ceramics

Article

Influence of a Bleaching Agent on the Color Stabilityof Indirect Composite Resins Immersed in Dyes

Daniele M. dos Santos *, Emily V. F. da Silva , Juliani B. Mendonça, Denis Cetrangolo,Fernanda P. de Caxias and Marcelo C. Goiato

Department of Dental Materials and Prosthodontics, Aracatuba Dental School,Sao Paulo State University (UNESP), Aracatuba, Sao Paulo 16015-050, Brazil;emilyvfs@yahoo.com.br (E.V.F.d.S.); juliani_mendonca@hotmail.com (J.B.M.);dcetrangolo.3006@gmail.com (D.C.); fpc.bra@gmail.com (F.P.d.C.); m.goiato@unesp.br (M.C.G.)* Correspondence: danielamicheline@foa.unesp.br; Tel.: +(55)-18-3636-3287; Fax: +(55)-18-3636-3245

Received: 31 January 2019; Accepted: 26 March 2019; Published: 1 April 2019�����������������

Abstract: This study aimed to evaluate the effect of a bleaching agent on the color of extrinsicallypigmented indirect composite resins. Samples of five resins (Adoro, Resilab, Cristobal, Sinfony,Epricord) were manufactured and divided into five groups: red wine, coffee, orange juice, Coca-Cola,and artificial saliva (control). The stained samples were immersed in a 38% hydrogen peroxidesolution for 30 min per week, over three weeks. Color readings were performed at the initial state(L0), after 21 days of dye immersion (∆E1, L1), and after 7 (∆E2, L2), 14 (∆E3, L3), and 21 days(∆E4, L4) of bleach immersion. Data were subjected to ANOVA and Tukey’s honestly significantdifference (HSD) test (α = 0.05). The color alteration was greater in ∆E1, regardless of color solution,indicating extrinsic pigmentation. The Resilab group exhibited greater ∆E1 values than the otherresins. The bleaching agent promoted bleaching action on the surfaces of the materials studied,removing the previously impregnated pigments.

Keywords: composite resins; bleaching agents; color; staining

1. Introduction

Beauty standards directly influence dental esthetics. Therefore, dental procedures that involveesthetics, such as restorations with composite resins and bleaching treatments, are under constantdevelopment [1].

The chromatic alteration of composite resins can be caused by intrinsic or extrinsic factors.The intrinsic factors are related to chemical and physical reactions in the deepest portions of therestoration, in addition to changes in temperature and humidity. The extrinsic factors are related tothe adsorption or absorption of colored substances. In addition, the presence of hydrophilic particleswithin the resinous matrix, with the capacity to absorb water, and the size and distribution of theparticles could provoke chromatic alterations of the restoration [2,3].

A material must have a natural appearance, biocompatibility, and longevity to be used in dentalapplications [4]. Indirect resin composites incorporate some advantages of porcelain into the compositeresins without presenting inherent limitations [5]. In addition to having lower costs than porcelains,they possess better properties than direct resins: reduced polymerization shrinkage, increased flexuralstrength, resistance to abrasion and fracture, and increased color stability, presenting excellent clinicalresults [2,3,6].

Despite mechanical polishing being able to remove superficial stains from restorations made fromcomposite resins [7], the use of bleaching agents could give better results in the removal of stains fromthese materials [8,9]. Different substances can be used as bleaching agents, such as carbamide peroxide

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and hydrogen peroxide [9]. For in-office application, Opalescence Xtra Boost is a hydrogen peroxidegel with a chemical activation that has a neutral pH, can be used efficiently and safely, and providesappropriate results in a short period of time [10].

Therefore, the objective of this study was to evaluate the efficacy of the use of bleaching agents onthe color stability of extrinsically pigmented indirect composite resins. The null hypothesis was thatthe bleaching agent was not effective for removing impregnated pigments, originating from stainingsolutions from the surfaces of the tested indirect composite resins.

2. Materials and Methods

Five different brands of B2 (dentine)-colored indirect composite resins were evaluated (Table 1):Adoro (Ivoclar Vivadent Ltda., São Paulo, São Paulo, Brazil), Resilab Master (Wilcos do Brasil, Indústriae Comércio Ltda., Petrópolis, Rio de Janeiro, Brazil), Cristobal (Dentisply Ceramco, Burlington, NJ,USA), Sinfony (3M, Campinas, São Paulo, Brazil), and Epricord (Kuraray Noritake Dental, Tokyo,Japan) (Figure 1) [11]. Twenty-five samples from each brand were manufactured and divided into fivegroups, according to the type of staining solution (red wine, coffee, orange juice, and Coca-Cola) orartificial saliva (control group) (Table 2).

Table 1. Indirect composite resins used for specimen confection.

Brand Chemical Composition Polymerization

Adoro17–19% of dimethacrylate, 82–83%copolymers of silicon oxide, and 1%stabilizers, catalysts, and pigments.

Pre-polymerization in a Targis Quick unit (halogenlamp, intensity of 600 mW/cm2). Resinimpregnated with glycerin gel. Polymerization in aLunamat 100 unit, with eight lamps emittingfluorescent light in a mirrored environment for25 min (10 min with light, 10 min with heat at1040 ◦C and 5 min with cooling unit) at a totalpower of 750 W.

