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| ORIGINAL RESEARCH |
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| Year : 2019 | Volume
: 11
| Issue : 6 | Page : 412-416 |
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Evaluation of color and translucency of a recently developed bulk-fill resin composite with enhanced opacity: An in vitro
Youssef A Algarni
Assistant Professor of Endodontics, Restorative Dental Science Department, Faculty of Dentistry, King Khaled University, Abha, Saudi Arabia
| Date of Web Publication | 26-Nov-2019 |
Correspondence Address:
Dr. Youssef A Algarni
Assistant Professor of Endodontics, King Khaled University, B.O Box 7565, Abha 62527.
Saudi Arabia
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jioh.jioh_247_19
Aims and Objectives: This study aimed to analyze the color and translucency of a recently introduced bulk-fill resin composite with enhanced opacity. Materials and Methods: Twenty A3 shade composite disks, each of Filtek Bulk Fill (BF) and Filtek One Bulk Fill (OBF), were prepared with 4mm thickness. Two different backgrounds (white and black) and an intrinsic color for each material were used to ascertain the translucency parameter (TP) between white and black backgrounds, and to simulate oral environment darkness (between the black background and the intrinsic color of resin composite). Data collected were analyzed by the Mann–Whitney U test (P < 0.05). Results: The OBF disks showed significantly higher TP values (P < 0.001) than those of the BF. Regarding the ΔE* values for the masking ability of the oral cavity darkness, although OBF showed a statistically better masking ability than BF at 4mm thickness (z = 2.63, P = 0.009), none of them recorded the clinically acceptable threshold. Conclusion: The composition of the resin was shown to have a clear effect on the translucency and masking ability. The clinical significance is that whereas OBF appears to outperform BF, neither of their performances reach clinical acceptability. Keywords: Bulk fill, color, translucency
How to cite this article:
Algarni YA. Evaluation of color and translucency of a recently developed bulk-fill resin composite with enhanced opacity: An in vitro. J Int Oral Health 2019;11:412-6 |
How to cite this URL:
Algarni YA. Evaluation of color and translucency of a recently developed bulk-fill resin composite with enhanced opacity: An in vitro. J Int Oral Health [serial online] 2019 [cited 2023 Oct 5];11:412-6. Available from: https://www.jioh.org/text.asp?2019/11/6/412/271781 |
| Introduction | |  |
Resin composites have achieved popularity as direct restorative materials because of their excellent aesthetic properties, low cost, and excellent longevity.[1] However, clinicians might encounter difficulties in matching their colors to that of the surrounding dentitions because of the dissimilarity in optical properties between tooth structure and restorative resin composites.[1],[2] Polymerization shrinkage and the depth of cure of resin composites have been a disadvantage.
Bulk-fill resin composites have been introduced to shorten the restoration procedure by allowing 4-mm-thick increments to be light-polymerized and thereby reduce technique sensitivity[3],[4]. However to achieve a deeper penetration of light needed for curing, most bulk-fill composites have higher translucency.[5],[6] Nevertheless, this beneficial property could compromise the aesthetics of the restoration, especially in anterior restorations or discolored teeth, by transmission of the background color.[7],[8]
The translucency can be measured in terms of the translucency parameter (TP) or contrast ratio (CR). TP is the difference in color between a uniform thickness of the material over a white background and a black background[9],[10],[11] and is an indicator of the masking ability.[7],[12] The CR is the percentage of spectral reflectance of a specimen over a black background as compared with a white background. Therefore, a material having high CR would be relatively opaque with lower translucency.[13],[14]
The dissimilarity between the refractive indices of the monomers and the fillers are mainly responsible for the translucency of the resin composites. The lesser the mismatch, the higher will be the translucency of the cured material. This property is essential for materials beyond the usual 2-mm increments suggested for restorative composite procedures.[15]
A recent study investigated the effect of two light-curing protocols on mechanical behavior of three bulk-fill resin composites considering their optical properties. The authors concluded that the higher irradiance in a shorter time interval compromises the mechanical behavior of the resin composites, which may result in undesirable clinical outcomes.[16] In another recent study, the effect of water sorption and solubility on the color stability of bulk-fill resin composites was compared with conventional composite wherein the authors reported that bulk-fill resin composite yielded better color stability as compared with conventional resin composite.[17]
A new bulk-fill resin composite has recently been launched that purports to have greater opacity. The manufacturer claimed that “Because of a scientifically designed refractive index mismatch between the inorganic fillers and the organic resin matrix, there is increase in the contrast ratio. Consequently, the cured material exhibited a greater final opacity due to the improved aesthetics of the restoration”.[18] A recent study also reported that bulk-fill composites have a greater radiopacity than dentin and enamel.[19] Therefore, this study aimed to analyze the translucency of the newly developed bulk-fill resin composite with enhanced opacity. In addition, its ability to mask the oral cavity darkness was assessed. The two null hypotheses tested were as follows:
(1) The translucency values of bulk fill and one bulk fill have no significant difference and (2) the masking ability values of bulk fill and one bulk fill have no significant difference.
