In Vitro Evaluation of the Color Variation of Two Bulk Fill Resin Composites Immersed in Four Different Pigmented Beverages: A Comparative Study

ABSTRACT

Aim:

The aim of the study was to conduct a comparative in vitro evaluation of the color stability of two contemporary bulk fill resin composites, Filtek One Bulk Fill (FO-BF), and Tetric N-Ceram Bulk Fill (TNC-BF), following immersion in four common pigmenting beverages at distinct time intervals.

Materials and Methods:

Eighty composite discs (n = 40 per resin type) were fabricated and subdivided into four groups for immersion in Coca-Cola®, coffee, red wine, or green tea. Color measurements were performed using a digital spectrophotometer at baseline and after 3, 12, and 24 h of immersion. Color variation (ΔE) was calculated using the CIEDE2000 formula. The data were analyzed using Welch’s analysis of variance, Student’s t-test, and Friedman’s test, with statistical significance set at P < 0.05.

Results:

Red wine induced the most substantial and rapid color change in both FO-BF and TNC-BF resins at all evaluation times (P < 0.05). Coffee also produced significant discoloration in TNC-BF after only 3 h (P < 0.05). The color variation produced by red wine surpassed the clinically acceptable threshold (ΔE > 3.3) in both composites within 3 h. Coffee produced clinically unacceptable staining in TNC-BF at 3 h and in FO-BF at 12 h. By 24 h, all tested beverages caused clinically unacceptable discoloration in both materials (P < 0.05).

Conclusion:

The color stability of bulk fill composites is significantly influenced by the type of beverage and exposure duration. Red wine is a potent staining agent, causing rapid and clinically unacceptable discoloration in both tested materials. These findings underscore the importance of material selection and patient counseling on dietary habits to ensure the long-term aesthetic success of composite restorations.

INTRODUCTION

Resin composite is one of the most widely used materials for dental restorations due to its aesthetic appeal, functionality, and durability.[1] Over time, patient expectations have increased, favoring restorations that are not only functional but also visually indistinguishable from natural teeth.[2,3] As a result, the optical properties of resin composites have been enhanced to achieve superior color matching with dental tissues.[1,2,3,4,5] Among these properties, color stability — the ability to maintain consistent appearance over time — is particularly important.[6]

Traditionally, composite resins have been applied using an incremental layering technique. However, this approach has drawbacks, such as void formation, contamination, poor interlayer adhesion, and extended clinical time.[7] To overcome these limitations, a new generation of nano-filled composites called bulk fill resin composites was developed. These materials allow for single-increment placement of 4–5 mm layers, streamlining the restorative procedure.[8,9]

Bulk fill composites differ from conventional ones in composition and filler content, leading to reduced polymerization stress and improved light-curing reactivity.[7,10] Consequently, they offer promising physical-mechanical properties, including enhanced fracture toughness,[11] flexural strength,[12,13] surface hardness,[13,14] and surface roughness.[14]

Although mechanical properties have been extensively studied, there is a need for further research on the optical behavior of these materials, especially color stability. Several intrinsic factors — such as resin matrix hydrolysis, filler particle size, polymerization efficiency, and monomer conversion — can influence discoloration.[15,16] In addition, extrinsic factors such as exposure to staining agents found in beverages such as coffee, tea, cola, and red wine also play a role.[15,16,17] These drinks can penetrate the resin matrix and release low-polarity pigments, leading to visible color changes.[17]

Given the wide variety of bulk fill composites available, dentists must carefully choose materials based on their performance and optical stability. Furthermore, they should provide guidance to patients regarding dietary habits to help preserve restoration aesthetics.

Therefore, the aim of this study was to evaluate the in vitro color variation of two bulk fill resin composites after immersion in four different pigmented beverages at multiple time points. The null hypotheses were: 1. There are no significant differences in color variation between the two resins across different beverages, and 2. No significant differences exist in color variation over time.

