Abstract
Objective
To analyze the color stability of Bulk-fill resins immersed in chicha morada and light-cured at different distances (0 mm, 2 mm and 4 mm).
Methods
This in vitro experimental study included a total of 216 Bulk-fill resin discs. The specimens were distributed into nine groups of 24 discs based on the type of resin (3M ESPE® Filtek™ Bulk Fill®, Ivoclar® Tetric N-Ceram Bulk Fill® and FGM® Opus Bulk-fill APS®), light-curing distances (0, 2 and 4 mm) and staining solution (control with distilled water and Naturalle® chicha morada). Color measurements were taken 24 hours after fabrication and immersion in distilled water and Naturalle® chicha morada at 24 hours, 1 week and 3 weeks.
Results
Light-curing distances affected the color stability of the resins with 3M ESPE® and Ivoclar®, thus exhibiting significant color changes at all evaluated time points when immersed in chicha morada. For the Delta (ΔE) value 3M ESPE® and Ivoclar® resin discs immersed in chicha morada showed significant changes at 24 hours 1 week and 3 weeks (p = .001, p = .000 and p = .000; and p = .000 p = .000 and p = .000 respectively). However, FGM® resin discs exhibited significant changes only at 24 hours and 1 week (p = .000 and p = .001). FGM® showed better color stability compared to 3M ESPE® and Ivoclar® at 3 weeks of immersion in chicha morada. All three commercial brands showed a significant decrease in the "L" value as immersion time in chicha morada increased.
Conclusions
The study concluded that FGM® demonstrated better chromatic stability over time compared to 3M ESPE® and Ivoclar® Ceram, which exhibited significant color changes influenced by immersion duration and photopolymerization distance.
Keywords: MeSH Terms: Composite Resins, Colorimetry, Fermented Beverages
Author Keywords: In vitro studies, Dental materials, Polymerization
Introduction
Currently, composite resins play a significant role in dental esthetics as they allow for a natural and conservative finish in restorations (1, 2). Color stability is a crucial property of composite resins as it directly influences esthetics and patient acceptance. Bulk-fill resins have gained popularity due to their ability to be placed in thicker layers and their clinical efficiency without compromising their mechanical and optical properties. However, their behavior regarding discoloration in environments simulating real oral conditions remains a significant challenge in restorative dentistry (3–5).
"Chicha" a fermented beverage commonly consumed in some Latin American regions, especially in Peru, is known for its intense pigments which can affect esthetic properties of resins thereby altering the color stability of dental materials (6). Additionally, factors related to the photopolymerization process such as the distance between the light source and the material can significantly influence the final properties of composite resins including their resistance to discoloration While the wavelength is determined by the type of light source and remains constant, the intensity of light decreases with distance potentially affecting the degree of conversion. This, in turn plays a crucial role in determining the mechanical properties and color stability of the resins (7-9).
This in vitro study aimed to evaluate the color stability of bulk-fill resins exposed to chicha considering the following three photopolymerization distances: 0 mm, 2 mm and 4 mm. The hypothesis proposed that the color stability of bulk-fill resins significantly decreases as the photopolymerization distance increases and that exposure to chicha as a staining agent generates greater color alteration in samples photopolymerized at greater distances. The study sought to determine optimal conditions to minimize discoloration by providing key information for clinical practice. Furthermore, it aimed to contribute to improving the predictability of long-term esthetic outcomes in restorations using bulk-fill resins.
Materials and methods
This study was approved by the Research Committee of Universidad Científica del Sur (approval number PRE-8-2023-00101), and it was conducted following the CRIS (Checklist for Reporting In-vitro Studies) guidelines (10) with a detailed list of required elements included in the supplementary material.
Study design and study groups
The project was designed as an in vitro study. Sample size was calculated using the G*POWER program based on pilot study results with a 95% confidence level and a 5% significance level. The mean values of two control groups (distilled water and Naturalle® chicha morada) at a photopolymerization distance of 4 mm (1) were considered using a mean and standard deviation of 238 and 852 respectively resulting in a total sample size of 216.
The sample (N = 216) was divided into three main groups (n = 72) according to the resin brands evaluated: 3M ESPE® Filtek™ Bulk Fill® (3M ESPE®), Ivoclar® Tetric N-Ceram Bulk Fill® (Ivoclar®) and FGM® Opus Bulk-fill APS® (FGM®). Each main group was further subdivided into six subgroups (n = 12) based on the three photopolymerization distances (0 mm, 2 mm and 4 mm) and the two immersion solutions (Naturalle® chicha morada and distilled water as a control).
Preparation of the disks and photoactivation
Resin discs were fabricated using a custom-made stainless steel surgical matrix designed for the study to standardize specimen dimensions measuring 5 mm in diameter and 3 mm in thickness. The matrix was placed on a glass plate and a layer of Portugal® petroleum jelly was applied inside to prevent adhesion. The resin was packed in a single increment using a Hu-Friedy® Teflon composite spatula. A strip of Airon Maquira® celluloid was then placed over the resin, and pressure was applied using a glass plate to remove excess material and achieve a uniform surface. Finally, a layer of glycerin was applied to inhibit the oxygen inhibition layer before proceeding with photopolymerization.
Photopolymerization of the discs was performed according to the manufacturer's instructions using an LED curing light (Elipar Freelight 2 3M ESPE®) with an intensity of 2700 mW/cm2 verified with a high-frequency radiometer (30 MHz-8 GHz Easyover®). The curing time was 20 seconds at the following three photopolymerization distances: 0 mm 2 mm and 4 mm. The distances were standardized using custom-made aluminum spacers designed for the experiment (11) Specimens were immersed in distilled water and stored in an incubator at 37°C for 24 hours to complete the polymerization process (1)
Sample immersion in coloring substances
The staining solution used was Naturalle® chicha morada while the control solution was distilled water. The discs were immersed in 10 ml of each solution which was renewed every 48 hours to prevent microbial proliferation. At each renewal interval (every 48 hours), the specimens were rinsed with distilled water for 30 seconds dried with Elite Professional® absorbent paper and re-immersed in fresh solution. The total immersion period was divided into the following time points: no immersion (T0), 24 hours (T1), one week (T2) and three weeks (T3). At the end of the immersion periods, the specimens were again rinsed with distilled water for 30 seconds dried with Elite Professional® absorbent paper and placed on a light background for color recording (12).
