###### Abstract  
The elimination of necrotic and inflamed pulp tissue, dentin debris, and microorganisms is essential for the success of endodontic treatment. However, the root canal's complexity has led to incomplete cleaning and disinfection. This study aims to compare the efficacy of the penetrability of three different irrigation activating techniques to the apical third of the root canal. Sixty sound single-rooted human mandibular premolars are prepared with rotary instrumentation under continuous sodium hypochlorite irrigation. Three irrigation activation techniques are utilized: group 1 (n = 20), conventional needle irrigation (CN); group 2 (n = 20), side-vented endodontic needle irrigation (EN); and group 3 (n = 20), manual activation irrigation with gutta-percha cone (MA). The penetrability is assessed with the aid of a radiopaque irrigation solution using digital radiography in conjunction with cone-beam computed tomographic (CBCT) measurements. Data are analyzed using a statistical package for social sciences (SPSS), using multiple comparisons to compare the baseline and test values. One-way analysis of variance with post hoc analysis (Tukey honestly significant difference) is performed to detect the statistically significant differences between groups. Manual activation (MA) shows effective delivery of the irrigant into full WL, followed by endodontic needle (EN) and conventional (CN) methods of activation (\(\rho<0.001\)). The results of the present study show that maximum penetrability of the irrigant is observed with manual activation (MA) using a gutta cone in comparison with the conventional needle (CN). irrigation techniques; endodontics; irrigation penetration; digital radiography; CBCT 2023374363743 Endodontic irrigation solutions have an important role during and after instrumentation by eradicating microorganisms and dissolving debris, remaining dentin chips as well as tissue remnants from the prepared root canal through a flushing mechanism so as to assure a clean and disinfected environment that is suitable for receiving the proper obturating material [3; 4; 5]. The challenging complexity of the root canal morphology, as well as its unique and unlimited variations, could have a negative effect on the elimination of all bacteria and debris inside the root canal [6]. However, cleaning and shaping per se do not disinfect the root canal system [7]. Proper root canal instrumentation coupled with an effective irrigation delivery technique is required to provide optimal disinfection of the root canal system. Efficient irrigation techniques are capable of debriding the complete canal system by delivering an adequate volume of the irrigation solution to reach the full working length of the root canal [8; 9]. Various irrigation devices and techniques were developed to improve active root canal irrigation, and to reach an ideally cleaned and disinfected root canal space. In recent years, several modifications have been introduced to the needle-tip design to improve irrigation effectiveness. There are two types of root canal irrigation activation techniques, namely: manual delivery agitation techniques using files and gutta-percha cones and machine-assisted irrigation agitation techniques using sonic and ultrasonic systems [10; 11; 12; 13; 14]. Sodium hypochlorite (NaOCl) is commonly used for irrigation due to its antibacterial nature and ability to remove organic necrotic remnants within the smear layer during endodontic treatment [12; 13; 14]. Sodium hypochlorite can be considered as the most well-known type of irrigation used that has the ability to disintegrate and totally remove the remaining bacterial biofilms which persist in the root canal space. However, and despite its tissue-dissolving and antibacterial capabilities, it should be always used with caution to avoid any detrimental drawbacks that may be related to its cytotoxicity and adverse effect on dentin properties.