10.24873/j.rpemd.2025.09.1437

Original Research

 

Impact of coffee exposure on the color adjustment potential of universal-shade resin composites: an in vitro study

Impacto da exposição ao café no potencial de ajuste de cor de compósitos de resina de tonalidade universal: um estudo in vitro

 

Berkant Sezer¹ 0000-0001-9731-6156

Tuğba Misilli^2,* 0000-0003-0019-4872

Mehmet Buldur² 0000-0001-9103-0069

¹ Department of Pediatric Dentistry, School of Dentistry, Çanakkale Onsekiz Mart University, Çanakkale, Türkiye.

² Department of Restorative Dentistry, School of Dentistry, Çanakkale Onsekiz Mart University, Çanakkale, Türkiye.

 

^*Correspondence to:

 

Article history:

Received 1 April 2025

Accepted 29 July 2025

Available online 29 September 2025

 

Abstract

Objectives: This study aimed to evaluate the color adjustment potential (CAP) of a universal- shade composite resin applied to acrylic teeth of different shades under various storage conditions and over different time intervals.

Methods: A universal-shade composite (Omnichroma; Tokuyama, Tokyo, Japan) and acrylic molar teeth in three shades (A1, A2, D4) were used. Two types of samples were prepared: dual-shade (Class I restorations with 5-mm diameter and 2-mm depth in acrylic teeth) and single-shade (artificial tooth replicas). Specimens were stored in either distilled water or coffee. Color measurements were performed using a spectrophotometer at baseline, 1 day, 1 week, and 1 month. Color differences (ΔE00) were calculated using the CIEDE2000 formula. ΔE00 values were analyzed with two-way ANOVA and Tukey’s tests. CAP00 values were analyzed using the three-way ANOVA for intergroup comparisons and repeated measures ANOVA with Bonferroni tests to assess time-related effects.

Results: At baseline, the ΔE00 values were lowest in the A1 group for both sample types, followed by A2 and D4. After 1 month, coffee immersion led to significantly higher ΔE00 values than distilled water in all groups. CAP00 values significantly decreased between 1 week and 1 month in coffee-stored samples. All shade and storage subgroups showed a significant time-dependent increase in CAP00 (p < 0.05).

Conclusions: One-month storage in distilled water enhanced CAP in all groups. In turn, prolonged coffee exposure increased color differences and diminished the color harmony of restorations over time. (Rev Port Estomatol Med Dent Cir Maxilofac. 2025;66(3):115-123)

 

Keywords: Coffee, Color, Coloring agentes, Composite dental resin, Dental materials.

 

Resumo

Objetivos: Este estudo teve como objetivo avaliar o potencial de ajuste de cor (CAP) de uma resina composta de cor universal aplicada a dentes artificiais de diferentes tonalidades, sob diferentes condições de armazenamento e em vários intervalos de tempo.

Métodos: Uma resina composta de cor universal (Omnichroma; Tokuyama, Tóquio, Japão) e dentes molares artificiais em três tonalidades (A1, A2, D4) foram utilizados. Dois tipos de amostras foram preparados: restaurações de tonalidade dupla (Classe I) e réplicas de dentes artificiais de tonalidade única. As amostras foram armazenadas em água destilada ou café. As medições de cor foram realizadas com um espectrofotômetro no momento inicial e ao fim de 1 dia, 1 semana e 1 mês. As diferenças de cor (ΔE00) foram calculadas utilizando a fórmula CIEDE2000. Os valores de ΔE00 foram analisados com ANOVA de dois fatores e testes de Tukey. Os valores de CAP00 foram analisados com ANOVA de três fatores para comparações entre grupos e ANOVA de medidas repetidas com testes de Bonferroni para avaliar os efeitos ao longo do tempo.

Resultados: No momento inicial, os valores de ΔE00 foram mais baixos no grupo A1 para ambos os tipos de amostras, seguidos por A2 e D4. Após 1 mês, a imersão em café resultou em valores de ΔE00

significativamente superiores aos da água destilada em todos os grupos. Os valores de CAP00 diminuíram significativamente entre 1 semana e 1 mês nos grupos armazenados em café. Todos os subgrupos de tonalidade e armazenamento apresentaram um aumento significativo do CAP00 ao longo do tempo (p < 0,05).

