Effects of Additional Vertical Movements on the Torque, Force, and Root Canal Shaping Performance of Nickel-Titanium...

Area of Science:

• Endodontics
• Dental Materials Science

Background:

• Nickel-titanium rotary instrumentation techniques, particularly optimum torque reverse (OTR) motion, require further optimization.
• The impact of specific manipulation strategies, like "forced in-and-out motion," on instrumentation performance is not well-understood.

Purpose of the Study:

• To evaluate the effect of "forced in-and-out motion" during OTR activation on ProTaper NEXT instrumentation performance.
• To determine the optimal duration of downward movement within the OTR cycle for enhanced efficiency and safety.

Main Methods:

• Automated instrumentation in simulated J-shaped resin canals using ProTaper Next X1-X3 files.
• Comparison of continuous rotation (CR), OTR without in-and-out motion (OTR-N), and OTR with varying downward movement durations (0.25s, 1.0s, 2.0s).
• Evaluation of maximum torque/force, instrumentation time, and canal-centering ratio using statistical analysis (two-way ANOVA).

Main Results:

• OTR with 0.25s and 1.0s downward movement significantly reduced clockwise torque and downward force compared to other groups.
• Continuous rotation and OTR with 0.25s downward movement showed higher canal-centering deviations apically.
• The 0.25s downward movement group exhibited the longest instrumentation time.

Conclusions:

• Incorporating a 1.0-second "forced in-and-out motion" during OTR with ProTaper NEXT files effectively reduces torque and force generation.
• This technique improves instrumentation efficiency by minimizing canal deviation without prolonging procedure time.
• The findings suggest a refined OTR protocol for safer and more effective root canal preparation.