Silver Diamine Fluoride Applications in Dentistry: Review Article

The worth of using Silver Diamine Fluoride (SDF) during COVID-19 pandemic has highly increased due to its low invasiveness and non-aerosolizing technique. The blend of silver and fluoride in an alkaline solution has a great action in arresting active enamel and dentin carious lesions, also acting as a desensitizer to lessen dentine hypersensitivity in adults, this review article was conducted to highlight the SDF mechanism of action, clinical applications


Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus ,
and Veillonella parvula are well-known species that are connected directly to DC, when their prevalence increases they cause demineralization of enamel crystals owing to a high concentration of organic acids which drops the PH and causes a disproportion in the balance between the tooth mineral content and oral plaque (2) , with time persistent loss of tooth surface minerals leads to cavity formation in tooth enamel and dentin which if not treated will advance rapidly to pulpal tissues causing infection, pain, and ultimately tooth loss (3,4) .  (18,15) .

5-SDF should not be used in pregnant or
breastfeeding patients, especially when adding the potassium iodide (KI) following the use of SDF to prevent discoloration (during the first six months) due to concern of overloading the developing thyroid with iodide (19) . -

Mechanism of action of SDF
The exact mechanism for SDF action is still unknown however, there are three proposed theories suggesting that the ions of fluoride act mostly on the tooth structure for remineralization, while the antimicrobial action comes from the silver ions like other heavy metals (20) .
-The first proposed theory for the

SDF mechanism
Al-Rafidain Dental Journal, Vol. 22, Issue No.2, 2022 (363-375) 366 Is the obturation of dentinal tubules: The dentinal tubules are the chief penetration path of caries in dentin, Shimizu and Shah (1974), found that the dentinal area treated with SDF reduced in dye permeability and augmented in electrical resistance because they confirmed the existence of silver ions in the dentinal tubules (21) . These silver compounds in the dentinal tubules will obliterate them and inhibit the invasion and/or the growth of cariogenic microorganisms by the oligodynamic effect of silver (22) . When the dentinal tubules become obturated, the dentinal surface area will decrease and the silver particles will cover the peritubular zone which is the part of dentin that demineralized easily and ends the dentine collagen degradation, this mechanism was enhanced by Zhao et al. (23) . The topical application of SDF on exposed dentine leads to the creation of deposits that to some extent plug dentinal tubules, and this could be the reason for using SDF as a desensitizing agent for hypersensitive dentine (24) .
-The second proposed theory for the SDF mechanism is the cariostatic action that results from the reaction between tooth mineral component

and SDF products:
After SDF is applied to carious lesion in dentin, the free calcium ions in the hydroxyapatite interact with fluoride ions from SDF to form calcium fluoride and fluorapatite (Ca10(PO4)6OH2-xFx) at the same time, silver ions interact with the free phosphate to form a deposit of silver phosphate (Ag3PO4), these deposits have also been detected in deeper layers of the dentinal tubules (25) . The treated tooth surface that has been fluoridated is more acid-resistant than the normal tooth structure, thus the augmented hardness and mineral density will remarkably affect the lesion depth and lessen it (26) .
-The third proposed theory for the SDF mechanism is the ant-enzymatic actions resulting from the reaction between the organic component of the tooth and Ag(NH3)2F: The ionic silver can switch off almost all macromolecule within its atmosphere, the bactericidal effect of silver can inhibit the enzyme actions and dextran prompted clumping of cariogenic strains of Streptococcus mutans (27) .
In general, the anti-caries effect of SDF may be owing to its antimicrobial action plus its chemical interaction with the tooth surface, and this interaction is more important than the antimicrobial effect because SDF cannot decrease lactate production even though it had significantly decreased the cariogenic microorganism (28) .

