Introduction: This study compared the ability of different approaches to supplement the antibacterial effects of chemomechanical preparation in ovalshaped root canals. Methods: Long oval canals from extracted teeth infected with Enterococcus faecalis (ATCC 29212) were chemomechanically prepared up to a 40/04 rotary BioRaCe instrument using 2.5% NaOCl irrigation and then subjected to two supplementary protocols. In the passive ultrasonic irrigation (PUI)/ chlorhexidine (CHX) group, canals were subjected to PUI for the activation of NaOCl followed by a final rinse with 0.2% CHX digluconate solution. In the Hedstr€om group, canals received additional Hedstr€om filing directed towards the buccal and lingual canal recesses. Bacteriological samples were taken before and after preparation, after PUI or Hedstr€om instrumentation, and after CHX final rinsing. Results: Chemomechanical preparation and the supplementary steps promoted a highly significant bacterial reduction (P < .001). Quantitative (reduction in levels) and qualitative (frequency of negative cultures) analyses showed that PUI alone or Hedstr€om filing did not significantly increase bacterial reduction (P > .05). Further rinsing with CHX also failed to significantly increase bacterial elimination when compared with post-PUI samples. However, the cumulative antibacterial effects of PUI and CHX final rinse were effective in significantly reducing bacterial counts to levels below those achieved after preparation (P = .03). This combined PUI/CHX approach also resulted in a significant increase in the incidence of negative cultures (P = .04). Conclusions: Findings suggest that there may be a benefit of using the PUI for the activation of NaOCl followed by a final rinse with CHX as supplementary steps in the treatment of infected oval-shaped root canals.