Applications Of Silver Nanoparticles In Dentistry

Nanotechnology is a booming ield of research and innovation that aims at building materials on the scale of atoms and molecules. Essentially Nanotechnology is characterized as the plan, characterisation, creation and utilization of structures, gadgets and frameworks by controlled control of size and shape at the nanometer scale. It is a booming ield of this 21st century. Silver Nanoparticles are known for their various physical, chemical and quantum properties that make them unique. They have got excellent antimicrobial properties that extend their applications nearly in every sphere of life. Apart from the antimicrobial property, they show excellence in their Antiin lammatory and Anti-oxidation properties. Silver nanoparticles also have many optical, mechanical, biological and chemical properties that attribute to their enhanced performances in the evaluation and clinical assessments of mechanical devices and other biomaterials. Uses of SilverNanoparticles in the ield of dentistry is remarkable. Silver nanoparticles can be used in association with dental acrylic resins, intracanal medication and in implant coatings. The current study aims at discussing the applications of silver nanoparticles in various aspects of dentistry.


INTRODUCTION
Nanotechnology is a booming ield of research and innovation that aims at building materials on the scale of atoms and molecules. Essentially Nanotechnology is characterized as the plan, characterisation, creation and utilization of structures, gadgets and frameworks by controlled control of size and shape at the nanometer scale. The revolution created by Nanotechnology in almost every aspect of science ranging from cosmetics to Biotechnology is tremendous (Rajeshkumar and Malarkodi, 2014). It's a contribution to the ield of Dentistry is remarkable. Especially Silver nanoparticles had got great applications in Dentistry ( Figure 1). Silver nanoparticles are nano-scale particles that are made of silver between 1nm and 100nm in size (Mohamed, 2014). Silver nanoparticles are largely composed of Silver oxide (Das, 2019). They have got a large surface to bulk silver atom ratio (Pranati et al., 2019). The uniqueness of the silver nanoparticles attributes to their physical and quantum properties . They have got excellent antimicrobial properties that extend their applications nearly in every sphere of life (Vanaja, 2013). The Silver nanoparticles will go and bind with the sul hydryl groups that are present in the bacteria's DNA and proteins. They cause unwinding of DNA, alter the hydrogen bonding and cause interference to Cell wall synthesis and cell division. Apart from the antimicrobial property, they have got excellent Anti-oxidation and Anti-in lammatory properties. Silver nanoparticles also have many optical, mechanical, biological and chemical properties that attribute to their enhanced performances in the evaluation and clinical assessments of mechanical devices and other biomaterials. Their measurable results are characterized by their special mechanical and physical-chemical properties. Their increased surface area permits the coordination of various ligands. Therefore, they are well recognized for their usage in the diagnosis and treatment of many diseases. Applications of silver nanoparticles in dentistry is a growing ield that has enhanced and stabilized various biomaterials and devices that are already in use in dentistry. Silver nanoparticles can be used in association with dental acrylic resins, intracanal medication and in implant coatings. Silver nanoparticles can also be used as an anticaries formulation, in combination with local anaesthesia, in treatment of oral cancers. They also serve as an excellent choice of iller materials (Rajeshkumar, 2016;Rajeshkumar et al., 2016). Their application in Prosthodontics and Restorative dentistry is remarkable. The current study discusses the various applications of silver nanoparticles in dentistry.
More than 40 articles had been reviewed for the construction of the article. The articles were retrieved with the help of search engines like Google Scholar, Pubmed, Biorxiv and Chemrxiv. As this is a review article no approvals were required for the publication of the article

