Purpose: The aim of this study was to assess the fracture resistance of PEEK endocrowns and post-retained PEEK crowns with two preparation designs (ferrule and without ferrule). Materials and methods: Eighty sound human mandibular first
premolars were selected. Teeth were divided into 4 main groups (n= 20): Group1: Were assigned for endocrown preparation with Butt joint. Group 2: Were assigned for endocrown preparation with Shoulder finish line. Group 3: Were assigned for PEEK post & core preparation without ferrule. Group 4: Were assigned for PEEK post & core preparation with ferrule. Endocrowns of both Group 1 and Group 2 were made of PEEK material veneered with composite. Both Group 3 and Group 4 were covered with PEEK crowns veneered with composite. All Restorations either PEEK post & cores or
endocrowns and final crowns were sandblasted with 110 Mm aluminium oxide. Finally, cemented with self-adhesive resin cement (G-Cem cement). Results: The highest mean value was recorded in Post & core with ferrule (above CEJ) (1262.29±65.02), followed by Endocrown with Butt Joint (1101.44 ± 81.7), then Endocrown with Shoulder finish line (890.99±75.42), with the least value recorded in Post & core without ferrule (below CEJ) (726.03±71.26). Statistically, ANOVA test showed a considerable difference between groups (p=0.00). Tukey's post hoc test showed a considerable difference between each 2 groups. Conclusion: It was concluded that the mandibular premolarsthat were restored by PEEK Post-cores covered with crowns which designed with ferrule recorded the highest fracture resistance load.