Selenium nanoparticles as a biological safe endodontic irrigant improving root canal sealing

Elimination of Enterococcus faecalis (E. faecalis) biofilms from root canals remains a critical challenge in root canal treatment. Sodium hypochlorite (NaOCl) is the gold standard due to its potent antimicrobial and tissue-dissolving properties. However, its cytotoxic effects and risk of dentinal erosion necessitate the development of safer alternatives. This study evaluates the antibacterial efficacy, cytocompatibility, and dentinal interactions of selenium nanoparticles (SeNPs) as a potential endodontic irrigant. SeNPs were synthesized using an ascorbic acid-mediated approach and characterized for physicochemical properties. Antibacterial activity was assessed against E. faecalis (ATCC 47077) using the minimum inhibitory concentration (MIC) method. Cytotoxicity was evaluated on oral epithelial cells (OECs) and human gingival fibroblasts (HGFs) using an MTT assay. Extracted single-rooted teeth were inoculated with E. faecalis biofilms for 21 days and divided into NaOCl and SeNPs groups. After irrigation, dentinal surfaces were examined using scanning electron microscopy (SEM). Bacterial scores were analyzed using Kruskal-Wallis test, followed by Dunn–Bonferroni post hoc analysis, setting p < 0.05 to be significant. SeNPs exhibited spherical morphology with an average size of 93.15 nm and good colloidal stability. MIC determination revealed effective antibacterial activity at ~ 128 µg/mL. SeNPs demonstrated an acceptable safety margin relative to the antibacterial concentration with an IC50 of 626 µg/mL on OECs and 809 µg/mL on HGFs, supporting their potential for clinical use. SEM revealed a relative bacterial reduction between irrigants, NaOCl (2.5%) and SeNP (128 µg/mL), where NaOCl-treated dentin disclosed complete removal of the smear layer with open tubules. Meanwhile, SeNP-treated dentin exhibited partial tubule occlusion and scattered nanoparticle deposits. SeNPs demonstrate promising antimicrobial efficacy, biocompatibility, and favorable dentinal interactions. Their ability to reduce bacterial load while potentially sealing dentinal tubules highlights their suitability as a safer, multifunctional alternative to conventional irrigants for root canal disinfection.