Australian Dental Journal

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1 Australian Dental Journal The official journal of the Australian Dental Association SCIENTIFIC ARTICLE Australian Dental Journal 2012; 57: doi: /j x Tooth whitening with hydrogen carbamide peroxides in association with a paste at different proportions AAM de Vasconcelos,* AGG Cunha,* BCD Borges,* CT Machado,* AJS dos Santos* *School of Dentistry, Potiguar University (Laureate International Universities), Natal, Brazil. ABSTRACT Background: Different enhanced peroxide formulations have been developed to overcome mineral loss during tooth whitening. This study investigated the impact on tooth whitening from combining a paste with home peroxide agents at several proportions. Methods: Ninety bovine incisors were randomly allocated into nine groups (n = 10) and exposed to 7.5% hydrogen peroxide (HP), 16% carbamide peroxide (CP), a paste (Tooth Mousse MI Paste, GC Corporation, Tokyo, Japan) and blends of HP CP:MI at three proportions (1:1, 2:1 and 1:2). Tooth whitening was performed for 14 days and its effectiveness was measured by a spectrophotometer utilizing the CIE L*a*b* system (DE, DL*, Da* and Db*). Colour readings were measured at baseline (T0), 7 days of bleaching (), 14 days of bleaching () and 7 days after the end of bleaching (). Data were analysed by two-way ANOVA for paired averages followed by the Tukey s test and Pearson s correlation at 5%. Results: Although CP produced the greatest colour change (DE), all whitening protocols were considered to be effective regardless of the presence. In general, greater changes in DE, DL*, Da* and Db* were detected at, with exhibiting similar results to those at. A greater number of strong correlations with DE values was found for a* (11 15). Conclusions: Within the limitations of this study, the results indicate that the paste did not affect tooth whitening efficacy. Keywords:, tooth whitening, carbamide peroxide, hydrogen peroxide, colour change. Abbreviations and acronyms: CIE = Commission Internationale de l Eclairage; = casein phosphopeptide-amorphous calcium phosphate. (Accepted for publication 6 October 2011.) INTRODUCTION Seeking a more aesthetically pleasing smile has become quite common among patients in the last few decades, 1 and tooth colour stands out as one of their top concerns. 2 With careful diagnosis and appropriate attention to technique, tooth whitening can be considered a conservative and safe approach to treat discoloured teeth. 3 Home bleaching techniques have received worldwide acceptance 4 after being described for the first time in 1989 by Haywood and Heymann. 5 It is now a common practice to whiten discoloured teeth using low concentrations of carbamide and hydrogen peroxides. 1,6 Several methods have been available to evaluate the efficacy of tooth whitening: shade guides, photography, colorimeters, spectrophotometers and computer digitization. 7 9 The CIE L*a*b* system provides a useful tool for quantifying colour properties of teeth and it is believed to be the most complete colour space according to the Commission Internationale de l Eclairage (CIE). 10 Bleached teeth have increased L* values with subsequent reduction in b* values whilst a* values are known to have a minimal influence on this process Despite such reports, few studies have found a linear correlation between each of the L*a*b* parameters and the colour variations expressed in DE in an attempt to establish which of the parameters could strongly influence the total colour change of a tooth. When it comes to tooth whitening, sensitivity is still the most common adverse effect. According to this ª 2012 Australian Dental Association 213

2 AAM de Vasconcelos et al. model, peroxide solutions introduced into the oral environment contact available dentinal surfaces and cause retraction of odontoblastic processes, resulting in rapid fluid movement inside the dentinal tubules. This ultimately manifests in stimulation of mechanoreceptors at the pulp periphery. 14 Demineralization of dental structure due to the low ph of some bleaching agents, presence of by-products originated from protein denaturation (e.g. urea), long exposure of tooth surface and bleaching concentrations have all been reported 1,15 17 in connection with increased tooth sensitivity. To overcome mineral loss, different enhanced carbamide peroxide formulations have been developed. The addition of fluoride and calcium has also been described by other investigators. 