Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 11 1 2014 02 15 1 9 Puneet Ahuja Post Graduate Student, Department of Conservative Dentistry and Endodontics Meenakshi Ammal Dental College, Chennai, India. Suresh Nandini Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College, Chennai, India. Suma Ballal Professor, Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College, Chennai, India. Natanasabapathy Velmurugan Professor, Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College, Chennai, India. 2015 10 16 The aim of this study was to assess the efficacy of apical negative pressure (ANP), manual dynamic agitation (MDA), passive ultrasonic irrigation (PUI) and needle irrigation (NI) as final irrigation activation techniques for smear layer removal in curved root canals.Mesiobuccal root canals of 80 freshly extracted maxillary first molars with curvatures ranging between 25° and 35° were used. A glide path with #08-15 K files was established before cleaning and shaping with Mtwo rotary instruments (VDW, Munich, Germany) up to size 35/0.04 taper. During instrumentation, 1 ml of 2.5% NaOCl was used at each change of file. Samples were divided into 4 equal groups (n=20) according to the final irrigation activation technique: group 1, apical negative pressure (ANP) (EndoVac); group 2, manual dynamic agitation (MDA); group 3, passive ultrasonic irrigation (PUI); and group 4, needle irrigation (NI). Root canals were split longitudinally and subjected to scanning electron microscopy. The presence of smear layer at coronal, middle and apical levels was evaluated by superimposing 300-μm square grid over the obtained photomicrographs using a four-score scale with X1,000 magnification.Amongst all the groups tested, ANP showed the overall best smear layer removal efficacy (p < 0.05). Removal of smear layer was least effective with the NI technique.ANP (EndoVac system) can be used as the final irrigation activation technique for effective smear layer removal in curved root canals. https://fid.tums.ac.ir/index.php/fid/article/view/573 https://fid.tums.ac.ir/index.php/fid/article/download/573/548