Tasdemir, Er, Celik, Yildirim et al11 demonstrated ultrasonically activated K to include ultrasonic devices in canal irrigation; files’ ability to cut dentin. However, the results of these devices also increase the tissue-dissolving studies evaluating root canal preparations carried capabilities of NaOCl solution.24 out with ultrasonic devices differ considerably. Recently, with its gradually increasing Several studies have reported that the use of popularity, passive ultrasonic activation of oscillating instrumentation, with ultrasonically endodontic instruments has been suggested as powered devices, are superior to conventional a means to improve canal debridement,29,30 canal enlarging methods for preparing root canals and/ disinfection31,32 and canal sealing.33 PUI also has or eliminating debris.12-14 In contrast, Cymerman been recommended for removing Ca(OH)2 from et al15 reported no significant difference the root canal.34,35 However, whether PUI as an between hand and ultrasonic instrumentation. effective irrigation method causes extrusion Other studies found hand instrumentation to of irrigant from the apical foramen remains be superior to ultrasonic technique.16-19 Ahmad unknown. The purpose of the present study was to et al20,21 reported that ultrasonically activated evaluate in vitro the amount of irrigant extruded devices bend inside the canal or contact the apically from extracted teeth during PUI using canal’s walls, restricting their own vibration and 2.5% NaOCl solution. cleaning activities. This uncontrolled action of the file during MAtERIALS ANd MEtHodS ultrasonic preparation is the reason that Specimen preparation ultrasonics is not routinely used for shaping.22 Twenty extracted human single rooted However, it has been shown that ultrasonically maxillary and mandibular incisors with mature driven files are effective for the “irrigation” of apices were used in this study. They had straight root canals.21 Therefore, the use of ultrasonics in root canals of similar size to reduce effects canals has evolved from primary instrumentation of canal size and curvature on the extrusion of to a passive cleaning technique. PUI was first irrigant. Radiographic images from the buccal and described by Weller et al,23 and “passive activation” proximal aspects of each sample were exposed. in this technique means that the instrument Teeth with extremely large canals and open apex inside the canal does not contact the canal’s in the radiographic images were excluded from walls. During PUI, a small file or smooth wire the study. After hard and soft tissue remnants (e.g., size 15) that is placed at the center of the were cleaned, the teeth were kept in a 10% root canal after shaping the canal, and when this formalin solution before use. file or wire is activated ultrasonically, “acoustic Standard access preparation was streaming” occurs.21 Acoustic streaming creates accomplished using high-speed diamonds and small, intense, circular fluid movement (i.e., water spray. A size 10 K file (VDW Antaeos, eddy flow) around the instruments. The eddying Munich, Germany) was placed into the canal until occurs closer to the tip than in the coronal end it was visible at the apical foramen. The working of the file, with an apically directed flow at the length (WL) was established 1 mm short of this tip.24 Because the root canal is enlarged, the length. Each root canal’s apical dimension was file or wire can vibrate freely in a way to enable determined in accordance with the size of the acoustic streaming, and it transfers its energy biggest file that closely contacted the canal’s to the irrigant inside the canal.21 This acoustic walls in WL without applying any force. Only root streaming, which is created by the instrument canals with an apical diameter from sizes 15-20 passively activated with ultrasonic energy, were used. The teeth were decoronated in order increases the cleaning effect of the irrigant inside to obtain root segments approximately 14 mm the canal by means of hydrodynamic cutting long. power.25 Various studies have shown that NaOCl used with PUI removes more dentin debris, Instrumentation and collection of extruded planktonic bacteria and pulp tissue from the root irrigant canal than syringe irrigation.26-28 An increase in Each canal’s coronal aspect was flared using the temperature of the irrigant may be a reason Gates Glidden drills sizes 2-4 (Dentsply Maillefer, July 2008 - Vol.2 199 European Journal of Dentistry