Core–Shell Silver Nanoparticles in Endodontic Disinfection Solutions Enable Long-Term Antimicrobial Effect on Oral Biofilms

To achieve effective long-term disinfection of the root canals, we synthesized core–shell silver nanoparticles (AgNPs@SiO₂) and used them to develop two irrigation solutions containing sodium phytate (SP) and ethylene glycol-bis­(β-aminoethyl ether)N,N,N′,N′-tetraacetic acid (EGTA), respectively. Ex vivo studies with instrumented root canals revealed that the developed irrigation solutions can effectively remove the smear layer from the dentinal surfaces. Further in vitro experiments with single- and multispecies biofilms demonstrated for the first time that AgNPs@SiO₂-based irrigation solutions possess excellent antimicrobial activities for at least 7 days, whereas the bare AgNPs lose the activity almost immediately and do not show any antibacterial activity after 2 days. The long-term antimicrobial activity exhibited by AgNPs@SiO₂ solutions can be attributed to the sustainable availability of soluble silver, even after 7 days. Both solutions showed lower cytotoxicity toward human gingival fibroblasts compared to the conventionally used solution (3% NaOCl and 17% EDTA). Irrigation solutions containing AgNP@SiO₂ may therefore be highly promising for applications needing a long-term antimicrobial effect.