Antimicrobial silver seems to have returned to dentistry, causing a paradigm shift in the management of caries lesions in children, and surpassing invasive dentistry and costly surgeries, in which a relapse is not uncommon.

Historical background

The historical use of silver in medicine can be seen as early as the 1800s, when the antimicrobial effect of silver was established in previous Mediterranean and Asian civilizations’ use of silver foil to disinfect wounds. It was also exhibited in the act of dropping silver coins in water containers of American travelers in the 1880s in order to set back the growth of bacteria and algae.¹ Following successful practices in medicine, the dawn of silver in dentistry arose in 1891 when Stebbins declared the arrest of caries lesions by applying silver nitrates.² On the scent of these findings, the combination was further developed by Howe, who enhanced and stabilized the antimicrobial effect by adding ammonia to the silver nitrate, making it more applicable to early cavitated lesions and even to infected root canals;³ the solution came to be known as “Howe’s solution.”

Silver diammine fluoride (SDF) was originally hypothesized in Japan in 1969 as a PhD thesis.⁴ The powerful combination of silver antimicrobial properties with high fluoride doses produced a precipitate that plugs the dentinal terminals and, furthermore, diminished hypersensitivity.⁵

Composition

The combination of silver and fluoride is present in various formulas and concentrations. Silver fluoride and SDF are similar in their silver and fluoride contents, but differ as the latter contains ammonia, which plays an important role in keeping the concentration steady.⁶ SDF is available at various concentrations (Table 12-1). However, results of a randomized clinical trial in 2018 showed that SDF potency to arrest caries lesions at 38% concentration is superior to lower concentrations,⁷ but that an increase in staining was positively associated with higher concentrations and frequent applications (Fig 12-1).⁸ In order to counter the staining effect of SDF, a few studies have reported promising results by applying a saturated solution of potassium iodide immediately after SDF application. Potassium iodide is believed to minimize staining of dentin caries while the caries-arresting effect of SDF remains unaffected.^9,10

Table 12-1 Various SDF products, manufacturers, SDF concentrations, and main ingredients

Mechanism of action

The mechanism of action of SDF has long been a topic of debate. In 1972, it was suggested that SDF’s potency against caries lesions stems from the silver antibacterial traits embedded in the end product of the SDF reaction at the tooth level. The reaction precipitates silver phosphate (Ag₃PO₄) and calcium fluoride (CaF₂), with the latter being responsible for the delivery of high doses of fluoride, enhancing the chances of successful caries arrest.⁵ A recent review proposed three modes of actions of SDF in favor of caries arrest and prevention (Fig 12-2).¹¹ The first action was backed by a few studies where a lower number and suppression of growth of bacterial colonies were reported after SDF application,^12,13 thus supporting the hypothesized bactericidal effect of silver ions on cariogenic bacteria. More broadly, the second and third actions of SDF were evidenced with studies denoting its contribution to remineralization and inhibition of demineralization in enamel and dentin surfaces,^14,15 and its aid in preventing dentin collagen matrix collapse.^16,17

Indications

In 2014, SDF was cleared by the US Food and Drug Administration primarily as a treatment for dentinal sensitivity,¹⁸ which is also the primary indication of the only SDF product available in Europe. Its efficiency in reducing dentin hypersensitivity is also helpful in pediatric dentistry for management of hypersensitivity in teeth diagnosed with molar incisor hypomineralization (MIH), through sole application or in combination with high-viscosity glass-ionomer cement, an approach known as the silver modified atraumatic restorative technique (SMART).¹⁹ However, further research on its effectiveness for treatment of MIH is still needed.

Table 12-2 Recommendations for case selection according to the American Academy of Pediatric Dentistry (AAPD) guidance²⁵

Contraindications and side effects

Despite the scarce data on the prevalence of allergy to silver,²⁶ children with a known chemical allergy to silver should not be treated with SDF. Additionally, the requirement for pulpal treatment of teeth undergoing irreversible pulpitis or necrosis contraindicates the therapeutic use of SDF in the line of treatment.²⁵ It is also preferable to avoid SDF contact with sensitive open mouth sores (eg, herpetic gingivostomatitis, ulcerative gingivitis) until symptoms diminish.

The high fluoride concentration (44,800 ppm) of SDF at 38% may raise a concern regarding safety, as well as the risk of inducing dental fluorosis. Contrarily, a randomized clinical trial conducted in 2017 reached a safe verdict on treatment with SDF at different concentrations for preschool children as it did not result in any serious hazards or systemic illness.⁸ Reports of gingival swelling and pain were rare, and all bleached gingivae after SDF contact resolved without interference within 2 days.⁸ In favor of minimizing such events, it is reasonable to recommend proper isolation of the treatment area and avoidance of oversaturation of the microbrush with SDF solution in order to minimize gingival contact during application.

On the other hand, researchers identified the main flaw of treatment with SDF: permanent black staining of the caries lesions.^8,21,27 Many efforts have been made to reduce this nonesthetic drawback of SDF. Alongside the previously mentioned positive reports of minimizing discoloration by the additional use of potassium iodide following SDF application,^10,28 an innovative form of silver fluoride called nano silver fluoride (NSF) is believed to be an effective anti-caries agent without the staining consequences.²⁹

Under the scope of parental acceptability and satisfaction, opinions of parents can be controversial following treatment of their children with SDF due to different cultures and esthetic priorities. However, a recent survey among a diverse group of parents recorded high rates of parents who prefer dental health to dental esthetics in their children, while those who perceived the staining effect of SDF as unacceptable still agreed to the esthetic compromise in favor of avoiding the hazards of treatment under general anesthesia.³⁰ Informed consent, detailing the predicted staining of treated lesions, is recommended.²⁵

Clinical application

The application of SDF is technically a simple procedure to perform in terms of clinical dexterity. Nevertheless, the suitability of this treatment modality for the specific patient/caregiver and tooth should be carefully considered, taking into account the indications previously mentioned.

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