Abstract: An instrument for boring dental radicular canals in which the conicity of the active part of the tapered stem of the instrument is not constant but the angle of its opening is greater at its rear portion, positioned beyond the diameter D.sub.9, than the angle of opening of its front portion positioned between its end and the diameter D.sub.9 so that a dental canal bored with the instrument has a bell-mouthed shape.

Abstract: The length of the active part of each drill of the set is inversely proportional to the diameter of the cutting edge of each drill, that prevents the drills of the set being too much engaged in the coronary canal, since the depth of the working depends with precision from the used drill.

Abstract: The central part of the instruments of the boring set, prior to the portion having the cutting edges, has a section of a polygonal shape. The lateral faces of the central part are either convex, for the instruments of small diameter, plane for the instruments of middle diameter and concave for the instruments of largest diameter, in such a way that the curve of the bending moments of the instruments of the set is substantially rectilinear. Thus the variation of the bending moments of the instruments is linear, while, in previously known sets of instruments, the curve is exponential. Hence, the flexibility of the instruments of the set is satisfactory for the entire set of instruments, while; in the known conventional sets, if previously flexibility of the small instruments of the set is satisfactory, the instruments of largest diameter will be too rigid, and vice versa.

Abstract: A set of instruments for boring of radicular dental canals, in which the diameter D1 of each instrument, measured at the root of the pointed end portion thereof, varies according to a geometrical progression as well as the diameter D2 of each instrument measured at the root of the cutting edges. Hence, the variation is more pronounced for the diameters D2, larger than the diameters D1, than it is for the diameters D1. The conicity of the stem of the instruments increases in this manner from one instrument to another, so as to permit a the dentist to form the radicular canals with a specially funnelled shape which is best suited for some obturations, especially those to be treated with gutta-percha.

Abstract: A set of instruments for boring dental radicular canals in which the conicity of the rear part of the set positioned beyond the diameter D.sub.9 of the instruments, increases more for the first instruments of the set than for the last ones. The conicity of the front part of the instruments does not increase much for the first instruments of the set, but does increase for the last ones. Hence, while using successively the instruments of a set, the dentist bores first the coronary portion of the tooth, then its medium portion and then its apical portion. The end part of the instruments, between the point thereof and their diameter D.sub.3, situated at 3 mm from the point, is provided with one or several grooves for elimination of the dental scraps, but which have no cutting edges so that this part of the instruments functions only for their guidance.