In Vitro Evaluation of Oral Irrigator–Assisted Mouthrinse Application on Color Stability of Single-Shade Nanohybrid Resin Composites

Summary

This protocol describes an in vitro method to evaluate how different mouthrinse formulations and application methods influence the color stability of single-shade nanohybrid resin composites, demonstrating measurable differences between treatment conditions.

Abstract

Color stability is a key determinant of the long-term esthetic performance of resin-based restorative materials. Single-shade nanohybrid resin composites, developed to simplify shade selection, remain susceptible to extrinsic discoloration and routine oral hygiene procedures. This study aimed to evaluate color stability following coffee staining and subsequent use of different mouthrinse formulations applied with or without an oral irrigator. Disc-shaped specimens were fabricated, stained with coffee, and subjected to mouthrinses using either static immersion or oral irrigator–assisted delivery. Color measurements were obtained at baseline, after staining, and after mouthrinse application, and color changes (ΔE₀₀) were calculated for discoloration after coffee staining (ΔE₁), color change after mouthrinse application (ΔE₂), and total color change (ΔE₃) using the CIEDE2000 formula. Statistical analysis was performed using robust three-way ANOVA with trimmed means. Surface morphology was additionally evaluated using environmental scanning electron microscopy. The results demonstrated that coffee staining resulted in a clinically unacceptable color change in all groups (ΔE₀₀ > 0.8). Composite type significantly influenced color change after coffee staining (ΔE₁) and total color change (ΔE₃) (p < 0.001). Mouthrinse type significantly affected color change after mouthrinse application and total color change (ΔE₂ and ΔE₃) (p = 0.001). Application method significantly affected total color change (ΔE₃) (p < 0.001). Subgroup analysis revealed that within the Charisma Diamond One composite (DO), ΔE₃ values were significantly higher in the oral irrigator group compared to direct immersion (p = 0.001), and within the irrigator group, the DO composite exhibited significantly higher ΔE₃ values than the Vittra APS Unique composite (p = 0.001). These findings demonstrate that composite formulation and mouthrinse application method significantly influence post-staining color stability, with oral irrigator use exacerbating discoloration in certain materials. Clinically, this suggests that restorative material selection and oral hygiene practices should be carefully considered to minimize esthetic degradation.

Introduction

The demand for highly esthetic restorative materials has led to the development of resin composites designed to mimic the optical properties of natural dental tissues. Among these, single-shade nanohybrid resin composites have gained increasing attention due to their chameleon-like blending ability, simplified shade selection, and reduced clinical complexity^1,2,3. Despite these advantages, their long-term esthetic performance remains strongly dependent on resistance to extrinsic discoloration caused by dietary chromogens and routine oral hygiene practices⁴.

Extrinsic staining is a well-recognized challenge for these materials, and coffee is one of the most commonly used staining agents in laboratory investigations. Its concentrated yellow-brown pigments readily penetrate the resin matrix and filler–matrix interface, resulting in clinically perceptible color changes (ΔE₀₀ ≈ 0.8)^5,6,7,8,9. Previous in vitro studies have demonstrated that coffee-induced staining frequently exceeds established acceptability thresholds (ΔE₀₀ ≈ 1.8)⁹, emphasizing the need for standardized protocols to evaluate optical stability under simulated oral conditions¹⁰. In addition, studies incorporating aging protocols such as thermocycling and simulated tooth brushing have shown that combined chemical, mechanical, and environmental factors can significantly influence staining response, highlighting the importance of comprehensive evaluation models that better simulate oral conditions^11,12,13.

Routine oral hygiene products, including toothpastes and mouth rinses, may also influence optical performance and surface characteristics. Mouthrinses are widely incorporated into daily oral care regimens, and their chemical constituents—including alcohol, detergents, oxidizing agents, and fluoride—have been reported to interact with resin-based materials, potentially affecting optical and surface properties. Variations in formulation have also been shown to influence the color-alteration patterns of previously stained materials ^14,15,16.

