Note: Descriptions are shown in the official language in which they were submitted.
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ANTI--C~RVATU~E DENTAL ROOT CANAL SHAPING FILE
3 ~ackground of the Invention
4 1. Field of the Invention.
The present invention relates generally to endodontic instruments
6 and, more particularly, to root canal files or reamers used in the
7 cleaning of material present in the root canal of a human tooth and for
8 enlarging and shaping the root canal so that it may be prepared for
9 filling.
~. Description of the Prior Art.
11 A relatively common but difficult dental procedure is the
12 cleaning and filling of the root canal of a patient's tooth. In the
~3 performance of a root canal procedure, a hole is first cut in the crown
14 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
16 interior of the jaw for incisor teeth. Small endodontic instruments
17 known generally as root canal files are then used to clean out the
18 material present in the root canal, and to shape the root canal so that
19 a tapered filling material may be inserted into the root canal to fill
it. An exa~ 1~ of such an instrument, also called a broach, is shown in
~ -. c~ ~.~ S S
21 /Patent Des. 250,54~.
22 Two types of instruments are in general use as root canal files,
23 namely the Hedstrom instrument and the K-type instrument. The K-type
24 instrument is an axially twisted, tapered, triangular or square
cross-sectional shaft which has three or four spiral cutting edges along
26 the tapered shaft and a conical tapered tip on the end thereof. The
27 Hedstrom-type instrument is a lathe-cut file having a round tapered
~8 shaft with one or two spiral cutting flutes machined into the shaft all
29 the way to the tip. The main difference resulting from the construction
of the two types of files is that the K-type file will cut in either
31 rotational direction, or when moved up and down, while the Hedstromrtype
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1 file will cut only when moved up and down in the root canal.
2 When a root canal is being cleaned and shaped, a series of files
3 having increasing diameters is used to gradually enlarge the root canal.
4 The files are held between the thumb and forefinger of one hand by the
dentist. Each file in a set of the known prior art has an identical
6 taper from one end to the other. For example, in a typical K-type file
7 set the taper is 0.32 millimeters on every file, with the files coming
8 in a number of sizes. The size number characterizing the file is the
9 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
11 than this tip diameter. A complete set will include sizes 06, 08, 10,
12 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 110, and 120,
13 while sizes 8-60 will typically be used. Hedstrom-type instruments
14 similarly come in sets of increasing size, typically from 0.10 to 1.40
millimeter tip size, with .15-.60 millimeter tip sizes typically being
16 used.
17 Unlike the files, root canals are seldom straight. If the files
18 which are used deviate substantially from the original curvature of the
19 root canal, the tooth may be irreversibly damaged. If the file is too
straight and cuts through the side of the root, which is referred to as
21 a perforation of the root, the tooth must then be removed. If the tip
22 of the file does not follow the curvature of the canal and bores a
23 passage branching out from the root canal, which i9 referred to as
24 ledging, surgical correction of the problem is necessitated.
It is therefore apparent that the files must be bent prior to
26 insertion into the root canal and use of the files to prepare the root
27 canal. In addition to bending the file, it is necessary to pull a
28 precurved file along the outside of the canal curvature when shaping the
canal to avoid perforating the root. This technique is called an
31 1
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1 anti-curvature motion, is difficult to teach to dentists, and is
2 time-consuming for even the most skilled practitioners to perform.
3 It is thus apparent tha t the art of root canal filing is one
4 which requires great skill to prevent damage to the tooth. The
~ technique used with a set of files having an identical taper to clean
6 and shape the root canal is referred to as the "step-back" technique,
7 with each successively larger file being used further back from the end
8 of the canal. This technique is, at best, a difficult and
9 time-consuming method.
A slightly different file is disclosed in U.S. Patent 4,536,159,
11 to Roane. The Roane file rounds the cutting edges near the tip of the
12 file, in an attempt to prevent the file from ledging the root canal.
