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Year : 2016  |  Volume : 19  |  Issue : 1  |  Page : 46-50
Color changes in resin cement polymerized with different curing lights under indirect restorations

1 Department of Prosthetic Dentistry, Faculty of Dentistry, Atatürk University, Erzurum, Turkey
2 Department of Restorative Dentistry, Faculty of Dentistry, Atatürk University, Erzurum, Turkey

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Date of Submission01-Sep-2015
Date of Decision19-Nov-2015
Date of Acceptance01-Dec-2015
Date of Web Publication5-Jan-2016


Aim: The aim of the study was to investigate the effects of different interface materials and curing units on color changes in a resin cement material.
Materials and Methods: Three interface materials and different curing systems, quartz-tungsten-halogen and polywave and monowave light-emitting diode (LED) light curing units, were studied at two-time intervals. Polystyrene strip was used as a control group. All measurements were made on a white background for standard color measurement. According to the CIE L*a*b* color space, the baseline color values of each specimen were measured. Differences between the measurements were calculated as ΔE, ΔL, Δa, and Δb. Data were analyzed using analysis of variance (ANOVA) and Duncan's tests (α = 0.05) with SPSS 20.0 software (SPSS Inc., Chicago, IL, USA). ANOVA revealed significance for interface materials and curing units and time for ΔE (P < 0.05).
Results: Interaction between polymerizing units, material and time was not significant (P > 0.05). Monowave LED exhibited significantly higher color changes than the other units ([P < 0.05] [ΔE 2.94 ± 0.44]). QTH promoted composite specimens significantly less color change ([P < 0.05] [ΔE 0.87 ± 0.41]).
Conclusion: This study concluded that color of resin cement used in the adhesion of indirect restorations was affected by curing device light and indirect restoration material type.

Keywords: Color change; curing unit; indirect restoration; resin cement

How to cite this article:
Bayindir F, Ilday NO, Bayindir YZ, Karatas O, Gurpinar A. Color changes in resin cement polymerized with different curing lights under indirect restorations. J Conserv Dent 2016;19:46-50

How to cite this URL:
Bayindir F, Ilday NO, Bayindir YZ, Karatas O, Gurpinar A. Color changes in resin cement polymerized with different curing lights under indirect restorations. J Conserv Dent [serial online] 2016 [cited 2023 Sep 24];19:46-50. Available from:

   Introduction Top

Ceramic and composite resin, esthetic dental materials are continuously developing to meet functional and esthetic demand. Indirect restorations require appropriate cement for long-term use in changeable oral conditions and also to meet patients' esthetic expectations. In success of indirect restorations, esthetic quality of the material is not the only criterion to be considered. It is important that indirect restorations are firmly attached to the tooth structure with resin-based cement. [1]

Several different types of light curing unit (LCU), from conventional quartz-tungsten-halogen (QTH) lamps to argon laser, have been employed. QTH lamps emit light when electrical energy heats a small tungsten filament to high temperatures. QTH-curing lights work at wavelengths of 400 to 500 nm with output ranging from 400 to 800 mW/cm 2 . [2]

Light-emitting diode (LED) or solid-state LED, instead of the hot filaments used in halogen bulbs, LEDs use junctions of doped semiconductors for generating light. These units are cordless, small, lightweight, and battery-powered. [3] Recently, "polywave" LED units (with two or more spectral peaks) have been introduced using two or more different LED colors, meaning that their spectral output ranges from blue (460 nm) to violet wavelengths (410 nm) of light. These lights can polymerize composite resins containing both conventional and alternative photoinitiators. Since most manufacturers of direct resin-based restorative materials do not provide details about the photoinitiators contained in their products, selecting an optimal combination of restorative resin and LCU is problematic.

Narrow blue LED light spectra emission is ideal for photopolymerization of camphorquinone containing materials, but this may not be such efficient when other photoinitiators, such as 1-phenyl-1,2-propanedione, are present in very light composite shades (high color value) used for repair of bleached teeth. This situation was addressed by manufacturing dual-wave (or "polywave") LED LCUs, emitting in the violet (410 nm) and blue (470 nm) component of the light spectrum. [4] The third generation, polywave LEDs are used in these LED LCUs. While many publications have discussed the physical properties of LED light-cured materials, few have investigated the color stability of resin-based restorative materials when cured with QTH and LED lights. Monowave and polywave LED LCUs and QTH LCUs have not previously been compared in terms of efficiency in curing resin cement under indirect restorative materials. [5],[6]

