Metallurgical characterization of M-Wire nickel-titanium shape memory alloy used for endodontic rotary instruments during low-cycle fatigue.

Abstract

INTRODUCTION:

Rotary instruments made of a new nickel-titanium (NiTi) alloy (M-Wire) have shown improved cyclic fatigue resistance and mechanical properties compared with those made of conventional superelastic NiTi wires. The objective of this study was to characterize microstructural changes of M-Wire throughout the cyclic fatigue process under controlled strain amplitude.

METHODS:

The average fatigue life was calculated from 30 M-Wire samples that were subjected to a strain-controlled (≈ 4%) rotating bend fatigue test at room temperature and rotational speed of 300 rpm. Microstructural evolution of M-Wire has been investigated by different metallurgical characterization techniques, including differential scanning calorimetry, Vickers microhardness, and transmission electron microscopy at 4 different stages (as-received state, 30%, 60%, and 90% of average fatigue life).

RESULTS:

During rotating bend fatigue test, no statistically significant difference (P > .05) was found on austenite finish temperatures between as-received M-Wire and fatigued samples. However, significant differences (P < .05) were observed on Vickers microhardness for samples with 60% and 90% fatigue life compared with as-received and 30% fatigue life. Coincidentally, substantial growth of martensite grains and martensite twins was observed in microstructure under transmission electron microscopy after 60% fatigue life.

CONCLUSIONS:

The results of the present study suggested that endodontic instruments manufactured with M-Wire are expected to have higher strength and wear resistance than similar instruments made of conventional superelastic NiTi wires because of its unique nano-crystalline martensitic microstructure.

• Authors: Jia Ye, Yong Gao
• Journal: Journal of endodontics (J Endod) Vol. 38 Issue 1 Pg. 105-7 (Jan 2012) ISSN: 1878-3554 [Electronic] United States
• PMID: 22152631 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Chemical References

• Dental Alloys
• titanium nickelide
• Martensite
• Austenite
• Nickel
• Titanium

Topics

• Calorimetry, Differential Scanning
• Dental Alloys (chemistry)
• Equipment Design
• Equipment Failure
• Hardness
• Humans
• Materials Testing
• Metallurgy
• Microscopy, Electron, Transmission
• Nickel (chemistry)
• Pliability
• Root Canal Preparation (instrumentation)
• Rotation
• Stress, Mechanical
• Surface Properties
• Temperature
• Titanium (chemistry)