Introduction

Aesthetic dentistry significantly enhances smile and patient confidence. Composite resins are widely used for anterior and posterior restorations due to their aesthetic appeal, strength, and affordability [1]. However, achieving a satisfactory color match remains a clinical challenge.

Multishade composites provide excellent aesthetic effects through layering, but require precise shade selection and higher inventory, increasing chairside time and clinical complexity [2]. To streamline restorative procedures, monoshade composites, such as Omnichroma and Vittra APS Unique, have been introduced. Recently proposed Vittra APS Unique incorporates zirconium silicate fillers and advanced polymerization system (APS), claiming improved shade-matching and curing efficacy without added pigments [3].

Long-term color stability of restorations is crucial for their success, as discoloration in dental composites can result from both internal properties and external influences from commonly consumed beverages [4]. While multishade composites have been studied extensively, limited data exists on color stability of newer monoshade systems, such as Vittra APS Unique. This study compared the color stability of monoshade and multishade composite resins after immersion in tea, beer, and artificial saliva.

Objectives

The objective of this study was to evaluate and compare the color stability of monoshade and multishade composite resins when immersed in various common beverages over a period of 28 days.

Material and methods

For sample size calculation, the power analysis used color change (ΔE) as the primary outcome. According to the results of a pilot study, the effect size for a repeated measures ANOVA within-between (W/B) interaction was 0.707. The minimum estimated sample size was 60 specimens (10 specimens per group) (α = 0.05, β = 0.8). Sample size was calculated using G*Power version 3.1.9.2 (version XX, IBM Corp., Armonk,
NY, USA).

Sixty disk-shaped specimens (8 mm diameter × 2 mm
thickness) were fabricated using a standardized plastic mold. Two composite resins were evaluated: Group 1 (n = 30): Monoshade composite (Vittra APS Unique, FGM, Brazil), and group 2 (n = 30): Multishade composite (Brilliant NG, Coltene, Switzerland).

Composite material was placed into the molds, positioned on a glass slide, and covered with another micro­scopic glass slide and Mylar strip to ensure uniform thickness and surface finish. Specimens were light-cured through the top glass slide with a LED curing unit (Unicorn, Denmark; 650 mW/cm²) for 40 seconds from both top and bottom surfaces.

All specimens were finished and polished using the Super Snap polishing system (Shofu Inc., Kyoto, Japan) in sequential order. Each disc was subjected to constant pressure for 30 seconds. After polishing, specimens were stored in distilled water at 37°C for 24 hours. To simu­late one year of aging, thermocycling (10,000 cycles, 5-55°C, 30 seconds dwell time) was performed, and then baseline color values were recorded using a colorimeter (Smart Color Solutions, India) against a white background using the CIELAB system.

Specimens were subdivided into three subgroups based on immersion media (n = 10 each): Subgroup S: artificial saliva (pH 6.75 ± 0.15); Subgroup T: tea (15 g of loose-leaf tea boiled in 1 l water for 5 min); Subgroup B: commercial beer (Budweiser Magnum, India).

Each specimen was immersed in 5 ml of the respective solution at 37°C. Solutions were replaced on day 7,
14, and 21. Color measurements were taken at day 1
(24 hrs.), day 7, and day 28 using the CIEDE2000 (ΔE₀₀) formula. All measurements were performed under standardized lighting conditions. Data were statistically analyzed using SPSS software G*Power version 3.1.9.2 (version XX, IBM Corp., Armonk, NY, USA). Intragroup comparisons were analyzed with paired t-tests, while intergroup differences were evaluated using one-way analysis of variance (ANOVA), followed by post hoc test where applicable. A significance level of p < 0.05 was considered statistically significant.

Results

Of the 60 composite resin disks subjected to immersion in different medias, all showed change in color over a period of time with variable ΔE values. A significant
difference was observed in ΔE values at 24 hrs. (0.0046), day 7 (0.0085), and day 28 (0.0007) for specimens exposed to tea in group 1 (Vittra APS, Unique) and group 2
(Brilliant NG, Coltene) at 0.05 level of significance (p > 0.05), as presented in Table 1. Visual examination corroborated the colorimeter finding (Figure 1).

Immersion in saliva in both groups caused the highest difference in color stability (ΔE) at day 7 and it was the lowest at 24 hrs., respectively. Similarly for beer, the largest change in color stability (ΔE) was observed at day 7 and the smallest change in ΔE was observed at 24 hrs. for both the composite resins. However, for immersion in tea, the greatest change in color stability (ΔE) was observed at day 28 and the smallest ΔE value was observed at 24 hrs. for both the groups, respectively (Table 2).

