Comparison of Color Stability Between Single-Layer Bulk-Fill Composites and Bilayer Conventional and Bulk-Fill Composites

Article information

J Korean Acad Pediatr Dent. 2025;52(3):266-276

Publication date (electronic) : 2025 August 22

doi : https://doi.org/10.5933/JKAPD.2025.52.3.266

Department of Pediatric Dentistry, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Republic of Korea

Corresponding author: Hong-Keun Hyun Department of Pediatric Dentistry, Dental Research Institute, School of Dentistry, Seoul National University, 101 Daehak-ro, Jongno-gu, Seoul, 03080, Republic of Korea Tel: +82-2-6256-3262 / Fax: +82-2-6256-3266 / E-mail: hege1@snu.ac.kr

Received 2025 March 19; Revised 2025 April 17; Accepted 2025 April 21.

Abstract

This study aimed to evaluate the color stability and translucency of bulk-fill resin-based composites when used alone versus when capped with a conventional composite resin. Three bulk-fill composites (Tetric N-Ceram Bulk Fill, Beautifil-Bulk Restorative, and Filtek One Bulk Fill Restorative) and one conventional composite (Filtek Z250 Universal Restorative) were used. A total of 48 disk-shaped specimens (diameter: 10 mm, thickness: 2 mm) were fabricated using three types of bulkfill composites and one conventional composite resin. In addition, 36 bilayered specimens were prepared by combining 1 mm of each bulk-fill composite with a 1 mm layer of a conventional composite resin on top. Color measurements were conducted using a spectrophotometer, and the specimens were stored in either distilled water or tea for four weeks. Color differences (ΔE*_ab) were calculated based on the Commission Internationale d’Eclairage L*a*b* system, and translucency parameters were determined. While color stability was maintained in distilled water, immersion in tea caused significant discoloration, exceeding both the perceptibility and acceptability thresholds. Tetric N-Ceram Bulk Fill exhibited the highest color stability, followed by Filtek One Bulk Fill Restorative and Beautifil-Bulk Restorative. Bulk-fill composites with a capping layer demonstrated similar or superior color stability to that of uncapped specimens. The translucency of the bulkfill composites was higher than that of the conventional composites, with the bilayer specimens showing intermediate values. Therefore, capping bulk-fill composites with a conventional composite resin may improve long-term color stability while slightly reducing translucency, ultimately enhancing esthetic outcomes in posterior restorations.

Keywords: Bulk-fill composite resin; Color stability; Translucency; Capping layer

Introduction

Bulk-fill resin-based composites have emerged as a modern restorative option for posterior teeth, designed to simplify clinical protocols and enhance procedural efficiency [1]. By reducing polymerization shrinkage and shrinkage stress, bulk-fill composites allow for singlelayer placement with thicknesses of up to 4 – 5 mm, contrasting with the traditional incremental technique, which requires 2 mm layers for adequate polymerization. This contributes to reduced operative time and improved clinician convenience [2].

Regarding low-viscosity bulk-fill composites, the use of a conventional nanohybrid composite as a capping layer is recommended to enhance their mechanical properties [3]. Low-viscosity bulk-fill materials exhibit relatively lower microhardness and wear resistance, which may compromise the longevity of restorations if left uncapped [4]. Recent advancements have led to the development of high-viscosity bulk-fill composites with enhanced mechanical performance, potentially reducing the necessity for an additional capping layer [5]. However, applying a conventional composite as a capping layer is still considered beneficial in clinical situations where restorations are subjected to occlusal stress [6]. Nevertheless, the effect of this bilayer technique on the long-term color stability of bulk-fill composites remains unclear.

Color stability is a critical determinant of the long-term esthetic success of composite restorations, particularly given the growing demand for esthetics by patients, even in posterior regions. The discoloration of composite materials is influenced by both intrinsic and extrinsic factors. The intrinsic factors include the chemical composition of the resin matrix, such as the type and size of the filler particles and the photoinitiator system. Extrinsic factors are associated with the absorption of chromogenic agents from dietary substances, beverages, and environmental exposure [7]. Translucency is also a crucial optical property of resin-based composites that significantly influences the esthetic integration of restorations with natural teeth. Appropriate translucency allows restorations to mimic the light-transmitting characteristics of enamel, achieving a natural appearance [8]. Conversely, high translucency in bulk-fill composites may compromise esthetics by causing a grayish appearance, especially in deep cavities where light transmission is excessive [9].

