Addition of Antimicrobial Agent Increased Antibacterial Activity of Ammonium Hexafluorosilicate

Objectives: Ammonium hexafluorosilicate [SiF: (NH₄)₂SiF₆] was prepared in order to overcome the tooth discoloration caused by diamine silver fluoride [AgF: (NH₃)₂AgF] application. However, the antibacterial activity of SiF seems to be less than AgF. To increase the antibacterial activity, various antibacterial agents were added to SiF solution for the prevention of dental caries. The aim of this study was to evaluate the antibacterial activity of SiF with the addition of antibacterial agents on Streptococcus mutans biofilm. Methods: Various antibacterial SiF solutions were prepared with the addition to chlorhexidine (CHX), cetylpyridinium chloride (CPC), isopropyl methylphenol (IPMP), or epigallocatechin gallate (EGCG), respectively. Hydroxyapatite (HAP) pellets were treated with SiF solution with or without antibacterial agents for 3 min. Also, AgF was used as positive control. Then the HAP pellets were immersed in BHI inoculated with S. mutans standardized suspension (10⁵ cells/ml) for 12 h at 37 ◦C. The number of S. mutans cells adhered to each HAP pellet was evaluated by SEM observation and calculating colony forming unit (CFU). Results: SEM observation demonstrated that growth of S. mutans on the HAP was significantly inhibited treated by SiF with the addition of antibacterial agents. In quantitative analysis, non-treated sample have shown 1890.7x10⁴ CFU/mL. AgF and SiF treated samples have shown 2.0x10⁴ CFU/mL and 122.7x10⁴ CFU/mL, respectively. Also, CFU of SiF with antibacterial agent treated samples have shown 790.8x10⁴ CFU/mL (CHX), 2.0x10⁴ CFU/mL (CPC), 670.7x10⁴ CFU/mL (IPMP), and 857.5x10⁴ CFU/mL (EGCG), respectively. Addition of CPC to SiF is effective in inhibiting bacterial growth, although, antibacterial activity of SiF was reduced by the addition of other antibacterial agents. Conclusion: The addition of CPC to SiF solution reduced the number of adhering S. mutans as the same level of that of AgF, therefore, it may have a potential for the prevention of dental caries.