Conventional methods used to control bacterial biofilm infection in root canals have poor efficacy, causing repeated and chronic infections, which pose a great challenge to clinical treatment. Microbubbles, due to their small size and ultrasound (US)-enhanced cavitation effects, have attracted considerable clinical attention. They possess the potential for therapeutic application in restricted spaces. We address the above problem with a strategy for the restricted space of root canals. Herein, phase-change nanodroplets (P-NDs) exposed to US are combined with common antibacterial drugs to disrupt a 7 day Enterococcus faecalis biofilm in an in vitro human tooth model. Specifically, the preparation of P-NDs is based on secondary cavitation. Their average particle size is ∼144 nm, and the stability is favorable. The clearance effect for the biofilm is notable (the disruption rate of P-NDs + US is 63.1%, P < 0.01), while the effect of an antibacterial in conjunction with 2% chlorhexidine (Chx) is significant (the antibiofilm rate of P-NDs@2% Chx + US is 96.2%, P < 0.001). Furthermore, biocompatibility testing on human periodontal ligament fibroblasts demonstrated that P-NDs are safe. In summary, the strategy that we have proposed is suitable for the removal of biofilms in root canals. Notably, it also has great potential for application in the treatment of bacterial infections in restricted spaces.
Keywords: biofilm; chlorhexidine; nanodroplet; root canal; ultrasound-activated.