Influence of Use of Opaque Single-Shade Composite Resin and Residual Dentin Thickness on the Esthetic Performance of Single-Shade Composite Resin
Article information
Abstract
This study aimed to analyze the effect of combining a single-shade composite resin with an opaque single-shade composite resin on the color adjustment potential (CAP) and color difference (ΔE*ab) of restorations at various residual dentin thicknesses. One single-shade composite resin (Omnichroma [OM]), one opaque single-shade composite resin (Omnichroma Blocker [OB]), and two multi-shade composite resins (Filtek Z350 XT [FT] A2D shade and Estelite Sigma Quick [ES] OA2 shade) were included in this study. Using first molar denture teeth in A2 shade, both single and dual specimens were fabricated at residual dentin thicknesses of 0, 1, and 2 mm. The translucency parameter (TP), ΔE*ab , and CAP were calculated for the control group and 3 experimental groups. The FT group exhibited the highest ΔE*ab values and the lowest CAP (p < 0.0083), while the highest TP values were observed in the control group (p < 0.0083). CAP and ΔE*ab did not show significant differences based on residual dentin thicknesses in most groups. TP was significantly higher at 0 mm residual dentin thickness than at 1 mm and 2 mm in all groups (p < 0.0167). When the perceptibility threshold was set at ΔE*ab ≤ 2.0, the ES and OB groups exhibited color differences within the threshold. These findings suggest that combining a singleshade composite resin with an opaque single-shade composite resin can contribute to the esthetic performance of restorations.
Introduction
Achieving a shade that harmonizes with natural teeth is a significant clinical challenge in composite resin restorative treatments. Composite resin is widely used as a restorative material in dentistry, playing a significant role in esthetic restoration for both permanent and primary teeth, especially in pediatric dentistry [1,2]. The success of composite resin restorations largely depends on the form and function restoration of the teeth while maintaining esthetics. Numerous studies have used the Commission Internationale d’Eclairage L*a*b* (CIE L*a*b*) technique to assess the color compatibility of composite resins, revealing that these factors are directly associated with patients’ esthetic satisfaction. Such analyses are considered essential references for achieving natural restorative outcomes in clinical practice [3-6].
Single-shade composite resins offer the advantage of easily adapting to various tooth shades. However, in cases of Class III and IV cavities, or deep cavities, there is a potential risk of dark background colors reflecting through the restoration. As a result, the restoration shade may deviate from the desired appearance or appear overall darker, leading to a mismatch with the patient’s expectations for a natural shade [4,7-9]. To address these color-matching challenges, manufacturers have developed an opaque single-shade composite resin known as Omnichroma Blocker. By effectively blocking dark or discolored areas, the opaque single-shade composite resin allows the restoration surface to reflect a more natural shade.
Although the clinical usefulness of combining a single-shade composite resin with an opaque singleshade composite resin is well recognized, studies on the specific effects of this combination on the color of the final restoration remain limited. Most previous studies have primarily focused on the masking effects of opaque single-shade composite resins. However, there are limited studies evaluating the influence of combining single-shade composite resins with opaque single-shade composite resins, particularly comparing the effects of opaque single-shade and opaque multi-shade composite resins on the final shade of restorations. Furthermore, studies examining the impact of opaque single-shade composite resins on the esthetics of final restorations provide insufficient data on how the thickness of the residual tooth structure, especially the residual dentin thickness beneath the cavity, affects restoration outcomes.
The residual dentin thickness affects the esthetics of dental restorations [10]. Thin residual structures allow internal dark structures, such as the pulp chamber or dark background, to show through more easily, causing the restoration to fail to blend naturally with the original tooth color. In such cases, using an opaque-shade composite resin to block the effects of the dark background can effectively enhance the esthetic quality of the restoration.
Previous studies reported that single-shade composite resins tend to have high translucency, which can reveal the surrounding dark shades [4]. By using an opaque single-shade composite resin to block this effect, the final color of the restoration can be adjusted to appear more natural. Therefore, this study aimed to evaluate the effects of using opaque single-shade composite resin and residual dentin thickness beneath the cavity on the color difference (ΔE*ab) and color adjustment potential (CAP) of single-shade composite resin restorations.
