INTRODUCTION: It was the goal of this study to compare different NaOCl activation schemes regarding a desired and an untoward outcome. Ultrasonic tips and a currently marketed sonic system were used in conjunction with a 2.5% sodium hypochlorite solution. Necrotic pulp tissue dissolution in simulated accessory canals and transportation of the main canal were assessed. METHODS: Epoxy resin models (10 per group) with a curved simulated main root canal and two simulated accessory canals filled with necrotic bovine pulp tissue were irrigated passively with one of three ultrasonic setups (straight stainless steel files, prebent stainless steel files, or nickel-titanium tips) or a sonic device in conjunction with a plastic tip. Activation was performed four times for 30 seconds with replenishment of the NaOCl solution in between. All the files/tips had a 2% taper and a 0.15-mm tip diameter according to the manufacturer. Data from superimposing and analyzing digital photos before and after treatment were statistically analyzed using one-way analysis of variance followed by Bonferroni's correction for multiple comparisons (alpha < 0.05). RESULTS: Passive ultrasonic irrigation (PUI) in all the groups dissolved significantly more tissue than sonic activation (p < 0.05). No detectable canal transportation with sonic activation was observed. The difference in this outcome was not significant compared with ultrasonically activated nickel-titanium tips, whereas the straight stainless steel files caused significantly more ledging compared with these setups (p < 0.05). CONCLUSION: Under the current conditions, PUI with a nickel-titanium tip promoted superior tissue-dissolving effects over sonic irrigant activation while maintaining simulated canal anatomy.