| Materials and Methods | | |
Study design
This cross-sectional in vitro study was carried out at the Dental Materials Laboratory, Department of Restorative Dental Sciences, King Khalid University College of Dentistry, Abha, Kingdom of Saudi Arabia.
Materials
Two bulk-fill composites of shade A3 were used: Filtek Bulk-Fill posterior (BF; 3M ESPE, St. Paul, MN) and Filtek One Bulk Fill (OBF; 3M ESPE, St. Paul, MN). The specifications of the materials used are shown in [Table 1].
Forty cylindrical resin composite disks (n = 20/material) were processed using split Teflon molds having a width of 10mm (diameter) and thickness of 4mm. The composites were inserted into the molds on a Mylar matrix. After that, the surfaces of the specimens were sheltered by another Mylar matrix and a glass plate. A steel block weighing 500g, which was obtained from King Khalid University College of Engineering, was used to apply a standardized constant pressure to obtain a uniform thickness. An LED curing light (Elipar FreeLight 2, 3M ESPE, St. Paul, MN, light output: 1226 mW/cm2) was used to photo-polymerize the specimens as per the manufacturer’s instructions. The amount of the light curing unit was confirmed using a radiometer (Demetron/Kerr, CT-100, Danbury, CT). Finally, the specimens were kept dry at 37 °C in an oven for 24h after removal of the Mylar matrix.
Background preparation
Two backgrounds were used in this study: a white tile (CIE L* = 98.35, a* = –0.2, and b* =1.16) and a black tile (CIE L* = 2.88, a* = –0.12, and b* = –1.09).
| Color Measurements | | |
The color was examined using a spectrophotometer (Cary 5000 UV–Vis–NIR, Agilent Technologies, Santa Clara, USA) in the reflectance mode relative to the standard illuminant D65, excluding the ultraviolet light. The size of aperture was 3mm, and the illuminating and viewing configurations were CIE diffuse/8° geometry. In consideration of the optical contact between the specimen and the backings, saturated sucrose solution was used to reduce the edge-loss effect. As per the manufacturer’s instructions, the instruments were calibrated before each color measurement. Three measurements were taken for each specimen and the average was recorded.
| Evaluation of Intrinsic Color Differences | | |
The intrinsic CIE L*, a*, and b* (CIELAB) values were measured at 4mm thickness for each resin composite on a neutral-grey background (CIE L* = 76, a* = –0.4, and b* = 0.00).[20],[21],[22]
| Translucency Measurement | | |
Translucency was measured in terms of the TP. The CIELAB coordinates (L*, a*, and b*) of the specimens were measured at 4mm thickness. L* denotes the lightness, which ranged from zero (black) to 100 (white). a* and b* are the chromaticity coordinates in the red–green axis (−a* = green and +a* = red) and the yellow–blue axis (−b*= blue and +b* = yellow), respectively.[20] The differences in CIELAB color coordinates between the white and black backgrounds were calculated to obtain the TP according to the following formula[19]: 
where the subscripts W and B refer to the color coordinates over the white and black background, respectively.
