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Table of Contents   
ORIGINAL RESEARCH  
Year : 2020  |  Volume : 31  |  Issue : 4  |  Page : 589-592
Antibacterial activity of a glass ionomer containing silver nanoparticles against Streptococcus mutans and Streptococcus sanguinis


1 Department of Pediatrics, Faculty of Dentistry, Shahed University, Tehran, Iran
2 Department of Periodontics, Faculty of Dentistry, Shahed University, Tehran, Iran
3 Department of Microbiology, Faculty of Medicine, Shahed University, Tehran, Iran
4 Department of Operative Dentistry, Faculty of Dentistry, Shahed University, Tehran, Iran

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Date of Submission14-Feb-2018
Date of Decision01-Dec-2018
Date of Acceptance22-Aug-2019
Date of Web Publication16-Oct-2020
 

   Abstract 


Aim: Nano-sized metal particles exhibit special biological, chemical, and physical properties. The aim of this study was to evaluate the effect of incorporating silver nanoparticles into a resin-modified glass ionomer (GI) on its antimicrobial property. Materials and Methods: Antibacterial action of GI samples containing 0, 40, 80 ppm silver nanoparticles against standard strains of Streptococcus sanguinis and Streptococcus mutans were assessed by agar diffusion and direct contact tests. Data were analyzed using analysis of variance and Duncan test (P < 0.05). Results: Agar diffusion test showed no bacterial inhibition zone, but direct contact test exhibited significant antimicrobial activity against S. sanguinis and S. mutans in resin containing 80 ppm of nanosilver. Conclusion: Incorporation of a certain amount of silver nanoparticles into GI can increase its antimicrobial activity compared to the original material.

Keywords: Antibacterial, glass ionomer, silver nanoparticles

How to cite this article:
Moshfeghi H, Haghgoo R, Sadeghi R, Niakan M, Rezvani MB. Antibacterial activity of a glass ionomer containing silver nanoparticles against Streptococcus mutans and Streptococcus sanguinis. Indian J Dent Res 2020;31:589-92

How to cite this URL:
Moshfeghi H, Haghgoo R, Sadeghi R, Niakan M, Rezvani MB. Antibacterial activity of a glass ionomer containing silver nanoparticles against Streptococcus mutans and Streptococcus sanguinis. Indian J Dent Res [serial online] 2020 [cited 2020 Oct 31];31:589-92. Available from: https://www.ijdr.in/text.asp?2020/31/4/589/298397



   Introduction Top


Glass ionomer (GI) is one of the commonly used tooth-colored materials in restorative dentistry. It has advantages such as ability to form chemical bonds with tooth structures, having expansion coefficients and elastic modulus comparable to tooth structure, antibacterial activity and no polymerization shrinkage.[1],[2] However, because of its low mechanical properties, it cannot withstand occlusal forces in the posterior areas of the oral cavity.[3] Currently, nanoparticles have been added to GI to enhance its physical characteristics.[3],[4],[5],[6],[7],[8],[9] Silver nanoparticles have significant antimicrobial activity against a wide range of microorganisms due to their small size and large surface area.[10] The results of several studies have shown the antibacterial effect of nanosilver on oral Streptococcus species especially Streptococcus mutans, which is one of the most important bacteria involved in the caries formation.[11],[12],[13],[14],[15],[16] Li et al. evaluated long-term antimicrobial effect of GI cements containing silver nanoparticles and showed that fresh samples had strong antimicrobial activity against S. mutans.[9] Paiva et al. incorporated nanosilver into GI cements and demonstrated their antimicrobial properties against  Escherichia More Details coli and Streptococcus mutans.[8] It seems that the incorporation of silver nanoparticles to GI can improve its antimicrobial properties. The aim of the present research was to evaluate the antimicrobial activity of GI containing silver nanoparticles against S. mutans and S. sanguinis.


   Materials and Methods Top


Materials

Silver nanoparticles (Nanoshel LLC, Willmington, Delaware, USA) with average particle size of 20-30 nm and light-cured resin-reinforced restorative GI (Fuji II LC, GC Corporation, Tokyo, Japan) were used in this experiment.

