The root canal instrument for preparing a housing for a pivot inside dental roots includes a working part extending along a longitudinal axis. A cross-section of a frustoconical envelope of the working part embodying an elliptical section or an ovoid section or an oblong section or a section of the type includes a front circle portion and a rear circle portion joined by two side bend portions. A diameter of the front circle portion is longer than or equal to a diameter of the rear circle portion.