MATERIALS AND METHODS

STUDY DESIGN

This longitudinal in vitro experimental study was conducted between December 2022 and January 2023 at the School of Stomatology of the Universidad Privada San Juan Bautista (UPSJB) and at a High Technology Laboratory accredited under ISO/IEC 17025 standards, in Lima, Peru. The study was approved by the Institutional Research Ethics Committee of UPSJB (approval No. 480-2022-CIEI-UPSJB) and adhered to the CRIS (Checklist for Reporting in vitro Studies) guidelines.[18]

SAMPLE SIZE AND GROUP ALLOCATION

A total of 80 specimens was determined by power analysis using G*Power 3.1.9.7, informed by a preliminary pilot of five specimens per subgroup for each of the two resin types across four beverage conditions. Calculations assumed α = 0.05, 1 − β = 0.80, and an effect size of 3.31 based on analysis of variance (ANOVA) requirements. Forty disk-shaped specimens of Tetric® N-Ceram Bulk Fill IVA (Ivoclar Vivadent, Schaan, Liechtenstein) and 40 of Filtek® One Bulk Fill Restorative A2 (3M ESPE, St. Paul, MN, USA) were fabricated with identical dimensions. Each resin cohort (n = 40) was then randomly split into four sets of 10 specimens, each set assigned to immersion in one of the following solutions: Coca-Cola®, coffee, red wine, or green tea [Figure 1].

Figure 1.

Random distribution of groups according to type of resin composite and pigmented beverages

CHARACTERISTICS AND SAMPLE PREPARATION

The composite resin discs were fabricated by a single operator with a metal mold measuring 10 mm in diameter and 3 mm in thickness, using the monoblock technique on a glass base with the aid of a resin spatula (Optrasculp, Ivoclar Vivadent, Schaan, Liechtenstein).[19] Then, a celluloid matrix was placed on the mold and a 1 mm thick glass slide was placed on top to ensure that the upper and lower surfaces were parallel and light-cured with a Bluephase N G4 lamp (Ivoclar Vivadent, Schaan, Liechtenstein) at 1000 mW/cm² for 20 s.[19] The samples were removed from the mold and visually evaluated for voids and surface defects; defective samples were excluded from the study.

The surfaces of all resin composite blocks were polished by the same operator, using a micromotor and contra-angle handpiece (NSK, Tokyo, Japan) and a four-step coarse-to-fine grit disc system (Sof-Lex, 3M ESPE, St Paul, SM, USA) according to the manufacturer’s instructions.[14,19] After polishing, the samples were stored at 37°C for 24 h in distilled water to rehydrate and complete polymerization.[14,19]

IMMERSION PROTOCOL

The samples of each resin composite (n = 40) were divided into four subgroups (n = 10): coke, coffee, red wine, and green tea [Table 1]. Coke and red wine were used directly without any preparation and coffee was prepared by mixing 25 g in 250 mL boiled water.[16,20] Green tea was prepared by steeping a pre-made tea bag (30 g) in 200 mL of hot water.[21] It was placed in individual sealable containers and steeped for 3, 12, and 24 h. All samples were stored in a dark place at 37°C.[16,20,21] The immersion media were replaced on a daily basis.[16,21]

Table 1.

Solutions tested

Product	pH	Manufacturer
Coffee	5.45	Nescafé ®, Nestlé, Switzerland
Red wine	3.82	Los árboles Malbec, Navarro Correas, Argentina
Coke	2.40	The Coca-Cola Company, USA
Green tea	2.93	Pure green tea, Wawasana, Peru

COLOR MEASUREMENT

Color measurements were performed using a spectrophotometer (Vita Easyshade®, V Zahnfabrik, Bad Säckingen, Germany) in accordance with ISO/Commission Internationale d’Eclairage (CIE) 11664-6:2022 CIELAB standards.[22] The individual color parameters (L*, a*, and b*), representing brightness, red-green, and blue-yellow values, respectively, were recorded.[16,17] Each sample was measured twice, and the mean of the two readings was calculated. The device was calibrated according to the manufacturer’s instructions before each test.[16,17] To ensure accurate readings, the probe tip was positioned perpendicular to the center of each specimen and aligned with the sample surface. All measurements were performed against a white background under standardized positioning, angulation, and D65 ambient lighting conditions.[19]

