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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 5  |  Issue : 2  |  Page : 74-78

Comparison between nanohybrid filler and submicron composite resin shade on color changes after polymerization


1 Department of Conservative Dentistry, Faculty of Dentistry, Trisakti University, Jakarta, Indonesia
2 Department of Oral Pathology, Faculty of Dentistry, Trisakti University, Jakarta, Indonesia

Date of Submission19-Feb-2021
Date of Decision31-Mar-2021
Date of Acceptance29-Apr-2021
Date of Web Publication23-Jun-2021

Correspondence Address:
Ade Prijanti Dwisaptarini
Department of Conservative Dentistry, Faculty of Dentistry, Trisakti University, Jakarta.
Indonesia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/SDJ.SDJ_69_21

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  Abstract 

Background: Initial color determination of composite resins before polymerization is crucial to achieve an esthetic result that mimics the original tooth color. A filler particle size and composition affect the color change of the composite resin after polymerization despite the improvement in the chemical composition and filler of the composite resin. Objective: The effects of nanohybrid filler and submicron composite resin shade on color changes after polymerization were determined. Methods: Disc-shaped composite resin samples (diameter and thickness of 12 mm and 2 mm, respectively) were categorized into six groups, with each group containing 10 plates, according to the shade and type of filler (nanohybrid UD1, UD2, UD3; submicron OA1, OA2, OA3). Digital photographs were taken before and after polymerization. The changes in color (ΔE*ab values) were determined using software via eLABor_aid. Result: Only the Micerium EHRi UD1 composite resin group exhibited ΔE*ab < 3.3. The independent t-test revealed significant differences in the ΔE*ab (P < 0.05) between the nanohybrid and submicron composite resins in all shade groups (A1, A2, and A3). One-way analysis of variance revealed significant differences in ΔE*ab (P < 0.05) among A1, A2, and A3 between the nanohybrid and submicron composite resin groups. Tukey’s post hoc test revealed significant differences in ΔE*ab (P < 0.05) for the Micerium EHRi UD1 group compared with those of the UD2 and UD3 groups, as well as in the case of the Tokuyama Palfique OA1 group compared with those of the OA2 and OA3 groups. Conclusion: Nanohybrid filler and submicron composite resin shade affected color changes after polymerization. Compared to the darker color groups, brighter shades (UD1 and OA1) exhibited a lower-intensity color change.

Keywords: Color difference, filler, nanohybrid filler, particle size


How to cite this article:
Irawan RS, Dwisaptarini AP, Istanto E, Sudiono J. Comparison between nanohybrid filler and submicron composite resin shade on color changes after polymerization. Sci Dent J 2021;5:74-8

How to cite this URL:
Irawan RS, Dwisaptarini AP, Istanto E, Sudiono J. Comparison between nanohybrid filler and submicron composite resin shade on color changes after polymerization. Sci Dent J [serial online] 2021 [cited 2021 Jul 31];5:74-8. Available from: https://www.scidentj.com/text.asp?2021/5/2/74/319053




  Background Top


Initial color determination of composite resins prior to polymerization is a key clinical procedure in esthetic restorations to obtain good esthetics and mimic the natural tooth color. After treatment, typical complaints of the restoration color being different from the natural tooth color are often noted. Apart from inaccurate color determination, different restoration colors are also related to the color changes of the composite resins after polymerization, which may be caused by the characteristics of materials and the wavelength utilized in polymerization.[1] The type and size of the filler, the amount of inorganic fillers, the composition of the resin matrix, and the type and concentration of the photo-initiator affect the degree of polymerization of the material. In addition, the wavelength of the emitted light as well as light intensity and duration are also known to affect material polymerization.[2]

There are several opinions regarding whether the shade of composite resins affects the color change after polymerization. Shade is related to the chroma and hue levels of a composite resin. Seghi, et al. have reported that the color change of a monochromatic composite with a bright shade is greater than that with a dark shade,[3] while Yap, et al. have reported the opposite result.[4] Sabatini has reported that the color change of the A3 shade group is more significant than that of the bleach color group.[2] Lee, et al. have investigated nanofilled composite resins and concluded that compared with a microfilled one, the more translucent the composite, the more visible the color and translucency changes after curing and polishing.[5]