6 Recently, a new calcium phosphate remineralization technique based on casein phosphopeptide-amorphous calcium phosphate () (Recaldent TM CAS- RN ) has been developed. 18 This nanocomplex acts as a calcium and phosphate reservoir that attaches itself to dental plaque and tooth surfaces. In this sense, might rapidly obliterate the dentinal tubules by rapid precipitation of calcium phosphate crystals on the surface and also inside the dentinal tubules, increasing remineralization and decreasing sensitivity. The association of a paste (Tooth Mousse MI Paste TM MI, GC Corporation, Tokyo, Japan) with carbamide peroxide has been investigated. Some studies have suggested that TM MI can be used concurrently with a tooth whitening agent in a 1:1 proportion without hindering its bleaching effect. However, there has been no report in the literature evaluating the influence of a combination of TM MI with either hydrogen or carbamide peroxide at different proportions. Thus, the aim of the present study was to investigate the impact of TM MI on tooth whitening when concomitantly using either hydrogen or carbamide peroxide at different proportions. In addition, this study also investigated the linear correlation between the L*a*b* parameters and colour changes (DE). The hypotheses tested are that: (1) the association of tooth whitening agents with a paste at several proportions will not reduce the bleaching efficacy; and (2) a similar correlation between each of the L*a*b* parameters and DE will occur. MATERIALS AND METHODS Experimental design The factors under study were: (1) nine different types of bleaching protocols 7.5% hydrogen peroxide (HP) only, 16% carbamide peroxide (CP) only, TM MI Paste only and blends of HP or CP:TM MI at three proportions (1:1; 2:1, 1:2); and (2) four different time points baseline (T0), 7 days of bleaching (), 14 days of bleaching () and 7 days after the end of bleaching (). Manufacturing data, chemical components and batch numbers of the materials used in this study are listed in Table 1. The experimental units consisted of 90 crowns of bovine incisors randomly assigned to nine groups (n = 10) and subjected to different time intervals according to the manufacturer instructions for each product (Table 2). Specimen preparation Ninety newly-extracted permanent bovine central incisors were selected and stored under refrigeration in a saturated thymol solution until preparation for testing. Teeth with any visible cracks or hypoplastic defects were excluded. The roots were sectioned 2 mm apically to the cemento-enamel junction using disposable double-face diamond discs (KG Sorensen, Barueri, Brazil). The entire crown went through a process of artificial staining according to a method described elsewhere. 20,22 A mixture (1:1) of 1 litre of red wine (Galiotto, Flores da Cunha, RS, Brazil) and black tea (Castellari, Guararema, SP, Brazil) was prepared. The tea solution was produced by boiling 2 g of tea leaves in 100 ml of distilled water for five minutes. The solution was filtered to separate the tea from the infusion. Each tooth was immersed in 10 ml of the staining solution for 7.5 days at 37 C. After staining, the specimens were positioned in a plastic mould and embedded using a self-curing polystyrene resin (Piraglass, Piracicaba, SP, Brazil). The enamel surfaces of the teeth were grounded flat using SiC paper-grits #120, #320 and #400, and then polished with #600, #1200 and #2400 grit aluminium oxide abrasive papers containing a 0.1 lm alumina polishing suspension (Pantec, Panambra, Brazil). These steps were carried out on a polishing machine (APL-4, Arotec, São Paulo, SP, Brazil), exposing an area of enamel of 10 mm in diameter. In between the stages of wearing polishing, the samples were cleaned in an ultrasonic cleaner (Ultrasonic Cleaner, Odontobrás, São Paulo, Brazil) and immersed in distilled water for five minutes. Tooth whitening procedures The whitening procedure was performed over 14 days according to the manufacturer s instructions. For each specimen, a tray was fabricated in a vacuum plasticizer (Plastivac P7, Bioart, São Carlos, SP, Brazil) using lowdensity polyethylene plates (FGM, Joinville, SC, Brazil). The blends were prepared freshly by mixing the bleaching gel (HP or CP) to the paste until obtaining a homogeneous mixture which was loaded 214 ª 2012 Australian Dental Association