13 While the Roane file may reduce or eliminate occurrences of ledging, it
14 will not do anything about the more serious problem of perforating the
15 curved roots of teeth~
16 Other types of files have been developed for similar purposes.
17 The U.S. patent 4,260,379 of Graves et al discloses a file of rhomboidal
18 cross section in which a tapered blade is ground to develop an oblique
19 parallelogram and twisted. McSpadden patent 4,299,571 discloses a file
20 with a blunt tip with approximately 3 mm of non-cutting file provided
21 adjacent the end. Patent 4,332,561, also of McSpadden, combines the
22 pilot tip of the earlier McSpadden patent with a double fluted design to
23 develop a Hedstrom-type file.
24 It is therefore apparent that it would be desirable to have a
2~ e design which coald eliminate or redace the instrnces of both
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1 ¦ ledging and perforation. Achieving these objectives is the main object
2 ¦ of the present invention. In adaition, it is an object of the present
31 invention to minimize the time and effort necessary to clean and shape
4 ¦ the root canal. Finally, the present invention also seeks to reduce the
51 level of training and skill necess~ry to properly perform root canal
6 ¦ operations.
7 l
~¦ Summarv of the Invention
9¦ The disadvantages and limitations of the background art discussed
10 ¦ above are overcome by the present invention. The present invention
11 ¦ differs significantly and advantageously from the files discussed above
12 ¦ in two respects. ~irst, rather than using a series of files of
13 ¦ differing sizes but the same taper, the present invention uses a series
14 ¦ of files with different tapers. Secondly, one side of the files does
15 ¦ not have a cutting surface thereon.
16 With regard to the first feature of the present invention,
17 ¦ several advantages over the art are achieved by using files with
18 ¦ different tapers. ~he purpose of endodontic shaping procedures is to
19 ¦ create a continuously tapering preparation which is narrowest at the end
20 ¦ of the canal, and widest near the crown of the tooth. Rather than doing
21 ¦ this by the difficult and time-consuming step-back technique, the
22 ¦ present invention uses progressively greater tapers on a succession of
23 ¦ files to effectively and efficiently clean and shape the root canal.
24 l By using a series of files with differing tapers, it has been
25 ¦ determined that the root canal may be prepared by using only three or
26 ¦ four files instead of the nine or ten files required by conventional
27 files. While it is readily apparent that the use of only three or four
28 ¦ tools instead of nine or ten tools is desirable from a standpoint of
29 ¦ efficiency, it should be noted that the result is at least as good as
30 ¦ that obtained by conventional files, and in most cases the result is
31 ~ better.
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1 Since the design of files taught by the present invention uses
21 different tapers, the tip of the file is not used to cut as in files
31 with a standard taper. Whereas standard file sets have increasing tip
41 diameters in the sequence of files, the tip diameters of files
5 ¦ constructed according to the present invention are all identical or
6 ¦ nearly identical. Under the present invention, the difference in file
7 ¦ size occurs along the files in increasing amounts from the tip to the
8 ¦ end nearest the bandle, and it is at the end nearest the handle that the
9 ¦ largest variation in diameter between files occurs.
10 ¦ Since the tip size remains constant under the present invention,
11 ¦ and since the tip is not used for cutting to the extent in previous file
12 ¦ designs, the tip may be rounded, thus preventing ledging of the root
13 I canal. This benefit is obtained as an incidental advantage to the
14 varying of tapers between files.
The second important difference between the present invention and
16 the art is that files constructed according to the teachings of the
17 present invention have a ~safe edgeU on the cutting flutes. ThiS safe
18 edge is along one side of the file, and will not cut when the file is
19 used. By properly positioning the file, the safe edge will be facing
the inside curvature of the root canal, and will not cut through the
21 side of the root even if the file is not properly bent. It may thus be
22 perceived that the problem of perforating the root is also eliminated by
23 the files of the present invention.
24 In addition, since the anti-curvature motion is no longer
necessary, the time as well as the skill needed to perform the root
26 canal procedure is greatly reduced. The present invention thus
27 represents a great improvement in the dental arts, in that the procedure
28 is simpler, easier, and requires fewer tools. In addition, the
29 potential negative effects of the performance of a root canal, namely
perforating the root or ledging the canal passage, are essentially
32 eliminated. The present invention achieves these advantages with no
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1 relative disadvantages.