Compared with those containing large-sized spherical fillers, materials containing small-sized irregular fillers exhibit a higher light transmission intensity and narrower light distribution. There was a significant correlation between the filler specific surface area and the color change of the material containing the filler. This result revealed that the shape of the filler particles, particle size, and filler content significantly affect the transmission and diffusion characteristics of light and color of the composite resin.[6] Some of the commercially available composite resins exhibit different sizes as well as types of filler particles to improve the physical properties of the composite resin after polymerization.[7]

Changes in the color and color coordinates of composite resins after polymerization have been widely examined.[1] However, studies on color changes based on various shades have not been conducted to the best of our knowledge. Various studies have reported that color changes after polymerization still occur in all composite resins despite several improvements in the chemical composition and filler of the composite resin.[8] Such color changes may cause clinical esthetic problems; hence, the determination of an appropriate shade must be considered.[9] In this study, the effects of the nanohybrid filler and dentin shade of the submicron composite resins on color changes after polymerization were investigated.


  Materials and Methods Top


This research was conducted as a laboratory experiment. A nanohybrid filler (Micerium ENA HRi, Italy) and a submicron filler (Tokuyama Palfique LX5, Japan) composite resin in the shape of discs were used as the research sample, which was fabricated using a porcelain sampler device. The diameter and thickness of each disc were 12 mm and 2 mm, respectively. The color assessment of all samples was conducted before and after polymerization by using a light-emitting diode (LED) light-curing unit, and measurements were made at the center point of the disc of each sample.

Disc was fabricated by placing mylar strips on the top surface of the composite resin in the porcelain sampler, followed by pressing them using glass slabs to prevent possible distortion in thickness. The samples were then categorized into six groups according to the shade and type of filler. The groups consisted of nanohybrid groups (UD1, UD2, and UD3) and submicron groups (OA1, OA2, and OA3).

Before polymerization, all samples were photographed along with a gray card against a white background using a digital camera (Sony Corp., Tokyo, Japan) and a 90-mm macro-lens equipped with a polarized filter. The distance between the lens and sample was 30cm. Then, samples were polymerized by light-curing using an LED with an intensity of 1000 mW/cm2 according to the manufacturer’s specifications (Ledex, DentMate Technology Co. Ltd., New Taipei City, Taiwan) for 20s. The distance between the light-curing tip and the sample was 2 mm, with perpendicular direction at an angle of 90°. After polymerization, the second photograph was taken by utilizing the same protocol as conducted before polymerization. Photograph files were saved in RAW format. The photographs were processed using Adobe Photoshop software (Adone Inc., USA) to determine the values of ΔL*, which indicates the value of the color, as well as Δa* and Δb*, which indicate the hue and chroma. The color change (ΔE*ab) was calculated by ΔE*ab = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2.

Statistical analysis

Data were analyzed using SPSS Statistics software (IBM, Armonk, USA). The independent t-test was used to analyze the ΔE*ab differences between the shades of nanohybrid and submicron groups. To analyze the ΔE*ab differences within shades in the nanohybrid group and submicron group, the analysis of variance (ANOVA) test was used. Tukey’s post hoc test was used to determine which of the groups have a significant ΔE*ab difference from the ANOVA test.


  Results Top


Based on the obtained results, almost all of the tested groups of the nanohybrid composite resins exhibited ΔE* ≥ 3.3, except for the UD1 group, which exhibited ΔE* = 1.25. On the other hand, all of the tested groups of the submicron composite resins exhibited ΔE* ≥ 3.3. The complete mean and standard deviation of all groups can be seen in [Table 1]. This result indicated that a significant color change in the nanohybrid UD2 and UD3 groups can be observed by the human eye, as well as the entire submicron group, before and after polymerization.
Table 1: ΔE*ab mean values for the nanohybrid and submicron composite resins

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The independent t-test revealed a significant difference in the ΔE*ab values between the nanohybrid and submicron composite resins in every shade group (i.e., A1, A2, and A3) (P < 0.05). The ΔE*ab value for the submicron composite resin group was greater than that for the nanohybrid group [Table 2].
Table 2: Difference in ΔE*ab values between the nanohybrid and submicron composite resins