ResilabMaster

Small particles with a mean size of 0.05 mm,53% of ceramic filler particles, BisGMA(bisphenol A-glycidyl methacrylate),BisEMA (ethoxylated bisphenol A-dimethacrylate), UDMA (urethanedimethacrylate), TEGMA (tri-ethyleneglycol dimethacrylate), aluminumborosilicate, highly dispersible silica,photoinitiators, inhibitors, and pigments.

Pre-polymerization for 4 min in an EDG-Lux unit(400–500 mW/cm2) with temperature notexceeding 50 ◦C. Final polymerization for 8 min inan EDG-Lux unit (400–500 mW/cm2).

Cristobal 74% pyrogenic silica particles, barium glass,and borosilicate.

Pre-polymerization in an MPa 2000 unit for 90 s(200 mW/cm2) in the first cycle and then for 75 s(800–1000 mW/cm2) in the second cycle. Finalpolymerization in a Post Cure unit for 8 min at 80◦C.

Sinfony

48% organic matrix (UDMA), 40%strontium glass (macroparticle of 0.6 µm),5% pyrogenic silica (microparticle of 0.06µm), 5% glass ionomer cement particles, 1%silane and 1% initiator.

Pre-polymerization for 15 s in Visio Alfa Light andVisio Beta Vario Light units used with a Visio BetaVacuum pump (470 mW/cm2). Finalpolymerization in two stages: 1 minute of lightemission in air followed by 14 min of lightemission in vacuum in Visio Beta.

Epricord

53% ceramic filler content, 25%multifunctional polymers and 22%conventional resin photoinitiators. Themean particle size is 0.6 µm.

Pre-polymerization for 30 s in a Kota unit. Finalpolymerization for 180 s with a halogen lamp (600mW/cm2) in a Kota unit.

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Figure 1. Indirect composite resin sample.

2.1. Manufacturing of Samples

The samples were manufactured in a cast stainless steel matrix (10 mm length × 5 mm width × 1.5 mm thickness) according to the recommendations of the manufacturers (Table 1) [10]. After the final polymerization, the samples were polished in a semi-automatic polishing machine (Ecomet 300PRO, Buehler, Lake Bluff, IL, USA), running at 300 rpm, with metallographic sandpaper of 240, 400, 800, and 1200 grit (Buehler, Lake Bluff, IL, USA), under constant irrigation with water. The polishing of the samples was finalized using a felt disc with diamond solution (Buehler, Lake Bluff, IL, USA). Each sample had its thickness checked, with the assistance of a digital caliper (500-171-20B, Mitutoyo, Tokyo, Japan), in order to ensure the correct dimensions. All samples were stored in a digital bacteriologic incubator (CIENLAB Equipamento Científicos Ltda., Campinas, São Paulo, Brazil), in distilled water at 37 ± 1 °C for 24 hours, before the initial color reading [3].

Table 2. Immersion solutions used in the study.

Solution Brand Chemical Composition

Red wine Periquita dry red wine, José

Maria Da Fonseca Vinhos S.A., Azeitão, Portugal

Red grape varieties, conservative INS 220 (sulfur dioxide, SO2), sulphurous acid, and 12.7% alcohol.

Coffee Coffee Pilão, Sara Lee, Jundiaí,

São Paulo, Brazil Roasted and ground coffee.

Orange juice

Coca-Cola, Ribeirão Preto, Brazil Orange juice, water, sugar, orange pulp, natural flavors, ascorbic acid, and citric acid.

Coca-Cola Coca-Cola, Ribeirão Preto, Brazil Carbonated water, sugar, cola nut extract, yellow dye IV, acidulant INS 338, and natural flavors.

Artificial saliva

Farmácia de Manipulação Apothicário, Araçatuba, Brazil

[KCl (0.4 g·L−1), NaCl (0.4 g·L−1), CaCl2·2H2O (0.906 g·L−1), NaH2PO4·2H2O (0.690 g·L−1), Na2S·9H2O

(0.005 g·L−1), and urea (1 g·L−1)].

2.2. Process of Immersion

Each sample was placed in a flask containing 1 mL of a specific solution (Table 2), and sealed to prevent its evaporation. Immersed in the solutions, which were substituted daily, the samples were stored in an incubator at 37 ± 1 °C for 4 hours per day for 21 days. When not immersed in the solution, they were stored in artificial saliva [12].

After the immersion, all samples were subjected to the 38% hydrogen peroxide bleaching agent (Opalescence Xtra Boost, Ultradent, South Jordan, Utah, USA) for 30 minutes per week, for 3 weeks, according to the recommendation from the manufacturer [13]. During this period, the samples continued to be stored in the incubator at 37 ± 1 °C for 21 days. When not immersed in the bleaching solution, they were stored in artificial saliva [13].

Figure 1. Indirect composite resin sample.

2.1. Manufacturing of Samples

The samples were manufactured in a cast stainless steel matrix (10 mm length × 5 mm width ×1.5 mm thickness) according to the recommendations of the manufacturers (Table 1) [10]. After thefinal polymerization, the samples were polished in a semi-automatic polishing machine (Ecomet300PRO, Buehler, Lake Bluff, IL, USA), running at 300 rpm, with metallographic sandpaper of240, 400, 800, and 1200 grit (Buehler, Lake Bluff, IL, USA), under constant irrigation with water.The polishing of the samples was finalized using a felt disc with diamond solution (Buehler, Lake Bluff,IL, USA). Each sample had its thickness checked, with the assistance of a digital caliper (500-171-20B,Mitutoyo, Tokyo, Japan), in order to ensure the correct dimensions. All samples were stored in a digitalbacteriologic incubator (CIENLAB Equipamento Científicos Ltda., Campinas, São Paulo, Brazil), indistilled water at 37 ± 1 ◦C for 24 h, before the initial color reading [3].