Materials and Methods
1. Preparation of the specimen
1) Experimental composite resins and teeth preparation
In this study, three types of composite resins were used as masking materials. These included two types of multishade composite resins (Filtek™ Z350 XT (FT), 3M ESPE, St. Paul, MN, USA) and (ESTELITE® SIGMA QUICK (ES), Tokuyama Dental, Tokyo, Japan) and one type of opaque single-shade composite resin (Omnichroma Blocker (OB), Tokuyama Dental). Table 1 shows information on the 4 composites. The specific shades of the multi-shade composite resins were A2D for FT and OA2 for ES. A singleshade composite resin (Omnichroma (OM), Tokuyama Dental) was used as the restorative material layered over the masking materials.
Information on the experimental composite resins used in this study
First molar denture teeth (Biotone denture teeth®, Dentsply Sirona, Charlotte, NC, USA) were used in this study. The denture teeth were standardized to the A2 shade based on an earlier study on the color of early permanent teeth [11,12]. The prepared teeth were classified according to the study process (Fig. 1).
Schematic diagram of the study process.
OM: Omnichroma; FT: Filtek Z350 XT; ES: Estelite sigma quick; OB: Omnichroma Blocker.
In this study, the Translucency Parameter (TP), ΔE*ab , and CAP were measured using the specimens fabricated for this study. CAP refers to the ability of a composite resin to visually harmonize its shade with the surrounding tooth structure or adjacent composite resin of a different shade. This property is evaluated by comparing the color of the composite resin when it is used alone and when it is applied in a simulated clinical restoration, thereby assessing how the resin’s shade adjusts in response to its environment [13].
For the measurement of CAP, both single and dual specimens were fabricated. The single specimen represents the composite resin in isolation and was prepared using only the experimental composite resin in the form of a denture tooth resembling the natural morphology. The dual specimen simulates a clinical restoration scenario, where a cavity was prepared in the denture tooth and restored with the composite resin. The TP and ΔE*ab values were measured using the dual specimens, which replicate actual restoration conditions.
2) Single specimen preparation
The fabrication process of the single specimen is shown in Fig. 2. For single specimens, a first molar denture tooth was replicated using the experimental composite resin. To create molds with depths of 2, 3, 4, and 5 mm, the denture teeth were trimmed at the base with a diamond disk so that the central heights matched the desired depths. Each trimmed denture tooth was placed on a flat glass slab, and silicone impression material (Exafine Putty Type, GC Co., Tokyo, Japan) was used to fabricate the corresponding molds. In groups using masking materials, OM was filled into the 2 mm deep mold, and light curing was performed for 15 seconds using a VALO light-emitting diode (Ultradent Products Inc., South Jordan, UT, USA). In all stages, light curing was carried out at a distance of 2 mm from the specimen surface using the high-power mode of the LED curing unit (1400 mW/cm²). After curing, the specimen was removed from the 2 mm deep mold and placed in a 3 mm deep mold. Then, a 1 mm layer of masking material was added on top, and the specimen was light-cured. Once the 3 mm high specimen was completed, it was used to create 4 and 5 mm high specimens. The 3 mm high specimen was placed in 4 and 5 mm deep molds, respectively, and an additional layer of OM with thicknesses of 1 and 2 mm was added on top and light-cured. For the control group without the masking material, OM was layered in molds of 3, 4, and 5 mm depths at 2 mm increments, with each layer light-cured for 15 seconds. Before light curing, all specimens were leveled at the bottom using a mylar strip and a glass slab. The single specimens were polished under water cooling according to the manufacturer’s instructions using a series of Soflex ™ Contouring and Polishing Discs (3M ESPE, St. Paul, MN, USA). In total, 120 specimens were prepared, with 10 specimens for each type of experimental composite resin at specimen heights of 3, 4, and 5 mm.
Procedure for fabricating a single specimen.