Conventional in vitro evaluations of composite discoloration have primarily relied on static immersion models, which offer simplicity and reproducibility but fail to replicate the dynamic conditions encountered during clinical use¹⁷. Previous studies have focused on the effects of staining agents, mouthrinse composition, and aging protocols on optical stability, largely under static conditions. However, these approaches do not account for the hydrodynamic forces and pressure variations generated by adjunctive oral irrigators, which may influence fluid–material interactions and alter discoloration behavior^18,19,20.

To date, the effect of different mouthrinse application methods—particularly oral irrigator–assisted delivery—on optical stability has not been systematically investigated. Therefore, the present study directly compares static immersion and oral irrigator–assisted mouthrinse application to evaluate their effects on discoloration behavior in single-shade nanohybrid resin composites. The novelty of this study lies in the incorporation of a standardized oral irrigator model to simulate dynamic fluid application conditions. It was hypothesized that composite type, mouthrinse formulation, and application method would not result in significant differences in color stability.

Protocol

This study was conducted at the Department of Restorative Dentistry, Faculty of Dentistry, Marmara University, Istanbul, Turkey. No human or animal subjects were involved; therefore, institutional ethical approval was not required. The reagents and equipment used in this study are listed in the Table of Materials. Figure 1 illustrates the experimental workflow used in this study. Specimen preparation was first performed to fabricate disc-shaped composite samples (8 mm × 2 mm). Baseline color measurements were then obtained prior to staining. All specimens were subsequently immersed in a coffee solution for 12 days to induce discoloration, followed by post-staining color measurements. After staining, the specimens were divided into experimental groups, in which five different solutions (including distilled water [DW] as a control) were applied either using an oral irrigator or by direct immersion for an equivalent simulated clinical duration. Finally, color measurements were performed after treatment to evaluate overall color change.

Figure 1: Experimental workflow for color stability evaluation. Flow diagram illustrating the experimental procedure, including specimen preparation, baseline color measurement (T₀), coffee staining (12 days), post-staining color measurement (T₁), and mouthrinse application using either static immersion or oral irrigator–assisted delivery. Final color measurements (T₂) were obtained to calculate color changes (ΔE₁, ΔE₂, and ΔE₃). Please click here to view a larger version of this figure.

Specimen Preparation

Two nanohybrid, single-shade resin composites were used in this study: Charisma Diamond One (DO) and Vittra APS Unique (VU). The material specifications are presented in Table 1.

Resin Composite	Manufacturer	Type	Resin Matrix	Filler Composition / Size	Filler Content (wt% / vol%)	Lot Number
Charisma Diamond One (DO)	Kulzer, Germany	Nanohybrid	UDMA; TCD-DI-HEA; TEGDMA	B₂O₃–F–Al₂O₃–SiO₂; silica; TiO₂; fluorescent and metallic oxides; organic pigments (5–20 µm)	81 / 64	N010209
Vittra APS Unique (VU)	FGM, Brazil	Nanohybrid	UDMA; TEGDMA	Zirconia and silica fillers (200 nm)	82 / 72	230921

Table 1: Composition and properties of the resin composites used in this study. Material type, manufacturer, resin matrix composition, filler characteristics, filler content (wt% / vol%), and lot numbers of the single-shade nanohybrid resin composites evaluated. Abbreviations: UDMA = urethane dimethacrylate; TEGDMA = triethylene glycol dimethacrylate; TCD-DI-HEA = tricyclodecane dimethanol diacrylate; TiO₂ = titanium dioxide; YbF₃ = ytterbium trifluoride; B₂O₃–F–Al₂O₃–SiO₂ = boro-fluoro-aluminosilicate.

