Effect of Preceding Enlargement Steps on Real-Time Torque Generation and Post-Instrumentation Mechanical Properties of Rotary Nickel-Titanium Finishing Instruments.

INTRODUCTION

This study evaluated the influence of instrumentation sequence on real-time torque generation and post-instrumentation mechanical properties of finishing instruments in two nickel-titanium (NiTi) rotary systems.

METHODS

Standardized simulated canals in resin blocks were prepared using HyFlex EDM OGSF (HEDM) and RACE EVO (RAVO) with three sequences: direct finishing, initial enlargement-finishing, and initial enlargement-intermediate shaping-finishing. Real-time torque was recorded using a torque acquisition module coupled to an endodontic motor. Maximum torque, mean peak torque, integrated torque, and total sequence-integrated torque were calculated. The finishing instruments were then subjected to cyclic fatigue testing in an artificial canal with a 35° curvature and torsional resistance testing.

RESULTS

Preceding enlargement instruments significantly reduced the maximum torque, mean peak torque, and integrated torque of the finishing instrument in both systems (P < .05). In HEDM, total sequence-integrated torque was lower in both sequential groups than in the direct finishing group (P < .05), whereas no significant difference was found among RAVO sequences. Cyclic fatigue resistance of the HEDM Finisher increased significantly with sequence expansion (P < .05), whereas that of the RAVO 30/.04 file did not differ among sequences. The HEDM Finisher showed reduced maximum torsional strength and increased distortion angle with sequence expansion, whereas the RAVO 30/.04 file differed only in toughness.

CONCLUSION

The use of preceding enlargement instruments reduced the peak and integrated torque generated by the finishing instrument in both NiTi rotary systems, whereas its effects on total sequence-integrated torque and post-instrumentation fracture resistance were system-dependent.