Previous studies have compared the color stability of conventional composites with those of bulk-fill composites [10-12]. However, limited research exists on the color stability of conventional composites layered over bulkfill composites. Therefore, this study aimed to evaluate and compare the color stability and translucency of bulkfill composites when used independently versus when capped with a conventional composite resin.

The first null hypothesis states that there is no difference in the color stability between specimens made entirely of bulk-fill composites and those composed of a double layer of conventional and bulk-fill composites. The second null hypothesis states that there is no difference in the translucency properties between these two specimen groups.

Materials and Methods

1. Preparation of the specimens

This study evaluated three bulk-fill composite resin products: Tetric N-Ceram Bulk Fill (TN; Ivoclar Vivadent AG, Schaan, Liechtenstein), Beautifill-Bulk Restorative (BF; Shoufu, Kyoto, Japan), and Filtek One Bulk Fill Restorative (FO; 3M ESPE, St. Paul, MN, USA). Additionally, one conventional composite resin, Filtek Z250 Universal Restorative (FZ; 3M ESPE), was included (Table 1). Disk-shaped specimens were fabricated using cylindrical polyvinyl siloxane molds. The specimens were polymerized for 40 seconds under an LED curing unit (Valo, Ultradent, South Jordan, UT, USA) with a 12 mm tip diameter, positioned within 1 mm of each specimen side, at an irradiance of 1000 mW/cm². A total of 48 specimens (diameter: 10 mm, thickness: 2 mm) were fabricated out of three types of bulk-fill composites and one conventional composite resin (n = 12 per material) (Fig. 1A). Another 36 specimens were prepared by layering 1 mm of each bulk-fill resin with 1 mm of the FZ composite (n = 12 per material) (Fig. 1B). The specimens’ diameters and thicknesses were measured to the nearest 0.01 mm using a Vernier caliper. To ensure a flat surface, polymerization was performed through a transparent Mylar strip. The specimens were then stored in distilled water at 37 for 24 hours to complete the polymerization.

Table 1.

Information on the composites according to the manufacturers

Fig 1.

Photographs of the specimens used in this study. (A) 2 mm of each composite material and (B) 1 mm of each bulk-fill resin and 1 mm of conventional composite layered.

2. Colorimetric evaluation

Color measurements were obtained using a spectrophotometer (CM-700d, Konica Minolta, Osaka, Japan) with the specular component excluded. Measurements were taken against both black and white backgrounds, with each specimen measured thrice on the center surface after being washed with distilled water and dried using Kimtech wipers (Yuhan-Kimberly, Kimcheon, Korea). All measurements were performed on the top surface of the specimens. For specimens composed of both bulk-fill and conventional composite layers, the conventional composite layer was considered as the top surface in accordance with clinical application, and measurements were performed on this layer (Fig. 1). The same examiner conducted all procedures at the same location, and the spectrophotometer was zero-calibrated before each measurement.

The mean (SD) Commission Internationale d’Eclairage (CIE) L*a*b* values measured on a white background were 95.3 (0.0), -0.6 (0.0), and 3.2 (0.0), respectively, whereas the corresponding values on a black background were 27.8 (0.0), 0.7 (0.0), and -0.1 (0.0).

3. Staining solution preparation and color measurement

Two storage solutions were prepared: distilled water (DW) and tea (Table 2). The composite resin groups (n = 6 per group) were immersed in each storage solution within sealed plastic containers consisting of 42 compartments. The specimens were stored in a lightblocked, temperature-controlled chamber (1010-B, Mingtu Machinery Equipment, Guangzhou, China) at 37. CIE color measurements were performed 24 hours after specimen preparation and subsequently at intervals of 1 day, 1 week, 2 weeks, 3 weeks, and 4 weeks after immersion in the staining solutions. To prevent bacterial contamination, all solutions were refreshed every 2 days.