Color recording
Two observers (D.S.R. and D.L.M.) recorded the color through triplicate measurements using a Vita Easyshade Advance 40 digital spectrophotometer (VITA® Bad Säckingen Germany) in a laboratory setting with natural light following the manufacturer's instructions. The device was calibrated every 15 color readings. The tip of the digital reading device was placed on the specimen. Measurements were taken according to total immersion periods: T0 T1 T2 and T3. The color difference (ΔE) between two time points was calculated using the CIELAB color space formula, where "L" represents lightness "a" represents the green-red axis and "b" represents the blue-yellow axis (13):
 |
Data analysis
The data analysis was performed using Stata 17®. To assess the normality of the data, the Shapiro-Wilk test was used. If the data followed a normal distribution, a one-way ANOVA F test was used for analysis. For non-normally distributed data, the Kruskal-Wallis test was applied. Post hoc comparisons for ANOVA were conducted using the Bonferroni test, while post hoc comparisons for the Kruskal-Wallis test were performed using the Mann-Whitney U test. P-values ≤ .005 were considered statistically significant.
Data for value L, A and B were represented in graphs lines that connect mean values across distances to visualize trends, additionally a 3D scatter plot was created using Python (Matplotlib)® to analyze ΔE values across photoactivation distances, resin brands, and immersion substances over three evaluation times (24 hours, 1 week, 3 weeks).
Results
The initial "L*" values showed no significant differences across resin discs at various photopolymerization distances (p = .012). However, significant changes were observed in subsequent evaluations depending on immersion time and the substance used: 3M ESPE® resin discs immersed in chicha morada exhibited a significant decrease in the "L*" value at three weeks as the photopolymerization distance increased (p = .000). Conversely, the Ivoclar® resin discs immersed in chicha morada showed significant changes in the "L*" value as early as T1 (24 hours), depending on the photopolymerization distance (p < .005), [TABLE 1].
Table 1. Resin composition.
| Type of Resin | Brand | Batch Numbers | Composition | Weight | Shade |
| Filtek one Bulk-fill restorative | 3M ESPE® Filtek™ Bulk Fill® | NF29092 | All fillers are a combination of a non-agglomerated/non-aggregated 20 nanometer (nm) silica filler a non-agglomerated/aggregated 4 to 11 nm zirconia filler an aggregated silica/zirconium clustered filler (composed of 20 nm silica and 4 to 11 nm zirconium) and an ytterbium trifluoride filler composed of 100 nm agglomerated particles The inorganic filler loading is approximately 765% by weight (585% by volume) Filtek One Bulk-fill Restorative contains UDMA AFM diurethane-DMA and 1 12-dodecane-DMA) | 4gr | A2 |
| Opus Bulk-fill APS | Ivoclar® Tetric N-Ceram Bulk Fill® | 130222 | Urethane dimethacrylate monomers stabilizers photoinitiator composition (APS) and co-initiators; inorganic filler of silanized silicon dioxide (silica) stabilizers and pigments | 4 gr | A2 |
| Tetric N Ceram Bulk-fill Refill | FGM® Opus Bulk-fill APS® | Z051PT | The monomeric matrix is composed of dimethacrylates (19-21% by weight) The total content of inorganic filler is 75-77% by weight or 53-55% by volume The fillers consisting of barium glass prepolymer ytterbium trifluoride and mixed oxide It also contains additives catalysts stabilizers and pigments (<10% by weight) The particle size of inorganic filler ranges from 004 to 3 μm The average particle size is 06 μm | 35 gr | IVA |
Similarly, the FGM® resin discs immersed in chicha morada displayed significant changes in the "L*" value at T1 related to photopolymerization distance (p < .005). Additionally, at 24 hours, the Ivoclar® resin discs immersed in chicha morada showed a significant increase in the "L*" value at 0 mm compared to 2 mm (p = .000), and the FGM® discs also exhibited significant differences (p = .004). By week 1, the 3M ESPE® discs showed a notable reduction in the "L*" value at 4 mm compared to 0 mm (p = .003), while Ivoclar® discs also showed significant changes (p = .002), but no significant differences were observed for FGM® discs (p = .012). At week 3, the "L*" values of the Ivoclar® discs immersed in chicha morada continued to show significant differences depending on the photopolymerization distance (p = .000) [TABLE 2].
Table 2. Comparison of the "L" value for light-curing distances according to resin brand immersion substance and evaluation time.
