Comparison of Optical Properties in Single-Shade and Multi-Shade Composite Resins
Article information
Trans Abstract
This study aimed to evaluate the differences in optical properties, such as color and translucency, between single-shade composite resins (Omnichroma) and multi-shade composite resins (Filtek Z350XT). Furthermore, the study assessed the influence of the surrounding structure’s shades on the shade matching of Omnichroma. Two types of disc-shaped specimens were prepared: Single specimen (diameter, 8.0 mm; thickness, 1.0 and 2.0 mm), consisting of either Omnichroma or Filtek Z350XT in the A1B, A2B, and A3B shades, and dual specimen (diameter, 8.0 mm; thickness, 2.0 mm), featuring a bottom layer (diameter, 8.0 mm; thickness, 1.0 mm) of Filtek Z350XT in the A1B, A2B, and A3B shades, and a top layer (diameter, 8.0 mm; thickness, 1.0 mm) filled with Omnichroma. Commission Internationale d’Eclairage L*a*b* color measurements and calculations for color differences (ΔE*ab) and translucency parameters (TP) of each specimen were performed. Omnichroma exhibited a lighter, more greenish, and blueish color compared to the Filtek Z350XT in A1B, A2B, and A3B shades. With increased thickness, Omnichroma became more yellowish, whereas Filtek Z350XT became less yellowish. Additionally, when Omnichroma was applied over Filtek Z350XT in dual specimens, the yellowness increased further beyond Omnichroma’s original yellowness level. Consequently, Omnichroma achieved clinically acceptable shade matching, especially in the A3 shade, because it aligns well with the original high yellowness of the A3 shade. Additionally, Omnichroma’s superior shade-matching ability was attributed to its higher translucency compared to Filtek Z350XT. Therefore, Omnichroma might be considered useful in pediatric dentistry by simplifying the shade selection process.
Introduction
Children and adolescents require significant dental procedures for aesthetic restorations due to acute and fast progression of the carious process, high risk of traumas[1], discoloration, early loss of teeth, misalignment, and any shape and size abnormality of tooth[2].
Composite resin is a popular and valuable option for aesthetic restoration in pediatric dentistry due to the following advantages: excellent esthetics with natural color matching, minimal removal of healthy tooth structure, ease of repair, and cost-effectiveness[3]. Furthermore, high mechanical durability and wear resistance make composite resin a better choice of dental restoration[4].
The proper shade selection for composite resin is critical to successfully achieving aesthetic restoration. Optical properties such as translucency, fluorescence, and opalescence should be considered in the shade matching of composite resin, in addition to surface gloss and how the material interacts with light through reflection, refraction, transmission, absorption, and scattering[5]. Thus, even though commercial composite resins are labeled as the same shade based on their chroma and hue, their actual color may vary among different manufacturers and products[6,7]. Therefore, clinicians encounter difficulties in achieving accurate shade selection for composite resin restorations when relying solely on their VITA classical shade guide, which ranges from A1 to D4. Various layering techniques have been employed to match the shade and optical properties of composite resins to those of natural teeth, including opaque dentin, transparent dentin, enamel, and incisal edge, by considering specific optical parameters[8]. However, these layering techniques increase the sensitivity and chair time, which can be particularly challenging when treating uncooperative children and adolescents.
To overcome shade matching difficulties of composite resins, single-shade composite resins have recently been introduced. Omnichroma (Tokuyama Dental, Tokyo, Japan) is the first commercially available single-shade composite resin that uses structural colors and comprises uniform supra-nano SiO2 and ZrO2 spherical fillers with a particle size of 260 nm. Unlike conventional multi-shade composite resins that contain pigments, Omnichroma fillers produce a red to yellow structural color, combined with the reflected color from the surrounding teeth, allowing it to blend with different colors of the natural teeth[9]. Therefore, Omnichroma, a single-shade composite resin, is used to enable proper shade matching with only one shade, thereby reducing the time and effort needed for shade matching in pediatric dental treatments.
Previous studies on Omnichroma, a single-shade composite resin, have been mostly focused on its shade-matching ability with the natural teeth[10,11], acrylic resin denture teeth[12,13], and other composite resins[14-16]. These studies compared Omnichroma’ s shade-matching ability to that of conventional multishade composite resins. However, only a few studies have evaluated the color and translucency parameters of a single-shade composite resin itself, compared to the conventional multi-shade composite resin. Thus, this study aimed to evaluate the difference in optical properties, such as color and translucency parameters, between single-shade and multi-shade composite resins. Furthermore, this study aimed to assess the influence of the surrounding structure’s shades on shade matching of the single-shade composite resin.
