An instrument for drilling dental root canals includes a tapered rod having over at least a part of its length—the active part—a polygonal cross-section forming at least two cutting edges, the active part terminating by a point and being defined by an envelope of cylindrical or conical shape, whose longitudinal axis coincides with the instrument's axis of rotation. The active part has a first portion extending from the point and a second portion extending following the first portion towards the rear of the active part. At least one cross-section of the first portion has a centre of mass located on the axis of rotation and the cutting edges are located on the envelope. Any cross-section of the second portion has a centre of mass offset with respect to the axis of rotation and at least one cutting edge defined by the cross-section is located set back.
