Shape Memory Alloys (SMAs) are widely used in dentistry area and especially for endodontic files. The NiTi SMA is adopted for its biocompatibility and its flexibility. A new generation of endodontic files, manufactured with a single crystal Cu-based SMA are under development. They present a low stiffness due to large reversible transformation strains. This communication presents the analysis of superelastic behaviour of those endodontic files under bending, torsion and combined bending-torsion loadings. The finite element code Abaqus® made possible this analysis thanks to its user-subroutine UMAT. It allowed implementing a developed thermo-mechanical nonlinear constitutive model describing all the specificities of SMAs, [1]. This model was adopted for this finite element analysis. Corresponding material parameters was identified starting from experimental tensile test carried out on wires of the same Cu-based single crystal SMA. A parameterized geometrical model of the endodontic file was designed with CATIA® and imported in Abaqus® in order to analyse the effect on the global behaviour of the following geometrical parameters: length, conicity, pitch and the tip section size. Obtained results of this finite element analysis allowed defining the available domain of these geometrical parameters regarding to stiffness and strength constraints. They also leaded to an optimal design of this endodontic file minimising the bending and torsion stiffness and the stress state reminding lower compared to the SMA yield stress and maximizing the phase transformation area of the endodontic file.