Materials and Methods
This study used a single-shade composite resin, Omnichroma in universal shade, and multi-shade composite resins, Filtek Z350XT (3M ESPE, St. Paul, MN, USA) in A1B, A2B, and A3B shades. Table 1 shows the descriptive information about each material.
Detailed information about the materials used in the study
1. Specimen preparation
Cylindrical stainless steel molds (diameter, 8.0 mm; thickness, 1.0 and 2.0 mm) were used to prepare two types of specimens. Single specimens (diameter, 8.0 mm; thickness, 1.0 and 2.0 mm) comprised only of Omnichroma or Filtek Z350XT (shades A1B, A2B, and A3B) (n = 6). Then, the composite resins were packed into the mold in one increment by compressing them between two glass slides and mylar strips. A glass slide was placed to ensure uniform specimen thickness and distance from the specimens’ surface to the light-curing unit. The mylar strip was placed over the mold to reduce the polymerization reaction inhibition by oxygen and ensure smooth surfaces. Then, specimens were light-irradiated through the glass slide at 1000 mW/cm2, for 20 s from both top and bottom surfaces, with a light-emitting diode curing unit (Valo, Ultradents, South Jordan, UT, USA). Dual specimens (diameter, 8.0 mm; thickness, 2.0 mm) comprised a bottom (diameter, 8.0 mm; thickness, 1.0 mm) of Filtek Z350XT (shades A1B, A2B, and A3B) and a top (diameter, 8.0 mm; thickness, 1.0 mm) filled with Omnichroma (n = 6). Dual specimens were fabricated by developing single specimens (diameter: 8.0 mm, thickness: 1.0 mm) comprising Filtek Z350XT first. These previously obtained 1.0 mm-thick Filtek Z350XT specimens were plugged into the bottom of the 2.0 mm-thick mold, and the upper remaining 1.0 mmthick space was filled using an Omnichroma. Covering with glass slides and mylar strips, followed by curing of dual specimens, was performed similarly as for single specimens. The single and dual specimen surfaces were not polished after curing, and only edge flashing was carefully removed. The specimens were then dried for 24 hours before the color measurement.
The present study used specific codes for each specimen. The single specimens comprising Omnichroma or Filtek Z350XT in A1B, A2B, and A3B shades were labeled as OM, A1, A2, and A3, respectively. The dual specimens were labeled with codes OMA1, OMA2, and OMA3 based on the shades of the bottom component of Filtek Z350XT. Fig. 1 illustrates the schematic representation of single and dual specimens and their codes.
Schematic representation of single and dual specimens and the specimen code.
OM: Omnichroma; A1: Filtek Z350XT (shade A1B); A2: Filtek Z350XT (shade A2B); A3: Filtek Z350XT (shade A3B) of single specimens (thickness, 1.0 and 2.0 mm); OMA1: Omnichroma + Filtek Z350XT (shade A1B); OMA2: Omnichroma + Filtek Z350XT (shade A2B); OMA3: Omnichroma + Filtek Z350XT (shade A3B) of dual specimens.
2. Color measurement
A spectrophotometer (CM-700d, Konica Minolta, Osaka, Japan) with specular component excluded (SCE) geometry was used to measure the center of the top surface of each specimen for the Commission Internationale d’Eclairage (CIE) L*a*b* parameters. The L* value determines the lightness from black to white. The a* (red-green coordinate) and b* values (yellow-blue coordinate) denote hue and chroma factors. The spectrophotometer had a measuring port with a 3.0 mm aperture diameter and used CIE diffuse/8° geometry for both illumination and viewing configurations. The equipment was performed for zero and white calibrations immediately before each set of measurements using the calibration plate supplied by the manufacturer. The color was measured on the standard illuminant D65 over white (L* = 87.62 ± 0.13, a* = 1.41 ± 0.02, b* = -4.19 ± 0.13) and black backgrounds (L* = 26.38 ± 0.01, a* = 0.34 ± 0.01, b* = -0.94 ± 0.01). The measurements were repeated three times for each specimen under each background, and average values for six specimens of the same group were calculated.
3. Calculation of the color difference
Using single specimens alone, ΔE*ab_SINGLE was calculated from the CIEL*a*b* value difference (ΔL*SINGLE, Δa*SINGLE, and Δb*SINGLE) between Omnichroma and Filtek Z350XT (shades A1B, A2B, and A3B) with the same thickness (1.0 and 2.0 mm). ΔL*SINGLE, Δa*SINGLE, Δb*SINGLE, and were calculated using the following formula:
ΔL*SINGLE = L*OM ‒ L*A1,A2 or A3 (same thickness)
Δa*SINGLE = a*OM ‒ a*A1,A2 or A3 (same thickness)
Δb*SINGLE = b*OM ‒ b*A1,A2 or A3 (same thickness)
ΔE*ab_SINGLE = [(ΔL*SINGLE)2 + (Δa*SINGLE)2 + (Δb*SINGLE)2]1/2 (same thickness)
ΔE*ab_DUAL was calculated from ΔL*DUAL, Δa*DUAL, and Δb*DUAL between dual specimens and 2.0 mm-thick single specimens of Filtek Z350XT (shades A1B, A2B, and A3B) for each corresponding shade.
