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 Table of Contents  
ORIGINAL RESEARCH
Year : 2017  |  Volume : 8  |  Issue : 3  |  Page : 65-69

Comparison of color stability of two resin composites in blood area


1 Department of Operative Dentistry, Faculty of Dentistry, Azad University, Khorasgan (Isfahan Branch), Iran
2 Dental Materials Research Center, Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Science, Isfahan, Iran
3 Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Science, Isfahan, Iran
4 Dentist, Privait Practice, Isfahan, Iran

Date of Web Publication8-Aug-2017

Correspondence Address:
Farzaneh Shirani
Dental Materials Research Center, Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Science, Isfahan
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/denthyp.denthyp_27_17

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  Abstract 

Introduction: Color change of composite restorations in different color media over time is a common problem in esthetic dentistry, creating the need to replace the restoration and spending a great deal of cost and time by patients. The aim of this study is in vitro comparison of color stability of resin composites in blood area. Materials and Methods: Fifteen disk-shaped specimens of each resin composite (valux plus and filtek supreme) were prepared. The samples were kept in distinct water containers for 24 h in order for the primary water absorption to happen by restorative materials. Then, for 1 month, they were immersed in blood every day for 20 min. The color values (L*, a*, and b*) were measured using the CIE L*a*b* system. The color change values were calculated before and after 1, 7, and 30 days of immersion. The amounts of ΔE1, ΔE7, ΔE30 for each group were calculated with ΔE = [(ΔL*)2 + (Δa*)2 +(Δb*)2]½. Repeated measures and paired t-tests and one-way analysis of variance (ANOVA) were applied for the statistical analysis. Results: The discoloration in two groups was not significant and visually perceptible. However, microhybrid samples at primary time (less than 7 days), under the significant level, showed more discoloration, but nanofilled’s samples discoloration increased till the 30th day. Conclusion: Blood as a biological agent that contains globulin as a large molecule, did not have a significant impact on changing the color of the resin composite.

Keywords: Blood, CIELAB system, color stability in composite, spectrophotometer


How to cite this article:
Malekipour MR, Shirani F, Taromi Z, Shahnazari S. Comparison of color stability of two resin composites in blood area. Dent Hypotheses 2017;8:65-9

How to cite this URL:
Malekipour MR, Shirani F, Taromi Z, Shahnazari S. Comparison of color stability of two resin composites in blood area. Dent Hypotheses [serial online] 2017 [cited 2017 Aug 22];8:65-9. Available from: http://www.dentalhypotheses.com/text.asp?2017/8/3/65/212433




  Introduction Top


Composite resins are among the most frequently used dental materials for aesthetic restorations in dental practice due to their ability to bond to enamel and dentine, resemblance to tooth structures in color and mechanical properties, ease of chair-side applications, and relatively low costs. Though the quality of composite resin restorations has improved with the advent of new technology in material sciences in recent years, discoloration of the composite resin materials remains to be a major problem in long-term clinical studies.[1],[2] Color stability over time is one of the important criteria for the composite selection and affects the long-term esthetic of restoration. A major disadvantage of resin composites is their tendency to discolor, which may be a major factor in the replacement of restorations.[3]

Three types of discoloration are described in the literature: (1) External discolorations due to plaque accumulation and surface stains, (2) surface or sub-surface alterations resulting in a superficial degradation or a slight penetration and adsorption of staining agents to the superficial layer of composite resins and, (3) intrinsic discolorations due to physicochemical reactions in the composite matrix, in surface and deeper layers of the material, triggered by UV irradiation, thermal energy, or humidity.[4]

The discoloration of resin-based restorative materials may be the result of several extrinsic or intrinsic factors. External discoloration can be caused by oral habits such as tobacco use and certain dietary patterns, along with bad oral hygiene. Intrinsic factors such as alterations of the resin matrix, filler, loading and particle size distributions, and type of photoinitiator discolor the resin material itself.[5]

Numerous in vitro studies have demonstrated that common drinks and food ingredients, such as coffee, tea, red wine, fruit juices, and sport drinks, could cause significant change in surface color of the composite resin materials.[4],[5],[6],[7],[8],[9],[10] It was found that certain food colorants (e.g., coffee and red wine) may cause more severe staining than others. Ugur E et al. assessed the effects of three sports drinks on the color stability of two nanofilled and two microhybrid composite materials stated that effect of a solution on color stability of composite materials depends on the type of solution, exposure time, and composition of the material.[5]

Nihan et al. evaluated the effects of different finishing and polishing techniques on the surface roughness and color stability of nanocomposites and stated that composites with smaller filler size do not necessarily show low surface roughness and discoloration. Staining of composite resins was dependent on monomer structure, as well as surface irregularities.[11]

Addition of a small amount of triethylene glycol dimethacrylate (TEGDMA) into a bisphenol A-glycidyl methacrylate (Bis-GMA) based resin matrix may significantly increase the water absorption of the composite material. TEGDMA contains a central repeating ethoxy group that has high affinity with water molecule through hydrogen bonding to oxygen, thus resulting in increased surface hydrophilicity of composite materials.[6]

