Oral Sciences n3 Braz J Oral Sci. 14(4):272-275 Original Article Braz J Oral Sci. October | December 2015 - Volume 14, Number 4 Influence of shade, curing mode, and aging on the color stability of resin cements Janes Francio Pissaia1, Gisele Maria Correr1, Carla Castiglia Gonzaga1, Leonardo Fernandes da Cunha1 1 Universidade Positivo – UP, Dental School, Department of Operative Dentistry, Curitiba, PR, Brazil Correspondence to: Janes Francio Pissaia Graduate Program in Dentistry, Universidade Positivo, Curitiba, PR, Brazil Rua Professor Pedro Viriato Parigot de Souza 5300 - Curitiba - PR - CEP: 81280-330 Phone: 55 46 99301204 E-mail: janespissaia@hotmail.com Abstract The color stability of resin cements is essential for aesthetic restorations. Aim: To evaluate the influence of shade and aging time on the color stability of two light-cured and two dual-cured resin cements. Methods: The CIE-Lab color parameters (n=6) were measured immediately after sample preparation and at 7, 30 and 90 days of aging in distilled water. The color difference (∆E) was calculated and then analyzed by three-way ANOVA for repeated measures and Tukey’s HSD test (α=0.05). Results: ∆E was higher for transparent resin colors, followed by dark and light colors. The mean values of ∆E were lower for both light-cured resin cements compared to the dual-cured cements. As the aging time increased, ∆E values increased. Conclusions: The light-cured resin cements showed greater color stability. The lighter shades of luting were more likely to display a greater color change. Keywords: aging; color; dental cements; esthetics; dental materials. Introduction Resin-based cements have been extensively applied for aesthetic restorations with translucent material, like dental ceramic veneers1-2. It is essential that the color of the aesthetic materials remains stable over a long period in the oral environment3-4. Previous studies have described color changes occurring in direct dental composites5-9. However, as Koishi et al. have remarked4, the color stability of luting composites requires careful analysis. Luting composites and direct composite resins have similar compositions (in terms of the polymer matrix and fillers), and therefore the color stability of luting composites may be affected by chemical components. Inorganic oxide additives are typically used to create material shades that match the color of the tooth or other restorative materials used with resin-based cements10. Depending on the manufacturer, one or multiple shades may be applied. Uchida et al. reported that the discoloration of a direct composite resin is influenced by shade selection8: the lighter the shade, the higher the tendency for discoloration. As direct composite materials and luting cements have similar chemical components (organic matrix and fillers), the color stability of resin-based cements may also be affected by shade selection. Resin-based cements may be classified based on whether they are chemically cured, light-cured or dual-cured materials11. Light-cured resin cements present increased working time and the removal of excesses of material is easier than for chemically cured materials. On the other hand, dual-cured luting materials contain compounds for both chemical and light curing, and consequentially these materials possess beneficial traits from both polymerization systems. The combination of curing systems used with dual-cured resin cements is reported to reduce the number Received for publication: November 18, 2015 Accepted: December 11, 2015 http://dx.doi.org/10.1590/1677-3225v14n4a04 of remaining double bonds, which improves the degree of conversion12. As the color of resin-based materials is related to the degree of conversion13-14, dual-cured luting materials should show better color stability than the light-cured resin cements. In the case of aesthetic restoration materials, such as ceramic veneers, the color stability of the resin-based cement employed for the cementation procedure may be as important for the long-term clinical success of the restoration as the mechanical properties of veneering material. When ultrathin ceramic veneers are used, the color of the resin-based cement plays a major role. The aim of this study was to evaluate the color stability of four different luting cements with variations in curing mode, shade and aging time. The experimental design tested three null hypotheses: that there might be no difference in color stability between the evaluated shades, that the method of polymerization might not influence the color stability, and that aging in water might induce no changes in color. Material and methods Three shades (transparent, clear, and dark) of each four resin-based cements (Rely X Veneer 3M/ESPE, Germany, light-cured; Choice 2 Bisco, USA, light-cured; Variolink II Ivoclar-Vivadent, Germany, dual-cured; and AllCem FGM, Brazil, dual-cured) were evaluated in this study. The key attributes of each material are in Table 1. All specimens were prepared in controlled relative humidity (55±5%) and temperature (23±1 ºC). Each luting composite was mixed in accordance with the manufacturer’s instructions. Six disk specimens, 5 mm diameter and 1 mm thick, were prepared for each shade and material. Each specimen was made by inserting the resin-based cement into a Teflon mold ring and pressed between two 1-mm-thick glass slides under finger pressure. All samples were continuously light-cured with a LED light source (Dental Woodpecker LED, 1200 mW/cm 2), according to the manufacturer’s instructions (Rely X Veneer 3M/ESPE - 30 s,; Choice 2 Bisco – 40 s; Variolink II Ivoclar-Vivadent – 40 s; and AllCem FGM – 40 s), by placing the light tip on the glass slide covering the entire area of each specimen. Specimens were stored in dark canisters containing distilled water at 37 °C for 24 h. The color of each specimen was first determined after 24 h, and this was defined as the baseline color evaluation. The color measurements were performed with an EasyShade spectrophotometer (Vita Zahnfabrik, Bad