ΔL*DUAL, Δa*DUAL, Δb*DUAL, and ΔE*ab_DUAL were calculated using the following formula:
ΔL*DUAL = L*OMA1,OMA2 or OMA3 ‒ L*A1,A2 or A3 (for each corresponding shade)
Δa*DUAL = a*OMA1,OMA2 or OMA3 ‒ a*A1,A2 or A3 (for each corresponding shade)
Δb*DUAL = b*OMA1,OMA2 or OMA3 ‒ b*A1,A2 or A3 (for each corresponding shade)
ΔE*ab_DUAL = [(ΔL*DUAL)2 + (Δa*DUAL)2 + (Δb*DUAL)2]1/2 (for each corresponding shade)
Fig. 2 depicts the schematic illustration of the calculation of ΔL*SINGLE, Δa*SINGLE, b*SINGLE, ΔL*DUAL, Δa*DUAL, Δb*DUAL, ΔE*ab_SINGLE, and ΔE*ab_DUAL between specimens.
Schematic showing the specimen arrangement used to calculate color differences.
The obtained ΔE*ab_SINGLE and ΔE*ab_DUAL were compared to 50 : 50% perceptibility threshold (PT) of 1.2 and 50 : 50% acceptability threshold (AT) of 2.7[17].
4. Calculation of translucency parameter
The translucency parameter (TP) was calculated with CIEL*a*b* values measured on black and white backgrounds for each specimen using the following formula:
TP = [(L*B ‒ L*W)2 + (a*B ‒ a*W)2 + (b*B ‒ b*W)2]1/2
“B” and “W” represent black and white, respectively.
5. Statistical analysis
All statistical analyses were performed using SPSS Statistics software version 29.0 (IBM Corp., Armonk, NY, USA). The Shapiro-Wilk test was performed to assess the normality of parameters. Since the CIEL*a*b* values, Δ L*SINGLE, Δa*SINGLE, Δb*SINGLE, ΔL*DUAL, Δa*DUAL, Δb*DUAL, ΔE*ab_ SINGLE, ΔE*ab_DUAL, and TP values were normally distributed, parametric tests were performed. One-way analysis of variance (ANOVA) was used to analyze and compare CIEL*a*b* and TP values among different specimen shades with the same thickness and specimen type. This statistical method also evaluated the effect of Filtek Z350XT shades on ΔL*SINGLE, Δa*SINGLE, Δb*SINGLE, Δ L*DUAL, Δa*DUAL, Δb*DUAL, ΔE*ab_SINGLE, and, ΔE*ab_DUAL. Based on the results of the Levene’s test, which assesses the homogeneity of variance, post hoc comparisons were performed using either Tukey’s or Dunnett’s T3 test. In addition, the independent t-test was performed to assess the impact of specimen thickness on CIEL*a*b* and TP values for each shade. Furthermore, this statistical method was used to compare CIEL*a*b* values between the 2.0 mm-thick single specimens of Filtek Z350XT and dual specimens for each corresponding shade. All statistical analyses were conducted with an alpha significance level of 0.05.
Results
Fig. 3 presents a photo of representative single and dual specimens.
Representative single and dual specimens with specimen codes (A) 1.0 mm-thick single specimens, (B) 2.0 mm-thick single specimens, and (C) dual specimens.
OM: Omnichroma; A1: Filtek Z350XT (shade A1B); A2: Filtek Z350XT (shade A2B); A3: Filtek Z350XT (shade A3B) of single specimens (thickness, 1.0 and 2.0 mm); OMA1: Omnichroma + Filtek Z350XT (shade A1B); OMA2: Omnichroma + Filtek Z350XT (shade A2B); OMA3: Omnichroma + Filtek Z350XT (shade A3B) of dual specimens.
1. Influence of composite resin shade and specimen thickness on CIEL*a*b* values of single specimens
CIEL*a*b* values of single specimens on the white background are shown in Table 2 and Fig. 4. Fig. 4A depicts the L* values of single specimens. Regardless of the composite resin shade, all specimens (OM, A1, A2, and A3) became significantly darker as the thickness increased, as indicated by decreased L* values (p < 0.0001). In both 1.0 and 2.0 mm thickness, L* values were highest in OM, followed by A1, A2, and A3. However, no significant difference was observed between OM and A1 in 1.0 mm thickness (p= 0.371), and no significant difference was also observed among OM, A1, and A2 in 2.0 mm thickness (p > 0.05).