After immersing the composite resin discs in the test beverages for 3 h, color measurements were taken. The same samples were then re-immersed until a total exposure time of 12 h was reached, followed by a second color assessment. The procedure was repeated to reach a final exposure time of 24 h, after which a third color evaluation was conducted. Before each color measurement, the discs were rinsed with distilled water and dried with absorbent paper.[16,17] The same operator performed all measurements in the same environment. The color change was calculated using the CIEDE2000 color system and the following formula[16,17,22]:

where ΔL, ΔC, and ΔH represent the differences in luminance, chroma, and hue, respectively, between the initial and subsequent color measurements.[22]

STATISTICAL ANALYSIS

Statistical analysis was performed using SPSS version 28.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics included measures of central tendency (mean and median) and dispersion (standard deviation and interquartile range). The Shapiro–Wilk, Levene, and Mauchly tests were used to assess normality, homogeneity of variances, and sphericity, respectively. As the data followed a normal distribution but violated the assumption of homogeneity of variances, Welch’s robust ANOVA with Games–Howell post hoc analysis was applied for cross-sectional comparisons. Student t test was used to compare the two resin composites immersed in the same solution. For longitudinal comparisons, Friedman’s test with Bonferroni-adjusted post hoc analysis was employed. Statistical significance was set at P < 0.05.

RESULTS

On examining the effects of four different beverages on the Filtek One Bulk Fill (FO-BF) resin composite, it was observed that red wine exhibited the most pronounced color variation. This was evident at all-time points, including at 3 h (P < 0.05), 12 h (P < 0.05), and 24 h (P < 0.05). Moreover, the color of the resin changed in a clinically unacceptable way (ΔE > 3.3) from 3 h of immersion in red wine, while coffee did so from 12 h, and finally coke and green tea did so at 24 h [Table 2 and Figure 2].

Table 2.

Comparison of the color variation (ΔE) of two resin composites immersed in different beverages at 3, 12, and 24 h

Resin composite	Beverage	n	At 3 h				P*	At 12 h				P*	At 24 h				P*
			Mean	SD	95% CI			Mean	SD	95% CI			Mean	SD	95% CI
					LL	UL				LL	UL				LL	UL
FO-BF	Coke	10	1.83A,B	0.66	1.35	2.30	<0.001*	2.54A	0.47	2.21	2.88	<0.001*	8.53A	0.64	8.07	9.00	<0.001*
	Coffee	10	2.47A,#	0.38	2.20	2.75		7.11B,#	1.03	6.37	7.84		12.47B,#	1.27	11.56	13.37
	Red wine	10	4.42C	0.69	3.93	4.91		8.54C	1.19	7.68	9.39		18.01C,#	2.01	16.57	19.44
	Green tea	10	1.73B	0.44	1.41	2.04		2.62A	0.30	2.40	2.84		13.06B,#	0.38	12.79	13.33
TNC-BF	Coke	10	1.75A	0.18	1.62	1.88	<0.001*	2.43A	0.36	2.17	2.69	<0.001*	8.77A	0.63	8.31	9.22	<0.001*
	Coffee	10	3.38B,$	1.20	2.51	4.24		5.61B,$	0.72	5.09	6.12		11.34B,$	1.08	10.57	12.11
	Red wine	10	4.38B	0.76	3.84	4.92		8.63C	0.45	8.31	8.96		19.74C,$	1.20	18.88	20.60
	Green tea	10	1.70A	0.41	1.40	1.99		2.32A	0.43	2.01	2.63		13.63D,$	0.47	13.29	13.96

FO-BF = Filtek One Bulk Fill, TNC-BF = Tetric N-Ceram Bulk Fill, n = sample size, SD = standard deviation, 95% CI = 95% confidence interval, LL = lower limit, UL = upper limit.

