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ORIGINAL RESEARCH
Year : 2019  |  Volume : 11  |  Issue : 2  |  Page : 76-82

Spectrometric analysis of intentionally stained hybrid and nanohybrid composites – An In vitro study


1 Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Jamia Millia Islamia, New Delhi, India
2 Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, KGMC, Lucknow, Uttar Pradesh, India
3 Department of Periodontics, Pt. B. D. Sharma, PGIMS Dental College, Rohtak, Haryana, India

Date of Submission31-Aug-2019
Date of Acceptance27-Sep-2019
Date of Web Publication23-Dec-2019

Correspondence Address:
Dr. Babita Meena
Room No. 313, Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Jamia Millia Islamia, New Delhi - 110 025
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jicdro.jicdro_26_19

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   Abstract 


Background: This study aims to investigate the effects of different staining solutions on the color stability of hybrid composites and nanohybrid composites. Materials and Methods: One hundred and ten composite resin samples were made in disc shape and divided into two groups, comprising 55 samples each of hybrid composite samples and nanohybrid composite samples. Both the groups were further divided into experimental group of fifty samples and control group of five samples. Hybrid experimental group and nanohybrid experimental group were again divided into five subgroups according to immersion medium, namely coffee, tea, coke, turmeric, and red wine. Each subgroup was comprised of ten samples. Both the control group samples were immersed separately into distilled water. Solutions were changed daily. Color measurements were obtained using spectrophotometer on the 1st, 7th, and 30th days. For statistical evaluation, analysis of variance and Tukey's tests were used at a significance level of 0.05. Results: Color change of materials in staining agents ranked in this increasing order: water < cola < tea < coffee < turmeric < red wine. Nanohybrid composite resin showed lesser perceptible color changes in comparison to hybrid composite. Conclusions: The tested hybrid composite resins were more susceptible to discoloration in comparison to nanohybrid composite resins.

Keywords: Composite resins, discoloration, esthetics, shrinkage, spectrophotometer


How to cite this article:
Meena B, Hasija M, Wadhwani K K, Wadhwa D. Spectrometric analysis of intentionally stained hybrid and nanohybrid composites – An In vitro study. J Int Clin Dent Res Organ 2019;11:76-82

How to cite this URL:
Meena B, Hasija M, Wadhwani K K, Wadhwa D. Spectrometric analysis of intentionally stained hybrid and nanohybrid composites – An In vitro study. J Int Clin Dent Res Organ [serial online] 2019 [cited 2020 Oct 26];11:76-82. Available from: https://www.jicdro.org/text.asp?2019/11/2/76/273763




   Introduction Top


Dental composite resins evolved as restorative material owing to their properties such as esthetics, strength, and better marginal adaptation. Conventional composite resins are replaced by nanohybrid composites since initial composite resins were more prone to fracture leakage and postoperative sensitivity due to bigger filler size. With the advent of newer technology in the last few years, composite resins showed a remarkable improvement in its physical properties. Nanohybrid composite materials have very low rate of polymerization shrinkage which in turn increases the marginal adaptability of composite resins. Composite resins are superior esthetic restorative material which can provide wide range of shades allowing near invisible restoration of teeth. Along with the esthetic properties unlike silver amalgam restorations, there is no need to give retentive features in cavity for restoration with composite resins. Hence, composite resins can save a healthy tooth structure.

There are several downsides to composite resins such as shorter life span of restorations, technique sensitive, and more expensive than traditional restorative materials. Another major disadvantage is the discoloration of composite restorative materials. This discoloration is attributed to several intrinsic and extrinsic factors. The resin matrix has been reported as being critical to color stability, and staining may be associated with a high resin content and water absorption.[1] Extrinsic factors include adsorption or absorption of colorants from exogenous sources such as coffee, tea, nicotine, food colors, and mouth rinses. In wet environment due to polymerization reaction, composite resin materials are reported with several physical changes. Polymerization reaction leads to the inward movement of water molecules causing mobilization of ions within the matrix and outward movement of unreacted ionomers and ions leached from fillers and activators.[2] Composite resin shrinkage and loss of weight are reported because of elution of leachable components, whereas hygroscopic absorption of water results in swelling of materials and increase in weight. This process may cause softening of the resin matrix and reduction of stain resistance. Variousin vitro studies performed to check the color stability of composite resin restorative materials using different staining solutions such as tea, coffee, red wine, tobacco, cola, and juices.[3],[4] The most commonly used staining solutions were red wine and coffee because there is broad consensus that they may cause severe staining of composite resin materials. Other than discoloration of surface, several adverse effects are also observed with resin-based materials such as change in gloss, increased surface roughness, and decreased microhardness.[5] Hence, this study was planned and aimed to evaluate the discoloration effects of coffee, tea, red wine, turmeric, aerated drinks, and distilled water on two different resin-based composite materials.


