A comparison of two reciprocating instruments using bending stress and cyclic fatigue tests

Area of Science:

• Endodontics
• Dental Materials Science
• Biomaterials Engineering

Background:

• Nickel-titanium (NiTi) rotary instruments are crucial in endodontic procedures.
• Understanding the mechanical properties, such as bending resistance and cyclic fatigue life, is essential for clinical success and preventing instrument fracture.
• WaveOne and Reciproc are commonly used single-file systems with distinct geometric designs.

Purpose of the Study:

• To conduct a comparative evaluation of bending resistance, static and dynamic cyclic fatigue life, and fracture type between WaveOne 25-08 and Reciproc 25-08 NiTi instruments.
• To investigate the influence of instrument geometry and cross-sectional design on mechanical performance.

Main Methods:

• Sixty 25-08 NiTi instruments (30 WaveOne, 30 Reciproc) from three batches were tested.
• Bending resistance was assessed using a cantilever-bending test on a universal testing machine.
• Static and dynamic cyclic fatigue tests were performed using a custom device with a metal block simulating an artificial canal (1.77 mm diameter, 20.00 mm length).
• Fracture analysis was conducted using a scanning electron microscope.

Main Results:

• The WaveOne instrument exhibited significantly lower flexibility compared to the Reciproc instrument (p < 0.05).
• The Reciproc instrument demonstrated superior resistance in both static and dynamic cyclic fatigue tests (p < 0.05).
• Instrument geometry and transverse cross-section were identified as critical factors influencing resistance to bending and cyclic fracture.

Conclusions:

• The Reciproc 25-08 instrument offers greater resistance to static and dynamic cyclic fatigue than the WaveOne 25-08 instrument.
• The WaveOne 25-08 instrument is less flexible than the Reciproc counterpart.
• Both instrument designs displayed ductile-type fracture characteristics, indicating a degree of plastic deformation before failure.