|Year : 2016 | Volume
| Issue : 1 | Page : 42-48
Color stability of nano-filled, micro-hybrid, and silorane-based dental composite resin materials
Mohsen Saud M ALShetili1, Mohammad Al-Omari2
1 Department of Conservative Dentistry, East Riyadh Specialized Dental Centre, Ministry of Health, Riyadh, Kingdom of Saudi Arabia
2 Department of Restorative, Riyadh Colleges of Dentistry and Pharmacy, Riyadh, Kingdom of Saudi Arabia
|Date of Web Publication||18-Jan-2016|
Mohsen Saud M ALShetili
P.O Box: Almuwansiah 7477, Riyadh 4161-13253
Kingdom of Saudi Arabia
Source of Support: None, Conflict of Interest: None
Aim: The purpose of this study was to investigate the color stability of nano-hybrid, micro-hybrid, and silorane-based composite resin restorative materials upon exposure to staining agents.
Materials and Methods: One hundred twenty composites samples were prepared, 40 from each composite material (Filtek ® Z350, Filtek ® P90, and Filtek ® Z250). The specimens were randomly divided into four groups (10 of each sample). The specimens were incubated for 24 h in distilled water and then for 72 h in corresponding mediums (distilled water, red grape juice, green tea, coffee). The color of all the specimens was assessed before and after exposure with a spectrophotometer and total color change (ΔE) was calculated using ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2. The data were analyzed with one-way analysis of variance (ANOVA) and Kolmogorov-Smirnov and the means of the solutions were compared by Tukey's honestly significant difference (HSD) (P < 0.05).
Result: The lowest dicoloration was observed in Filtek ® LS P90 but it was not significant while the most discoloration was observed in Filtek ® Z350 and Filtek ® Z250. Also, coffee showed a highly significant (P > 0.05) discoloration compared with other media.
Conclusions: Within the limitations of this study, it may be concluded that silorane-based composites are more resistant to discoloration than bis-GMA-based composites and coffee had the highest effect on composite discoloration compared to other media.
Keywords: Color, composite, micro-hybrid, silorane, nano-filled
|How to cite this article:|
ALShetili MM, Al-Omari M. Color stability of nano-filled, micro-hybrid, and silorane-based dental composite resin materials. Saudi J Oral Sci 2016;3:42-8
|How to cite this URL:|
ALShetili MM, Al-Omari M. Color stability of nano-filled, micro-hybrid, and silorane-based dental composite resin materials. Saudi J Oral Sci [serial online] 2016 [cited 2020 Jan 18];3:42-8. Available from: http://www.saudijos.org/text.asp?2016/3/1/42/174336
| Introduction|| |
Aesthetic restorative materials have been widely used in dentistry in both anterior and posterior restorations. They are presented in various types with different physical characteristics, colors, and shades. At present, there are four types of direct aesthetic restorations that are commonly used in dentistry: Resin composites, polyacid-modified resin composites (compomers), glass-ionomers, and resin-modified glass-ionomers. Resin composites were introduced in to dentistry in early 1970s and are widely used as direct aesthetic restorations (Craig et al., 2006). 
Considering aesthetics, composites offer advantages over other direct aesthetic materials regarding shade stability and durability. However, when compared with porcelain veneers and ceramic crowns, composite restorations have several significant disadvantages despite of the continuous improvements (Hickel et al., 2004).  Polymerization shrinkage, secondary caries, plaque accumulation, and discoloration are among the major disadvantages of composite restorations (Stober et al., 2001).  In fact, discoloration of composite resins can be induced due to several intrinsic and extrinsic factors.
In visible light-cured composite resin, camphorquinone is generally used as the photo initiator to allow composite setting. However, composite resin discoloration can occur if its curing process is inadequate (Manabe et al., 2009)  where the unconverted (photo initiator) will cause a yellowish discoloration of the restoration. Furthermore, other components of the photo initiator system, namely, tertiary aromatic or aliphatic amines, which act as so-called synergists or accelerators also tend to cause yellow or brown discoloration of composite restorations under the influence of light or heat (Janda et al., 2004). 
Also, extrinsic factors such as absorption or adsorption of extrinsic stains are considered a major problem of aesthetic restorations. Several authorities (Eriksen and Nordbo, 1978; Patel et al., 2004; Ghahramanloo et al., 2008) ,, suggested that there were at least three mechanisms that might contribute to the formation of extrinsic stains:
- Production of colored components in plaque by chromogenic bacteria;
- Retention of colored substances from dietary constituents passing through the oral cavity; and
- Formation of colored products from the chemical transformation of pellicle components.