| Immersion times | Substance | Resin Brand | Photoactivation Distance | P value | ||
| 0 mm | 2 mm | 4 mm | ||||
| No immersion | Chicha morada | 3M ESPE® | 7.921 ± 0.167Aa | 7.952 ± 0.243Aa | 7.878 ± 0.123Aa | 0.011 |
| Ivoclar® | 7.521 ± 0.146Aa | 7.529 ± 0.169Aa | 7.494 ± 0.236Aa | 0.089 | ||
| FGM® | 7.542 ± 0.250Aa | 7.680 ± 0.149Aa | 7.598 ± 0.289Aa | 0.038 | ||
| Distilled water | 3M ESPE® | 8.016 ± 0.271Aa | 8.055 ± 0.294Aa | 7.862 ± 0.310Aa | 0.024 | |
| Ivoclar® | 7.643 ± 0.141Aa | 7.518 ± 0.130ABa | 7.463 ± 0.208Ba | 0.002 | ||
| FGM® | 7.429 ± 0.201Aa | 7.542 ± 0.135Aa | 7.604 ± 0.183Aa | 0.005 | ||
| 24 hours | Chicha morada | 3M ESPE® | 7.422 ± 0.017Ab | 7.409 ± 0.285Ab | 7.323 ± 0.172Ab | 0.015 |
| Ivoclar® | 7.347 ± 0.245Ab | 6.878 ± 0.217Bb | 7.600 ± 0.397Aa | 0.000 | ||
| FGM® | 7.006 ± 0.183Ab | 7.325 ± 0.215Bb | 7.075 ± 0.980Bb | 0.004 | ||
| Distilled water | 3M ESPE® | 7.856 ± 0.278Aa | 7.746 ± 0.223Ab | 7.813 ± 0.206Aa | 0.050 | |
| Ivoclar® | 7.529 ± 0.127Ab | 7.647 ± 0.297Aa | 8.049 ± 0.290Bb | 0.000 | ||
| FGM® | 7.620 ± 0.249Ab | 7.599 ± 0.164Aa | 7.809 ± 0.243Ab | 0.001 | ||
| 1 week | Chicha morada | 3M ESPE® | 7.962 ± 0.341Aa | 7.306 ± 0.400Bb | 7.084 ± 0.251Bc | 0.003 |
| Ivoclar® | 7.011 ± 0.113Ac | 6.572 ± 0.379Bc | 6.738 ± 0.270Bb | 0.002 | ||
| FGM® | 6.753 ± 0.308Abc | 6.763 ± 0.312Ac | 6.073 ± 1.003Bc | 0.012 | ||
| Distilled water | 3M ESPE® | 8.914 ± 0.759Ab | 8.251 ± 0.590Ba | 7.912 ± 0.212Bab | 0.034 | |
| Ivoclar® | 7.673 ± 0.092Aa | 7.590 ± 0.142Aa | 7.491 ± 0.217Aa | 0.067 | ||
| FGM® | 7.518 ± 0.247Aab | 7.553 ± 0.170Aa | 7.680 ± 0.213Aab | 0.001 | ||
| 3 weeks | Chicha morada | 3M ESPE® | 7.473 ± 0.341Ab | 7.415 ± 0.412Ab | 6.842 ± 0.223Bd | 0.056 |
| Ivoclar® | 6.846 ± 0.144Ac | 6.649 ± 0.203Bc | 6.668 ± 0.206ABb | 0.000 | ||
| FGM® | 6.524 ± 0.184Ac | 6.567 ± 0.255Ac | 6.004 ± 1.066Bc | 0.015 | ||
| Distilled water | 3M ESPE® | 7.966 ± 0.251Aa | 8.006 ± 0.364Aab | 8.069 ± 0.295Ab | 0.000 | |
| Ivoclar® | 7.513 ± 0.111ABb | 7.426 ± 0.142Ab | 7.620 ± 0.173Ba | 0.087 | ||
| FGM® | 7.522 ± 0.214Aab | 7.583 ± 0.237Aa | 7.771 ± 0.338Aab | 0.004 | ||
| Note: Values are expressed as means ± standard deviations Different letters within a row indicate statistically significant differences between photoactivation distances for each resin brand and immersion substance at each evaluation time (p < 005) | ||||||
Concerning the "a*" value, the 3M ESPE®, Ivoclar®, and FGM® resin discs immersed in chicha morada displayed significant changes in color (p < 005) [Table 3] . Specifically, at T0 (no immersion), the 3M ESPE® discs showed a significant decrease in "a" value as the photopolymerization distance increased (p = 0032), while FGM® discs displayed a significant increase (p = 0032) After 24 hours, both the 3M ESPE® (p = 0024) and FGM® (p = 0012) discs immersed in chicha morada continued to exhibit notable changes depending on photopolymerization distance. Ivoclar® discs, although initially showing no significant difference, demonstrated borderline significant changes at 24 hours (p = .005). At 1 week, Ivoclar® resin discs immersed in chicha morada exhibited significant variations in "a" values based on photopolymerization distance (p = .002), whereas FGM® discs showed no significant changes (p = .012) [TABLE 3].
Table 3. Comparison Of The "A" Value For Light-Curing Distances According resin brand immersion substance and evaluation time.