Table 2. Immersion solutions used in the study.

Solution Brand Chemical Composition

Red winePeriquita dry red wine, José MariaDa Fonseca Vinhos S.A., Azeitão,

Portugal

Red grape varieties, conservative INS 220 (sulfurdioxide, SO2), sulphurous acid, and 12.7% alcohol.

Coffee Coffee Pilão, Sara Lee, Jundiaí, SãoPaulo, Brazil Roasted and ground coffee.

Orange juice Coca-Cola, Ribeirão Preto, Brazil Orange juice, water, sugar, orange pulp, naturalflavors, ascorbic acid, and citric acid.

Coca-Cola Coca-Cola, Ribeirão Preto, Brazil Carbonated water, sugar, cola nut extract, yellow dyeIV, acidulant INS 338, and natural flavors.

Artificial saliva Farmácia de ManipulaçãoApothicário, Araçatuba, Brazil

[KCl (0.4 g·L−1), NaCl (0.4 g·L−1), CaCl2·2H2O(0.906 g·L−1), NaH2PO4·2H2O (0.690 g·L−1),

Na2S·9H2O (0.005 g·L−1), and urea (1 g·L−1)].

2.2. Process of Immersion

Each sample was placed in a flask containing 1 mL of a specific solution (Table 2), and sealed toprevent its evaporation. Immersed in the solutions, which were substituted daily, the samples werestored in an incubator at 37 ± 1 ◦C for 4 h per day for 21 days. When not immersed in the solution,they were stored in artificial saliva [12].

After the immersion, all samples were subjected to the 38% hydrogen peroxide bleaching agent(Opalescence Xtra Boost, Ultradent, South Jordan, Utah, USA) for 30 min per week, for 3 weeks,according to the recommendation from the manufacturer [13]. During this period, the samplescontinued to be stored in the incubator at 37 ± 1 ◦C for 21 days. When not immersed in the bleachingsolution, they were stored in artificial saliva [13].

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2.3. Reading of the Color Alteration

The readings of the color alteration were performed in the following periods: initial (L0), after 21days of immersion in the color solutions (∆E1 and L1), after 7 days of immersion in the bleachingagent (∆E2 and L2), after 14 days of immersion in the bleaching agent (∆E3 and L3), and after 21 daysof immersion in the bleaching agent (∆E4 and L4). The readings of the color alteration (∆E) andluminosity (L*) of the samples were performed with the assistance of a reflection spectrophotometer(UV-2450, Shimadzu Corp., Kyoto, Japan) [14,15]. Color alterations (∆E) were calculated by means ofthe L*a*b* system, as established by the CIE—Commission Internacionale de l’Eclairage [16].

2.4. Statistical Analysis

The data describing the color alteration (∆E) and the L* (CIELab) coordinates obtained weresubjected to the three-way analysis of variance (ANOVA) with repeated-measure factors, and theTukey honestly significant difference (HSD) test (α = 0.05), in order to detect statistically significantdifferences between the analyzed factors.

3. Results

From the results, it was observed that interactions between the type of resin, the staining solutionused, and the period of analysis significantly affected the color alteration (∆E) (P < 0.001) (Table 3) andthe L* coordinate (P < 0.001) (Table 4).

The color alteration was greatest at ∆E1, regardless of the staining solution and the compositeresin analyzed, indicating pigmentation of the materials after immersion. The Resilab group exhibitedthe greatest values of ∆E1, when compared to the other resins. From the analyses of ∆E2, ∆E3, and ∆E4,it was concluded that the bleaching agent produced a bleaching action on the surfaces of the materialsstudied, removing the previously impregnated pigments (Tables 5–9).

By considering the L* coordinate (Figures 2–6), it was verified that the bleaching agent permittedan increase in the lightness of the materials studied, after the immersion in the coloring solutions.This indicates a bleaching action on the surface.

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2.3. Reading of the Color Alteration The readings of the color alteration were performed in the following periods: initial (L0), after

21 days of immersion in the color solutions (ΔE1 and L1), after 7 days of immersion in the bleaching agent (ΔE2 and L2), after 14 days of immersion in the bleaching agent (ΔE3 and L3), and after 21 days of immersion in the bleaching agent (ΔE4 and L4). The readings of the color alteration (ΔE) and luminosity (L*) of the samples were performed with the assistance of a reflection spectrophotometer (UV-2450, Shimadzu Corp., Kyoto, Japan) [14,15]. Color alterations (ΔE) were calculated by means of the L*a*b* system, as established by the CIE—Commission Internacionale de l’Eclairage [16].

2.4. Statistical Analysis

The data describing the color alteration (ΔE) and the L* (CIELab) coordinates obtained were subjected to the three-way analysis of variance (ANOVA) with repeated-measure factors, and the Tukey honestly significant difference (HSD) test (α = 0.05), in order to detect statistically significant differences between the analyzed factors.

3. Results

From the results, it was observed that interactions between the type of resin, the staining solution used, and the period of analysis significantly affected the color alteration (ΔE) (P < 0.001) (Table 3) and the L* coordinate (P < 0.001) (Table 4).