3 ~rief Description of the Drawing
4 A better understanding of the present invention may be had from a
consideration of the following detailed description, ~aken in
6 conjunction with the accompanying drawing in which:
7 Fig. 1 is a somewhat schematic view of a root canal in a tooth,
8 with the portion to be removed shown in dotted lines;
9 Fig. lA shows a conventional Hedstrom-type file;
Fig. 2 shows the final intrusion of the tips of each of eleven
11 conventional files into the root canal of Fig. 1, thereby illustrating
12 the step-back technique;
13 Fig. 3 is a schematic view of the conventional file of Fig. lA
14 being used to clean and shape the root canal, and specifically
illustrates both perforating and ledging of the root canal;
16 Fig. 4 shows the seven sizes of variable taper filling material
17 which are co~ercially available for selection in filling a prepared
18 root canal;
19 Fig. 5 illustrates the seven sizes of files of comparable
dimension, constructed according to the teachings of the present
21 invention, with the handles removed for purposes of the illustration
22 from six of the files;
23 Fig. 6A illustrates the cutting portion of one of the files of
24 Fig. 5, specifically showing the rounded tip, and also the safe edge in
plan view;
26 Fig. 6B illustrates the cutting portion of one of the files of
27 Fig. 5, specifically showing the rounded tip, and also the safe edge in
28 side view;
29 Fig. 7A shows the flat surface of the handle of one of the files
of Fig. 5, which is used to orient the safe edge of the file, in plan
31 view;
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1 Fig. 7B shows the flat surface of the handle of one of the files
2 of Fig. 5, which is used to orient the safe edge of the file, in side
3 view; and
4 Fig. 8 shows a precision template for measuring taper size for
selecting a file or a filling.
7 Detailed Description of the Preferred Embodiment
8 Before discussing the present invention, it is helpful to discuss
9 briefly the root canal procedure as shown in Eigs. 1-3. Fig. 1 shows a
tooth 10 located in the bone 12 of a jaw. The tooth 10 in Fig. 1 is an
11 incisor, and the opening in the crown of the tooth 10 is cut on the side
12 of the tooth 10 in the interior side of the jaw (not shown), which
13 opening is generally indicated at 14. The tooth 10 has a root canal 16
14 therein, extending from the interior of the crown of the tooth 10 to the
tip of the tooth 10 which is embedded in the bone 12.
16 Also shown in Fig. lA is a Hedstrom-type file 20, having a handle
17 22 supporting the file 20. The file 20 has a sharp tip 24, which is
18 needed since each successive file in a series has a larger diameter at
19 the tip. It should be noted that while the discussion of the prior art
uses as an example a Hedstrom-type file, it is equally applicable to
21 other configurations of like-tapered root canal file designs.
22 Similarly, as will become evident later, the description of the
23 preferred embodiment will discuss modifications to a HedstrOm-type file,
24 and this discussion will also not be a limitation of the present
invention to use with a Hedstrom-type design.
26 Referring now to Fig. 2, the file 20 is shown inserted into the
27 root canal 16, which is enlarged from the view shown in Fig. 1. With
28 conventional files, the step-back technique discussed above is used,
29 with each progressively larger file being inserted shallower and
shallower into the root canal 16. The nu~ers along the root canal 16
312 near the tip end of the root canal 16 represent the maximum extent to
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1 which different size files are inserted, with file sizes from 10 to 60
2 ( representing tip diameters from 0.10 to 0.60 millimeters) being used.
3As mentioned above, between nine and eleven files are re~uired, with
4more occasionally being necessary.
5Referring next to Fig. 3, the file 20 is shown inser ted into a
6root canal 30 in a molar tooth 32. As apparent, for the molar tooth 32
7a hole 34 to admit the file 20 is present in the biting surface of the
8tooth 32. Since the file 20 was not curved enough, it has perforated
9the curved root canal 30 at the location indicatea by the reference
10numeral 36. As mentioned above, perforation can also occur when the
11file 20 is not pulled against the outside curve of the root canal 30 by
12using the anti-curvature motion discussed above.
