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J Mater Sci Mater Med. 2018 Aug 7;29(8):131. doi: 10.1007/s10856-018-6140-7.

Mechanism of fracture of NiTi superelastic endodontic rotary instruments.

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School of Dentistry, Universitat Internacional de Catalunya, Barcelona, Spain.
Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Technical University of Catalonia (UPC), Barcelona, Spain.
Faculty of Odontology, University of Seville, Seville, Spain.
MDRCBB-Minnesota Dental Research Center for Biomaterials and Biomechanics, Department of Restorative Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, USA.


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 (Ms, Mf, As and Af) and enthalpies of transformation were determined by calorimetry. Critical stresses until fractureβ→SIM, σSIM→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 Ms and As 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.

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