The color alteration was greatest at ΔE1, regardless of the staining solution and the composite resin analyzed, indicating pigmentation of the materials after immersion. The Resilab group exhibited the greatest values of ΔE1, when compared to the other resins. From the analyses of ΔE2, ΔE3, and ΔE4, it was concluded that the bleaching agent produced a bleaching action on the surfaces of the materials studied, removing the previously impregnated pigments (Tables 5–9).

By considering the L* coordinate (Figures 2–6), it was verified that the bleaching agent permitted an increase in the lightness of the materials studied, after the immersion in the coloring solutions. This indicates a bleaching action on the surface.

Figure 2. Mean values of L* coordinates of Adoro resin for each color solution used, in each period evaluated. Different small letters indicate statistically significant differences (P < 0.05) between different color solutions in the same period. Different capital letters indicate statistically significant differences (P < 0.05) between different periods for the same color solution.

Figure 2. Mean values of L* coordinates of Adoro resin for each color solution used, in each periodevaluated. Different small letters indicate statistically significant differences (P < 0.05) between differentcolor solutions in the same period. Different capital letters indicate statistically significant differences(P < 0.05) between different periods for the same color solution.

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Figure 3. Mean values of L* coordinate of Resilab resin for each color solution used, in each period evaluated. Different small letters indicate statistically significant differences (P < 0.05) between different color solutions in the same period. Different capital letters indicate statistically significant differences (P < 0.05) between different periods for the same color solution.

Table 3. Three-way analysis of variance (ANOVA) with repeated-measure factors for color alterations (ΔE) of indirect composite resins.

SS df MS F P Resin 6566.386 4 1641.597 2142.478 <0.001

Solution 131.647 4 32.912 42.954 <0.001 Resin × Solution 458.558 16 28.660 37.404 <0.001 Between subjects 172.398 225 0.766

Period 19,564.573 2.845 6877.370 5664.649 <0.001 Period × Resin 12,870.394 11.379 1131.055 931.611 <0.001

Period × Solution 930.291 11.379 81.754 67.338 <0.001 Period × Resin × Solution 3266.354 45.516 71.762 59.108 <0.001

Within subjects 777.105 675 1.151 P < 0.05 denotes statistically significant difference.

Table 4. Three-way analysis of variance (ANOVA) with repeated-measure factors for L* coordinate of indirect composite resins.

SS df MS F P Resin 23,185.790 4 5796.447 1693.562 <0.001

Solution 200.716 4 50.179 14.661 <0.001 Resin × Solution 829.049 16 51.816 15.139 <0.001 Between subjects 770.093 225 3.423

Period 8636.929 3.071 2812.801 1324.969 <0.001 Period × Resin 25,959.112 12.282 2113.535 995.580 <0.001

Period × Solution 2326.537 12.282 189.422 89.227 <0.001 Period × Resin × Solution 4517.111 49.129 91.943 43.310 <0.001

Within subjects 1466.683 900 1.630 P < 0.05 denotes statistically significant difference.

4. Discussion

The null hypothesis tested, that the bleaching agent was not effective for the removal of pigments originating from staining solutions from the surface of indirect resins, was rejected. This is because

Figure 3. Mean values of L* coordinate of Resilab resin for each color solution used, in each periodevaluated. Different small letters indicate statistically significant differences (P < 0.05) between differentcolor solutions in the same period. Different capital letters indicate statistically significant differences(P < 0.05) between different periods for the same color solution.

Table 3. Three-way analysis of variance (ANOVA) with repeated-measure factors for color alterations(∆E) of indirect composite resins.

SS df MS F P

Resin 6566.386 4 1641.597 2142.478 <0.001Solution 131.647 4 32.912 42.954 <0.001

Resin × Solution 458.558 16 28.660 37.404 <0.001Between subjects 172.398 225 0.766

Period 19,564.573 2.845 6877.370 5664.649 <0.001Period × Resin 12,870.394 11.379 1131.055 931.611 <0.001

Period × Solution 930.291 11.379 81.754 67.338 <0.001Period × Resin × Solution 3266.354 45.516 71.762 59.108 <0.001

Within subjects 777.105 675 1.151P < 0.05 denotes statistically significant difference.

Table 4. Three-way analysis of variance (ANOVA) with repeated-measure factors for L* coordinate ofindirect composite resins.

SS df MS F P

Resin 23,185.790 4 5796.447 1693.562 <0.001Solution 200.716 4 50.179 14.661 <0.001

Resin × Solution 829.049 16 51.816 15.139 <0.001Between subjects 770.093 225 3.423

Period 8636.929 3.071 2812.801 1324.969 <0.001Period × Resin 25,959.112 12.282 2113.535 995.580 <0.001

Period × Solution 2326.537 12.282 189.422 89.227 <0.001Period × Resin × Solution 4517.111 49.129 91.943 43.310 <0.001

Within subjects 1466.683 900 1.630P < 0.05 denotes statistically significant difference.

4. Discussion

The null hypothesis tested, that the bleaching agent was not effective for the removal of pigmentsoriginating from staining solutions from the surface of indirect resins, was rejected. This is because the

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bleaching agent produced a bleaching action on the surfaces of the materials studied, removing thepreviously impregnated pigments (Tables 5–9, Figures 2–6).

It can be verified, through the results (Tables 5–9), that the delta of the color for all samples wasgreater than 3.3 in all color solutions. This indicates, by spectrophotometric analysis, an alterationof color which is visually perceptible and clinically unacceptable from the point of view of esthetics(∆E < 3.3) [17,18].