3 paste and at-home bleaching Table 1. Materials used in this study Commercial brand and manufacturer Batch number Chemical composition White Class with Calcium (FGM Dental Products, Joinville, SC, Brazil) % hydrogen peroxide gel, neutralized carbopol, potassium nitrate, sodium fluoride, aloe vera, calcium gluconate, stabilizer, deionized water and surfactant Whiteness Perfect (FGM Dental Products, Joinville, SC, Brazil) % carbamide peroxide, neutralized carbopol, potassium nitrate, sodium fluoride, humectant (Glycol) and deionized water MI Paste (GC Corporation, Tokyo, Japan) M Pure water,, D-sorbitol, propylene glycol, silicon dioxide, titanium dioxide, xylitol, phosphoric acid, flavouring, zinc oxide, sodium saccharin, ethyl p-hydroxybezoate, magnesium oxide, guar gum, propyl p-hydroxybezoate and butyl p-hydroxybezoate Artificial saliva (Farmafórmula, Natal, RN, Brazil) K 2 KPO 4, 70% sorbitol, NaF, KCl, NaCl, MgCl 2.6H 2 0, Nipagin, Sodium Benzoate and Hydroxyethylcellulose Table 2. Experimental groups Group Proportion of peroxide:mi Paste Application time per day HP only 1:0 = 7.5% HP (3 ml):without 60 min HP(1:1) 1:1 = 7.5% HP (1.5 ml): (1.5 ml) 60 min HP(2:1) 2:1 = 7.5% HP (2 ml): (1 ml) 60 min HP(1:2) 1:2 = 7.5% HP (1 ml): (2 ml) 60 min CP only 1:0 = 16% CP (3 ml):without 4 hours CP(1:1) 1:1 = 16% CP (1.5 ml): (1.5 ml) 4 hours CP(2:1) 2:1 = 16% CP (2 ml): (1 ml) 4 hours CP(1:2) 1:2 = 16% CP (1 ml): (2 ml) 4 hours only 0:1 = without bleaching agent: (3 ml) 2 min HP: hydrogen peroxide; CP: carbamide peroxide; : CPP- ACP paste; app: application. into a 3 ml syringe (Embramac, Itajaí, SC, Brazil). Both the peroxides and the paste alone were also loaded into 3 ml syringes. The content of each syringe was enough to bleach the teeth for 7 days, after which it needed to be replenished. A volume of 0.04 ml of each bleaching agent was applied daily to the enamel surface. The individual mould was positioned onto each specimen and stored in a receptacle containing artificial saliva at 37 C. After 4 hours for carbamide peroxide and 60 minutes for hydrogen peroxide, the gel was rinsed off the enamel surface with running distilled water for 15 seconds. When not in contact with either of the bleaching agents, the specimens were kept immersed in artificial saliva at 37 C. This medium was changed daily. by the spectrophotometer with regards to the three coordinate values (L*, a*, b*) as established by the CIE. 23 These values enable the location of an object colour in a three-dimensional colour space. The L* axis represents the degree of lightness within a sample and ranges from 0 (black) to 100 (white). The a* plane represents the degree of green red colour ()a* = green and +a* = red) whilst the b* plane represents the degree of blue yellow colour within the sample ()b* = blue and +b* = yellow). 23 The colour of the specimens was evaluated before (T0), 7 days of bleaching (), 14 days of bleaching (, end of bleaching protocol) and 7 days after the end of bleaching (). For the CIE L*a*b* data, colour was compared using the following parameters: DL*, Da*, Db* and total colour difference (DE) as calculated by the following equation: 23 DE=[(DL*) 2 + (Da*) 2 +(Db*) 2 ] 1 2. Statistical analysis Colour change data measured through the CIE L*a*b* system were analysed by two-way ANOVA for repeated measurements and the Tukey s post hoc test. Linear correlations between DEandDL, DE and Da, and DE and Db were evaluated by the Pearson s correlation test. All tests were performed using the SigmaStat 5 Software (SigmaStat, Windows Version 5.03, Copyrightª Systat Software, Inc., City, Germany) with a 5% level of significance. Colour assessment In the present study, the colour of the specimens was assessed by a spectrophotometer (Easy Shade, Vident, Brea, CA, USA). In order to standardize the area of the tooth for shade taking, a silicon index covering the entire specimen was fabricated with an impression material (Clonage, DFL, Rio de Janeiro, RJ, Brazil). A perforation compatible with the size of the spectrophotometer tip (6 mm diameter) was made with a scalpel blade in the centre of the exposed facial surface. Colour measurement outcomes were provided RESULTS DE There were statistically significant differences between the bleaching protocols (p = ) and the time points (p < ). Table 3 displays the mean values (and standard deviations) of colour change (DE values). At 21 days, all protocols were considered effective and statistically similar with regards to bleaching effectiveness, except for the groups that received either ª 2012 Australian Dental Association 215

