Aim: the aim of this study was to evaluate the fracture resistance ofEndodontically treated teeth restored with two all ceramic crowns, bonded to different foundation restorations, under thermal cycling and cyclic loading.Materials and Methods: Twenty extracted single root lower premolar were selected, restored in saline solution. All teeth were decoronated 2mm above cement-enamel junction, and then embedded in acrylic resin blocks, 2mm below the cement-enamel junction. All teeth were endodontically treated and prepared to receive glass fiber post. Especially designed mold was fabricated to standardized core build up. Teeth were divided into main groups: group (I); teeth built up by methacrylate composite core material, group (II): teeth built up by silorane composite core material. Each group was further subdivided into two subgroups according to the type of crown selected: Subgroup (A): teeth restored with zirconia all ceramic crowns. Subgroup (B): teeth restored with e-max empress all ceramic crowns. All crowns were cemented with adhesive resin cement. All samples subjected to thermal cycling. Fracture resistance tested under cyclic loading using universal testing machine.Results: Independent t-test revealed that, zirconia crowns had an insignificant lower fracture resistance values (832.3 ±131.76) than e.max crowns (959.11±290.06) when silorane core material was used, while zirconia crowns showed significantly higher mean values(1107.46±113.04) than e.max crowns (895.30±40.15) when methacrylate core material was used. Silorane core materials had insignificant higher fracture resistance values (959.11± 290.06) than methacrylate core materials (895.30±40.15) when e.max crown was used, while methacrylate core material showed significantly higher values (1107.46±113.04) than silorane core material when zirconia crown was used (P≥0.05).Conclusion: Zirconia crowns with methacrylate core material showed the highest fracture resistance compared to the pother tested combinations. Silorane composite core material represented a satisfactory alternative core build up material under e.max ceramic restorations, but it is not the best choice under the zirconia ceramic restorations.