Disc-shaped specimens (8 mm in diameter and 2 mm in thickness) were fabricated using standardized prefabricated silicone molds. The resin composite was inserted into the mold in a single increment using a flat-ended plastic filling instrument and adapted against the mold walls to ensure complete filling and minimize void formation. Transparent polyester strips were placed on both the top and bottom surfaces, and the material was pressed between glass plates (cement glass) to obtain flat and smooth surfaces and ensure standardized thickness. The final thickness of each specimen was measured using a digital caliper (accuracy: ±0.01 mm), and specimens deviating from the target thickness (2.00 ± 0.05 mm) were discarded and remade. Specimens were examined under a stereomicroscope at 20× magnification under standardized illumination conditions. The entire upper surface of each specimen was systematically scanned for surface defects, including air voids, porosities, or irregularities. Specimens exhibiting any detectable defect at this magnification were excluded and replaced.

Polymerization was carried out using a light-curing unit operating at 1000 mW/cm² with a wavelength range of 385–515 nm. The output intensity of the device was verified using a radiometer prior to specimen preparation. The light-curing unit was positioned using a support setup to maintain the curing tip in direct contact with the polyester strip and perpendicular (90°) to the specimen surface, ensuring consistent positioning throughout the curing process. Each specimen was light-cured for 20 s from the top surface, followed immediately by 20 s from the bottom surface under the same conditions.

After polymerization, the specimen surfaces were rinsed under running DW for 10 s using a dental unit water spray. The spray was applied at a perpendicular angle (90°) to the specimen surface using a support-based positioning setup, in which the specimen and spray tip were aligned. The distance between the spray tip and the specimen surface was set to 5 cm and controlled using a measuring tool. The specimens were then stored individually in closed glass containers containing DW at 23°C ± 1°C for 24 h prior to finishing and polishing. The containers were kept closed to prevent evaporation and placed in a cabinet to minimize light exposure. Finishing and polishing were performed on both surfaces of each specimen using aluminum oxide abrasive discs (coarse, medium, fine, and superfine) in sequential order with a low-speed handpiece operating at 10,000 rpm. Each disc was applied for 20 s using a consistent rotational movement across the entire surface to ensure uniform treatment. All finishing and polishing procedures were performed by the same operator to minimize operator-related variability. Final polishing was performed using a diamond polishing system under the same operational conditions (10,000 rpm) for 20 s per step, following the same motion pattern. All specimens were then stored in DW at 23°C ± 1°C for an additional 24 h prior to staining to allow for post-curing stabilization, including diffusion of unreacted components and equilibration under standardized conditions.

Sample size was determined using power analysis performed with G*Power, with a significance level (α) of 0.05, a power of 95%, and an effect size (f) of 0.401, based on previously published data²¹. The minimum required total sample size was calculated to be 160 specimens, corresponding to 8 per subgroup. To account for the use of robust statistical methods involving trimmed means, which reduce the effective sample size by excluding a proportion of extreme values, and to compensate for potential specimen loss during preparation and analysis, the sample size per subgroup was increased to 10, yielding a total of 200 specimens.

Coffee Staining Procedure

A coffee staining solution was prepared by dissolving 3 g of instant coffee powder in 50 mL of DW heated to 100°C. The solution was stirred for 30 s until complete dissolution was achieved to ensure concentration uniformity. The solution was then transferred to a closed container, placed in a controlled room environment (23°C ± 1°C), and allowed to cool to the target temperature prior to use. Each specimen was individually immersed in 5 mL of coffee solution in closed cylindrical glass vials (inner diameter: approximately 15 mm; height: approximately 40 mm) to ensure a consistent specimen-to-solution ratio and complete immersion. The volume of 5 mL per specimen was selected to standardize exposure conditions and to ensure that all specimens were fully covered by the staining solution without contact with the container walls. All specimens were stored at 23°C ± 1°C in a temperature-controlled room throughout the 12-day immersion period. The vials were kept tightly closed to prevent evaporation and placed in a closed cabinet to minimize light exposure and external contamination. This immersion protocol has been widely used, and a 12-day immersion period has been reported to correspond to approximately one year of clinical staining under in vitro conditions³. To maintain consistent staining conditions and minimize microbial growth, the coffee solution was renewed at fixed 24 h intervals. At the same time each day, the specimens were removed from the vials using clean tweezers, gently rinsed with DW for 5 s, and transferred to freshly prepared coffee solution in new, clean vials containing 5 mL of solution. The containers were kept closed throughout the procedure, and all steps were performed under consistent laboratory conditions for all specimens.

