Color Differences of Polimerized Resin-Based Composites and Corresponding Shade Guides

Featured Application

Color selection when performing an aesthetic dental restoration is essential for the clinician and the patient to obtain an optimal result. Taking into account the color difference (ΔE₀₀) of each composite with the VITAPAN Classical^Ⓡ shade guide or with the manufacturers’ commercial guide allows for more precision with shade selection in aesthetic dentistry.

Abstract

Objective: The purpose of this study is to analyze and compare the colors (A2, A3 and A3.5) of polymerized resin-based composites (RBCs) with respect to the shade numbers within each product line and the VITAPAN Classical^® shade guide they purported to represent. Methods: Three A-shades (A2, A3 and A3.5) from four RBC products (Harmonize^®, Empress^® Direct^®, Grandio^® and Filtek^® 500) were compared within the VITAPAN Classical^® shade guide and within their own commercial shade guide. Nine disk-shaped specimens, 6 mm in diameter and 2 mm thick, were prepared for each RBC color (three of each color). The color measurements were made according to the CIE L*a*b* color scale (quantifying L*c*h*a*b* values) using a Vita Easyshade Compact IV^® digital spectrophotometer. We calculated the CIEDE2000 color differences between polymerized composites and shade guides, as well as between composites. The values obtained from composites and samples of the color guides in the CIE L*a*b* space were represented by ICC3D software (Version 1.2.9) Results: The ANOVA test verified the existence of statistically significant differences between composites for the same shades (p < 0.05) except for shade A2. CIEDE2000 color differences between composites and the VITAPAN Classical^® shade guide ranged from 3.5 to 13.1 depending on the composite and the shade. Conclusions: There were color differences among the polymerized resin-based composites, between these and their own shade guides/manufacturer’s commercial guides, and between the former and the corresponding samples of the VITAPAN Classical^® shade guide. Clinical significance: Color selection when performing an aesthetic dental restoration is essential for the clinician and the patient to obtain an optimal result. Taking into account the color difference (∆E₀₀) for each composite with the VITAPAN Classical^® shade guide or with the manufacturers’ commercial guide allows for more precision with shade selection in aesthetic dentistry.

1. Introduction

The tooth color characterization and reproduction raises the challenge of aesthetic and restorative dentistry [1]. A perfect agreement between natural teeth and dental restoration is the quality requirement for the patient and the key to a successful result [1]. However, obtaining an exact color match in restorations may be a complicated, and, at times, frustrating experience [2].

Shade determination in dentistry can be classified as either instrumental or visual [3]. Visual determination can be carried out by comparing patients’ teeth with a shade guide, the most frequently used method [4,5]. A shade guide is made up of a set of colors designed to represent the range of colors in human dentition [6]. Most composite manufacturers cross-reference their colors to the VITAPAN Classical^® shade guide in particular (Vita Zahnfabrik H. Rauter GmbH & Co KG, Bad Säckingen, Germany), which is a universally accepted shade guide [7]. The range of colors for VITAPAN’s guide is split into four groups assigned with the letters A, B, C and D, depending on the hue, and also classified according to increasing chroma and decreasing value, which are designated in numerical order (e.g., A1, A2, A3) [8]. According to the manufacturer, these shades are reddish-brown, reddish-yellow, grayish and reddish-gray, respectively [9].

Instrumental shade determination can be performed with spectrophotometers, colorimeters and digital camera systems with their corresponding software [5,10]. Instrumental color measurement could be preferred over visual color determination because instrumental readings are objective and more rapid [5]. Spectrophotometers calculate tooth color by measuring the quantity and spectral composition of the light reflected from the tooth’s surface [11]. They express the results in the CIE L*a*b*, as well as in another or several conventional shade guides [11]. The CIE L*a*b* space was developed by the International Commission on Illumination (CIE for short in French, standing for Commission internationale de l’éclairage) in 1978 [12]. In the CIE L*a*b* colorimeter system, all of the colors that are visible can be described [13] and represented by way of a point in the space. L* characterizes the lightness of a color and can range between 0 (dark) and 100 (light); a* defines a color on a red–green axis; and b* defines a color on a blue–yellow axis.