Conclusões: O armazenamento por um mês em água destilada melhorou o CAP em todos os grupos. Por outro lado, uma exposição prolongada ao café aumentou as diferenças de cor e reduziu a harmonia estética das restaurações com o tempo. (Rev Port Estomatol Med Dent Cir Maxilofac. 2025;66(3):115-123)

 

Palavras-chave: Café,Cor,Agentes corantes,Resina composta,Materiais dentários.

 

Introduction

In the field of restorative dentistry, facilitating treatment processes has always been an important goal in the material development process. Significant progress has been made with innovations such as universal adhesive systems,¹ high-power light-curing units,² and bulk-fill composites.³ A recent breakthrough has been the development of universal- shade (single-shade) composite resins. These resins can

mimic any tooth shade with a single application, thus eliminating the complexity of applying multiple layers of various shades to mimic the natural tooth appearance during restoration procedures.^{1, 4}

Universal-shade composite resins were pioneered by Omnichroma (Tokuyama, Tokyo, Japan), and their key feature has earned a place in dental terminology as “chameleon effect.”

This effect is attributed to smart chromatic technology, which relies on structural color, through a phenomenon where specific wavelengths of light are reflected due to the interaction of light with the material’s uniformly arranged nano-structured fillers. According to its manufacturer’s information, Omnichroma does not contain pigments; it is produced using the sol-gel method with spherical SiO2 and ZrO2 particles of equal size and 260-nm diameters. This regular supra-nanostructure is responsible for developing structural color within the range from yellow to red.^{4 - 6} Smooth, uniformly spaced, and arranged spherical fillers facilitate light transmission throughout the restoration, reflecting the color of the surrounding cavity and demonstrating superior color blending ability.⁷As a result, it claims to match all 16 VITA Classic shade guide colors from A1 to D4.

Color compatibility, interactions, and stability are critical factors for evaluating the clinical performance of composite resins.⁸ The color matching and interaction properties of universal-shade composites have been addressed in many studies using instrumental and/or visual methods. Studies have shown that these composites are compatible with a wide range of shades in restoration applications on human teeth,^{6, 9} and they can also adapt to color changes after teeth whitening.¹⁰ Color shifting has also been investigated by placing these universal-shade materials into cavities prepared in composite substrates with different shades, showing effective blending properties in this clinical scenario simulating restoration repair.^{11, 12}

Color stability or instability is associated with aging and discoloration after restoration application.^{13, 14} The various physicochemical conditions in the oral environment can alter the chemical structure of composite resins, and exposure to multiple beverages containing specific chromogens, especially throughout the day, leads to inevitable color changes in restorations.¹⁵ Studies investigating how universal-shade resin composites respond to these external factors have shown that they exhibit similar discoloration potential compared to traditional composites.^{16, 17} On the other hand, as the optical properties of an aged composite resin restoration change, color matching can become even more complex.¹⁸

Color perception relies primarily on how light is reflected or transmitted by an object and is perceived visually. In dental practice, shade selection can be conducted through several approaches, including visual comparison using shade guides, spectrophotometry, colorimetry, and computer-assisted digital imaging analysis.²⁰ Although visual assessment remains the most common technique, it is subject to variability caused by factors such as ambient lighting conditions, observer fatigue, the clinician’s experience, and even gender differences.^21,22

Digital color measurement devices may minimize these subjective influences by offering a more objective alternative due to reducing environmental and observer-related biases. Instruments like spectrophotometers and colorimeters have been widely employed to quantify natural tooth color, aiding in the accurate selection of composite resin shades.^{23, 24} Spectrophotometers, known for their precision and versatility in color science, operate by detecting the intensity of light reflected from a surface at narrow wavelength intervals across the visible spectrum (400–700 nm).²⁵ The VITA Easyshade spectrophotometer, for example, integrates components including a light source, optical dispersion elements, a measurement system, a sensor, and signal processing units to convert reflected light

into analyzable data. The spectral information obtained must then be translated into clinically relevant shade values to facilitate dental color matching.^{25, 26}

Based on this information, the research question of this study is whether a restoration made with universal-shade composite resin, in the long term, loses or maintains its compatibility with the substrate material in terms of discoloration.

