a,n a Federal University of Paraiba, Health Science Center, Operative Dentistry Department, Universidade Federal da Paraíba, Departamento de Odontologia Restauradora, Cidade Universitária, 58051-900 João Pessoa, PB, Brazil b Federal University of Goias, School of Dentistry, Universidade Federal de Goiás, Faculdade de Odontologia, Praça Universitária esquina com 1ª Avenida, s/n, Setor Universitário, 74605-220 Goiânia, GO, Brazil c Federal University of Campina Grande, Health and Rural Technology Center, Academic Unit of Biological Sciences, Universidade Federal de Campina Grande, Centro de Saúde e Tecnologia Rural, Unidade Acadêmica de Ciências Biológicas, Av. Universitária, s/n, Santa Cecília, 58708-110 Patos, PB, Brazil d Federal Center of Technological Education in Rio de Janeiro, Laboratório de Compósitos e Adesivos Av. Maracanã, 229-Bloco E-5º andar, 20271-110 Rio de janeiro, RJ, Brazil
art ic l e i nf o
a b s t r a c t
Available online 29 August 2013
This study evaluated the effect of different bleaching techniques on the bond strength of pre-existing adhesive restorations in enamel and dentin. Hydrogen peroxide-based bleaching gels with different concentrations (7.5% and 35%) were used on composite restorations of Adper Single Bond 2 (3M/ESPE, St. Paul, USA) and Filtek Z250 (3M/ESPE, St. Paul, USA). Twenty human third molars were randomly divided into 8 groups: GE—enamel control; GE7.5—bleaching using 7.5% hydrogen peroxide; GE35—bleaching using 35% hydrogen peroxide; GE 7.5þ35—bleaching using 7.5% and 35% hydrogen peroxide; GD—dentin control; GD7.5—7.5% hydrogen peroxide; GD35—35% hydrogen peroxide; and GD 7.5þ 35—7.5% and 35% hydrogen peroxide. Bleaching was performed using long clinical application-time to low concentration gel, and short clinical application-time to high concentration gel. Unbleached specimens were stored in artificial saliva for 14 days. Specimens subject to micro-shear testing and data were analyzed by Analysis of Variance and Tukey's test (p¼ 0.05). Enamel micro-shear bond strength was reduced after 7.5% hydrogen peroxide and after association of 7.5% and 35% hydrogen peroxide. Bleaching treatment altered dentin bond strength only when using 7.5% hydrogen peroxide. The results suggest that the bond strength of the restorations was influenced by the clinical extent of bleaching-gel application time and was not dependent on bleaching-gel concentration. & 2013 Elsevier Ltd. All rights reserved.
Keywords: Enamel Dentin Dental adhesives Hybrid layer
1. Introduction Tooth whitening, or bleaching, has gained enormous acceptance as well as popularity in the search for an esthetically pleasing smile [1,2]. Reports have indicated that it is a conservative and effective technique to treat discolored and stained anterior teeth [3–5]. Stains contain chromophoric groups, made up of many conjugated carbon–carbon double bonds that absorb light in the visible range of the spectrum and thus appear colorful to the human eye [3,6,7]. The bleaching process is based on a complex oxidation reaction in which oxygen-free radicals, due to their low molecular weight, infiltrate through the enamel and
n
Corresponding author. Tel.: þ 55 83 3216 7250; fax: þ 55 83 3216 7409. E-mail address: [email protected] (H. Lemes Carlo).
0143-7496/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijadhadh.2013.08.009
dentin substrates [8,9]. The product releases free radicals that break up conjugation either by cleavage of, or addition to carbon– carbon double bonds [10]. Once the conjugation is broken up, these molecules no longer absorb in the visible range of the spectrum [1–3,6,7]. At present, there is a broad range of bleaching agents available, containing varying concentrations of carbamide peroxide, hydrogen peroxide and sodium perborate [4,11,12]. Vital tooth bleaching systems include dentist-supervised at-home (nightguard) and in-office techniques, and the combination of the two (at-home þ in-office). For home bleaching, a relatively low concentration of whitening agent (10–22% carbamide peroxide gel or 3–9,5% hydrogen peroxide gel) is typically used, and is applied to the teeth by means of a custom-fabricated mouth guard that is worn for at least 2 weeks. Whereas, for in-office bleaching, relatively high concentrations of whitening agents are generally used, for
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example, 20–35% hydrogen peroxide or 35% carbamide peroxidecontaining products, for shorter periods of time [9,13,14]. In nonvital tooth bleaching, the medicament (sodium perborate) is placed in the pulp chamber, sealed, left for 3–7 days, and afterwards, it is replaced regularly until an acceptable degree of lightening is achieved [8,11,14]. The widespread use of bleaching agents has caused concern with regard to their oxidizing effects on soft tissues, dental structures and restorations. Alterations in enamel surface topography have been observed after application of at-home bleaching [15–18] and in-office bleaching [19–21] products. Alterations have also been detected in dentin after both of the mentioned techniques [4,14,22]. The deleterious effect of bleaching on the bond strength of resin materials has been observed [23–25]. However, the effect of bleaching solution on pre-existing restoration bonded interfaces has not yet been completely determined. Bleaching gels may contain solvents and other components, which might contribute to increase the solubility or degradation of adhesives and composite resins, compromising the longevity of restorations that are not indicated for replacement [26]. Thus, the aim of this research was to conduct an in vitro study to evaluate the effects of the application of hydrogen peroxide bleaching gel of different concentrations, using different techniques, on the micro-shear bond strength between dental substrates (enamel and dentin) and composite resin. The null hypothesis was that the bond strength would not be influenced by the bleaching agent application in any of the groups tested.
30 s in enamel and 15 s in dentin. After this they were rinsed for 30 s and Absorbent paper was used to remove the excess moisture (Snack, Melhoramentos Papéis Ltda., Caieiras, SP, Brazil). The adhesive system (Single Bond 2–3M/ESPE, St. Paul, MN, USA) was applied on enamel and dentin, according to the manufacturer's instructions. Customized 0.5 mm-thick elastomer molds with cylinder-shaped orifices (1.2 mm in diameter), were placed on the tooth surfaces, allowing delimitation of the bonding area. After photo-activating the bonding agent for 10s (LED light curing unit, Coltolux LED—Coltène/Whaledent, Cuyahoga Falls, OH, USA), the orifices were filled with composite resin (Filtek Z250—3M/ ESPE, St.Paul, MN, USA)—3M/ESPE, St. Paul, MN, USA) and then photo-activation was repeated for 40 s. The output irradiance of the curing unit was 850 mW/cm2, confirmed with a digital power meter (Ophir Optronics, Danvers, MA, USA). After storing the specimens in distilled water at 37 1C for 24 h, all resin cylinders were checked at 40 magnification. Those presenting flaws, irregularities or bonding defects were eliminated. Next, the specimens were randomly divided into two control groups and six experimental groups, according to the hydrogen peroxide concentration and bleaching treatment used:
GE: Enamel control. GD: Dentin Control. GE7.5: Enamel submitted to bleaching treatment using 7.5% hydrogen peroxide.
