Are metal-based antibacterial gels a potential alternative for disinfection in contemporary endodontics?

This study aimed to assess the effectiveness of a novel antimicrobial gel, containing copper and silver nanoparticles, for use in root canal disinfection. Copper and silver-based gels were created in-house, using a support network of biocompatible polymers, including polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and polyethylene glycol (PEG). Six experimental groups were created, three containing silver ions and three copper ions, where the PVA, PVP and PEG ratios were also adjusted in each group to test the gel’s physical state. One control contained no metal nanoparticles. The gels surface characteristics, roughness, mechanical properties, and flowability, were characterised using a combination of atomic force microscopy, scanning electron microscopy, transmission electron microscopy and Rheometery. Further biological testing measured the gels cytotoxicity levels, using human periodontal ligament cells, and the anti-microbial effects against E. Faecalis and a multi-species bacteria biofilm. Each gel demonstrated high levels of viscosity, which was lowered in gels containing a reduced PVA concentration. The overall antimicrobial properties of the gels increased in those with a higher dissolution, lower porosity, and reduced surface roughness. Copper nanoparticles were shown to be significantly more effective against E. Faecalis, compared with silver. Gels containing higher PVA levels, and silver nanoparticles, had greater toxicity levels against human cells, however, testing was not possible for most experimental groups as the gels dissolved before measurements took place. The antimicrobial properties of all gel formulations were significantly less effective than sodium hypochlorite (after 1 h), but a similar outcome was detected in comparison with calcium hydroxide (after 7 days). Developing an antimicrobial gel is highly dependent upon numerous compositional factors, where development is still at the early stages. The use of copper nanoparticles appeared to be more appropriate for use in canal disinfection, compared with silver that also had higher levels of human cell toxicity. The ratios selected for the biocompatible polymers had a critical impact on the physical state, antimicrobial, and toxicity levels. At present, antimicrobial gels are not as effective as sodium hypochlorite.