It is known that the alterations of the color of composite resins are multifactorial, involvingintrinsic and extrinsic factors [19–21]. The intrinsic factors are related to the chemical stability of thematerial, which depends on the fractional conversion of the monomers present in the resinous matrix.The presence of residual monomers in the resinous material induces susceptibility to pigmentation byabsorption of external substances [22].

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the bleaching agent produced a bleaching action on the surfaces of the materials studied, removing the previously impregnated pigments (Tables 5–9, Figures 2–6).

Figure 4. Mean values of L* coordinate of Epricord resin for each color solution used, in each period evaluated. Different small letters indicate statistically significant differences (P < 0.05) between different color solutions in the same period. Different capital letters indicate statistically significant differences (P < 0.05) between different periods for the same color solution.

Figure 5. Mean values of L* coordinate of Cristobal resin for each color solution used, in each period evaluated. Different small letters indicate statistically significant differences (P < 0.05) between different color solutions in the same period. Different capital letters indicate statistically significant differences (P < 0.05) between different periods for the same color solution.

Figure 4. Mean values of L* coordinate of Epricord resin for each color solution used, in each periodevaluated. Different small letters indicate statistically significant differences (P < 0.05) between differentcolor solutions in the same period. Different capital letters indicate statistically significant differences(P < 0.05) between different periods for the same color solution.

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the bleaching agent produced a bleaching action on the surfaces of the materials studied, removing the previously impregnated pigments (Tables 5–9, Figures 2–6).

Figure 4. Mean values of L* coordinate of Epricord resin for each color solution used, in each period evaluated. Different small letters indicate statistically significant differences (P < 0.05) between different color solutions in the same period. Different capital letters indicate statistically significant differences (P < 0.05) between different periods for the same color solution.

Figure 5. Mean values of L* coordinate of Cristobal resin for each color solution used, in each period evaluated. Different small letters indicate statistically significant differences (P < 0.05) between different color solutions in the same period. Different capital letters indicate statistically significant differences (P < 0.05) between different periods for the same color solution.

Figure 5. Mean values of L* coordinate of Cristobal resin for each color solution used, in each periodevaluated. Different small letters indicate statistically significant differences (P < 0.05) between differentcolor solutions in the same period. Different capital letters indicate statistically significant differences(P < 0.05) between different periods for the same color solution.

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Figure 6. Mean values of L* coordinates of Sinfony resin for each color solution used, in each period evaluated. Different small letters indicate statistically significant differences (P < 0.05) between different color solutions in the same period. Different capital letters indicate statistically significant differences (P < 0.05) between different periods for the same color solution.

Table 5. Mean values of color alterations (∆E) of Adoro resin for each staining solution, before and after bleaching treatment.

Resin Staining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva Adoro ∆E1 6.59 Aa 5.99 Aab 5.42 Ab 6.14 Aab 0.57 Bc

∆E2 2.79 Bb 5.05 Ba 1.89 Bc 2.20 Bbc 0.45 Bd ∆E3 3.40 Ba 2.47 Cb 1.89 Bb 2.47 Bb 1.96 Ab ∆E4 0.76 Ca 0.66 Da 1.20 Ba 1.22 Ca 0.85 Ba

Means followed by the same capital letter in column do not differ (P < 0.05; Tukey). Means followed by the same lowercase letter in the line do not differ (P < 0.05; Tukey).

Table 6. Mean values of color alterations (∆E) of Resilab resin for each staining solution, before and after bleaching treatment.

Resin Staining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva Resilab ∆E1 13.49 Ad 29.44 Ac 35.64 Aa 34.53 Ab 33.68 Ab

∆E2 8.15 Ba 4.61 Bb 1.18 Dc 1.87 Cc 1.34 Cc ∆E3 5.13 Ca 3.19 Cb 2.26 Ccd 1.77 Cd 2.93 Bbc ∆E4 4.56 Dab 3.87 BCab 3.53 Bb 4.77 Ba 1.98 BCc Means followed by the same capital letter in column do not differ (P < 0.05; Tukey).

Means followed by the same lowercase letter in the line do not differ (P < 0.05; Tukey).

Table 7. Mean values of color alterations (∆E) of Epricord resin for each staining solution, before and after bleaching treatment.

Resin Staining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva Epricord ∆E1 12.78 Ab 13.84 Aa 11.54 Ac 11.54 Ac 11.53 Ac

∆E2 5.52 Bab 6.16 Ba 4.05 Cc 4.20 Cc 5.09 Cb ∆E3 6.32 Ba 5.93 Ba 6.35 Ba 5.94 Ba 6.28 Ba ∆E4 2.50 Ca 0.95 Cb 1.08 Db 0.84 Db 0.88 Db Means followed by the same capital letter in column do not differ (P < 0.05; Tukey).

Figure 6. Mean values of L* coordinates of Sinfony resin for each color solution used, in each periodevaluated. Different small letters indicate statistically significant differences (P < 0.05) between differentcolor solutions in the same period. Different capital letters indicate statistically significant differences(P < 0.05) between different periods for the same color solution.

Table 5. Mean values of color alterations (∆E) of Adoro resin for each staining solution, before andafter bleaching treatment.