In addition, the CR was determined at 4mm thickness.[11],[14],[23] The CR was calculated in accordance to the following formula: CR =YB/YW, where the subscripts YB and YW refer to spectral reflectance over black and white backgrounds, respectively.
| Masking Ability Measurement | | |
The CIELAB color differences (ΔE*) were also calculated while simulating the darkness of an oral cavity (between the black background and the intrinsic color of the resin composite)[6],[11],[20] using the following formula:
where the subscripts B and I refer to CIELAB values of each specimen on a black background and the CIELAB values of the intrinsic color of each material.
| Statistical Analysis | | |
The recorded data were analyzed with the Statistical Package for the Social Sciences software version 22.0 (SPSS, Chicago, IL). The data were not normally distributed in some groups as shown by the Shapiro–Wilk test (P < 0.05). The Mann–Whitney U test was used to compare results between the two materials. All statistical tests were set at a level of significance of α = 0.05. The clinical relevance for the CIELAB color difference, ΔE*, was evaluated in this study in terms of 50:50% perceptibility (ΔE* = 1.74)[24] and 50:50% acceptability (ΔE* = 2.7).[25],[26]
| Results | | |
Descriptive statistics were expressed as the mean ± standard deviations. The CIELAB values of each bulk-fill composite at 4mm thickness are presented in [Table 2]. The TP and masking ability of the oral cavity darkness are shown in [Table 3]. | Table 2: Intrinsic color (CIE L*,a*,b*) values (means and standard deviations) of bulk-fill resin composites at 4mm thickness
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,  | Table 3: ΔL*, Δa*, Δb*, and ΔE* values (means and standard deviations) of bulk fill resin composites at 4mm thickness on two backgrounds
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The OBF composite material showed significantly higher TP values (z = 4.7, P < 0.001) than BF at 4mm thickness. As for the CR, there was no significant difference (z = 1.6, P = 0.12) between BF (CR = 0.77 ± 0.008) and OBF (CR = 0.75 ± 0.004).
Regarding the ΔE* values for the masking ability of the oral cavity darkness, although OBF showed a statistically better masking ability than BF at 4mm thickness (z = 2.63, P = 0.009), neither of them recorded the clinically acceptable threshold (ΔE* = 2.7).
| Discussion | | |
Discoloration has been measured widely using spectrophotometers and colorimeters as they annihilate subjective errors.[27] Majority of these color measurement devices use ΔE obtained from the Commission International de I’Eclairage CIE (L*a*b*) color system to determine color changes because it is appropriate in the measurement of small color differences.[28] The greatest advantage of this as a means for describing and characterizing color is its consistency and additionally, its color values on the three axes are closely matched to the human interpretation of color.[29]
In restorative dentistry, appearance is influenced not just by color but also by geometric features such as the surface roughness, gloss, haze, and translucency.[30] In anterior restorations or discolored teeth, the compatibility of the color of the restoration with the natural tooth structure becomes more challenging because of the transmission of the underlying color.[7]
Bulk-fill composites differ from most of the conventional composite resins because of their increased depth of cure, which could mainly be associated with an increase in translucency.[31],[32] In this study, the intrinsic color, translucency, and masking ability were analyzed with a spectrophotometer, and the color change was expressed in ΔE*, units which is the sum of the change in the L, a, and b parameters, calculated from the repeated color measurements.
