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Among the different types of nanomaterials, metallic nanomaterials – especially silver nanomaterials – have shown great promise for biomedical applications. Silver nanomaterials in medicine enable researchers and clinicians to enhance medical imaging by providing more detailed images of cellular processes. They support medical diagnosis with molecular contrast agents and materials to enable earlier and more accurate initial diagnosis. Silver nanomaterials also improve drug delivery by increasing solubility and thus enhancing bioavailability. They are also used in cancer therapy to kill drug-resistant tumor cells and improve treatment efficacy by low-targeting and delivery of these anti-cancer drugs to tumor tissues..số 8
SNPs materials also attract public attention because of their exceptional antibacterial activity with low toxicity and low cost. They are used in low concentrations and do not induce bacterial resistance. Different antibacterial activities of silver nanomaterials have been proposed although the exact mechanism of the antibacterial effect of silver nanomaterials has not been fully elucidated. SNPs release silver ions that penetrate the microbial membrane and disrupt deoxyribonucleic acid transcription and protein synthesis. In addition, silver ions can inactivate respiratory enzymes and eventually cause cell lysis. Silver nanoparticles from nanomaterials can accumulate in the pores of the cell wall and cause membrane denaturation. They are also capable of penetrating bacterial cell walls and cytoplasmic membranes, causing denaturation of cell walls and cytoplasmic membranes. 11
Researchers investigated the use of silver nanomaterials in dental materials as an antimicrobial agent for clinical care. For example, silver nanoparticle modified implants have been developed to prevent infection around the implant. Many studies have investigated SNPs material for the prevention of dental caries. Silver nanoparticles are incorporated into orthodontic adhesives and brackets to prevent tooth decay, which is a common complication of orthodontic treatment. Silver nanoparticles can also be added to restorative materials to prevent secondary caries, which is a common cause of unsuccessful restorations.. 14 The application of silver nanomaterials to combat tooth decay, including inhibiting biofilm formation and correcting the balance of demineralization and remineralization, is a promising avenue for prevention and treatment. Caries. However, a search found rare reviews of silver nanomaterials for preventing tooth decay. Therefore, the aim of this study was to perform a systematic review of the use of silver nanomaterials for the prevention of dental caries.
Materials and methods for finding information about nano silver
Two independent investigators (Yin and Zhao) performed literature searches to identify publications using four commonly used databases: Embase, Medline, PubMed, and Scopus. The search is limited to publications in English. They searched the publications using the keywords ((silver nanoparticles) OR (AgNPs) OR (silver nanoparticle) OR (silver nanoparticle)) AND ((cavities) OR (cavities)). No publication year limit has been set and the last search was made on February 29, 2020 ( Image 1 ).
Research selection and data extraction
An initial literature search found 376 potentially eligible publications (95 articles in PubMed, 67 articles in Embase, 132 articles in Scopus, 82 articles in Medline). A total of 132 duplicate records of publications were removed ( Image 1). Another 164 publications were removed after screening titles and abstracts because these 164 were literature reviews, studies on other silver compounds, non-cavity related studies, and other studies. Other unrelated rescues. Full text was collected for the remaining 80 publications. A manual search of the references of these 80 selected publications did not identify any additional publications that met the inclusion criteria. Fourteen publications were excluded because they did not study the effects of silver nanomaterials on pathogenic bacteria or dental hard tissues. The remaining 66 publications that met the eligibility criteria were included in this review. The studied silver nanomaterials are classified as silver nanoparticles (n=21), silver fluoride nanoparticles (n=7), silver nanoparticle resins (n=31).,
Application of silver nanomaterials in tooth decay prevention
21 publications have studied the use of silver nanoparticles to prevent tooth decay. Eighteen of them reported the synthesis of silver nanoparticles and silver nanomaterials, which have the potential to manage caries. One study used silver nanoparticles in dentifrice. 15 One study reported that coating silver nanoparticles on orthodontic brackets to prevent tooth decay. Seven studies have reported the use of fluoride SNPs for early enamel remineralization and prevention of dentin caries.. 16 – 22 31 studies used silver nanoparticles to prevent tooth decay. Silver nanoparticles have been added to restorative materials, such as resins and adhesives, to prevent secondary decay.. 23 ,24 Các Silver nanoparticles are also incorporated into the resin of orthodontic materials, such as adhesives, elastomers and removable spacers, to prevent tooth decay. A clinical trial reported that dental fillings with SNPs were superior to traditional fillings in preventing caries in first permanent molars. 26 Seven studies examined glass ionomer cements with SNPs for the prevention of tooth decay. Six of them used ionomer glasses with silver nanoparticles as orthodontic cements to prevent tooth decay. The remaining research applies it as a restorative material to prevent secondary caries. 27
Effect of silver nanomaterials on Cariogenic bacteria
