University of Hertfordshire


  • André Carvalho
  • Manuel Freitas
  • Luís Reis
  • Diogo Montalvao
  • Manuel Fonte
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Original languageEnglish
Pages (from-to)34-41
JournalProcedia Structural Integrity
Journal publication date4 Mar 2016
Publication statusPublished - 4 Mar 2016
Event1st International Conference on Structural Integrity - Madeira, Funchal, Portugal
Duration: 1 Sep 20154 Oct 2015


Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough transformations in recent years when
stainless steel was replaced by Nickel-Titanium (NiTi). NiTi alloys used in Endodontics possess superelastic properties at body
temperature (37C) that bring many advantages on the overall performance of the root-canal treatment. They can follow curved root
canals more easily than stainless steel instruments and have been reported to be more effective in the removal of the inflamed pulp
tissue and protection of the tooth structure. However, these instruments eventually fracture under cyclic bending loading due to
fatigue, without any visible signals of degradation to the practitioner. This problem brought new challenges on how new instruments
should be tested, as NiTi alloys are highly non-linear and present a large hysteresis cycle in the Elastic domain. Current existing
standards are only available for Stainless Steel testing. Thus, many authors have attempted to design systems that can test NiTi
endodontic files under fatigue loads. However, no approach has been universally adopted by the community yet, as in most cases
they are based on empirical set ups. Following a more systematic approach, this work presents the results of rotary fatigue tests
for several NiTi wires from different manufacturers (Memry™ and Euroflex™ ).The formulation is presented, where the material
strength reduction can be quantified from the determination of the strain and the number of cycles until failure, as well numerical
FEM simulation to verify the analytical model predictions.

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