Mouthrinse Application

All specimens were labeled with unique identification numbers prior to coffee staining to enable tracking of measurements. Following the staining procedure, the specimens were randomly allocated to the experimental groups using a computer-generated randomization sequence created in Microsoft Excel, in which the specimens were randomly ordered and then equally distributed among the groups. Each specimen was treated individually during the application procedures. Four commercially available mouthrinse solutions were included in the study: Colgate Plax Whitening + Charcoal (CP), Crest 3D White (CW), Listerine Fresh Burst (LF), and Sensodyne Pronamel (SP), along with DW as the control solution. These were abbreviated as CP, CW, LF, SP, and DW, respectively. The composition and active ingredients of the mouthrinse solutions are presented in Table 2.

Mouthrinse Type	Abbreviation	Manufacturer	Active Ingredients
Alcohol-containing mouthrinse	LF	Johnson & Johnson, UK	Alcohol, menthol, eucalyptol, thymol, methyl salicylate, benzoic acid, poloxamer 407, sodium benzoate, sorbitol solution, water, flavor
Charcoal-containing mouthrinse	CP	Colgate-Palmolive, USA	Water, sorbitol, propylene glycol, PEG-40 hydrogenated castor oil, flavor, sodium saccharin, menthol, eugenol, sodium fluoride, charcoal powder
Hydrogen peroxide–based mouthrinse	CW	Procter & Gamble, USA	Water, glycerin, hydrogen peroxide, propylene glycol, sodium hexametaphosphate, poloxamer 407, sodium citrate, flavor, sodium saccharin, citric acid
Fluoride-containing mouthrinse	SP	GSK, UK	Water, sorbitol, propylene glycol, potassium nitrate, PEG-60 hydrogenated castor oil, poloxamer 407, flavor, sodium fluoride, citric acid, sodium saccharin
Distilled water (control)	DW	N/A	N/A

Table 2: Composition of mouthrinse solutions used in the study. Mouthrinse types, abbreviations, manufacturers, and principal active ingredients of the solutions evaluated. Distilled water served as the control condition. Abbreviations: LF = alcohol-containing mouthrinse; CP = charcoal-containing mouthrinse; CW = hydrogen peroxide–based mouthrinse; SP = fluoride-containing mouthrinse; DW = distilled water.

The experimental design included three independent variables: composite type (DO and VU), mouthrinse type (CP, CW, LF, SP, and DW), and application method (direct immersion and irrigator-assisted application). The suffix “-D” indicates direct immersion, whereas “-I” indicates irrigator-assisted application. Accordingly, each subgroup was defined by a combination of solution type and application method (e.g., CP-D and CP-I). The distribution of experimental groups is summarized in Table 3.

Composite Type	Group No.	Irrigator Group	Direct Immersion Group
DO	1	CP-I	CP-D
	2	CW-I	CW-D
	3	SP-I	SP-D
	4	LF-I	LF-D
	5	DW-I	DW-D
VU	6	CP-I	CP-D
	7	CW-I	CW-D
	8	SP-I	SP-D
	9	LF-I	LF-D
	10	DW-I	DW-D

Table 3: Grouping of specimens according to composite type, mouthrinse, and application method. Experimental groups were defined based on composite type (DO and VU), mouthrinse type, and application method (oral irrigator or direct immersion). Abbreviations: DO = composite material DO; VU = composite material VU; CP = charcoal-containing mouthrinse; CW = hydrogen peroxide–based mouthrinse; SP = fluoride-containing mouthrinse; LF = alcohol-containing mouthrinse; DW = distilled water; I = oral irrigator application; D = direct immersion.