This study aims to examine the color adjustment potential (CAP) of a universal-shade composite resin in Class I restorations prepared on acrylic teeth with different shades (A1, A2, and D4), following exposure to coloring agents (distilled water and coffee) for 24 hours, 1 week, and 1 month, to understand how well it preserves color stability and aesthetic appeal. The primary null hypothesis was that the shade of the substrate, the storage medium, and the immersion time would have no significant effect on the CAP00 value of the universal-shade composite resin. The secondary hypothesis was that no interaction would be observed between these variables.

Material and Methods

According to the results of AlHamdan et al.¹⁶ and using a three-way analysis of variance (ANOVA), G*Power software (version 3.1, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany) with α = 0.05, power (1-β) = 0.95, effect size = 0.8465196, and common standard deviation of 0.46526874, the total sample size required was 27 (3*9). Therefore, the experimente was conducted with n = 10 for each subgroup.

This study used sixty left mandibular first molar (#36) acrylic teeth without root extensions, containing only crown morphology (provided by Tokuyama Dental, Japan). Circular cavities were prepared on the teeth’s occlusal surfaces, with 2-mm depth (measured from the lingual groove) and 5-mm diameter. The measurements were determined using a Nordent Periodontal Probe N116 (Nordent Manufacturing, USA).

The acrylic teeth were bilayered to mimic the optical behavior of natural teeth and to enhance the reliability of the color evaluations. Shades A1, A2, and D4 were selected to reflect a clinically relevant range of tooth shades: A2 is among the most frequently observed natural shades,²⁷ while A1 and D4 represent the lighter and darker ends of the shade spectrum commonly encountered in daily clinical practice within the VITA Classical scale.

A single layer of universal-shade composite resin Omnichroma was placed in all cavity preparations. The occlusal surface of the restoration was flattened to allow measurement with a spectrophotometer. The composite restorations were polymerized for 20 seconds using an LED light-curing unit (D-light Pro; GC Europe, Leuven, Belgium) with an average light intensity of 1400 mW/cm², according to the manufacturer’s instructions. The light intensity of the device was checked with an integrated radiometer every three polymerizations. Subsequently, finishing and polishing were performed on the restoration

surfaces using a two-step polishing system (Enhance & PoGo; Dentsply, Konstanz, Germany) with a slow-speed handpiece.

The visual schematics of the restorations prepared in the acrylic teeth is shown in Figure 1a.

 

Figure 1. Step-wise experimental design

 

The restored acrylic teeth were divided into three groups of 20 teeth according to the three different tooth shades.

Then, the teeth in each group were randomly divided into two subgroups (n = 10) to be stored in either distilled water or coffee (Figure 1b). To mimic dietary staining, a coffee solution containing 2 g of granulated coffee (Nescafé Gold; Nestlé, Vevey, Switzerland) was prepared by dissolving the poder in 200 ml of boiling water (at approximately 100°C) and allowed to steep for 1 minute. The specimens were immersed while the solution was still hot (at approximately 90–95°C), simulating intraoral exposure to freshly brewed coffee. Based on studies by Ertaş et al.,28 which indicate that immersion in beverages for 24 hours corresponds to 1 month in vivo, in this study, the samples were stored in solutions for 30 days, simulating a clinical lifespan of 2.5 years. Throughout the study, the solutions were refreshed every 24 hours in the same way.²⁸

Color measurements were repeated immediately after the completion of restorations and then after 1 day, 1 week, and 1 month of immersion in distilled water or coffee. Samples removed from the solutions at all evaluation periods were rinsed under running water for 10 seconds, dried with blotting paper, and then left to air dry. Measurements were performed using an intraoral spectrophotometer (VITA Easyshade V; VITA Zahnfabrik, Bäd Säckingen, Germany) on a neutral gray background (L* ≈ 50), in accordance with standard protocols for reducing ambient light interference. The device features a measurement tip with a diameter of approximately 5 mm, which was positioned perpendicular to the measured surfaces during all evaluations. To obtain color parameters from acrylic teeth, the device probe was placed on the buccal surfaces of the teeth. To obtain color parameters of Omnichroma, the device probe was positioned perpendicular to the composite restorations on the occlusal surfaces of the resin teeth.

Following the manufacturer’s instructions, the device tip was positioned perpendicular to the measured area as illustrated in Figure 1c.