GE35: Enamel submitted to bleaching treatment using 35% hydrogen peroxide.
GE7.5 þ35: Enamel submitted to bleaching treatment using the
2. Materials and methods
association of 7.5% and 35% hydrogen peroxide.
Commercial brand names, chemical composition and material manufacturers are presented in Table 1. In order to obtain specimens for the micro-shear bond strength test, the experimental set-up shown in Fig. 1 was carried out [27]. Twenty sound human third molars that were refrigerated in a solution of 0.1% thymol (LabSynth Produtos para Laboratórios Ltda., Diadema, SP, Brazil) for adequate decontamination prior to its manipulation for no longer than three months after extraction and placed in distilled water for 24 h before beginning the experiment. The teeth used in this study were obtained under Protocol no. 081/2010, which was analyzed and approved by the Research Ethics Committee, Lauro Wanderley University Hospital, Federal University of Paraiba. The specimens were prepared using a flexible diamond disc at low speed (n. 7020—KG Sorensen, Barueri, SP, Brazil) and under water cooling to perform two cuts. In the first, the tooth root was removed and in the second the crown was divided in the mesiodistal direction. After sectioning forty hemi-crowns were obtained, which were embedded in acrylic resin (Vipi, Pirassununga, SP, Brazil). The surfaces were wet-ground with 180, 220, 400 and 600-grit SiC abrasive papers, in order to create a smooth, flat enamel and dentin surface. The enamel and dentin surfaces were treated with 37% phosphoric acid (Adper Scotchbond—3M/ESPE, St. Paul, MN, USA) for
GD7.5: Dentin submitted to bleaching treatment using 7.5% hydrogen peroxide.
GD35: Dentin submitted to bleaching treatment using 35% hydrogen peroxide;
GD7.5þ35: Dentin submitted to bleaching treatment using the association of 7.5% and 35% hydrogen peroxide.
Groups not submitted to bleaching agent (control) were kept in artificial saliva at 37 1C for 14 days. Treatment with 7.5% hydrogen peroxide was carried out using 0.02 ml of the agent administered at the adhesive interface in a daily period of 1 h for 14 days. During the bleaching period, specimens were placed in 100% relative humidity at 37 1C. After daily bleaching, the specimens were thoroughly rinsed with deionized water. During the time when no bleaching treatment was being performed, the specimens were kept in artificial saliva at 37 1C. The specimens were tested 24 h after the end of the bleaching regimen on the 14th day. Groups submitted to 35% hydrogen peroxide received 0.02 ml of the agent administered at the adhesive interface in three rounds. During each round the product was applied for fifteen minutes and repeated twice; there was a time interval of three days between rounds. During the bleaching period, specimens were placed in 100% relative humidity at 37 1C. After bleaching, the specimens
Table 1 Materials tested—commercial brand names, manufacturer, batch number, and composition.n Material
Composition
Adper single bond 2 (3M/ESPE, St Paul, MN, USA) Silane treated silica (nanofiller), Bis-GMA, HEMA, dimethacrylate, methacrylate functional copolymer of polyacrylic and polytaconic acid, water, ethyl alcohol Filtek Z250 (3M/ESPE, St Paul, MN, USA) Silane treated ceramic, BISEMA, UDMA, BISGMA, TEGDMA White class 7.5% (FGM, Joinvile, SC, Brazil) Hydrogen peroxide 7.5%, carbopol, potassium nitrate, sodium fluoride, calcium digluconate, water Whiteness HP (FGM, Joinvile, SC, Brazil) Hydrogen peroxide 30–35%, thickener, red dye, glycol, water n
According to manufacturer's information.
Batch number 9UU N148344BR 2012.FEB 180111
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Fig. 1. Experimental design of the study. (1) Removal of the tooth root; (2) division of the crown in the mesio-distal direction; (3) teeth embedded in acrylic resin showing flat surface of enamel and middle dentin after wet-grinding; (4) elastomer mold with cylinder-shaped orifices positioned on the surface; (5) resin cylinders after polymerization; (6) bleaching treatment of the experimental groups; (7) no treatment of the control group; and (8) micro-shear test. Table 2 Mean bond strength values in MPa ( 7 standard deviation) and Tukey Post-hoc.
Enamel Dentin
Control
7.5% hydrogen peroxide
35% hydrogen peroxide
35%þ 7.5% hydrogen peroxide
34.66A ( 7 9.74) 27.41a ( 7 7.30)
11.19C ( 73.81) 15.28b ( 76.13)
30.61AB (7 11.01) 26.86a (7 6.40)
23.78B ( 77.53) 25.15a ( 76.13)
Values with identical capital letters indicate no significant difference—Tukey Post-Hoc test (P40.05). Values with identical lower case letters indicate no significant difference—Tukey Post-Hoc test (P40.05).
were rinsed with deionized water. During the time when no bleaching treatment was being performed, the specimens were kept in artificial saliva at 37 1C. The specimens were tested 24 h after the end of the bleaching regimen on the 9th day. Groups submitted to 35% and 7.5% hydrogen peroxide received 0.02 ml of the first agent administered at the adhesive interface in one round; the product was applied for fifteen minutes and repeated twice. On the following day 0.02 ml of the second agent was administered at the adhesive interface in a daily period of 1 h for 7 days. During the bleaching period, specimens were placed in 100% relative humidity at 37 1C. After bleaching, the specimens were rinsed with deionized water. During the time when no bleaching treatment was being performed, the specimens were kept in artificial saliva at 37 1C. The specimens were tested 24 h after the end of the bleaching regimen on the 8th day. For the micro-shear test, the tooth embedded in acrylic resin was placed in a device with 25 mm-diameter at the base of the testing machine in left lateral position (Fig. 1). A thin steel wire (0.2 mm in diameter) was looped around each composite resin cylinder and aligned with the bonding interface (Fig. 1). The test was conducted in a universal testing machine (model AG-IC; Shimadzu, Kyoto, Japan), at a crosshead speed of 0.5 mm/min until failure. Micro-shear bond strength calculations were made using the following equation: s ¼L/A, where s is the ultimate shear strength (MPa), L is the shear loading at the moment of failure (N), and A is the bonding area (mm2). For each group, 5 specimens were tested, consisting of four cylinders constructed on the enamel and four on dentin per specimen. The cylinders were considered as experimental unit. Bond strength data were submitted to an exploratory analysis that showed the data could be evaluated by parametric tests due to normal distribution (Kolmogorov–Smirnov test and Shapiro– Wilk test—α ¼0.05) and homogeneity (Levene's test—α¼0.05) indicating the use of one-way Analysis of Variance and Tukey's Test at a 5% level of confidence. The fractured specimens were examined by optical microscopy at 200 magnification. Failure modes were classified as follows: adhesive failure (Mode 1), cohesive failure within enamel/dentin (Mode 2), cohesive failure
within composite resin (Mode 3), or mixed failure involving bonding agent and enamel/dentin (Mode 4).