ResinStaining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva

Adoro ∆E1 6.59 Aa 5.99 Aab 5.42 Ab 6.14 Aab 0.57 Bc∆E2 2.79 Bb 5.05 Ba 1.89 Bc 2.20 Bbc 0.45 Bd∆E3 3.40 Ba 2.47 Cb 1.89 Bb 2.47 Bb 1.96 Ab∆E4 0.76 Ca 0.66 Da 1.20 Ba 1.22 Ca 0.85 Ba

Means followed by the same capital letter in column do not differ (P < 0.05; Tukey).Means followed by the same lowercase letter in the line do not differ (P < 0.05; Tukey).

Table 6. Mean values of color alterations (∆E) of Resilab resin for each staining solution, before andafter bleaching treatment.

ResinStaining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva

Resilab ∆E1 13.49 Ad 29.44 Ac 35.64 Aa 34.53 Ab 33.68 Ab∆E2 8.15 Ba 4.61 Bb 1.18 Dc 1.87 Cc 1.34 Cc∆E3 5.13 Ca 3.19 Cb 2.26 Ccd 1.77 Cd 2.93 Bbc

∆E4 4.56 Dab 3.87BCab 3.53 Bb 4.77 Ba 1.98 BCc

Means followed by the same capital letter in column do not differ (P < 0.05; Tukey).Means followed by the same lowercase letter in the line do not differ (P < 0.05; Tukey).

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Table 7. Mean values of color alterations (∆E) of Epricord resin for each staining solution, before andafter bleaching treatment.

ResinStaining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva

Epricord ∆E1 12.78 Ab 13.84 Aa 11.54 Ac 11.54 Ac 11.53 Ac∆E2 5.52 Bab 6.16 Ba 4.05 Cc 4.20 Cc 5.09 Cb∆E3 6.32 Ba 5.93 Ba 6.35 Ba 5.94 Ba 6.28 Ba∆E4 2.50 Ca 0.95 Cb 1.08 Db 0.84 Db 0.88 Db

Means followed by the same capital letter in column do not differ (P < 0.05; Tukey).Means followed by the same lowercase letter in the line do not differ (P < 0.05; Tukey).

Table 8. Mean values of color alterations (∆E) of Cristobal resin for each staining solution, before andafter bleaching treatment.

ResinStaining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva

Cristobal ∆E1 8.57 Aab 9.27 Aa 8.54 Aab 8.58 Aab 8.39 Ab∆E2 6.51 Ba 4.10 Bb 2.91 Bc 3.32 Bc 0.82 Cc∆E3 1.31 Cbc 1.85 Cab 0.74 Cc 0.77 Cc 2.40 Ba∆E4 0.69 Cbc 2.02 Ca 0.58 Cc 1.69 Cab 2.06 Ba

Means followed by the same capital letter in column and do not differ (P < 0.05; Tukey).Means followed by the same lowercase letter in the line do not differ (P < 0.05; Tukey).

Table 9. Mean values of color alterations (∆E) of Sinfony resin for each staining solution, before andafter bleaching treatment.

ResinStaining Solution

Red Wine Coffee Orange Juice Coca-Cola Saliva

Sinfony ∆E1 11.22 Aa 9.95 Ab 8.83 Ac 8.06 Ac 8.25 Ac∆E2 5.87 Ba 2.76 Bb 0.84 Cc 1.39 Cc 1.01 Cc∆E3 2.24 Cab 2.40 Ba 1.39 Cb 2.34 Ba 2.48 Ba

∆E4 1.55 Cb 2.02 Bab 2.83 Ba 1.89BCab

1.83BCab

Means followed by the same capital letter in column do not differ (P < 0.05; Tukey).Means followed by the same lowercase letter in the line do not differ (P < 0.05; Tukey).

Despite the versatility and good esthetic results of resinous materials, the absorption of stainingagents is still the most prominent reason for chromatic alterations of these materials, and staining ofrestorations [23]. Among the liquid solutions tested in the present study, red wine (greater ∆E1 forAdoro and Sinfony), coffee (greater ∆E1 for Epricord and Cristobal), and orange juice (greater ∆E1for Resilab) affected the color stability the most, with a statistically significant difference from theother solutions (Tables 5–9). According to some studies, coffee possesses a great capacity for staining,caused by absorption and adsorption of yellow pigments of low polarity, which possess a chemicalaffinity to the polymeric phase of the resinous material [19,24,25]. Similar to coffee, some studiesdemonstrate the great effect that red wine shows in pigmentation of resinous materials, due to thealcohol it contains [24,26]. Orange juice contains citric acid, which could influence the pigmentation ofmaterials [27].

Several studies have also demonstrated a staining potential of tea, showing greater pigmentationthan coffee [28] and grape juice [29], for example. The color alteration is a result of theaflavins presentin tea leaves, which produce a yellowish-brown stain [16]. Therefore, this staining solution should beevaluated in further studies for a better understanding of its behavior.

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Many times, dental surgeons perform superficial polishing of the material, trying to minimizestaining and to remove extrinsic pigments from the surface of the restoration, thus increasing thelongevity of the restoration. However, some studies affirm that bleaching agents could also be capableof removing intrinsic and extrinsic stains from restorations [8,9,30,31]. This was observed in thepresent study, in which the values of ∆E2, ∆E3, and ∆E4 indicated that the bleaching agent effectivelydecolored the surfaces of the materials (Tables 5–9). Nonetheless, to evaluate only the ∆E values couldinduce an error, since the color of these materials is affected by a combination of intrinsic and extrinsicfactors, and the correlations in the results obtained by existing laboratory methods, such as the CIEL*a*b*, are poor [32], many times making it necessary to evaluate each coordinate.