Shade matching, whether by visual or instrumental methods, requires an understanding of color harmony and tolerance. In other words, what color difference (ΔE) is perceptible to the human eye. The ΔE value of 2.5 exhibited a borderline value recognizable to all people in a color test. [7] Color changes are considered visually perceptible when ΔE >1 and clinically acceptable when ΔE <3.3. The CIE L*a*b* - based color difference formula is most widely used. CIE L*a*b* color appearance attributes are frequently used to calculate CIE L*a*b* color difference (ΔE) as equations. [8],[9]

Color differences (ΔE) were calculated using the CIELAB35 color notation system namely, L* (lightness, ranging from 0 to 100 with higher numbers being brighter), a* (green-red direction), and b* (blue is the yellow direction). CIELAB parameters (L*, a*, and b*) of each specimen were recorded at initial (i) and at final (f). [10]

The purpose of this study was, therefore, to evaluate the effect of color changes in a resin cement material polymerized under different restorations using different light polymerizing units. The hypothesis of this study would be different curing systems and different interface materials effects the resin cement color stability at different time interval.

   Materials and Methods Top

Experimental design

Conventional halogen (QTH), polywave and monowave LED LCUs, and interface materials (polystyrene strip, ceramic, and composite resin) were used. A list of the curing lights, including specifications and manufacturers, is given in [Table 1] (Kuraray, Japan, Lot: 0015 AA) resin cement was used for all test groups.
Table 1: Curing regimes and curing conditions

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The protocol involved 18 groups (n = 5); three interface materials and three different curing systems at two-time intervals. Ninety specimens, 1 mm thick and 5 mm in diameter, were prepared. Resin cement was firmly pressed under a 5 kgf load for 3 min in a Teflon cylindrical mold under a glass slide covered by a polystyrene strip (KerrHawe Stopstrip, KerrHawe SA, Bioggio, Switzerland, Lot: 70501264) to produce a uniform thickness. Resin cements were polymerized on interfaces prefabricated from ceramic (A2 Vita Porcelain, Säckingen, Germany) and composite resin (A2 Esthet X HD, Dentsply, Caulk, Milford, DE, Lot No: 090119) for simulated ceramic or composite restoration. Excess resin was removed before polymerization. Polystyrene strip was used as a control group.

The resin cement was exposed to light through the upper glass slide in contact with a curing 9-mm light tip for 20 or 40 s in the case of QTH units, 20 or 40 s for monowave LED units, and 3 or 6 s for polywave LED units [Table 1]. The output of the curing light was checked with a radiometer (Curing Radiometer, Model 100, Kerr Corp., Orange, CA, USA). No polishing techniques were used in order to avoid modification of the surfaces that might have influenced the results.

Color measurements

The color of each specimen was measured three times; before polymerization and twice after polymerization (20/40 s for QTH and monowave LED and 3/6 s for polywave LED) using a colorimeter (Shade Eye NNC, Shofu, Japan). The measurements were performed, according to the CIE L*a*b* system, and mean L*, a*, and b* values for each material were calculated. The total color change (ΔE) obtained was calculated for each specimen using the equation:

Where ΔL*, Δa*, and Δb* are differences in the respective values before and after polymerization. All measurements were made on a white-colored sheet for standard color measurement.

Statistical analysis

Statistical analysis was performed on SPSS 20.0 (SPSS Inc., Chicago, IL, USA). Means and standard deviations were calculated. Data obtained were analyzed using three-way analysis of variance (ANOVA) followed by Duncan test significant difference tests for comparisons among groups at a 0.05 level of significance.

   Results Top

Resin cement colorimetric values (L*a*b*) of the resin cement polymerized under ceramic and composite discs with three light polymerizing units before and after polymerization are given in [Table 2]. Color changes (ΔE) of all test groups are presented [Table 3] and [Figure 1].
Figure 1: Color changes (ΔE) of all test groups are presented

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Table 2: L*, a*, b values (mean ± SD) of the test groups (n=5)

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Table 3: DE values and ±SD of the test groups (n = 5)

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Three-way ANOVA revealed significance for interface materials and curing units in relation to ΔE (P < 0.05). The interaction between polymerizing units, material and time was not significant (P > 0.05) [Table 4].
Table 4: Results of three-way ANOVA

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Both interface materials, ceramic and composite resin are induced less color change than the control group (P < 0.05). Monowave LED exhibited significantly higher color changes than the other materials (P < 0.05) (ΔE 2.94). Composite specimens with QTH induced significantly less color changes ([P < 0.05] [ΔE 0.87 ± 0.41]) [Figure 1].