For the static immersion method, each specimen was individually immersed in 5 mL of the assigned mouthrinse solution in closed cylindrical glass vials of consistent size to ensure standardized exposure conditions. The selected volume ensured complete immersion of each specimen without contact with the container walls. All specimens were stored at 23°C ± 1°C in a temperature-controlled room for a total duration of 12 h. This duration was selected to represent the cumulative effect of routine mouthrinse use, corresponding to twice-daily exposure to mouthrinse for 1 min per application, and has been reported to approximate one year of clinical use under in vitro conditions¹⁷. As this method involved passive immersion, no flow rate or device-defined output setting was applicable; standardization was ensured by maintaining identical solution volume (5 mL), container dimensions, and exposure conditions for all specimens. All specimens were processed under the same laboratory conditions and time schedule to minimize intergroup variability. For the oral irrigator application, an oral irrigator mounted in a custom support setup was used to standardize specimen positioning and irrigation parameters. The oral irrigator device was secured within the setup to maintain a perpendicular orientation relative to the specimen surface. Each specimen was positioned and stabilized within a holder designed to prevent movement during irrigation. This setup was used to maintain a fixed spatial relationship between the irrigator tip and the specimen throughout each application. The irrigator tip was maintained in a fixed and stationary position relative to the specimen surface throughout each application, without lateral or sweeping movement. The specimen holder and the irrigator tip were aligned on parallel axes, and the distance between the irrigator tip and the specimen surface was adjusted to 2 mm using a digital caliper. This configuration ensured consistent positioning, orientation, and distance for all specimens. The irrigator was operated at the medium pressure setting corresponding to level 3 on the device, which provides a manufacturer-defined pressure range of approximately 55–65 psi. Prior to each use, the device setting was checked to ensure consistent operation at this level. As the device does not provide a direct quantitative flow rate value, output was standardized by maintaining the same device setting, fixed tip distance (2 mm), perpendicular orientation, and consistent operating conditions throughout all procedures. The solution flow was maintained at a constant level throughout the procedure by keeping the reservoir filled with the test solution. During irrigation, the reservoir was inspected at regular intervals and refilled as needed to maintain continuous and uninterrupted flow, ensuring consistent exposure conditions for all specimens.

Each specimen was exposed to the irrigator continuously for 10 min at fixed 7-day intervals, once per week for a total of 4 consecutive weeks. All applications were performed at the same time of day to ensure consistency. This exposure protocol was designed to represent routine oral irrigator use, corresponding to twice-daily application for approximately 3 s per surface, and has been reported to approximate one year of clinical use under in vitro conditions¹⁸. After each application, the specimens were rinsed with DW using a dental unit air–water spray for 10 s. The spray was applied at a perpendicular angle (90°) to the specimen surface using a support-based setup, in which the spray tip and specimen were aligned on parallel axes. The distance between the spray tip and the specimen surface was set to 5 cm and controlled using a measuring tool. Between application sessions, specimens were stored individually in closed glass containers filled with DW at 23°C ± 1°C. The containers were kept closed to prevent evaporation and placed in a cabinet to minimize light exposure. The storage solution was renewed at fixed 24 h intervals at the same time each day.

Color Measurement

Measurements were obtained using a spectrophotometer equipped with a contact-type probe (5 mm in diameter) and an internal LED light source. The device was operated in restorative mode, according to the manufacturer’s instructions, to ensure consistent, reproducible measurements. It was calibrated before each measurement session using the manufacturer’s standard white calibration block. The calibration procedure was performed by placing the probe tip in direct contact with the calibration block and initiating calibration mode via the device interface. Calibration was repeated until a valid reading was obtained prior to specimen measurement.

