Cleaning and shaping of root canals is a crucial step in endodontic treatments. Irrigation allows removal of residual tissues in the canal that cannot be cleaned by instrumentation alone. This study evaluates and compares the efficiency of XP-endo Finisher (XPF), EndoActivator (EA) and Passive Ultrasonic Irrigation (PUI) I. IntroductionThe goal of endodontic therapy is the removal of all vital or necrotic tissues, microorganisms, and microbial by-products from the root canal system. The root canal system is highly complex and variable and has limited our ability to clean and disinfect it predictably. Shaping of root canals is performed almost entirely by using hand and rotary instrumentation techniques . Peters et al., using micro computed tomography scans before and after mechanical instrumentation found that, regardless of the instrumentation technique, 35% or more of the root canal surfaces (including canal fins, isthmuses, and cul-de-sacs) remained uninstrumented [2] . Thus, instrumentation alone does not fully prepare the root canal system for obturation, and disinfection is the key to the augmentation of instrumentation process and optimization of the obturation process [3] . Disinfection is comprised of the removal of the tissue remnants and the associated bacteria in the root canal system through flushing with irrigating solution. The key is to remove as much tissue remnant as possible and the more thorough the process of irrigation, the lower the remaining level of bacteria [4] . Optimal irrigation is based on the use of a combination of two or more irrigating solutions, in a specific sequence, to obtain the goals of effective and safe irrigation predictably. Traditionally, delivery of the irrigant solutions into the root canal system have been done using plastic syringes and metal needles of different sizes and tip designs. However, research and clinical experience have shown, that this classic approach typically results in irrigation that is ineffective, especially in areas such as fins, anastomoses, and the most apical region of the root canal system. Therefore, many of the irrigation solutions have been modified chemically and many mechanical devices have been developed for the improvement of the effectiveness and penetration of irrigation [5] . In spite of the recent advances in irrigation systems, it is still not possible to remove all debris from the root canal systems. Inadequate canal debridement can lead to a decrease in endodontic success [6] . For this reason, different irrigation systems were used in this study and the cleaning efficiency of each system was evaluated and compared to find which system is more preferable for the cleaning of root canals.
II. Materials and MethodsSixty freshly extracted human maxillary molar teeth with straight palatal root canals collected from different specialized dental centers were used in this study.Immediately after extraction; bone, calculus, stains and soft tissues on the tooth surface were removed manually by the use of a cumine [7] , disin...