Table 2.

Information on the immersion solutions according to the manufacturers

4. Calculation of color differences and translucency parameters

The color difference (ΔE^*_ab ) between measurements taken at different time points and the initial measurement within each group was calculated using the following formula.

ΔEab∗=[(ΔL∗)2+(Δa∗)2+(Δb∗)2]0.5

The calculated color differences were compared with the 50 : 50% perceptibility threshold (PT) of 1.2 and the 50 : 50% acceptability threshold (AT) of 2.7 to assess color stability and quantify the magnitude of change [13]. Additionally, the translucency parameter (TP) for each group was calculated to evaluate the changes in each specimen’ s translucency over time. The formula for calculating the TP over a white (W) and a black (B) background is provided below.

TP=[(L∗W−L∗B)2+(a∗W−a∗B)2+(b∗W−b∗B)2]0.5

5. Statistical analysis

The normal distribution of ΔE^*_ab and TP values was evaluated using the Kolmogorov-Smirnov test. For normally distributed data, the paired t-test was employed for comparisons. For non-normally distributed data, the Wilcoxon signed-rank test was applied. When both normality and homogeneity of variance (as assessed by Levene’s test) were confirmed, analysis of variance was employed to evaluate differences within the groups. Post hoc comparisons were conducted using either Tukey’s or Dunnett’s T3 method, depending on the Levene statistic outcome. For data that did not follow a normal distribution, the Kruskal-Wallis test with Bonferroni correction was used. Statistical analyses were conducted using SPSS Statistics software version 26.0 (IBM, Somers, NY, USA), with a significance level of α = 0.05.

Results

Table 3 presents the CIE L*a*b* values measured for each specimen at various storage times. In the FZ, BF, FZ + TN, and FZ + BF groups, the a* values increased for both storage solutions. While L* and b* values remained stable in DW, the tea solution decreased the L* values and increased the b* values over time. For the TN group, L* and a * values remained stable in DW, whereas b* values increased slightly. In contrast, all three values increased over time when the specimens were immersed in the tea solution. Similarly, in the FO and FZ + FO groups, the CIE values remained stable throughout all measurement periods in DW but increased when stored in the tea solution.

Table 3.

Mean (standard deviation) CIE values of specimens with different immersion media over time measured on a white background

The mean TP values measured during the experimental period are shown in Table 4. Among the composite materials, TN exhibited the highest TP value, followed by BF and FO, whereas FZ exhibited the lowest translucency. The bulk-fill composites showed higher TP values than the conventional and bilayer composites. Overall, the TP values of all experimental groups were relatively low, whereas the SD was relatively high in the tea solution.

Table 4.

Translucency parameter of the specimens in different storage solutions during the experimental period

Fig. 2 presents a graph illustrating the changes in CIE values over time for each group. When stored in DW, all groups remained stable. In contrast, when stored in tea, ΔE_ab gradually increased over time. Among all groups, BF exhibited the highest color difference on day 29, whereas FZ + FO exhibited the lowest color difference.

Fig 2.

Mean ΔE^*_ab color differences at each time point under different storage solutions. (A) distilled water and (B) tea. Values with the same lowercase letter are not significantly different. Vertical bars are the standard deviation.

FZ: Filtek Z250 A1 shade; TN: Tetric N Ceram Bulk Fil IVA shade (universal A shade); BF: Beautifil Bulk Restorative A shade; FO: Filtek one bulk Fil Restorative A1; PT: perceptibility threshold; AT: acceptability threshold.

Discussion

The first null hypothesis, stating that there is no difference in color stability between bulk-fill composite specimens and bilayer specimens composed of conventional and bulk-fill composites, was rejected.

