Background. If a temporary restoration is in the esthetic area and needs to be worn for a long time, the color stability of temporary materials becomes an important factor.
Objectives. The aim of this in vitro study was to evaluate the long-term effects of various staining solutions on the color stability of different temporary materials produced with the computer-aided design and computer-aided manufacturing (CAD/CAM) technology.
Material and methods. In the study, the following materials were used: VITA CAD-Temp® (group 1); Ceramill® Temp (group 2); and Telio® CAD (group 3). Forty disk-shaped specimens (10 mm in diameter, 2 mm in thickness) of each material (N = 120) were produced with a CAD/CAM system. Staining solutions – of tea (A), of coffee (B) and cola (C) – and distilled water (D, control) were used, and color was evaluated before and after storing the samples in the solutions. Measurements were taken with a spectrophotometer and the color parameters (L*, a*, b*, and ΔE) were calculated according to the Commission internationale de l’éclairage system (CIELab). The results were evaluated with the two-way analysis of variance (ANOVA) and Tukey’s tests (α = 0.05).
Results. Clinically perceivable (ΔE00 > 0.8) and statistically significant (p < 0.001) color differences were detected in all specimens. The highest ΔE00 value was found in the Ceramill Temp specimens. In addition, the highest ΔE00 values were noted for the specimens stored in cola and the coffee solution for all groups. The lowest ΔE00 value was observed for the groups stored in the tea solution.
Conclusions. Clinically perceivable color changes were observed in all the specimens kept in the solutions. Color changes were greater for cola and coffee as compared to tea.
Keywords: CAD/CAM, coloring, temporary dental prosthesis
Temporary restorations are important to protect the prepared teeth, to restore the lost function, phonetics and esthetics, and to prevent tooth sensitivity.1 Polymethylmethacrylate (PMMA) is the most commonly used traditional material for temporary restorations. Among available dental resins, this compound has excellent physical properties, including durability, color stability and marginal adaptation. Recently, high-density blocks and disks with highly cross-linked PMMA acrylic resin have been introduced for processing with the computer-aided design and computer-aided manufacturing (CAD/CAM) technology. These products have been recommended for temporary restorations in long-term dental treatment, including preparing implant-supported prostheses,2, 3 as they have better properties as compared to traditional materials.4, 5 If a temporary restoration is in the esthetic area and needs to be worn for a long time, the color stability of temporary materials becomes an important factor.6 In such areas, a temporary restoration should not only have an initial color match, but also provide an esthetic appearance throughout its use.7 As dental resins absorb liquid regardless of their chemical composition, discoloration may occur when the material is exposed to solutions such as coffee, tea, red wine, chlorhexidine, or bleaching agents.8, 9, 10, 11 In the Commission internationale de l’éclairage color system (CIELab), the degree of color change is expressed as ΔE, and the following formula is used (Equation 1):
ΔL*, Δa*, Δb* – differences in the color parameters.
A value of zero for ΔE indicates that 2 colors are identical, while a value other than zero indicates a color change.12 In previous studies, color differences between 2 specimens have been clinically evaluated using the CIELab color system.13 However, the system has limitations, including tone values.14 Therefore, other CIELab-based color difference formulas have been developed.15 A recent study suggested that CIEDE2000 could better evaluate color differences.16 This formula includes specific corrections for the interaction between chroma and color differences in the blue region as well as a modification of the CIELab coordinate that affects colors with low chroma.17
The aim of this study was to investigate the effects of various solutions on the long-term color stability of different types of prefabricated disk materials for CAD/CAM systems. The null hypothesis was that the solutions used would affect the long-term color stability of prefabricated disk and block materials for CAD/CAM systems.