These coordinates, which are obtained with an electronic color measurement device, can be compared, making it possible to estimate color differences between two points (∆E* _ab) (1). Despite this, in 2001, the CIEDE2000 formula was published by the CIE [14], which also allows color differences to be calculated and is considered to be more sophisticated than its predecessor [15].

Resin-based composites (RBCs) have been widely used in direct restorative procedures [16]. Nowadays, there are two main nano-sized composite categories on the market: nanofilled and nanohybrid composites [17]. The latter deals with combining nanometer and micrometer-sized fillers [17].

The VITAPAN Classical^® shade guide is in wide use and many composite brands base their shade selection on this guide and adopt the standard A, B, C and D assignations of the VITAPAN Classical tabs. Various manufacturers offer their own color guides, while others suggest comparing them to commercial color guides [18]. It should be noted that there is no standardization regarding the manufacturing of color guides.

The selection of the ideal color in RBC restorations with the correct opacity and translucency is essential to achieve a natural look to the final restoration. Other aspects, such as the thickness and/or the surface texture of the outer layer, influence the final appearance of the RBCs’ restorations [19,20]. Most RBC color guides are made of plastic but very few of them are made of composite materials. Some commercial companies provide a ceramic color guide, while others offer a painted plastic color guide [19]. They can also differ in other features such as the shape of the samples, their thickness, or the type and material of the handling grip [19].

Moreover, there is no standardization regarding the nomenclature of colors in these color guides. Each manufacturer uses its own color designation for its composites and often uses the names from the VITAPAN Classical^® shade guide. However, there is no precise match between the manufacturers’ color classification and the VITAPAN^® shade guide [21].

Meanwhile, selecting a composite resin color can be a complicated and inaccurate process if a satisfactory result is sought [1]. Cosmetic criteria can vary from one individual to the next and are dependent on their level of education, their age and their social environment [22,23,24]. Environmental factors, such as light conditions, can also play an important role in the selection [25]. Firstly, it has been proven that there are variations for the same color depending on the manufacturer [26] and secondly that the hue (how color families are distinguished from one another), chroma (intensity/saturation of the hue) and value (the amount of white in an object, distinguishing light and dark colors) from different cosmetic restorative materials did not match what was included in the VITAPAN Classical^® shade guide [27]. Furthermore, despite a perfect color match, composites show color instability due to different agents like liquids, stains or smoke [16,28].

There is evidence that reveals that the VITAPAN Classical^® shade guide shows differences among its own guides [29,30]. In addition, shade guides must be disinfected after each use, in accordance with the requirements set by the Occupational Safety and Health Administration (OSHA). It has been suggested that this procedure may cause variations in color samples [2].

Therefore, the purpose of this study is to analyze and compare the colors (A2, A3 and A3.5) of current RBCs with respect to the shade numbers within each product line and the VITAPAN Classical^® shade guide, showing its CIEDE200 values. We also aim to evaluate and represent graphs of the CIE L*a*b* space, showing the CIELAB value with the color difference. The null hypothesis is that there are no significant color differences between the RBCs and the VITAPAN Classical^® shade guide or the RBCs and their own commercial color guides.

2. Materials and Methods

2.1. Fabrication and Color Measurement of the RBC Specimens

Four RBC brands (Harmonize^®, Empress^® Direct^®, Grandio^® and Filtek^® 500) were compared to the color standards established for the three VITAPAN Classical shade guides (A2, A3 and A3.5) and corresponding RBC shade tabs. For each of the shades noted above, three specimens of each brand were fabricated. The name, manufacturer, composition, filler size and filler information of the composites are presented in

Table 1. Characteristics of the RBCs used.

Product Name	Manufacturer	Composition Type	Filler Size	Filler (Weight %)
Harmonize® (LOT number 8609456)	Kerr (Brea, CA, USA)	Nanohybrid composite	5–400 nm	81%
Empress Direct® (LOT number Y42709)	Ivoclar-Vivadent (Schaan, Liechtenstein)	Nanohybrid composite	0.04–3 µm	79%
Grandio® (LOT number 1924504)	Vocco (Cuxhaven, Germany)	Nanohybrid composite	0.01–0.1 µm	84%
Filtek 500® (LOT number N898020)	3M (Saint Paul, MN, USA)	Nanohybrid composite	0.6–1.4 µm	78.5%

.