   Materials and Methods Top


This anin vitro study evaluated the influence of five staining solutions – coffee, tea, aerated drinks (Coca-Cola), turmeric, and red wine on the color stability of one hybrid and one nanohybrid composite, after three immersion periods of 1, 7, and 30 days.

Hybrid composite resin Filtek Z250 (3M, ESPE) of A3 shade was compared with nanohybrid composite resin Filtek Z350 (3M, ESPE) of the same shade. Staining solutions which were included in the study were coffee powder (Nescafe Classic, Nestle), tea bags 2 × 2 g (Yellow Label, Lipton), turmeric powder (MDH), red wine (Jacob's Creek, Vintage-2006), aerated drink (Coca-Cola), and distilled water as a control.

Sample preparation

A two-piece Teflon mold of diameter 50 mm and thickness 2 mm with three 10-mm holes was used to make the disc-shaped composite specimens of diameter 10 mm and thickness 2 mm. A cellophane sheet was placed over the mold and pressed uniformly. Extra flash was removed, and the material was made flush with the top of the mold surface. Disks were light-cured in a standard mode for 20 s having a light intensity of 400 mW/cm2 from the top only. No polishing was done to avoid any alteration in the surface texture, which may influence the results [Figure 1] and [Figure 2].
Figure 1: a two-piece Teflon mold of diameter 50 mm and thickness 2 mm with three 10-mm holes was used to make the disc-shaped composite specimens

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Figure 2: disc-shaped composite specimens of diameter 10 mm and thickness 2 mm

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Then, the baseline color values of each specimen were measured with spectrophotometer.

A total of 110 samples were prepared and divided into two parts, comprising 55 samples each (Part I and Part II).

  • Part I of 55 samples was prepared with hybrid composite
  • Part II of 55 samples was prepared with nanohybrid composite [Figure 3].


Coffee solution was prepared by pouring 4 g of instant coffee powder (Nescafe Classic) into a 200 ml of boiling water and after stirring for 1 min filtered through a filter paper. Tea solution was prepared by immersing two prefabricated tea bags of 2 g into 200 ml of boiling water for 3 min and then filtering through a filter paper. Turmeric solution is prepared by dissolving 4 g of turmeric powder in 200 ml of water. All solutions were prepared daily.
Figure 3: distribution of samples

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All the samples of hybrid and nanohybrid composites were immersed into coffee, tea, turmeric solution, red wine, and Coca-Cola; recordings were made at the interval of 1, 7, and 30 days with spectrophotometer. Solutions were changed daily [Figure 4].
Figure 4: all the samples of hybrid and nanohybrid composites were immersed in coffee, tea, turmeric solution, red wine, and Coca-Cola

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All the samples of the control group (CH and CNH) were immersed in distilled water and were examined, at the interval of 1, 7, and 30 days with spectrophotometer.

Evaluation under spectrophotometer

A visible range (350 nm to 800 nm) was taken to observe the amount of absorbance of color (stain) for each sample. The amount of absorbance was recorded at 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, and 800 nanometers; the value at 400 nm wavelength was taken as standard value for each sample and compared to calculate the mean of color change for every sample. These mean values were calculated on the 1st, 7th, and 30th days of experiment to notice the color changes. Hence, the percentage of absorbance of color was selected as criteria of color change in a particular sample.

All the samples when removed from staining solutions were thoroughly washed under running water, dried with absorbent paper, and then placed in viewing port for color measurement in spectrophotometer.

