Group P: prefabricated PEEK post and composite core (two-piece)
CEREC
PEEK posts were produced by a CAD-CAM system (Roland, DWX-50, Japan). Virtual images were obtained with the intraoral scanning system (CEREC Omnicam, Sirona, Germany) by scanning a Radix® prefabricated Fiber Post size 2 (Dentsply, Switzerland). After developing the milling plan, 29 posts were milled from the filled PEEK disc (PEEK OPTIMA®; Juvora Ltd., Wyre, Lancashire, UK). The PEEK posts were sandblasted with 50 μm Al2O3 (Masel, USA) for 15 s at a pressure of 1.5 bar, then cleaned in an ultrasonic cleaner (Guangdong, China) for 1 min; the posts were checked to ensure it’s correctly seated in the canal, then they were shortened to its final length of 12 mm with a diamond disc (Komet, Germany), finally, cleaned with alcohol and dried with water-free air. The post-cementation was done using Rely Xtm U200 Automix (3 M ESPE, USA) self-adhesive resin cement according to manufacturer instructions (Table 
The compositions and working properties of the resin sealer and the resin cement used in the study< 20% epoxy resinNS calcium phosphateNS zirconium dioxideNS calcium oxideNS ethylene glycol salicylate2.5–10% N, n-dibenzyl-5-oxanonandiamin-1,92.5–10% amantadine