Material and methods
Three types of prefabricated temporary restoration disks for CAD/CAM systems were tested (Table 1):
– VITA CAD-Temp® blocks (VITA Zahnfabrik H. Rauter, Bad Säckingen, Germany) consisting of a microparticle filler, fiber-free, homogeneous, high-molecular-weight and cross-linked acrylate polymer; this structure is referred to by VITA as the MRP (Microfilled Reinforced Polyacrylate) material and contains 14% SiO2 microparticles as fillers18;
– Ceramill® Temp (Amann Girrbach, Koblach, Austria) made of PMMA and methacrylic acid ester-based cross-linked polymers that can be easily processed19; and
– Telio® CAD blocks (Ivoclar Vivadent, Schaan, Liechtenstein) consisting of 99.5% cross-linked PMMA and 0.5% pigment; these blocks have a high material homogeneity and do not exhibit polymerization shrinkage, as they are produced industrially like other CAD/CAM blocks.20
A wax pattern, 2 mm in thickness and 10 mm in diameter, was prepared and scanned in a CAD system, and the obtained images were transferred to digital media as a stereolithography (STL) file. VITA shade 1M2, corresponding to A1, was used for VITA CAD-Temp, and for Telio CAD and Ceramill Temp – a light disk corresponding to shade A1.
The specimens were divided into 3 groups according to the different temporary materials used. A total of 120 specimens (N) were milled, with 40 specimens for each group. These groups were further divided into 4 subgroups for different solutions, including the control group (n = 10). For the analysis of color stability, distilled water and 3 different staining solutions were prepared: tea (Yellow Label Tea; Lipton, Rize, Turkey); coffee (Nescafé Classic; Nestlé, Vevey, Switzerland); and cola (Coca-Cola; Coca-Cola Co., Istanbul, Turkey) (Table 2). For the tea solution, 1 teabag was placed in 200 mL of boiled water for 10 min. The coffee solution was prepared by pouring 15 g of coffee powder into 500 mL of boiled water, followed by mixing. The front surfaces of the specimens were polished under water cooling for 10 s with 400-, 800-, 1,200-, and 2,400-grit SiC abrasive papers, respectively.
For initial color measurements, a clinical spectrophotometer device (VITA Easyshade® Advance; VITA Zahnfabrik H. Rauter) utilizing the CIELab color system was used. The instrument was calibrated before each measurement, and the specimens were individually numbered after being washed with distilled water and dried. The CIELab values were obtained with the spectrophotometer, with 3 different points measured for each specimen and the mean value calculated. Color measurements were taken before soaking the specimens in the solutions and after 21 days of storage in the solutions. Measurements were done in a single-tooth mode at the same time of day, under the same conditions, on a white background. They were performed by a single investigator and the CIELab parameters were recorded.
The solutions were exchanged every 2 days to prevent plaque formation during soaking, and the specimens were cleaned with a conventional toothbrush (Macleans® brand toothbrush; GlaxoSmithKline, Brentford, UK) and toothpaste (Aquafresh® brand toothpaste, mild and minty flavor; GlaxoSmithKline). Color differences were converted to CIEDE2000 and recorded as ΔE00. Recently, some studies established 50:50% color difference thresholds in dentistry.21, 22 The CIELab 50:50% perceptibility threshold (PT) was ΔEab = 1.2 and 50:50% acceptability threshold (AT) was ΔEab = 2.7, whereas the CIEDE2000 (ΔE00) 50:50% PT was ΔE00 = 0.8 and 50:50% AT was ΔE00 = 1.8.21, 22 These values were included in the ISO/TR 28642:201623 and should be applied to all issues related to the quality of tooth color matching in dentistry. They can serve as quality controls to guide the selection of esthetic dental materials, evaluate their clinical performance, and interpret visual and instrumental findings in clinical dentistry, dental research, and subsequent standardization.24 Thus, in this study, PT ΔE00 > 0.8 was accepted.
Color differences (ΔE00) for different materials before and after soaking in the solutions are shown in Figure 1. The ΔE values for the specimens kept in different solutions were compared via the two-way analysis of variance (ANOVA). The analysis showed that the Ceramill Temp specimens had the highest statistically significant ΔE00 values (p < 0.001). The clinical color matching in all specimens was ΔE00 > 0.8; therefore, all were classified as clinically perceivable. The two-way ANOVA indicated statistically significant differences in the ΔE00 values for the material and solution types (p < 0.010). In addition, the interaction between the material type and the solution type was statistically significant (p < 0.010). The results represent the ΔE00 values for different material specimens stored in different solutions. According to this, the mean ΔE00 value for the specimens kept in distilled water was found to be 1.67; thus, it was a perceivable change as well (ΔE00 > 0.8).