4 AAM de Vasconcelos et al. Table 3. Mean values and standard deviations of DE according to groups and time points Group PH only (2.34) Bab (2.32) Aab 9.07 (1.42) Bab PH(1:1) (4.09) ABab (3.30) Aab 8.94 (2.26) Bab PH(2:1) 9.03 (2.14) ABab 10.7 (1.64) Aab 7.57 (1.21) Bab PH(1:2) 8.77 (2.82) Aab (2.54) Aab 6.38 (1.76) Bb CP only (2.49) ABa (3.31) Aa (4.23) Ba CP(1:1) (4.33) Ba (4.94) Aa (5.40) Ba CP(2:1) (4.25) ABab (2.43) Aab 9.19 (2.46) Bab CP(1:2) (4.00) Bab (2.19) Aab (2.87) Bab only 4.97 (4.14) Bb 7.07 (6.47) Ab 5.59 (6.62) ABb PH: hydrogen peroxide; CP: carbamide peroxide; : MI paste containing casein phosphopeptide-amorphous calcium of phosphate. Values followed by same capital letters horizontally and same small letters vertically are not significantly different according to ANOVA and Tukey s post hoc test (p < 0.05). ΔE 15,00 13,00 11,00 9,00 7,00 5,00 3,00 the only or the HP (1:2) protocol, both of which exhibited the lowest values of DE. Regardless of the whitening agent, the mixture of with bleaching agents did not influence the efficiency of peroxides. There was an increase in DE values following the second week of bleaching. The greatest colour change took place at but decreased at, with statistically significant differences. However, comparing all groups altogether, no difference was found between and (Fig. 1). The use of a paste alone was able to produce bleaching. However, it produced the lowest total colour change of all the protocols tested. Greater colour changes were associated with the CP only group regardless of the time point. DL* With regards to this parameter, no statistically significant difference was observed between the bleaching protocols (p > 0.05). However, differences between the time points (p < 0.01) did occur. In general, DL* values were similar at and at, except for the HP(1:1) HP(2:1) HP(1:2) CP(1:1) CP(2:1) CP(1:2) -only Fig. 1 Dispersion graph exhibiting the evolution of DE values according to each time point. : 7 days of bleaching; : immediately after bleaching; : 7 days after the end of the bleaching regimen. ΔL CP1:1 group which exhibited increased values at. Figure 2 displays the results for lightness, showing a decrease at. Greater increases in DL* were associated with the CP only group (at and at ) and with the CP1:1 (at ). Da* For this parameter, statistically significant differences were observed between the bleaching protocols (p < 0.01) and the time points (p < 0.01). The Da* values at were similar to those at in all groups, with a significant increase at in some of them. Figure 3 shows a homogeneous pattern between the groups with a decrease at and an increase at. Whilst the smallest alterations were, regardless of time point, linked to the only group, the most noticeable changes were associated with the CP only group. Db* With regards to Db*, there were statistically significant differences between the bleaching protocols (p < 0.01) and the time points (p < 0.01). The Db* values at HP1:1 HP2:1 HP1:2 CP1:1 CP2:1 CP1:2 -only Fig. 2 Dispersion graph exhibiting the evolution of DL values according to each time point. : 7 days of bleaching; : immediately after bleaching; : 7 days after the end of the bleaching regimen. Δa HP1:1 HP2:1 HP1:2 CP1:1 CP2:1 CP1:2 -only Fig. 3 Dispersion graph exhibiting the evolution of Da values according to each time point. : 7 days of bleaching; : immediately after bleaching; : 7 days after the end of bleaching. 216 ª 2012 Australian Dental Association

5 paste and at-home bleaching Δb were similar to those at for all groups, except for the only ( =, =, ) and the HP1:2 ( = > ) groups. In general, there was a greater reduction in b* values at and an increase at (Fig. 4). However, the only group produced a remarkable decrease in b* at (negative values), after which the values became positive, indicating that the increases in yellow were beyond baseline values. The pattern was homogeneous for all groups, except for the group of only. As in the previous parameter, the HP1:1 HP2:1 HP1:2 CP1:1 CP2:1 CP1:2 -only Fig. 4 Dispersion graph exhibiting the evolution of Db values according to each time point. : 7 days of bleaching; : immediately after bleaching; : 7 days after the end of bleaching. Table 4. Linear correlations between DE and DL*, DE and Da*, and DE and Db* at different time points Groups Time points DE DL DE Da DE Db HP only r 2 = 0.28 r 2 = 0.78 r 2 = 0.58 p = 0.17 p = p = 0.03 r 2 = 0.36 r 2 = 0.76 r 2 = 0.7 p = 0.11 p = 0.01 p = r 2 = r 2 = 0.57 r 2 = 0.18 p = 0.5 p = 0.03 p = 0.29 HP + r 2 = 0.66 r 2 = 0.74 r 2 = 0.58 p = p = p = r 2 = 0.4 r 2 = 0.53 r 2 = 0.47 p = p = p = r 2 = 0.15 r 2 = 0.8 r 2 = 0.41 p = 0.05 p = p = CP only r 2 = 0.81 r 2 = 0.71 r 2 = 0.53 p = p = p = 0.04 r 2 = 0.73 r 2 = 0.73 r 2 = 0.84 p = p = p = r 2 = 0.85 r 2 = 0.85 r 2 = 0.91 p = p = p = CP + only r 