| Immersion times | Substance | Resin Brand | Photoactivation Distance | P value | ||
| 0 Mm | 2 Mm | 4 Mm | ||||
| No immersion | Chicha morada | 3M ESPE® | 0.064 ± 0.024Aa | 0.045 ± 0.025Aa | 0.019 ± 0.019Ba | 0.032 |
| Ivoclar® | 0.213 ± 0.048Aa | 0.183 ± 0.032Aa | 0.186 ± 0.046Aa | 0.199 | ||
| FGM® | 0.073 ± 0.044Aa | 0.092 ± 0.056Aa | 0.160 ± 0.119Aa | 0.032 | ||
| Distilled water | 3M ESPE® | 0.033 ± 0.022Aa | 0.061 ± 0.035Aa | 0.048 ± 0.027Aa | 0.061 | |
| Ivoclar® | 0.176 ± 0.013Aa | 0.178 ± 0.031Aa | 0.189 ± 0.036Aa | 0.508 | ||
| FGM® | 0.059 ± 0.049Aa | 0.086 ± 0.046ABa | 0.136 ± 0.078Bab | 0.037 | ||
| 24 hours | Chicha morada | 3M ESPE® | 0.109 ± 0.069Aa | 0.131 ± 0.100Ab | 0.147 ± 0.060Abc | 0.024 |
| Ivoclar® | 0.041 ± 0.035Ab | 0.130 ± 0.067Ba | 0.141 ± 0.166ABa | 0.053 | ||
| FGM® | 0.268 ± 0.158Ab | 0.124 ± 0.086Aa | 0.211 ± 0.239Aa | 0.012 | ||
| Distilled water | 3M ESPE® | 0.076 ± 0.056Ab | 0.046 ± 0.066Aa | 0.030 ± 0.026Aab | 0.563 | |
| Ivoclar® | 0.152 ± 0.031Aa | 0.194 ± 0.044Ba | 0.269 ± 0.082Cb | 0.000 | ||
| FGM® | 0.062 ± 0.043Aa | 0.134 ± 0.077Ba | 0.209 ± 0.104Bb | 0.000 | ||
| 1 week | Chicha morada | 3M ESPE® | 0.127 ± 0.083Aa | 0.087 ± 0.095Aab | 0.149 ± 0.109Ab | 0.035 |
| Ivoclar® | 0.062 ± 0.067Ab | 0.212 ± 0.153Ba | 0.180 ± 0.113Ba | 0.023 | ||
| FGM® | 0.361 ± 0.161Ab | 0.289 ± 0.103Ab | 0.299 ± 0.340Aa | 0.127 | ||
| Distilled water | 3M ESPE® | 0.039 ± 0.024Aa | 0.035 ± 0.036Aa | 0.014 ± 0.041Ab | 0.348 | |
| Ivoclar® | 0.096 ± 0.157Ab | -0.082 ± 0.151Ab | -0.086 ± 0.161Ac | 0.678 | ||
| FGM® | 0.052 ± 0.075Aa | -0.015 ± 0.076Ab | -0.112 ± 0.117Bc | 0.012 | ||
| 3 weeks | Chicha morada | 3M ESPE® | 0.118 ± 0.110Aa | 0.080 ± 0.124Aab | 0.105 ± 0.087Ac | 0.568 |
| Ivoclar® | 0.033 ± 0.058Ab | 0.124 ± 0.065Ba | 0.171 ± 0.070Ba | 0.001 | ||
| FGM® | 0.294 ± 0.144Ab | 0.277 ± 0.122Ab | 0.343 ± 0.341Aa | 0.154 | ||
| Distilled water | 3M ESPE® | 0.014 ± 0.036Ac | 0.004 ± 0.064Ab | -0.024 ± 0.057Ac | 0.000 | |
| Ivoclar® | -0.106 ± 0.152Ab | -0.109 ± 0.169Ac | -0.099 ± 0.157Ac | 0.875 | ||
| FGM® | 0.013 ± 0.077Aa | -0.045 ± 0.067Ab | 0.011 ± 0.169Aac | 0.875 | ||
| Note: Values are expressed as means ± standard deviations Different letters within a row indicate statistically significant differences between photoactivation distances for each resin brand and immersion substance at each evaluation time (p < 005) | ||||||
Similarly, regarding the "b*" value, all three resins studied showed significant changes in color variation (p < .005) [Figure 1; Table 4]. At T0, the "b" value increased significantly for 3M ESPE® and Ivoclar® resins immersed in chicha morada as the photopolymerization distance increased (p = .001 for both), while FGM® showed no significant differences (p = .005). In distilled water, 3M ESPE® and Ivoclar® also displayed significant variations (p = .005 and p = .000, respectively). After 24 hours, 3M ESPE® discs in chicha morada showed a significant rise in "b" value at 4 mm (p = .000), with similar trends for Ivoclar® (p = .000) FGM® exhibited non-linear changes (p = .000). In distilled water, significant changes were observed for Ivoclar® and FGM® (p = .000 and p = .000), while 3M ESPE® remained stable (p = .018). At 1 week, 3M ESPE® resins showed a decrease in "b" value with increasing distances (p = .000), while Ivoclar® and FGM® displayed moderate changes (p = .004 and p = .000, respectively). In distilled water, significant differences were noted only for 3M ESPE® (p = .001). By 3 weeks, 3M ESPE® discs in chicha morada exhibited the highest "b" values at 4 mm (p = .000), with Ivoclar® also showing significant increases (p = .002). FGM® resins remained unchanged (p = .010). In distilled water, only 3M ESPE® showed significant variation (p = .035) [FIGURE 1] [TABLE 4].
Figure 1.
Analysis Effect of Resin Brand and Immersion Substance A) L Value, B) A Value and C) B Value
Table 4. Comparison Of The "B" Value For Light-Curing Distances According To resin brand immersion substance and evaluation time.