The average L*, a*, b* values of three repeated measurements were calculated for each restoration and acrylic tooth.

After each of the three measurements, the device’s calibration was checked. Then, using the Excel spreadsheet application, the color difference (ΔE00) values between the acrylic teeth and

the occlusal restorations were calculated with the formula below:²⁹ (Figure 6)

 

Figura 6

 

Following the recommendations for dental research and in vivo instrumental color analysis, the KL, KC, and KH parametric factors were adjusted to 2:1:1.30 The color difference calculations at baseline, 1 day, 1 week, and 1 month were recorded as ΔE00_dual values. Based on the literature, the 50:50% perceptibility (PT00) and 50:50% acceptability (AT00) thresholds were established at > 0.8 and ≤ 1.8, respectively, in line with previous CIEDE2000-based dental color research.³¹

The CAP00 index was used to calculate the CAP.32 For this purpose, color difference values obtained from dual-shade (restored) samples (ΔE00_dual) after exposure to distilled water/coffee solution at baseline, 1 day, 1 week, and 1 month, as well as color difference values obtained from single-shade samples (ΔE00_single), were used. The single-shade samples consist of the acrylic tooth without cavity preparation and its replica made from composite resin. Thus, the color difference value ΔE00_single corresponds to the color difference between these two individual samples. Moreover, a comparison was made with a reference ΔE00_single value to track the time-dependent change in CAP. The color parameters of single-shade acrylic resin tooth samples were recorded from the flat buccal surfaces before preparation. For single-shade composite samples, Omnichroma resin replicas were made from silicone molds obtained from acrylic teeth (n = 10). The same procedures for polymerization and finishing/polishing were followed. Then, the averages of L*, a*, and b* measurements obtained from the buccal surfaces of single-shade acrylic and composite artificial teeth were used in the CIEDE2000 color difference formula to obtain Figure 1. Step-wise experimental design a reference ΔE_{00_single} value for each shade of acrylic teeth (A1, A2, D4). The calculated reference ΔE00_single values in distilled water and coffee, respectively, were 4.06 ± 0.84 and 4.36 ± 0.79 for A1, 10.75 ± 0.62 and 10.33 ± 0.65 for A2, and 12.39 ± 0.46 and 12.53 ± 0.57 for D4. CAP00 index values for each time period (baseline, 1 day, 1 week, 1 month) were then calculated using the following formula: CAP00 = 1 - ΔE00_dual / ΔE00_single. The distinction between dual and single-color measurement methods is visually presented in Figure 1d.

The data were analyzed using the statistical software program SPSS (version 23.0) (IBM; Chicago, IL, USA). According to the Shapiro-Wilk test, the data showed a normal distribution. For color-matching assessment, a two-way ANOVA with a post hoc Tukey’s test was applied to the ΔE00 values obtained for each immersion time. CAP00 values were analyzed using threeway ANOVA for intergroup comparison, repeated measures ANOVA to determine the effect of immersion time, and, subsequently, Bonferroni tests. A p-value lower than 0.05 was considered statistically significant.

Results

According to the two-way ANOVA, only the substrate shade main factor had a statistically significant effect on the baseline color difference values (ΔE00). The substrate shade and storage media main factors and the substrate shade*storage media interaction were also statistically significant at 1 day, 1 week, and 1 month (p < 0.001; Table 1). The color difference values for each time period are shown in Table 2. Accordingly, ΔE00 values obtained from single-shade and dual-shade samples before exposure to any solution were lowest in the A1 group, followed by the A2 and D4 groups, respectively. The highest ΔE00_dual values after exposure to different solutions were observed in the D4 shade-distilled water subgroup at the 1-day and 1-week evaluations and in the D4 shade-coffee subgroup at the 1-month evaluation. The lowest ΔE00_dual values were observed in the A1 shade-distilled water subgroup in all three evaluation points and in the A1 shade-coffee and A2 shade-coffee subgroups at the 1-week evaluation.

 

Table 1. Effect of storage media and substrate shade on color matching values (ΔE00) at each immersion time.

Two-way analysis of variance, df: Degree of freedom. Bold values mean statistical significance.

 

Table 2. Mean ΔE_{00_single} and ΔE_{00_dual} values±standard deviations at baseline, 1 day, 1 week, and 1 month.