*Based on Welch’s ANOVA robust test (P < 0.05, significant differences). A, B, and C: Different letters in the same column according to each resin composite indicated significant differences based on Games Howell post hoc (P < 0.05). Different symbols in the same column (# and $) indicated significant differences (P < 0.05) according to Student’s t-testwhen comparing the two composite resins immersed in the same beverage

Figure 2.

Color variation (ΔE) of Filtek One Bulk Fill resin composite immersed in different beverages over time

It was observed that the Tetric N-Ceram Bulk Fill (TNC-BF) resin composite experienced significant color variation when immersed in four different beverages. At 3 h, red wine and coffee were exhibited the most pronounced color change (P < 0.05). However, at 12 and 24 h, only wine showed a statistically significant color difference (P < 0.05). Furthermore, red wine and coffee showed a clinically unacceptable color change (ΔE > 3.3) after 3 h of immersion, while coke and green tea showed a clinically unacceptable color change after 24 h (P < 0.05) [Figure 3].

Figure 3.

Color variation (ΔE) of tetric N-Ceram Bulk Fill resin composite immersed in different beverages over time

In terms of color variation when comparing the two resin composites after immersion in the same type of beverage, it was observed that coffee affected the TNC-BF resin more at 3 h (P = 0.046), while at 12 and 24 h it affected the FO-BF resin more (P = 0.002 and P = 0.047; respectively). In addition, red wine and green tea affected the TNC-BF resin more at 24 h (P = 0.034 and P = 0.008; respectively). Finally, coke affected the two composite resins similarly at all times tested (P > 0.05) [Table 2].

The longitudinal analysis showed that for both resin composites, color variation increased significantly over the 24-hour immersion period ( P < 0.001). Bonferroni post-hoc tests confirmed that this change was progressive, revealing statistically significant differences between the 3-hour, 12-hour, and 24-hour measurement intervals [Table 3].

Table 3.

Comparison of the color variation (ΔE) of two resin composites immersed in different beverages at 3, 12, and 24 h

Resin composite	Beverage	n	At 3 h		At 12 h		At 24 h		P*
			Median	IQR	Median	IQR	Median	IQR
FO-BF	Coke	10	1.83X	1.45	2.67X,Y	0.66	8.49Y	1.21	<0.001*
	Coffee	10	2.33X	0.59	6.74X,Y	1.48	12.27Y	1.40	<0.001*
	Red wine	10	4.27X	1.14	8.30X,Y	1.71	17.82Y	2.65	<0.001*
	Green tea	10	1.67X	0.84	2.68X,Y	0.60	13.11Y	0.63	<0.001*
TNC-BF	Coke	10	1.73X	0.26	2.44X,Y	0.60	8.62Y	1.04	<0.001*
	Coffee	10	3.54X	2.40	5.49X,Y	1.41	11.32Y	1.77	<0.001*
	Red wine	10	4.29X	1.38	8.68X,Y	0.77	20.02Y	1.92	<0.001*
	Green tea	10	1.72X	0.71	2.34X,Y	0.63	13.62Y	0.66	<0.001*

FO-BF = Filtek One Bulk Fill, TNC-BF = Tetric N-Ceram Bulk Fill, IQR = interquartile range.

*Based on Friedman’s test (P < 0.05), significant differences; X and Y: different letters in the same row indicated significant differences (P < 0.05) based on Bonferroni post hoc

DISCUSSION

The present study evaluated the in vitro color variation of two bulk fill resins, immersed in different pigmenting beverages. The results showed that FO-BF and TNC-BF presented significant differences in color stability when immersed in coke, coffee, red wine, and green tea at 3, 12, and 24 h. In addition, significant changes in color variation were observed between 3 and 12 h of immersion. Therefore, the two null hypotheses formulated were rejected.

