The present invention concerns an endodontic instrument or drill-bit for preparing a tooth of a patient, in particular an instrument for cleaning the root canal that follows the natural geometry of said canal. The root canal geometry is not straight or linear, but is curved or non-uniform. The endodontic instrument is made of a shape memory material having a first static state with a substantially straight geometry to facilitate the instrument being inserted partially into the said root canal and a second dynamic state corresponding to a structured geometry, a supple flexible behaviour, in which the endodontic instrument is set rotating to clean the said root canal following its natural geometry. The instrument has a rigid tip arranged to be mounted on a rotating support and a working sector arranged to be engaged in said root canal, when the instrument is in its dynamic state, the working sector consists of a first substantially straight active segment disposed in the extension of the said rigid tip, this first active segment being prolonged by a second active segment having a free end and having a curved shape between the point where the said first active segment and a free end meet. The shape memory material is a shape memory metal alloy in which the transition from the martensitic phase to the austenitic phase occurs naturally at a body temperature between 32°C and 37°C, the instrument being in its dynamic state at this temperature.