Silver Nanoparticles In Implantology
Titanium dental implants are the most widely used implants in dentistry (Zhao et al., 2009). The main complication of implantology is the presence of implant surface infection. In Spite of usage of aseptic surgical protocols during the surgery, infections tend to occur post-surgery (Rodriguez, 2017). Silver nanoparticles are greatly known for their antimicrobial properties. Thus incorporation of silver nanoparticles in the titanium implants may prevent peri-implantitis and other bacterial infections. Soo-Hyoen Choi et al. has compared the conventional uncoated implants with implants coated with silver loaded polydopamine coating. The pure titanium is immersed in dopamine hydrochloride or in the HCl buffer solution and in 50 mL silver nitrate solutions for about 24 hours with different concentrations for 30 minutes and thus the implant coating was formed (Choi et al., 2019). Results showed that there were signi icantly lower numbers of microbial colonies (Streptococcus mutans, Porphyromonas gingivalis) in the surface-modi ied titanium than those with the uncoated titanium (Choi et al., 2019). The silver-coated implants maintained the lag phase of both the bacteria whereas the conven-tional implants did not maintain the same and the lag phase had been changed to exponential phase after 9 hrs for Streptococcus mutans and 15 h for Porphyromonas gingivalis (Choi et al., 2019). Bio Tian et al. has studied the antimicrobial properties of the implants with Silver nanoparticle-loaded hydroxyapatite coatings. The study has shown that the AgNP-HAC surfaces were found to be superior to a conventional titanium alloy in terms of induction of osteogenic differentiation in the stromal cells (Tian, 2016). Another study has shown that the antimicrobial effect of the nanoparticle coated implants to be about 64.6% which is statistically signi icant (Lampé et al., 2019). A study by Gunputh et al. has reported that the AgNP coated implants have exhibited more than 80 per cent microcidal activity on evaluation with LIVE/DEAD assay (Gunputh et al., 2020). The study has also shown that the coatings over the implants had very good stability. Li et al. have stated that the silver nanoparticles of bigger size which are of 5 to 25-nanometer diameter have got a greater antimicrobial effect than the nanoparticles of smaller diameter (Li, 2013a). A study by Lu et al. shows the signi icant antimicrobial properties of the Silver nanoparticle incorporated titanium implants (Lu, 2011). Including the distribution of size, density, adhesion, depth pro ile are the factors that attribute to the overall uniqueness of the silver nanoparticles (Zhao et al., 2009).

Silver Nanoparticles In Conservative Dentistry
Composite resins are restorative materials that are best known for their mechanical properties. They show excellent esthetics and load-bearing properties (das Neves et al., 2014). But the main disadvantage is that they accumulate more bio ilm on their surface than any other restorative material, thus leads to plaque formation, which inally results in caries. Many researchers worldwide are working tirelessly in improving the quality and durability of the resins. On that note, It is seen that AgNP incorporation in the composite resins can enhance the antimicrobial properties of the composite resins. The Silver nanoparticles can be compacted within the composite resins by adjusting the quantity of the iller particles that are being used. Addition of silver nanoparticles to the composite resins can be achieved by making some slight modi ications in the iller particles of the composite resins. A study by Patrícia Bolzan Agnelli das Neves et al. states that the silver nanoparticle incorporated composite resins had become more resistant to bio ilm formation and at the same time there had been no compromise in the physical and mechanical properties of the composites (das Neves et al., 2014). Another study by Shahin Kasraei et al. has examined the antimicrobial activities of the Silver nanoparticle incorporated composite resins. Direct contact test was done for the evaluation (Kasraei et al., 2014). The modi ied resins had shown higher antibacterial effects against the oral pathogens, namely Streptococcus mutans and Lactobacillus (Kasraei et al., 2014). The study results of a similar study by Li et al. show that the bio ilm formation and acidity were reduced by the AgNP incorporated Composite resins and the number of microorganisms had been signi icantly reduced (Li, 2013b). A study by Zhang et al. shows that there is no change in the cytotoxicity of the primer due to the incorporation of AgNPs in the adhesive syments (Zhang, 2013). Thus modi ied composite resins with silver nanoparticles embedded are much more antimicrobial than standard composite resins.

Silver Nanoparticles In Endodontics
Most of the Endodontic treatment failures are attributed to the formation of secondary caries (Leonardo, 1984). The Bacteria are the ones that cause secondary caries and peri radicular infections. The formation of secondary caries can be prevented by performing a proper cleaning and shaping of the root canal with good disinfectants. Sodium Hypochlorite is the best root canal irrigant known till date (Leonardo, 1984). But their cytotoxic activity towards the periapical tissues has paved the way for new attempts in discovering a root canal irrigant that is potent as Sodium hypochlorite and with relatively less toxicity. On that note, Silver nanoparticle solutions can be considered to be used as a inal root irrigant. A study by Samiei M et al. had tested the antibacterial activities of Sodium hypochlorite and Silver nanoparticle solutions against the Enterococcus faecalis bacterial species. The results show that there was no difference between 5.25% NaoCl and 0.005% AgNps (Samiei, 2013). Silver nanoparticle solution is more effective than NaoCl as it works at a relatively lower concentration. But a study by Rodrigues et al. contradicts the above statement reporting that Silver nanoparticle solution was not as effective as conventional root canal irrigants when it was tested against E. faecalis (Rodrigues et al., 2018). Another study results show that Gallic acid mediated synthesis of silver nanoparticles of 10 nm had presented a bactericidal activity against E. faecalis and this was same as that of sodium hypochlorite solution (González-Luna, 2016). It also states that silver nanoparticles have the capacity to remove smear layers (González-Luna, 2016).
Another advancement is the development of Silver nanoparticle incorporated Gutta perchas in obturating a root canal. Gutta Perchas is the most commonly used root canal obturating materials. AgNps incorporated Gutta perchas can aid in the prevention of accumulation of microbial colonies in the root canals. A study by Shantiaee et al. has compared the biocompatibility of the nanosilver incorporated Gutta perchas. The study had compared the nanosilver-coated gutta-perchas with the normal gutta-perchas on mouse ibroblasts in order to measure their cytotoxicity (Shantiaee, 2011). After 24 hrs, the cytotoxicity values were measured. It was found that the cytotoxicity values of both of them were similar. The cytotoxicity values of nanosilvercoated gutta-perchas reached the lowest after one week (Shantiaee, 2011). Though the signi icance is only quite higher than the conventional Gutta perchas, Nanosilver Gutta Perchas is still better than the former as they have better antimicrobial properties and relatively lesser cytotoxicity.