Most of the publications (59/67) showed that silver nanomaterials have antibacterial effects mainly against Streptococcus mutans. Table 1 Summary 59 published research on antibacterial effects of silver nanomaterials against pathogenic bacteria. Among them, studies measured antibacterial properties using monotypic bacteria, such as Streptococcus, Lactobacillus, Enterococcus and Pseudomonas , and studies used oral microcosm. Most studies measured bactericidal properties in vitro, while only four were performed in vivo, including two animal studies and two clinical trials.. 13 , 28 – 30 The results of the minimum inhibitory concentration and the minimum bactericidal concentration of silver nanomaterials against pathogenic bacteria have been highly variable in different studies. 31 – 33 The agar diffusion test demonstrated that the disc treated with SNPs material had a larger zone of inhibition than that treated with water. 34 In addition, the number of colony forming units demonstrates that silver nanomaterials have the ability to inhibit bacterial growth. 29 They also revealed that biofilms treated with silver nanomaterials had fewer bacteria than membranes treated with water. 35 The survival rate of bacteria in the biofilm was significantly lower after the application of silver nanomaterials than after the application of water. 36 Furthermore, biofilms treated with SNPs reduced metabolic activity, lactic acid production and glucosyltransferase gene expression.. 37 It has been shown that silver nanoparticles with smaller sizes have stronger antibacterial effects. 38 Meanwhile, the antibacterial properties improved with increasing concentration of silver nanoparticles in the material. 39 Capping agents can also affect the bacteriostatic action of silver nanoparticles. 40
Effect of silver nanomaterials on enamel and dentures
Several (11/67) studies reported inhibition of enamel and dentin demineralization under acid or cariogenic effects. Table 2 summarizes published studies on the influence of silver nanomaterials on the mineral content of enamel and dentin. Acoustic glazes treated with silver nanomaterials had a shallower depth of injury than glazes treated with water after biofilm challenge. 23 Also, artificially decayed enamel can be treated with silver nanoparticles to increase micro-hardness. 41 An orthodontic frame coated with silver nanoparticles reduces the incidence of caries on the incisor surface in the rat mouth. In addition, resins with silver nanoparticles can increase the microscopic hardness of caries after acid challenge (pH cycle). A dental filling with silver nanoparticles reduced mineral loss of children’s first molars in a clinical trial. 26 Six studies investigated the remineralization effect of fluoride SNPs. Acoustic glaze treated with nanosilver fluoride has similar value in micro-hardness to glaze treated with sodium fluoride. 18 , 19 The micro-hardness value of enamel caries treated with nano silver fluoride was higher than that of caries treated with sodium fluoride. 20However, no difference in mineral content could be detected between decayed enamel treated with nano silver fluoride and sodium fluoride by optical coherence tomography. 16 Nano silver fluoride prevented tooth decay in children in two clinical trials. 17 , 21
Silver nanoparticles give antibacterial effect to silver nanomaterials. Although the exact mechanism of the antibacterial effect of silver nanoparticles has not been fully elucidated, different antibacterial activities have been proposed. Silver nanoparticles can release silver ions. The released silver ions can enhance the permeability of the cytoplasmic membrane and lead to the disruption of the bacterial envelope. After penetrating the cell membrane, silver ions can inactivate respiratory enzymes and disrupt the production of adenosine triphosphate. Silver ions can also inhibit deoxyribonucleic acid replication and protein synthesis. 45
In addition to releasing silver ions, SNPs can kill bacteria on their own. SNPs can accumulate in pits that form on the cell wall after they attach to the cell surface. In addition, the accumulated silver nanoparticles can cause denaturation of cell membranes. Silver nanoparticles are also capable of penetrating bacterial cell walls and subsequently altering the structure of cell membranes due to their nanoscale size. 46
The antibacterial effect of SNPs against pathogenic bacteria is related to the properties of silver nanoparticles in nanomaterials. The literature reviews concluded that the smaller silver nanoparticles exhibited stronger antibacterial activity against planktonic Streptococcus mutans. . 31 , 38 , 47 – 49
In addition, capping agents affect the ability of silver nanoparticles to inhibit pathogenic bacteria . 40
Silver nanomaterials reduce lactic acid production in biofilms. It is incidental evidence that silver nanomaterials have the ability to reduce tooth demineralization. The assessment of mineral content is essential to demonstrate that silver nanomaterials can inhibit tooth demineralization. Soundproof enamel treated with SNPs reduces mineral loss after biofilm challenge. This demonstrated that SNPs could prevent tooth decay by reducing the demineralization effect through reducing the acid produced by the biofilm. A study using chemical modeling (i.e., no bacteria) showed that silver nanoparticles increased the microscopic hardness of enamel caries. SNPs can penetrate severe lesions and attach to hydroxyapatite crystals.20
Although silver nanomaterials have antibacterial and remineralizing properties, they are very susceptible to oxidation and agglomeration. The stability of silver nanomaterials is an important factor affecting the antibacterial effect of silver nanomaterials. However, no publications have reported their long-term stability, and very few studies have investigated the long-term antibacterial effects of SNPs..