In this study, color measurement was performed with a Vita EasyShade Compact IV^® dental spectrophotometer (Vita Zahnfabrik, Bad Säckingen, Germany) by placing the device sensor in direct contact with the resin composite surface by three measurements per sample per VITAPAN Classical tabs (n = 108). We used a 2 mm-thick polytetrafluoroethylene (Teflon) sheet, into which we made holes with an external 6 mm diameter trephine, so that it matched the diameter of the spectrophotometer sensor. We then proceeded to place three samples per composite brand and color into it. Therefore, nine discs (6 mm in diameter and 2 mm thick) from each resin material were fabricated by placing the material into a polytetrafluoroethylene sheet mold and light-curing them for 20 s after placing a mylar strip on either side of the mold and pressing it gently to remove excess material using microscopic slides. The RBCs were cured with a light polymerization unit (Smart Lite Pro, Dentsply Sirona, York, PA, USA) following the manufacturer’s instructions and irradiance values were frequently checked by using a digital radiometer (Bluephase Meter II, Ivoclar Vivadent Inc., Amherst, NY, USA) so that they were above 1000 mW/cm². After polymerization, the specimen was measured with a digital caliper (500-181, Mitutoyo, Tokyo, Japan) with a precision of 0.05 mm. The surface was examined by visual inspection, and the specimen was rejected if there were any defects or irregularities. All color measurements were made post-curing, and between fabrication and color measurement, specimens were stored in a darkened area and protected from damage. CIELAB values were recorded using the spectrophotometer in tooth measurement mode as described above with the probe positioned in the hole.

The color was evaluated according to the CIE L*a*b* color notation system, recording the parameters L* (lightness), a* (reddish-green) and b* (yellowish-blue) per sample and the mean values were calculated. All color measurements were performed according to the CIEDE2000 color coordinates for the standard D65 illumination against a white background (L: 94.6, a: 0.2, b: −0.8), at a stable ambient temperature of 23 °C (73.4 °F) and by the same operator (D.F.M.).

2.2. Color Measurement of Vita Shade Tabs

Three VITAPAN Classical^® shade guides (Vita Zahnfabrik H. Rauter Gmbh & Co KG, Bad Säckingen, Germany), which had already been used in a dental practice three years earlier, were chosen. In addition, three VITAPAN Classical^® tabs were chosen from each color guide: A2, A3 and A3.5. The nine shade guide samples were cleaned with disinfectant wipes (DisCide Ultra, Palmero Healthcare, Stratford, CN, USA) and placed in a sample holder made specifically to hold the samples for color measurement.

For the preparation of the sample holder, a transparent dappen glass (Henry Schein Inc., Melville, NY, USA) was filled with putty (Virtual putty, Ivoclar Vivadent, Schaan, Liechtenstein). The shade guide sample was put in the center of the putty and left to harden. With a clear 4 mm thermoplastic plate (Clear-Mouthguard, Henry Schein Inc., Melville, NY, USA), we made a round lid with the same diameter as the smaller outer diameter of the clear dappen glass. With an external 6 mm diameter trephine, we perforated the center of the lid so that it would match the middle third of where the color sample was located.

We made three measurements per color sample per guide with a Vita EasyShade Compact IV^® spectrophotometer (Vita Zahnfabrik, Bad Säckingen, Germany). We recorded the CIE L*a*b* values and calculated the mean values.

2.3. Color Measurement of RBC Shade Guides

Color guides for each of the following composites, which are included in our study, were selected: Harmonize^®, Empress Direct^® and Grandio^®. The composite Filtek 500^® does not have its own color guide, and the manufacturer recommends using the VITAPAN Classical^® shade guide. On the other hand, the Harmonize^® composite does not include the color A3.5 in its guide, but it is marketed nonetheless.

We recorded data from three color samples for each guide, corresponding to the colors A2, A3 and A3.5. The color guide samples were cleaned with a disinfectant wipe (DisCide Ultra, Palmero Health Care, Stratford, CN, USA) and placed on a sample holder with the same design used to hold the samples from the VITAPAN Classical^® shade guide (Figure 1). The average values of the obtained data were calculated.

