Mechanism of fracture of NiTi superelastic endodontic rotary instruments

• Published in: Journal of materials science. Materials in medicine Vol. 29; no. 8; pp. 131 - 6
• Main Authors: Gil, Javier, Rupérez, Elisa, Velasco, Eugenio, Aparicio, Conrado, Manero, José María
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.08.2018; Springer Nature B.V
• Subjects: Biomaterials; Biomaterials Synthesis and Characterization; Biomedical Engineering and Bioengineering; Biomedical materials; Calorimetry; Ceramics; Chemistry and Materials Science; Composites; Enthalpy; Fractures; Glass; Heat measurement; Heat treating; Heat treatment; Intermetallic compounds; Materials Science; Natural Materials; Nickel titanides; Plates (structural members); Polymer Sciences; Regenerative Medicine/Tissue Engineering; Scanning electron microscopy; Superelasticity; Surfaces and Interfaces; Thin Films; Time of use
• ISSN: 0957-4530; 1573-4838
• DOI: 10.1007/s10856-018-6140-7

The aim is to investigate the premature catastrophic fracture produced for different periods during clinical endodontic treatment of two brands of NiTi endodontic rotary instruments. 3 samples as-received, 6 samples used with patients for 2 and 7 h and 5 samples fractured were studied for each brand of endodontic NiTi rotary instruments. Transformation temperatures (M s , M f , A s and A f ) and enthalpies of transformation were determined by calorimetry. Critical stresses until fracture (σ β→SIM , σ SIM→β ) were obtained using an electromechanical testing machine. The samples were also visualized by Scanning Electron Microscopy. Calorimetric studies have shown an increase of the M s and A s transformation temperatures with time of use as well as a decrease of their stress transformations. Moreover, reverse transformation enthalpies decreased along the time. The enthalpies of transformation decreased because martensitic plates were anchored, which prevented their transformation to austenite; thus losing its superelastic effect. The stabilisation of the martensitic plates induced the collapse of the structure and so the main cause for the fracture. The heat treatment proposed has been increased the life in service of NiTi superelastic endodontic instruments recovering theirs superelastic effect.