Self-Heating of Superelastic NiTi Shape Memory Alloys for Fatigue Study of Endodontic Files

With their superelasticity, shape memory alloys wires are used as the base of endodontic files. These files are used in the dental field to prepare root canals of teeth. During their use, file separation by fatigue can occur and complicates the realized operation. Unfortunately, the fatigue property of shape memory alloys remains an unexplored area and their fatigue is not taking into account in dimensioning of the endodontic files. In this study, we focus on the fatigue of superelastic NiTi and on the self-heating phenomena. This study begins by using this fast method based on self-heating to determine fatigue properties. Self-heating measurements under cyclic loading have been set up on dog-bone samples. Using a modeling based on dissipation and thermo-mechanical coupling, self-heating results have been reproduced and in addition with a fatigue model we can predict fatigue properties of our samples. These results have been validated by fatigue tests at low and high number of cycles. With this fast method, process parameters effects as electropolishing or heat treatment on fatigue properties have been studied. Finally, the model which has been identified on dog-bone samples has been used to predict fatigue life of endondontic files.