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

Abstract

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. 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. 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. The results show that the moment and stress calculated for an instrument under bending can be considerably decreased after some cyclic work. 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.