Supervisor : Abeer Hashem Mahran, Mohamed Alaa Fakhr. Includes Arabic Summary.Shafik, Marian Safwat,2024-05-272024-05-272024.EG-CaMIUDNT Ths675 M.Sc. 2024https://iorep.miuegypt.edu.eg/handle/20.500.13071/241DISSERTATION NOTE-Degree type M.Sc.DISSERTATION NOTE-Name of granting institution Misr International University, Faculty of Oral and Dental MedicineIncludes bibliographic references.Tooth fracture is one of the undesirable phenomena of endodontically treated teeth and usually leads to extraction which is a major problem especially for teeth in the aesthetic zone. Endodontically treated teeth are generally weaker than sound teeth as a result of loss of sound tooth structure due to caries, access cavity and root canal instrumentation. Aim of the study: The aim of this study was to evaluate and compare the influence of different access cavity designs :(Conservative access cavity (CEC), Truss access cavity (TREC) and traditional access cavity (TEC)) and the remaining tooth structure on the fracture resistance of endodontically treated teeth. Methodology: 42 mature double rooted maxillary first premolars were randomly divided into a control group and three equal test groups according to the access cavity design prepared: CEC, TREC and TEC which were further subdivided according to the number of remaining walls either three or two remaining walls. CBCT was used to locate the root canal orifices for the preparation of the conservative access cavity designs. 24 sound upper first premolars were imaged with CBCT which were assigned to CEC and TREC. After CBCT scanning different access cavity designs were prepared, while teeth in the control group remained intact and were only evaluated for the fracture strength. After access cavity prepartion, a standeridized MO and MOD cavities were made using flat ended diamond fissure bur with rounded angles for the occlusal cavity. Then all teeth (control and test groups) were embedded in self-cure acrylic resin to form acrylic blocks to undergo the fracture resistance test, all teeth were loaded in a universal testing machine with a static loading perpendicular to the long axes of the teeth till fracture then the forces for failure were recorded (Newton), tabulated and statically analyzed.92 pages : illustrations, photo ; 29 cm + 1 CD-ROM (4 3/4 in.)Endodontics