Synthesis of silver core-shell nanoparticles and their influence on an experimental resin endodontic sealer: An in vitro analysis.

Abstract

To avoid root canal recontamination and endodontic treatment failure, endodontic sealers with antibacterial activity could be an alternative. Silver nanoparticles have antibacterial activity and this study aimed to synthesize Ag@SiO2 nanoparticles, incorporate them into an experimental endodontic resin sealer and evaluate their influence on physicochemical and biological properties. Ag@SiO2 nanoparticles were produced using the sol-gel process, based on the Stöber method. The particles were characterized in terms of their chemical structure by Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), UV-Vis spectral analysis, scanning electron microscopy, and transmission electron microscopy, where the particle morphology and diameter were analysed. A dual-cured experimental endodontic resin sealer was formulated using 70 wt% UDMA, 15 wt% GDMA, and 15 wt% BisEMA. The photoinitiators were added separately in two pastes. The Ag@SiO2 nanoparticles were incorporated into the endodontic sealer at the concentrations of 2.5wt%, 5wt%, and 10wt%, and a control group without nanoparticles was also formulated. The endodontic sealers were evaluated for their flow, film thickness, degree of conversion, softening in solvent, radiopacity, cytotoxicity and antibacterial activity immediately and after 9 months in water storage. Silver was detected in the chemical characterization of Ag@SiO2 that presented a spheric regular shape and average 683.51 nm ± 93.58 diameter. Sealers presented adequate flow and film thickness while radiopacity values were below the ones required by ISO 6876. All groups underwent softening after immersion in a solvent. The 10wt% groups showed a higher loss of subsurface hardness (∆KHN%). No reduction in cell viability was observed. Enterococcus faecalis viability in biofilm was reduced in 10wt% groups after 24 h and 9months. The addition of 10wt% Ag@SiO2 reduced E.faecalis viability at immediate and longitudinal analysis while maintaining the physicochemical properties of developed sealers.