Values of the L* coordinate (Figures 2–6) extend from 0 (black) to 100 (perfect white), describingthe luminosity of the sample. It was observed that after the immersion in the staining solutions used,the bleaching agent produced an increase in the lightness of the resins analyzed, resembling the initialvalues. This indicates that removal of the pigments impregnated on the surfaces of the materialsstudied could have occurred.

However, this may not occur clinically, since the effects of the solutions tested could be modified bythe action of bacterial biofilms and saliva. The laboratory tests, in which immersions of these restorativematerials are performed in different solutions, are biased by disregarding these factors [9]. In addition,the bleaching agents could also provoke the detachment of charged particles from the surface ofthe resinous materials, since hydrogen peroxide can cause oxidation and reduction reactions [33,34].This action could lead to an increase in the superficial roughness, facilitating even more staining of thematerial when it is again exposed to staining solutions [8,9,30]. Therefore, more in vitro studies thatsimulate the effects of these factors, and laboratory methods that possess a strong correlation betweenthe laboratory tests and the results found in clinics, are necessary.

In the present study, a challenge was performed, which consisted of periods of exposure tosolutions intercalated with periods of exposure to saliva, simulating oral conditions with highaccuracy. The clinical implication of this study is that the greatest color alteration was observedin ∆E1, independent of color solution, indicating extrinsic pigmentation. The Resilab group exhibitedgreater values of ∆E1 when compared to the other resins. The 38% hydrogen peroxide-based bleachingagent effectively bleached the surfaces of the materials studied. Therefore, these findings are importantto patients and can help scientists and professionals in their clinical practice.

5. Conclusions

Based on the results obtained, and considering the limitations of this study, it can be concludedthat the 38% hydrogen peroxide-based bleaching agent produced a bleaching action of the surfaces ofthe materials studied, removing the previously impregnated pigments.

Author Contributions: In regards to the contributions of each author, all authors contributed equally to thework. M.C.G. and D.M.d.S. participated in the concepts and coordination of the study, performed the studydesign, and drafted the manuscript. E.V.F.d.S., J.B.M. and D.C. conceived the study, fabricated the samples,and participated in assays, as well helped draft the manuscript. F.P.d.C. performed the statistical analysis andparticipated in interpretation of data. All authors read and approved the final manuscript.

Funding: This research was funded the Sao Paulo Research Foundation, grant number 2012/13244-2.

Acknowledgments: This work was supported by the Sao Paulo Research Foundation [Process 2012/13244-2].

Conflicts of Interest: The authors declare no conflict of interest.

References

1. Torres, C.R.G.; Ribeiro, C.F.; Bresciani, E.; Borges, A.B. Influence of hydrogen peroxide bleaching gels ofcolor, opacity, and fluorescence of composite resins. Oper. Dent. 2012, 37, 526–531. [CrossRef]

2. Jain, V.; Platt, J.A.; Moore, B.K.; Borges, G.A. In vitro wear of new indirect resin composites. Oper. Dent. 2009,34, 423–428. [CrossRef] [PubMed]

Ceramics 2019, 2 244

3. Kim, S.H.; Lee, Y.K. Changes in color and color coordinates of an indirect resin composite during curingcycle. J. Dent. 2008, 36, 337–342. [CrossRef] [PubMed]

4. Okulus, Z.; Buchwald, T.; Voelkel, A. Characterization of light-cured, dental-resin-based composites. J. Appl.Polym. Sci. 2015, 132, 42812. [CrossRef]

5. Leinfelder, K.F. New developments in resin restorative systems. J. Am. Dent. Assoc. 1997, 128, 573–581.[CrossRef]

6. Peutzfeldt, A.; Asmussen, E. The effect of postcuring on quantity of remaining double bonds, mechanicalproperties, and in vitro wear of two resin composites. J. Dent. 2000, 28, 447–452. [CrossRef]

7. Anfe, T.E.; Agra, C.M.; Vieira, G.F. Evaluation of the possibility of removing staning by repolishing compositeresins submitted to artificial again. J. Esthet. Restor. Dent. 2011, 23, 260–267. [CrossRef] [PubMed]

8. Villalta, P.; Lu, H.; Okte, Z.; Garcia-Godoy, F.; Powers, J.M. Effects of staining and bleaching on color changeof dental composite resins. J. Prosthet. Dent. 2006, 95, 137–142. [CrossRef] [PubMed]

9. Türkün, L.S.; Türkün, M. Effect of bleaching and repolishing procedures on coffee and tea stain removalfrom three anterior composite veneering materials. J. Esthet. Restor. Dent. 2004, 16, 290–301. [CrossRef][PubMed]

10. Opalescence Boost. Available online: https://www.ultradent.com/products/categories/whitening/in-office/opalescence-boost (accessed on 10 March 2019).