The CIEDE2000 formula (ΔE₀₀) was used to study the differences between the samples:

$$∆\mathrm{E}00={\left[{\left.\left( \frac{∆L’}{kLSL}\right.\right)}^2+{\left.\left( \frac{∆C’}{kcSc}\right.\right)}^2+{\left.\left( \frac{∆H’}{kHSH}\right.\right)}^2+RT\left.\left( \frac{∆C’}{kcSc}\right.\right)\left.\left( \frac{∆H’}{kHSH}\right.\right)\right]}^{1/2}$$

Via the ICC3D software (1.2.9, Interactive Color Correction in 3 Dimensions) from the Norwegian Color and Visual Computing Laboratory (Trondheim, Norway) and ColorThink Pro (Chromix, Seattle, WA, USA), we represented the mean values obtained graphically in the CIE L*a*b* space not just for the composites but also for the sample color guides.

2.4. Data Analysis

The statistical evaluation was performed using the statistical program R (R 3.5.1, R Foundation for Statistical Computing, Vienna, Austria) for Windows. The differences between the samples of each color for each composite and their corresponding colors in the VITAPAN Classical^® shade guide, between the colors of the composite samples and the corresponding colors in their own/manufacturer’s shade guides, between the shade guides of the different composites and the VITAPAN Classical^® shade guide, and finally, between composite samples from a range of commercial companies for each color were studied.

Firstly, the mean of the measurements recorded for each color sample from the VITAPAN Classical^® shade guide was calculated to establish the values of L*, C*, h*, a* and b*. Similarly, the mean of the recorded data was calculated for the color guides of the composites and for the composite samples.

CIELAB and CIEDE2000 color formulas were used to calculate color differences between the three VITAPAN Classical^® shade tabs and each corresponding RBC. Finally, the ΔE₀₀ for each specimen was calculated.

With the purpose of establishing whether there were statistically significant differences in determining the color of composite samples using the VITAPAN Classical^® shade guide or the individual color guides of each composite, the non-parametric Mann–Whitney U test was employed. A p-value less than 0.05 was considered statistically significant.

Quantitative variables were presented as means (with corresponding standard deviations). The Shapiro–Wilk test was used to check for normality in all groups corresponding to a selection of material for each color. Additionally, the Levene test was employed to validate the hypothesis of equal variances among different material groups for each color. The one-way analysis of variance (ANOVA) was conducted to compare the four groups of composite material for each of the three shades considered. A p-value less than 0.05 was considered statistically significant.

3. Results

The results of the analysis of the correlation between the color shade guides (VITAPAN Classical^® shade guide and the commercial/manufacturer’s composite shade guide) and polymerized composites are listed in the tables below. In

Table 2. CIE L*C*h*a*b* values for the colors A2, A3 and A3.5 of the VITAPAN Classical^® shade guide.

Color	L*	C*	h*	a*	b*
A2	78.8	18.5	86.2	1.2	18.5
A3	75.9	21.2	84.9	1.9	21.1
A3.5	74.1	26.8	86.9	1.4	26.8

, the mean values obtained are shown for the L*C*h*a*b* parameters for the colors A2, A3 and A3.5 of the VITAPAN Classical^® shade guide.

In

Table 3. CIE L*C*h*a*b* values for the colors A2, A3 and A3.5 per composite.

Color A2	L*	C*	h*	a*	b*
Empress®	87.3	43.3	86.6	2.6	43.2
Filtek®	81.7	25.1	89.4	0.3	25.1
Harmonize®	84.1	38.7	85.2	3.3	38.6
Vocco®	83.8	29.6	89.5	0.3	29.6
Color A3
Empress®	88.1	46.8	86.5	2.8	46.7
Filtek®	79.7	30.2	90.1	−0.01	30.2
Harmonize®	79.7	41.1	85.7	3.1	41.0
Vocco®	80.1	28.3	89.3	0.3	28.3
Color A3.5
Empress®	84.9	47.4	85.8	3.5	47.2
Filtek®	77.9	33.4	89.1	0.6	33.4
Harmonize®	79.6	40.0	85.1	3.4	39.9
Vocco®	78.6	29.3	88.5	0.7	29.3

, the mean values obtained are shown for the L*C*h*a*b* parameters for the composites Empress^®, Filtek^®, Harmonize^® and Vocco^® for colors A2, A3 and A3.5 color.