| Immersion times | Substance | Resin Brand | Photoactivation Distance | P value | ||
| 0 Mm | 2 Mm | 4 Mm | ||||
| No immersion | Chicha morada | 3M ESPE® | 1.552 | 1.786 | 1.749 | 0.001 |
| Ivoclar® | 1.423 | 1.606 | 1.722 | 0.001 | ||
| FGM® | 1.258 | 1.039 | 1.085 | 0.055 | ||
| Distilled water | 3M ESPE® | 1.604 | 1.844 | 1.823 | 0.050 | |
| Ivoclar® | 1.500 | 1.633 | 1.699 | 0.000 | ||
| FGM® | 1.208 | 0.981 | 1.263 | 0.011 | ||
| 24 hours | Chicha morada | 3M ESPE® | 1.76 | 1.982 | 2.183 | 0.006 |
| Ivoclar® | 1.388 | 1.482 | 1.689 | 0.003 | ||
| FGM® | 1.334 | 1.007 | 1.228 | 0.008 | ||
| Distilled water | 3M ESPE® | 1.559 | 1.735 | 1.710 | 0.188 | |
| Ivoclar® | 1.399 | 1.579 | 1.665 | 0.004 | ||
| FGM® | 1.277 | 0.923 | 1.083 | 0.000 | ||
| 1 week | Chicha morada | 3M ESPE® | 2.186 | 1.951 | 1.685 | 0.000 |
| Ivoclar® | 1.683 | 0.174 | 1.461 | 0.045 | ||
| FGM® | 1.306 | 1.367 | 1.465 | 0.007 | ||
| Distilled water | 3M ESPE® | 2.144 | 2.150 | 1.829 | 0.019 | |
| Ivoclar® | 1.593 | 1.723 | 1.597 | 0.089 | ||
| FGM® | 1.339 | 1.276 | 1.421 | 0.098 | ||
| 3 weeks | Chicha morada | 3M ESPE® | 2.357 | 2.742 | 3.213 | 0.000 |
| Ivoclar® | 1.512 | 1.623 | 1.885 | 0.026 | ||
| FGM® | 1.412 | 1.090 | 1.306 | 0.102 | ||
| Distilled water | 3M ESPE® | 1.688 | 1.844 | 1.741 | 0.354 | |
| Ivoclar® | 1.351 | 1.480 | 1.647 | 0.235 | ||
| FGM® | 1.414 | 0.966 | 1.077 | 0.067 | ||
| Note: Values are expressed as means ± standard deviations Different letters within a row indicate statistically significant differences between photoactivation distances for each resin brand and immersion substance at each evaluation time (p < 005) | ||||||
Regarding Delta (ΔE) values, the 3M ESPE® resin discs immersed in chicha morada showed significant changes at 24 hours, 1 week, and 3 weeks (p < .005) [Figure 2; Table 5]. At 24 hours, 3M ESPE® exhibited increasing ΔE values with greater photopolymerization distances, peaking at 4 mm (p = .001). Ivoclar® showed the highest ΔE value at 2 mm (p = .000), while FGM® displayed significant but inconsistent changes (p = .000). When immersed in distilled water, significant variations were observed across all resins, particularly for Ivoclar® at 4 mm (ΔE = 674 ± 215, p = .000).
Figure 2.
3D Scatter Plot with Connecting Lines: ΔE Changes by Photoactivation Distance, Immersion Substance, and Evaluation Time
Table 5. Comparison Of Delta (ΔE) For Light-Curing Distances According To resin brand immersion substance and evaluation time.
| Immersion times | Substance | Resin Brand | Photoactivation Distance | P value | ||
| 0 Mm | 2 Mm | 4 Mm | ||||
| 24 hours | Chicha morada | 3M ESPE® | 5.66 ± 2.54Aa | 7.03 ± 3.26Aa | 7.74 ± 3.61Aa | 0.012 |
| Ivoclar® | 3.62 ± 1.59Aab | 6.86 ± 1.29Ba | 4.64 ± 1.79Aa | 0.005 | ||
| FGM® | 6.40 ± 3.50Aa | 4.13 ± 1.83Aa | 6.99 ± 10.84Aab | 0.003 | ||
| Distilled water | 3M ESPE® | 2.78 ± 2.33Aa | 4.72 ± 3.61Aa | 3.43 ± 2.47Aa | 0.039 | |
| Ivoclar® | 1.74 ± 0.78Aa | 4.20 ± 1.94Ba | 6.74 ± 2.15Ca | 0.008 | ||
| FGM® | 2.80 ± 1.30Aa | 2.38 ± 1.32Aa | 4.11 ± 4.90Aa | 0.049 | ||
| 1 week | Chicha morada | 3M ESPE® | 7.33 ± 3.68Aa | 3.39 ± 2.11Bb | 6.03 ± 2.89Aa | 0.000 |
| Ivoclar® | 4.90 ± 1.71Aa | 4.52 ± 3.58Aa | 10.15 ± 4.52Bb | 0.006 | ||
| FGM® | 5.63 ± 2.12Aa | 7.60 ± 1.23Ab | 12.28 ± 2.76Ba | 0.012 | ||
| Distilled water | 3M ESPE® | 12.19 ± 6.64Ab | 7.05 ± 4.25Ba | 2.57 ± 1.27Ca | 0.000 | |
| Ivoclar® | 3.90 ± 1.78Ab | 4.89 ± 1.98Aa | 7.27 ± 3.01Ba | 0.007 | ||
| FGM® | 3.65 ± 2.44Aa | 5.07 ± 1.55Ab | 5.95 ± 2.45Ba | 0.168 | ||
| 3 weeks | Chicha morada | 3M ESPE® | 5.85 ± 2.48Aa | 8.85 ± 3.35Ba | 15.59 ± 2.27Cb | 0.000 |
| Ivoclar® | 2.70 ± 1.23Ab | 5.46 ± 3.74Ba | 6.14 ± 1.53Ba | 0.006 | ||
| FGM® | 5.34 ± 2.86Aa | 4.62 ± 3.58Aab | 5.61 ± 4.37Ab | 0.458 | ||
| Distilled water | 3M ESPE® | 10.63 ± 5.48Ab | 5.05 ± 2.57Ba | 2.54 ± 1.28Ca | 0.000 | |
| Ivoclar® | 3.14 ± 0.63Ab | 3.52 ± 1.40Aa | 2.50 ± 1.29Ab | 0.269 | ||
| FGM® | 3.95 ± 2.01Aa | 4.72 ± 1.63Ab | 5.62 ± 3.13Aa | 0.487 | ||
| Note: Values are expressed as means ± standard deviations Different letters within a row indicate statistically significant differences between photoactivation distances for each resin brand and immersion substance at each evaluation time (p < 005) | ||||||
After 1 week, 3M ESPE® discs in chicha morada exhibited a significant reduction in ΔE at 2 mm (p = .000), while Ivoclar® demonstrated its highest ΔE value at 4 mm (p = .000), FGM® showed a notable increase in ΔE with distance, reaching a peak at 4 mm (ΔE = 1228 ± 276, p = .001). In distilled water, 3M ESPE® experienced a sharp decrease in ΔE from 0 mm to 4 mm (p = .000). Ivoclar® and FGM® also displayed significant variations, with the latter showing more stable ΔE values (p = .000 and p = .016, respectively)
At 3 weeks, 3M ESPE® immersed in chicha morada reached its highest ΔE value at 4 mm (ΔE = 1559 ± 227, p = .000), while Ivoclar® showed moderate increases at both 2 mm and 4 mm (p = .000) FGM® exhibited stable ΔE values without significant changes (p = .045). In distilled water, 3M ESPE® maintained the same trend of decreasing ΔE values with distance (p = .000), whereas Ivoclar® and FGM® showed no significant differences across distances (p = .026 and p = .048, respectively (TABLE 6).