3) Dual specimen preparation
The fabrication process of the dual specimen is shown in Fig. 3. The bases of the denture teeth were trimmed with a diamond disk to achieve central heights of 3, 4, and 5 mm. Since the occlusal surface of the molar denture teeth used in this study was not flat, the speci-men height was measured based on the center of the occlusal surface. The height of each specimen at its center was measured using a micrometer (Mitutoyo digimatic micrometer, Mitutoyo Co., Kanagawa, Japan). Forty specimens were prepared for each height group. Cylindrical cavities, 3 mm deep and 4 mm in diameter, were created at the center of the occlusal surface using #330 and #556 carbide burs, with the residual dentin thicknesses beneath the cavity set to 0, 1, or 2 mm, respectively. The thicknesses of the remaining dentin were measured using a micrometer. The cavities were rinsed using a 3-way syringe, gently air-dried, and an 8th-generation bonding agent (Scotchbond™ Universal Adhesive, 3M ESPE) was applied to the cavity walls. The excess bonding agent was removed by air-blowing, followed by light curing. In groups using masking material, a 1 mm layer of the masking material was first applied and light-cured, followed by filling the remaining cavity with OM. After applying the opaque-shade composite resin, the thickness was verified to be precisely 1 mm using a micrometer before light curing. Conversely, in the control group without the masking material, the 3 mm depth cavity was incrementally filled with OM alone to a thickness of 2 mm. For specimens with a residual dentin thickness of 0 mm, a Mylar strip was placed beneath the cavity to ensure a flat base for the restoration. Each resin layer was light-cured for 15 seconds. In total, 120 specimens were prepared, with 10 specimens for each type of experimental composite resin and at specimen height of 3, 4, and 5 mm.
Procedure for fabricating a dual specimen.
All specimens were stored in saline for 24 hours before color measurement.
2. Color measurement
In this study, the CIE L*a*b* color system was used. The values utilized by CIE are denoted as L* , a* , and b* , collectively referred to as the CIE L*a*b* color measurement method. To measure the CIE L*a*b* parameters of the restorations, a colorimeter (Shade Eye-NCC, Shofu Co., Kyoto, Japan) was used. Each specimen was measured 3 times at the same location, and the average value was recorded. To minimize inter-operator variability, all procedures in this study were performed by a single examiner. Because natural light can vary depending on the time of day, all experiments were conducted after sunset to prevent potential errors caused by such variations. In addition, blinds were drawn over all windows to block any external light sources. Accordingly, the light source used for the shade measurement of the restorations was limited to the artificial lighting provided by the laboratory lights.
For dual specimens, L*a*b* parameters at the center of the occlusal surface of the denture tooth were measured against a black background before cavity preparation. For dual specimens, after 24 hours post-composite resin filling, each specimen was lightly wiped with gauze, and the L*a*b* parameters at the center of the restoration were measured against black and white backgrounds. For single specimens, the same methods were used to measure L*a*b* parameters at the center of the occlusal surface against a black background. The colorimeter was calibrated following the manufacturer’s instructions prior to measurement.
3. Calculation of the Translucency parameter, Color difference (ΔE*ab), and Color adjustment potential measurement
1) Translucency parameter
The TP of each material was calculated using the following formula [4,8]:
Here, the subscripts W and B represent the color indicators measured against white and black backgrounds, respectively. A higher TP value indicates greater translucency.
2) Color difference (ΔE*ab)
ΔE*ab was calculated based on L*a*b* values measured on a black background pre- and post-restoration of dual specimens, using the following formula:
A smaller ΔE*ab value indicates a smaller color difference between the compared specimens.
3) Color adjustment potential
CAP was calculated using L*a*b* values measured on a black background with the following formula [3]:
ΔESingle represents the color difference between the single specimen and the unrestored first molar denture tooth, whereas ΔEDual represents the color difference between the dual specimen and the first molar denture tooth before dual specimen preparation. A higher CAP value indicates a greater color adjustment capability of the restorative material.
Subsequently, the means and standard deviations of ΔE*ab , CAP, and TP were calculated for each experimental composite resin.