The bilayer specimens demonstrated similar or higher color stability than the single-layer bulk-fill composites when stored in tea solution, unlike when stored in DW. Color stability is crucial for the clinical success of resin composites, as discoloration can arise from both external and internal factors [14]. External factors include exposure to ultraviolet light, temperature fluctuations, water absorption, and the uptake of staining agents from various foods and beverages [7]. Previous studies have shown that composite resins are particularly susceptible to color instability when exposed to staining media such as red wine, coffee, cola, and tea [15-17]. In this study, the degree of color changes in resin composites stored in DW and tea was evaluated. The polarity of the yellow pigments in tea plays a crucial role in resin composite discoloration. More hydrophilic composites, or those with higher water sorption rates, tend to absorb larger quantities of tea pigments, resulting in increased staining. This discoloration results from a combination of water sorption, pigment diffusion, and the mildly acidic nature of the staining solution [15,18]. Consistent with previous findings, composites immersed in tea exhibited significantly greater discoloration than those stored in DW [12,17].

Internally, the composite material’s composition plays a significant role in discoloration. Variations in the resin matrix composition, filler types, and photoinitiator systems contribute to the differences observed in discoloration among resin composites [19]. Composites with hydrophilic resin matrices tend to absorb more water, thereby facilitating pigment uptake and resulting in more pronounced staining [20]. Previous studies have reported that bisphenol glycidyl dimethacrylate (Bis-GMA)-based composites, when combined with triethylene glycol dimethacrylate (TEGDMA), exhibit higher water absorption, making them more susceptible to discoloration [21]. In contrast, composites containing urethane dimethacrylate (UDMA) tend to demonstrate improved color stability [22]. Additionally, ethoxylated bisphenol A dimethacrylate (Bis-EMA), a highly hydro-phobic monomer, has been shown to enhance color stability in composites [23,24].

Consistent with previous findings, this study demonstrated that BF, containing Bis-GMA and TEGDMA, exhibited the highest degree of discoloration, followed by FO, which incorporated a UDMA-based matrix. Conversely, FZ and TN, both containing Bis-EMA, demonstrated the highest color stability. Bilayer composites capped with conventional composites showed discoloration comparable to that of the underlying bulk-fill material but exhibited less discoloration than single-layer bulk-fill composites. This reduction in discoloration may be attributed to the visual influence of the conventional composite layer placed on the surface, which helps to conceal color changes originating from the discolored bulk-fill resin underneath. Previous studies have shown that placing a composite layer with higher color stability over a discolored substrate can significantly reduce visible color changes in restorations [25,26]. In addition, the optical properties of conventional composites, such as their lower translucency, further contribute to minimizing the impact of internal discoloration on the final appearance [27,28].

The choice and concentration of photoinitiators are also crucial factors influencing color stability. Composites using camphorquinone (CQ) as the sole photoinitiator may undergo yellowing over time due to the presence of chromophores in CQ [29]. Therefore, some composites incorporate alternative photoinitiators, such as Ivocerin and Lucirin TPO, alongside CQ. This polymerization mechanism introduces structural differences that contribute to a more efficient curing process and enhance color stability by reducing the reliance on CQ [30]. In this study, FZ, FO, and BF utilized a CQ-only photoinitiator system, whereas TN integrated Ivocerin and Lucirin TPO. Consistent with previous findings, TN demonstrated relatively superior color stability due to the higher polymerization efficiency achieved with the combination of TPO and CQ, along with a reduced CQ content.

The second null hypothesis, stating that there is no difference in the translucency properties between bulkfill composites and bilayered conventional and bulkfill composites, was also rejected. Bulk-fill composites generally require higher translucency to allow deeper light penetration and ensure proper polymerization even in thicker layers. Previous studies reported that lowviscosity bulk-fill resins exhibit higher TP values than high-viscosity composites due to their lower inorganic filler content and higher proportion of the organic resin matrix [3,31,32]. Consistent with the existing literature, this study showed that BF, FO, and TN have higher TP values than FZ and bilayer composites.

The variation in translucency among these composites is influenced by their composition. For example, the S-PRG filler used in BF, with its tri-laminar structure, restricts light transmission [33]. FO contains zirconia/silica fillers that partially replace particulate glass fillers, enhancing mechanical resistance but decreasing light transmittance due to zirconia’s high refractive index, which may have contributed to FO’s decreased translucency [33-35]. A previous study also reported that TN exhibited the highest TP values, likely due to the presence of ytterbium trifluoride, consistent with this present study’s findings [36].

