Note: Descriptions are shown in the official language in which they were submitted.
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MULTI-TAPERED DENTAL FILES
The present invention relates generally to endodontic
instruments and, more particularly, to root canal files used in
the cleaning of material present in the root canal of a human
tootli~ and for enlarging and shaping the root canal so that it
maybe prepared for filling.
A relatively common but difficult dental procedure is
the,'shaping, cleaning, and filling of the root canal of a
patient's tooth. In the performance of a root canal procedure,
a hole ' is first cut in the crown or exposed portion of the
tooth, typically either in the biting surface of the tooth, for
posterior teeth, or in the side of the tooth on the interior of
the jaw for incisor teeth. Small endodontic instruments known
generally as root canal files are then used to clean out the
material present in the root canal, and to impart a tapered
sliap~' to the , root canal so that filling material may be
inserted into the root canal to seal it.
,, ,
When a root canal is being cleaned and shaped, in one
particular preparation system, a series of files having
increasing diameters are used to gradually enlarge the root
canal.'yThe files are held between the thumb and forefinger of
one .hand by the dentist. Each file in one set of the known
prior~~art has an identical taper from one end to the other of
the''cut'ting flutes portion. For example, in a typical K-type
file~.:set the taper is 0.32 millimeters on every file over the
standard 16 mm length of cutting flutes, or 0.02 mm of taper/mm
of';f~.ute length. This taper is sometimes referred to as a
standard ISO (International Standards Organization) taper.
Although these file sets have identical tapers, they come in a
number:of sizes. The size number characterizing the file is
the,~;'diameter of the file at the tip in hundredths of a
millimeter, and the diameter of the file at the large end is
thus~,0.32 millimeters greater than this tip diameter. A
complete set will include sizes 06, 08, 10, 15, 20, 25, 30, 35,
40, 45; 50, 55, 60, 70, 80, 90, 100, 110, 120, 130, and 140,
while sizes 08-60 will typically be used. Some manufacturers
make certain half-sizes, or off-standard sizes.
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Root canals are seldom straight and there is always
the~possibility of causing irreversible damage to roots and
root,'canals during shaping procedures, depending on the
thinness of the root and severity and location of the root
canal curvatures. If too large a file is advanced too far into
a curved root canal, it may easily cut through the side of the
root; which is referred to as a perforation of the root, and
usually. the tooth must then be extracted.
' Another cause of root perforation is the inadvertent
introduction of large engine-driven Gates-Glidden or Peezo burs
into the middle third of thin, curved roots. Quite often, when
these burs are new and sharp, the operator will intend to use
one of the larger sizes only at the orifice of the canal but
will helplessly watch the'bur grab the canal walls and pull
itself.~into dangerous depths in the root.
' ' While perforation is probably the worst outcome of
mistakes in shaping procedures, there is a more common problem
in near-perforations and root weakening caused by overzealous
widening of the canal preparation. It is well documented in
the~endodontic literature that adequate shape in the cervical
two-thirds of the canal preparation is mandatory to accomplish
adequate cleaning of the canal, to provide necessary control of
instruments in the delicate apical regions of the canal, and to
effectively obturate the whole root canal space. However, it
is~.difficult to determine the fine line between creating
adequate access' and dangerous over-instrumentation, as all of
these procedures are accomplished in microscopic root canal
systems that are hidden from direct view.
Furthermore, if the tip of the file does not follow
the curvature of the canal and bores a passage branching out
from the root canal, which is referred to as ledging, surgical
correction of the problem is often necessitated. It is thus
apparent that the art of root canal shaping is one which
requires great skill to prevent damage to the tooth and to
Create a tapered canal preparation conducive to ideal filling
of 'the canal.
One technique used with a conventional set of files
having identical tapers to clean and shape the root canal is
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referred to as the "step-back" technique. A series of file
sizes from 08 to 60 (12 instruments) are introduced into the
canal from smallest to largest with each successively larger
file, being used farther back from the end of the canal.
