Comparative Evaluation of the Shaping Performance of Four Thermally Treated Single-File Systems in Simulated S-Shaped Canals

This article aims to compare the shaping performance of four thermally treated single-file systems in simulated S-shaped root canals. Sixty standardized double-curved resin canals were randomly assigned to four groups (n = 15) and prepared using Plex RC-One (25/0.06), R-Motion (25/0.06), WaveOne Gold (25/0.07) in reciprocating motion, and XP-Endo Shaper (27/0.01) in continuous rotation. Pre- and post-instrumentation images were superimposed, and resin removal was measured at 12 predefined levels. Canal enlargement (diameter increase) and canal transportation were calculated for apical, middle, and coronal regions. Data were analyzed using repeated-measures linear mixed-effects models (LMM) to account for within-specimen dependency and level-specific effects. Fifty-eight specimens were included in the final analysis; two R-Motion canals were excluded due to apical ledge formation. The repeated-measures LMM analysis demonstrated significant effects of instrumentation system (p = 0.002), canal level (p < 0.001), and group × point interaction (p < 0.001), indicating level-dependent shaping behavior. WaveOne Gold demonstrated the greatest enlargement, whereas XP-Endo Shaper exhibited the most conservative shaping behavior, particularly in the coronal and middle regions. Canal transportation values were generally low for all systems. Although transportation patterns varied according to canal level (p < 0.001) and group × point interaction (p < 0.001), no significant overall intergroup differences were detected (p = 0.581). All systems were capable of preparing S-shaped canals with acceptable shaping ability and generally low canal transportation. However, shaping behavior was system- and region-dependent. WaveOne Gold demonstrated the greatest canal enlargement, whereas XP-Endo Shaper exhibited a more conservative shaping pattern while maintaining comparable apical enlargement. These findings suggest that shaping behavior in S-shaped canals is highly site-specific and influenced by instrument design, metallurgy, and kinematics in double-curved anatomies.