The synergistic antimicrobial effect by mechanical agitation and two chlorhexidine preparations on biofilm bacteria.

INTRODUCTION Irrigation of the root canal with antibacterial solutions is considered an essential part of root canal treatment in endodontics. The purpose of this study was to investigate whether mechanical agitation (ultrasonic or sonic) improves the effectiveness of chlorhexidine against biofilm bacteria in vitro. METHODS Collagen-coated hydroxyapatite (CHA) disks were exposed to dispersed subgingival plaque for 3 weeks at 37 degrees C. The multispecies biofilms established were subjected for 1 and 3 minutes to CHX-Plus (Vista Dental Products, Racine, WI) and 2% chlorhexidine (CHX), with or without mechanical agitation. After treatment, the amount of dead bacteria in biofilms was analyzed by viability staining and confocal laser scanning microscopy (CLSM). The morphology of biofilms, with or without mechanical agitation, was also examined by CLSM. RESULTS The structure of the biofilm did not show any obvious change when the solutions surrounding the biofilm were exposed to continuous ultrasonic or sonic agitation. The combined use of mechanical agitation and chlorhexidine had a more pronounced antimicrobial effect against the biofilms than either one alone. Sonic activation (EndoActivator; Advanced Endodontics, Santa Barbara, CA) showed the highest levels of bactericidal activity with CHX-Plus after both exposure times. The proportion of killed bacteria also depended on the type of irrigant (p < 0.001) and the time of exposure (p < 0.001). CONCLUSIONS The low-intensity ultrasonic or sonic agitation that does not disrupt biofilm or disperse the biofilm bacteria improves the action of disinfectants against biofilm bacteria.