ORIGINAL ARTICLE Endodontics Effect of passive ultrasonic irrigation and manual dynamic irrigation on smear layer removal from root canals in a closed apex in vitro model Syed Mukhtar-Un-Nisar Andrabi 1 , Ashok Kumar 1 , Afaf Zia 2 , Huma Iftekhar 1 , Sharique Alam 1 & Shiraz Siddiqui 1 1 Department of Conservative Dentistry and Endodontics, Dr Ziauddin Ahmad Dental College, Aligarh Muslim University, Aligarh, Uttar Pradesh, India 2 Department of Periodontics and Community Dentistry, Dr Ziauddin Ahmad Dental College, Aligarh Muslim University, Aligarh, Uttar Pradesh, India Keywords ethylenediaminetetraacetic acid, irrigant activation, manual dynamic irrigation, passive ultrasonic irrigation, smear layer. Correspondence Syed Mukhtar-Un-Nisar Andrabi, Assistant Professor, Department of Conservative Dentistry and Endodontics, Dr Ziauddin Ahmad Dental College, Aligarh Muslim University, Aligarh, Uttar Pradesh 202002, India. Tel: +91-97197-15939 Email: mukhtarandrabi@gmail.com Received 17 September 2012; accepted 26 December 2012. doi: 10.1111/jicd.12033 Abstract Aim: To compare the effect of passive ultrasonic irrigation with manual dynamic irrigation on smear layer removal from root canals using a closed apex in vitro model. Methods: The root canals of 45 freshly-extracted human single-rooted mandib- ular premolar teeth were prepared by the Pro-Taper rotary system to an apical preparation of F4 size. Prepared teeth were randomly divided into three groups; two experimental groups and one control group (n = 15) on the basis of the type of activation of final irrigation as follows: (a) Group A, 3% sodium hypochlorite (NaOCl) and 17% ethylenediaminetetraacetic acid (EDTA), no activation received; (b) Group B, 3% NaOCl and 17% EDTA, ultrasonic activa- tion with a small file; and (c) Group C, 3% NaOCl and 17% EDTA, manual activation with a master gutta-percha point. The prepared teeth were decoro- nated and split into two halves longitudinally, and observed under a scanning electron microscope to assess the removal of the smear layer. Results: In the apical-third region, the mean smear scores for groups B and C were significantly less than those of Group A (control group) (P < 0.05). Conclusion: Both activation techniques are important adjuncts in removing the smear layer, with manual dynamic activation being a simpler, safer, and more cost-effective technique. Introduction The removal of the smear layer generated during mechan- ical instrumentation achieves complete debridement and disinfection of the root canal system. 1 The smear layer consists of organic and inorganic substances, including fragments of odontoblastic processes, microorganisms, their by-products, and necrotic materials. 1–3 When left unremoved, it prevents the penetration of intracanal med- icaments into dentinal tubules, and influences the adapta- tion of filling materials to canal walls. 4,5 The most commonly-advocated protocol for the efficient removal of smear layer is the alternate use of sodium hypochlorite (NaOCl) with ethylenediaminetetraacetic acid (EDTA) as initial and final rinses. 6,7 This combination ensures effec- tive smear layer removal in the coronal and middle thirds, but is less effective in the apical third, owing to the inability of the irrigating solutions to reach the apical third of the root canals. 7,8 For effective action, these solutions must come into contact with the entire surface of the root canal walls. However, the complex anatomy of the root apex and the vapor lock effect in the apical-third region prevent the conventional static irrigation from wetting the entire ª 2013 Wiley Publishing Asia Pty Ltd 1 Journal of Investigative and Clinical Dentistry (2013), 4, 1–6