Although low translucency does not always guarantee better esthetics, the relatively high translucency of bulkfill composites compared to conventional composites may lead to a greyish appearance, especially in deep cavities [9]. Translucent materials can transmit or reflect the color of surrounding structures, potentially altering the final shade of the restoration [37]. In this study, the use of a conventional composite as a capping layer reduced the overall translucency. Consistent with these findings, previous studies have suggested that placing a less translucent composite over bulk-fill layers can compensate for light absorption and minimize undesirable color shifts [9].

With increasing patient demand for esthetic restorations, even in posterior teeth, clinicians should consider applying a conventional composite as a capping layer over bulk-fill composites to reduce long-term discoloration. The selection of bulk-fill composites should take into account formulation differences, as materials vary in both color stability and translucency. Although higher translucency enhances curing depth and natural appearance, excessive translucency may also make discoloration more noticeable. Therefore, achieving a balance between translucency and color stability is essential for long-term esthetic success.

Given that this was an in vitro study, the findings may not fully replicate intraoral conditions in which additional factors such as salivary flow, enzymatic activity, and mechanical wear can affect the color stability of the resin composites. Moreover, in clinical situations, only the occlusal or external surface is directly exposed to the oral environment and staining agents. However, in this study, all surfaces of the specimens were immersed and equally exposed to potential discoloring agents. As a result of this difference, the degree of discoloration observed in this study may not accurately reflect that which occurs in actual clinical conditions. Future clinical studies are necessary to validate these findings and evaluate the long-term esthetic performance of bulk-fill composites under real-world conditions.

Conclusion

Within the limits of this in vitro study, the color stability of all composites was maintained when stored in distilled water. In contrast, all color changes observed in the tea solution over time exceeded the AT and PT values. Among the bulk-fill composites studied, TN exhibited the highest color stability, followed by FO and BF. The bulkfill composites capped with conventional composites demonstrated similar or higher color stability than that of bulk-fill composites alone. Regarding the TP values, those of the bulk-fill composites exhibited were higher than those of the conventional composites, whereas the bilayer composites showed intermediate values. From an esthetic perspective, using bulk-fill composites capped with conventional composites may help minimize longterm color changes, thereby improving the overall durability of the restoration’s appearance.

Notes

Conflicts of Interest

The authors have no potential conflicts of interest to disclose.

CRediT Authorship Contribution Statement

Hyunduk Kim: Writing – original draft preparation, Investigation, Visualization, Data curation. Hyuntae Kim: Methodology, Validation. Ji-Soo Song: Data curation, Validation. Mohammad AlQarni: Visualization. Mohammad Alkeshan: Visualization. Teo Jeon Shin: Formal analysis, Methodology. Young-Jae Kim: Resources, Supervision. Jung-Wook Kim: Resources, Supervision. Ki-Taeg Jang: Resources, Supervision. Hong-Keun Hyun: Conceptualization, Supervision, Project administration, Writing – review and editing.

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Code	Composite	Organic matrix	Filler	Shade	Lot number
FZ	Filtek Z250 Universal Restorative (3M ESPE, St. Paul, MN, USA)	Bis-GMA, UDMA, Bis-EMA	60% by volume.	A1	10351963
Modified zirconia/silica.
Particle size of 0.01 to 3.5 microns
TN	Tetric N-Ceram Bulk Fill (Ivoclar Vivadent AG, Schaan, Liechtenstein)	Bis-GMA, UDMA, Bis-EMA	53-55% by volume.	IVA	Z04WC6
Barium glass, prepolymer, ytterbium trifluoride, mixed oxide.
Particle size of 0.04 to 3 microns
BF	Beautifil-Bulk Restorative (Shofu, Kyoto, Japan)	Bis-GMA, UDMA, Bis-MPEPP, TEGDMA	74% by volume.	Universal A	122266
S-PRG filler based on fluoro-boraluminosilicate glass
FO	Filtek One Bulk Fill Restorative (3M ESPE, St. Paul, MN, USA)	AUDMA, AFM, diurethane-DMA, 1,12-dodecane-DMA	58.5% by volume.	A1	NE86675
Combination of a non-aggregated 20 nm silica filler, a non-aggregated 4 to 11 nm zirconia filler, an aggregated zirconia/silica cluster filler.
Average cluster particle size of 0.6 to 20 microns (silica: 20 nm, zirconia: 4 to 11 nm), and a ytterbium trifluoride filler consisting of agglomerate 100 nm particles