Additionally, between four and six sizes of Gates-Glidden or
Peezo burs are similarly used in this step-back manner,
comprising a total of 16 to 18 instruments.
An improvement of the step-back procedure is
disclosed in my patent 6,053,735, entitled ROOT CANAL
PREPARATION METHOD, the disclosure of which is incorporated
herein by reference as though set out in haec verba. The
disclosed improved endodontic procedure includes using either
files or burs in a first crown-down procedure, then using the
instruments in a reverse sequence in a serial step-back
procedure, followed by finishing preparation of the root canal
with selected instruments in a second crown-down procedure.
Either conventional root canal files of standard taper or
variably-tapered files may be used.
My prior patent 5,897,316 discloses the use of
variably-tapered files in what is referred to as the Greater
Taper System. The disclosure of that patent is incorporated
by reference herein as though set out in haec verba.
The purpose of endodontic shaping procedures is to
create a continuously tapering preparation which is narrowest
at the end of the canal, and widest near the crown of the
tooth By using files that vary in their tapers, it has been
determined that root canals may often be prepared by using a
single shaping file instead of the 16 to l8 files required by
conventional ISO-tapered instruments. While it is readily
apparent that the use of only one tool instead of 16 to 18
tools is desirable from the standpoint of efficiency, it should
also be noted that the use of variably tapered files provides
for. ideal root canal shaping results by practitioners having
less,training and experience. Rather than creating a tapered
carialy shape by the difficult and time-consuming step-back
technique, the Greater Taper Systems simply requires that a
shaping instrument of appropriate taper be worked to the full
length of the canal. In addition to the greatly improved ease
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and simplicity o:f shaping canals with a single instrument, this
s
provides, for the first time, a pre-defined shape throughout
the full length of the canal.
One of the most important advantages provided by pre
y defined root canal preparations is the resultant ability to
optimize cleaning and filling procedures in root canal systems.
Since the design of files taught by the Greater Taper System
involves different tapers, the tips of the shaping files are
not used to cut a path in the canal as in files with standard
tapers. Whereas standard ISO file sets have the same tapers
but increasing tip diameters in the sequence of:files, the tip
diameters of a set of shaping files of the Greater Taper
SystemT'~ may be the same for files of different tapers. There
may also be different sets of these~shaping files which differ
in their tip diameters, i.e. one set of shaping files with
tapers'of .04, .06, .08, .10, and .12 mm/mm and the same 0.2 mm
~,
tip diameters; another set of shaping files with the same range
oftapers but with 0.35 mm tip diameters, etc. And finally,
the,Greater Taper SystemTM includes sets of shaping files with
" ,
similar non-ISO tapers which vary by evenly or proportionally
increasing tip diameters.
Moreover, shaping files of the Greater Taper SystemT'°I
can be safely used in curved canals and/or thin roots in spite
of ~ their greater rates of taper. This is accomplished very
effectively by the specification of progressively shorter flute
lengths as files in a set have progressively greater tapers,
thereby~limiting their maximum flute diameters. Without this
feature, the shank-end flute diameters of variably-tapered
shaping files become wider and stiffer as the tapers of these
instruments increase, and their potential for lateral
perforation or weakening of the root increases as well.
While limiting the maximum flute diameter of these
increasingly tapered shaping files allows their safe use, this
feature is extremely important in a broader sense. Using a
single shaping file instead of the usual 15-18 instrument set
means that the final shape through the full length of that
canal is pre-defined, unlike the shaping result when six
different sizes of Gates-Glidden burs are used progressively
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shallower in the coronal portions of~the root canal. It is
extremely common for Gates-Glidden and Peezo burs to be used
too, deeply in thin roots, risking weakening and perforation.
,..
Simply limiting the maximal flute diameters of shaping files
allows, for the first time in the field of endodontics,
enlargement of the coronal two-thirds of a canal to an extent
that~is exactly adequate to clean the tiny apical regions of
the. canal and to maintain control ~of shaping and filling
instruments in that region, but not a bit larger.