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One-way ANOVA revealed a significant difference in the ΔE*ab value only between the shades in both nanohybrid and submicron groups, with P < 0.05. Based on Tukey’s post hoc test, a statistically significant difference in the ΔE*ab value was observed in the nanohybrid UD1 group compared with UD2 and UD3 groups (P < 0.05), but a significant difference between the UD2 and UD3 groups was not observed (P = 1.00). The ΔE*ab value in the submicron group revealed a significant difference between the OA1 group compared with the OA2 and OA3 groups (P < 0.05), but a significant difference for the OA2 group compared with the OA3 group was not observed (P = 0.82) [Table 3].
Table 3: Difference in the ΔE*ab values based on the shade of the composite resins

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  Discussion Top


Composite resins have been commonly used as materials for direct restorations due to their esthetic properties and good functional resistance. Typically, composite resins are classified on the basis of filler characteristics, particularly their particle size. The different types of inorganic fillers affect the application characteristics and their physical properties. The development of filler characteristics is marked by the presence of nano- and submicron-sized particles, which are intended to produce materials with good polished quality and durable glossy surface.[10]

Typically, dentin-layered composite resins exhibit a single hue with a wide variety of chroma with opacities that resemble actual dentin, while enamel-layered composite resins determine the tint and opacity level depending on the enamel thickness.[11] The wide variation in the dentin-layered composite resin may increase the possibility of errors in color determination as it considerably affects the hue and chroma; in addition, the dentin layer thickness may also affect the value (brightness).[12] Hence, in this study, attention is paid to the dentin layer.

The eLABor_aid technique is an accurate method to assess the ΔE*ab value. It was possible to perform white balance settings and brightness correction on digital photographs of composite resin discs because a white balance gray reference card was provided for the purpose of standardizing colors on digital camera photographs.[13] The ΔE*ab value describes the extent of color change that occurs.[14]

Several factors such as the shade, light-curing duration, increase in thickness, light-curing system, cavity diameter and location, the distance of the light-curing tip from the composite resin surface, filler type, and temperature affect the degree of polymerization of the composite resin.[8] With the decrease in the size of the composite resin filler particles, light penetration decreased as small particles emit light, which is observed for hybrid composites that contain microparticles.[15]

The color of the composite resin used for esthetic restorations should not be affected by the polymerization process. However, in reality, after polymerization, the composite resin exhibited a significant color change, and it varied for each brand and depended on the composite resin composition. The color change after polymerization indicated a change in chroma characteristics. Generally, after polymerization, composite resins exhibit a brighter color, as well as become more translucent, due to the shift in the b* value toward the blue area, leading to the decrease in yellow chroma.[9] The color change due to this polymerization process may be caused by changes in the optical properties of the resin that occur during the cross-linking process of monomers into polymer chains.[2]

Depending on the type of material, the color change (ΔE*ab) of the composite resin after polymerization ranged between 3.1 and 7.4. A ΔE*ab value of 3.3 is considered to be clinically visible, while a color change with ΔE*ab ≥ 3.3 is considered to be invisible according to several studies reported previously.[2],[5] This study revealed that the color change of the resin group nanohybrid composites in the ΔE*ab range of 1.25–10.27 and that of the submicron composite resin groups is in the ΔE*ab range of 13.07–15.64. Nanohybrid UD2 and UD3 composite resin groups, as well as submicron OA1, OA2, and OA3 composite resin groups, exhibited ΔE*ab > 3.3 after polymerization, indicating that the color change that occurs after polymerization can be observed clinically with the naked eye. On the other hand, the UD1 nanohybrid composite resin group exhibited ΔE*ab = 1.25; hence, the color change is not visible to the human eye.

