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Objectives:This study was designed to evaluate the fracture resistance of retreated roots using different rotary retreatment systems.Methods:Forty eight freshly extracted human canine teeth with single straight root canals were instrumented sequentially increasing from size 30 to a size 55 using K-files whit a stepback technique. The teeth were randomly divided into three experimental and one control groups of 12 specimens each. The root canals were filled using cold lateral compaction of gutta-percha and AH Plus (Dentsply Detrey, Konstanz, Germany) sealer in experimental groups. Removal of gutta-percha was performed with the following devices and techniques: ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland), R-Endo (Micro-Mega, Besançon, France), and Mtwo (Sweden & Martina, Padova, Italy) rotary retreatment systems. Control group specimens were only instrumented, not filled or retreated. The specimens were then mounted in copper rings, were filled with a self-curing polymethylmethacrylate resin, and the force required to cause vertical root fracture was measured using a universal testing device. The force of fracture of the roots was recorded and the results in the various groups were compared. Statistical analysis was accomplished by one-way ANOVA and a post hoc Tukey tests.Results:There were statistically significant differences between the control and experimental groups (P<.05). However, there were no significant differences among the experimental groups.Conclusions:Based on the results, all rotary retreatment techniques used in this in vitro study produced similar root weakness.

The aim of this study was to evaluate conventional syringe irrigation and three different irrigant activation techniques' effectiveness for smear layer removal in the absence and presence of intracanal‐separated file (SF) fragment. Mandibular anterior teeth (160 total) with single canal were used and each root canal preparation was finished with the ProTaper Universal F1. The samples were randomly divided into eight equal groups with n = 20 in each group. The Protaper Universal F3 file was used to simulate intracanal file separation in four groups. To remove the smear layer, final irrigation for each group was performed with conventional syringe irrigation (CSI), EndoActivator, Vibringe, and passive ultrasonic irrigation (PUI). The roots were divided into two longitudinal parts and evaluated with scanning electron microscopy, and two observers scored smear layers at 1, 2, and 3 mm away from the minor foramen. The data were analyzed using the Kruskal–Wallis and Mann–Whitney U tests (p < .05). PUI significantly removed the smear layer better at all levels than other nonseparated file groups (p < .05). In the presence of intracanal SF, PUI had the most efficiency loss. Sonic techniques and CSI revealed statistically better smear layer removal efficiency than PUI at 3 mm level in the presence of SF (p < .05). The intragroup score analysis at all levels revealed that there were less smear layers at 3 mm than at 1 mm in all SF groups (p < .001). As a conclusion, sonic/ultrasonic methods did not yield better irrigant by‐passing than CSI in the presence of intracanal SF.

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