Mean and standard deviation of CIEL*a*b* values of single specimens on a white background
Mean CIE L*a*b* values of single specimens on a white background. (A) L* value, (B) a* value, (C) b* value.
*: Significant differences in values between 1.0 mm and 2.0 mm thickness of single specimens within the same composite resin shade based on the independent t-test (p < 0.05).
Different subscript letters indicate significant differences depending on composite resin shade within the same thickness according to the one-way AONVA (p < 0.05).
OM: Omnichroma; A1: Filtek Z350XT (shade A1B); A2: Filtek Z350XT (shade A2B); A3: Filtek Z350XT (shade A3B) of the single specimen (thickness, 1.0 and 2.0 mm).
Fig. 4B shows the a* values of single specimens. Regardless of the composite resin shade, all specimens (OM, A1, A2, and A3) became significantly more reddish as the thickness increased, as indicated by the increase in a* values (p < 0.0001). In 1.0 mm-thick specimens, OM had the lowest a* value, followed by A1, A2, and A3, and significant differences were observed among the four groups (p < 0.0001). This result revealed that OM was more significantly greenish than A1, A2, and A3 in 1.0 mm thickness. However, in 2.0 mm-thick specimens, A1 showed the lowest a* value, followed by OM, A2, and A3, whereas no significant difference was observed between OM and A1 (p= 0.752), indicating that OM with increased thickness had similar redness with A1.
Fig. 4C shows the b* values of single specimens. With decreased b* values, yellowness significantly decreased as the specimen thickness increased in A1, A2, and A3 (p= 0.047, p= 0.001, p < 0.0001, respectively). Conversely, as indicated by increased b* values, yellowness significantly increased as the specimen thickness increased in OM (p < 0.0001). In 1.0 mm-thick specimens, OM had the lowest b* value, followed by A1, A2, and A3, and significant differences were observed among the four groups (p < 0.0001). However, in 2.0 mm-thick specimens, A1 had the lowest b* value, followed by A2, OM, and A3, with significant differences among the four groups (p < 0.05).
2. Influence of composite resin shade of the bottom component on CIEL*a*b* values of dual specimens
CIEL*a*b* values of dual specimens on white background are shown in Table 3 and Fig. 5. Fig. 5A shows the L* values of dual specimens. The L* value was lowest in OMA3, followed by OMA2 and OMA1. No significant difference was observed between OMA1 and OMA2 (p= 0.628). Fig. 5B presents the a* values of dual specimens. The a* value was lowest in OMA1, followed by OMA2 and OMA3, and significant differences were observed among the three groups (p < 0.0001). Fig. 5C depicts the b* values of dual specimens. The b* value was lowest in OMA1, followed by OMA2 and OMA3, and a significant difference was observed among the three groups (p < 0.0001).
Mean and standard deviation of CIEL*a*b* values of dual specimens on a white background
Mean CIE L*a*b* values of dual specimens on a white background. (A) L* value, (B) a* value, (C) b* value.
Different subscript letters indicate significant differences depending on the shades of bottom components in dual specimens based on the one-way ANOVA (p < 0.05).
OMA1: Omnichroma + Filtek Z350XT (shade A1B); OMA2: Omnichroma + Filtek Z350XT (shade A2B); OMA3: Omnichroma + Filtek Z350XT (shade A3B) of dual specimens.
3. Influence of composite resin shade and specimen thickness on TP of single specimen
The TP values of single specimens are shown in Table 4 and Fig. 6. Regardless of composite resin shade, all specimens (OM, A1, A2, and A3) exhibited significantly decreased TP values as the thickness increased (p < 0.0001). In both 1.0- and 2.0 mm-thick specimens, OM exhibited the highest TP values, followed by A3, A2, and A1, and no significant difference was observed between A1 and A2 (p= 0.771 for 1.0 mm thickness and p= 0.935 for 2.0 mm thickness).
Mean and standard deviation of translucency parameter (TP) of single specimens
Mean translucency parameter (TP) of single specimens.
*: Significant differences in TP values between 1.0 mm and 2.0 mm thickness of single specimens within the same composite resin shade based on the independent t-test (p < 0.05).
Different subscript letters indicate significant differences depending on composite resin shade within the same thickness based on the one-way ANOVA (p < 0.05).