3. Results Table 2 shows the mean micro-shear bond strengths and standard deviations for the experimental groups. One-way ANOVA revealed significant difference among the enamel groups (p ¼ 0.0001) and dentin groups (p¼ 0.0001) for the interaction between bleaching treatment and a specific dental substrate. Tukey's test showed that the enamel micro-shear bond strength of the control group presented no significantly higher mean values compared with 35% hydrogen peroxide treatment, and presented significantly higher mean values when compared with the treatment using 7.5% concentration. The association of 35%þ7.5% hydrogen peroxide did not show higher values compared with 35% hydrogen peroxide treatment and significantly higher mean values when compared with 7.5% hydrogen peroxide and control. Considering the results of the dentin groups it was observed that the micro-shear bond strength of the control group presented no significantly higher mean values in comparison with 35% hydrogen peroxide, and with the associated treatment (35%þ 7.5%). The 7.5% hydrogen peroxide treatment presented significantly lower mean values when compared with the other groups. Optical examination of the fractured interfaces showed that on enamel and dentin of both unbleached and bleached specimens, the fractures occurred in the adhesive layer close to the substrate (Mode 1), in the substrate (Mode 2) and/or involving bonding agent and enamel/dentin (mixed failure—Mode 4). Fig. 2 presents these results.
4. Discussion The present study evaluated the influence of different bleaching protocols on the micro-shear bond strength of composite resin
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100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
MODE 4 MODE 3 MODE 2 MODE 1
GE
GE 7.5
GE 35 GE 7.5+35
GD
GD 7.5
GD 35 GD 7.5+35
Fig. 2. Failure analysis of fractured interfaces in enamel and dentin of unbleached and bleached specimens. Mode 1—fractures in the adhesive layer close to the substrate; Mode 2—fractures in the substrate; Mode 3—cohesive failure within composite resin; and Mode 4—fractures involving bonding agent and enamel/ dentin (mixed failure).
restorations in enamel and dentin. Different concentrations of hydrogen peroxide and different application protocols were analyzed. A decrease was observed in the bond strength to both substrates after bleaching treatment using the 7.5% concentration or its association with the 35% concentration on enamel. The high concentration used for short periods was shown to be better than the use of low concentration for extended periods. Therefore, the main hypothesis of the present study was not accepted. Bleaching is a widely used conservative treatment for pigmented or darkened teeth, and hydrogen peroxide is one of the primary agents used [28]. Because it has a low molecular content, its degradation releases oxygen free radicals (dOH anddOOH), or the perhydroxyl anion (–OOH), which are able to penetrate the enamel and move along the dental structure reaching the dentin [8–10]. The hydrogen peroxide concentration of commercial products varies from 3% to 35% [9,14]. No difference was observed in the degree of bleaching achieved in whitening treatments with hydrogen peroxide or carbamide peroxide, irrespective of the concentration, at the end of treatment [29–31]. However, a much faster bleaching effect is obtained with high concentration gels. Therefore, higher concentrations are used when a faster bleaching result is desired [32]. Analysis of the enamel/dentin failure modes showed similar results for both bleached and unbleached samples. It was observed a prevalence of mixed failures involving bonding agent and enamel/dentin and occasionally it was observed adhesive failure and cohesive failure within enamel/dentin. One of the theories regarding the deleterious effect of bleaching on tooth structure and resin based materials is related to the reactive oxygen released and its accumulation [33]. The physical properties of restorative materials, such as microhardness, flexural strength, flexural modulus, and fracture toughness influence the quality and durability of restorations [34]. It has been claimed that peroxides induce oxidative cleavage of polymer chains, and therefore unreacted double bonds are expected to be the most vulnerable parts of the polymers. Moreover, free radicals induced by peroxides may impact the resin–filler interface and cause filler– matrix debonding and a slight, but statistically significant, increase in surface roughness [12,35,36]. Mortavazi et al. [37] also reported increased microleakage at dentinal margins, which compromised the marginal seal of class V composite resin restorations. Concerns have been expressed as regards the safety of bleaching agents for use on tooth structure. A decrease was observed in the mean of the areas of the biological phosphate bands at the superficial and subsuperficial level of enamel after bleaching, probably due to hydroxyapatite dissolution [38]. Changes in surface roughness and surface microhardness [4], porosities on the surface of transversely fractured enamel prisms [39] and reduction in fracture toughness and tensile strength have also been observed [21,40]. Bleaching treatment may alter the dentin chemical structure by loss of organic components (calcium and phosphorus) [41] and act in intertubular and peritubular dentin by breaking the
polypeptide chains and degrading connective tissue components, particularly collagen and hyaluronic acid [42]. These morphological alterations increase dentin permeability [43], reduce surface microhardness [4], and increase metalloproteinases-mediated collagen degradation [14]. The hydrogen peroxide released from bleaching agents can diffuse through enamel and dentin and penetrate the pulp chamber and one of the hypotheses to explain the occurrence of post-bleaching sensitivity is that its degradation products could trigger a local pulp inflammatory reaction, ranging from a mild inflammatory reaction to an acute inflammation or even partial necrosis of the coronal pulp tissue [44]. The indirect cytotoxicity of the active compounds released from bleaching gels is related to their concentration in the agents as well as the contact time with enamel [44,45]. The peroxide diffusion is application timedependent and longer application times may result in higher penetration. The clinical application of high-concentrated hydrogen peroxide bleaching gel on enamel presents toxic effects to odontoblast-like cell cultures [44] as well as the daily application of low-concentrated agents used in the at-home bleaching technique can increase the damages to the dental pulp cells [45]. The null hypothesis of the present study was rejected for the enamel substrate groups treated with 7.5% hydrogen peroxide and the association of 7.5% and 35%, since the control group presented higher micro-shear bond strength values. The null hypothesis was also rejected for the dentin substrate subjected to 7.5% concentration, because the other groups presented higher bond strength values. These results allow the observation that the prolonged use of low concentration gel, indicated for the at-home technique, significantly decreased the bond strength values after bleaching, and it can be affirmed that enamel/dentin composite restorations seem to be more sensitive to the activity of the product. Clinically, the bleaching agents are applied to intact surfaces, and to cavities involving enamel and dentin substrates. The micro-shear testing method used small areas of ground enamel and dentin surfaces, which may accelerate or exaggerate the effects of dental bleaching on dental hard tissues and resins. Nevertheless, even considering it as an exaggerated understanding of the effect of the product, it is important to recognize that there may be a negative effect of its use. It is well known that clinicians frequently need to change resinbased composite restorations in anterior teeth after bleaching, because the restoration color is not altered by the bleaching procedure. However, there was no understanding of the need to replace restorations where esthetics was not a primordial consideration. In the present study, the bond strength of restorative material to enamel and dentin was reduced after the use of lowconcentration bleaching agents. Although laboratory tests do not reproduce intraoral conditions, this study gives support to better understanding of the interaction of bleaching agents with dental substrates. However, further investigations are needed to clarify and understand this phenomenon.