Preparation of GI samples

Nanosilver was weighed and added to GI powder to prepare weight fractions of 40, 80 ppm. They were mixed manually for 20 min using a mortar and pestle to achieve a homogenous mixture. Nanoparticles' distribution in the samples was evaluated under a scanning electron microscope (SEM, Hitachi, S 4160, Japan) to confirm uniform mixture of silver particles and GI powder.

Antibacterial tests

The antimicrobial activity of GI containing 0, 40, and 80 ppm of silver nanoparticles was tested against standard strains of S. mutans (ATCC 25175) and S. sanguinis (ATCC 10556). GI samples were prepared according to the manufacturer's instruction, placed in a metal disc-shaped mold (six mm in diameter and one mm in height) and then cured with Coltolux light emitting diode (LED) light-curing unit (Coltène/Whaledent, NY, USA).

Agar diffusion test

After activation of lyophilized bacteria, suspensions of the organisms were prepared at 0.5 McFarland turbidity standard (108 CFU/ml). A total of 20 μl of the bacterial suspension was swabbed uniformly across Mueller-Hinton agar plates (Liofilchem Co., Italy) with a sterile swab in all directions. Then, GI discs were lightly pressed onto the agar surface under aseptic conditions.

In well method, holes with 6 mm diameter were punched in Mueller-Hinton agar plates with a sterile puncher, 20 μl of the bacterial suspension was swabbed across the plates and GI discs were placed in wells which contained sterile Mueller-Hinton broth media. All plates were incubated at 37°C and inspected for bacterial inhibition growth zone at 24, 48, and 72 h and 1 week after incubation. Antibacterial activity was assessed by measuring the diameter of growth inhibition zone. Agar diffusion test was repeated 5 times.

Direct contact test (DCT)

Polymerized GI discs (6 × 1 mm) were placed in the sterile well plates. A total of 20 μl of 0.5 McFarland standard of bacterial suspensions (S. mutans and S. sanguinis) was added into wells in Mueller-Hinton broth medium (Liofilchem Co., Italy) and incubated for 24 h at 37°C. Then, 10 μl of these media was cultured on blood agar (Liofilchem Co. Italy) and again incubated at 37°C. After 24 h, the number of colonies (colony-forming unit = CFU) per milliliter was calculated using ImageJ software. Each test was repeated three times.

Statistical analysis

Data analyses were carried out with SPSS 18.0 (SPSS Inc, Chicago, USA). Normality of the data was assessed with Kolmogorov-Smirnov test. Data were analyzed using ANOVA and Duncan test. Statistical significance was set at P < 0.05.


   Results Top


Agar diffusion test

There was no bacterial growth inhibition zone around any of the specimens after 24, 48, 72 h, and 1 week of incubation.

DCT

The effect of silver nanoparticles on both S. sanguinis and S. mutans was similar and an increase in the amount of nanosilver resulted in reduced bacterial growth for both bacteria. When the bacterial inhibitory effect of 0, 40, and 80 ppm groups was compared, there was no significant difference between the 0 and 40 ppm groups, while the difference between 0 and 80 ppm groups and 40 and 80 ppm groups was significant (P = 0.004). These results were similar for both bacteria [Figure 1].
Figure 1: The mean ± standard error colony count of S. mutans and S. sanguinis in the three study groups

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   Discussion Top


In the present study, 40 and 80 ppm silver nanoparticles were added to GI to evaluate its antimicrobial property against S. mutans and S. sanguinis. These amounts were chosen based on the results of a previous study, in which adding small amounts of nanosilver particle to GI enhanced its compressive strength, but amounts more than 80 ppm showed a negative impact on its mechanical property.[17] All the samples were set using the same technique and under similar conditions.

