The Potential Effect of Silver Nanoparticles to Inhibit Microbial Activity in Orthodontic Adhesive Appliances: A Literature Review

Silver nanoparticles have been the focus of research in various areas of dentistry, including orthodontics. Orthodontic treatment requires a long period of time, so the brackets are in the oral cavity for a long time. This can potentially trigger the formation of white spot lesions because plaque sticks more easily to the surrounding enamel. Using silver nanoparticles mixed with orthodontic adhesives has been reported to increase antibacterial and antimicrobial characteristics. This literature review aims to investigate the effect of adding silver nanoparticles to orthodontic adhesive devices in inhibiting antimicrobial activity. This study method was carried out by searching the online electronic databases PubMed, Science Direct, and Google Scholar with the keywords "silver nanoparticles AND antimicrobial", "silver nanoparticles AND orthodontic adhesive", "silver nanoparticles AND composite resin", which is an original article published the year 2019-2023. The results of research from 10 articles that met the inclusion criteria showed that orthodontic adhesives with silver nanoparticles effectively inhibited microbial activity, such as Streptococcus mutans (S.mutans), Lactobacillus acidophilus (L.acidophilus), Streptococcus sanguinis (S.sanguinis) and Candida albicans through increased release of Ag+ ions. Silver has been known to have effects, including producing minimal bacterial resistance compared to antibiotics. Even though it results in a decrease in the shear bond strength (SBS), the decrease level is still within clinically tolerable limits. It can be concluded that research needs to continue to be developed to obtain the right concentration and composition of the addition of silver nanoparticles so that an orthodontic adhesive material is obtained that is not only superior in its antibacterial properties but also in its mechanical properties.


INTRODUCTION
In recent years, orthodontic treatment has become increasingly popular because it can improve dental function and facial appearance.Using orthodontic brackets requires a strong attachment to tooth enamel to achieve the therapeutic goals of orthodontic treatment.The attached bracket can become an area that increases plaque buildup and makes it difficult to clean the bond area, causing enamel demineralization. 1.
Demineralization that occurs on the tooth * Corresponding author, e-mail: nurmasita.fk@ub.ac.id surface causes the formation of white spot lesions (WSLs), which can result in caries. 2 Prevalence of patients undergoing orthodontic treatment The incidence of WSLs can reach more than 60%. 3,4Several strategies have been tested to minimize the occurrence of WSLs, including improved oral hygiene, dietary modification, and topical fluoride application.However, this is promising because it cannot rely only on patient compliance. 5he increasing popularity of nanotechnology in clinical dentistry today, combined with its particular antibacterial properties is fueling its application in orthodontic materials.Contemporary approaches primarily investigate the impact of antibacterial carriers incorporated into orthodontic adhesives or cements or used to coat orthodontic appliances to suppress bacterial accumulation, thereby anticipating the formation of WSLs. 5 If a material for attaching brackets with nanotechnology could be found that could prevent bacterial growth, then the patient cooperation required for oral hygiene may be reduced.
Silver nanoparticles (AgNPs) have been introduced as antimicrobial agents.Microbial cell death occurs due to the formation of reactive oxygen on the surface of AgNPs or through the release of free silver ions (Ag+).AgNPs have attractive properties such as chemical stability, catalytic activity, and high conductivity.The surface of AgNPs has reactive oxygen or the release of free silver ions can cause microbial cell death through cell membrane disruption and DNA modification; thus, imparting antibacterial and antifungal properties to silver nanoparticles.Silver nanoparticle material became a discovery when used in orthodontic adhesives by adding silver nanoparticles with unique antibacterial characteristics. 5AgNPs have antibacterial capabilities against gramnegative and positive bacteria, including strains resistant to several drugs. 6This literature review study aims to determine how adding silver nanoparticles to orthodontic adhesive devices inhibits microbial activity, especially in the oral cavity.

MATERIALS AND METHODS
Literature search to obtain information on several online electronic databases PubMed, Science Direct, and Google Scholar with the keywords "silver nanoparticles AND antimicrobial", "silver nanoparticles AND orthodontic adhesive", "silver nanoparticles AND composite resin".The inclusion criteria in the literature search were original articles in English, the publication year 2019-2023, full access, full text, international scale scientific articles, and results related to the application of silver nanoparticles to orthodontic adhesives as an antimicrobial agent.Meanwhile, the exclusion criteria are scientific articles, literature reviews, and systematic reviews, which have unrelated variables and explanations.Several articles were excluded with certain considerations, namely articles not included in the inclusion criteria and did not specifically discuss the application of adding silver nanoparticles to orthodontic adhesives as an antimicrobial agent.After review, 10 articles met the criteria.

RESULT
After a literature search was carried out and then linked to the inclusion/exclusion criteria, 10 articles were taken that met the criteria.Table 1 highlights the main findings of the included studies.Using fifty bovine incisors divided by composite.Transbond XT resin as control group (G1), Experimental composite without Ag@SiO2 NPs (G2); Experimental composite with 0.5% Ag@SiO2 NPs (G3); Experimental composite with 1% Ag@SiO2 NPs (G4); Experimental composite with 3% Ag@SiO2 NPs (G5).