11. Dos Santos, D.M.; De Paula, A.M.; Bonatto, L.d.R.; Da Silva, E.V.; Vechiato Filho, A.J.; Moreno, A.; Goiato, M.C.Influence of colorant solutions in properties of indirect resin composites. Am. J. Dent. 2015, 28, 219–223.[PubMed]

12. Fontes, S.T.; Fernández, M.R.; Moura, C.M.; Meireles, S.S. Color stability of a nanofill composite: Effect ofdifferent immersion media. J. Appl. Oral Sci. 2009, 17, 388–391. [CrossRef] [PubMed]

13. Barbosa, C.M.; Sasaki, R.T.; Florio, F.M.; Basting, R.T. Influence of time on bond strength after bleaching with35% hydrogen peroxide. J. Contemp. Dent. Pract. 2008, 9, 81–88. [PubMed]

14. Goiato, M.C.; Zuccolotti, B.C.; Moreno, A.; Dos Santos, D.M.; Pesqueira, A.A.; de Carvalho Dekon, S.F.Colour change of soft denture liners after storage in coffee and coke. Gerondontology 2011, 28, 140–145.[CrossRef] [PubMed]

15. Mancuso, D.N.; Goiato, M.C.; Zuccolotti, B.C.R.; Moreno, A.; Dos Santos, D.M. Evaluation of hardness andcolour change of soft liners after accelerated ageing. Prim. Dent. Care 2009, 16, 127–130. [CrossRef]

16. Oguz, S.; Mutluay, M.M.; Dogan, O.M.; Bek, B. Color change evaluation of denture soft lining materials incoffee and tea. Dent. Mater. J. 2007, 26, 209–216. [CrossRef]

17. Ruyter, I.E.; Nilner, K.; Moller, B. Color stability of dental composite resin materials for crown and bridgeveneers. Dent. Mater. 1987, 3, 246–251. [CrossRef]

18. Noie, F.; O’Keefe, K.L.; Powers, J.M. Color stability of resin cements after accelerated aging. Int. J. Prosthodont.1995, 8, 51–55. [PubMed]

19. Samra, A.P.B.; Pereira, S.K.; Delgado, L.C.; Borges, C.P. Color stability evaluation of aesthetic restorativematerials. Braz. Oral Res. 2008, 22, 205–210. [CrossRef] [PubMed]

20. Festuccia, M.S.; Garcia, L.d.F.; Cruvinel, D.R.; Pires-De-Souza, F.d.C. Color stability, surface roughnessand microhardness of composites submitted to mouthrinsing action. J. Appl. Oral Sci. 2012, 20, 200–205.[CrossRef] [PubMed]

21. Lee, Y.K.; Yu, B.; Lim, H.N.; Lim, J.I. Difference in the color stability of direct and indirect resin composites.J. Appl. Oral Sci. 2011, 19, 154–160. [CrossRef]

22. Nakazawa, M. Color stability of indirect composite materials polymerized with different polymerizationsystems. J. Oral Sci. 2009, 51, 267–273. [CrossRef]

23. Domingos, P.A.; Garcia, P.P.; Oliveira, A.L.; Palma-Dibb, R.G. Composite resin color stability: Influence oflight sources and immersion media. J. Appl. Oral Sci. 2011, 19, 204–211. [CrossRef]

24. Fujita, M.; Kawakami, S.; Noda, M.; Sano, H. Color change of newly developed esthetic restorative materialimmersed in food-simulating solutions. Dent. Mater. J. 2006, 25, 352–359. [CrossRef]

25. Ertas, E.; Güler, A.U.; Yücel, A.C.; Köprülü, H.; Güler, E. Color stability of resin composites after immersionin different drinks. Dent. Mater. J. 2006, 25, 371–376. [CrossRef]

26. Guler, A.U.; Yilmaz, F.; Kulunk, T.; Guler, E.; Kurt, S. Effects of different drinks on stainability of resincomposite provisional restorative materials. J. Prosthet. Dent. 2005, 94, 118–124. [CrossRef]

Ceramics 2019, 2 245

27. Catelan, A.; Briso, A.L.; Sundfeld, R.H.; Goiato, M.C.; dos Santos, P.H. Color stability of sealed compositeresin restorative materials after ultraviolet artificial aging and immersion in staining solutions. J. Prosthet.Dent. 2011, 105, 236–241. [CrossRef]

28. Khokhar, Z.A.; Razzoog, M.E.; Yaman, P. Color stability of restorative resins. Quintessence Int. 1991, 22,733–737.

29. Crispin, B.; Caputo, A. Color stability of temporary restorative materials. J. Prosthet. Dent. 1979, 42, 27–33.[CrossRef]

30. Turker, S.B.; Biskin, T. Effect of three bleaching agents on the surface properties of three different estheticrestorative materials. J. Prosthet. Dent. 2003, 89, 466–473. [CrossRef]

31. Cehreli, Z.C.; Yazici, R.; Garcia-Godoy, F. Effect of home-use bleaching gels on fluoride releasing restorativematerials. Oper. Dent. 2003, 28, 605–609. [PubMed]

32. Bayne, S.C. Correlation of clinical performance with ‘in vitro tests’ of restorative dental materials that usepolymer-based matrices. Dent. Mater. 2012, 28, 52–71. [CrossRef] [PubMed]

33. Malkondu, Ö.; Yurdagüven, H.; Say, E.C.; Kazazoglu, E.; Soyman, M. Effect of bleaching on microhardnessof esthetic restorative materials. Oper. Dent. 2011, 36, 177–186. [CrossRef] [PubMed]

34. Durner, J.; Stojanovic, M.; Urcan, E.; Spahl, W.; Haertel, U.; Hickel, R.; Reichl, F.X. Effect of hydrogen peroxideon the three-dimensional polymer network in composites. Dent. Mater. 2011, 27, 573–580. [CrossRef][PubMed]

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