The comparison of color changes based on the filler type revealed significant differences in the ΔE*ab values of the A1, A2, and A3 shade groups between the nanohybrid and submicron composite resins. Different filler types of these two composite resin groups contributed to the difference in their refractive indices. The refractive index of the nanohybrid group was greater than that of the submicron group. Diamantopoulou, et al.[16] have reported that the difference in refractive indices of the filler and matrix decreases after polymerization. This refractive index change, in turn, affects the L* value or the brightness of the composite resin color. The increase or decrease in the L* value depends on the type of material and shade.[1] Arikawa, et al.[6] have reported that the filler and particle size considerably affect the optical properties and color of the composite resin. The difference in color lies in a* and b* values, which describe the chromatic component of a color. Kim and Lee also reported changes in red-green (a*) and yellow-blue (b*) chroma in composite resins after polymerization.[1]

The difference in ΔE*ab values was observed between shades within the nanohybrid and submicron composite resin groups. A significant difference in ΔE*ab values between the nanohybrid UD1 group compared with those of UD2 and UD3 groups was observed, as well as in the case of the submicron OA1 group compared with those of OA2 and OA3 groups. However, a significant difference in the ΔE*ab values of the UD2 compared with the UD3 group was not observed, as well as in the case of the OA2 compared with the OA3 group. These results indicated that compared with the darker color group, the lighter shade (i.e., UD1 and OA1) exhibits a lower-intensity color change. This result is in agreement with that reported by Yap, et al.[4] Sabatini[2] have reported that the color change in the A3 shade is greater than that in the bleach color, while Strazzi-Sahyon, et al.[17] have reported that a lower light-curing intensity and darker composite resin color are negatively correlated with a high degree of resin matrix color change.[17] This can be affected by the presence of immersed water, which replaces the monomers that are not completely cured.[17]

Lee, et al. have reported that compared with the conventional color, the more translucent the composite color, the greater the color change after curing and polishing.[5] Compared with other composite resins, the nanohybrid UD1 composite resin exhibited the highest translucency after polymerization.[16] The results obtained herein contradicted that reported by Lee, et al. because the UD1 group in this study exhibited the smallest color change, which was related to the change in the L* value that occurred after polymerization. The L* value of the nanohybrid composite resin group decreased after polymerization, but the L* value of the submicron composite resin group increased after polymerization.

This study revealed that the nanohybrid and submicron groups exhibit a color change of the composite resin after polymerization; moreover, shade also affected the color change of the composite resin after polymerization, suggesting that in clinical applications, the color changes that occur due to polymerization may cause errors in color selection, leading to unaesthetic restorations, especially in the anterior tooth area. The use of a traditional shade guide such as the Vita Classical will not provide results due to the difference in the color between the shade guide and the various brands of composite resins on the market, as reported by Park and Lee.[18] They stated that the color distribution of composite resins is different from one brand to another. There was a shade mismatch between the Vita Classical shade guide and the composite resin that has been observed in 34 out of 41 variations of shades tested from various brands.[18]

A preliminary mock-up trial on restored teeth with a polymerized layer of dentin and enamel polymerized beforehand is recommended to avoid color selection errors due to the color change of the composite resin that occurs after polymerization.[16] This preliminary trial process starts with layering the dentin composite layer of an appropriate thickness, followed by layering the enamel layer to simulate the layer on the natural tooth. Color determination after polymerization with a light-curing unit may provide a more accurate color, leading to an esthetically good restoration.


  Conclusions Top


Based on the results obtained in this study, nanohybrid filler and submicron composite resin shade affected color changes that occurred after polymerization. Color changes, such as the brightness and chromatic of color, were observed. Compared with the darker color group, the lighter shades (i.e., UD1 and OA1) exhibited a lower-intensity color change. The color change after polymerization was clearly visible in the UD2 and UD3 nanohybrid composite resin groups, as well as in the OA1, OA2, and OA3 submicron groups, while the UD1 nanohybrid composite resin group did not exhibit a color change after polymerization, which could be observed with the naked eye.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors declare no conflict of interest.



 
  References Top

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Hein S, Tapia J, Bazos P. eLABor_aid: A new approach to digital shade management. Int J Esthet Dent 2017;12: 186-202.  Back to cited text no. 13
    
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Diamantopoulou S, Papazoglou E, Margaritis V, Kakaboura A. Change of optical properties of contemporary polychromatic resin composites after light curing and finishing. Int J Esthet Dent 2014;9:224-37.  Back to cited text no. 16
    
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  [Table 1], [Table 2], [Table 3]



 

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