Streptococcus mutans
Incorporating silicon dioxide-coated silver nanoparticles at a concentration of 3 wt% into dental adhesives reduced the population of Streptococcus mutans around orthodontic brackets.The SBS value also decreased compared to the 1% group.However, the difference was not significant with the control group

Streptococcus mutans
The number of bacteria significantly decreased at 1% copper oxide and 1% silver oxide, whereas there was no significant difference between the other and the control groups.On day 30, the colonies had grown in all groups but did not show significant differences from the control group.The materials used in the study on the antimicrobial effect of silver nanoparticles in orthodontics adhesive included extracted human premolars. 7,10nother study used bovine incisors, and one study was conducted in vivo using an animal study, male Wistar rats. 8,145,16 All studies evaluated the antimicrobial effectiveness of silver nanoparticles against bacteria that contribute to tooth demineralization, Streptococcus mutans.The use of one type of bacteria was analyzed by making different AgNPs mixture concentrations.][13][14][15][16] Almost all studies focus on the addition of silver nanoparticles to orthodontic adhesives.One study compared the effectiveness of adding silver nanoparticles with materials other than silver, namely hydroxyapatite, zinc oxide, titanium oxide, and copper oxide. 15][16] Four of them investigated the shear bond strength properties, where one study measured the shear strength of Silicon Dioxide Composite coated silver nanoparticles and produced the same shear strength properties as the control group. 16

DISCUSSION
Although the field of orthodontics has made progress, the use of dental brackets still carries the risk of causing WLS, which often cannot be cured.Therefore, antimicrobial properties become another desirable property of orthodontic adhesives as the dental brackets adhere to the enamel and remain in the oral cavity for at least two years.
One of the most commonly used nanomaterials as a specialist antimicrobial is nanoparticles (NPs). 7Nanoparticles are created with special properties that make them highly sought after in materials science and biology.Among various types of nanoparticles, silver nanoparticles have been extensively researched in recent years.These nanoparticles typically contain 20 to 15,000 silver molecules with a spacing of less than 100 nm. 17everal methods have been used to assess the potential effect of silver nanoparticles in inhibiting the antimicrobial activity of orthodontic adhesive devices.The use of human premolars and cow teeth gave the same results, showing the effectiveness of adding silver nanoparticles. 7,10,145,16 Silver nanoparticles can be added to dental appliance materials.This material can be used directly in restorative treatment, incorporated into orthodontic adhesives, membranes that can be used to regenerate tissue in periodontal treatment, adhesive materials for making prosthetic dentures, and titanium coatings for dental implant treatment. 18Placement of titanium coatings for implanted teeth are known to activate the immune system causing a reaction between the host and the biomaterial. 19In the context of orthodontic adhesives, silver nanoparticles may provide several advantages.Research findings showed that incorporating silver nanoparticles into orthodontic adhesives can improve antibacterial and antimicrobial characteristics. 7ilver has been known to provide effects including (1) minimal bacterial resistance compared to antibiotics, (2) constant ion release and long-term antibacterial effect; and (3) biocompatibility with human cells. 10Silver nanoparticles are considered the best choice for antibacterial applications due to their great potency and broad-spectrum activity.The adhesive containing silver nanoparticles has important antibacterial activity against Streptococcus mutans, which has been reported in all the results of this study.Silver nanoparticles showed resistance to Streptococcus mutans' ability to weaken dentin bond strength.The study found that adhesives modified with silver nanoparticles showed antibacterial activity for less than six months. 10,13,15Silver nanoparticles have also been shown to have potent antibacterial properties against cariogenic microbes, including Lactobacillus acidophilus (L.,16 The antibacterial activity of AgNPs is because bacteria cannot resist them.Silver (Ag) also has antiviral and antifungal properties.Its effectiveness against Candida albicans was reported by Mojgan et al. l, 2021. 16This property is characterized by an increase in the release of Ag+ ions resulting from the use of finer AgNPs with a particle size of less than 10 nm compared to larger AgNPs.Overall, these things can result in DNA damage, ribosome instability, enzyme interactions, cell death, and cell leakage. 10,20ncreasing the quality of composite resin by incorporating silver nanoparticles into the composite resin does show good antimicrobial properties.However, this addition is contrary to aesthetic purposes because it can cause a dull gray color change in the composite caused by silver nanoparticles. 16Meanwhile, shear bond strength in orthodontic brackets that were attached using a binder with AgNPs decreased in trials compared to the control group. 13,16This was because silver nanoparticle composite's shear strength and surface roughness decreased along with increasing concentrations of AgNPs mixed in the orthodontic adhesive.However, all levels of SBS, whether containing nanosilver or not, are above the range of 6-8 MPa so they can still be tolerated clinically (15.3-27.6MPa). 10,14,20

CONCLUSION
The main advantage of using silver nanoparticles in orthodontic cement was its ability to inhibit the growth of bacteria and microorganisms around orthodontic brackets and adhesive-coated tooth surfaces.It could help reduce the risk of infection and improve oral hygiene during orthodontic treatment.The antibacterial properties of silver nanoparticles could also help prevent plaque formation and tooth decay due to food retention around orthodontic brackets.The disadvantage was the reduction in surface roughness, thereby reducing the shear strength, although it was still within tolerable limits.Therefore, research and development on the use of silver nanoparticles in orthodontic adhesives needs to continue to be carried out to obtain the right composition.

Table 1 .
Antimicrobial Effect of Silver Nanoparticles in Orthodontics Adhesive