Silver

The majority of released silver ions precipitate with chloride or phosphate anions or bind to albumins, macroglobulins, or tissue debris. While bound silver ions do not exert antibacterial actions, they may potentially play a role in silver toxicity in case of chronic exposure. Silver ions mediate antibacterial effects via disrupting the bacterial, fungal, and protozoal cell membranes; they bind to disulphide in membrane proteins, readily allowing penetration through the membranes and intracellular absorption via pinocytosis. They may also bind to negatively-charged peptidoglycans in the cell wall via electrostatic interactions, leading to disruption of membrane transport function and loss of structural integrity. Silver ions also bind to and oxidize sulphydryl groups (SH) in bacterial cytoplasmic enzymes to aberrate their function in metabolic processes. Silver nanoparticles may cause an increase in reactive oxygen species (ROS) inside the microbial cells leading to metal-induced oxidative stress and cell damage. They also modulate cellular signal system via inhibition of phosphorylation of essential bacterial proteins to eventually cause cell death. It is also reported that silver ions also attach to guanine in bacterial DNA, which inhibits DNA replication. While it is not fully understood, the mode of action of silver compounds in preventing and arresting dental caries is thought to involve inhibition of the demineralization process in addition to cytoplasmic and membrane function perturbation mentioned above. Silver compounds may directly interact with hydroxyapatite, a major tooth component.