Iranian Dental Association Journal of Iranian Dental Association 3060-8201 38 3-4 2026 09 28 Effect of Selenium Nanoparticles on Streptococcus Mutans Biofilm Gene Expression Using Real Time PCR 72 81 10.34172/jida.2303 EN Niyousha Noorullahi https://orcid.org/0000-0002-8469-0912 Farid Abbasi https://orcid.org/0000-0002-2584-757X Aliye Sehatpour https://orcid.org/0000-0003-1303-0244 Ronak Bakhtiari https://orcid.org/0000-0002-3778-5732 Journal Article 10.34172/jida.2303 2025 11 24 2026 02 15 Background: Streptococcus mutans is one of the main causes of dental caries. Although several nanoparticles have been investigated as antimicrobial agents, the antibiofilm potential and mechanistic action of biosynthesized selenium nanoparticles (SeNPs) remain insufficiently characterized. This study aimed to test the hypothesis that biosynthesized SeNPs inhibit S. mutans growth and biofilm formation through downregulation of the biofilm-associated gtfB gene. Methods: SeNPs were biosynthesized using Artemisia scoparia extract and characterized for nanoscale morphology. Their antibacterial activity against S. mutans was assessed using standard in vitro susceptibility assays, while antibiofilm effects were evaluated using biofilm detection methods. The impact of SeNPs exposure on gtfB gene expression was analyzed by RT-PCR and compared with untreated controls. Results: The biosynthesized SeNPs demonstrated significant antibacterial activity against S. mutans and induced a reduction in biofilm-associated phenotypic characteristics. Gene expression analysis revealed significant downregulation of gtfB expression in treated samples compared with untreated controls. Conclusion: Within the limitations of an in vitro model, biosynthesized SeNPs demonstrated antibacterial and antibiofilm activity against S. mutans, likely mediated through inhibition of gtfB expression. These findings suggest that SeNPs may serve as a promising adjunctive strategy for controlling cariogenic biofilms. However, further in vivo studies and comparative evaluations with existing antimicrobial agents are required to establish clinical relevance.