In

Table 4. CIE L*C*h*a* and b* values for the colors A2, A3 and A3.5 from the RBC shade guides.

Color Guides	Color	L*	C*	h*	a*	b*
Empress®	A2	81.6	36.2	88.2	1.1	36.2
Empress®	A3	80.2	32.4	88.1	1.1	32.4
Empress®	A3.5	76.3	37.9	87.4	1.7	37.9
Harmonize®	A2	71.9	17.9	84.9	1.6	17.9
Harmonize®	A3	69.8	20.6	85.7	1.5	20.5
Harmonize®	A3.5	-	-	-	-	-
Vocco®	A2	79.5	34.1	89.6	0.2	34.1
Vocco®	A3	77.9	34.4	88.4	1	34.3
Vocco®	A3.5	74.6	34.2	88.7	0.8	34.2

, the CIE L*C*h*a* and b* values for the colors A2, A3 and A3.5 from the shade guides of Empress^®, Harmonize^® and Vocco^® composites can be seen. Data for the A3.5 color from the Harmonize^® composite guide are shown because this color is not included in its guide. Data for the Filtek^® composite were not available as the manufacturer did not supply its own color guide.

Table 5. CIEDE2000 (ΔE00) values for composites vs. VITAPAN Classical^® shade guide.

Color	Composite	ΔE00
A2	Empress®	11.9
A2	Filtek®	4.4
A2	Harmonize®	9.7
A2	Vocco®	6.5
A3	Empress®	13.1
A3	Filtek®	5.5
A3	Harmonize®	8.8
A3	Vocco®	5.3
A3.5	Empress®	10.8
A3.5	Filtek®	4.1
A3.5	Harmonize®	6.7
A3.5	Vocco®	3.5

shows the comparison between each color per composite and its matching color for the VITAPAN Classical^® shade guide in CIEDE2000 values. The results for ΔE₀₀ are shown, which indicate the existing color difference with respect to the same color from the VITAPAN Classical^® shade guide.

Table 6. CIEDE2000 (ΔE00) values for samples of Empress^®, Harmonize^® and Vocco^® composites and their respective shade guides.

Color	Composite	CIEDE2000
A2	Empress®	4.6
A2	Harmonize®	12.6
A2	Vocco®	3.5
A3	Empress®	7.4
A3	Harmonize®	11.3
A3	Vocco®	2.3
A3.5	Empress®	6.8
A3.5	Vocco®	3.5

shows the CIEDE2000 (ΔE₀₀) values between the composite shade guides and cured resin-based composite samples for each color. The different ΔE₀₀ values are shown, indicative of the existing color differences.

Table 7. CIEDE2000 (ΔE00) values for the manufacturers’ composite shade guides and the VITAPAN Classical^® color guide.

Color	Composite	CIEDE2000
A2	Empress®	8.2
A2	Harmonize®	5.1
A2	Vocco®	7.2
A3	Empress®	6.1
A3	Harmonize®	4.6
A3	Vocco®	6.2
A3.5	Empress®	4.8
A3.5	Vocco®	3.2

shows the CIEDE2000 (ΔE₀₀) values for the shade guides of the composites and the VITAPAN Classical^® shade guide for each color.

To complement the numerical values obtained and present the results in a more visual and easily comparable way, especially as the dataset is large, we developed Figure 1, Figure 2 and Figure 3.

In Figure 1, Figure 2 and Figure 3, the graphical representation in the CIE L*a*b* space for the colors A2, A3 and A3.5 are displayed for the VITAPAN Classical^® shade guide with the corresponding colors for the composites Empress^®, Filtek^®, Harmonize^® and Vocco^®. Each dot represents one of the composites or the shade guide. The color guide is blue, the Empress^® composite is violet, Harmonize^® is pink, Vocco^® is green, and Filtek^® is black.

In Figure 4, the graphical representation of the three colors of the VITAPAN Classical^® shade guide, A2 (green), A3 (red) and A3.5 (black) can be seen.

The color difference CIELAB (ΔEab) between each color of each composite and its corresponding color in the VITAPAN Classical^® shade guide can be observed in Figure 1, Figure 2 and Figure 3 as the Euclidean distance between points.