4. Statistical analysis
Statistical analysis was performed using IBM SPSS version 28.0 (SPSS Inc., Chicago, IL, USA). The normality of the data was assessed using the Shapiro-Wilk test. Since the data did not follow a normal distribution, the Kruskal-Wallis test was used to evaluate statistical significance. The TP values, ΔE*ab , and CAP of the experimental composite resins were compared using Bonferroni post-hoc analysis. Comparisons of the 4 composite resin groups were conducted at a significance level of p < 0.0083, and comparisons of the 3 residual dentin thicknesses within the same resin were conducted at a significance level of p < 0.0167.
Results
1. Translucency parameter
The mean and standard deviation (SD) of the TP for each group are presented in Table 2 and Fig. 4. The control group revealed significantly higher TP values than the FT and OB groups across all residual dentin thicknesses (p < 0.0083). The control group also exhibited significantly higher TP values than the ES group at a residual dentin thickness of 1 mm (p < 0.0083), but there were no significant differences at other thicknesses. No significant differences were observed among the experimental groups at any residual dentin thickness. For all resin types, a residual dentin thickness of 0 mm showed significantly higher TP values compared to 1 and 2 mm (p < 0.0167), with no significant difference between 1 and 2 mm (Table 2, Fig. 4).
Translucency parameters of each group
Means and standard deviations of the translucency parameter values according to the materials and residual dentin thicknesses. Different uppercase letters in a row indicate a significant difference among the 4 composite resin groups (p < 0.0083). Different lowercase letters in a column indicate a significant difference among the 3 residual dentin thicknesses (p < 0.0167). Control: Control group; FT: Filtek™ Z350 XT; ES: ESTELITE® SIGMA QUICK; OB: Omnichroma Blocker.
2. Color difference (ΔE*ab)
The mean and SD of ΔE*ab for each group are presented in Table 3 and Fig. 5. The FT group showed significantly higher ΔE*ab values than other groups at residual dentin thicknesses of 1 and 2 mm (p < 0.0083). At a residual dentin thickness of 0 mm, the FT group showed significantly higher ΔE*ab values compared to the control and ES groups (p < 0.0083). At all levels of residual dentin thicknesses, there were no significant differences among the control, ES, and OB groups. Furthermore, changes in residual dentin thickness did not result in significant differences within any of the groups (Table 3, Fig. 5).
Color difference (ΔE*ab) of each group
Means and standard deviations of color difference (ΔE*ab) values according to materials and residual dentin thicknesses. Different uppercase letters in a row indicate a significant difference among the 4 composite resin groups (p < 0.0083). Different lowercase letters in a column indicate a significant difference among the 3 residual dentin thicknesses (p < 0.0167). Control: Control group; FT: Filtek™ Z350 XT; ES: ESTELITE® SIGMA QUICK; OB: Omnichroma Blocker.
3. Color adjustment potential
The mean and SD of CAP for each group are presented in Table 4 and Fig. 6. The FT group exhibited significantly lower CAP values than the control group at a residual dentin thickness of 0 mm (p < 0.0083). At a residual dentin thickness of 1 mm, the FT group showed significantly lower CAP values compared to the control and ES groups (p < 0.0083). At a residual dentin thickness of 2 mm, the FT group had significantly lower CAP values than the other groups (p < 0.0083). Significant differences according to residual dentin thickness were not observed within any group, except for the OB group. In the OB group, the CAP value at a residual dentin thickness of 0 mm was significantly lower than at 2 mm (p < 0.0167, Table 4, Fig. 6).
Color adjustment potential of each group
Means and standard deviations of the color adjustment potential values according to materials and residual dentin thicknesses. Different uppercase letters in a row indicate a significant difference among the 4 composite resin groups (p < 0.0083). Different lowercase letters in a column indicate a significant difference among the 3 residual dentin thicknesses (p < 0.0167). Control: Control group; FT: Filtek™ Z350 XT; ES: ESTELITE® SIGMA QUICK; OB: Omnichroma Blocker.