Silver Nanoparticles In Prosthodontics
Dental Porcelain ceramics are the most used ixed denture prosthesis. They are mostly used in anterior teeth replacements for their excellent Esthetics. However, they are brittle and tend to get fractured easily. A study shows that Vickers hardness and Fracture toughness had been increased by the incorporation Of Silver nanoparticles in the porcelain material (Uno, 2013). Another study shows that Silver Nanoparticles had the capability of enhancing the porcelain prosthesis mechanical properties (Fujieda, 2012). The study shows that AgNPs also increase Young's modulus of the prosthetic material (Fujieda, 2012). In this aspect, Silver nanoparticles are found to be more effective than the Platinum Nanoparticles.
Silicone arti icial substitutions are used in making Maxillofacial prosthesis (Meran, 2018). These prostheses are used in replacing the lost facial parts, also in restoring and maintaining the health of the tissues and in improving esthetics. The factors that affect their stability are infection and contamination. Nanosilver incorporated prosthesis has shown activity against the Candida albicans species without causing any cytotoxic effects on the ibroblast cells (Meran, 2018). The incorporation of AgNPs had no effects or least effects on the colour of the prosthesis (Han, 2010). Denture bases coated with Silver nanoparticles can prevent Stomatitis.

Silver Nanoparticles In Orthodontics
The worst problem in dental care is white spot lesion formation on enamel during the Orthodontic treatment (Akhavan, 2013). The lactic acid production by bacterial species such as Strepto- Figure 1: Silver nanoparticles in Dentistry coccus mutans and low oral pH attributes to the White spot lesion formation. On the other hand, removal of dental plaque mechanically is very dif icult with the obstructing Orthodontic brackets. Preventing Orthodontic adhesives for a longer period is important in preventing enamel demineralisation. The AgNp incorporated adhesive primer had inhibited the growth of Streptococcus mutans (Mohamed, 2014). It is found to enhance the dispersion and penetration of the antimicrobial agents onto the surface of the enamel than the other composites which attributes to its lower viscosity and wettability (Mohamed, 2014). The Silver nanoparticles had no effects on the primer's physical and chemical properties.

Silver Nanoparticles In Oral Cancer Therapy
Oral cancer is a more prevalent and fulminant cancer that invades tissues, undergoes metastasis and inally culminates in the death of the patient (Alkis et al., 2015). Oral cancer is often diagnosed at an untreatable condition where the cancerous cells are malignant and have developed immunity against the therapeutic drugs (El-Sayed et al., 2005). A study by Kah et al. has explained the mechanism by which the nanoparticles that are conjugated with nanoparticles can target and illuminate the tumour cells. It was done with the help of optical imaging technique (Kah, 2007). Silver Nanoparticles are extensively applied in drug delivery systems. Silver nanoparticles have caused better selective accumulation of cis Diamine dichloro platinum in the cancer cells while decreasing its ability to undergo metastasis (Ge and Kang, 2011). It makes the particles to low in the circulatory system for a long time so that it can facilitate their accumulation speci ically onto the tumour tissues.

CONCLUSIONS
The widespread use of the nanosilver particles in various aspects of Dentistry attributes for the excellent antimicrobial properties of the AgNPs. The review article had discussed the various uses of AgNPs in different ields of dentistry such as Implantology, Conservative Dentistry, Restorative Dentistry, Prosthodontics, Orthodontics and in Oral Cancer Therapy. Further investigations of Silver nanoparticles in vivo have to be carried out to enlighten and increase the clinical application of Silver Nanoparticles in every aspect of Dentistry.