Experimental: Single-file rotary instrumentation (One Curve)

Patients received root canal treatment using a single-file rotary system (OneCurve) in the MB2 canals of maxillary first molars. OneCurve 25/.04 rotary file was used at 300 rpm and 2.5 Ncm torque.

Experimental: Two-file rotary instrumentation (Perfect Minimally Invasive)

Root canal treatment was performed using a two-file system (Perfect Minimally Invasive; Perfect Medical Instruments Co. Ltd, China). A 10/.06 Shaper file was used with brushing motion in the coronal and middle thirds, followed by a 25/.04 Finisher file in the apical third. Files operated at 300 rpm and 2.0-2.5 Ncm torque under continuous irrigation.

Experimental: Three-file rotary instrumentation (VDW Rotate)

Root canal instrumentation was performed using a three-file system (VDW Rotate; VDW GmbH, Germany). Instrumentation was performed sequentially using 15/.04, 20/.05, and 25/.04 files for the coronal, middle, and apical thirds, respectively, with brushing-pecking motions in 2-3 mm increments under continuous irrigation. Files were operated at 300 rpm and 1.8 Ncm torque in the MB2 canal of maxillary first molars.

Experimental: Four-file rotary instrumentation (Perfect Advanced Kit)

Root canal instrumentation was performed using a four-file rotary system (Perfect Advanced Kit; Perfect Medical Instruments Co. Ltd, China). Coronal enlargement was initiated with a 10/.07 Opener file at 300 rpm and 2.5 Ncm torque. A 10/.04 file was then used at 250 rpm and 2.0 Ncm torque to reach the apical third. Final shaping was completed with 17/.05 and 25/.04 files at 300 rpm and 2.5 Ncm torque. A crown-down technique was applied using brushing-pecking motions in 2-3 mm increments. After each file, the canal was irrigated thoroughly and file flutes were cleaned to prevent debris accumulation.