-Clinical Applications of SDF -For High Caries Prevalence of Young Children
To treat DC in young patients, the conventional way involves removing the infected dentin either by rotary dental handpiece or sharp spoon excavator, the yielded pressure from using these instruments can trigger anxiety and fear for young patients, while when using SDF as a cariostatic agent, the dental caries progression is arrested or decelerated, and carious lesions removal will be postponed at another date as the child's capability to explain fear is increased with time (29) . In Japan, SDF has ∼80% efficacy in arresting carious lesions in enamel and dentin (30) .
The American Association of Pediatric Dentists and the American Dental Association have recommended the use of SDF for arresting cavitated carious lesions in primary teeth (31) .
Recently SDF has been used as Silver modified atraumatic restorative treatment (SMART), the technique treated carious lesions first with SDF and then restored with a glass ionomer, this method can efficiently arrest caries without further removal of tooth structure, which is a promising treatment approach in early childhood caries and root caries in elderly patients, SMART has a part to play in the secondary and tertiary prevention of caries and should be executed in community dentistry programs globally (1) .

-Arrest Dental Caries in Anterior
Deciduous Teeth of Children, Early

Childhood Caries (ECC)
In preschool kids have what is called ECC as numerous primary teeth are attacked by caries, ECC may be delineated as the incidence of one or more decayed, missing (due to caries), or filled tooth surfaces in the primary teeth of a child about 5-6 years of age or below (32) . fluoride is shown to be more effective on smooth tooth surfaces than that of the pit and fissure areas (35) . Sato et al. (29) and Nishino and Massler (36)

-Inhibit Secondary Caries
Secondary or recurrent caries usually occur at the margins of an existing restoration, it is one of the main causes for the restoration of teeth in the long term (37) . About 25% of  (40) .  (41) . An annual application of 5% sodium fluoride varnish or 38% SDF solution is capable to decrease the initiation of carious root lesions by 64% and 71% correspondingly (42) , Tan  in arresting dental caries on root surfaces (43,44) .

-Arrest Root Caries
A systematic review by Gao et al, revealed that 38% of SDF was able of arresting active DC by 81%, and similarly (30) , another systematic review by Hendre et al, found that the three years prevented a fraction of root caries with SDF was 71% greater than with the placebo (45) . Annual professional applications of 38% SDF for middle-aged and older adults were valuable in reducing carious lesions on roots in several clinical trials (46) .

-Desensitize Sensitive Teeth
Dentin hypersensitivity is categorized by varying grades of pain which is usually started with thermal, tactile, chemical, evaporative, or osmotic stimuli, and takes place on an exposed dentin surface (47) . SDF can be used to treat dentin hypersensitivity and the clinical process involves isolating the hypersensitive teeth with cotton rolls then gently drying out the area to be treated, with a disposable micro-brush SDF is applied, Knight and co-workers in their study suggested applying KI instantly after SDF application, their justification for this addition was that KI further reduces dentin permeability was when applied after SDF (48) .
Gottlieb found that there is a mutual factor concerning the mechanism of desensitizing hypersensitive dentin and arresting DC (49) , also it might possible to measure the SDF caries arresting action in relation to the desensitizing action since the SDF can occlude the dentinal tubules and gives promising results in treating patients with dentin hypersensitivity (12) .

-Treat Contaminated Root Canals
The eradication of microorganisms from the root canal spaces is a vital step for an effective endodontic therapy, Okamoto et al., can diminish microbial biofilms formed inside the dentinal tubules and the silver salts that are formed earlier in the dentinal tubules prevent the reinfection of these tubules because of their low solubility (51) . Mathew et al. (52) found that SDF can successfully eliminate the microorganisms that exist in the canal and circumpulpal dentin when using it as an endodontic irrigant. Recently a ten folds dilution of SDF solution with a concentration of 38% has been developed for intracanal irrigation and is being used with a remarkable clinical success rate (53) .

-Limitations of SDF
The use of SDF is still limited even with its high efficacy, for of its potential to black staining the carious tooth structure, owing to the formation of insoluble silver phosphate (Ag3PO4), which is brown in color, but quickly turns to black in the existence of reducing agents, or the sunlight exposure (54) .
Even though this black staining is a sign of the successful anti-caries effect of the SDF, it also presents an aesthetic worry for many parents of patients, particularly when used in anterior teeth (18) .  (57) . Recently, the incorporation of glutathione biomolecule (GSH) into SDF has shown favorable results in a reduction of SDF staining, GSH is an intracellular, non-protein thiol that performs as an antioxidant and is also a metal ion chelator (58) . Sayed et al, (57)