Instrumentation and obturation
SMEAR LAYER
Root canal instrumentation was performed with a crown-down technique using F1, F2, and F4 ProTaper Universal files (Dentsply-Sirona). In addition, 2.0 mL of 2.5% sodium hypochlorite (NaOCl) solution was used after each instrument change using 30-gauge side-vented irrigation needles. After cleaning and shaping the root canals, a final flush with 1.0 mL EDTA 17%, followed by 5.0 mL of 2.5% NaOCl to remove the smear layer. Finally, the root canals were flushed with 3.0 mL of distilled water and dried with paper points. A single-cone obturation technique with an F4 gutta-percha master cone (Maillefer-Dentsply, Ballaigues, Switzerland) and sealer (Adseal resin-based root canal sealer, Meta Biomed, Cheongju, Korea) was used to fill the root canals. The teeth were stored in an incubator at 37° C with 100% relative humidity.