Fatigue testing of controlled memory wire nickel-titanium rotary instruments

Area of Science:

• Materials Science
• Biomaterials Engineering
• Dental Materials

Background:

• Nickel-titanium (NiTi) files are crucial in endodontics.
• Improving fracture resistance of NiTi files is a key manufacturing goal.
• Novel alloys and manufacturing processes are being developed for enhanced NiTi file performance.

Purpose of the Study:

• To evaluate the fatigue behavior of NiTi instruments manufactured from a novel controlled memory NiTi wire (CM Wire).
• To compare the fatigue performance of CM Wire instruments against conventional NiTi files.

Main Methods:

• Rotational bending tests were performed on various NiTi instruments (ProFile, Typhoon, Typhoon CM, NEYY, NEYY CM) at 35° and 45° curvatures.
• The number of revolutions to fracture (N(f)) was recorded.
• Fracture surfaces were analyzed using scanning electron microscopy to assess crack initiation sites and dimple area percentages.

Main Results:

• CM Wire instruments exhibited a 3-to-8-fold increase in N(f) compared to conventional NiTi files (P < .05).
• CM instruments predominantly showed multiple crack origins (50%-92%), unlike conventional files (58%-100%) which typically had one.
• Dimple area fractions were significantly smaller in CM NiTi instruments (P < .01).
• Instrument configuration (square vs. triangular) significantly impacted lifetime on CM wire at both curvatures (P < .01).

Conclusions:

• Material properties, specifically the use of CM Wire, substantially influence fatigue lifetime.
• NiTi instruments made from CM Wire demonstrate significantly higher N(f) and lower surface strain amplitude than conventional NiTi wire files with identical designs.