Antimicrobial Activity of Topical Potassium Iodide and Silver Solutions

Objectives: Commercially available topical silver compound solutions such as Riva Star (SDF) and Riva Star Aqua (RSA) (both SDI, Australia) contain 3.16M silver diamine fluoride and 3.16M silver fluoride, respectively. These products are available as ‘two-step applications’ which involve the application of potassium iodide solution (provided by the manufacturer) after the silver compounds to minimise the black staining produced by silver. These topical silver compounds are used clinically for their bactericidal and cariostatic effects. The aim was to investigate the antimicrobial properties of SDF and RSA, with and without KI.
Methods: Minimum bactericidal concentrations (MBC) were determined for Streptococcus mutans for the following test solutions (at a concentration of 3.16M): Silver Diammine Fluoride (SDF – Step1), Silver Fluoride (RSA – Step 1), Silver Diammine Fluoride + Potassium Iodide (SDF – Step 1&2), Silver Fluoride+Potassium Iodide (RSA – Step 1&2, SDI). Control solutions at the same concentration were: potassium iodide (Step2, SDI), silver nitrate (Chem Cruz, California), potassium fluoride (Sigma-Aldrich, USA), silver nitrate + potassium fluoride (Sigma-Aldrich, Chem Cruz). MBC assays were carried out in a 96-well plate format with S.mutans bacterial suspensions at 0.1 OD₆₀₀ under aerobic conditions.
Results: Minimum bactericidal concentrations for the tested solutions are given in Table 1. KI very significantly reduces the bactericidal efficacy of both SDF and RSA, by (approximately 10⁶).
Conclusions: SDF and RSA have a strong antibacterial effect. The addition of KI to SDF and RSA reduces their antibacterial effect considerably. Although the two-step application of KI after SDF and RSA may reduce the black staining of the carious lesion, it significantly reduces the cariostatic bactericidal action.