Therefore, factors such as diet (coffee, tea, and red wine), smoking, some medicaments, and daily teeth-cleaning (that induce rough surface) contribute to extrinsic stain development in composite restorations (Scotti et al., 1997). 
Recently, nano-filled composite materials have been developed. It contains submicrometer particles (nanofillers) to further enhance the optical and physical properties of the resins. Nanofilled composites have been recommended by manufacturers to be suitable for both anterior and posterior restorations. Furthermore, manufactures claim that nanofill composite has been improved to be similar to ceramics in its shade selection and color stability. However, its long-term clinical performance and color stability are yet to be assessed and proved (Yannikakis et al., 1998). 
Also, there is a silorane-based dental resin composite, which contains a matrix consisting siloxanes and oxiranes, which differs from the matrix of conventional composite. Manufacturers have introduced a new matrix, which they claim provides silorane-based composites with low-polymerization shrinkage and resists discoloration. Silorane-based composites polymerize by open ring polymerization reaction, which was developed to minimize polymerization shrinkage and polymerization stress. It provides a high-performance bond to the tooth with a significantly lower shrinkage than all methacrylate composites. Also, it is performed better in durability and is resistant to discoloration. Silorane-based composites are classified as microhybrid composites (Weinmann et al., 2005).  Although nano-filled and Z250 have the same matrix, bis-GMA, they have different fillers utilizing different technologies, which create a controversy in the literature regarding the resistance to discoloration (Yazici et al., 2007). 
Therefore, the purpose of this study was to investigate the discoloration resistant to a nano-hybrid (Filtek R Z350), micro-hybrid (Filtek R Z250), and silorane-based (Filtek R P90) composites resin restorative materials upon exposure to different staining agents.
| Materials and Methods|| |
This is a laboratory-based study conducted to determine the color stability of a new generation of direct restorative composite resin. Composite materials utilized in the study along with their manufacturer's and chemical composition have presented in [Table 1]. Filtek ® Z350 (nano-hybrid) Filtek ® P90 (silorane) and Filtek ® Z250 (microhybrid) were assessed using four immersion media: Coffee, red grape juice, green tea, and distilled water [Table 2]. The pH of the immersion media was verified by a pH meter (PM 608 Plus, A nalion, Ribeir Preto, SP, Brazil) to confirm its acidity, and the shade of the composites specimens were assessed using a spectrophotometer (Gretage Machbeth, 617 Little Bratin Road, New Windsor, NY, USA).
One hundred twenty composite disc-shaped specimens (9 mm in diameter and 2 mm in thickness) were prepared, 40 from each composite material (Filtek ® Z350, Filtek ® P90, and Filtek ® Z250) using prefabricated plastic molds [Figure 1]. The materials were handled and inserted in the mold according to the manufacturer's instructions. The specimens were then soaked in the solution.
The composite discs were prepared as follows: After insertion of the composite material into the plastic mold the material was held between two microscopic glass slides, each covered with a transparent polyester strip (Mylar, Henry Schein, Melville, NY, USA) to have a smooth glossy surface of the sample [Figure 2], and the two slides were pressed gently together to allow the escape and removal of the excess material; care was taken to prevent entrapment of air bubbles and void formation in the composite disc.
Then, specimens were polymerized using a composite light cure unit (LED Radii, SDI, Bays Water, VC, Australia; 1,400 mW/cm 2 power density) for 40 s of exposure time at both sides [Figure 3]. The light cure tip was kept at a fixed distance of 1 mm from each specimen surface. To standardize the samples' thickness, a digital caliper (ultra-cal mark III, Folow Corp., Sylvac, Switzerland) was used to ensure that each sample thickness was 2 mm [Figure 4] (any sample thicker than 2 mm was excluded and replaced with a new sample with accurate thickness).
|Figure 4: Composite specimens of Filtek Z 250 ready for immersion in different staining solutions|
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After that, all the specimens were stored in distilled water and incubated for 24 h at 37° C. Then, the samples were randomly divided into four groups with 10 specimens of each material, to be immersed in different staining solutions (coffee, green tea, artificial red grape juice, and distilled water) [Figure 4], [Figure 5] and [Figure 6].
|Figure 5: Composite specimens of Filtek Z 350 ready for immersion in different staining solutions|
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|Figure 6: Composite specimens of Filtek Z P 90 ready for immersion in different staining solutions|
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To prepare the solutions of coffee; a 30 g (Nescafe Classic, AM Main, Frankfort, Deutschland) was poured into 100 mL boiling distilled water. The green tea solution was prepared by immersing five prefabricated doses of tea bags (Lipton Uniliver Gulf FZE, Dubai, UAE) into 500 mL boiling distilled water for 10 min. The red grape solution was obtained from (Alrabee red grape juice, Alrabee, Riyadh, KSA). Also, distilled water was used as the control group. After that, 10 specimens from each material were immersed in their respective staining solutions and incubated for 36 h in the incubator at 37° C, as shown in [Figure 7].
