The aim of this study was to compare, in vitro, the cleaning efficacy of three different irrigation techniques: syringe irrigation (Navitip) using NaOCl, sonic irrigation system (EndoActivator), and passive ultrasonic irrigation system (PUI) on debris and smear layer distribution in the root canal at three different levels. Materials and Methods: Sixty freshly extracted single-rooted human mandibular premolars were decoronated to a standardized length of twenty millimeters. Specimens were shaped to IRace 25 size and irrigated with 3 mL 2.5% NaOCl between instrumentation. Teeth were divided randomly into three equal groups: Group I (n=20): Irrigation manually with a syringe (Navitip) (n=20), irrigation was done with 3 mL 2.5% NaOCl for one minute using 30 gauge needle. Group II (n=20): Final rinse with 3 ml 2.5% NaOCl activated for one minute with passive sonic irrigation system (endoactivator). Group III (n=20): Final rinse with 3 ml 2.5% NaOCl activated for one minute with PUI system. Root canals were then split longitudinally and field emission scanning electron microscopy was used to eval¬uate endodontic smear layer and debris removal from the instrumented root canals. This was done using a scale from 0-5 as described by Hulsmann et al. Results of this study showed that Both (PUI) and (EndoActivator®; Dentsply) have resulted in superior removal of smear layer and debris when compared to needle-and-syringe irrigation. Conclusion: None of the techniques completely removed all the smear layer and debris from root canal walls at the apical part of the canal. However, PUI system showed significantly better cleaning than needle and sonic systems in the entire length of the root canal
