Year : 2009 | Volume
: 20 | Issue : 1 | Page : 60--64
An evaluation of the color stability of tooth-colored restorative materials after bleaching using CIELAB color technique
Y Madhukar Rao, V Srilakshmi, K Karpaga Vinayagam, L Lakshmi Narayanan
Department of Conservative Dentistry and Endodontics, Saveetha Dental College and Hospitals, Chennai, India
Y Madhukar Rao
Department of Conservative Dentistry and Endodontics, Saveetha Dental College and Hospitals, Chennai
Aims and Objective: The aim of this laboratory study was to evaluate the effect of three home bleaching agents: Vivastyle Paint On, Vivastyle, and Opalascence PF on the color stability of the microfilled composite Durafill, the nanofilled composite Filtek Z 350, and the glass ionomer cement Fuji II.
Materials and Methods: There were 3 groups in this study (n=40)-Group I: durafill, Group II: Filtek Z 350, and Group III: Fuji II. Each group was further subdivided into 4 subgroups (n=10), Subgroup A: bleaching with Vivastyle Paint On, Subgroup B: bleaching with Vivastyle, Subgroup C: bleaching with Opalascence PF, and Subgroup D: control specimens stored in distilled water. Bleaching was carried out following the manufacturer«SQ»s instructions for a period of 14 days. At the end of the bleaching regimen, the specimens were tested for color change using the CIELAB technique and a reflectance spectrophotometer.
Results: The data was subjected to statistical analysis. A Kruskal-Wallis variance analysis and Mann Whitney U test were done to determine the significant color change of the restorative materials. All restorative materials demonstrated a significantly higher color change (ΔE) with Vivastyle ( P < 0.0001). The mean color change of GIC (11.4 ± 0.3) was the highest among the materials followed by Durafill (7.5 ± 0.1). Filtek z 350 (0.3 ± 0.1) showed the least color change with all the bleaching agents.
Conclusion: Glass ionomer cement showed the highest color change followed by the microfilled composite. The nanofilled composite was found to be highly stable in terms of color.
|How to cite this article:|
Rao Y M, Srilakshmi V, Vinayagam K K, Narayanan L L. An evaluation of the color stability of tooth-colored restorative materials after bleaching using CIELAB color technique.Indian J Dent Res 2009;20:60-64
|How to cite this URL:|
Rao Y M, Srilakshmi V, Vinayagam K K, Narayanan L L. An evaluation of the color stability of tooth-colored restorative materials after bleaching using CIELAB color technique. Indian J Dent Res [serial online] 2009 [cited 2015 Apr 26 ];20:60-64
Available from: http://www.ijdr.in/text.asp?2009/20/1/60/49071
One of the reasons for seeking cosmetic dental care is discoloration of the anterior teeth. Even those whose teeth are of normal color often want them whiter. With careful case selection, diagnosis, and treatment planning, bleaching can change a patient's smile dramatically. Vital tooth bleaching with peroxide is one of the most common cosmetic procedures to achieve this requirement.
Bleaching involves an oxidation process by which the molecules causing discoloration are chemically modified.  Oxygenating agents like carbamide peroxide or hydrogen peroxide are used for effective bleaching. The application of these agents is performed in the office by clinicians or at home by patients ultimately resulting in high patient satisfaction. The efficacy of bleaching depends on the type of stain, its etiology, the duration of the bleaching agent application, and the concentration of the peroxide used. 
However, these bleaching agents were found to have a profound influence on the color behavior of tooth-colored restorations or perhaps even deteriorate them.  Effects of various bleaching agents on restorative materials may require the replacement of existing restorations for esthetic reasons.  Component systems of different restorative materials such as monomer systems in composites and acid components in glass ionomer cements (GIC) may show varied responses to bleaching agents.
Colorimetry is a branch of the science of color based on the digital expression of the color perceived from the object. In assessing chromatic differences, generally two systems are used: the Munsell color system and the Standard Comision Internationale de L, Eclairage (CIELAB) Color System. The American Dental Association recommends the use of the CIELAB color differential system.  According to this system, all colors in nature are obtained through the blending of 3 basic colors: red, blue, and green in various proportions [Figure 1].
The aim of this investigation was to test the influence of three different bleaching systems on the color stability of three tooth-colored restorative materials using the CIELAB color technique and a reflectance spectrophotometer.
Materials and Methods
Three different tooth-colored restorative materials were selected for this study. Characteristics of the materials according to the manufacturers are given in [Table 1]. Shade A2 was selected for the composite materials. The materials were divided into three groups as follows:
Group I (n = 40): microfilled composite, Durafill (Heraeus kulzer, Germany, Batch No.: 010141)
Group II (n = 40): nanofilled composite, Filtek Z 350 (3M, U.S.A., Lot No.: 5BA)
Group III (n = 40): glass ionomer cement, Fuji II (GC, Japan, Lot No.: 0601121)
The specimens were fabricated using plexiglass discs 6 mm in diameter and 2 mm in depth covered by polyethylene sheets and pressed flat with glass plates. The chemically cured glass ionomer cement was mixed as per the manufacturer's instructions and packed into the discs. The composite materials were placed incrementally in two stages and cured for 20 seconds after each increment with a LED curing light system (Bluephase C 5, Ivoclar Vivadent) through the glass and polyethylene sheets on the top and bottom of the specimens. The intensity of the curing unit was checked and standardized using the in-built curing radiometer at 650 mW/cm 2. The composite specimens were polished with a soflex disc (3M dental products) starting with coarse discs and ending with extra fine discs. Following a light curing of the composite material and setting of GIC, the specimens were placed in distilled water at 37°C.
Each group was further subdivided into 4 subgroups of 10 specimens each. The specimens were subjected to bleaching agents following the manufacturer's instructions. The details of the bleaching agents used are given in [Table 2].