5. Conclusion Within the limitations of this study, it was shown that 7.5% hydrogen peroxide bleaching agent could significantly affect the micro-shear bond strength between the restoration and dental substrates (enamel and dentin). It was also observed that the association of 7.5% and 35% hydrogen peroxide significantly affected the micro-shear bond strength between restoration and enamel. The damage caused to the restoration/dental structure bond strength by the bleaching agent was a result of prolonged use of the bleaching gel and was not related to peroxide concentration.
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Acknowledgments This study was partially supported by the Brazilian National Research Council (CNPq). The authors thank the Laboratory of Quick Solidification for allowing the use of their equipment; Mr. Marconi Queiroga Sarmento for executing the experimental design of the study (Fig. 1) and FGM and 3M/ESPE for providing the materials used in this study. References [1] Barcellos DC, Benetti P, Fernandes Jr. VVB, Valera MC. Effect of carbamide peroxide bleaching gel concentration on the bond strength of dental substrates and resin composite. Operative Dentistry 2010;35:463–9. [2] Far C, Ruse ND. Effect of bleaching on fracture toughness of composite-dentin bonds. Journal of Adhesive Dentistry 2003;5:175–82. [3] Haywood VB. Nightguard vital bleaching: current concepts and research. Journal of the American Dental Association 1997;128(4):392–498 ;128 (Suppl.):1-64 o http://jada.ada.org/content/by/year/19974 . [4] Faraoni-Romano J, da Silveira AG, Turssi CP, Serra MC. Bleaching agents with varying concentrations of carbamide and/or hydrogen peroxides: effect on dental microhardness and roughness. Journal of Esthetic and Restorative Dentistry 2008;20:395–402. [5] Pugh Jr. G, Zaidel L, Lin N, Stranick M, Bagley D. High levels of hydrogen peroxide in overnight tooth-whitening formulas: effects on enamel and pulp. Journal of Esthetic and Restorative Dentistry 2005;17:40–5. [6] Haywood VB, Heymann HO. Nightguard vital bleaching. Quintessence International 1989;20:173–6. [7] Lynch E, Sheerin A, Samarawickrama DY, Atherton MA, Claxson AW, Hawkes J, et al. Molecular mechanisms of the bleaching actions associated with commercially-available whitening oral health care products. Journal of the Irish Dental Association 1995;41:94–102. [8] Plotino G, Buono L, Grande NM, Pameijer CH, Somma F. Nonvital tooth bleaching: a review of the literature and clinical procedures. Journal of Endodontics 2008;34:394–407. [9] Joiner A. The bleaching of teeth: a review of the literature. Journal of Dentistry 2006;34:412–9. [10] Feinman RA, Madray G, Yarborough D. Chemical, optical, and physiologic mechanisms of bleaching products: a review. Practical Periodontics and Aesthetic Dentistry 1991;3:32–6. [11] Vieira C, Silva-Sousa YT, Pessarello NM, Rached-Junior FA, Souza-Gabriel AE. Effect of high-concentrated bleaching agents on the bond strength at dentin/ resin interface and flexural strength of dentin. Brazilian Dental Journal 2012;23:28–35. [12] Attin T, Hannig C, Wiegand A, Attin R. Effect of bleaching on restorative materials and restorations—a systematic review. Dental Materials 2004;20:852–61. [13] Joiner A. Review of the effects of peroxide on enamel and dentine properties. Journal of Dentistry 2007;35:889–96. [14] Toledano M, Yamauti M, Osorio E, Osorio R. Bleaching agents increase metalloproteinases-mediated collagen degradation in dentin. Journal of Endodontics 2011;37:1668–72. [15] Potocnik I, Kosec L, Gaspersic D. Effect of 10% carbamide peroxide bleaching gel on enamel microhardness, microstructure, and mineral content. Journal of Endodontics 2000;26:203–6. [16] Zalkind M, Arwaz JR, Goldman A, Rotstein I. Surface morphology changes in human enamel, dentin and cementum following bleaching: a scanning electron microscopy study. Endodontics and Dental Traumatology 1996;12:82–8. [17] Lopes GC, Bonissoni L, Baratieri LN, Vieira LC, Monteiro Jr. S. Effect of bleaching agents on the hardness and morphology of enamel. Journal of Esthetic and Restorative Dentistry 2002;14:24–30. [18] Basting RT, Rodrigues AL, Serra MC. Micromorphology and surface roughness of sound and demineralized enamel and dentin bleached with a 10% carbamide peroxide bleaching agent. American Journal of Dentistry 2007;20:97–102. [19] Berger SB, Cavalli V, Martin AA, Soares LE, Arruda MA, Brancalion ML, et al. Effects of combined use of light irradiation and 35% hydrogen peroxide for dental bleaching on human enamel mineral content. Photomedicine and Laser Surgery 2010;28:533–8. [20] Bistey T, Nagy IP, Simo A, Hegedus C. In vitro FT-IR study of the effects of hydrogen peroxide on superficial tooth enamel. Journal of Dentistry 2007;35:325–30. [21] Cavalli V, Arrais CA, Giannini M, Ambrosano GM. High-concentrated carbamide peroxide bleaching agents effects on enamel surface. Journal of Oral Rehabilitation 2004;31:155–9.
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Effect of peroxide-based bleaching agents on enamel ultimate tensile strength. Operative Dentistry 2005;30:318–24. [41] Kawamoto K, Tsujimoto Y. Effects of the hydroxyl radical and hydrogen peroxide on tooth bleaching. Journal of Endodontics 2004;30:45–50. [42] Zimmerman B, Datko L, Cupelli M, Alapati S, Dean D, Kennedy M. Alteration of dentin–enamel mechanical properties due to dental whitening treatments. Journal of the Mechanical Behavior of Biomedical Materials 2010;3:339–46. [43] Carrasco LD, Froner IC, Corona SA, Pecora JD. Effect of internal bleaching agents on dentinal permeability of non-vital teeth: quantitative assessment. Dental Traumatology 2003;19:85–9. [44] Soares DG, Ribeiro AP, da Silveira Vargas F, Hebling J, de Souza Costa CA. Efficacy and cytotoxicity of a bleaching gel after short application times on dental enamel. Clinical Oral Investigations. http://dx.doi.org/10.1007/ s00784-012-0883-1, in press. [45] Lima AF, Ribeiro AP, Soares DG, Sacono NT, Hebling J, de Souza Costa CA. Toxic effects of daily applications of 10% carbamide peroxide on odontoblastlike MDPC-23 cells. Acta Odontologica Scandinavica 2013;71:1319–25 http://dx.doi.org/10.3109/00016357.2012.762992.