	Brand name	Manufacturer	Composition
Tea	17 Cha	Namyang, Cheonan, Korea	White mulberry leaves, Safflower seeds, Green tea, Cormus fruits, Buck wheat, Solomon’s seal, Semen cassia, Chinese wolf berries, Job’s tears, Bitter orange Peels, Ganoderma lucidum karst, Chicory, Barley, Phellinus linteus, Corn, Brown rice, Inonotus obliquus

Table 3.

Mean (standard deviation) CIE values of specimens with different immersion media over time measured on a white background

Group	Storage Time
FZ	Day 0	Day 1	Day 8	Day 15	Day 22	Day 29
L *
DW	69.0 (0.8) Aa	68.7 (0.6) Aa	68.7 (0.7) Aa	68.8 (0.6) Aa	68.8 (0.5) Aa	68.6 (0.6) Aa
Tea	69.0 (0.7) Aa	66.7 (1.0) Ba	65.3 (1.6) Bab	64.7 (0.7) Bbc	63.5 (1.0) Bc	63.1 (1.0) Bd
a *
DW	1.3 (0.1) Aa	1.3 (0.1) Aa	1.3 (0.1) Aa	1.5 (0.1) Aab	1.5 (0.2) Aab	1.6 (0.2) Ab
Tea	1.4 (0.2) Aa	1.6 (0.2) Aab	2.1 (0.4) Bbc	2.3 (0.5) Bc	2.4 (0.2) Bc	2.5 (0.3) Bc
b *
DW	12.8 (0.9) Aa	12.9 (0.8) Aa	12.9 (0.7) Aa	13.1 (0.8) Aa	13.1 (0.6) Aa	13.2 (0.7) Aa
Tea	12.6 (0.3) Aa	12.8 (0.3) Aa	13.0 (0.5) Aab	13.5 (0.8) Aab	14.1 (1.1) Abc	14.8 (1.0) Bc
TN	Day 0	Day 1	Day 8	Day 15	Day 22	Day 29
L *
DW	70.1 (0.7) Aa	69.3 (0.5) Aa	69.6 (0.5) Aa	69.7 (0.5) Aa	69.6 (0.4) Aa	69.1 (0.6) Aa
Tea	70.2 (1.1) Aa	68.9 (0.7) Ab	68.6 (0.7) Bb	66.9 (0.8) Bc	65.3 (0.7) Bd	64.2 (0.8) Be
a *
DW	1.7 (0.2) Aa	1.7 (0.1) Aa	1.7 (0.1) Aa	1.8 (0.2) Aa	2.0 (0.1) Aa	1.9 (0.1) Aa
Tea	1.6 (0.1) Aa	2.6 (0.2) Bb	2.7 (0.7) Bb	3.3 (0.3) Bc	4.0 (0.1) Bd	4.5 (0.2) Be
b *
DW	14.1 (0.7) Aa	15.0 (0.9) Ab	15.0 (0.6) ABb	15.5 (0.5) Ab	15.5 (0.8) Ab	15.5 (0.5) Ab
Tea	13.9 (1.0) Aa	15.1 (0.5) Ab	14.4 (0.4) Aab	14.7 (0.4) Bab	14.8 (0.1) Aab	16.0 (0.7) Ac
BF	Day 0	Day 1	Day 8	Day 15	Day 22	Day 29
L *
DW	72.4 (0.4) Aa	72.2 (0.5) Aa	72.2 (0.5) Aa	71.9 (0.6) Aa	71.8 (0.7) Aa	71.5 (0.8) Aa
Tea	71.8 (1.1) Aa	68.2 (1.3) Bb	67.3 (0.4) Bb	64.4 (1.1) Bc	62.0 (1.4) Bd	60.1 (1.1) Be
a *
DW	1.6 (0.1) Aa	1.6 (0.1) Aa	1.7 (0.2) Aa	1.8 (0.2) Aab	2.0 (0.1) Ab	2.0 (0.1) Ab
Tea	1.7 (0.1) Aa	2.9 (0.2) Bb	3.5 (0.4) Bb	5.7 (0.3) Cc	6.4 (0.6) Ccd	7.1 (1.1) Cd
b *
DW	9.9 (0.8) Aa	9.9 (0.7) Aa	9.6 (0.8) Aa	10.1 (0.8) Aa	10.3 (0.7) Aa	10.3 (0.8) Aa
Tea	9.3 (0.7) Aa	13.0 (0.6) Bb	17.1 (0.7) Cc	19.4 (1.3) Bd	19.7 (1.2) Cd	19.9 (0.7) Cd
FO	Day 0	Day 1	Day 8	Day 15	Day 22	Day 29
L *
