## 2 Materials and Methods  
A pilot study was conducted before proceeding in our experimental research to calculate the sample size accurately using G*Power (Version 3.1) [20]. Accordingly, a total of sixty extracted human mandibular premolars were used in this study that were further divided into three main groups consisting of twenty samples for each group, in accordance with the previously calculated sample size. The teeth were characterized by being single-rooted premolars with a single-canal, completely formed apex and devoid of any caries, restorations or morphological anomalies. Any teeth with incomplete root development, root resorption, caries or fractures were excluded from the current study. The 60 selected premolars were cleaned by immersion in a soln. of 5.25% NaOCl for 20 min and wiped with a soaked gauze to remove the organic debris and soft tissue remnants. This was followed by storing the premolars in normal saline soln. until the start of the experiment. Access cavity preparations were performed on all samples, and a size #10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was introduced into the canals to check for apical patency and maintain a glide path. The length of each canal was determined and then adjusted to be 0.5 mm from the apex. Each sample was mounted on an acrylic block and numbered. All the canals were then prepared using EdgeFile X7 (Edge Endo; Albuquerque, NM, USA), size 17/0.04 and 25/0.04, respectively, with the aid of an X-Smart rotary contra-angle motor (Dentsply, Sirona, Canada) at a speed of 350 rpm and a torque of 2.5 Ncm, under constant irrigation with 2 mL of 5.25% NaOCl. Recapitulation using a 3 mm syringe and a 27-gauge needle was performed in between the different files. At the end of the preparation, all canals were dried using paper points. The 60 premolars were divided into three groups, twenty premolars each, according to the irrigation activation technique used, and a radiopaque solution (Omnipaque) was used for final irrigation to facilitate X-ray visualization of the solution penetration depth in millimeters. A digital X-ray image was obtained using (Kodak Dental Imaging Software 6.12.10.0) to record the penetration depth that was doublechecked once more using cone-beam computed tomography (CBCT) performed with the aid of a Galileos machine (Sirona Dental Systems GmbH, Bensheim, Germany), with scan parameters of 98 Kv, mA: 3-6 and exposure 14 s; field of view was 15 \(\times\) 12 cm, and voxel size was 0.125 mm. The three tested groups were classified as follows according to three different irrigation techniques:  
Group 1: Conventional needle with passive irrigation (CN), n = 20. Group 2: Side-vented endodontic needle (EN), n = 20. Group 3: Manual agitation with fitted gutta-percha (MA), n = 20. In the first group, the conventional needle \"CN\" (Monoject(tm) Endodontic Needles and Syringes) was placed inside the canal, and for final irrigation, iohexol (Omnipaque) solution was used passively. A radiograph was obtained to measure the penetration length compared to the working length (Figure 1). In the second group, a contrast medium was delivered into the canal using a side-vented endodontic needle \"EN\" (Max-I-Probe; Dentsply Limited, Weybridge, Surrey, UK). A radiograph was performed to measure the penetration length compared to the working length (Figure 2). Figure 1: Irrigation with conventional needle (CN) and its digital radiographic image. Figure 2: Irrigation with side-vented endodontic needle (EN) and its digital radiographic image. In the third group, the first irrigation was delivered through the conventional needle. Then an apically fitting gutta-percha master cone (Dentsply Maillefer, Ballaigues, Switzerland) was placed inside the canal for manual agitation \"MA\". Pumping and up-and-down movements were performed with the gutta-percha point. The radiograph was obtained, and the measurement was recorded (Figure 3).