OM: Omnichroma; A1: Filtek Z350XT (shade A1B); A2: Filtek Z350XT (shade A2B); A3: Filtek Z350XT (shade A3B) of single specimens (thickness, 1.0 and 2.0 mm).
4. Difference in CIEL*a*b* values (∆L*SINGLE, ∆a*SINGLE, and ∆b*SINGLE) and color difference (∆E*ab_SINGLE) between Omnichroma and Filtek Z350XT in single specimens
∆L*SINGLE, ∆a*SINGLE, and ∆b*SINGLE values between OM and A1, A2, and A3 of single specimens with the same thickness on the white background are shown in Table 5 and Fig. 7A - 7C. For 1.0 mm thickness, the magnitude of ∆L*SINGLE was lowest in the OM and A1 group, followed by OM and A2, and highest for OM and A3. No significant difference was observed between the OM and A1 group and the OM and A2 group (p= 0.074). Similarly, for 1.0 mm thickness, the magnitudes of ∆a*SINGLE and ∆b*SINGLE were lowest between OM and A1, followed by OM and A2, and highest between OM and A3, with significant differences among them (p < 0.0001). Similarly, for 2.0 mm thickness, the magnitudes of ∆L*SINGLE and ∆ a*SINGLE were lowest in the OM and A1 group, followed by OM and A2, and highest between OM and A3. However, ∆b*SINGLE was lowest in OM and A2, followed by OM and A3, and highest for OM and A1, with significant differences among the three groups (p < 0.0001). This result of ∆b*SINGLE in 2.0-mm thickness indicates that OM became significantly more yellowish, approaching the A2 shades with increasing thickness.
Mean and standard deviation of ΔL* SINGLE, Δa* SINGLE, Δb* SINGLE, and ΔE* ab_SINGLE on white background
Mean ΔL*SINGLE , Δa*SINGLE , Δb*SINGLE , and ΔE*ab_SINGLE on a white background. (A) ΔL*SINGLE , (B) Δa*SINGLE , (C) Δb*SINGLE , (D) ΔE*ab_SINGLE . The dotted line represents a 50 : 50% acceptability threshold (AT) of 2.7, and the dashed line represents a 50 : 50% perceptibility threshold (PT) of 1.2.
Different subscript letters indicate significant differences between the groups according to the one-way ANOVA (p < 0.05). OM: Omnichroma; A1: Filtek Z350XT (shade A1B); A2: Filtek Z350XT (shade A2B); A3: Filtek Z350XT (shade A3B) of single specimens (thickness, 1.0 and 2.0 mm).
Additionally, the calculated ∆E*ab_SINGLE values for each shade are presented in Table 5 and Fig. 7D. In the 1.0 mm thickness, ∆E*ab_SINGLE value was lowest in the OM and A1 group (1.34 ± 0.35), which is below the 50 : 50% AT of 2.7 but above the 50 : 50% PT of 1.2. ∆E*ab_SINGLE values were higher for the OM and A2 (5.62 ± 0.45) and highest for the OM and A3 (10.36 ± 0.43), which both exceed the 50 : 50% AT of 2.7. The three ∆E*ab_SINGLE values were found to be significantly different (p < 0.0001). In the 2.0 mm thickness, ∆E*ab_SINGLE value was lowest in the OM and A2 group (2.21 ± 0.14), that is, lower than the 50 : 50% AT of 2.7 but higher than the 50 : 50% PT of 1.2. However, ∆E*ab_SINGLE values were higher in the OM and A1 (4.00 ± 0.29) and highest in the OM and A3 (5.87 ± 0.15), both higher than the 50 : 50% AT of 2.7. The three ∆E*ab_SINGLE values were found to be significantly different (p < 0.0001).
5. Differences in CIEL*a*b* values (∆L*DUAL, ∆a*DUAL, and ∆b*DUAL) and color difference (∆E* ab_DUAL) between dual specimen and the 2.0 mm-thick single specimen of Filtek Z350XT
∆L*DUAL, ∆a*DUAL, and ∆b*DUAL values between dual specimens (OMA1, OMA2, and OMA3) and 2.0 mm-thick single specimens of Filtek Z350XT (A1, A2, and A3) for each corresponding shade on the white background are shown in Table 6 and Fig. 8A - 8C. The magnitude of ∆ L*DUAL value is highest in the OMA3 and A3 group, followed by OMA1 and A1, and lowest in the OMA2 and A2 group. No significant difference was observed between the OMA1 and A1 group and the OMA2 and A2 group (p= 0.899). Dual specimens (OMA1 and OMA2) became darker, indicating negative ∆L*DUAL values, compared to single specimens (A1 and A2), respectively; however, differences were not significant (p= 0.290 and p= 0.867, respectively). Conversely, the dual specimen (OMA3) became lighter compared to the single specimen (A3) with significant difference (p < 0.0001).