In another study, nanohybrid composite resin showed less color stability despite having a higher degree of conversion.[7]

Discoloration can be assessed visually and by using instrumental techniques. Instrumental techniques eliminate the subjective interpretation inherent in a visual color comparison. Thereof, spectrophotometers and colorimeters are widely used tools to detect the color changes in dental restorative materials.[5]

Considering the risk of gingival bleeding immediately after restoration procedure and along then for reasons such as gingivitis and bleeding while brushing or during finishing and polishing, The aim of this study was to investigate the effects of a biological fluid such as blood in discoloration of the composite resin materials using a reflection spectrophotometer based on CIELAB (Commission International de l’éclairage L* a* b*) color system.

The null hypothesis of this research study was that blood media have no effect on the color stability of nanofilled and microhybrid composite resins at different times.


  Materials and Methods Top


Thirty disk-shaped material specimens (fifteen nanofilled composite and fifteen microhybrid composite), 10 mm in diameter and 2 mm in thickness were prepared using a prefabricated cylindrical mold, with the desired dimensions. To prevent formation of unpolymerized air inhibited layer and creating smooth surface, two glass plates were placed under and over the mold.

The characteristics of the resin composites, which were used in this study, are listed in [Table 1].
Table 1: Characteristics of the resin composites used in the study

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The blood used in this study was complete blood count (CBC) testing blood which contains 0.25 ± 1.5 ethylenediamine tetraacetic acid (EDTA) as its preservative. Red blood cells remain alive for 35 days.

The composites were cured for 40 s using a light curing unit (coltolux 2.5-Coltene Whaledent Inc/USA) with a light output power of 500 mW/cm2. To ensure adequate curing, the specimens were cured for another 20 s after the glass blocks were removed.

The upper side of the composites was marked for color testing. In the next step the specimen surfaces were polished using grit-1000 silicon carbide paper disks (soflex-3M ESPE-Ultra thin/USA). It was expected that polishing helped with creating conditions that were closer to the clinical circumstances.

Restoration colors were determined using a spectrophotometer (Spectra Flash 600 data Color International, USA).The samples were placed in distilled water for 24 h. Then, the samples were immersed in 37°C incubated blood for 20 min every day for 1 month (this immersion was repeated 30 times for each sample).

Prior to testing the color change with a spectrophotometer and after removing the samples from the blood media, the specimens were sanitized from contaminants with an ultrasonic cleaner (SONICA Mod 2200 mh-Soltec 230/240v/ITALY), washed in distilled water for 5 min, and dried with absorbent paper towels.

After the specified time (1 day, 1 week and 1 month after the beginning of the experiment) the samples were analyzed using the colorimetric spectrophotometer. The spectrophotometer was calibrated with white light in each session. The aperture size was set to 6 mm and the specimens were exactly aligned with the spectrophotometer.

The color change was determined and reported according to the CIELAB color system which defines the color along the three axes L *, a *, and b *. ΔE was used as the indicator of the overall evaluation of color differences that was calculated using the following formula:



Data were analyzed using the SPSS 12 (IBM SPSS Statistics for Windows, Version 12.0. Armonk, NY: IBM Corp.). Repeated measures analysis of variance (ANOVA) were applied for each group separately and if it was significant, the paired t-test was also applied. The ANOVA test was used for the end color changes between different groups at different time durations. To compare the differences in two groups at each time independent t-test was performed. P-value less than 0.05 was considered as a significant level. Limit of discoloration detection was 1.84 to 2.69.


  Results Top


[Table 2] shows the discoloration mean and the standard deviation of composite resins obtained at intervals of 1 day, 7 days, and 30 days.
Table 2: The comparison between average color changes ΔE in each group for different time durations

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The ANOVA for frequent data shows that the reaction between time and group is not significant. In other words, the difference of average changing ΔE in two groups is not significant (P = 0.161).


  Discussion Top


L *, a*, b *values of CIELAB system were obtained from spectrophotometer and ΔE index were used as an overall evaluation of the color difference to calculate the different periods of immersion. Since ΔE demonstrates the relative color changes that the observer may report for the material in different periods, it can be concluded that ΔE is more meaningful than the individual values of L *, a *, and b *.[12]

According to the results of this study, the upper limit of discoloration detection was 2.69 ± 1.03. Um and Ruyter confirmed the upper limit of acceptability in subjective visual evaluations as ΔE = 3.3.[13] Color differences of aesthetic restorations presenting ΔE > 1 are visually perceptible and considered acceptable up to a ΔE of 3.3.[11] In our study, discoloration below ΔE = 3.3 was considered acceptable. Discoloration in two groups was not significant and visually perceptible for different time durations. However, a person trained in color recognition may be able to detect a ΔE value of 1.5 to 2.5 units.[14]

According to the results of this study, although discoloration of microhybrid composite was not statistically significant over time, most of its discoloration was observed just 1 day after the immersion remaining relatively constant. It seems that in the early times of the study, color absorption of microhybrid composite reached its maximum level. Since the nanofilled resin composites demonstrate the smoothest surface after polishing compared to microhybrid resin composites,[15] the amount of its color changes is less than that of the microhybrid resin composite in early stages of immersion.