Discussion
Both CAP and color difference are used as indicators to evaluate the esthetic performance of dental restorative materials. In this study, significantly lower CAP values were observed in the FT group, followed by the OB, ES, and control groups in that order. However, this did not correspond to the results for color difference, represented by ΔE*ab . The ΔE*ab was significantly higher in the FT group, followed by the control, OB, and ES groups.
In addition to color difference, CAP reflects the ability to adjust for discrepancies with surrounding colors. Contributing factors to CAP include the translucency of the material, interaction with the background, color difference with the existing tooth structure, and the physical properties of the material. CAP tends to increase with higher translucency of the material [13,14]. Due to the high translucency and structural color characteristics of OM, the control group exhibited higher CAP values than other groups, demonstrating strong color adjustment capabilities.
As a parameter, CAP is designed to quantify the physical aspect of blending influenced by translucency [13]. It is measured as the ratio of color difference values between 2 objects: ΔEDual , observed within a surrounding medium and ΔESingle , evaluated independently [15]. Transparent materials may exhibit larger ΔEDual values due to their interaction with the surrounding environment, but CAP increases primarily because the increase in ΔESingle is even greater. In contrast, materials with high opacity do not exhibit a significant increase in ΔESingle values, while the increase in ΔEDual leads to a decrease in CAP value [16]. In this study, the control group exhibited significantly greater TP values compared to most other experimental groups across various residual dentin thicknesses (p < 0.0083). When the difference in translucency between the compared restorative materials is large, as observed in this study, ΔESingle value of the material with higher translucency increases, resulting in higher CAP values. Consequently, the ΔEDual / ΔESingle ratio decreases, masking the high ΔEDual values. These relationships suggest that the control group, which exhibited higher TP values, also showed the highest CAP. This could explain why color difference and CAP did not align.
Considering the threshold for clinically acceptable color difference, varying assessments may arise depending on the ΔE*ab value standards applied. ΔE*ab values exceeding the threshold may indicate challenges in achieving color matching in actual clinical settings, suggesting an increased likelihood that patients may perceive the color difference, potentially leading to esthetic dissatisfaction. Clinically acceptable ΔE*ab thresholds are generally reported as ΔE*ab ≤ 2.0 – 3.7 and these standards may vary based on specific visual conditions and observer variables [17-19].
In this study, when ΔE*ab ≤ 3.3 [19] is set as the threshold, the color difference in the FT group could be evaluated as exceeding the clinically acceptable level. Furthermore, if a stricter standard of ΔE*ab ≤ 2.0 [17] is applied, the FT group exceeded the clinically acceptable threshold at all levels of residual dentin thickness, while the control group exceeded the threshold at 0 and 1 mm residual dentin thickness. ΔE*ab values exceeding the threshold may indicate challenges in achieving color matching in actual clinical settings, suggesting an increased likelihood that patients may perceive the color difference, potentially leading to esthetic dissatisfaction. In addition, the results observed in the control group suggest that when residual dentin thickness is less than 2 mm, the use of OM alone in deep cavities may lead to suboptimal esthetic outcomes. Therefore, in cases where residual dentin thickness is less than 2 mm in deep cavities exceeding 3 mm, the use of a composite resin with higher opacity may contribute positively to the final esthetics of the restoration. However, since this study was designed with a focus solely on residual dentin thickness, the findings may not be directly applicable to clinical situations such as proximal caries in anterior teeth where enamel remains on the surface. Thus, further research is needed to investigate the color changes of single-shade composite resins according to variations in residual enamel thickness.