All color measurements were performed against a standardized neutral gray background (Munsell N5), consisting of a matte, non-reflective calibration card to minimize background light interference. The background corresponded to CIE Lab* values of approximately L* = 50.0, a* = 0.0, and b* = 0.0, representing an achromatic mid-gray reference. To ensure standardized and reproducible probe positioning, a custom-made positioning jig was used to stabilize both the specimen and the spectrophotometer probe. This setup ensured that the probe tip was maintained in a fixed perpendicular orientation (90°) relative to the specimen surface, with consistent contact pressure throughout all measurements. The measurement location was standardized by marking the exact center of each specimen using a digital caliper during specimen preparation. All measurements were taken from this predefined central reference point to eliminate positional variability. For repeated measurements, the probe was fully repositioned between each reading. Specifically, the probe was lifted completely from the surface and realigned using the positioning jig before each measurement to account for potential placement variability. Three consecutive measurements were obtained from the same predefined central point under identical conditions and averaged for analysis.

The average L*, a*, and b* values were used to calculate color change using the CIEDE2000 (ΔE₀₀) formula. The ΔE₀₀ values were calculated using a custom implementation of the CIEDE2000 algorithm in Microsoft Excel, based on CIELAB color space coordinates (Equation 1):

   (1)

Here, ΔL′, ΔC′, and ΔH′ represent the lightness, chroma, and hue differences, respectively; S_L, S_C, and S_H are the corresponding weighting functions; k_L, k_C, and k_H are parametric correction factors (set to 1 in this study); and R_T is a rotation term accounting for the interaction between chroma and hue differences. Color change was calculated using the CIEDE2000 (ΔE₀₀) formula based on the L*, a*, and b* coordinates obtained at each measurement time point. Specifically, ΔE₁ was calculated using the color coordinates measured at baseline (T₀) and after coffee staining (T₁), ΔE₂ using the coordinates obtained at T₁ and after mouthrinse application (T₂), and ΔE₃ using the coordinates measured at T₀ and T₂. Thus, each ΔE value represents a pairwise comparison of L*, a*, and b* values between the corresponding measurement time points⁹.

Surface Morphology Analysis

Representative specimens (n = 16) were selected for surface morphology evaluation using a predefined, reproducible selection protocol to minimize selection bias. Specimen selection was performed using a computer-generated randomization procedure from the available pool at each experimental stage. A total of 16 specimens were analyzed, distributed as follows: T₀ (n = 4), T₁ (n = 4), and T₂ (n = 8). For T₀ and T₁, specimens were randomly selected without subgroup differentiation, as no experimental grouping was present prior to the mouthrinse application stage. For T₂, specimens were randomly selected to represent the different experimental conditions, ensuring inclusion of samples from each solution type and application method.

Prior to imaging, all specimens were sputter-coated with a gold–palladium layer under controlled vacuum conditions (~0.05 mbar) to ensure surface conductivity. The coating thickness was maintained at 10 nm to provide adequate conductivity while preserving surface topography. Surface analyses were performed using scanning electron microscopy (SEM) with an environmental scanning electron microscope operated in low-vacuum mode at a chamber pressure of 110 Pa, with an accelerating voltage of 10.0 kV. Low-vacuum conditions were selected to minimize charging effects and allow stable imaging of resin-based materials without additional conductive artifacts. Specimens were mounted on aluminum stubs using double-sided conductive carbon tape and positioned such that the specimen surface was oriented perpendicular to the electron beam. All specimens were mounted using a standardized protocol to ensure consistent imaging geometry. Imaging conditions were defined by the accelerating voltage (10.0 kV) and working distance (kept constant throughout all measurements), while the spot size setting (3.0, instrument-specific) was maintained constant throughout the study.

Micrographs were obtained from a standardized central region of each specimen. The imaging location was defined as the geometric center of the specimen surface, determined during specimen preparation using a digital caliper and used consistently for all measurements. The SEM beam was aligned with this predefined reference point for all image acquisitions. Images were acquired at magnifications of ×2500, ×5000, and ×10000, with one image captured per magnification, to evaluate surface morphological changes associated with coffee staining and mouthrinse application.

