Effectiveness of Different Disinfection Protocols on the Reduction of Bacteria in Enterococcus faecalis Biofilm in Teeth with Large Root Canals

Introduction: This study compared the effectiveness of different disinfection protocols in reducing bacteria in an Enterococcus faecalis biofilm in teeth with large root canals. Methods: Fifty-five roots were prepared from human mandibular premolars with large single root canals, and 50 roots were infected with E. faecalis for 21 days. Four roots were observed using scanning electron microscopy to verify biofilm formation. The remaining specimens were assigned into 5 experimental groups and a sterile control group: mechanical instrumentation using files size 6090 and 2.5% sodium hypochlorite (NaOCI) (MI-N), irrigation with 2.5% NaOCI (IR-N), irrigation with 2.5% NaOCI using intermittent passive ultrasonic irrigation (PUI-N), irrigation with normal saline, and no intervention (initial). After root canal disinfection, dentin specimens were collected for microbial analysis. Mean colony forming units were determined and compared between groups using 1-way analysis of variance. Results: The lowest number of intracanal bacteria (24.5 colony-forming units/mL) was recovered from the MI-N group followed by the PUI-N and IR-N groups. The irrigation with normal saline group did not show a significant reduction compared with the initial group. However, there were significant differences between groups (P < .01). The remaining bacteria in the PUI-N group was 4.5-fold lower compared with the IR-N group; however, it was 1862-fold higher compared with the MI-N group. Conclusions: MI-N was the most effective method to disinfect large root canals. Although ultrasonic activation enhanced the efficacy of root canal irrigation, it could not substitute for mechanical instrumentation even in large root canals with unlimited irrigant access to the apical portion.