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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for boring dental radicular
canals by means of a set of instruments which are successively passed
through the said canals.
The invention also relates to a set of instruments for carrying out the
method in which each instrument comprises a tapered stem provided, on at
least a part of its length which constitutes its active portion, at least
one helicoidal cutting edge. This stem presents a conicity, the angle or
opening of which is higher, at its rear end, than the angle at its front
end.
2. Description of the Prior Art
The boring of dental radicular canals comprises a first step called
catheterization, which consists in engaging into the radicular canal a
very fine instrument, up to the apical foramen. This operation is always
performed manually.
The widening of the radicular canal is effected by several operations which
can be performed either manually or by means of instruments mechanically
driven. For this second step, two methods can be used: The first one,
called "step back" consists of introducing into the canal a succession of
instruments, the diameters of which are successively increasing, while
reducing the part of the length of the canal which is bored at each
application of an instrument having increasing diameter. This method is
relatively long and does not permit the dentist to observe, so far as it
is possible, the work which has been effected. The second method, called
"crown-down", consists of opening, in a first step, the coronary portion
of the tooth, then to enter, by means of a set of instruments which
successively increase in fineness up to the apical zone of the tooth.
The known sets of instruments permitting carrying out of these methods are
usually mounted in a hand-piece rotating slowly (250 to 500 t/min.); they
are formed, in most of the cases, of a nickel-titanium alloy, and belong
to three families:
The first family comprises a set of instruments formed of a short cutting
portion, followed by a thin and flexible collet which is itself connected
to a handle which is secured to a hand-piece to enable mechanical driving
of the instrument. The diameter of the active portion of the instrument
increases according to an arithmetic progression, the interval between two
numbers of the instruments of the set being of 0.025 mm.
A second family comprises instruments the active portion of which, of a
length of 16 mm, has a conicity of 0.04 mm per millimeter of length. This
active portion is immediately followed by a cylindrical portion to permit
connection with the handle of the instrument. The progression of the
diameter at the point of the end of the active portion of the instrument
is of 29% between each number of the instruments of the set.
Finally, a last family comprises instruments having an active length of 16
mm and presenting a conical envelope, all of these instruments having the
same diameter at their end. Their conicity increases 0.05 mm for each
number of the instruments of the set.
SUMMARY OF THE INVENTION
The object of the present invention is to furnish on the one hand a new
boring method for dental radicular canals, after the step of catheterism,
and on the other hand new instruments permitting carrying out this method,
which is safer and more efficient than the known methods. This new method
is also more rapid and does not need as many instruments as the known
methods.
Moreover, the instruments used for carrying out this method produce borings
which are more regular, having a continuous wall, that is not always the
case with the known instruments.
These purposes are achieved because, in the method of the present
invention, one attacks first the coronary portion of the tooth by means of
the first instrument of the set, then the medium portion of the tooth, by
means of the next instruments of the set, and finally the apical portion
of the tooth by means of the last instruments of the set.
The purposes are also reached due to the fact that, in the set of
instruments of the invention, the conicity of the stem of the instruments
increases, on the rear portion of the active length of the instruments,
more for the first instruments of the set than for the last ones, while,
on the contrary, on the front portion of their active part, it is the
conicity of the last instruments of the set which increases more than the
conicity of the first instruments of the set.
The various features of the invention will be apparent from the following
description, drawings and claims, the scope of the invention not being
limited to the drawings themselves as the drawings are only for the
purpose of illustrating ways in which the principles of the invention can
be applied. Other embodiments of the invention utilising the same or
equivalent principles may be used and structural changes may be made as
desired by those skilled in the art without departing from the present
invention and the purview of the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of an instrument for the boring of dental
radicular canals.
FIG. 2 represents the profile of five instruments for the boring of dental
radicular canals belonging to a set of such instruments, and
FIG. 3 represents the superposed profile of the five instruments of FIG. 2.
In FIGS. 2 and 3 the diameter of the instruments has been exaggerated with
respect to their length, so as to render more visible the variations of
the conicity of the instruments.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The instrument represented in FIG. 1 comprises stem 1 of circular
cross-section, made of a nickel-titanium alloy, engaged, at its rear part,
in a handle 2 intended to be engaged in a hand-piece to enable mechanical
driving of the instrument.