Table 6. Comparison of color stability for light-curing distances according to resin brand immersion substance and evaluation time.
| Color Stability | |||
| 24 hours | 1 week | 3 weeks | |
| By substance adjusted to resin type | |||
| Distilled water | 0.120 | 0.708 | 0.005 |
| Purple Chicha morada | 0.024 | 0.009 | 0.000 |
| By distance | |||
| 0mm | |||
| Adjusted to substance | 0.000 | 0.000 | 0.188 |
| Adjusted to substance and type of resin | 0.000 | 0.000 | 0.001 |
| 2mm | |||
| Adjusted to substance | 0.407 | 0.482 | 0.000 |
| Adjusted to substance and type of resin | 0.002 | 0.001 | 0.000 |
| 4mm | |||
| Adjusted to substance | 0.947 | 0.010 | 0.000 |
| Adjusted to substance and type of resin | 0.000 | 0.004 | 0.000 |
| Note: P-values are shown for comparisons of color stability between photopolymerization distances, analyzed by resin type, immersion substance, and evaluation time | |||
Discussion
The aim of this in vitro study was to evaluate the color stability of bulk-fill resins immersed in chicha morada and photopolymerized at distances of 0 mm 2 mm and 4 mmn. The results showed significant color changes in the discs of all three commercial bulk-fill resins evaluated. All brands experienced a significant decrease in the "L*" value as immersion time in the chicha morada increased (p < 005). Chromatic stability depended on both immersion time and photopolymerization distance.
The findings of this study may be related to the presence of different photoinitiators in the bulk-fill resins. In addition to camphorquinone, these resins may contain alternative photoinitiators such as trimethylbenzoyl-diphenyl-phosphine oxide (TPO) phenylpropanedione (PPD) or Ivocerin. These photoinitiators enable more efficient polymerization in thicker layers and could influence the material's chromatic stability (14–16).
The greatest color difference was observed in 3M ESPE® discs followed by Ivoclar® a finding consistent with Bahbishi et al. (17) who studied color difference and microhardness in four bulk-fill resins immersed in different solutions finding that these two brands exhibited lower color stability. These changes may be due to the composition of the material under study. Additionally, it is reported that samples exposed to staining solutions for longer periods were associated with greater color changes regardless of the solution type used (18–20).
Regarding changes in the "a*" parameter, it was observed that the 3M ESPE® resin discs maintained stability in this value regardless of photopolymerization distance. In contrast, the Ivoclar® Ceram discs showed significant changes as the distance increased (p < .005), while the FGM® discs showed no variations in "a*" at any time. These differences could be explained by variations in the chemical composition of the resins and their interaction with the pigments present in the chicha morada.
Regarding changes in the "b*" parameter, the 3M ESPE® and Ivoclar® Ceram resin discs showed an increase as the photopolymerization distance increased from 0 mm to 4 mm. This reflects that with greater distance there is a higher difference in color stability which agrees with results reported by Ciocan et al. (21). These modifications in the distances at which the light source is placed could directly affect the mechanical properties of the resins and the polymerization depth achieved (22).
A previous study by Noufal et al. (14), evaluated the color stability of a bulk-fill resin and a flowable resin using non-carbonated beverages such as Appy Fizz®. While this beverage is not natural like chicha morada, its results provide an interesting point of comparison. Unlike our findings, this study showed that bulk-fill resins exhibited greater color change compared to flowable resins. In that study, ΔE variations were not significant among the different resin types except for the 3M ESPE® discs photopolymerized at 4 mm and exposed for 3 weeks where significant differences were observed (p > .005).
It is important to highlight that previous studies have used carbonated or caffeine-containing beverages as pigmenting agents (23). For example, Özyurt and Kurt (22) evaluated the chromatic stability of conventional and bulk-fill resins using coffee and soft drinks. In contrast, our study, which used a non-carbonated, natural beverage reported that bubbles in beverages may affect the material surface causing roughness that allows pigment penetration (24).
The "L*" values significantly decreased in all three commercial brands evaluated (3M ESPE® Ivoclar® and FGM®) as immersion time increased (p < .005). These findings partially align with the results of Şişmanoğlu and Sengez (25), who reported discoloration above the clinically acceptable threshold (ΔE > 27) in all resins studied when exposed to acidic beverages. However, in their research, orange juice caused greater discoloration than Coca-Cola®, while in our study case chicha morada proved to be a potent pigmenting agent for all resins tested. It is important to mention that the "L*" value is related to lightness, being essential for chromatic stability and clinical success of restorative treatments as the human eye perceives these variations more sharply due to the higher presence of rods over cones in the vision organ (26).
The "a*" and "b*" values varied depending on the resin brand and photopolymerization distance suggesting that resin composition and curing conditions influence its susceptibility to pigment. These results coincide with findings by Acuña et al. (27), who identified chicha morada as the beverage causing the most significant color changes in composite resins reaching perceptible levels to the human eye (ΔE > 33). In the present study, the 3M ESPE® resin discs photopolymerized at 4 mm and exposed for 3 weeks showed the most significant ΔE changes (p < .005), thus highlighting the importance of photopolymerization distance in chromatic stability. These results emphasize the importance of considering both resin composition and curing conditions when selecting materials for restorations in esthetically-critical areas. In addition to the above mentioned, it is important to note that our study aligns with emerging research trends, as seen in recent investigations that evaluate the clinical performance of bulk-fill composites, analyze the impact of rapid polymerization on material properties, and assess the influence of different light-curing technologies on composite effectiveness (28-30).