Contents lists available at ScienceDirect
International Journal of Adhesion & Adhesives journal homepage: www.elsevier.com/locate/ijadhadh
Influence of hydrogen peroxide-based bleaching agents on the bond strength of resin–enamel/dentin interfaces Victor França Didier a, André Ulisses Dantas Batista a, Robinsom Viégas Montenegro a, Rodrigo Borges Fonseca b, Fabíola Galbiatti de Carvalho c, Silvio de Barros d, Hugo Lemes Carlo a,n a Federal University of Paraiba, Health Science Center, Operative Dentistry Department, Universidade Federal da Paraíba, Departamento de Odontologia Restauradora, Cidade Universitária, 58051-900 João Pessoa, PB, Brazil b Federal University of Goias, School of Dentistry, Universidade Federal de Goiás, Faculdade de Odontologia, Praça Universitária esquina com 1ª Avenida, s/n, Setor Universitário, 74605-220 Goiânia, GO, Brazil c Federal University of Campina Grande, Health and Rural Technology Center, Academic Unit of Biological Sciences, Universidade Federal de Campina Grande, Centro de Saúde e Tecnologia Rural, Unidade Acadêmica de Ciências Biológicas, Av. Universitária, s/n, Santa Cecília, 58708-110 Patos, PB, Brazil d Federal Center of Technological Education in Rio de Janeiro, Laboratório de Compósitos e Adesivos Av. Maracanã, 229-Bloco E-5º andar, 20271-110 Rio de janeiro, RJ, Brazil
art ic l e i nf o
a b s t r a c t
Available online 29 August 2013
This study evaluated the effect of different bleaching techniques on the bond strength of pre-existing adhesive restorations in enamel and dentin. Hydrogen peroxide-based bleaching gels with different concentrations (7.5% and 35%) were used on composite restorations of Adper Single Bond 2 (3M/ESPE, St. Paul, USA) and Filtek Z250 (3M/ESPE, St. Paul, USA). Twenty human third molars were randomly divided into 8 groups: GE—enamel control; GE7.5—bleaching using 7.5% hydrogen peroxide; GE35—bleaching using 35% hydrogen peroxide; GE 7.5þ35—bleaching using 7.5% and 35% hydrogen peroxide; GD—dentin control; GD7.5—7.5% hydrogen peroxide; GD35—35% hydrogen peroxide; and GD 7.5þ 35—7.5% and 35% hydrogen peroxide. Bleaching was performed using long clinical application-time to low concentration gel, and short clinical application-time to high concentration gel. Unbleached specimens were stored in artificial saliva for 14 days. Specimens subject to micro-shear testing and data were analyzed by Analysis of Variance and Tukey's test (p¼ 0.05). Enamel micro-shear bond strength was reduced after 7.5% hydrogen peroxide and after association of 7.5% and 35% hydrogen peroxide. Bleaching treatment altered dentin bond strength only when using 7.5% hydrogen peroxide. The results suggest that the bond strength of the restorations was influenced by the clinical extent of bleaching-gel application time and was not dependent on bleaching-gel concentration. & 2013 Elsevier Ltd. All rights reserved.
Keywords: Enamel Dentin Dental adhesives Hybrid layer
1. Introduction Tooth whitening, or bleaching, has gained enormous acceptance as well as popularity in the search for an esthetically pleasing smile [1,2]. Reports have indicated that it is a conservative and effective technique to treat discolored and stained anterior teeth [3–5]. Stains contain chromophoric groups, made up of many conjugated carbon–carbon double bonds that absorb light in the visible range of the spectrum and thus appear colorful to the human eye [3,6,7]. The bleaching process is based on a complex oxidation reaction in which oxygen-free radicals, due to their low molecular weight, infiltrate through the enamel and
n
Corresponding author. Tel.: þ 55 83 3216 7250; fax: þ 55 83 3216 7409. E-mail address: [email protected] (H. Lemes Carlo).
0143-7496/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijadhadh.2013.08.009
dentin substrates [8,9]. The product releases free radicals that break up conjugation either by cleavage of, or addition to carbon– carbon double bonds [10]. Once the conjugation is broken up, these molecules no longer absorb in the visible range of the spectrum [1–3,6,7]. At present, there is a broad range of bleaching agents available, containing varying concentrations of carbamide peroxide, hydrogen peroxide and sodium perborate [4,11,12]. Vital tooth bleaching systems include dentist-supervised at-home (nightguard) and in-office techniques, and the combination of the two (at-home þ in-office). For home bleaching, a relatively low concentration of whitening agent (10–22% carbamide peroxide gel or 3–9,5% hydrogen peroxide gel) is typically used, and is applied to the teeth by means of a custom-fabricated mouth guard that is worn for at least 2 weeks. Whereas, for in-office bleaching, relatively high concentrations of whitening agents are generally used, for
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example, 20–35% hydrogen peroxide or 35% carbamide peroxidecontaining products, for shorter periods of time [9,13,14]. In nonvital tooth bleaching, the medicament (sodium perborate) is placed in the pulp chamber, sealed, left for 3–7 days, and afterwards, it is replaced regularly until an acceptable degree of lightening is achieved [8,11,14]. The widespread use of bleaching agents has caused concern with regard to their oxidizing effects on soft tissues, dental structures and restorations. Alterations in enamel surface topography have been observed after application of at-home bleaching [15–18] and in-office bleaching [19–21] products. Alterations have also been detected in dentin after both of the mentioned techniques [4,14,22]. The deleterious effect of bleaching on the bond strength of resin materials has been observed [23–25]. However, the effect of bleaching solution on pre-existing restoration bonded interfaces has not yet been completely determined. Bleaching gels may contain solvents and other components, which might contribute to increase the solubility or degradation of adhesives and composite resins, compromising the longevity of restorations that are not indicated for replacement [26]. Thus, the aim of this research was to conduct an in vitro study to evaluate the effects of the application of hydrogen peroxide bleaching gel of different concentrations, using different techniques, on the micro-shear bond strength between dental substrates (enamel and dentin) and composite resin. The null hypothesis was that the bond strength would not be influenced by the bleaching agent application in any of the groups tested.