Säckingen, Germany) according to the CIE- Lab (Commision Internationale de l’Eclairage) L*, a*, b* coordinates. The CIE L* parameter corresponds to the degree of light and darkness, whereas a* and b* coordinates correspond to red or green (+a*=red, -a*=green) and yellow or blue (+b*=yellow, -b*=blue), respectively. The specimens were then stored in dark canisters containing distilled water at 37 °C, and the color values were again measured after 7, 30 and 90 days. The specimens were placed on a white background during the measurement to prevent potential absorption effects on any of the measured color parameters. The mean of three measurements on each sample was used to represent the average values of the color parameters of each sample and these average values were used for the overall data analysis. The CIE-lab coordinates were used to calculate the color difference (∆E) between the baseline color measurement and the aged specimens. Before each color measurement, the immersed specimens were dried with absorbent paper. The ∆E for each experimental time was calculated using the following equation: ∆E = [(∆L*)2 + (∆a*)2 + (∆b*)2]1/2 where ∆L*, ∆a*, and ∆b* are the differences in the respective values before and after aging. The ∆E values were analyzed by three-way ANOVA for repeated measures and Tukey’s HSD test (α=0.05). Results The mean values of ∆E for the three different variables in this study, along with standard deviations, are in Tables 2-4. Significant effects of curing mode, shade and aging time on the color stability were observed. As shown in the results of resin shade comparison in Table 2, ∆E values were the highest for translucent resins (p=0.000009), and lowest for clear and dark resins. There were no significant differences 273273273273273 Influence of shade, curing mode, and aging on the color stability of resin cements Braz J Oral Sci. 14(4):272-275 Material Curing Color Color Color Mode Transparent Clear Dark Choice 2 Light-cured Translucent A1 A2 Bisco Rely X Veneer Light-cured Translucent A1 A3 3M/ ESPE Variolink II Dual-cured Transparent Light Yellow-A1 Opaque Yellow-A3Yellow/ Ivoclar-Vivadent White (110/A1) Universal (210/A3) AllCem Dual-cured Transparent A1 A3 F G M Table 1.Table 1.Table 1.Table 1.Table 1. Materials used in the present study. 274274274274274 Material Mean S D Choice 2 2.79 A* 0.71 Rely X Veneer 3.49 A 0.77 Variolink II 3.60A 1.42 AllCem 4.48B 0.99 Table 3. Table 3. Table 3. Table 3. Table 3. Mean ∆E values and corresponding SDs for the tested four resin-based cements. *different letters indicate statistically significant difference between group ∆∆∆∆∆E (days) Mean S D 7 2.79A* 0.51 30 3.73B 1.01 90 4.25C 1.40 Table 4. Table 4. Table 4. Table 4. Table 4. Mean ∆E values and corresponding SDs for different aging times. *different letters indicate statistically significant difference between group Influence of shade, curing mode, and aging on the color stability of resin cements Braz J Oral Sci. 14(4):272-275 C o l o r Mean S D Clear 3.12A* 0.74 Dark 3.25 A 1.13 Transparent 4.41 B 1.04 Table 2.Table 2.Table 2.Table 2.Table 2. Mean ∆E values and corresponding standard deviations (SDs) between different shades of resin-based cements. *different letters indicate statistically significant difference between group between clear and dark shades of the tested materials. Comparing the four resins in terms of the type of curing, the dual-cured AllCem cement had higher ∆E values when compared to light-cured materials (Table 3) (p=0.000016). No significant difference was found between the dual-cured cement Variolink II and the light-cured materials. When aging time was considered, the mean values of ∆E increased with time from 7 to 30 to 90 days (Table 4, p=0.000000). Discussion All three evaluated null hypotheses in the present study were rejected: the experimental results revealed that the color stability varied among resin shades, curing methods and specimen aging times. Storage in water is frequently used for in vitro aging of restorative composite materials. In this study, water exposure for longer periods of time caused increased changes in the CIE color space coordinates of the composites (Table 4). It is well known that water absorbed in the polymer matrix causes filler matrix debonding and hydrolytic degradation of the filler15-16, and it also could change the refractive index of the material4. Therefore, the increase of the ∆E values might be affected by water sorption in the used luting composites. The ∆L values increased as the immersion period increased, suggesting that the color of a luting composite tends to darken over long-term clinical use4. Other researchers have demonstrated that composite materials undergo discoloration by exposure to sources like UV light, visible light and/or heating6,17. In prosthetic composites, Ruyer et al. reported that color changes with ∆E values lower than 3.3 were acceptable18; Turgut et al. reported that ∆E values lower than 3.5 were also acceptable19. After aging, all specimens showed changes in ÄE values, but almost all the color differences had acceptable values. However, the mean ∆E values for transparent resin shades and for the dual-curable resin cement were above the acceptable. After 30 and 90 days of laboratory aging, ∆E values were also higher than acceptable. These results are related to the used method, because the uncovered resin disks used in this study, similar to those used in previous reported ageing tests 20-22, have increased exposure to potentially damaging environmental factors. Different number of samples are used for this kind of research; for example, Uchida et al. 1998 used 3 samples per group8. On the other hand, five specimens were prepared for each group by Koishi et al. 20024, Lu and Powers 200423, Furuse et al. 20086. In the present study, six samples were enough to provide statistically significant difference, thus no more samples were fabricated. The effect of shades on the color stability of luting composites was statistically significant. The relative values of DE*ab were dark=clear