Statistical significance is calculated from the mean measurements of the staining of specimens in different staining solutions after different immersion periods. For statistical evaluation, analysis of variance and Tukey's tests were used at a significance level of 0.05. The post hoc test was applied where a significant difference was detected. Independent variables were as follows: (1) tested material, (2) immersion solution, and (3) time of immersion.


   Results Top


Irrespective of type of media and time of observation, the mean color absorbance was found to be significantly higher in the hybrid group (0.190 ± 0.065 units) as compared to the nanohybrid group (0.152 ± 0.029 units) (P < 0.001), thereby showing that the perception of color was significantly lower in the nanohybrid group as compared to the hybrid group.

The efficiency of the two groups in different media and at different time intervals has been studied in the following sections.

Impact of material

Overall, the minimum absorbance was observed in control medium for both the groups (0.111 ± 0.006 for the hybrid group and 0.106 ± 0.005 units for the nanohybrid group), whereas the maximum value was observed for wine (0.280 ± 0.033 for the hybrid group and 0.183 ± 0.011 units for the nanohybrid group) [Table 1].
Table 1: Comparison of color absorbance in different media at different time intervals

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Statistically significant differences were seen among different media for overall, day 1, day 7, and day 30 irrespective of type of composite used. At all the time intervals, the mean absorbance for the control group was minimum, whereas it was maximum for the wine group except on day 1 when the maximum value was for turmeric staining solution. As compared to control medium, all the media had significantly lower mean absorbance values. The difference was maximum between the control group and the wine group (P < 0.001), and it was minimum between the control group and the coke group (P = 0.006). Among other media too, a statistically significant difference was seen for all the comparisons except between tea and coke [Table 2].
Table 2: Comparison of absorbance levels in different media - overall (both hybrid and nanohybrid groups)

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On the basis of the above comparisons, the order of absorbance in different media was as follows:

Control < Coke ~ Tea < Coffee < Turmeric < Wine.

Impact of time

Overall (irrespective of media and type of composite), the mean absorbance was maximum at day 30 and minimum at day 7. Except for turmeric, in all the media, there was an increment in absorbance with the passage of time. In turmeric, there was a decrease in absorbance at day 7; however, at day 30, the value was maximum. In all the groups except wine, the mean change at different time intervals was statistically significant. In wine, although there was a steady increase in mean absorbance with time, the change was not statistically significant (P = 0.400).

Overall, no significant difference was seen between day 1 and day 7 and day 7 and day 30 mean values. However, the difference between day 1 and day 30 and day 7 and day 30 was significant [Table 3].
Table 3: Day wise comparison - overall (irrespective of type of composite)

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   Discussion Top


Due to excessive demands of cosmetic restoration in present-day practice, it has become important to determine which ones are susceptible to discoloration. To ensure excellent esthetics, it is necessary for tooth-colored materials to have color stability, and hence, they should be resistant to surface staining. Among tooth-colored restorative materials, composite resins are the most commonly used direct tooth-colored restorative materials.

In many situations, the composites are primarily intended to solve an esthetic complaint rather than a functional problem. For example treatment of dysmorphias or discolorations, diastema closure and treatment of large carious lesions and trauma in anterior teeth.[6] Because of these requirements, the uses of resin composites have increased manifolds. Color stability over a period of time of the restoration is an important factor in the success of an esthetic restoration. An unacceptable color match is one of the major reasons for replacement of composite restoration. Physical nature of food such as consistency, temperature and leaching of pigments may affect the color stability of restorative materials. The nature of resin also accounts for some differences in staining potential. Staining susceptibility of resin composites might be attributed to their degree of water sorption and hydrophilicity of the matrix resin. If the resin composite can absorb water, then it is also able to absorb other fluids, which results in its discoloration. Water sorption occurs mainly as direct absorption in the resin matrix. The glass filler particles will not absorb water into the bulk of the material but can adsorb water onto the surface. Thus, the amount of water sorption is dependent on the resin content of the resin composite and the quality of the bond between the resin and the filler. Extra water sorption may decrease the life of resin composites by expanding and plasticizing the resin component, hydrolyzing the silane, and causing microcrack formation. Therefore, the microcracks or the interfacial gaps at the interface between filler and matrix allow stain penetration and discoloration.[7] It has been shown that hydrophilic materials have a higher degree of water sorption and a relatively higher discoloration value with staining solutions than hydrophobic materials.

