Cleaning and shaping

A conventional access cavity was prepared in each tooth using a high speed round bur and an endo—Z bur (DentsplyMaillefer, Ballaigues, Switzerland) under copious water cooling. The crowns of all teeth were sectioned using a diamond stone to obtain a standardized tooth length of 15 ± 1 mm. A size 10 k-file (DentsplySirona,Tulsa, USA) was introduced into the mesiobuccal canal of each tooth until the tip became just visible at the apical foramen to confirm canal patency. The working length was then established at 1 mm short from the apical foramen. A glide path was established using size 10 and 15 k-files (DentsplySirona,Tulsa,USA). ProTaper Next (PTN) system (DentsplyMaillefer, Ballaigues, Switzerland) activated by the X-Smart plus endodontic motor (DentsplyMaillefer, Ballaigues, Switzerland) was used for root canal preparation according to the manufacturer's instructions. PTN X1 file (17/04 apical taper) was introduced into the canal until reaching the working length. Then the PTN X2 file (25/06 apical taper) was used to finish canal preparation. During instrumentation, canal irrigation was done after each file change with 2 ml of 2.5% sodium hypochlorite (Clorox Co, 10 ^th of Ramadan, Egypt) and patency was re-assessed using a size #10 k –file. Irrigation was performed using a 30 gauge side vented needle (Endo-Top®, PPH CERKAMED, StalowaWola, Poland) with an insertion depth of 2 mm short of the working length (WL). After completion of instrumentation, the smear layer was removed with the final rinse of 5 ml of 17% EDTA(Calix E, Dharma, Miami, Florida, USA) for one minute followed by 5 ml of 2.5% NaOCl.