Table 8. The p-values of the VITAPAN Classical^® shade guide and the respective manufacturers’ RBC shade guides.

Composite	Color	CIEDE2000 RBCs—Shade Guides	CIEDE2000 RBCs—VITAPAN C® Shade Guide	p-Value
Empress®	A2	4.6	11.8	0.1
Harmonize®	A2	12.6	9.6	0.4
Vocco®	A2	3.5	6.4	0.1
Empress®	A3	7.4	13.1	0.1
Harmonize®	A3	11.3	8.8	0.1
Vocco®	A3	2.3	5.3	0.2
Empress®	A3.5	6.8	10.8	0.1
Vocco®	A3.5	3.5	3.5	0

shows the resulting data from the non-parametric Mann–Whitney U test, which was applied to study the existence of statistically significant differences in the determination of color for the composite samples using the VITAPAN Classical^® shade guide and the individual color guides of each composite.

There were no statistically significant differences (p > 0.05) between the determination of the colors of the composite samples using their respective color guides or the VITAPAN Classical^® shade guide, for any color or composite.

Likewise, we analyzed the existence of statistically significant color differences between all the composites for each of the colors studied. The color A2 showed statistically significant differences in the Filtek^® and Empress^® composites (p = 0.0170025 < 0.05). The color A3 showed statistically significant differences between the pairs of materials studied. These results are shown in

Table 9. p-value between material pairs for the color A3.

Material Pairs	p-Value
Filtek®–Empress®	p = 0.0002430 < 0.05
Harmonize®–Empress®	p = 0.0095420 < 0.05
Vocco®–Empress®	p = 0.0001984 < 0.05
Harmonize®–Filtek®	p = 0.0396577 < 0.05
Vocco®–Harmonize®	p = 0.0289988 < 0.05

.

The analysis of the color A3.5 also showed significant differences between the material pairs (

Table 10. p-values between material pairs for the color A3.5.

Material Pairs	p-Value
Filtek®–Empress®	p = 0.0000011 < 0.05
Harmonize®–Empress®	p = 0.0000476 < 0.05
Vocco®–Empress®	p = 0.0000006 < 0.05
Harmonize®–Filtek®	p = 0.0010546 < 0.05
Vocco®–Harmonize®	p = 0.0002764 < 0.05

).

4. Discussion

In this study, the color differences between composite resins, their own commercial shade guides and the VITAPAN Classical^® shade tabs were evaluated.

There are many variables that affect the color selection process [30] and that complicate dentists’ decisions when they need to carry out restorative treatment or procedures, particularly if it is for cosmetic reasons.

The visual method [5] is most frequently employed for the color section in dentistry, which uses shade guides to make comparisons, especially the VITAPAN Classical^® shade guide. Evidence points towards the guide not showing its standard colors [30,31] while, at the same time, variations in tones have been observed in the guide upon being disinfected after use [9,32]. For these reasons and to define their distribution in the chromatic space, we decided to calculate the L*C*h*a*b parameters of the same guide with the Vita EasyShade compact IV^® spectrophotometer (Vita Zahnfabrik, Bad Säckingen, Germany). This spectrophotometer showed 96.4% repeatability of measurements and 92.6% accuracy [33]. With the aim of guaranteeing spectrophotometer repeatability, establishing a color register system via a repositioning system was paramount, an endorsed requirement in “in vivo” [34] and “in vitro” [9,30,35,36] studies alike. Fernández Millán et al. (2020) highlighted how important it is for the position of the spectrophotometer sensor for repeatability and reliability to be assured for the measurements [34]. Keeping this in mind, we agreed with the opinion that the external diameter of the spectrophotometer head should coincide with the registration area [9,35]; if it were not restricted [30], measurement errors could occur because variations in the positioning of the tool head would be permitted. Likewise, it should be considered that this device is generally not recommended for “in vitro” studies [37].

The L*C*h*a*b parameter measurements obtained with the Vita EasyShade Compact IV^® spectrophotometer (Vita Zahnfabrik, Bad Säckingen, Germany) for the colors A2, A3 and A3.5 from the VITAPAN Classical^® shade guide neither coincided with any of the previously mentioned studies [31,35] nor other existing papers [38,39,40].

