A stainless steel size 10 hand k-file (Dentsply Maillefer, Ballaigues, Switzerland) was inserted into the canal up to the apical foramen. The working length was confirmed at 1 mm from the length of the canal. A single experienced operator performed two mesial root canal preparations with iRace files (FKG Dentaire) according to the manufacturer’s instructions. Apical enlargements were prepared to apical sizes of #25/0.04 (Group #2504), #30/0.04 (Group #3004), #35/0.04 (Group #3504), and #40/0.04 (Group #4004) using the following sequence of instruments: 15/0.06 working length (WL), 25/0.04 WL, 30/0.04 WL, 35/0.04 WL, and 40/0.04 WL. The X-Smart (Dentsply Maillefer) electric motor was used with the rotation speed adjusted to 250 rpm and 1 Ncm torque. After four gentle in-and-out strokes, the instrument was removed from the canal, and the canal was cleaned until the WL was reached.
According to previously published work,2 (link),22 (link) the root canals were irrigated with 2 mL of 5.25% NaOCl for 1 minute, delivered by a side-vented irrigating tip (Max-i-Probe; Hawe-Neos, Dentsply, Bioggio, Switzerland) placed 2 mm short of the WL of each rotary instrument. At the end of the preparation, the canals were flushed with 10 mL of 5.25% NaOCl for 5 minutes, followed by 2 mL of 17% EDTA for 5 minutes. The canals were then dried with paper points.
According to previously published work,2 (link),22 (link) the root canals were irrigated with 2 mL of 5.25% NaOCl for 1 minute, delivered by a side-vented irrigating tip (Max-i-Probe; Hawe-Neos, Dentsply, Bioggio, Switzerland) placed 2 mm short of the WL of each rotary instrument. At the end of the preparation, the canals were flushed with 10 mL of 5.25% NaOCl for 5 minutes, followed by 2 mL of 17% EDTA for 5 minutes. The canals were then dried with paper points.