Symbols (¥, δ, ‡) indicate significant differences between shades within each column (p < 0.05).

Letters (a,b,c,d,e) indicate significant differences between shade*storage media interactions within each column (p < 0.05).

Note: Symbols and letters are randomly assigned and serve purely for grouping purposes — they do not reflect ranking.

 

When considering each substrate shade in terms of diferente storage media, the A2 and D4 groups showed lower ΔE00_dual values after 1 day and 1 week of exposure to coffee compared to distilled water. In the A1 group, however, storage in distilled water resulted in lower ΔE00_dual values compared to coffee after 1 day, but statistically similar values were found after 1 week. After 1 month, storage in coffee resulted in significantly higher ΔE_{00_dual} values for all groups compared to distilled water.

The three-way ANOVA conducted to determine the effects of substrate shade (F = 89.193, p < 0.001), storage media (F = 43.447, p < 0.001), and immersion time (F = 116.263, p < 0.001) on the CAP00 value of Omnichroma revealed that all three main factors had statistically significant effects. The interaction between these factors was also significant (p < 0.001; Figures 2, 3, and 4). The time-dependent CAP00 graph for each shade-storage media subgroup during the experiment is shown in Figure 5. According to repeated measures ANOVA, time-dependent changes in CAP00 values were statistically significant for each shade-storage media subgroup (p < 0.05). Bonferroni tests revealed statistically significant differences between the 1-day and 1-month measurements for the A1 shade-distilled water subgroup (p = 0.024), between baseline and 1-month measurements for the D4 shade-distilled water subgroup (p = 0.003), and between baseline and 1-day (p < 0.001), 1-week (p < 0.001), and 1-month (p = 0.001) measurements for the A2 shade-distilled water subgroup. For the subgroups immersed in coffee solution, a statistically significant increase was observed between all immersion times except for baseline and 1-day measurements for the A1 shade-coffee subgroup (p < 0.05).

 

Figure 2. Results from a three-way ANOVA carried outto evaluate CAP00 according to substrate shade

 

Figure 3. Results from a three-way ANOVA carried out to evaluate CAP00 according to storage media

 

Figure 4. Results from a three-way ANOVA carried out to evaluate CAP00 according to immersion time

 

Figure 5. Line graph of CAP00 measurements according to shade and solution during the storage time (p = 0.029 for A1-distilled water; p < 0.001 for A1-coffee, A2-distilled water, A2-coffee, and D4-coffee; p = 0.003 for D4-distilled water).

 

Discussion

This study used the CIEDE2000 color difference formula and the color adjustment potential (CAP00) equation to analyze the potential color shift towards the substrate’s color that resin composites undergo when exposed to colorants. Accordingly, the color matching with the substrate material after color changes over time in composite restorations was evaluated relative to the initial color difference values. Based on the significant changes observed in CAP00 values across diferente immersion media and time intervals, both the primary and secondary null hypotheses were rejected.

In all dual-shade samples, the CIEDE2000 color differences between the resin tooth and the restoration surface were initially considerably higher than the generally accepted acceptability threshold for ΔE00 (AT00 ≤ 1.8), as reported in ISO/TR 28642:2016 and more recent perceptibility/acceptability consensos studies.^{31, 33} Omnichroma initially exhibited a lower color difference (ΔE00) from the high-value VITA A1 substrate resin tooth and matched better than the low-value VITA D4 substrate shade. Similarly, Iyer et al.³⁴ reported that among universal- shade composites, Omnichroma exhibited better compatibility with lighter color shades (A2, B1, and B2) in resin teeth.

Another study reported that the color-matching ability of a universal-shade resin composite (Omnichroma) was influenced by tooth color.¹⁶ Forabosco et al.¹⁰reported a significant decrease in the color difference value of Omnichroma with brighter shades after bleaching in human teeth. The authors thus noted the advantage of universal color composites in simplifying the technique, shortening the process, and eliminating the need to replace existing restorations when bleaching occurs.⁵

The high ΔE values observed for the D4 group may not only reflect restoration-substrate mismatch but could also be partially due to the reduced measurement precision of spectrophotometers in darker and more chromatic shade areas. While specific data on D4 are scarce, the literature indicates that the peripheral regions of the VITA Classical shade scale—such as C and D groups—may pose greater challenges in accurate color measurement due to their higher chromaticity and lower frequency in calibration sets.³⁵