The stem 1 is tapered, its front part, indicated at L, being provided with
two helicoidal grooves 3, having each a cutting edge. At the end of the
instrument, along a length indicated by L', of about 3 mm, ending in a
point indicated by D.sub.3, expressing the diameter of the instrument at
this point, the cutting edge of the helicoidal grooves 3 has been
eliminated so that, along this length, the instrument does not cut and the
grooves are provided only to eliminate the chips or scraps of the dental
material removed by the instrument. The number of the cutting grooves can
be greater than two.
From point D.sub.9 of the instrument, situated at a distance L" from point
D.sub.3 of 6 mm, that is to say at a distance of 9 mm from the point of
the instrument, the conicity of the instrument increases slightly as shown
by the first instrument, indicated by reference 1a of FIG. 2.
The instrument retains this new conicity up to point D.sub.16 which is
situated at the end of its active portion L.
The second instrument of the set of FIG. 2, designated by reference 1b, is
distinguished from the first one by the fact that the angle or opening of
the conicity of its portion situated between the points D.sub.9 and
D.sub.16 increases more than for the instrument 1a.
The same is true for the third instrument, designated by reference 1c, of
the set of FIG. 2.
The difference of conicity of the rear part of the active length of the
instruments, from their point D.sub.9, appears clearly in FIG. 2, where
the profile of the instrument 1a has been indicated in dot-and-dash lines
on the instrument 1b, and the profile of the instrument 1b has been
indicated on the instrument 1c.
FIG. 2 also shows that the conicity of the front part of the instruments
1a, 1b and 1c, between the end of these instruments and their diameter
D.sub.9, is the same for these three instruments.
So far as the fourth instrument of the set is concerned, designated by
reference Id, the conicity of its front part, before the diameter D.sub.9,
increases with respect to that of the instrument 1c. The conicity of its
rear part increases also with respect to the instrument 1c, but to a
lesser degree. This is the same for the fifth and last instrument of the
set, designated by reference 1e, in which the conicity of its front and
rear parts increases with respect to the instrument 1c.
The set of instruments of the invention permits the dentist who has
manually executed the first step of the boring, called catheterism,
consisting in engaging into the canal a very fine instrument, up to the
apical formamen, to then use successively, the instruments 1a to 1e of the
set, mechanically driven, while starting with instrument 1a and ending
with instrument 1e.
This successive use of the several instruments of the set permits a
progressive working, to be effected each instrument broadening or widening
a specific portion of the radicular canal while being guided, up to the
apex, by its ending front part which does not cut. This also permits the
dentist to avoid deviations and offsets with respect to the natural curve
of the initial canal.
It is coronary portion of the canal which is bored the first, that produces
a maximum output of dental scraps and optimal conditions of work for the
next instrument. Incidentally, in this manner, the risk of producing an
infection by the introduction of decayed dental tissue to the apex is
highly reduced. The median portion of the tooth is bored next, and its
apical portion is bored last.
The end of the apical portion is not needlessly bored due to the fact that
the end part of the instrument, the conicity of which will be of 2% for
example, on a length of 3 mm, has no cutting edges.
The present method of boring and the set of instruments for carrying out
the method enable realization of a canal which is more bell-mouthed and
especially more regular, that results in conditions of obturation of the
canal which are optimum. The passage of the last instrument 1e results in
finishing boring.
The radicular canal which is bored as here-above mentioned has no solution
of continuity along its surface, forming stairs as is the case when known
instruments, especially instruments of the so-called type of Gates, are
used.
In the example as disclosed and represented, the conicity of the
instruments of the set varies only in one point, at the level of the
diameter D.sub.9. One could however provide the case where the conicity
will vary in more than one point, for instance at the level of the
diameter D.sub.9 and of the diameter D.sub.13 situated at 13 mm from the
point of the instrument.
In the same manner, the open-trumpet-shape of the instrument could be
achieved by a continuous variation of the angle of its cone. In this case,
the generating line of its surface will not be constituted by a broken
line, as in the case of the example which has been disclosed and
represented, but by a curve urging towards the central axis of the
instrument, beyond the end thereof.
Preferably, the conicity of the front part of the instrument, positioned
forward of the diameter D.sub.9 thereof, will be of the order of 2%, the
conicity of the rear part being variable from 4.5% to almost 6%.
The number of the instruments of the set could be greater or less than
five, which is the case of the example as disclosed and represented.
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