DW	68.5 (0.7) Aa	68.2 (1.0) Aa	68.0 (0.9) Aa	68.1 (0.9) Aa	68.1 (0.8) Aa	67.9 (1.1) Aa
Tea	70.4 (0.4) Ba	67.1 (0.8) Ab	66.1 (0.6) Bb	62.9 (0.6) Bc	59.9 (0.8) Bd	58.7 (0.8) Be
a *
DW	3.3 (0.1) Aa	3.3 (0.1) Aa	3.2 (0.9) Aa	3.3 (0.2) Aa	3.3 (0.2) Aa	3.3 (0.1) Aa
Tea	3.5 (0.2) Aa	4.1 (0.2) Bab	4.4 (0.6) Bb	5.6 (0.5) Bc	6.1 (0.5) Ccd	6.6 (0.4) Cd
b *
DW	15.2 (0.6) Aa	15.0 (0.4) Aa	14.8 (0.5) Aa	14.7 (0.4) Aa	14.4 (0.5) Aa	14.3 (0.4) Aa
Tea	14.6 (0.3) Aa	15.6 (0.7) Ab	15.6 (0.5) Ab	16.8 (1.0) Bc	18.0 (0.4) Bd	18.5 (0.5) Bd
FZ + TN	Day 0	Day 1	Day 8	Day 15	Day 22	Day 29
L *
DW	69.5 (0.6) Aa	69.0 (1.5) Aa	69.3 (1.0) Aa	69.5 (1.2) Aa	69.2 (0.7) Aa	69.1 (0.7) Aa
Tea	69.1 (0.7) Aa	66.9 (0.6) Bb	66.1 (0.7) Bb	64.8 (1.3) Bc	63.4 (0.6) Bd	62.3 (1.6) Bd
a *
DW	1.5 (0.2) Aab	1.3 (0.2) Aa	1.4 (0.2) Aab	1.5 (0.1) Aab	1.6 (0.1) Ab	1.6 (0.1) Ab
Tea	1.5 (0.1) Aa	1.6 (0.1) Aa	2.3 (0.3) Bb	2.7 (0.3) Bb	3.4 (0.5) Bc	4.0 (0.5) Bc
b *
DW	11.3 (0.5) Aa	11.1 (0.8) Aa	10.4 (1.7) Aa	10.3 (2.2) Aa	10.3 (2.1) Aa	11.4 (0.6) Aa
Tea	11.7 (0.6) Aa	12.1 (0.6) Bab	12.8 (0.8) Bb	12.9 (0.8) Bb	14.0 (0.8) Bc	14.5 (0.8) Bc
FZ + BF	Day 0	Day 1	Day 8	Day 15	Day 22	Day 29
L *
DW	69.7 (1.2) Aa	69.7 (1.1) Aa	69.2 (1.2) Aa	68.9 (1.3) Aa	69.2 (1.6) Aa	69.2 (1.4) Aa
Tea	69.7 (0.8) Aa	67.5 (1.0) Bb	66.7 (1.1) Bbc	65.3 (0.5) Bc	63.6 (0.9) Bd	62.8 (0.9) Bd
a *
DW	1.3 (0.1) Aa	1.3 (0.1) Aa	1.4 (0.0) Aab	1.4 (0.1) Aab	1.6 (0.2) Ab	1.5 (0.1) Aab
Tea	1.4 (0.3) Aa	2.1 (0.5) Bab	2.5 (0.3) Bbc	3.0 (0.3) Bc	3.9 (0.6) Bd	4.4 (0.7) Bd
b *
DW	11.1 (0.6) Aa	11.2 (0.6) Aa	11.3 (0.3) Aa	11.3 (0.5) Aa	11.5 (0.5) Aa	11.4 (0.5) Aa
Tea	10.3 (0.6) Aa	14.0 (0.7) Bb	15.6 (0.8) Bc	16.4 (0.5) Bcd	17.6 (0.9) Bd	20.7 (0.9) Be
FZ + FO	Day 0	Day 1	Day 8	Day 15	Day 22	Day 29
L *
DW	69.1 (1.0) Aa	68.6 (1.1) Aa	68.7 (1.0) Aa	68.5 (1.0) Aa	68.7 (0.9) Aa	68.7 (1.0) Aa
Tea	67.4 (0.9) Ba	65.1 (1.2) Bb	65.7 (1.0) Bb	65.3 (1.1) Bb	64.4 (1.0) Bb	62.9 (1.1) Bc
a *
DW	2.3 (0.2) Aa	2.1 (0.2) Aa	2.1 (0.1) Aa	2.3 (0.3) Aa	2.3 (0.1) Aa	2.3 (0.1) Aa
Tea	2.4 (0.3) Aa	2.6 (0.3) Bab	2.9 (0.2) Bb	3.4 (0.3) Bc	3.5 (0.3) Bcd	3.9 (0.4) Bd
b *
DW	12.2 (0.5) Aa	12.2 (0.6) Aa	12.1 (0.6) Aa	12.7 (0.5) Aa	12.4 (0.7) Aa	12.5 (0.7) Aa
Tea	12.1 (0.9) Aa	13.0 (1.6) ABa	11.8 (0.5) Aa	12.2 (0.4) Aa	12.7 (0.6) Aa	13.7 (1.0) Ba