Unfortunately, most materials exhibit color changes ranging from light cream to yellowish or light brown due to exposure to organic pigments found in food and beverages.³⁶ In clinical scenarios involving prolonged exposure to a coloring solution, it is important to examine how these new-generation composites with CAP interact with the substrate tissue. The coffee solution contains low-polarity yellow stain molecules, which potentially cause staining due to their affinity for the polymer network.³⁷

Researchers have stated that coffee provides pigments that are adsorbed and absorbed by the substrate composite resin, leading to discoloration on the material’s surface and in deeper layers.^{28 38} It is also believed that the high coffee temperature could facilitate the restoration’s staining process.³⁹ Furthermore, previous studies have reported that Omnichroma exhibits color stability comparable to traditional composite resin in coffee.¹⁶ In the current study, after 1 month, the coffee solution led to higher color difference values than the control environment across all shades, with the highest values observed in the D4 tone. Um and Ruyter⁴⁰ have noted that colorants in coffee adhere to the surface and then become fixed, thus making staining from coffee more pronounced. Lago et al.⁴¹ emphasized that when staining occurs due to external factors, it happens synergistically with cumulative material degradation.

The CAP00 values, which evaluate the time-dependent color match between the universal-shade composite and the substrate, increased noticeably after 1 month compared to baseline in the distilled water environment, showing relatively consistent trends from 1 day on, as expected. Research indicates that most clinically significant color changes occur after the initial polymerization and within 24 hours. After 24 hours, the color change over 1 month remains negligible and does not significantly contribute to the total color change. The increase in color change observed within the first 24 hours is attributed to the change in optical properties of the resin during the post-irradiation polymerization reaction, which is known to occur following light activation of the composites and can last up to 24 hours.⁴²

A CAP00 of 0.50 (corresponding to a 50% ΔE00 reduction in dual-shade samples compared to single-shade samples) is considered a threshold for effective blending.12 The data from the current study show that the CAP00 values of samples immersed in distilled water approached the threshold value after 24 hours compared to baseline, but remained above the threshold only for A2-shade samples. In contrast, when examining the ΔE00_dual values, the lowest color difference was observed in the A1 shade for all evaluation periods (1 day, 1 week, 1 month). This difference between the two parametersarises from the higher level of ΔE00_single in the A2-shade samples.

Although better color-matching results were obtained in the A1 shade from the beginning, it can be said that there is a higher CAP in the A2 shade. This suggests that diferente substrate shades may affect the blending capacities of these materials. Furthermore, considering a previous study that established a CAP (using the CIE L*a*b* color difference formula) value of 0.20 as the threshold for effective blending with denture tooth shade, only the values obtained in the coffee solution after 1 month fell below this threshold.⁴³ Additionally, in the same study, it was reported that instrumental (CAP-I) and visual (CAP-V) measurements performed on the A2 denture tooth yielded higher results for most of the tested resin composites, similar to the findings in the current study.

Many studies in the literature report conflicting results regarding color matching with Omnichroma and high ΔE00 values.^{44, 45} In the study by Vaizoğlu et al.,⁴⁶ significant changes were observed in the ΔE00 values after traditional composites repaired with universal resin composites were colored with coffee. In another study, Omnichroma was the composite that changed color the most, and repairing composites with the same resin yielded the best results.⁴⁷ Pereira-Sanchez et al.,⁴³ based on both instrumental and visual evaluations, stated that

Omnichroma exhibited the greatest color mismatch in their study. The differences in the results from these studies can largely be attributed to the methods used.

