The present invention concerns an endodontic instrument (10) 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 instrument (10) comprises a rigid tip (11) arranged to be mounted on a rotating support (102) of an apparatus (103) called a contra-angle, and a working sector (12). Said working sector (12) comprises a free end section (13), and is arranged to be engaged in said root canal (101). The working sector (12) consists of a first substantially straight active segment (14), disposed in the extension of said rigid tip (11), and at least one second active segment (15) comprising said free end section (13). In the static state, said second active segment (15) is substantially straight and in said dynamic state said second active segment (15) has a curved shape.