Mean and standard deviation of ΔL* DUAL, Δa* DUAL, Δb* DUAL, and ΔE* ab_ DUAL on white background
Mean ΔL*DUAL , Δa*DUAL , Δb*DUAL , and ΔE*ab_DUAL on a white background. (A) ΔL*DUAL , (B) Δa*DUAL , (C) Δb*DUAL , (D) ΔE*ab_DUAL . The dotted line represents a 50 : 50% acceptability threshold (AT) of 2.7, and the dashed line represents a 50 : 50% perceptibility threshold (PT) of 1.2.
Different subscript letters indicate significant differences between the groups based on the one-way ANOVA (p < 0.05). OMA1: Omnichroma + Filtek Z350XT (shade A1B); OMA2: Omnichroma + Filtek Z350XT (shade A2B); OMA3: Omnichroma + Filtek Z350XT (shade A3B) of dual specimens; A1: Filtek Z350XT (shade A1B); A2: Filtek Z350XT (shade A2B); A3: Filtek Z350XT (shade A3B) of single specimens (thickness, 2.0 mm).
The magnitude of ∆a*DUAL value is highest in OMA3 and A3, followed by OMA2 and A2, and lowest in OMA1 and A1. Significant differences were observed among the three groups (p < 0.0001). All dual specimens (OMA1, OMA2, and OMA3) became more greenish, indicating negative ∆a*DUAL values, compared to the single specimens (A1, A2, and A3) with significant differences (p < 0.0001).
The magnitude of ∆b*DUAL value is lowest in OMA3 and A3, followed by OMA2 and A2, and highest in OMA1 and A1. Significant differences were observed among the three groups (p < 0.0001). Dual specimens (OMA1 and OMA2) became more yellowish, indicating positive ∆b*DUAL values compared to single specimens (A1 and A2) respectively, with significant differences (p < 0.0001). However, dual specimens (OMA3) became more bluish compared to single specimens (A3), with a significant difference (p < 0.0001).
Additionally, the calculated ∆E*ab_DUAL values for each shade are presented in Table 6 and Fig. 8D. The ∆E*ab_DUAL between OMA1 and A1 was 3.27 ± 0.31, which is higher than the 50 : 50% AT of 2.7. Conversely, the lowest ∆E*ab_DUAL was observed in OMA3 and A3 (2.12 ± 0.10), followed by OMA2 and A2 (2.25 ± 0.31), which were both lower than the 50 : 50% AT of 2.7 but higher than the 50 : 50% PT of 1.2. ∆E*ab_DUAL values between the OMA3 and A3 group and the OMA2 and A2 group were not significantly different (p= 0.683).
Discussion
In selecting shades for the multi-shade composite resin material, shade A1B, A2B, and A3B were selected based on findings from several studies, indicating that these shades are most common in the maxillary permanent and primary incisors of children[18-20].
In this study, composite resin specimens were unpolished to prevent any influence that finishing and polishing might have on color perception. A previous study has shown that polishing can alter the color and translucency of composite resin materials[21]. Furthermore, using a mylar strip produced smoother surfaces of composite resins, eliminating the need for further polishing.
In the previous studies[12,22,23] that evaluated the shade matching performance of single-shade composite resin with adjacent composite resin material, the single-shade composite resins were applied in the cavities confined by surrounding walls. This setup was designed to simulate clinical conditions where cavities are surrounded by dental hard tissues. However, our study involved placing single-shade composite resins directly over the base composite resins without any surrounding walls. This approach aimed to mimic clinical situations for class III or IV restorations of the anterior teeth with minimal surrounding dental hard tissue.
A spectrophotometer can operate two different measuring geometries: specular component included (SCI) and specular component excluded (SCE). In the SCI mode, both specular and diffused reflected light are measured, allowing the determination of intrinsic color without being affected by a specimen’s surface condition, such as whether it is polished or rough. Conversely, the SCE mode excludes the specular reflected light and is similar to the view perceived by the human naked eye. Therefore, the SCE mode is considered to provide a better assessment of the color appearance attributes of the specimens in clinical settings. Consequently, our study used SCE mode for color measurement[24].
In the current study, in 1.0 mm-thick single specimens, Omnichroma exhibited statistically equal or higher L* values and lower a* and b* values compared to Filtek Z350XT in A1B, A2B, and A3B shades on a white background. This result indicates that Omnichroma has a lighter and more greenish and blueish color compared to the conventional multi-shade composite resin, Filtek Z350XT in A1B, A2B and A3B shades, a finding consistent with that of a previous study[25]. The Omnichroma manufacturer and previous studies[9,26] indicated that the uniform 260 nm spherical filler particles of Omnichroma enable it to reflect red to yellow wavelengths of the incident light. However, our study’s result suggested that the red to yellow hue was weaker in Omnichroma compared to the conventional multi-shade composite resins.