2 = 0.58 r 2 = 0.68 r 2 = 0.66 p = p = p = r 2 = 0.4 r 2 = 0.68 r 2 = 0.4 p = p = p = r 2 = 0.61 r 2 = 0.91 r 2 = 0.74 p = p = p = r 2 = 0.96 r 2 = 0.75 r 2 = 0.04 p = p = p = 0.6 r 2 = 0.98 r 2 = 0.80 r 2 = 0.19 p = p = p = 0.27 r 2 = 0.96 r 2 = 0.88 r 2 = 0.18 p = p = p = 0.29 greatest changes in Db* were associated with the CP only group. Linear correlations The correlation coefficient indicated that there were strong, moderate and weak linear correlations between DE and the other three parameters (DL*, Da* and Db*). Table 4 shows the r 2 values for all linear correlations. In the CP groups, the DE appeared to have been influenced by all parameters in a more homogeneous way. However, for hydrogen peroxide, the parameters Da* and Db* appeared to have achieved the strongest linear correlations. The CPP- ACP only group exhibited stronger correlations with DL* and Da*. A greater number of strong correlations with DE values were found for a* (11 15) and L* (07 15) whereas b* showed moderate correlations (07 15) more frequently. No weak correlations were found for Da*. DISCUSSION The first hypothesis tested in this investigation was validated since the combination of tooth whitening agents with paste at several proportions did not reduce the bleaching efficacy. This finding corroborates with previous reports where no reduction in the bleaching potential was observed after mixing peroxide agents to the paste in a 1:1 proportion of peroxides: paste. Although the concentration of peroxides has been reduced (1 2, 1 3 or 2 3) after mixing them with the paste, this was not sufficient to affect colour change after a 14-day bleaching regimen. The CIEL*a*b* three-dimensional colour space system is the most frequently quoted index employed in dental bleaching research. 11 In this system, colour changes are expressed in DE. It has been reported that DE values of at least 3.3 are visually perceptible. 11,24 Because DE* values ranging from 5.59 to were obtained in the present study, all the protocols investigated herein were considered to be effective for tooth whitening, even the one containing only. Some studies have reported that colour changes are more influenced by L* and b* parameters where an increase in L* values coincides with a subsequent reduction in b* values. The a* values have been considered to be the axis with the lowest capacity to influence on this process ,25 Despite such reports, no linear correlation tests have been proposed to verify the actual influence of each factor on DE. In the present study, the a* parameter exhibited a higher number of strong correlations with DE, which explains its potential to significantly influence colour changes as well as L* and b* values. Thus, the second hypothesis ª 2012 Australian Dental Association 217

6 AAM de Vasconcelos et al. was rejected. Most studies where DL* and Db* were considered to be the main parameters to affect colour change have taken into account the fact that they obtained numerically higher means. However, the presence of higher means does not determine in itself the degree of linear relationship of one variable with another. In the present study, for example, the average values of DL*, Da* and Db* were respectively 5.85, 3.05 and In this sense, one would affirm that DL* and Db* would be associated with DE if a correlation test were not performed. Although these parameters (DL* and Db*) have presented higher values than those showed by Da*, it seems that Da* presented fewer variations in the values. For this reason, one can expect DE to have a significant linear dependence on a*. The reduction in b* values has been described as occurring more rapidly and to a greater extent than the L* component. Thus, the b* component could be considered a more important indicator of tooth whitening since the reduction in yellowness is more consistent than the increase in L* values. 26 However, consistent changes in L* and a* values were able to produce colour variations in the group that used only the paste containing. These changes were sufficient to make this protocol effective even without the addition of peroxides. Despite the low values, colour changes can be justified by the hypothesis that the remineralizing action of can also increase the lustre and translucency of the enamel. 