S. mutans Antisense vicK RNA Over-Expression Plus Antibacterial Dimethylaminohexadecyl Methacrylate Suppresses Oral Biofilms and Protects Enamel Hardness in Extracted Human Teeth

<i>Streptococcus mutans</i> (<i>S. mutans</i>) antisense <i>vicK</i> RNA (AS<i>vicK</i>) is a non-coding RNA that regulates cariogenic virulence and metabolic activity. Dimethylaminohexadecyl methacrylate (DMAHDM), a quaternary ammonium methacrylate used in dental materials, has strong antibacterial activity. This study examined the effects of <i>S. mutans</i> AS<i>vicK</i> on DMAHDM susceptibility and their combined impact on inhibiting <i>S. mutans</i> biofilm formation and protecting enamel hardness. The parent <i>S. mutans</i> UA159 and AS<i>vicK</i> overexpressing <i>S. mutans</i> (AS<i>vicK</i>) were tested. The minimum inhibitory concentration (MIC) and minimum bactericidal concentrations for planktonic bacteria (MBC-P) and biofilms (MBC-B) were measured. As the AS<i>vicK</i> MBC-B was 175 μg/mL, live/dead staining, metabolic activity (MTT), colony-forming units (CFUs), biofilm biomass, polysaccharide, and lactic acid production were investigated at 175 μg/mL and 87.5 μg/mL. The MIC, MBC-P, and MBC-B values for DMAHDM for the AS<i>vicK</i> strain were half those of the UA159 strain. In addition, combining <i>S. mutans</i> AS<i>vicK</i> with DMAHDM resulted in a significant 4-log CFU reduction (<i>p</i> < 0.05), with notable decreases in polysaccharide levels and lactic acid production. In the in vitro cariogenic model, the combination achieved the highest enamel hardness at 67.1% of sound enamel, while UA159 without DMAHDM had the lowest at 16.4% (<i>p</i> < 0.05). Thus, <i>S. mutans</i> AS<i>vicK</i> enhanced DMAHDM susceptibility, and their combination effectively inhibited biofilm formation and minimized enamel demineralization. The <i>S. mutans</i> AS<i>vicK</i> + DMAHDM combination shows great potential for anti-caries dental applications.