In our study, as the thickness of the single specimen increased, Filtek Z350XT of A1B, A2B, and A3B shades showed a decreased L* value, an increased a* value, and a decreased b* value, indicating a shift toward a darker, more reddish, and blueish color. In contrast, for Omnichroma, an increase in the thickness of the single specimen resulted in a decreased L* value, an increased a* value, and an increased b* value, indicating a shift toward a darker, more reddish, and yellowish color. Notably, b* value change for Omnichroma was more pronounced compared to that of a* value, indicating that increased yellowness was more significant than the slightly increased redness. A previous study also reported the same tendency where the b* value increased for Omnichroma and the b* value decreased for the conventional multi-shade composite resin of A2 shade as the thickness of specimens increased[27]. Therefore, to restore a deep cavity, shade matching with Omnichroma may be more effective when the adjacent tooth structure is darker and more yellowish. This conclusion is supported by a previous study[28], which assessed the influence of the cavity depth on the shade matching of Omnichroma. The study found that Omnichroma provided superior shade matching in the lighter and less yellowish A3 shade compared to the darker and more yellowish A4 shade at 1.0 mm and 2.0 mm cavity depths. However, at 3.0 mm and 4.0 mm cavity depths, the shade matching of Omnichroma became similar between the A3 and A4 shades.
Our study reported that the magnitude order of CIEL*a*b* values observed in dual specimens (OMA1, OMA2, and OMA3) aligns with the magnitude order of CIEL*a*b* values observed in the 1.0 mm-thick single specimens (A1, A2, and A3). This result indicates that Omnichroma reflects the underlying composite resin shade. High-translucency materials will have a high blending effect[29]. The current study reported that both 1.0 mm and 2.0 mm-thick single specimens of Omnichroma exhibited higher TP values compared to Filtek Z350XT in A1B, A2B, and A3B shades. This finding is consistent with those of previous studies[28,30], which also reported that Omnichroma demonstrated superior TP values compared to other multi-shade composite resins. Previous studies[31,32] have reported higher translucency for Bis-GMA-based composite resins compared to UDMA/TEGDMA-based composite resins. This might be due to the fact that Bis-GMA has a refractive index closer to that of silica fillers than UDMA/TEGDMA. Other studies[33,34] found a negative correlation between filler content and TP value when the filler size remains unchanged. However, our study yielded inconsistent results. Despite Omnichroma being based on a UDMA/TEGDMA matrix and having a higher filler content than Filtek Z350XT, based on Bis-GMA, Omnichroma exhibited greater translucency than Filtek Z350XT in the A1B, A2B, and A3B shades. Ultimately, the composite resin’s translucency is determined based on the difference between the refractive indices of the filler and the organic matrix. When refractive indices are very similar, the material appears highly translucent[35]. The high translucency of Omnichroma can be attributed to its unique combination of filler type (uniform 260 nm spherical particles) and filler content (79 wt%), allowing the refractive index of the polymerized resin matrix to closely match that of the filler[36]. Furthermore, the uniform spherical particles in Omnichroma are evenly spaced and arranged to enhance light transmission through the restoration[7,17].
The high translucency of Omnichroma offers a significant potential for blending to different shades, mainly for class I or II cavities. However, this high translucency could also limit its use in class III or IV cavities, where the surrounding tooth structure is insufficient. In such cases, the restoration may appear grayish due to the dark background from the oral cavity. To address this issue, the manufacturer developed an “Omnichroma Blocker” (Tokuyama Dental, Tokyo, Japan) specifically for anterior teeth restorations. This product enhances the integration of the restorative material with the adjacent dental structure, potentially mitigating the grayish appearance caused by high translucency[37].
This current study evaluated the shade-matching ability of Omnichroma on shades A1, A2, and A3, by assessing ∆E*ab_SINGLE and ∆E*ab_DUAL. ∆E*ab_DUAL was significantly lowest for the OMA3 and A3 group, followed by OMA2 and A2, and highest for OMA1 and A1. This result was interesting because ∆E*ab_SINGLE in both 1.0 mm and 2.0 mm thicknesses were found to be highest in the OM and A3 group.