30 s in enamel and 15 s in dentin. After this they were rinsed for 30 s and Absorbent paper was used to remove the excess moisture (Snack, Melhoramentos Papéis Ltda., Caieiras, SP, Brazil). The adhesive system (Single Bond 2–3M/ESPE, St. Paul, MN, USA) was applied on enamel and dentin, according to the manufacturer's instructions. Customized 0.5 mm-thick elastomer molds with cylinder-shaped orifices (1.2 mm in diameter), were placed on the tooth surfaces, allowing delimitation of the bonding area. After photo-activating the bonding agent for 10s (LED light curing unit, Coltolux LED—Coltène/Whaledent, Cuyahoga Falls, OH, USA), the orifices were filled with composite resin (Filtek Z250—3M/ ESPE, St.Paul, MN, USA)—3M/ESPE, St. Paul, MN, USA) and then photo-activation was repeated for 40 s. The output irradiance of the curing unit was 850 mW/cm2, confirmed with a digital power meter (Ophir Optronics, Danvers, MA, USA). After storing the specimens in distilled water at 37 1C for 24 h, all resin cylinders were checked at 40 magnification. Those presenting flaws, irregularities or bonding defects were eliminated. Next, the specimens were randomly divided into two control groups and six experimental groups, according to the hydrogen peroxide concentration and bleaching treatment used:
GE: Enamel control. GD: Dentin Control. GE7.5: Enamel submitted to bleaching treatment using 7.5% hydrogen peroxide.
GE35: Enamel submitted to bleaching treatment using 35% hydrogen peroxide.
GE7.5 þ35: Enamel submitted to bleaching treatment using the
2. Materials and methods
association of 7.5% and 35% hydrogen peroxide.
Commercial brand names, chemical composition and material manufacturers are presented in Table 1. In order to obtain specimens for the micro-shear bond strength test, the experimental set-up shown in Fig. 1 was carried out [27]. Twenty sound human third molars that were refrigerated in a solution of 0.1% thymol (LabSynth Produtos para Laboratórios Ltda., Diadema, SP, Brazil) for adequate decontamination prior to its manipulation for no longer than three months after extraction and placed in distilled water for 24 h before beginning the experiment. The teeth used in this study were obtained under Protocol no. 081/2010, which was analyzed and approved by the Research Ethics Committee, Lauro Wanderley University Hospital, Federal University of Paraiba. The specimens were prepared using a flexible diamond disc at low speed (n. 7020—KG Sorensen, Barueri, SP, Brazil) and under water cooling to perform two cuts. In the first, the tooth root was removed and in the second the crown was divided in the mesiodistal direction. After sectioning forty hemi-crowns were obtained, which were embedded in acrylic resin (Vipi, Pirassununga, SP, Brazil). The surfaces were wet-ground with 180, 220, 400 and 600-grit SiC abrasive papers, in order to create a smooth, flat enamel and dentin surface. The enamel and dentin surfaces were treated with 37% phosphoric acid (Adper Scotchbond—3M/ESPE, St. Paul, MN, USA) for
GD7.5: Dentin submitted to bleaching treatment using 7.5% hydrogen peroxide.
GD35: Dentin submitted to bleaching treatment using 35% hydrogen peroxide;
GD7.5þ35: Dentin submitted to bleaching treatment using the association of 7.5% and 35% hydrogen peroxide.
Groups not submitted to bleaching agent (control) were kept in artificial saliva at 37 1C for 14 days. Treatment with 7.5% hydrogen peroxide was carried out using 0.02 ml of the agent administered at the adhesive interface in a daily period of 1 h for 14 days. During the bleaching period, specimens were placed in 100% relative humidity at 37 1C. After daily bleaching, the specimens were thoroughly rinsed with deionized water. During the time when no bleaching treatment was being performed, the specimens were kept in artificial saliva at 37 1C. The specimens were tested 24 h after the end of the bleaching regimen on the 14th day. Groups submitted to 35% hydrogen peroxide received 0.02 ml of the agent administered at the adhesive interface in three rounds. During each round the product was applied for fifteen minutes and repeated twice; there was a time interval of three days between rounds. During the bleaching period, specimens were placed in 100% relative humidity at 37 1C. After bleaching, the specimens
Table 1 Materials tested—commercial brand names, manufacturer, batch number, and composition.n Material
Composition
Adper single bond 2 (3M/ESPE, St Paul, MN, USA) Silane treated silica (nanofiller), Bis-GMA, HEMA, dimethacrylate, methacrylate functional copolymer of polyacrylic and polytaconic acid, water, ethyl alcohol Filtek Z250 (3M/ESPE, St Paul, MN, USA) Silane treated ceramic, BISEMA, UDMA, BISGMA, TEGDMA White class 7.5% (FGM, Joinvile, SC, Brazil) Hydrogen peroxide 7.5%, carbopol, potassium nitrate, sodium fluoride, calcium digluconate, water Whiteness HP (FGM, Joinvile, SC, Brazil) Hydrogen peroxide 30–35%, thickener, red dye, glycol, water n
According to manufacturer's information.
Batch number 9UU N148344BR 2012.FEB 180111
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Fig. 1. Experimental design of the study. (1) Removal of the tooth root; (2) division of the crown in the mesio-distal direction; (3) teeth embedded in acrylic resin showing flat surface of enamel and middle dentin after wet-grinding; (4) elastomer mold with cylinder-shaped orifices positioned on the surface; (5) resin cylinders after polymerization; (6) bleaching treatment of the experimental groups; (7) no treatment of the control group; and (8) micro-shear test. Table 2 Mean bond strength values in MPa ( 7 standard deviation) and Tukey Post-hoc.
Enamel Dentin
Control
7.5% hydrogen peroxide
35% hydrogen peroxide
35%þ 7.5% hydrogen peroxide
34.66A ( 7 9.74) 27.41a ( 7 7.30)
11.19C ( 73.81) 15.28b ( 76.13)
30.61AB (7 11.01) 26.86a (7 6.40)
23.78B ( 77.53) 25.15a ( 76.13)
Values with identical capital letters indicate no significant difference—Tukey Post-Hoc test (P40.05). Values with identical lower case letters indicate no significant difference—Tukey Post-Hoc test (P40.05).