The ES and OB groups exhibited ΔE*ab values below 2.0 across all residual dentin thicknesses, indicating that these groups achieved esthetically favorable outcomes with minimal color differences. In a previous study, the effects of combining opaque single-shade composite resin with single-shade, multi-shade, and group-shade composite resins were compared in shallow 2 mm thick restorations, and no significant color differences were observed across all groups based on the use of opaque single-shade composite resin [20]. This study aimed to evaluate the effect of opaque single-shade composite resin in deeper cavities with a depth of 3 mm to examine its clinical significance in such settings. In the present study, a comparison between the control group and the OB groups revealed no significant differences in ΔE*ab . However, when compared based on the threshold of ΔE*ab ≤ 2.0, the OB groups demonstrated superior esthetics. These results suggest that the combination of opaque single-shade composite resin and single-shade composite resin can provide excellent esthetics in deep cavities with an A2 shade and that its performance is comparable to that of multi-shade opaque composite resin. However, as this study evaluated the use of OB in a fixed thickness of 1 mm, further research is needed to investigate the effect of varying OB thicknesses on the final shade of the restoration.
The study results revealed that the FT group exhibited low CAP values and high ΔE*ab values, failing to meet the expected clinical performance in color adaptability. The masking material replaces the underlying structure, allowing the application of the single-shade composite resin above to reflect a final shade that aligns with the underlying structure and remaining dentin. This approach is closely related to the structural color phenomenon, promoting natural harmony with the surrounding tooth shade [14,21,22]. One of the factors influencing ΔE*ab values is the color difference between the restoration and the existing tooth structure. Therefore, the degree to which the masking material matches the denture tooth can significantly influence ΔE*ab values. In this regard, multi-shade composite resins may exhibit relatively high ΔE*ab values when combined with singleshade composite resins due to the color difference with the existing tooth structure, implying the limitations in color compatibility.
Previous studies have indicated significant color differences between commercial resin composites and shade guides [23,24], as well as between opaque-shade composite resins and body-shade composite resins [25]. Consequently, the actual color of commercial opaqueshade composite resin may differ from the shade desired by clinicians for esthetic purposes, potentially having a more pronounced influence on the final restoration color when a single-shade composite resin is applied on top.
In this study, a trend of decreasing TP was observed as residual dentin thickness increased. This result is similar to findings in previous studies, which indicate a tendency for TP values to decrease as specimen thickness increases [26]. A thicker residual dentin also tended to decrease ΔE*ab values and increase CAP values. Unlike TP, which showed significant differences as the residual dentin thickness increased, ΔE*ab and CAP exhibited decreasing and increasing trends, respectively, with varying residual dentin thickness, but these differences were not statistically significant. This suggests that in deep cavities, while residual dentin thickness may influence the color compatibility of restorations, it does not significantly influence ΔE*ab and CAP values to a clinically meaningful extent.
This study has several limitations. In this study, the A2 dentin shade, which has relatively high opacity, was used for the same purpose as an opaque-shade composite resin. However, since it differs from opaque resins such as Omnichroma Blocker, the possibility that this difference may have influenced the experimental results was considered as one of the limitations of the study. In clinical applications, the change in tooth thickness before and after restoration is minimal, and the residual dentin thickness at the cavity base decreases as the cavity depth increases. This implies that variations in the proportions of residual dentin, opaque-shade composite resin, and the overlying restorative resin, depending on cavity depth, may affect the final color compatibility of the restoration. Therefore, further studies are needed to investigate the effects of these proportional changes in the same thickness. As this study was conducted in vitro, in vivo studies that reflect actual intraoral conditions are necessary. Various oral conditions can influence the color compatibility of restorative materials, so conducting studies in clinical settings is essential to obtain more reliable results.
Conclusion
The results of this study indicate that the combined use of single-shade composite resin and opaque single-shade composite resin in deep cavities with less than 2 mm of residual dentin thickness can have a positive effect on the final shade of the restoration. This combination showed ΔE*ab within clinically perceptible thresholds across all levels of residual dentin thickness. In the field of pediatric dentistry, opaque single-shade composite resin can be used as a primary material to mask dark colors in deep cavities, thereby contributing to the enhancement of the esthetics of the final restoration.
Notes
Conflicts of Interest
The authors have no potential conflicts of interest to disclose.
CRediT Authorship Contribution Statement
Suyeon Lee: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft. Juhyun Lee: Project administration, Validation, Writing – review & editing. Minho Hong: Writing – review & editing. Haeni Kim: Supervision, Validation, Writing – review & editing.