Endo training block

The artificial root canal blocks (n = 480) were made of resin with a curved root canal and a coronal reservoir resembling a pulp chamber (Endo Training Block; Dentsply Maillefer, Ballaigues, Switzerland). The root canals had a 16.5 mm working length with a degree of curvature of 45.2°, a taper of 0.02 and a radius of canal curvature of 6.1 mm [19 (link)]. Before the experiment, the model was immersed in 75% alcohol for 30 min, washed with 5 mL of ultrapure water, immersed in 5.25% NaOCl for 30 min, washed with 5 mL of distilled water, and dried at room temperature.

This experiment consisted of 20 simulated curved root canals (Endo Training Block; DentsplyMaillefer, Ballaigues, Switzerland) that were 16.5 mm long. The degree of curvature was 45.2°, and the radius of canal curvature was 6.1 mm, according to Schneider’s method.^{21 (link)} The canals were prepared to F3 (apical size 30 with a 0.09 taper) by the same operator using a ProTaperNiTi Rotary System (DentsplyMaillefer, Ballaigues, Switzerland) according to the manufacturer’s instructions.^{22 (link)} 5 mL of 2.5% NaOCl was used after each instrument, and 5 mL of distilled water was used as the final rinse. The simulated root canals were dried with paper points. The apical foramen was then filled with wax from the outside.^{22 (link)} Canals were filled with Ca(OH)₂ paste (UltracalXSOptident, International) using a 30-gauge NaviTip (Ultradent products Inc., South Jordan, UT, USA) starting from the apical aspect with the needle slowly advancing coronally until the paste was visualized at the canal orifice.^{6 (link)} The access cavities were sealed with a cotton pellet and temporary filling material (GC corporation, Tokyo, Japan). The root canals were stored at 37 °C and 100% relative humidity for 7 days.