When shaping files are used with rotary cutting
motions two primary problems are encountered, potential for
breakage and slowness of cutting. This is overcome in the
Greater Taper SystemTM by varying the flute pitch from an in-
line.reamer-like angle at the shank end of the instrument to a
more ;perpendicular K-type flute angle at the file tip. Instead
of,for in addition to, the above, the relative sharpness of the
cutting flutes is varied along the length of the files, being
sharpest at the strong shank end to allow for aggressive
cutting by the wider flutes, and dullest near the smaller, more
fragile tip of the file so these flutes can easily release from
the canal wall during rotation, thereby preventing file
breakage which can occur when the tip binds.
Despite the many benefits from using the files of the
Greater Taper SystemTM and the substantial improvements in those
files~as noted hereinabove, they still involve files having a
constant or fixed taper from shank to tip despite the
variability of taper from file to file. I have found that
there are occasions when the preparation of a particular root
.,
canal calls for a certain taper in one portion and a different
taper in another portion which at present requires that
different files be used to achieve the objective. I have
devised a multi-tapered file which presents at least two
different taper angles at different points between tip and
shank which substantially improve efficiency in preparing a
root canal. This multi-tapered file can be used to advantage
in,each of the procedures described hereinabove, as well as in
other procedures in the general field of endodontics.
In brief, particular arrangements of the present
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invention comprise tapered root canal files having at least two
different angles or degrees 'of taper along different portions
of their flute sections. For example, one particular file in
accordance with the present invention comprises a first portion
adjacent the tip of the file which has a 0.12 taper. This
extends over a selected distance back from the tip to a second
portion adj acent the shank in which the taper changes to a 0 . 02
taper (the standard ISO taper). This file is one of a set of
four, all having the same lengths from file to file for the
first and second portions, respectively, and the same 0.02
taper for the second portions, but in which the taper of the
first portion diminishes from file to file. The first file is
that having the 0.12 taper for the first portion. The next
file~has 0.10 taper for the first portion with the third. and
,. :, .
fourth files having a first portion taper of 0.08 and 0.06,
respectively. A second set of files is exactly like the just
mentioned set in all respects except for the taper in the
second portion being established at 0.04 mm/mm. For purposes
of distinguishing nomenclature, these two sets of files will be
designated as being in a first Group of files.
In another arrangement in accordance with the present
invention, multi-tapered files are provided in two similar sets
of:four which have their first portions of varying lengths;
ie: extending varying distances back from the tip. Since the
length; of the cutting portion of the file is the same from file
to file, as the length of the first portion increases with
diminishing tapers of 0.12, 0.10, 0.08 and 0.06, respectively,
.r
the~lengths of the second portions diminish accordingly. As
with'the two sets of files in the first Group, these two sets
offiles are provided with tapers of 0.02 and 0.04 mm/mm,
respectively, over the extent of the second; flute portion
adjacent the shank. These two sets of files will be referred
.:
to ws being in a second file Group.
A third Group comprises a single set of four files
which, like the first Group files, have equal lengths from file
to 'file of the first and second portions respectively.
However, in this third Group, the taper of the second portion
varies inversely with the variation in taper of the first
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portion from file to file. That is, as the taper of the first
portion of the Group III files diminishes from 0.12 for the
first file through 0.10 and 0.08 to 0.06 for the fourth file,
the taper of the second portion increases from 0.01 mm/mm for
the first file through 0.02 and 0.03 to 0.04 mm/mm for the
fourth file.
