Supervisor : Salma Elashry, Abeer Hashem, Amr Bayomy. Includes Arabic Summary.Helmy, Amr Emad Mohamed,2024-05-272024-05-272024.EG-CaMIUDNT Ths699 M.Sc. 2024https://iorep.miuegypt.edu.eg/handle/20.500.13071/249DISSERTATION NOTE-Degree type M.Sc.DISSERTATION NOTE-Name of granting institution Misr International University, Faculty of Oral and Dental MedicineIncludes bibliographic references.Endodontic treatment involves creating cavities for accessing root canal system through the pulp chamber in order to get the desired outcome. Thoroughly cleaning and shaping the root canal system is crucial for efficient root canal therapy, as it eradicates bacteria and eliminates contaminated dentin. The use of Ni-Ti rotary and reciprocating instruments has improved the root canal preparation procedure and led to a decrease in the necessary time. However, an increased taper might result in removal of radicular dentin and a decrease in the resistance to tooth fractures. To provide a less invasive treatment, files with a lower taper are used to do more preparations in the apical thirds while conserving dentin in the coronal and middle thirds. Using ultrasonic technology in irrigation can efficiently clean the walls of root canals and improve their antibacterial qualities. This study focuses on the preparation of 80 extracted mandibular molars, with a special emphasis on the mesio-buccal and mesio-lingual canals. The teeth were soaked in a sodium hypochlorite solution for 5 minutes to remove the periodontal ligament. The specimens were classified into four groups based on the final size and taper of the root canal preparation, using EdgeEndo NiTi rotary files. The samples were divided into two subgroups based on the irrigation protocol: Subgroup A did not include irrigant activation, whereas Subgroup B featured ultrasonic activation of the irrigant. Access cavity preparation is a conservative procedure that requires preserving the pericervical dentin and part of the chamber roof. The patency of the mesio-buccal and mesio-lingual canals was evaluated using a size 10 K-file. To clean and shape the samples, rotary files were used at a speed of 300 Rpm and a torque of 2.5 Ncm, with an NSK endodontic motor equipped with torque control.118 pages : illustrations, photo ; 29 cm + 1 CD-ROM (4 3/4 in.)Endodontics