Introduction: The aim of this experimental study is to compare the effectiveness of sonic device EndoActivator in biological cleaning of root canal in comparison with conventional syringe irrigation. Materials and Methods: Forty single-rooted and single-canal extracted teeth were randomly divided in two groups: in the control group (group 1), irrigation was performed with conventional syringe with passive irrigation and in the experimental group (group 2) the canal irrigation was performed with ultrasonic activation by EndoActivator system. Both groups canal roots were instrumented by using a crown-down technique with mounted modified tapered Nichel-Titanium instruments (Protaper system, Dentsply Maillefer, Ballaigues, Switzerland). The roots were longitudinally split and were grooved in the coronal, middle, and apical thirds. A Scanning electron microscopy at 1000x was used. SEM observation allowed to evaluate the amount of smear layer and inorganic debris in each third through a four value scale, further dentinal tubules perviety was evaluated. The obtained results were subjected by using the x Pearson test. Results: The group 1 root canals apical and middle thirds, showed less smear layer and inorganic debris removal than group 2, and the differences was statistically significant (P<0.05). No coronal thirds statistically significant differences were among groups (P >0.05). Conclusion: The protocol proposed in this study showed that the cavitation and the acustic streaming produced by EndoActivator improve debris and smear layer removal from canal root wall more than conventional syringe irrigation, not only in the coronal third but expecially in the middle and apical thirds.