Statistical Analysis

All statistical analyses were performed using R software with the WRS2 package. Data distribution was assessed using the Shapiro–Wilk test. As several variables did not conform to a normal distribution, robust statistical methods were applied. For the overall analysis, surface roughness and color values were evaluated using a three-way robust ANOVA to assess the effects of composite type, group, and period. For color change outcomes, ΔE₁, ΔE₂, and ΔE₃ values were analyzed separately using three-way robust ANOVA, with composite type, mouthrinse, and application method as independent factors. When significant effects were identified, post hoc multiple comparisons were performed using Bonferroni adjustment. Results are expressed as trimmed mean ± standard error, with standard errors estimated within the robust trimmed-mean framework implemented in the WRS2 package. The level of significance was set at p < 0.05.

Results

Specimen Preparation

Color change (ΔE) was evaluated across composite type, group, and different periods (ΔE₁, ΔE₂, and ΔE₃), corresponding to the sequential steps of the experimental protocol (Tables 4 and 5, Figure 2).

Effect	Q	p-value
Composit...

Discussion

Esthetic outcomes are central to the clinical success of resin composite restorations, as long-term color stability determines their ability to harmonize with surrounding dental tissues. Nanohybrid composites incorporating nanometric and submicron fillers have been developed to improve optical integration, polishability, and resistance to discoloration^22,23. More recently, single-shade resin composites have been introduced as a simplified alternative to conventio...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Aluminum oxide abrasive discs	3M ESPE, USA	Sof-Lex XT	Sequential finishing from coarse to superfine grit
Coffee powder (instant)	Nestlé, Switzerland	Nescafé Classic	Used for preparation of staining solution
Diamond polishing system	3M ESPE, USA	Sof-Lex Diamond Polishing System	Final polishing procedure
Distilled water	Botafarma, Turkey	Distilled Water	Storage and rinsing medium (control solution)
Environmental scanning electron microscope	Carl Zeiss, Germany	EVO MA10	Operated at 10 kV
Glass slide (cement glass)	AmScope, USA	BS-50P-100S-22	Used to flatten specimen surfaces
Light-curing unit	Ultradent, USA	VALO Cordless	Output verified (~1000 mW/cm²)
Microsoft excel spreadsheet	Microsoft Corp., Redmond, WA, USA	Excel	Used for CIEDE2000 calculations
Mouthrinse (Crest 3D White)	Procter & Gamble, USA	Crest 3D White	Hydrogen peroxide–based
Mouthrinse (Listerine Fresh Burst)	Johnson & Johnson, USA	Listerine Fresh Burst	Alcohol-containing
Mouthrinse (Colgate Plax Whitening + Charcoal)	Colgate-Palmolive, USA	Colgate Plax Whitening + Charcoal	Charcoal-containing
Mouthrinse (Sensodyne Pronamel)	Haleon, UK	Sensodyne Pronamel	Fluoride-containing
Oral irrigator	Procter & Gamble, USA	Oral-B Oxyjet MD20	Medium pressure setting (~55–65 psi)
Polyester strip	Extra Dental	Universal Strips	Used to reduce oxygen inhibition
Resin composite (Charisma Diamond One)	Kulzer, Germany	Charisma Diamond One	TCD-DI-HEA-based
Resin composite (Vittra APS Unique)	FGM, Brazil	Vittra APS Unique	APS technology
Silicone mold (prefabricated)	Hagiki, Turkey	Transparent	Disc-shaped (8 mm × 2 mm)
Spectrophotometer	VITA Zahnfabrik, Germany	Easyshade V	Used for color measurement
Stereomicroscope	Leica, Germany	Trinocular stereomicroscope	Used for defect inspection at 20× magnification
Statistical software	R Core Team	R version 4.2.2	Used for data analysis
Statistical software package	R Foundation for Statistical Computing, Austria	WRS2	Robust ANOVA (trimmed means)
Statistical power analysis software	Heinrich Heine University Düsseldorf, Germany	G*Power	Used for sample size calculation