Arresting Dentine Caries with Silver Diamine Fluoride: What's Behind It?

Unlike other fluoride-based caries preventive agents, silver diamine fluoride (SDF) can simultaneously prevent and arrest coronal and root dentine caries. The profound clinical success of SDF has drawn many clinicians and researchers to study the mechanism of SDF in arresting dentine caries. This critical review discusses how silver and fluoride contribute to caries arrest, in terms of their effects on bacteria as well as on the mineral and organic content of dentine. Silver interacts with bacterial cell membrane and bacterial enzymes, which can inhibit bacterial growth. Silver can also dope into hydroxyapatite and have an antibacterial effect on silver-doped hydroxyapatite. Furthermore, silver is also a strong inhibitor of cathepsins and inhibits dentine collagen degradation. Early studies proposed that silver hardened caries lesions by forming silver phosphate. However, recent studies found that little silver phosphate remained on the arrested dentine lesion. The principal silver precipitate was silver chloride, which could not contribute to the significant hardening of the arrested lesions. On the other hand, fluoride enhances mineral formation by forming fluorohydroxyapatite with reduced solubility. A significant increase in microhardness occurs with an elevated level of calcium and phosphorus but not silver on the surface layer of the arrested dentine caries lesion following SDF treatment. Fluoride also inhibits matrix metalloproteinases activities and therefore inhibits dentine collagen degradation. The combination of silver and fluoride in an alkaline solution has a synergistic effect in arresting dentine caries. The alkaline property of SDF provides an unfavorable environment for collagen enzyme activation. Understanding the mechanisms of SDF in arresting dentine caries helps clinicians to develop appropriate protocols for the use of SDF in clinical care.