The findings obtained in the present study showed that FO-BF and TNC-BF had greater color change when immersed in red wine at all immersion times. These findings may be due to the presence of flavonols, also known as tannins,[16,23,24,25] which during oxidation are converted to theaflavins and thearubigins. These chemical elements give red wine its distinctive dark hue and powerful flavor.[16,24,25] It is worth mentioning that TNC-BF was also affected by coffee, as it is a beverage that also contains flavonols,[16,24,25] so a color change was also expected in FO-BF. However, this was not affected during the first 3 h, which was discrepant with Serin-Kalay[15], Şişmanoğlu and Sengez[26], and Bahbishi et al.[27] These discrepancies could be due to methodological differences, as they used prolonged exposure times such as 7 days,[15] 30 days,[26] and up to 90 days.[27]

It has been reported that color variation is related to water absorption and hygroscopic expansion in the resin composite network, causing alteration of the filler/matrix combination.[15,28] Furthermore, Backes et al.[29] reported that water also functions as a vehicle for pigment penetration into the resin composite matrix. Therefore, a higher amount of resin matrix, especially one containing more hydrophilic monomers, promotes greater water sorption.[15,29,30,31]

Of the resin composites studied, TNC-BF features bisphenol glycidyl methacrylate and urethane dimethacrylate (UDMA) which are highly hydrophilic[26,32,33]; this has a direct impact on the color change of this resin. While FO-BF presents co-monomers such as aromatic UDMA that have different degrees of affinity for water.[32] In addition, FO-BF has higher inorganic filler content (76.5 wt%; 58.4 vol%) compared to TNC-BF (76% wt%; 54 vol%).[3] The higher volume of inorganic filler provides a more water-inert structure and better surface protection against the environment, and a coupling between the filler and the matrix, that is, more resistant to hydrolysis.[15] This also favored FO-BF and made it resistant to color change for the first 3 h; however, at 12 h both composites were affected by red wine and coffee, showing that both beverages produced an unacceptable medium-term color change (ΔE > 3.3).

At 24 h, all beverages had a clinically unacceptable effect (ΔE > 3.3) on the resin composites FO-BF and TNC-BF. However, it was surprising to find that red wine and green tea had the greatest effect on resin composites compared to coffee and coke. It is worth mentioning that green tea also has tannins that condense and are soluble in water, which causes the resin composite to darken. By absorbing water, the bond between the matrix and the filler is damaged generating microcracks through which the tannin penetrates into the resin and causes the color change.[33] Furthermore, Patil et al.[34] stated that the coloring effect of herbal infusions such as green tea increases with time, which could explain the greater color change at 24 h compared to coffee.

The acidic nature of coke (pH = 2.40) and green tea (pH = 2.93) suggests a greater potential for surface degradation of resin composite compared to coffee (pH = 5.45) and red wine (pH = 3.82), as the consumption of acidic beverages has been reported to produce greater alteration of physical and aesthetic properties.[26,35,36] However, according to the findings obtained, the presence of compounds such as tannins would also be associated with significant color change.

Of the beverages studied, red wine, coffee, and coke are the beverages that have been extensively studied regarding the color change they produce in composite resins. However, due to changing lifestyles and the increased availability of alternative over-the-counter herbal supplements,[34] green tea was also included in this research, as it is marketed and consumed worldwide.[37,38] The commonality of the beverages considered in this study is that they have an acidic pH, so it is still important to investigate their effects, as acidic solutions not only affect composite resins superficially but also internally due to the breakdown of filler particles as a result of chemical interaction with the organic matrix.[26]

The present study highlights the importance of resin composition as a crucial factor that clinicians must consider when selecting restorative materials. Color stability can vary over time, contingent on the patient’s habits. This has the potential to compromise the longevity and clinical success of the restoration. Therefore, it is incumbent on the clinician to consider the aforementioned factors when making decisions so that personalized and efficacious treatments can be provided over an extended time.

