Torque during canal instrumentation using rotary nickel-titanium files

Area of Science:

• Endodontics
• Biomaterials Science
• Mechanical Engineering

Background:

• Nickel-titanium (NiTi) engine-driven rotary instruments are widely used in endodontic therapy.
• Instrument fracture within the root canal is a significant clinical concern.
• Limited research exists on the dynamic torsional properties of NiTi rotary instruments.

Purpose of the Study:

• To quantify torque and apical force during simulated clinical use of a commercial NiTi rotary file system.
• To correlate measured torque during instrumentation with the torsional failure characteristics of the instruments.

Main Methods:

• Ten extracted human teeth with straight root canals (five small, five medium) were instrumented using Quantec Series 2000 NiTi files.
• Torque generated and apical force applied were continuously measured during instrumentation.
• Torsional failure testing was performed on the instruments.

Main Results:

• Apical forces applied were consistently low, generally below 150 g.
• Generated torque was influenced by instrument tip size, taper, and root canal dimensions.
• Instruments with 0.05 and 0.06 taper produced the highest torque, especially in smaller canals.
• Torque at failure was significantly higher than operational torque, though with substantial variability.

Conclusions:

• Clinical instrumentation with NiTi rotary files typically involves low apical forces.
• Torsional demands on NiTi instruments are dependent on file design and canal anatomy.
• Understanding the relationship between operational torque and failure torque is crucial for preventing instrument fracture.