FZ: Filtek Z250 A1 shade; TN: Tetric N Ceram Bulk Fil IVA shade (universal A shade); BF: Beautifil Bulk Restorative A shade; FO: Filtek one bulk Fil Restorative A1; DW: Distilled water.

Different letters indicate significant differences among groups. Uppercase letters are used when comparing within columns, and lowercase letters when comparing within rows.

Mean (SD) of CIE L*, a*, and b* measured on a white background was 95.3 (0.0), -0.6 (0.0), and 3.2 (0.0), respectively.

	Brand name	Manufacturer	Composition
Distilled water	Joysoo purified water	Joylife, Gimhye, Korea	Purified water
Tea	17 Cha	Namyang, Cheonan, Korea	White mulberry leaves, Safflower seeds, Green tea, Cormus fruits, Buck wheat, Solomon’s seal, Semen cassia, Chinese wolf berries, Job’s tears, Bitter orange Peels, Ganoderma lucidum karst, Chicory, Barley, Phellinus linteus, Corn, Brown rice, Inonotus obliquus

	Mean	SD	CV	95% CI
FZ
DW	9.1	0.1	0.01	9.0-9.2
Tea	7.5	1.4	0.19	6.3-8.6
TN
DW	14.9	0.5	0.04	14.5-15.4
Tea	14.7	1.6	0.11	13.4-15.9
BF
DW	13.4	0.1	0.01	13.3-13.5
Tea	11.2	1.9	0.17	9.7-12.7
FO
DW	11.8	0.2	0.02	11.6-11.9
Tea	10.1	1.8	0.18	8.6-11.5
FZ + TN
DW	10.5	0.4	0.04	10.2-10.8
Tea	9.8	1.0	0.10	9.0-10.6
FZ + BF
DW	9.9	0.3	0.03	9.7-10.2
Tea	9.6	1.8	0.19	8.2-11.1
FZ + FO
DW	9.7	0.3	0.03	9.5-10.0
Tea	8.6	1.4	0.16	7.4-9.7