   Discussion Top

This study investigated the color of indirect composite or ceramic restoration, after cementation with resin cement using differently LCUs. The tested hypothesis was accepted. The color stability of both indirect restorations and luting materials is important for the esthetics of laminate veneers, all-ceramic crowns, and indirect composite restorations. One of the most important benefits of ceramic crowns is the semi-translucency of the material that allows light transmission. This optical property improves the esthetics of ceramic crowns as compared to metal-ceramic crowns that do not allow light transmission through the metal. However, the translucency of esthetic indirect restorations is very important in terms of the complex color matching process. [11] Particular attention should be paid to the optical effects from any underlying color. The color of the tooth and the luting cement can affect the appearance of indirect restorations. Several studies have reported the importance of color to the clinical appearance of an esthetic crown. [7],[12]

Three different types of light sources were used in this study. LEDs are today being aggressively marketed. According to previous studies, LED LCUs have become the gold standard for photopolymerization of resin-based dental materials. Since contemporary LED lights provide superior irradiance, expanded lifetime, little light output degradation over time to QTH light, LED lights are expected to optimally polymerize resin materials as or even more effectively than QTH. [13],[14],[15] In the current study, color changes in specimens polymerized with monowave LED were statistically greater than those in halogen-based polymerizing units and polywave LED LCUs (P < 0.05).

Polywave LED devices portrayed as having maximum theoretical polymerization efficacy also have characteristics that need to be developed. In some of these "polywave" LED units, the spectral emission is not uniformly distributed across the light tip, further compounding the effects of beam inhomogeneity. Thus, some areas of the resin may not receive the required wavelengths. [16] This may explain the color changes in the specimens polymerized with polywave LED LCUs used in this study being greater than the color change values in specimens polymerized with monowave LED LCUs.

In the present study, significant difference was showed between interface materials prepared for the purpose of representing indirect restorations. The greatest color change was obtained in the control group since polymerization was more effective (P < 0.05). Ceramic and composite interface materials were seen to be able to cause a decrease in polymerization efficacy. Color change of the resin cement during polymerization is related to its chemical characteristic. Inadequate polymerization or cement type factors that may cause the color changes followed by polymerization. [17] Clearfil SA Cement is a dual cure cement and polymerized in two stages with physically and chemically. Such reaction may occur a higher monomer conversion which allows the polymerization of the deeper layers of the resin. However, the thickness and light transmittance of the indirect restoration, which applied on the resin cement, should be able to allow sufficient polymerization of the resin cement. In our study, the control group has showed the best polymerization because Mylar strip light passes directly. Similarly, the ceramic disc used in our study is more translucent than composite, and it was caused a higher polymerization by passing more light from composite block.

Several studies have measured the intensity of light polymerization units. Watanabe et al. [18] has shown that high-intensity LED unit is more effective than QTH units during polymerization of dual cure cement trough ceramic material. Arikawa et al. [19] has reported that LED units emit more homogenous light and thus yield more uniform distribution of surface hardness (Knoop hardness number) of a resin composite than halogen units. In our study, monowave LED exhibited significantly higher color changes. It means that best polymerization occurred in monowave led samples.

The color appearance of a layered ceramic disk specimen is strongly influenced by the core and veneer thicknesses and also by their interaction between them. [11] In contrast, a 1.0-mm thick IPS Empress 1 ceramic material was not affected by the shades of substrate and luting composite cement tested. [12] The effects of two different cement shades (Vita A1 and A3) and water storage on the leucite-reinforced ceramic color over time showed no changes in the experimental design may explain the different results from different studies, such as the contents of materials, color of the test specimens, and the color-measuring instruments. It is very difficult to reproduce the oral environment in the laboratory situations. It is also important to realize the impossibility of establishing exact comparability between in vitro and in vivo tests.

   Conclusion Top

Considering the methodology applied and the limitations of this in vitro study, it can be concluded that different curing units and interface materials have a significant effect on the final color of resin cement. More studies are now needed to evaluate the efficiency of polymerization of mono/polywave LED LCUs and to evaluate the effect of different interface materials on color stability of resin cement.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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Malhotra N, Mala K. Light-curing considerations for resin-based composite materials: A review. Part II. Compend Contin Educ Dent 2010;31:584-8.  Back to cited text no. 4
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Correspondence Address:
Dr. Ozcan Karatas
Department of Restorative Dentistry, Atatürk University, Erzurum
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.173198

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]

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