Discussion

Growing patient awareness of facial aesthetics has led to a higher demand for tooth-colored restorations. Achieving natural-looking restorations requires careful shade-matching, which can be challenging due to the complex interaction of light with tooth structure, including translucency, gloss, and surrounding shade [5]. For a restoration to blend well, its optical properties must closely match natural teeth [6].

Traditionally, multishade composites have been favored for their superior color-matching potential through layering techniques that mimic natural tooth anatomy. How­ever, their use demands greater clinical time, skills, and material inventory, which increases cost and complexity.

To simplify the restorative process, universal or monoshade composites have been developed. Materials, such as Omnichroma, leverage smart chromatic techno­logy and high translucency to blend with a range of tooth shades [7]. While effective in many cases, limitations exist, particularly in matching highly bleached teeth or achieving life-long results in anterior restorations requiring incisal translucency. Additionally, Omnichroma has shown greater susceptibility to discoloration in some previous in vitro studies compared to multishade systems [8-10].

Recent innovations, such as Vittra APS Unique, incorporate advanced nanotechnology and an adaptive polymerization system to address these shortcomings. Vittra APS Unique is reported to offer improved color stability, enhanced shade coverage (including bleached shades), and better handling properties [3]. Its optical and mecha­nical benefits suggest it may provide more consistent
aesthetic outcomes across diverse clinical scenarios.

Despite growing evidence comparing Omnichroma with multishade systems, data on newer monoshade composites, such as Vittra APS, remain limited. This study aims to bridge that gap by evaluating and comparing the color stability of mono- and multishade composites exposed to common staining agents.

In the current study, each composite specimen was submerged in 5 mL of artificial saliva, tea, and beer. Seve­ral studies have indicated that artificial saliva can contribute to the discoloration of composite resins [11-14]. Due to its neutral pH and its capability to replicate intraoral conditions where dental restorations are typically exposed, artificial saliva was used as the control medium in this study. Tea was selected due to its well-documented impact on resin aesthetics, as supported by multiple sources [8, 11, 12, 14-17]. Its role as a common warm beverage with known staining potential made it an ideal test medium. Preparation methods were adapted from Bahbishi et al. [12] and Tecke et al. [9]. Beer, though less studied, was chosen due to its acidity and common consumption, potentially affecting composite longevity and color retention.

Observations from the current study indicated color shifts in both monoshade (group 1) and multishade (group 2) composites following immersion in artificial saliva. Initial changes at 24 hrs. were minimal (ΔE = 2.85 and 3.09), peaking at days 7 (ΔE = 4.77 and 7.27), then stabilizing or slightly declining at days 28 (ΔE = 4.24 and 3.73). These shifts likely result from water sorption, which initially affects only surface layers, but eventually enables salivary constituents to diffuse into the matrix. By day 28, a balance may be reached between pigment penetration and leaching, explaining the observed stabilization. Similar patterns were reported by Prodan
et al. [18], who attributed discoloration to the hydrophilic nature of composite materials.

Beer immersion followed a similar trajectory. In group 1, ΔE peaked at day 7 (8.47) and declined by day 28 (4.45). Group 2 showed the highest discoloration on day 7 (8.58) and the lowest at 24 hrs. (4.52). This similarity with saliva may be due to the high water content in beer (90-94%). Although beer-specific studies are limited, discoloration may stem from increased matrix porosity due to water uptake and the presence of chromogens, such as caramel coloring. Composite resins are known to absorb water and pigmented fluids, which can lead to staining over time [19]. In addition, beer’s acidic pH may exacerbate resin degradation, facilitating pigment infiltration.

In the study, tea caused the most pronounced discoloration. In group 1 (Vittra APS Unique), ΔE value increased from 13.7 at 24 hrs. to 18.93 by day 28. Group 2 (Brilliant NG, Coltene) showed lower but still significant changes (7.2 to 10.78). Previous studies [20, 21] support this trend, with Ruyter et al. [22] explaining that tea’s polar chromogens initially adhere to surfaces and later diffuse into the matrix. This chemical affinity is heightened in hydrophilic resins. Although Ertas et al. [23] found no significant staining with tea, methodological differences may explain this discrepancy. Our continuous immersion protocol aimed to replicate real-life long-term exposure. These findings reinforce that darker beverages, such as tea, pose greater aesthetic risk of staining.