were rinsed with deionized water. During the time when no bleaching treatment was being performed, the specimens were kept in artificial saliva at 37 1C. The specimens were tested 24 h after the end of the bleaching regimen on the 9th day. Groups submitted to 35% and 7.5% hydrogen peroxide received 0.02 ml of the first agent administered at the adhesive interface in one round; the product was applied for fifteen minutes and repeated twice. On the following day 0.02 ml of the second agent was administered at the adhesive interface in a daily period of 1 h for 7 days. During the bleaching period, specimens were placed in 100% relative humidity at 37 1C. After bleaching, the specimens were rinsed with deionized water. During the time when no bleaching treatment was being performed, the specimens were kept in artificial saliva at 37 1C. The specimens were tested 24 h after the end of the bleaching regimen on the 8th day. For the micro-shear test, the tooth embedded in acrylic resin was placed in a device with 25 mm-diameter at the base of the testing machine in left lateral position (Fig. 1). A thin steel wire (0.2 mm in diameter) was looped around each composite resin cylinder and aligned with the bonding interface (Fig. 1). The test was conducted in a universal testing machine (model AG-IC; Shimadzu, Kyoto, Japan), at a crosshead speed of 0.5 mm/min until failure. Micro-shear bond strength calculations were made using the following equation: s ¼L/A, where s is the ultimate shear strength (MPa), L is the shear loading at the moment of failure (N), and A is the bonding area (mm2). For each group, 5 specimens were tested, consisting of four cylinders constructed on the enamel and four on dentin per specimen. The cylinders were considered as experimental unit. Bond strength data were submitted to an exploratory analysis that showed the data could be evaluated by parametric tests due to normal distribution (Kolmogorov–Smirnov test and Shapiro– Wilk test—α ¼0.05) and homogeneity (Levene's test—α¼0.05) indicating the use of one-way Analysis of Variance and Tukey's Test at a 5% level of confidence. The fractured specimens were examined by optical microscopy at 200 magnification. Failure modes were classified as follows: adhesive failure (Mode 1), cohesive failure within enamel/dentin (Mode 2), cohesive failure
within composite resin (Mode 3), or mixed failure involving bonding agent and enamel/dentin (Mode 4).
3. Results Table 2 shows the mean micro-shear bond strengths and standard deviations for the experimental groups. One-way ANOVA revealed significant difference among the enamel groups (p ¼ 0.0001) and dentin groups (p¼ 0.0001) for the interaction between bleaching treatment and a specific dental substrate. Tukey's test showed that the enamel micro-shear bond strength of the control group presented no significantly higher mean values compared with 35% hydrogen peroxide treatment, and presented significantly higher mean values when compared with the treatment using 7.5% concentration. The association of 35%þ7.5% hydrogen peroxide did not show higher values compared with 35% hydrogen peroxide treatment and significantly higher mean values when compared with 7.5% hydrogen peroxide and control. Considering the results of the dentin groups it was observed that the micro-shear bond strength of the control group presented no significantly higher mean values in comparison with 35% hydrogen peroxide, and with the associated treatment (35%þ 7.5%). The 7.5% hydrogen peroxide treatment presented significantly lower mean values when compared with the other groups. Optical examination of the fractured interfaces showed that on enamel and dentin of both unbleached and bleached specimens, the fractures occurred in the adhesive layer close to the substrate (Mode 1), in the substrate (Mode 2) and/or involving bonding agent and enamel/dentin (mixed failure—Mode 4). Fig. 2 presents these results.
4. Discussion The present study evaluated the influence of different bleaching protocols on the micro-shear bond strength of composite resin
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100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
MODE 4 MODE 3 MODE 2 MODE 1
GE
GE 7.5
GE 35 GE 7.5+35
GD
GD 7.5
GD 35 GD 7.5+35
Fig. 2. Failure analysis of fractured interfaces in enamel and dentin of unbleached and bleached specimens. Mode 1—fractures in the adhesive layer close to the substrate; Mode 2—fractures in the substrate; Mode 3—cohesive failure within composite resin; and Mode 4—fractures involving bonding agent and enamel/ dentin (mixed failure).
restorations in enamel and dentin. Different concentrations of hydrogen peroxide and different application protocols were analyzed. A decrease was observed in the bond strength to both substrates after bleaching treatment using the 7.5% concentration or its association with the 35% concentration on enamel. The high concentration used for short periods was shown to be better than the use of low concentration for extended periods. Therefore, the main hypothesis of the present study was not accepted. Bleaching is a widely used conservative treatment for pigmented or darkened teeth, and hydrogen peroxide is one of the primary agents used [28]. Because it has a low molecular content, its degradation releases oxygen free radicals (dOH anddOOH), or the perhydroxyl anion (–OOH), which are able to penetrate the enamel and move along the dental structure reaching the dentin [8–10]. The hydrogen peroxide concentration of commercial products varies from 3% to 35% [9,14]. No difference was observed in the degree of bleaching achieved in whitening treatments with hydrogen peroxide or carbamide peroxide, irrespective of the concentration, at the end of treatment [29–31]. However, a much faster bleaching effect is obtained with high concentration gels. Therefore, higher concentrations are used when a faster bleaching result is desired [32]. Analysis of the enamel/dentin failure modes showed similar results for both bleached and unbleached samples. It was observed a prevalence of mixed failures involving bonding agent and enamel/dentin and occasionally it was observed adhesive failure and cohesive failure within enamel/dentin. One of the theories regarding the deleterious effect of bleaching on tooth structure and resin based materials is related to the reactive oxygen released and its accumulation [33]. The physical properties of restorative materials, such as microhardness, flexural strength, flexural modulus, and fracture toughness influence the quality and durability of restorations [34]. It has been claimed that peroxides induce oxidative cleavage of polymer chains, and therefore unreacted double bonds are expected to be the most vulnerable parts of the polymers. Moreover, free radicals induced by peroxides may impact the resin–filler interface and cause filler– matrix debonding and a slight, but statistically significant, increase in surface roughness [12,35,36]. Mortavazi et al. [37] also reported increased microleakage at dentinal margins, which compromised the marginal seal of class V composite resin restorations. Concerns have been expressed as regards the safety of bleaching agents for use on tooth structure. A decrease was observed in the mean of the areas of the biological phosphate bands at the superficial and subsuperficial level of enamel after bleaching, probably due to hydroxyapatite dissolution [38]. Changes in surface roughness and surface microhardness [4], porosities on the surface of transversely fractured enamel prisms [39] and reduction in fracture toughness and tensile strength have also been observed [21,40]. Bleaching treatment may alter the dentin chemical structure by loss of organic components (calcium and phosphorus) [41] and act in intertubular and peritubular dentin by breaking the
polypeptide chains and degrading connective tissue components, particularly collagen and hyaluronic acid [42]. These morphological alterations increase dentin permeability [43], reduce surface microhardness [4], and increase metalloproteinases-mediated collagen degradation [14]. The hydrogen peroxide released from bleaching agents can diffuse through enamel and dentin and penetrate the pulp chamber and one of the hypotheses to explain the occurrence of post-bleaching sensitivity is that its degradation products could trigger a local pulp inflammatory reaction, ranging from a mild inflammatory reaction to an acute inflammation or even partial necrosis of the coronal pulp tissue [44]. The indirect cytotoxicity of the active compounds released from bleaching gels is related to their concentration in the agents as well as the contact time with enamel [44,45]. The peroxide diffusion is application timedependent and longer application times may result in higher penetration. The clinical application of high-concentrated hydrogen peroxide bleaching gel on enamel presents toxic effects to odontoblast-like cell cultures [44] as well as the daily application of low-concentrated agents used in the at-home bleaching technique can increase the damages to the dental pulp cells [45]. The null hypothesis of the present study was rejected for the enamel substrate groups treated with 7.5% hydrogen peroxide and the association of 7.5% and 35%, since the control group presented higher micro-shear bond strength values. The null hypothesis was also rejected for the dentin substrate subjected to 7.5% concentration, because the other groups presented higher bond strength values. These results allow the observation that the prolonged use of low concentration gel, indicated for the at-home technique, significantly decreased the bond strength values after bleaching, and it can be affirmed that enamel/dentin composite restorations seem to be more sensitive to the activity of the product. Clinically, the bleaching agents are applied to intact surfaces, and to cavities involving enamel and dentin substrates. The micro-shear testing method used small areas of ground enamel and dentin surfaces, which may accelerate or exaggerate the effects of dental bleaching on dental hard tissues and resins. Nevertheless, even considering it as an exaggerated understanding of the effect of the product, it is important to recognize that there may be a negative effect of its use. It is well known that clinicians frequently need to change resinbased composite restorations in anterior teeth after bleaching, because the restoration color is not altered by the bleaching procedure. However, there was no understanding of the need to replace restorations where esthetics was not a primordial consideration. In the present study, the bond strength of restorative material to enamel and dentin was reduced after the use of lowconcentration bleaching agents. Although laboratory tests do not reproduce intraoral conditions, this study gives support to better understanding of the interaction of bleaching agents with dental substrates. However, further investigations are needed to clarify and understand this phenomenon.
