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