In the direct contact test, the microorganisms and the material under study come into direct contact in vitro[9] and the turbidity or optical density value can be used to evaluate the antimicrobial effect of the material. The disadvantage of such measurement is that both the viable and killed bacteria are present in the microbial suspension.[18] A more accurate technique is to count the microbial colonies in order to determine the counts of viable bacteria at the end of each specific period, which we used in our experiment. Our results showed that the number of colonies of both bacterial species decreased with an increase in the amounts of silver nanoparticles in the GI. 80 ppm group exhibited a significant decrease in colony counts of S. mutans and S. sanguinis. In addition, both bacterial species exhibited comparable sensitivity to silver nanoparticles. Liu et al. evaluated the antimicrobial activity of several types of GI cements containing silver nanoparticles against S. mutans using agar diffusion test (ADT) and DCT techniques. The results of the two techniques were different. In the DCT technique, all the samples containing nanoparticles exhibited high antimicrobial effect but the effect decreased with the aging of the material.[9]

Despite the antibacterial effect of the GI cement,[1],[19],[20],[21] in the disc agar diffusion test of this experiment, growth inhabitation zone was not detected in any of the samples. In the previous studies, zones of growth inhibition had been observed in the agar medium; however, the difference in the results may be due to the different bacterial species and the cement types.[1],[11],[19],[22] In a study by Palenik, some S. mutans and S. sanguinis samples did not exhibit growth inhibition zones in the vicinity of different GI cements.[1] Loyola-Rodriguez showed in agar diffusion test that some S. mutans strains were resistant to GI cement and exhibited no growth inhibition zone.[19] Dastjerdi et al. showed that orthodontic GI was able to inhibit S. mutans in the agar medium.[20]

Liu et al. reported growth inhibition zones of S. mutans in GI cements with and without silver nanoparticles in freshly mixed samples, with no differences between the groups. They attributed this to the release of fluoride from the cement, and pointed out that maybe the release of silver ions from the cement is not sufficient to bring about an antimicrobial effect in the agar medium. In addition, they reported no antimicrobial effects on 2-day, 1-week, and 2-week old samples, which might be explained by the sudden release of fluoride or silver ions on the surface of the material.[9]

Magalhães et al. showed that incorporation of silver nanoparticles into GI cement increased the antimicrobial properties and the growth inhibition zone for S. mutans in the agar plates. It seems that greater antimicrobial effect of the mixture was mainly because of the direct contact between bacteria and silver nanoparticles in the resultant cement rather than the release of silver ions into the culture medium.[11] One of the reasons for the difference in the results of disc diffusion test between our study and other studies might be due to the different material types used and their diffusion characteristics. Another reason might be differences in the techniques used to mix silver nanoparticles with GI. In the study by Magalhães et al.,[11] silver nanoparticles were incorporated in a colloidal solution and added to mixed cements during manipulation, while in our study silver nanoparticles were incorporated into GI powder.

However disc diffusion technique is a standard and common method for evaluating the antimicrobial properties of different materials, the technique has some limitations, including the inability to indicate changes in antibacterial properties of the insoluble portion of the test materials and the progress of this property over time. Finally, the differences in the results between the direct contact test and disc diffusion test might be attributed to differences in the nature of the solid and broth media and also differences in the amount of antibacterial agents that are released from the cement into the two media. Nevertheless, the results of direct contact test indicated the antibacterial effect of GI cement containing silver nanoparticles.

Although the results of this study are somehow positive, further research is necessary on the cytotoxicity and biocompatibility of GI containing silver nanoparticles before its clinical application. In addition, the effect of incorporation of nanosilver in GI on other properties of the material including bond strength, wear, shear strength, the amount of fluoride released, and the pH should be evaluated.


   Conclusion Top


It appears that the incorporation of 80 ppm silver nanoparticles into GI improves the antibacterial properties of this material.

Acknowledgements

We thank Dr. D. Talei for his assistance in the statistical analysis of the research.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Dastjerdie EV, Oskoui M, Sayanjali E, Tabatabaei FS. In-vitro comparison of the antimicrobial properties of glass ionomer cements with zinc phosphate cements. Iran J Pharm Res 2012;11:77.  Back to cited text no. 20
    
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Correspondence Address:
Dr. Rokhsareh Sadeghi
Department of Periodontics, Faculty of Dentistry, Shahed University, 39 Italia St., Vesal Ave. Tehran, 1417755351
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdr.IJDR_115_18

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