Color testing of specimens
After sample immersion in its respective staining media, color measurements were taken for each specimen using a spectrophotometer R (Gretage Machbeth, Color eye 7000, NY, USA). During color measurement, a white background was used as a baseline. The spectrophotometer measures the specimen color based on the CIELab L*a*b* color space system, which allows the determination of color in the three-dimensional space. The L* represents the value (lightness or darkness). The a* value represents redness (positive a*) or greenness (negative a*) values while b* yellowness (positive b*) or blueness (negative b*) values. The color differences (ΔE) among the color coordinates were calculated by applying the formula ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2 in order to compare values before and after the storage treatment. Three measurements were performed with the changing position of the specimen, and thus, the machine automatically averaged the three readings for each specimen, which were recorded and used later for overall data analysis.
To be familiar with the color measurement and the spectrophotometer machine, a pilot experiment was performed using four specimens of each composite type before the proper experiment was performed.
Data were collected and analyzed using software Statistical Package for the Social Sciences (SPSS) version 16 (SPSS Inc., Chicago, IL, USA) using one-way analysis of variance (ANOVA). Kolmogorov-Smirnov and Tukey's honestly significant difference (HSD) as post hoc tests were used to determine the equality of variances, normality, differences among the composite groups, and among solutions within the same group.
| Results|| |
To perform ANOVA test accurately, the assumption of equal variance and normality was performed and it was not found to be satisfying (P value = 0.00). Therefore, the data were transformed by natural logarithm (ln) and Kolmogorov-Smirnov test was performed and showed that normality was satisficed (level test P value = 0.2). The ANOVA test was performed and the homogeneity was found to be satisfied (level test P value = 0.09). One-way ANOVA and Tukey's HSD as post hoc test were used to compare the mean differences among the composite groups and solutions within the same group at the level of significance of .05.
The mean and standard deviation values of color change ΔE of the specimens after immersion in the different types of media for each of the composite resin materials used in the study are summarized in [Table 1]. Filtek Z250 ® and Z350 ® composite materials showed significant color change (ΔE > 3.3) after immersion in all types of media while Filtek P90 composite showed less and no significant color change (ΔE < 3.3).
Also, this study showed that silorane-based composite (Filtek P90 ® ) and bis-GMA (Filtek ® Z350 and Filtek ® Z250) shifting to bluish discoloration. In addition, this study showed that Filtek ® Z350 and Filtek ® Z250 shifting to greenish discoloration while silorane did not [Table 3].
|Table 3: Mean and standard deviation of color changes of composites (ΔL, Δa, Δb, ΔE)|
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When comparing the composites groups with each other (ANOVA), [Table 2] shows significant differences (P value = 0.000) between Filtek ® Z350 and Filtek ® Z250. Also, there were insignificant differences (P value = 0.838) when comparing Filtek ® Z350 and Filtek ® Z250 with Filtek ® P90 [Table 4].
|Table 4: Square mean values and P values of discoloration among composite groups|
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The comparison of mean values of media using post hoc test to assess color changes within each composite group after exposure to the four different media beverages after 3 days are summarized in [Table 5] and [Figure 9].
|Table 5: Post hoc multiple (P values) comparison of color change among different media|
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In Z250, the mean of color change in red grape juice and coffee groups showed a significant color change (P = 0.047 and P = 0.000, respectively) when compared with the distilled water group while in green tea and coffee groups, the color change was not significant [Figure 8]. On the other hand, when red grape juice was compared with green tea and coffee there was no significant difference (P > 0.05) while it was significant (P = 0.047) with distilled water. Similarly, coffee showed a significant color change compared with distilled water and green tea.