The files of a fourth Group are like the files of the
second Group in that the lengths of the first and second
portions vary from file to file: i.e., beginning with the first
file, which has,the shortest first portion and thus the longest
second portion, the length of the first portion increases from
file; to file while the length of the second portion decreases
correspondingly. The taper of the first portion reduces from
file. to file, starting with a 0.12 taper, and reducing
progressively to 0.06 taper in the fourth file. ~ In this fourth
Group,v~unlike the second Group where the taper of the second
portion' is the same from file to file in a given set, the taper
of,the second portion increases from file to file as the taper
of the first portion reduces. Thus, for files in the fourth
Group, as the taper of the first portion reduces from 0.12
through 0.10 and 0.08 to 0.06 the tapers of the second portion
are. increasing from file to file. For a~file in the fourth
Group having a first portion taper of 0.12, the taper of the
second portion is 0.01. For the second file, which has a first
portion taper of 0.10, the taper of the second portion is 0.02.
For the third file with a first portion taper of 0.08, the
second. portion taper is 0.03. The fourth file has a first
portion taper of 0.06 while the taper of the second portion is
0.04;
Thus, arrangements in accordance with the present
invention provide multi-tapered sets of four files each. They
may'extend to sets of five or six, where appropriate. For
purpose of disclosure, these are organized in Groups I-IV.
Some of the Groups comprise two sets of files; some comprise a
single set, each having at least two portions of distinctly
different tapers. In each set, the tapers of the first
portions vary from one file to the next, beginning with a taper
of 0.12 for the maximum taper file and decreasing successively
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through 0.10 and 0.08 to the minimum taper file of 0.06 in the
first portion. Where the sets extend to five or six files, the
minimum taper of the first portion is 0.04 or 0.02,
respectively. In Groups I and II, one set comprises files
having a standard taper of 0.02 in the second portions thereof,
while: the other set provides a taper of 0.04 in the second
portions of the files.
The groups may also be distinguished by the
respective lengths of the two portions of a particular file.
In Groups I and III, the first portions of the files are all
the'same length. The lengths of the second portions are also
consistent from file to file. In the other Groups of files,
the~length of the first portion is shortest for the greatest
taper~(0.12) and increases correspondingly as the taper of the
first portion of the files reduces to the minimum taper at
0.06, with the lengths of the second portions being adjusted
accordingly. There may be additional files where the taper of
the~~first portion is 0.04 or 0.02, where appropriate.
In other Groups of files (Groups III and IV), the
tapers of the second portions of the files in a given set are
not fixed but vary inversely with the tapers of the first
portions ~ i . a . , as the tapers of the first portions reduce from
file to file, the tapers of the second portions increase.
In Groups II and IV, the location of the change
between tapers of the first and second portions varies in
distance from the tip. As that distance increases, from file
to vfile, the length of the second portions diminishes
accordingly.
It is possible to incorporate this multi-taper
feature in the various versions described above in files having
various types or forms of flutes, such as the K-type files and
the~Hedstrom-type files described hereinabove. Moreover, the
mult~i-taper feature of the present invention may be
incorporated in files having one or more helicoidal flutes or
in files having at least a single axial cutting edge.
One particular benefit of these particular
arrangements in accordance with the present invention stems
from their ability to clean out and shape the coronal portion
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of a, root canal, after which the flute portion adjacent the
.,.
shank takes over the shaping of the remaining portion of the
root canal, maintaining the desired taper of the second portion
of the selected file as the file is moved farther into the root
canal.
In the accompanying drawings:
FIG. 1 is a schematic view of a root canal in a
tooth, with a portion to be removed during root canal shaping
procedures shown in broken lines;
FIG. 2 shows a conventional ISO file of the prior
arty
;, , FIGS. 3A-3D are schematic views of a first Group of
four; multi-taper files in accordance with the present
inveiiti,on
.. .
~ FIGS. 4A-4D are schematic views of a second Group of
four '~ multi-taper files in accordance with the present
invent i'on
FIGS. 5A-5D are schematic views of a third Group of
four multi-taper files in accordance with the present
invention;
FIGS. 6A-6D are schematic views of a fourth Group of
foutr multi-taper files in accordance with the present
- invention; and
FIGS. 7A-7D are schematic cross-sectional views of
four 'different cross-sectional shapes for the cutting flutes of
thevmulti-taper files of the present invention.