In our study, the shade-matching ability of Omnichroma in dual specimens with different background colors improved as the color difference between the singleshade and the multi-shade composite resins of single specimens increased. This tendency was inconsistent with that of previous studies[22,25,38]. Similarly, these previous studies reported that the single-shade composite resin exhibited the best shade match for lighter shade with lower shade numbers, which contrasts with the findings of our study. This discrepancy may be attributed to the differences in methodology. Previous studies[22,25,38] applied the single-shade composite resins within cavities surrounded by the walls. Conversely, our study directly applied Omnichroma over a base composite resin without any surrounding structure. The shade-matching ability of restorations is significantly influenced by the adjacent structure’s color, defined by two effects: simultaneous color contrast and blending effect. Simultaneous color contrast occurs when color shifts toward the complementary color of the surrounding[39]. Conversely, the blending effect occurs when colors appear closer to each other when viewed together than when viewed separately[40]. Therefore, different setups of composite resin restorations across studies might lead to varied influences of adjacent structures’ color. Our setup eliminated the impact of the reflected light from the surrounding composite resin in the axial walls, allowing only for reflected light from the bottom surface, which may explain the difference in shade-matching ability of Omnichroma compared to the findings of previous studies.
Specifically, this present study found that the magnitudes of ∆L*DUAL and ∆a*DUAL were highest in the OMA3 and A3 group, whereas ∆b*DUAL was lowest in the OMA3 and A3 group. Therefore, the superior shade matching of Omnichroma in the A3 shade resulted from the similarity of b* values between the dual specimen (OMA3) and 2.0 mm-thick single specimen (A3). For A1 and A2 shades, b* values increased in dual specimen (OMA1 and OMA2) compared to the 2.0 mm-thick single specimen (A1 and A2), indicating that Omnichroma reinforced the yellowness. Interestingly, among the 1.0 mm-thick single specimens, OM exhibited the lowest b* values compared to A1, A2, and A3. In the A3 shade, however, b* values decreased in dual specimen (OMA3) compared to the 2.0 mm-thick single specimen (A3), resulting in the lowest magnitude of ∆b*DUAL. This occurred because the 2.0 mm-thick single specimen (A3) had the highest b* value (the greatest yellowness) compared to A1 and A2. In conclusion, the increased yellowness introduced by Omnichroma resulted in poor shade matching for the A1 and A2 shades. In contrast, Omnichroma demonstrated superior shade matching in the A3 shade due to its well alignment with the original high yellowness of the A3 shade. However, for the A2 and A3 shades, ∆E*ab_DUAL was lower than the 50 : 50% AT but higher than the 50 : 50% PT, indicating that Omnichroma exhibited visually perceptible but clinically acceptable shade matching in both A2 and A3 shades.
This study had several limitations. First, this study did not evaluate the influence of background color (white or black) on CIEL*a*b* values of the composite resins. The optical properties of transmitted light, including information about the background color, can influence the appearance of the composite resin[41]. A dark background (high hue and chroma) tends to absorb light, enhancing the expression of the structural color of the composite resin. Conversely, a bright background (low hue and chroma) causes light to scatter, weakening the structural color. Therefore, further research should compare the color development of composite resins on white and black backgrounds to gain a better understanding of Omnichroma’s optical properties and its effectiveness in dark oral cavities. The second limitation of this study is that Omnichroma’s shade-matching ability on the natural teeth was not evaluated. In contrast to the disc-shaped composite resin specimens, natural teeth are polychromatic, multi-layered, translucent, and curved, influencing how light is reflected or scattered. These factors can affect the performance of composite resins when applied to natural teeth. Therefore, further in vivo and in vitro studies using natural teeth should evaluate Omnichroma’s shade-matching capability on the natural teeth and determine its effectiveness in actual clinical situations.
Conclusion
In this study, the single-shade composite resin, Omnichroma, exhibited a lighter, more greenish, and blueish color, compared to the multi-shade composite resin, Filtek Z350 XT in A1B, A2B, and A3B shades. With increased specimen thickness, Omnichroma became significantly more yellowish, whereas Filtek Z350 XT in A1B, A2B, and A3B shades became less yellowish. Furthermore, when Omnichroma was applied over Filtek Z350XT, the yellowness of dual specimens further increased beyond the original yellowness level of Omnichroma. Therefore, Omnichroma demonstrated clinically acceptable shade matching, particularly in the A3 shade, aligning well with the original high yellowness of the A3 shade despite inherent color differences between Omnichroma and the A3 shade. Additionally, the superior shade-matching ability of Omnichroma can be attributed to its higher translucency compared to the Filtek Z350XT. These findings indicate that the single-shade composite resin, Omnichroma, might be a valuable option in pediatric dentistry by simplifying the shade selection process.
Notes
Conflicts of Interest
The authors have no potential conflicts of interest to disclose.