Another element to consider is the type of filler in composite materials, such as zirconia or barium glass, which significantly influences their interaction with staining agents Zirconia fillers, due to their dense and smooth surface, tend to be more resistant to yellowing and pigment absorption, as their structure limits the penetration of colorants. In contrast, barium glass fillers, being more porous, provide a greater surface area where pigments can adhere, making these materials more susceptible to discoloration. This porosity, along with a slightly rough texture, facilitates the penetration of staining agents present in beverages or foods, resulting in a more pronounced color change in resins with barium glass fillers compared to those with zirconia (22, 26).
Strengths and limitations
This study highlights several important strengths. First, it uses a well-structured in vitro design with appropriate controls, thus allowing the evaluation of color stability under controlled and reproducible conditions. Additionally, the inclusion of three commercial bulk-fill resin brands and evaluation at different photopolymerization distances provides a comprehensive and applicable comparative view. The choice of chicha morada, natural and culturally relevant pigment expands knowledge on understudied pigmenting agents, thus adding value both regionally and globally. Finally, the use of standardized tools like the Vita Easyshade® Advance 40 digital spectrophotometer ensured precision and reliability in color measurements.
The study has some limitations. Being an in vitro design, the results cannot be fully extrapolated to real clinical conditions where factors such as saliva, oral microbiota and masticatory forces may influence the color stability of resins. Additionally, the selection of a single pigmenting agent (chicha morada) may limit the generalizability of the findings to other commonly consumed agents. Finally, the use of a limited immersion time (three weeks) may not reflect long-term color changes in restorations.
Suggestions for future research and practical application
For future research, clinical studies evaluating color stability under real oral conditions considering factors such as saliva presence, mechanical wear and exposure to a variety of foods and drinks are suggested. It would also be valuable to explore other natural and synthetic pigmenting agents to broaden understanding of the interactions between resins and pigments. Lastly, research on improvements in the chemical composition of bulk-fill resins could help develop materials which are more resistant to discoloration.
The findings of this study have significant clinical implications. They can help dentists in selecting more suitable bulk-fill resins for restorations in patients with high consumption of pigmenting drinks such as chicha morada. Furthermore, they emphasize the importance of optimizing the photopolymerization technique, particularly the light application distance to minimize discoloration and improve long-term esthetic outcomes. These results may also guide resin manufacturers in developing products with greater resistance to pigmentation.
This study contributes to the knowledge of the chromatic stability of Bulk-fill resins when exposed to a natural soft drink such as chicha morada. The results can help dentists make better decision regarding resins, thus achieving the esthetic success of dental restorations.
Conclusions
The study showed that the "L*" value decreased with prolonged immersion in chicha morada indicating a reduction in chromatic stability. Regarding the "a*" value the 3M ESPE® resin exhibited instability, while Ivoclar® Ceram showed variations depending on the photopolymerization distance, and FGM® showed no significant changes. For the "b*"value, both 3M ESPE® and Ivoclar® Ceram discs exhibited increases related to the photopolymerization distance, while FGM® also presented significant alterations. Although the variations between the resins were generally minimal, notable differences were observed: in 3M ESPE® after one week and in Ivoclar® Ceram after three weeks, thus highlighting the influence of time on chromatic stability.
Footnotes
Conflicts of interest
The authors declare they have no conflicts of interest.
Funding
This study was financed by internal undergraduate funds from the Universidad Científica del Sur (No013-DGIDI-CIENTIFICA-2023-2).
REFERENCES
- 1.Backes CN, França FMG, Turssi CP, Amaral FLB, Basting RT. Color stability of a bulk-fill composite resin light-cured at different distances. Braz Oral Res. 2020;34:e119. 10.1590/1807-3107bor-2020.vol34.0119 [DOI] [PubMed] [Google Scholar]
- 2.Moon JD, Seon EM, Son SA, Jung KH, Kwon YH, Park JK. Effect of immersion into solutions at various pH on the color stability of composite resins with different shades. Restor Dent Endod. 2015;40(4):270–6. 10.5395/rde.2015.40.4.270 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Poole R, Kennedy OJ, Roderick P, Fallowfield J, Hayes PC, Parkes J. Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. BMJ. 2017;359:j5024. 10.1136/bmj.j5024 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Color stability of adhesive resin cements after immersion in coffee. Clin Oral Investig. 2014;18(8):2035–42. [DOI] [PubMed] [Google Scholar]
- 5.Marroquín-Soto Consuelo . Colán-Guzmán Paola del Rosario, Padilla-Avalos César-Augusto, Morales-Vadillo Rafael, Guevara-Canales Janet-Ofelia, Chávez-Zelada Germán. Estabilidad cromática de una cerámica de feldespato monocromática utilizada en sistema CAD/CAM sometida a inmersión de diferentes soluciones de tinción. J Interdiscip Dent. 2021;14(2):158–61. [Google Scholar]