27 This may explain in part why groups where the peroxides were mixed with TM MI did not show a reduction in bleaching effect. In the present investigation, the highest values of DE were observed immediately after completion of the bleaching regimen (). However, these changes were also produced during the first week of bleaching (). In addition, it was demonstrated 7 days after bleaching () that there was a regression in colour, with DE means returning to levels similar to those achieved within the first week of bleaching. Sulieman et al. 13 also reported that DE values increased from the first until the second week. However, the authors did not carry out post-bleaching follow-ups. Differently from the present study, an in vivo evaluation by Bernardon et al. 7 found no reduction in the values of DE until 6 weeks post-bleaching. These authors used a protocol in which the bleaching agent was in contact with the tooth for 8 hours daily. Despite the differences between in vitro and in vivo studies, bleaching time can be a determining factor for the regression of colour. As the present investigation already suggests that the bleaching effect of peroxides is not affected by TM MI, further clinical studies are necessary to investigate the in vivo efficacy of a mixture containing several proportions of TM MI and bleaching agents in reducing tooth sensitivity while improving brightness and translucency optical properties. CONCLUSIONS The combination of Tooth Mousse MI Paste and bleaching agents in several proportions did not affect tooth whitening. The Da* parameter presented a higher number of strong linear correlations with the total colour change (DE) of bleached teeth than did DL* and Db* for the bleaching agents analysed in this study. ACKNOWLEDGEMENTS The authors are grateful to FGM (Joinville, SC, Brazil), DFL (Rio de Janeiro, RJ, Brazil) and GC Corporation (Tokyo, Japan) for providing some of the materials used in this study. REFERENCES 1. Sasaki RT, Arcanjo AJ, Flório FM, Basting RT. 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7 paste and at-home bleaching 13. Sulieman M, MacDonald E, Rees JS, Newcombe RG, Addy M. Tooth bleaching by different concentrations of carbaminde peroxide and hydrogen peroxide whitening strips: an in vitro sudy. J Esthet Restor Dent 2006;18: Giniger M, Macdonald J, Ziemba S, Felix H. The clinical performance of professionally dispensed bleaching gel with added amorphous calcium phosphate. J Am Dent Assoc 2005;136: Arends J, Jongebloed WL, Goldberg M, Schuthof J. Interaction of urea and human enamel. Caries Res 1984;18: Mondelli RF, Azevedo JF, Franscisconi PA, Ishikiriama SK, Mondelli J. Wear and surface roughness of bovine submitted to bleaching. Eur J Esthet Dent 2009;4: Dietschi D, Benbachir N, Krejci I. In vitro colorimetric evaluation of the efficacy of home bleaching and over-the-counter bleaching products. Quintessence Int 2010;41: Reynolds E. Casein phosphopeptide-amorphous calcium phosphate: the scientific evidence. Adv Dent Res 2009;21: Manton DJ, Bhide R, Hopcraft MS, Reynolds EC. Effect of ozone and Tooth Mousse TM on the efficacy of peroxide bleaching. Aust Dent J 2008;53: Borges BC, Borges JS, de Melo CD, et al. Efficacy of a novel at-home bleaching technique with carbamide peroxides modified by and its effect on the microhardness of bleached enamel. Oper Dent 2011;36: Borges BC, Vasconcelos AA, Cunha AG, Pinheiro FH, Machado CT, Santos AJS. Preliminary clinical reports of a novel nightguard tooth bleaching technique modified by casein phosphopeptide-amorphous calcium phosphate (). Eur J Esthet Dent 2011;6: Kielbassa AM, Beheim-Schwarzbach NJ, Neumann K, Nat R, Zantner C. In vitro comparison of visual and computer-aided preand post-tooth shade determination using various home bleaching procedures. J Prosthet Dent 2009;101: Westland S. Review of the CIE system of colorimetry and its use in dentistry. J Esthet Restor Dent 2003;15(Suppl 1):S Vichi A, Ferrari M, Davidson CL. Color and opacity variations in three different resin-based composite products after water aging. Dent Mater 2004;20: Torres CRG, Wiegand A, Sener B, Attin T. Influence of chemical activation of a 35% hydrogen peroxide bleaching gel on its penetration and efficacy in vitro study. J Dent 2010;38: Goodson JM, Tavares M, Sweeney M, et al. Tooth whitening: tooth color changes following treatment by peroxide and light. J Clin Dent 2005;16: Singh RD, Ram SM, Shetty O, Chand P, Yadav R. Efficacy of casein phosphopeptide-amorphous calcium phosphate to prevent stain absorption on freshly bleached enamel: an in vitro study. J Conserv Dent 2010;13: Address for correspondence: Professor Boniek Castillo Dutra Borges School of Dentistry Potiguar University (Laureate International Universities) Av. Senador Salgado Filho Natal RN Brazil boniek.castillo@gmail.com ª 2012 Australian Dental Association 219