Color and translucency affected the properties of dental restorations as well as the polymerization of the RBCs [2,16]. Clinical comparisons between teeth and restorative dental material were carried out with a polymerized composite. For this reason, the study design employed polymerized RBCs.

Nevertheless, we standardized the size of each sample, which measured 6 mm in diameter and had a thickness of 2 mm. The 6 mm diameter coincided with the external diameter of the spectrophotometer head, thus reducing the likelihood of measurement errors [9,35]. By using this thickness, we concurred with Çelik et al. (2011) in considering that a reproducible thickness in clinical practice is important, although there is no consensus on this matter and some articles have used samples of 2 mm [41,42], 1.5 mm [38], 1 mm [16,43] or 1.2 mm [44]. However, there is consensus regarding D65 lighting conditions, and as with some previously mentioned authors [16,43,45], we decided to use these standards in our study. In addition, there was evidence that the background used to record color could influence the color of the samples [44]; the white background was standardized (L: 94.6, a: 0.2, b: −0.8) for this reason, so that it would not interfere with the registering process and would meet the previously mentioned D65 conditions. Furthermore, the composites used in this study were “body” type, which resulted in low translucency.

Most of the articles that were revised prepared composite samples with an even surface [43,44,45,46,47]. In our study, flat surfaces without any defects were achieved by pressing down the samples with flat objects such as a microscope slide, as researchers of other papers also described doing in their Material and Methods sections [2,43,44], and by using another polytetrafluoroethylene sheet [45]. Obtaining a flat surface is fundamental to reducing errors in spectrophotometer recording and reproducing similar conditions to clinical results.

Of course, it would be ideal if the specific color from the VITAPAN Classical^® shade guide of a composite did not differ from one’s own perception of it [31]. Nonetheless, various papers have shown differences between commercially available composites and the corresponding colors from the VITAPAN Classical^® shade guide [48,49]. Such differences may be due to different values in L*a*b* parameters. In our body of research, the actual difference between all of the composites studied and their respective colors from the VITAPAN Classical^® shade guide could be seen. These differences vary between composites, the lowest color difference being registered in the Vocco^® composite for the color A3.5 (ΔE₀₀ = 3.5) and the highest in the Empress^® composite for the color A3 (ΔE₀₀ = 13.1). The Empress^® and Harmonize^® composites showed higher ΔE₀₀ values than Filtek^® or Vocco^®, which might indicate that they were closer to the corresponding color from the VITAPAN Classical^® shade guide. For the color A2, the Filtek^® composite displayed less color difference from the guide (ΔE00 = 4.0) than Vocco^® (ΔE00 = 6.4); however, for the colors A3 and A3.5, the Vocco^® composite (ΔE00 = 5.3; ΔE00 = 3.5) demonstrated closer proximity to the VITAPAN Classical^® shade guide.

Paravina et al. (2019), with a 50:50% perceptibility threshold (PT) and a 50:50% acceptability threshold (AT), determined that ΔE00 values > 1.8 and ≤3.6 should be considered “moderately unacceptable” color differences; those >3.6 and ≤5.4 should be deemed “clearly unacceptable”; finally, if they are greater than 5.4, they should be regarded as “extremely unacceptable” [50]. The results obtained by analyzing the color difference between composite samples and the VITAPAN Classical^® shade guide showed that only the Vocco^® composite for the color A3.5 exhibited “moderately unacceptable” results with ΔE00 = 3.5. Results falling within the “clearly unacceptable” range included Filtek^® for the colors A2 and A3.5 with ΔE00 values of 4.0 and 4.1, respectively, and Vocco^® for the color A3 with ΔE00 = 5.3. All the other results for the composites fell into the “extremely unacceptable” range. The composite Empress^® showed the highest ΔE00 values for all three colors, with ΔE00 = 11.8 for the color A2, ΔE00 = 13.1 for the color A3, and ΔE00 = 10.8 for the color A3.5. The Empress^® composite was the most distant from the VITAPAN Classical^® shade guide. The color differences obtained showed a weak correlation between the composites studied and the color guide, according to previous studies [31,51]. These differences may be related to the manufacturing material or the curved geometry of the color guide samples. These factors could influence the reflection of light, varying the color measurements of the spectrophotometer.

