Smear Layer Removal Using Passive Ultrasonic Irrigation and Different Concentrations of Sodium Hypochlorite

Introduction: The present study evaluated the effect of passive ultrasonic activation (PUI) of EDTA solution followed by conventional irrigation with 2 concentrations of sodium hypochlorite (NaOCI) on smear layer removal. Methods: Fifty single-root mandibular premolars were chemomechanically prepared with ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) nickel-titanium rotary instruments and 1% NaOCI. The roots were cleaved, and the dentin surfaces were analyzed with scanning electron microscopy operated at a low vacuum. Images were obtained from previously demarcated areas in each root canal third. The teeth were reassembled and distributed into 5 groups according to the final irrigation protocols (n = 10): group 1, EDTA/PUI + 1% NaOCI; group 2, EDTA/PUI + 5% NaOCI; group 3, EDTA/CI + 1% NaOCI; group 4, EDTA/CI + 5% NaOCI; and group 5 (negative control), saline solution/PUI. After irrigation, the teeth were reseparated and prepared for conventional high-vacuum scanning electron microscopy of the same dentin surface that was previously analyzed. The amount of debris was classified using a 4-point scoring system. Data were analyzed with Kruskal-Wallis and Dunn tests at alpha = 0.05. Results: Groups 1 and 2, which used PUI and different concentrations of NaOCI, were not significantly different; however, they differed significantly from group 3 (P<.05). With respect to canal cleanliness at different root thirds, all groups showed the worst cleaning at the apical third. Conclusions: PUI activation of the EDTA irrigant is required when canal debridement is performed with EDTA and a lower concentration of NaOCI.