الفهرس 
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Abstract
Statement of problem: New treatment modalities have to be developed to restore endodontically treated teeth and enhance remaining tooth structure. Thus, endocrown restorations are a recent conservative concept to solve such problem. Aim of the study: To evaluate the effect of two materials (PEEK and zirconia) and two intracoronal depths (3 mm and 5 mm) on the fracture resistance of endocrown restorations. Materials and methods: Forty endodontically treated maxillary first molars were prepared for endocrown restorations. Specimens were divided into two main groups (n=20) according to the material used into PEEK (P) and zirconia (Z). The two main groups were subdivided into 2 subgroups (n=10) according to the extension depth of pulp chamber into short 3 mm depth (S) and long 5 mm depth (L). After teeth were prepared, all restorations were milled, then surface treatment to each material was done followed by using self-adhesive resin cement. All specimens were subjected to 5000 cycle of artificial aging between 5°C and 55°C. After thermal cycling, all specimens were loaded till failure by universal testing machine, then all failed restoration were evaluated by digital photos and SEM to determine the mode of failure. Results : The highest mean maximum load value recorded among group PL (2578.3±337 N) followed by PS then ZL with the least detected among ZS (2178.37±126 N, 1536.42±104 N and 1511.42±168 N, respectively). There was a statistical significant difference (p <0.05) between (PS and PL), (PS and ZS) and (PL and ZL). Only there was no statistical significant difference (p <0.05) between (ZS and ZL).