Statistical analysis revealed significant color change in both groups between 24 hrs. and day 7 in saliva (p < 0.05), with stabilization thereafter (p > 0.05), consistent with Domingos et al. [11]. Similarly, Rashidy et al.
[13] found no significant differences between monoshade and multishade composites in saliva, though tea and red wine led to unacceptable changes.

In terms of beer, group 1 exhibited significant color shifts (p < 0.05), while group 2 did not (p > 0.05). This disparity may be attributed to group 1 use of hydrophi­lic monomers, such as UDMA and TEGDMA, which increase water sorption. Fontes et al. [24] observed similar effects with acidic media, suggesting that low pH beverages promote pigment uptake by softening the resin surface.

Tea significantly affected both groups. Group 2 (Brilliant NG, Coltene) showed notable differences across all time points (p < 0.05), while group 1 (Vittra APS Unique) had significant changes between days 7 and 28. Tea immersion caused a statistically significant difference between groups at later intervals (p < 0.05), likely due to chromogen penetration and breakdown at the filler-matrix interface. Gupta et al. [16] noted analo­gous findings at elevated temperatures, with yellowing and reddening attributed to tea chromogens.

In both groups, tea caused the most discoloration, followed by beer and saliva. The multishade composite showed superior color stability compared to the monoshade, likely due to its matrix containing Bis-EMA and Bis-GMA, which are more hydrophobic and cross-linked. In contrast, the monoshade resin’s use of UDMA and TEGDMA increases water sorption. The nanohybrid filler structure, along with TEGDMA’s ethoxy groups, may enhance porosity and pigment retention.

Although the multishade composite demonstrated superior color stability, both materials showed susceptibility to discoloration, leading to the rejection of the null hypothesis. In multishade composites, pigment and moisture infiltration likely occur at incompletely sila­nized nanoparticle interfaces. Monoshade composites, with lower filler content, are similarly affected, as pigments accumulate in surface voids, intensifying staining and structural breakdown [18].

A key limitation of this in vitro study is its inability to fully replicate intraoral conditions, despite maintaining beverage temperatures at 37°C to simulate the oral environment. Complex variables, such as mechanical wear, salivary enzymes, and remineralization processes, were not reproduced. Moreover, detailed chemical analysis of beverages and resin components was beyond the study’s scope, which may have limited insights into the specific physicochemical interactions involved in discoloration. Future research should consider exploring these interactions at a molecular level.

Conclusions

Within the scope of this study, both monoshade (Vittra APS Unique) and multishade (Brilliant NG, Coltene) composites exhibited time-dependent discoloration in various media immersions. Saliva caused significant changes in both groups between 24 hrs. and
7 days. Beer led to significant staining in the monoshade group during this period, but not in the multishade one (Brilliant NG, Coltene). Tea caused consistent, notable discoloration in both materials, with the multishade resin (Brilliant NG, Coltene) affected at all time points, and the monoshade (Vittra APS Unique) primarily between days 7 and 28. While no statistically significant difference was observed between the two materials exposed to saliva and beer, tea immersion led to greater staining in the multishade composite (Brilliant NG, Coltene). Overall, the monoshade composite (Vittra APS Unique) demonstrated greater susceptibility to color changes across all media compared to the multishade resin (Brilliant NG, Coltene).

Clinical significance

Clinically, awareness of composite color stability is crucial, particularly for patients with frequent intake of chromogenic beverages. This study confirms that both types of composite discolor over time, with variations based on the staining agent. Tea caused more discoloration in the multishade resin, while the monoshade variant exhibited overall higher color instability. These observations emphasize the relevance of material selection based on individual dietary habits, and the importance of maintenance and periodic evaluation to ensure restoration longevity.

Disclosures

Author contributions: Conceptualization: P.M.; Metho­dology: S.U., V.N.; Questionnaire adaptation: S.U.; Inve­stigation and data collection: S.U.; Formal analysis: V.N.; Data curation: P.M.; Writing of original draft: S.U.; Writing – review and editing: P.M.; Supervision: V.N., P.M.; Project administration: P.M. All authors have read and agreed to the published version of the manuscript.

Funding: This research received no external funding.

Institutional Review Board statement: Not applicable.

Informed consent statement: Not applicable.

Data availability statement: The data presented in this study are available within the article. Additional information is available from the corresponding author and can be provided upon reasonable request.

Acknowledgments: None.

Conflicts of interest: The authors declare no conflicts of interest.

AI use statement: No artificial intelligence tools were used in the preparation of this manuscript.

References