In th'e schematic diagram of FIG. 1, a tooth 10 is
shown located in the bone 12 of a patient's jaw. The tooth 10
is an,incisor, and the opening in the crown of the tooth 10 is
cut.on the side of the tooth in the interior, which opening is
generally indicated at 14. The tooth 10 has a nerve canal 16
extending to the tip of the tooth which is embedded in the bone
12. ~'~.~~In the preparation of a root canal, the nerve canal 16 and
surrounding portion within the broken outline 14 is to be
removed,, for' subsequent filling with materials used in
completion of the root canal.
FIG. 2 shows a conventional root canal file of the
prior~art having a handle 22 supporting the file 20. The file
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has.a flute length X, a shank diameter Y and a tip diameter Z.
In.a'standard ISO file of this type, X equals 16 mm, Y equals
0.32 mm plus Z, and Z varies with the size of the file,
beginning at 0.06 mm for the smallest file and increasing to
1.4'mm for the largest file. The smallest file has a sharp tip
24, which is needed since each successive file in the series
has a larger diameter at the tip.
FIGS. 3A-3D schematically represent sets of four
multi-tapered files 31, 32, 33 and 34 in accordance with the
present invention. Each of the files is shown with a first
portion A adjacent the tip 40 and a second portion B remote
from , the tip, extending back to the shank, not shown. The
portions A and B have different tapers in the same file and the
taper in the first portion also varies from file to file. In
file 31 the taper of the first portion is 0.12. In file 32,
the:taper of the first portion is 0.10. In file 33, the taper
of the first portion is 0.08. In file 34, the taper of the
first portion is 0.06. For smaller files the taper of the
first portion may be 0.04 or 0.02, as appropriate. The same
variation of taper of the first portion from file to file of a
given set applies to all of the file sets disclosed herein.
In a first set of files represented by FIGS. 3A-3D,
the taper of the second portion B is 0.02 mm/mm. In a second
set of'files, also represented by the drawings of FIGS. 3A-3D,
the~taper of the second portion B is 0.04 mm/mm. The files of
FIGS. 3A-3D are the Group I files discussed hereinabove.
FIGS. 4A-4D schematically represent different sets of
files from those of FIGS. 3A-3D. These are the Group II files
discussed above. FIGS. 4A-4D show files 41, 42, 43 and 44 in
a mufti-tapered configuration. In each of the files 41-44,
there is a first portion A adjacent the tip 50,and a second
portion B remote from the tip, extending to the shank. In
these sets of files, each of the first portions is a different
length from those of the other first portions, being shortest
for the file 41 which has the greatest taper of the first
portion A (0.12) and increasing successively for files 42, 43
and 44 as the taper of the first portion diminishes. As with
the sets of files 31-34 of Group I, one set of files 41-44 has
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a taper of 0.02 mm/mm for the second portion B whereas another
sethas a taper of 0.04 mm/mm for the second portion B.
The respective lengths of the first and second
portions of the files of the files of the present invention are
detei~~mined on the basis of a number of factors, such as the
material of the files (whether nickel titanium, stainless steel
or-~some' other material), the specific tapers of the first and
second.portions~, file diameters, and the like. Selection of
the length L of the first portion fixes the length of the
second portion as 16-LA (for a file having a flute length of 16
mm.)'.
FIGS. 5A-5D schematically represent another set of
four,multi-tapered files 51, 52, 53 and 54 in accordance with
the :present invention. Each of the files is shown with a first
portion A adj acent the tip 60 and a second portion B remote
frorii:'the tip, extending back to the shank, not shown. The
portions A and B have different tapers in the same file and the
",
taper~in the first portion also varies from file to file. In
:c
fiTe''~51 the taper of the first portion is 0.12. In file 52,
theltaper of the first portion is 0.10. In file 53, the taper
of~'t$e'first portion is 0.08. In file 54, the taper of the
first portion is 0.06.