- 6.Korać S, Ajanović M, Džanković A, Konjhodžić A, Hasić-Branković L, Gavranović-Glamoč A, et al. Color stability of dental composites after immersion in beverages and performed whitening procedures. Acta Stomatol Croat. 2022;56(1):22–32. 10.15644/asc56/1/3 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Veček NN, Par M, Sever EK, Miletić I, Krmek SJ. The effect of a green smoothie on microhardness, profile roughness, and color change of dental restorative materials. Polymers (Basel). 2022;14(10):2067. 10.3390/polym14102067 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Tekçe N, Tuncer S, Demirci M, Serim ME, Baydemir C. The effect of different drinks on the color stability of different restorative materials after one month. Restor Dent Endod. 2015;40(4):255–61. 10.5395/rde.2015.40.4.255 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Moradas Estrada M, Álvarez López B. Polymerization dynamics focused on reducing or preventing shrinkage stress of current composite resins: A literature review. Av Odontoestomatol. 2017;33(6):261–72. [Google Scholar]
- 10.Krithikadatta J, Gopikrishna V, Datta M. CRIS Guidelines (Checklist for Reporting In-vitro Studies): A concept note on the need for standardized guidelines for improving quality and transparency in reporting in-vitro studies in experimental dental research. J Conserv Dent. 2014;17(4):301–4. 10.4103/0972-0707.136338 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Pacheco ETJ, Lopez MAC. Photopolymerization in dentistry. Braz J Health Rev. 2024;7(1):4210–20. 10.34119/bjhrv7n1-342 [DOI] [Google Scholar]
- 12.Diab RA, Yap AU, Gonzalez MAG, Yahya NA. Impact of light-curing distance on the effectiveness of cure of bulk-fill resin-based composites. Saudi Dent J. 2021;33(8):1184–9. 10.1016/j.sdentj.2021.01.003 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Bilgili Can D, Özarslan M. Evaluation of color stability and microhardness of contemporary bulk-fill composite resins with different polymerization properties. J Esthet Restor Dent. 2022;34(6):924–32. 10.1111/jerd.12879 [DOI] [PubMed] [Google Scholar]
- 14.Noufal ZM, Ganesh SB, Jayalakshmi S. Effect of carbonated beverages on the color stability of bulk and flowable composite resin. J Adv Pharm Technol Res. 2022;13 Suppl 1:S144–7. 10.4103/japtr.japtr_271_22 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Kowalska A, Sokolowski J, Bociong K. The photoinitiators used in resin-based dental composites: A review and future perspectives. Polymers (Basel). 2021;13(3):470–87. 10.3390/polym13030470 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.de Oliveira DCRS, Rocha MG, Gatti A, Correr AB, Ferracane JL, Sinhoret MAC. Effect of different photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths. J Dent. 2015;43(12):1565–72. 10.1016/j.jdent.2015.08.015 [DOI] [PubMed] [Google Scholar]
- 17.Bahbishi N, Mzain W, Badeeb B, Nassar HM. Color stability and micro-hardness of bulk-fill composite materials after exposure to common beverages. Materials (Basel). 2020;13(3):787. 10.3390/ma13030787 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Kumar MS, Ajay R, Miskeen Sahib SA, Chittrarasu M, Navarasu M, Ragavendran N, et al. Color stability assessment of two different composite resins with variable immersion time using various beverages: An in vitro study. J Pharm Bioallied Sci. 2017;9 Suppl 1:S161–5. 10.4103/jpbs.JPBS_149_17 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Hasan AK, Sunarintyas S, Irnawati D. Color stability of visible light cured composite resin after soft drink immersion. Dent J. 2009;42(3):123–5. 10.20473/j.djmkg.v42.i3.p123-125 [DOI] [Google Scholar]
- 20.Barutcigil Ç, Barutcigil K, Özarslan MM, Dündar A, Yilmaz B. Color of bulk-fill composite resin restorative materials. J Esthet Restor Dent. 2018;30(2):E3–8. 10.1111/jerd.12340 [DOI] [PubMed] [Google Scholar]
- 21.Ciocan LT, Biru EI, Vasilescu VG, Ghitman J, Stefan AR, Iovu H, et al. Influence of air-barrier and curing light distance on conversion and micro-hardness of dental polymeric materials. Polymers (Basel). 2022;14(24):5346. 10.3390/polym14245346 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Özyurt E, Kurt A. Color stability of bulk-fill resin composites exposed to caffeinated beverage: An in vitro study. Am J Dent. 2022. February;35(1):3–8. [PubMed] [Google Scholar]
- 23.Arruda B. Color stability of bulk-fill composite resins submitted to coffee staining. Braz Dent Sci. 2021;24(1):e2345. [Google Scholar]
- 24.Ali SAH, Alsedrani R, Alharbi N, Farah R, Alharbi E, Alkhuwaiter S. Impact of carbonated beverages on color stability and home bleaching efficacy of bulk-fill composite resins. Pediatr Dent. 2024;46(4):277–84. [PubMed] [Google Scholar]
- 25.Soner Ş, Görkem S. Effects of acidic beverages on color stability of bulk-fill composites with different viscosities. Odovtos. 2022;24(2):90–9. [Google Scholar]
- 26.Samra APB, Pereira SK, Delgado LC, Borges CP. Color stability evaluation of aesthetic restorative materials. Braz Oral Res. 2008;22:205–10. 10.1590/S1806-83242008000300003 [DOI] [PubMed] [Google Scholar]
- 27.Acuña ED, Delgado-Cotrina L, Rumiche FA, Tay LY. Effect of the Purple Corn Beverage “Chicha Morada” in Composite Resin during Dental Bleaching. Scientifica (Cairo). 2016;2016:2970548. 10.1155/2016/2970548 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Salem MN, Hassanein OE, ElKassas DW, Shaalan OO. 12-months Clinical Evaluation of Fiber Reinforced Bulk Fill Resin Composite versus Incremental Packing of Nanohybrid Resin Composite in Restoration of Deep Proximal Lesions of Permanent Molars: A Randomized Controlled Trial. Acta Stomatol Croat. 2022;56(3):267–80. 10.15644/asc56/3/5 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29.Klarić N, Macan M, Par M, Tarle Z, Marović D. Effect of Rapid Polymerization on Water Sorption and Solubility of Bulk-fill Composites. Acta Stomatol Croat. 2022;56(3):235–45. 10.15644/asc56/3/2 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 30.Marović D, Daničić P, Bojo G, Par M, Tarle Z. Monowave vs. Polywave Light-Curing Units: Effect on Light Transmission of Composite without Alternative Photoinitiators. Acta Stomatol Croat. 2024;58(1):30–8. 10.15644/asc58/1/3 [DOI] [PMC free article] [PubMed] [Google Scholar]