Use of self-heating to predict fatigue life of endodontic files made of superelastic NiTi Shape Memory Alloys

Endodontic files are used in the dental field to prepare root canals of teeth. Some of them are made with superelastic shape memory alloys in order to adapt to the shape of the canals. During the process, file separation by fatigue can occur and compromise the operation. Unfortunately, the fatigue of shape memory alloys has not been much studied and their fatigue is not taken into account in the dimensioning of endodontic files. In this study, we focus on the fatigue and the self-heating properties of superelastic NiTi. We begin by using this fast method based on self-heating measurements to determine fatigue properties of the material. This measurements were realized on dog-bone samples under cyclic loadings at various amplitudes. A model based on dissipation and thermo-mechanical coupling has been developed. It permits to reproduce self-heating results and then by choosing an adapted fatigue criteria we can predict fatigue properties of our samples. These results have been validated using classic fatigue tests on dog-bone samples. 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. These results have been validated by realizing rotating bending fatigue tests on these files.