' ' ' ~ In these files 51-54, the taper of the second portion
varies from file to file, increasing in taper as the taper of
the'fi.rst portion reduces. For the file 51, the taper of the
second portion is 0.01 mm/mm~ for the file 52, it is 0.02 for
1~
the file 53 it is 0.03; and for the file 54 the taper of the
second portion is 0.04 mm/mm. The files of FIGS. 5A-5D are the
Group III files discussed hereinabove.
;~ ~ FIGS. 6A-6D schematically represent still another set
of files in accordance with the invention, the Group IV files
discussed above. FIGS. 6A-6D show files 61, 62, 63 and 64 in
a inulti-tapered, configuration. In each of the files 61-64,
there is a first portion A adjacent the tip 70 and a second
portion, B remote from the tip, extending to the shank. In this
set~of files, each of the first portions is a different length
from'those of the other first portions, being shortest for the
file : 61 which ~ has the greatest taper of the first portion A
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(0:12) and increasing successively for files 62, 63 and 64 as
the. taper of the first portion diminishes, beginning at 0.10
for file 61 and extending to 0.06 for file 64. Smaller tapers
of~0~04 and 0.02 may be provided in fifth and sixth files, as
appropriate, if desired.
Thus the ratio of taper of the first portion to taper
of the second portion ranges between 3 and 6 for the set of
Group I files with a second portion taper of 0.02. Where the
smallest taper of the first portion is 0.02, the range of taper
ratios is from' 1 to 6.
In these files 61-64, the taper of the second portion
varies from file to file, increasing in taper as the taper of
the first portion reduces. For the file 61, the taper of the
second portion is 0.01 mm/mm; for the file 62, it is 0.02; for
the file 63 it is 0.03; and for the file 64 the taper of the
second portion is 0.04 mm/mm.
As a result of the use of multi-tapered files in
accordance with the invention for the preparation of root
canals in teeth, a better result can be obtained in less time
and'with resort to a lesser number of files. As one of the
multi-tapered files is driven deeper into the root of a tooth,
different portions of the cutting flute at different depths of
the .file become effective to shape the root canal to a finished
configuration in preparation for receiving the gutta percha or
other filling materials.
These files have been described as individual files,
having handles of the type shown in FIG. 2. However, these may
as well be adapted as instruments for use in powered drives.
The files may be of different shapes and cross
sectional configurations, corresponding but not limited to the
shapes represented schematically in FIGS. 7A, 7B, 7C and 7D.
FIG. 7A shows an instrument 120 in cross section with
three cutting edges 122, 124 and 126. Between the cutting
edges 122, 124 and 126 are three faces 123, 125 and 127,
respectively. These faces are generally shaped in cross
section to provide a positive rake angle or improved cutting
edges at 122, 124 and 126.
FIG. 7B shows an instrument 130 in cross section with
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three cutting edges 132, 134 and 136. Between the cutting
edges.~are three faces 133, 135 and 137. Each of the faces is
concave in cross section with a radial land as the flute edge.
The configuration of FIG. 7B provides improved cutting edges
132;'134 or 136; with reduced manufacturing costs compared to
FIG:.7A.
FIG. 7C shows, in cross section, an instrument 140.
'~his.instrument has a triangular cross section with planar
faces 143, 145 and 147 between cutting edges 142, 144 and 146.
FIG. 7D shows, in cross section, an instrument 150.
This; instrument, unlike the others, has two opposed cutting
surfaces 152, 154.
Although there have been described hereinabove
various specific arrangements of a MULTI-TAPERED DENTAL FILES
in,'accordance ~ with the invention for the purpose of
illustrating the manner in which the invention may be used to
advantage, it will be appreciated that the invention is not
liiriited thereto. Accordingly, any 'and all modifications,
variations or equivalent arrangements which may occur to those
skilled in the art should be considered to be within the scope
of the invention as defined in the annexed claims.
13