The mean ΔE00 value for the specimens kept in tea was 3.29, the mean ΔE00 value for the specimens kept in coffee was 4.10, and the mean ΔE00 value for the specimens stored in cola was 4.44. According to these results, the color change of the specimens kept in tea was less significant than of those kept in coffee and cola (Figure 2).
The hypothesis of the current study was accepted. Color stability is an important criterion for the selection of materials, especially for temporary restorations to be used for a long time in the anterior region.25 Although there are studies in the literature that examine the color stability of different types of temporary materials,26, 27, 28 no studies have been found where the current CAD/CAM-produced temporary materials are evaluated together.
Bayindir et al. studied the color change of autopolymerizing temporary prosthetic materials in various solutions.1 The highest ΔE value reported in this study was for the groups kept in coffee.1 Guler et al. investigated the color change of autopolymerizing and light-polymerized composite resin temporary restorations, reinforced microfill and microhybrid composite resins in various solutions.29 The lowest ΔE value was reported for the water, cola and cherry juice solution groups, while the highest ΔE value was observed in the materials stored in red wine. In addition, the highest color change was observed for a light-polymerized composite resin.29
Prefabricated, pre-polymerized resin blocks for the CAD-CAM technique have been introduced recently.30 These blocks are manufactured under more favorable and controlled production conditions, are used for temporary fixed dental prostheses, and have better properties than autopolymerizing temporary materials.31, 32 VITA CAD-Temp is an acrylic resin-based material, and Ceramill Temp and Telio CAD have PMMA content. In our study, the highest ΔE value was observed for the Ceramill Temp specimens containing PMMA.
Sham et al. also examined the color stability of 5 temporary restoration materials by immersing them in distilled water or coffee for 20 days.33 In their study, the minimum color change was observed for the materials containing bis-acryl methacrylate. In addition, it was reported that the materials containing poly(ethylmethacrylate) and PMMA stored in coffee showed a lesser color change as compared to those containing bis-acryl methacrylate.33 Haselton et al. also investigated the color change of 12 different temporary prosthetic materials in artificial saliva and the artificial saliva-coffee solution.9 The highest ΔE value was found for the bis-acryl resin-containing specimens stored in the artificial saliva-coffee solution for 4 weeks, and the lowest ΔE value – for the specimens with PMMA content.9
Interim crowns made by means of conventional methods were compared with those made with CAD/CAM by Almohareb et al., and it was found that those made with CAD/CAM were more color-stable.26 Telio CAD had the lowest ΔE value in all solutions and showed better color stability than other materials.26
Lauvahutanon et al. measured the ΔE values of CAD/CAM blocks after soaking in coffee and water.27 No significant color change was found for the specimens in water, while the specimens in coffee had an increased ΔE. Similarly, we observed a clinically perceivable color change for the specimens held in coffee. Two recent studies also reported a strong color change in temporary materials due to coffee.26, 34 This was attributed to the smaller molecular size along with the water absorption property of the tested materials.26, 34 Also, it was reported that coffee was a more coloring solution, whereas cola mostly influenced roughness.35
Stawarczyk et al. also measured the color change of resin blocks for CAD/CAM systems in the coffee, black tea and red wine solutions.28 Similar to the results of our study, color changes were observed in all groups. VITA CAD-Temp and the other CAD/CAM resins showed similar color stability.28 These findings indicate that prefabricated blocks produced for CAD-CAM systems have better physical properties than conventional materials. In the present study, such a comparison could not be made, as we did not use any temporary crown material polymerized by means of conventional methods. Another limitation of the current study is that the oral environment is different from in vitro conditions. Food, thermal and mechanical stresses, and their interactions may increase the color change in vivo.
According to the results of this study, the color stability of fixed temporary restorations depends on the type of the material used and the type of beverage. Although the color change of the specimens kept in tea was lesser than of those kept in coffee and cola, all changes were perceivable. Thus, the color stability of prefabricated temporary blocks for CAD/CAM systems needs to be improved.