When considering the CAP00 values of samples immersed in the coffee simulating the coloring environment, it is surprising that after 1 day, which simulates 1 month of exposure, all CAP00 values except for the A1 group (0.20) were above the threshold of 0.50. Previous studies evaluating the color stability of universal-shade composite, including Omnichroma, have reported that, although universal-shade composites exhibit some differences depending on the immersion environment, they have a high potential for color change.^{17, 48, 52} Earlier studies on the CAP00 values of universal-shade composites focused on blending effects superior to other multi-shade composites, which are visually and instrumentally correlated^{9, 43} and positively affect the color and translucency attributes.¹² However, limited evidence is available regarding the degree of CAP when these composites are subjected to conditions simulating intraoral aging. One study found that increased storage time and resin thickness positively influenced CAP00 values of class V universal-shade composite restorations with different thicknesses (2 and 3 mm) in acrylic denture teeth immersed in distilled water for 24 hours and 1 month.⁵² In the current study, similarly, the level of color matching increased over time in the control environment, while long-term exposure to a coloring environment had a negative impact. Another study that accounted for aging conditions (thermal aging for 10,000 cycles in distilled water) also found inadequate color-matching performance with high ΔE00 for universal-shade repair composites.¹⁸ However, unlike our study, they applied aging conditions before the repair application of universal-shade composites and did not consider CAP00 values. This study has certain limitations that should be acknowledged.

The investigation was limited to a single universal-shade composite resin (Omnichroma), selected intentionally to maintain material standardization and focus on the intrinsic behavior of a widely used representative. While this enhances internal consistency, future research should explore other single-shade composites with varying formulations to broaden the scope of applicability. Moreover, only coffee was used as the staining agent, chosen due to its established and reproducible staining capacity reported in prior literature. However, evaluating the effects of beverages with different pH levels or using multiple staining agentes would provide a more comprehensive understanding of real-life discoloration mechanisms. Simulated toothbrushing was not included in the protocol, as mechanical abrasion could interfere with surface integrity and introduce uncontrolled variables in color measurements. Likewise, salivar dilution and dynamic exposure to staining agents, which occur in the oral environment, were not replicated in order to preserve the conditions’ standardization. Finally, the immersion was performed under static conditions without agitation, consistent with previous in vitro protocols aimed at isolating the effects of storage medium and time. The absence of fluid motion may underestimate the staining potential of beverages, yet this approach allowed for more controlled assessment of color changes. These methodological choices, while limiting clinical mimicry, were implemented to ensure experimental reproducibility and internal validity.

Although some variables, such as the inherent glossiness of acrylic resin teeth and the inability to simulate the complex dynamics of the oral environment, could not be controlled, several standardization techniques were applied to minimize their impact. These included using prefabricated teeth with identical surface morphology, a consistent finishing and polishing protocol, and standardized spectrophotometer positioning under controlled lighting. These measures aimed to reduce operator and environmental bias and ensure reliable comparisons.

This study provides valuable insights into the color compatibility and long-term color stability of universal-shade composite resins, specifically Omnichroma, in restorative dentistry. By simulating real-life staining agents, the research enhances understanding of how these materials perform over time, offering essential information to improve aesthetic outcomes and durability in clinical practice. These findings help inform decisions regarding the use of universal-shade composites in long-term dental restorations. Therefore, the clinical relevance of these findings should be emphasized, especially when selecting restorative materials for long-term aesthetic stability.

Conclusions

When comparing the initial ΔE00_single and ΔE00_dual values, the lowest values were observed in the A1 shade, followed by A2 and D4 shades, respectively. After 1 month, the ΔE00 values obtained in the coffee environment were significantly higher for all groups than those in distilled water. Except for the values obtained after 1-month exposure to the coffee solution, the CAP00 values were positive for all groups and increased over time. The shade of the substrate resin tooth resulted in different CAP00 values, with the A2 shade demonstrating the highest performance in both immersion environments.

One-month storage in distilled water enhanced CAP in all groups. However, prolonged coffee exposure increased color differences and diminished the color harmony of restorations over time.

 

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^*Corresponding author:

Tuğba Misilli

E-mail address: dt.tugbay@outlook.com; tugbamisilli@comu.edu.tr

 

CRediT authorship contribution statement

Berkant Sezer: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Validation, Resources, Writing – review and editing. Tuğba Misilli: Methodology, Supervision, Formal analysis, Writing – original draft. Mehmet Buldur: Conceptualization, Methodology, Resources, Writing – review and editing.

 

Conflict of interest

The authors have no conflicts of interest to declare.

 

Ethical disclosures

Protection of human and animal subjects. The authors declare that no experiments were performed on humans or animals for this study.

Confidentiality of data. The authors declare that no patient data appear in this article.

Right to privacy and informed consent. The authors declare that no patient data appear in this article.

 

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This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).