Taking into account the CIEDE2000 values recorded between the studied composites and their respective color guides, it was demonstrated that the Harmonize^® composite resembled the VITAPAN Classical^® shade guide more closely than its own color guide. However, the Empress^® composite in all its colors and the Vocco^® composite for the colors A2 and A3 showed colors that were closer to their respective color guides. The latter composite displayed the same CIEDE2000 value (ΔE00 = 3.5) for the color A3.5 concerning both the VITAPAN Classical^® shade guide and its own color guide, making it equally similar or dissimilar to both guides. Vocco^® was the composite that presented the smallest color differences in relation to its respective color guide. These differences may be due to the manufacturing material of their own guides, the thickness of the samples or their geometry.

Taking into consideration the study by Paravina et al. (2019) [50] and the CIEDE2000 values obtained between the composite samples and their respective color guides, the color differences for the Vocco^® composite for the colors A2 (ΔE00 = 3.5), A3 (ΔE00 = 2.3) and A3.5 (ΔE00 = 3.5) should be considered “moderately unacceptable”; the Empress^® composite for the color A2 (ΔE00 = 7.4) should be thought of as “clearly unacceptable”; last of all, the Harmonize^® composite for the colors A2 (ΔE00 = 12.6) and A3 (ΔE00 = 11.3), as well as the Empress^® composite for the colors A3 (ΔE00 = 7.4) and A3.5 (ΔE00 = 6.8), should be deemed “extremely unacceptable”.

Considering the results obtained from comparing the color samples of the studied composites with their own color guides and the VITAPAN Classical^® color guide, it can be concluded that the color register can be established interchangeably with both guides as there were no statistically significant differences. However, when CIEDE2000 values were analyzed, which indicated the distance between colors, the composite colors were closer to their respective color guides than to the VITAPAN Classical^® color guide.

Our study highlights the need for more sophisticated color selection methods, such as color determination via spectrophotometry. We agree with Diamantopoulou et al. (2021) about all of the color guides used yielding unacceptable results and also with Ruiz-López J. et al. (2022) that it is necessary to improve commercially available dental shade guides [18,52]. The color measuring devices are especially useful for reducing subjective variables inherent in visual methods. Devices like spectrophotometers (e.g., Vita Easyshade) present high ICC and ROC values in vitro which validate their indication as color diagnostic tools [36]. Furthermore, it is necessary in clinical settings to control related effective factors or conditions to perform optimally [34,53]. Relative to tooth color observed in the population, shade guides do not provide a full range of choices, making clinical shade selection difficult. However, composite shade guides that do not match their purported color standards make this already difficult task even more difficult.

In our body of work, the position in the chromatic space of the colors A2, A3 and A3.5 from the VITAPAN Classical^® shade guide and of the Filtek^®, Harmonize^®, Vocco^® and Empress^® composites studied were represented by dots on a graph of the CIE L*a*b* space. We considered this visual representation to be easier to understand, especially for clinicians not used to scientific literature or research, than those in other papers, such as box-and-whisker plots [11], line graphs and scatter plots [6,8].

The color differences observed in the study were generally more major than we would expect and represent notable deviations from the stated VITAPAN Classical shade guide and corresponding composite shade guides. These results were in contrast to clinical experience. The human eye’s ability to perceive color differences related to the lightness, the chroma and the hue of the material is being evaluated. Due to the translucency of RBCs generally, color matching and the final clinical result are aided by the chameleon effect, as well.

The graphic representation allowed a single graph to display several values simultaneously (L*a*b*), directly showing lightness, the degree of yellowish-blue and that of reddish-green, while in the previously mentioned papers [5,6,8,11], one graph was used per value.

The CIELAB values were understood as the distance between the points, permitting various values to be compared simultaneously.

5. Conclusions

All the cured resin-based composites (RBCs) studied exhibited color differences in CIEDE2000 values compared to their respective colors in the VITAPAN Classical^® shade guide.

All the cured resin-based composites (RBCs) studied showed color differences in CIEDE2000 values concerning the shade guides provided by their manufacturers.

For the colors A3 and A3.5, all of the cured resin-based composites (RBCs) displayed statistically significant color differences, whereas for the color A2, it was only for two of them (Filtek^® and Empress^®).