Hybrid composite resin composites are called hybrid because they are made up of polymer groups (organic phase) reinforced by an inorganic phase. About 60% or more of the total content of hybrid composites is glasses of different sizes. Glass particle size ranges from 0.6 to 1 μm, and it also contains 0.04 μm-sized colloidal silica. These are the composites which are used in abundance currently in dental practice.

Nanotechnology has led to the development of a new composite resin characterized by containing nanoparticles measuring approximately 25 nm and nanoaggregates of approximately 75 nm. These are made up of zirconium/silica or nanosilica particles. The aggregates are treated with silane so that they bind to the resin, and it gives a high load, up to 79.5%.[8] As the particle size is smaller, resins made with this type of particle give the restoration a better finish, which is observed on its surface texture, and biodegrading of the material is reduced over the period of time. This technology has been widely accepted because of its mechanical properties. This resin indicated for use in the anterior and posterior sectors. It is also be mentioned that the smaller size of the particles leads to less curing shrinkage, which creates less cusp wall deflection. It also reduces the presence of microfissures in the enamel edges which are responsible for marginal leakage, color changes, bacterial penetration, and possible postoperative sensitivity.[9]

The precipitation of shrinkage during polymerization is the major disadvantage of light-cured composites.[10] Contraction in composites observed due to polymerization reaction along with closer packing of the molecules. This contraction creates mechanical stresses in the resin, which can disrupt the marginal seal between the composite restoration and the dentin or enamel. Polymerization shrinkage leads to several clinical problems, such as marginal discoloration, restoration fractures, solubility of the bonding system, and causing marginal leakage.[11]

The staining agents selected for this study are of common daily use and have a strong potential to stain tooth-colored restorative materials and thus have been used in many studies. First, the choice of staining solution in this study attempted to represent the diverse area of color spectrum. Water is colorless, coffee is light brown and tea is dark brown, coke is blackish brown, turmeric is yellow/orange, and red wine is burgundy in color.

Discoloration can be evaluated with different instruments and techniques. Color perception is a psychophysical phenomenon with variations, both between individuals and within an individual at different times. Instrumental measurement has the advantage of obviating the subjective errors of color assessment.[12] The quantitative assessment of minimal color change and differences exclusively by visual examination is not of much use. The results are too subjective to an observer's opinion and thus of low reproducibility. Reproducible, objective, and statistically utilizable results of color measurements can only be achieved in standardized color quantifying devices such as the spectrophotometer.

After staining, both composite resins tested had perceptible color changes. Color change of materials in staining agents ranked in this increasing order: water < cola < tea < coffee < turmeric < red wine. Similar results were reported in other studies also.[8] Wine had the most significant discoloration effect on samples, whereas the specimens in water showed the least color change.

The staining susceptibility of a material may be attributed to its resin or filler type.[13] As purported by the manufacturer, Filtek Z350 is a nanocomposite with a primary 20-nm silica filler and loosely bonded cluster zirconia/silica particle size ranging from 0.6 to 1.4 mm. Its resin matrix is composed of Bisphenol A-Glycidyl Methacrylate (Bis-GMA), urethane dimethacrylate (UDMA), Bisphenol A ethoxylated dimethacrylate (Bis-EMA), andTriethylene Glycol Dimethacrylate (TEGDMA). Filtek Z250 is containing Bis-GMA, Bis-EMA, and TEGDMA and 0.1- to 15-mm-sized fillers. The color shifts may be related to the structure of the resin matrix. Bis-GMA, Bis-EMA, and UDMA were presented in Filtek Z250, and Bis-GMA, Bis-EMA, UDMA, and TEGDMA were found in Filtek Z350. The fact that Filtek Z250 displayed more discolorations than the other materials in all solutions draws our attention to Bis-EMA, which is present only in its structure. However, that Bis-EMA used instead of TEGDMA present in the nanohybrid resin composite tested has a more hydrophobic structure than TEGDMA and cannot account for higher staining values of Filtek Z250 in comparison to the other materials.

