Torsional Resistance of Heat-Treated Nickel-Titanium Instruments under Different Temperature Conditions

Area of Science:

• Endodontics
• Materials Science
• Biomedical Engineering

Background:

• Nickel-titanium (NiTi) rotary instruments are widely used in endodontic treatments.
• The thermomechanical properties of NiTi alloys can influence instrument performance.
• Understanding how temperature affects the torsional resistance of NiTi instruments is crucial for clinical application.

Purpose of the Study:

• To compare the torsional resistance of four different heat-treated NiTi rotary instruments under room temperature (RT) and body temperature (BT) conditions.
• To evaluate the effect of temperature on the phase transformation and fracture characteristics of NiTi instruments.
• To provide clinical guidance on the use of heat-treated NiTi instruments at body temperature.

Main Methods:

• Four single-use NiTi rotary instruments (OneShape, OneCurve, WaveOne Gold, HyFlex EDM) were tested.
• Instruments were divided into RT and BT subgroups, with torsional resistance evaluated by maximum torque and distortion angle to fracture.
• Differential scanning calorimetry (DSC) analyzed phase transformation temperatures, and scanning electron microscopy (SEM) examined fracture surfaces.

Main Results:

• No significant difference in torsional resistance was found between RT and BT conditions for any of the tested NiTi instruments.
• Phase transformation analysis showed variations in austenite and martensite phases among instruments at different temperatures.
• SEM analysis revealed no topographical differences in fracture fragments between temperature groups.

Conclusions:

• The torsional resistance of heat-treated NiTi rotary instruments is not significantly affected by body temperature compared to room temperature.
• Clinicians can use these instruments confidently at body temperature without anticipating a decrease in torsional resistance.
• Temperature does not appear to be a critical factor influencing the mechanical performance of these specific NiTi instruments in endodontic procedures.