As a strength of this study, shade A2 was used in FO-BF resin composite and its equivalent shade in TNC-BF, because it is one of the most commonly used shades in clinical practice. In addition, the CIE L*a*b* system was used in the present study, as it has been widely used as an objective modality to evaluate the colorimetric properties of resin composites.[16,26] Another strength was that the Sof-Lex Disc polishing system was applied, as it has been reported to generate the lowest surface roughness with respect to other commonly used systems.[3,14] The decision to evaluate color changes of bulk-filling resins at 3, 12, and 24 h was made because these times simulate the initial exposures a resin may have in the mouth after placement. Therefore, this study aimed to evaluate the impact of immediate or rapid staining changes on the esthetic perception of the restoration in short-term. This evaluation is intended to guide postoperative recommendations to the patient, for example, avoidance of certain beverages shortly after placement of the resin composites used in this study. In addition, a comparison of these early-stage bulk fill resins may reveal substantial disparities in short-term pigmented beverage resistance that may not be discernible in long-term studies (extending over days or weeks).

Among the limitations, being an in vitro study, it was impossible to simulate the dynamic changes in pH caused by diet and saliva. Hence, the color change in vitro is greater than in the clinical setting since saliva has a protective and diluting effect in the oral cavity and prevents teeth staining and dental restorations.[32] Furthermore, sample handling, time before measurement, exposure to light, washing and drying of the samples, and procedures typical of an in vitro environment can influence color changes. In addition, the samples had flat surfaces, whereas resin composite restorations in the oral environment have irregular, convex, or concave surfaces.[27] In this study, the samples were immersed in static staining solutions, unlike in the oral cavity, where the solutions are in a dynamic state. Finally, factors such as thermal alterations or abrasion were not simulated; in this study, so it is suggested to include these variables in future studies. Furthermore, it is recommended that the resin composites color stability be analyzed, considering different polishing systems. Likewise, continuity to the research line of this study is recommended to evaluate the effects of these pigmenting beverages on their mechanical properties, such as surface roughness and microhardness, in the medium- and long-term immersion.

CONCLUSION

Red wine consistently induced the most significant discoloration in FO-BF and TNC-BF resin composites, while coffee discolored the TNC-BF resin composite after 3 h. Both resin composites showed less color change with coke at 24 h of immersion, with clinically acceptable values observed with coke and green tea up to 12 h of immersion. All beverages caused significant discoloration in both bulk fill resins after 24 h of immersion. These results highlight the critical role of beverage type and duration of exposure on the esthetics of bulk fill resin composites, emphasizing the need for patient counseling on pigment beverages and further clinical validation of material performance.

ACKNOWLEDGEMENT

We thank the “Grupo de Investigación Salud Estomatológica” (GISE) of the School of Stomatology of the UPSJB, Peru, for their constant support in the preparation of this manuscript.

CONFLICTS OF INTEREST

There are no conflicts of interest.

AUTHORS CONTRIBUTIONS

They conceived the research idea (CLR, CCR), elaborated the manuscript (CLR, JHE, RTV, EYB, LCR, MAV, and CCR), collected, tabulated the information (CLR and CCR), carried out the bibliographic search (CLR, LCR, and CCR), interpreted the statistical results (CCR and JHE), helped in the development of the discussion (CLR, LCR, and CCR), performed the critical review of the manuscript (CCR, JHE, and MAV). All authors approved the final version of the manuscript.

ETHICAL POLICY AND INSTITUTIONAL REVIEW BOARD STATEMENT

This study was approved by an institutional research ethics committee by letter No. 480-2022-CIEI-UPSJB.

PATIENT DECLARATION OF CONSENT

Not applicable.

DATA AVAILABILITY STATEMENT

The data that support the study results are available from the author (Dr. César Cayo-Rojas, e-mail: cesarcayorojas@gmail.com) on request.

Funding Statement

Nil.