Set of instruments of increasing dimension for the boring of radicular dental canals

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.

BACKGROUND OF THE INVENTION 
a) Field of the Invention 
This invention relates to a set of instruments of increasing dimension for 
the boring of radicular dental canals in which each instrument comprises a 
conical stem presenting at least one helicoidal cutting edge. 
b) Description of the Prior Art 
Such sets of instruments, constituted by files and reamers, are known per 
se. 
The instruments are formed with a series of terminal diameters, called D1, 
measured at the root of their ending portion which is not provided with a 
cutting edge. The diameter D1 of each instrument in the set is different, 
an is of a dimension, in most of the cases, of a value between 0.06 mm and 
1.4 mm. The variation of the diameters D1 can be an arithmetical series, 
that is to say a linear series, or a geometric one. In these instruments, 
the conicity of the stem is constant, whatever the terminal diameter may 
be, this conicity being generally expressed not by its angle at the apex 
but by the difference between the terminal diameter D1 and the terminal 
diameter, called D2, measured at the root of the helicoidal cutting edge 
or edges. The lenght of the part of the stem presenting the said edge or 
edges being generally of 16 mm, the difference between the terminal 
diameter and the diameter of the stem at the root of the edge or edges is 
most generally of 0.32 mm. 
The dentist who effects the boring of a radicular dental canal uses the 
instruments of the set while starting with an instrument of small diameter 
and while using then, successively, instruments of increasing diameter 
until the whole infected pulp is eliminated and the bored canal has a 
shape suitable for its obturation by means of gutta-percha or cement. 
The most modern odontological technique requires that one gives to the 
radicular canal a funnelled shape, the canal being large at its cervical 
part, near the crown of the tooth, and having to remain very narrow at its 
apical part, in the vicinity of the end of the dental root. As a matter of 
fact, this funnelled shape of the radicular canals once they have been 
bored is more suitable for an obturation by means of gutta-percha, that is 
a technique which is more and more in use. 
SUMMARY OF THE INVENTION 
The object of the present invention is to permit to realize, more easily 
than with the usual conventional instruments, a funnelled shape of the 
radicular canals. 
This object is achieved owing to the fact that the diameter D1 of each 
instrument, measured at the root of its terminal part, varies, from one 
instrument to another one, according to a geometrical progression, and by 
the fact that the diameter D2 of each instrument, measured at the root of 
its cutting part, varies too, from one instrument to another one, 
according to a geometrical progression.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The instruments as represented, in the number of three, while a set of 
instruments can comprise up to about twenty, comprise each a cylindrical 
stem 1 intended to be engaged either into a handle permitting the manual 
operation of the instrument, or into a handle engaged in a handpiece 
producing the mechanical driving of the instrument. 
The stem 1 is prolongated by a tapered portion 1a in which are provided 
helicoidal cutting edges 2 and which terminates at a conical point 3 which 
has no cutting edges. 
One will obtain this instrument for instance while starting from a circular 
stem the front part 1a of which will be tapered by working, and while 
working therein plane faces so that the tapered portion has a polygonal 
section, for instance of triangular or square shape. One will then submit 
this stem to a torsion, thus realizing the helicoidal edges 2. One could 
also work the cutting edges directly on the stem at the moment of giving 
it its tapered shape. 
The diameter of the stem at the root of its point, designated by D1, 
constitutes the nominal diameter serving to characterize the instrument, 
while the diameter designated by D2 is the diameter of the stem at the 
root of the cutting edges 2. 
The several instruments of the set distinguish from each other by their 
dimension, the diameters D1 and D2 varying, from one instrument to another 
one, according to a geometrical progression. 
The ratio of the geometrical progression of the diameters D1 could be the 
same as the ratio of the progression of the diameters D2. Since the 
diameters D2 are larger than the diameters D1, it follows that they 
increase more rapidly, so that the opening of the cone constituting the 
active part of the instruments increases, thereby imparting to the 
radicular canals a funnelled shape, in accordance with the object of the 
invention. 
One could also provide that the ratio of the geometrical progression of the 
diameters D1 be higher than the ratio of the geometrical progression of 
the diameters D2 while providing that the D2 diameters continue to 
increase more than the diameters D1, and also providing that the opening 
of the cone constituting the active portion of the instruments does not 
increase too greatly. 
One could also provide, for some applications, that the ratio of the 
geometrical progression of the diameters D1 be lower than the ratio of the 
geometrical progression of the diameters D2. 
In this last case, however, the relatively high progression of the 
diameters D2 could have for a consequence that the instruments of large 
dimension (those which are situated at the end of the set) become too 
rigid with respect to the ones of small dimension. As a matter of fact, 
the increase of the diameter has obligatorily for consequence to increase 
the rigidity of the stems, that, if it is too strong, can constitute a 
drawback. 
So that the flexibility of the different instruments of the set remains 
substantially the same, one could use different materials for the 
realization of the different instruments of the set or, at least, of some 
of them. One could also apply different thermic treatments to each 
instrument of the set or to a part thereof. One could also proceed to a 
different working of each instrument or of a part thereof, specially when 
the cutting edges are not obtained by a mere torsion of a tapered stem of 
polygonal section, so that the central part of the instruments remains 
substantially the same from one instrument to another one or does vary 
only according to a progression which is lower than that of the outer 
diameter of the instruments, so that the characteristics of flexibility be 
substantially maintained from one instrument to another one. 
The ratio of the geometrical progression of the diameters D1 and D2 of the 
instruments of the set can be, for instance, of 20%. In this case, if the 
smallest instrument of the set has a diameter D1 of 0.06 mm and a diameter 
D2 of 0.092 mm, the diameters D1 and D2 of the second instrument will be 
of 0.072 mm and of 0.110 mm, respectively. 
The following table indicates the diameters D1 and D2 of the eighteen 
instruments of the set in the specific case which is hereabove indicated, 
as well as, in the last column, the differences between D1 and D2. One 
sees that the difference is increasing, so that the opening of the cone of 
the tapered part of the instrument increases also. 
Owing to this arrangement, the radicular canals which are bored by means of 
these instruments, used successively in the increasing order, will be more 
funnelled that the ones realized by means of conventional sets of 
instruments, that facilitates the obturations, especially by means of 
gutta-percha. 
TABLE 
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No .O slashed. D1 
.O slashed. D2 
D1-D2 
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6 0.06 0.092 0.032 
7 0.072 0.110 0.038 
8 0.086 0.132 0.046 
1.0 0.103 0.159 0.056 
1.2 0.124 0.191 0.067 
1.4 0.149 0.229 0.080 
1.7 0.179 0.274 0.095 
2.1 0.215 0.330 0.115 
2.5 0.258 0.396 0.138 
3.1 0.310 0.475 0.165 
3.7 0.372 0.570 0.198 
4.4 0.446 0.683 0.237 
5.3 0.535 0.820 0.285 
6.4 0.642 0.984 0.342 
7.7 0.770 1.181 0.411 
9.2 0.924 1.417 0.493 
10.0 1.109 1.701 0.592 
13.3 1.331 2.041 0.710 
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