The most discoloration of nanofilled resin composite took place 30 days after the immersion. The degree of the discoloration of microhybrid resin composite was more than that of nanofilled 1 day after immersion, but 30 days after immersion the rate of the discoloration of nanofilled composite was more than that of microhybrid. Therefore, the nanofilled composite demonstrated more color changes over time. In light of this finding, it can be concluded that increased immersion time causes more color change. Indeed the discoloration of nanofilled composite has a cumulative effect over time and if the study would be continued, it seemed that the blood could have increased the color change that is visually perceptible.

It has been reported that an increase in the filler content in composites provides increased color stability, whereas a higher amount of resin volume portion has been reported to provide greater discoloration.[5] Filtek Supreme XT had a less inorganic volume and a greater resin matrix than ValuxTM Plus. Composites that have greater amount of resin matrix are more prone to water sorption and thus discoloration. In addition, the structure of the resin matrix has a direct impact on the discoloration of resin composite. Composites that have TEGDMA in their composition release large amounts of monomers in aqueous media when compared with those that are Bis-GMA-based and urethane dimethacrylate (UDMA) based, resulting in greater color alteration.[16],[17] In several studies, greater discoloration was obtained in composite resins that include TEGDMA, which might be responsible for the high water absorption and discoloration rates.[18]

Both composite resins include TEGDMA in their composition, probably the amount of this monomer in the composition of Filtek Supreme XT is more than ValuxTM Plus.

Villalta et al., Yazici et al., and Al Kheraif et al. also reported that the nanocomposites had a higher color change than the microhybrid composites after staining.[7],[19],[20]

As we know, blood is a biological environment and it generally consists of two components: Cellular components including red blood cells, white blood cells, and platelets. Red blood cells contain hemoglobin that is the iron containing and because red blood cells make up 40% to 45% of the blood, blood is seen red.

Plasma contains water, electrolytes and metabolites nutrients, and proteins such as albumin, immunoglobulin, and coagulation factors and many ions such as Na+, K+, Ca2+, Cl-, HCO3−, etc.[21]

Color changes due to blood as a biological agent containing the large globin molecule in comparison to the color changes due to dye molecules in other media such as tea, coffee, etc. are hardly comparable and concerns about small dye molecular is more than blood. Blood is a liquid that contains many molecules and each of them can be effective as a variable.

Usually it is reminded to patients that consumption of food and beverages which contain colorants, especially in the first week after placement of composite restorations, can change the color of the restoration. Similarly, control of gingival bleeding during treatment by the dentist and adequate health care by the patients are other important factors that should be considered in discoloration of composite restorations. In this study, the effect of blood in the discoloration of composites was assessed 24 h after sample preparation. However, immediately after restoration and removal of the wedge or during the finishing and polishing of restorations, gingival bleeding occurs when most of the post-irradiation polymerization take place in the first few minutes or 1 h after removal of the irradiation source continuing until 24 h later. Composite restorations are more prone to water absorption in this 24 h. It seems that the impact of bleeding on discoloration of recently cured composites is more than that of the complete polymerization of composite after 24 h (as the condition of this study). So, further studies can be conducted so that the recently cured composite is placed in blood area to assess its color changes in the early hours.

In addition, the discoloration caused by surface adsorption may be prevented by tooth brushing. In Bezgin’s study, it was assumed that brushing the specimens inhibited the adsorption of colorants onto the surface of the restorative materials and decreased the amount of color change over time.[22] More over dental-plaque-covered resin restorations are susceptible to surface staining and might be susceptible to softening caused by organic acids produced in dental plaque.[23] Several studies have investigated the process of biodegradation and color change of resin composites in the presence of salivary enzymes.[24],[25],[26] In the present study, these two factors were not considered that can be the limitations of this study.


  Conclusion Top


According to the results of this study, it can be concluded that the discoloration of samples did not reach statistical significance after 1 day of submersion in two groups. But in this range most changing was related to microhybrid samples. Also, the discoloration of the samples was not significant after 7 days and 30 days after immersion in two groups, but these slight changes nearing the border of significance indicated that the discoloration of nanofilled composite overtook compared to the discoloration of microhybrid composite during this period. According to the increasing rate of discoloration, it is possible that this difference will recognized if tests are continued after 30 days. The discoloration of nanofilled composite tends to have a cumulative effect over time and it seems that blood can affect color stability of nanofilled composites.

Financial support and sponsorship

Nil.

Conflicts of Interest

There are no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2]



 

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