Wall shear stress effects of different endodontic irrigation techniques and systems Narisa Goode a,1 , Sara Khan a,1 , Ashraf A. Eid b , Li-na Niu c , Johnny Gosier a , Lisiane F. Susin a , David H. Pashley d , Franklin R. Tay a,d, * a Department of Endodontics, Georgia Regents University, Augusta, GA, USA b Department of Dental and Biomedical Material Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan c Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, Xi’an, China d Department of Oral Biology, Georgia Regents University, Augusta, GA, USA j o u r n a l o f d e n t i s t r y 4 1 ( 2 0 1 3 ) 6 3 6 – 6 4 1 a r t i c l e i n f o Article history: Received 22 March 2013 Received in revised form 11 April 2013 Accepted 12 April 2013 Keywords: Apical fluid pressure Calcium hydroxide Canal fin Fluid flow rate Sodium hypochlorite Two-phase gas–liquid flow a b s t r a c t Objectives: This study examined de ´ bridement efficacy as a result of wall shear stresses created by different irrigant delivery/agitation techniques in an inaccessible recess of a curved root canal model. Methods: A reusable, curved canal cavity containing a simulated canal fin was milled into mirrored titanium blocks. Calcium hydroxide (Ca(OH) 2 ) paste was used as debris and loaded into the canal fin. The titanium blocks were bolted together to provide a fluid-tight seal. Sodium hypochlorite was delivered at a previously-determined flow rate of 1 mL/min that produced either negligible or no irrigant extrusion pressure into the periapex for all the techniques examined. Nine irrigation delivery/agitation techniques were examined: Navi- Tip passive irrigation control, Max-i-Probe 1 side-vented needle passive irrigation, manual dynamic agitation (MDA) using non-fitting and well-fitting gutta-percha points, EndoActi- vator TM sonic agitation with medium and large points, VPro TM EndoSafe TM irrigation system, VPro TM StreamClean TM continuous ultrasonic irrigation and EndoVac apical nega- tive pressure irrigation. De ´ bridement efficacies were analysed with Kruskal–Wallis ANOVA and Dunn’s multiple comparisons tests (a = 0.05). Results: EndoVac was the only technique that removed more than 99% calcium hydroxide debris from the canal fin at the predefined flow rate. This group was significantly different ( p < 0.05) from the other groups that exhibited incomplete Ca(OH) 2 removal. Conclusions: The ability of the EndoVac system to significantly clean more debris from a mechanically inaccessible recess of the model curved root canal may be caused by robust bubble formation during irrigant delivery, creating higher wall shear stresses by a two- phase air–liquid flow phenomenon that is well known in other industrial de ´ bridement systems. # 2013 Elsevier Ltd. All rights reserved. * Corresponding author at: Department of Endodontics, College of Dental Medicine, Georgia Regents University, Augusta, GA 30912-1129, USA. Tel.: +1 706 7212152; fax: +1 706 7218184. E-mail address: ftay@gru.edu (F.R. Tay). 1 These authors contributed equally to this work. Available online at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/jden 0300-5712/$ – see front matter # 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jdent.2013.04.007