Influence of cyclic loading in NiTi austenitic and R-phase endodontic files from a finite element perspective.

Objectives: This study aims to evaluate the effects of cyclic loading on the bending moments and the developed stress state of austenitic and R-phase endodontic files through finite element analysis. Materials and methods: The mechanical properties of two groups of NiTi wires, austenite and R-phase, were measured in samples at two different conditions: uncycled and cycled. The cycled condition was achieved by subjecting samples of the two groups to 80% of the corresponding fatigue life under rotating bending efforts. The measured mechanical properties were then used in the finite element analysis, where the boundary and loading conditions were set to replicate a standard bending test. Results: The results showed that mechanical cycling leads to decreasing stress levels and bending moments in the simulated files, especially in the austenitic ones. In comparison with austenite, R-phase presented a more stable mechanical behavior during cycling. Conclusions: The results show that the moment and stress calculated for an instrument under bending can be considerably decreased after some cyclic work. Clinical relevance: The fatigue related to the clinical use of an endodontic file decreases the moment (as well as the forces) imposed by the instrument during the shaping of a curved root canal. This decrease is directly related to the type of atomic array present in the alloy. [ABSTRACT FROM AUTHOR]