5. Conclusion Within the limitations of this study, it was shown that 7.5% hydrogen peroxide bleaching agent could significantly affect the micro-shear bond strength between the restoration and dental substrates (enamel and dentin). It was also observed that the association of 7.5% and 35% hydrogen peroxide significantly affected the micro-shear bond strength between restoration and enamel. The damage caused to the restoration/dental structure bond strength by the bleaching agent was a result of prolonged use of the bleaching gel and was not related to peroxide concentration.
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Acknowledgments This study was partially supported by the Brazilian National Research Council (CNPq). The authors thank the Laboratory of Quick Solidification for allowing the use of their equipment; Mr. Marconi Queiroga Sarmento for executing the experimental design of the study (Fig. 1) and FGM and 3M/ESPE for providing the materials used in this study. References [1] Barcellos DC, Benetti P, Fernandes Jr. VVB, Valera MC. Effect of carbamide peroxide bleaching gel concentration on the bond strength of dental substrates and resin composite. Operative Dentistry 2010;35:463–9. [2] Far C, Ruse ND. Effect of bleaching on fracture toughness of composite-dentin bonds. Journal of Adhesive Dentistry 2003;5:175–82. [3] Haywood VB. Nightguard vital bleaching: current concepts and research. Journal of the American Dental Association 1997;128(4):392–498 ;128 (Suppl.):1-64 o http://jada.ada.org/content/by/year/19974 . [4] Faraoni-Romano J, da Silveira AG, Turssi CP, Serra MC. Bleaching agents with varying concentrations of carbamide and/or hydrogen peroxides: effect on dental microhardness and roughness. Journal of Esthetic and Restorative Dentistry 2008;20:395–402. [5] Pugh Jr. G, Zaidel L, Lin N, Stranick M, Bagley D. High levels of hydrogen peroxide in overnight tooth-whitening formulas: effects on enamel and pulp. Journal of Esthetic and Restorative Dentistry 2005;17:40–5. [6] Haywood VB, Heymann HO. Nightguard vital bleaching. Quintessence International 1989;20:173–6. [7] Lynch E, Sheerin A, Samarawickrama DY, Atherton MA, Claxson AW, Hawkes J, et al. Molecular mechanisms of the bleaching actions associated with commercially-available whitening oral health care products. Journal of the Irish Dental Association 1995;41:94–102. [8] Plotino G, Buono L, Grande NM, Pameijer CH, Somma F. Nonvital tooth bleaching: a review of the literature and clinical procedures. Journal of Endodontics 2008;34:394–407. [9] Joiner A. The bleaching of teeth: a review of the literature. Journal of Dentistry 2006;34:412–9. [10] Feinman RA, Madray G, Yarborough D. Chemical, optical, and physiologic mechanisms of bleaching products: a review. Practical Periodontics and Aesthetic Dentistry 1991;3:32–6. [11] Vieira C, Silva-Sousa YT, Pessarello NM, Rached-Junior FA, Souza-Gabriel AE. Effect of high-concentrated bleaching agents on the bond strength at dentin/ resin interface and flexural strength of dentin. Brazilian Dental Journal 2012;23:28–35. [12] Attin T, Hannig C, Wiegand A, Attin R. Effect of bleaching on restorative materials and restorations—a systematic review. Dental Materials 2004;20:852–61. [13] Joiner A. Review of the effects of peroxide on enamel and dentine properties. Journal of Dentistry 2007;35:889–96. [14] Toledano M, Yamauti M, Osorio E, Osorio R. Bleaching agents increase metalloproteinases-mediated collagen degradation in dentin. Journal of Endodontics 2011;37:1668–72. [15] Potocnik I, Kosec L, Gaspersic D. Effect of 10% carbamide peroxide bleaching gel on enamel microhardness, microstructure, and mineral content. Journal of Endodontics 2000;26:203–6. [16] Zalkind M, Arwaz JR, Goldman A, Rotstein I. Surface morphology changes in human enamel, dentin and cementum following bleaching: a scanning electron microscopy study. Endodontics and Dental Traumatology 1996;12:82–8. [17] Lopes GC, Bonissoni L, Baratieri LN, Vieira LC, Monteiro Jr. S. Effect of bleaching agents on the hardness and morphology of enamel. Journal of Esthetic and Restorative Dentistry 2002;14:24–30. [18] Basting RT, Rodrigues AL, Serra MC. Micromorphology and surface roughness of sound and demineralized enamel and dentin bleached with a 10% carbamide peroxide bleaching agent. American Journal of Dentistry 2007;20:97–102. [19] Berger SB, Cavalli V, Martin AA, Soares LE, Arruda MA, Brancalion ML, et al. Effects of combined use of light irradiation and 35% hydrogen peroxide for dental bleaching on human enamel mineral content. Photomedicine and Laser Surgery 2010;28:533–8. [20] Bistey T, Nagy IP, Simo A, Hegedus C. In vitro FT-IR study of the effects of hydrogen peroxide on superficial tooth enamel. Journal of Dentistry 2007;35:325–30. [21] Cavalli V, Arrais CA, Giannini M, Ambrosano GM. High-concentrated carbamide peroxide bleaching agents effects on enamel surface. Journal of Oral Rehabilitation 2004;31:155–9.
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