Interestingly, in Filtek ® Z350 the mean of color change in red grape juice and coffee groups showed a significant discoloration when compared with the distilled water group (P = 0.047, P = 0.000 respectively), while on comparison of green tea with coffee, the color change was not significant (P = 0.000). On the other hand, when red grape juice was compared with green tea and coffee there was no significant difference (P > 0.05) while it was significant (P = 0.047) with distilled water. Similarly, coffee showed a significant color change compared with distilled water and green tea while in Filtek ® P90 groups, there was no significant (P > 0.05) color change difference among all media.
| Discussion|| |
Composites fillings discoloration can be measured by visual or instrumental techniques. It is well-known that color measurement using visual comparison is not a reliable method because of differences in color perception among persons. Therefore, instrumental techniques for color measurement using colorimetry or spectrophotometry machines were reported to be a reliable technique in dentistry (Johnston and Kao, 1989).  The value of ΔE represents relative color changes that an observer might report for a material after treatment or between time intervals. Any ΔE value more than 3.3 is accepted by most researchers (Ruyter et al ., 1987, Um and Ruyter, 1991) , to produce visually unacceptable discoloration and it was used as a gold standard. In this study, it was found that mean of ΔE for Filtek® Z250 and Filtek ® Z350 was more than 3.3, which was in line with the findings of Kim and Lee, 2008 and Furuse et al., 2008 , and controversial to findings of previous studies (Sarafianou et al., 2007; Sabatini et al., 2012) , where it was found that the Filtek ® Z350 (nano-filled) composite was highly resistant to discoloration with a mean of ΔE 3.3. Moreover, silorane-based composite had the lowest ΔE value 1.3 (which was less than 3.3, the gold standard) and this was controversial to the findings of Barutcigil and Yύldύz (2012) who reported that Filtek ® P90 discolored more than the Filtek ® Z250 and Filtek ® Z350.
According to the results of this study, we found that silorane-based composite (Filtek ® P90) shows shifting to bluish discoloration with Filtek ® Z350 and Filtek ® Z350, which is contrary to the findings of Janda et al., (2004)  who advocated that camphorquinone and amines could cause yellowish stain but the result of this study was in line with the finding of Sarafianou et al. (2007).  In addition, this study indicated that Filtek ® Z250 and Filtek ® Z350 shift to greenish discoloration while silorane (Filtek ® P90) does not; in the researchers' knowledge, no study has addressed this issue yet.
Moreover, findings of this study indicated that Filtek ® Z250 and Filtek ® Z350 were highly stained in the coffee solution and this correlated well with the ﬁndings of several previous studies (Scott et al., 1997; Yannikakis et al., 1998; Al-kheraif, 2011) ,, while Sepulveda-Navarro in 2011  showed contraindications to this study. In general, the major cause of discoloration because of staining solutions is due to extrinsic adsorption and absorption of pigments into the subsurface but intrinsic discoloration may also exist (Peutzfeldt et al., 2000).  Also, microcracks and microvoids located at the interface between the filler and the matrix are the most likely to allow penetration pathways for stain. The roughness of the surface caused by wear and chemical degradation may also affect gloss and consequently increase the extrinsic staining (Soderholm et al., 1984, Yu et al., 2009). ,
Coffee pigmentation originated from both mechanisms of adsorption of colorant on the surface and absorption in the subsurface layer of composites but discoloration is probably related to the compatibility of the polymeric phase of the composite resin where resin discoloration may be associated with its affinity for stains and water sorption because of its lower degree of monomer conversion (Dietschi et al., 1994).  This effect of the staining solutions on color changes in composites was dependent on both the immersion time and resin material (Yazici et al., 2007). 
In addition, fillers play an important role in the properties of composites. The particle size of a filler has a moderate influence on composites' properties (McKinney and Wu, 1985, Aguiar et al., 2007). , Wear of resin composites can cause debonding of the fillers from the resin matrix, thereby increasing the surface roughness and forming a surface susceptible to extrinsic stains (McKinney and Wu, 1985, Villalta et al., 2006). , Wear and surface degradation of composite restorations can also be influenced by the chemicals in the beverages (acidic media), resulting in unaesthetic external pigmentation while the water sorption ability of resin composites may also be influenced by the chemical composition of beverages, which represents an important discoloration factor of surface integrity of composites leading to discoloration (Fay et al., 1999).  In Filtek ® P90 the ytterbium tri fluoride filler contributes to fluoride release, which is a water soluble component and leaches out after immersion in a solution, which might affect its color stability (Iazzetti et al., 2000)  which interestingly Filtek ® P90 discoloration was not observed in this study.
| Conclusions|| |
Within the limitations of this study, it can be concluded that:
- Silorane-based composite (Filtek ® P90) showed high resistance to discoloration compared with bis-GMA (Filtek ® Z350 and Filtek ® Z250) composites, which showed lower resistance to discoloration.
- Coffee and red grape juice had the highest discoloration effect on composites, especially on Filtek ® Z350 and Filtek ® Z250.
- Distilled water and green tea had the lowest discoloration effect on all composite groups.
- Matrix chemistry of composite looks like it is the key of discoloration resistance of silorane-based composite.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]