The TP of a material measures the observed difference in color between a uniformly thick material over a white background and over a black background. The TP measurement provides a value corresponding to the common visual perception of translucency.[20] A higher value for TP represents greater translucency; that is, if a material is completely opaque, the value of TP is zero.[21],[33] Therefore, opacity is an important factor to be considered while evaluating the aesthetic property of restorative materials.[33]
In this study, the thickness of the bulk-fill resins was restricted to 4mm according to a study that reported that a 4mm thickness of the enamel shade is adequate to prevent the effect of the underlying color. Hence, the color of the samples at this thickness can be considered the inherent colors of the bulk-fill resins that have not been affected by underlying color.[13] Hence, 4-mm-thick disk specimens were prepared in this study and their colors were used as the intrinsic color of the composite resin [Table 2].
In addition to variations in thickness, changing the background color of the composite resins can alter the end result.[34] Therefore, in this study, standard white and black tiles were used as backgrounds. The results of this study with a black background were useful when anterior restorations required masking of dark oral background with the thickness of 4mm [Table 3].
Terms such as lighter, darker, great, small, acceptable, and perceptible are used to describe color differences for the estimation of color and is subjective and based on a range of conventionally accepted ΔE* values. The threshold for the clinically acceptable color difference has been reported as ΔE* ≤ 2.0,[35]ΔE* ≤ 3.3,[36] and ΔE* ≤ 3.7.[37]
The clinical relevance for the CIELAB color difference (ΔE*) was evaluated in this study in terms of 50:50% perceptibility (ΔE* = 1.74)[20] and 50:50% acceptability (ΔE* = 2.7).[24],[25] However, it has been stated that all threshold differences are dependent on visual conditions such as illuminant, object, viewing distance, and optical geometry, and also the observer variables such as subjective intra-observer and objective-intra-observer variables in color vision including normal and deficient.[9]
The color differences detected between different products of the same shade indicated clinically noticeable color differences (ΔE* above 1.74) and none of them recorded clinically acceptable threshold values (ΔE* above 2.7), in spite of being produced by the same manufacturer.
In this study, OBF showed significantly higher TP values (z = 4.7, P < 0.001) than BF at 4mm thickness. As for the CR, there was no significant difference (z = 1.6, P = 0.12) between BF (CR = 0.77 ± 0.008) and OBF (CR = 0.75 ± 0.004).
Regarding the ΔE* values for the masking ability of the oral cavity darkness, OBF showed a statistically significant better masking ability than BF at 4mm thickness (z = 2.63, P = 0.009), this can be explained by the basis that they had the highest L* values of inherent color. A larger L* value could be helpful in nullifying the effect of the dark background color of the oral cavity. The masking ability of the composite resins is also expected to be influenced by the presence of opacifiers, pigments, fillers, and other various additives. As commercially available composite resins were used in this study, it was difficult to determine the aspect that most critically affected the masking ability.
Many studies have reported on the translucency of composites resin, but none have investigated the new bulk-filling composites, which have been introduced primarily to be used in thicker layers. This study provides information on the relative translucency of a new product of the bulk-fill resin composite. However, the optical properties of the tested bulk-fill composites may be influenced by saliva, moisture, aging, and staining acquired in the oral environment over a period of time.[38] Hence, long-term observation along with simulation of the normal oral environment conditions may provide a better understanding of the optical properties of these materials.
Under the limitations of this study and as per the results of this study, the Null hypotheses tested were as follows:
- (1) The translucency values of BF and OBF have no significant difference.
- (2) The composition of BF and OBF was shown to have a clear effect on DE*ab and TP. So, the null hypothesis was rejected.
| Conclusion | | |
A statistically significant difference in TP was found between the OBF and BF composite resins. Regarding the ΔE* values for the masking ability of the oral cavity darkness, although OBF showed a statistically better masking ability than BF at 4mm thickness (z = 2.63, P = 0.009), none of them recorded the clinically acceptable threshold.
We must take the translucency, masking abilities, and color differences of the bulk-fill resin composites into consideration to achieve a clinically viable and acceptable color matching of the restoration.
Ethical consent and institutional review board statement
This is an in vitro study and has been conducted in accordance with the ethical principles mentioned in the declaration of Helsinki (2013).
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]
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