Effect of heat treatment on cyclic fatigue resistance, thermal behavior and microstructures of K3 NiTi rotary instruments. (November 2013)

• Record Type: Journal Article
• Authors: Chang, Seok Woo; Kim, Yu-Chan; Chang, Hyejung; Jee, Kwang-Koo; Zhu, Qiang; Safavi, Kamran; Shon, Won-Jun; Bae, Kwang-Shik; Spangberg, Larz Sw; Kum, Kee-Yeon
• Is Part Of: Acta odontologica Scandinavica. Volume 71:Number 6(2013)
• Page Start: 1656
• Page End: 1662
• Publication Date: 2013-11
• Subjects: Dentistry -- Periodicals; 617.6005
• DOI: 10.3109/00016357.2013.797101
• Languages: English
• ISSNs: 0001-6357

Abstract

<abstract> <title>Abstract</title> <p> <bold> <italic>Objective.</italic> </bold> The aim of this study was to investigate the effect of heat treatment on the cyclic fatigue resistance, thermal behavior and microstructural changes of K3 NiTi rotary instruments. <bold><italic>Materials and methods.</italic></bold> Twelve control (as-received) and 12 experimental (heat-treated) K3 NiTi rotary instruments were compared in this study. Those experimental K3 instruments were heated in a furnace for 30 min at 450°C and then quenched in water. The cyclic fatigue resistance was measured with a fatigue tester. The thermal characteristic and the microstructures of both instruments were investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), respectively. <bold><italic>Results.</italic></bold> There was a significant increase in the cyclic fatigue resistance between the heat-treated instruments and the as-received instruments (<italic>T</italic>-test, <italic>p</italic> < 0.05). DSC showed that the as-received and heat-treated samples were different, with an increased A<sub>f</sub> (austenite-finish temperature) for the latter. TEM analysis revealed that both as-received and heat-treated instruments were composed mainly of an austenite phase. However, the heat-treated samples had an increased appearance of larger grains, twinning martensite, TiO<sub>2</sub> surface layer and a Ni-rich inner layer. <bold><italic>Conclusions.</italic></bold> Heat treatment increased the cyclic fatigue resistance of NiTi files and changed the thermal behavior of the instruments without marked changes in the constituting phases of NiTi alloy.</p> </abstract>