An instrument for drilling dental root canals, includes a tapered rod having on at least an active part of its length, at least one helical flute defining at least one helical cutting edge. The instrument also has a helical hollow on a portion of the active part extending as far as the point of the rod. At least one of the edges defined by the helical hollow is coincident with the cutting edge, the hollow reducing the cutting angle of the cutting edge. Any cross-section of the active part has at least one convex side belonging to the helical flute. The closer the cross-section in question is to the point of the rod, the more the curvature at any point of the convex side increases and tends to approximate the curvature of the circumscribed circle of the cross-section and passing via the cutting edge defined by the helical flute.
