Effect of Different Downward Loads and Rotational Speeds on the Removal of Gutta-Percha and Root Canal Sealer Using a Nickel-Titanium Rotary Gutta-Percha Removal System: An Ex Vivo Study

Effective gutta-percha/sealer removal is essential for predictable nonsurgical endodontic retreatment, but the effects of key operational parameters on nickel–titanium rotary removal instruments remain insufficiently understood. This study aimed to examine how varying downward loads and rotational speeds affect the removal efficiency and torque/force generation of the HyFlex Remover. Sixty transparent straight resin canals filled with gutta-percha and AH Plus sealer were prepared using the HyFlex Remover at two rotational speeds (400 and 800 rpm) and three downward loads (2, 3, and 4 N; n = 10/group). The removal rate, calculated using micro-computed tomography, as well as removal time, maximum force, maximum torque, and cumulative torque were recorded and evaluated using two-way analysis of variance with Bonferroni correction (α = 0.05). The removal rate was consistently higher at 400 rpm than at 800 rpm (p < 0.001), while removal time and cumulative torque were greater at 400 rpm (p < 0.001). Maximum torque differed only between the 800-2 N and 800-4 N groups (p = 0.006). Maximum force increased with higher loads (p < 0.001), and at 3 N and 4 N, it was lower at 400 rpm than at 800 rpm (3 N: p = 0.039, 4 N: p < 0.001). Overall, lower downward loads reduced torque but prolonged working time, whereas higher rotational speeds shortened both working time and torque but decreased the removal rate.