Under normal curing conditions, a UDMA material showed lower water sorption than Bis-GMA.[14] It is apparent that the water sorption and solubility of resin composites are dependent on the type of resin matrix used. On the other hand, it was found that the water uptake in Bis-GMA-based resins increased from 3% to 6% as the proportion of TEGDMA increased from 0% to 1%. Surface discoloration is common finding among all studies. This is because of the hydrophobic monomers in composite resins. For instance, UDMA-based monomers display lower staining values compared to other dimethacrylate-based monomer types. UDMA seems more stain-resistant than Bis-GMA. The present study supported the fact as nanohybrid composite (contained a higher amount of UDMA) samples were reported with less staining in comparison to hybrid samples.[2] This may be also accounted for low viscosity and low water absorption of UDMA and its successful polymerization with visible light. It was found that incorporation of greater amounts of TEGDMA resulted in an increase in water uptake in Bis-GMA-based resins. Mazato et al. reported that this was due to increased surface hydrophilicity. Hydrophilic groups such as the ethoxy group in TEGDMA are thought to show affinity with water molecule by hydrogen bonding to oxygen.[15] Because of this reason, Filtek Z250 demonstrated more discoloration than Filtek Z350 for the staining solutions, especially for the wine group. It has been suggested that silanization of filler particles plays an important role in discoloration as does the type of the resin filler and matrix used in the resin-based composites. This is due to the fact that silane has high water absorption levels. High staining values of Filtek Z250 may be attributed to the high proportion of silane present in the structure of the material.

The color stability of dental composites is due to exogenous and endogenous reasons. Exogenous influences are staining foods or even mouth rinses. To avoid these discolorations, it is important to minimize the material's superficial roughness which is related to its polishability and thus to the size of its filler particles.[13] If intraoral liquids damage and/or roughen the surface chemically, color particles can penetrate more easily. These external color changes particularly can be eliminated by subsequently polishing the surface. However, if deeper layers are involved, the discoloration is mostly irreversible.


   Conclusions Top


Within the limitations of this study, the following conclusions were drawn:

  1. Overall, the mean color change in hybrid composite materials was higher as compared to nanohybrid material under different staining and time conditions
  2. Among different staining solutions, wine and turmeric had the maximum color change, whereas coke had the minimum under various time conditions for both the materials being compared
  3. The direction of difference in change in color in both the groups remained the same at different time intervals in different staining materials
  4. While, in all the staining solutions, there was an increment in absorbance with time, turmeric showed a unique pattern with an increase, followed by a fall and then an increase in absorbance.


Finally, we would like to emphasize that it is difficult to entirely correlate laboratory findings with the clinical behavior of any restoration since a number of factors are at play in oral environment that cannot be fully simulated in laboratory conditions. Therefore, to find a correlation between clinical studies and laboratory measurements, furtherin vivo clinical evaluation is suggested.

Clinical significance

Nanohybrid composite resins are the choice of material as an esthetic restorative material, especially in anteriors as they are showing lesser discoloration than hybrid composite resins. After placement, composite resin restorations in oral cavity patient should be instructed to decrease the intake of beverages and food colorants which all are mentioned in the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Koran P, Kürschner R. Effect of sequential versus continuous irradiation of a light-cured resin composite on shrinkage, viscosity, adhesion, and degree of polymerization. Am J Dent 1998;11:17-22.  Back to cited text no. 11
    
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Gupta R, Parkash H, Shah N, Jain V. Aspectrophotometric evaluation of color changes of various tooth colored veneering materials after exposure to commonly consumed beverages. J Indian Prosthodont Soc 2005;5:72-8.  Back to cited text no. 12
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Bagheri R, Burrow MF, Tyas M. Influence of food-simulating solutions and surface finish on susceptibility to staining of aesthetic restorative materials. J Dent 2005;33:389-98.  Back to cited text no. 13
    
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Imazato S, Tarumi H, Kato S, Ebisu S. Water sorption and colour stability of composites containing the antibacterial monomer MDPB. J Dent 1999;27:279-83.  Back to cited text no. 14
    
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Deepa CS, Krishnan VK. Effect of resin matrix ratio, storage medium, and time upon the physical properties of a radiopaque dental composite. J Biomater Appl 2000;14:296-315.  Back to cited text no. 15
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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