Subgroup A (n=10): Specimens were treated with Vivastyle Paint-On (6% CP) and left for 20 minutes duration after each application twice daily for 2 weeks [Figure 2].
Subgroup B (n=10): Specimens were treated with Vivastyle (16% CP) for a period of 1 hr once daily for 2 weeks [Figure 3].
Subgroup C (n=10): Specimens were treated with Opalascence PF (20% Cp) for a period of 1 hr once daily for 2 weeks [Figure 4].
Subgroup D (n=10): Control; Specimens were stored in distilled water at 37°C for 2 weeks.
Each day after the active bleaching period, the specimens were rinsed with distilled water to remove the bleaching agents. During the test period, the specimens were kept in distilled water at 37°C.
At the end of the bleaching regimens, color measurements of the control and the test groups were made with a reflectance spectrometer (Perkin Elmer) [Figure 5]. The CIELAB color system was used for the determination of the color difference. According to this system, colors in nature are obtained through the bleaching of three basic colors (red, blue, and green) in certain proportions.
L - Depicts the lightness/ value.
a - Depicts the chromacity in the red- green axis.
b - Depicts the chromacity in yellow- blue axis.
All specimens were measured twice and the average values of L, a, and b data were calculated. The calculation of the color variation (ΔE) between two color positions in the three dimensional L a b color space was done as follows:
ΔE= [(L 1 - L 2 ) 2 + (a 1 - a 2 ) 2 + (b 1 - b 2 ) 2 ]½
The data was subjected to statistical analysis. A Kruskal-Wallis variance analysis and Mann Whitney U test were done to determine the significant color change of the restorative materials.
All restorative materials demonstrated a significantly higher color change (ΔE) with Vivastyle (P  tooth whitening has become one of the most popular esthetic procedures offered by dentists.
There may be Class III, IV, and V tooth colored restorations on the teeth to be bleached. Hence, the most commonly used tooth-colored restorations such as Glass-ionomer cement (Fuji II), a microfilled composite (Durafill), and a nanofilled composite (Filtek Z-350) were selected for this study.
The interactions between the bleaching agents and the restorative material may result in the color change that may be perceived by the patient. If the restorative material matches the surrounding tooth structure perfectly before bleaching, they may no longer match once the teeth have become lighter and brighter as a result of bleaching thereby leading to a major esthetic failure.
Carbamide peroxide is used as a vehicle for transporting hydrogen peroxide, which is the active ingredient responsible for the bleaching action.  It degrades into approximately one third hydrogen peroxide and two thirds urea.  The free radicals that are formed eventually combine to form molecular oxygen and water. Some aspect of this chemical process might accelerate the hydrolytic degradation of restorative materials, as described by Soderholm, et al.  Chemical softening of the restorative materials might also occur if the bleaching products have a high concentration of hydrogen peroxide. 
The A2 shade was chosen for composite materials to minimize the effect of shade variation. In this study, three marketed bleaching systems that differed with respect to peroxide concentration and regimen were compared. This included Vivastyle Paint On (6% carbamide peroxide), Vivastyle (16% carbamide peroxide), and Opalescence PF (20% carbamide peroxide). The control specimens were used as a standard against which the aftereffects of bleaching on the restorative materials were compared. The restorative materials were subjected to bleaching agents according to the manufacturer's instructions for a period of 14 days.
The color of dental esthetic restorative materials is routinely measured with a colorimeter or a spectrophotometer. In assessing chromatic differences, generally the CIELAB (standardized commission International de Éclairage) is used. The color differential system was used in this study.
The lightening of the specimens was depicted as an increase in L while the actual hue - chroma change was demonstrated in changes in a or b. The amount of discoloration after a given period was represented by the color difference value (ΔE). The accepted change caused by these bleaching preparations produces a ΔE value of 2, which is less than that of visual perception. Thus, the human eye cannot detect a change in color of the material that has undergone a color change less than ΔE of 2.
Among the materials tested, Fuji II GIC showed the largest color difference of ΔE = 11.4, followed by Durafill (ΔE = 7.5), and Filtek Z-350 (ΔE = 0.3). Although Glass ionomer cements possess anticariogenic property, they lack color stability due to the polyacid content of the material.  In this study, for Fuji II GIC, a noticeable color change was observed. It can be explained by the degradation of metal polyacrlate salts.  Color changes of composites may be influenced by the differences in resin shades, the chemical activator, initiator and inhibitor, polymer quality, type and quantity of filler, oxidation of C=C double bonds, resin thickness, or storage methods of specimens during observation.  Among the composite materials tested in this study, Durafill showed moderate color change when compared with Filtek Z-350, which showed the least color change. This may be attributed to the amount of resin and filler particles present in the composite.  It is assumed that the resin component is the source of discoloration. Higher discoloration of the Durafill may be ascribed to the greater volume fractions of the resin matrix when compared with Filtek Z-350. The bleaching agents may also cause a decline of silica and silisium content, indicating erosion of the composite material. 
A color difference of ΔE = 2 in the CIELAB color systems is detectable by the human eye under uniformly controlled conditions. Therefore, a minimum difference of 2 can be used as criteria for the comparison of color changes in the restorative materials.
Within the limits of this study, it was observed that even low concentrations of bleaching agents had an influence on the color of restorative materials. Patients should be advised that existing restorations may not match their natural teeth after bleaching, and replacement may be required for esthetical reasons.
Under the limitations of this study, there was a hierarchy of color change by the type of material tested. GIC Fuji II demonstrated the highest color change followed by the microfilled composite Durafill. The nanofilled composite Filtek Z 350 showed the least color change suggesting that the nanofilled composite is highly resistant to color degradation.Δ
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