13Another problem shown in Fig. 3 is that the tip 24 of the file 20
14 has left the root canal 30 and cut a ledge along the outside curvature
15 of the root canal 30. Succeeding files may well become trapped in the
16 ledge also, and will not properly clean and shape the root canal 30.
17 The present invention eliminates both perforation and ledging of a root
18 canal, and in addition makes the root canal operation quicker and easier
19 to perform.
20There are, as mentioned previously, seven varying tapers for root
21 canal filling materials available from one particular vendor. These are
22shown in Fig. 4. The variable taper filling materials 41, 42, 43, 44,
2345, 46, and 47 vary in size with 41 being the smallest and 47 being the
24 largest.
25The preferred embodiment uses a series of seven files 51, 52, 53,
2654, 55, 56, and 57, which are shown in Fig. 5. ~ypically, only three or
27 four files will be used in cleaning and shaping the root canal, a vast
28 improvement over the art. Although only file 57 is shown with a handle
29 48, all of the files have handles, of course. The files 51, 52, 53, 54,
3055, 56, and 57 all have the same small diameter at the tips, with
31 different diameters at the ends opposite the tips, and hence different
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1 ¦ tapers.
2 ¦ This is a crucial departure from the art, the result of which,
3 ¦ with the other modifications described below, makes the root canal
41 procedure much quicker and easier to perform. Since the tip diameter of
5 ¦ each file 51, 52, 53, 54, 55, 56, and 57 is identical or nearly
~ ¦ identical, each file will be inserted all the way, unlike the previously
7 ¦ known files discussed above in conjunction with Fig. 2. The sizes of the
8 ¦ files 51, 52, 53, 54, 55, 56, and 57 correlate eYactly to the sizes of
9 ¦ the corresponding tapered filling materials 41, 42, 4~, 44, 45, 46, and
10 1 47.
11 ¦ Referring next to Figs. 6A and 6B, the other two features
12 ¦ constituting improvements over the prior art are apparent. The file 57,
13 ¦ like the other files 51, 52, 53, S4, 55 and 56, which are not shown in
14 ¦ detail, has a rounded tip 60, which will effectively and completely
15 ¦ prevent ledging. The rounded tip 60 is possible since all of the files
16 ¦ 51, 52, 53, 54, 55, 56, and 57 have the same or nearly the same small
17 ¦ tip diameter. This small tip diameter is small enough to allow entry of
18 ¦ each file all the way into the root canal.
19 ¦ Another feature of the preferred embodiment is also shown in
20 ¦ Figs. 6A and 6~. On one side of the file 57 there is a safe edge, which
21 ¦ cons~itutes a number of flat surfaces 62 on the otherwise sharp cutting
22 ¦ edges on that side of the file 57. The flat surfaces 62 may be machined
23 ¦ or polished onto the side of the file 57. Likewise, the files 51, 52,
24 53, 54, 55, and 56 all have safe edges.
By orienting the safe edge toward the inside curve of the root
26 canal when a file is in the root canal, perforating the root canal is
27 prevented. ~his obviates the need to use the anti-curvature motion
28 discussed above, and thereby minimizes both the time and level of skill
29 needed to clean and shape the root canal. The file 57 may be positioned
by providing a flat surface 64 on the handle 48, which flat surface 64
33l is oriented with the flat surfaces 62 on the file 57, as shown in Figs.
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1 7A and 7B.
2 Fig. 8 shows a precision template 70, having seven areas 71, 72,
3 73, 74, 75, 76, and 77 which are sized to exactly admit the seven
4 variable taper filling materials 41, 42, 43, 44, 45, 4Ç, and 47. The
template 70 may be used to select the size file to be used by
6 superimposing the template 70 on an X-ray of the tooth.
7 It may now be appreciated that the present invention possesses a
8 number of advantages over the art. Both ledging and perforating of the
9 root canal are prevented. Only three or four files of the present
invention are needed to perform a root canal operation, compared with
11 nine or eleven for other files. The root canal operation is easier,
12 safer, and more efficient to perform when using the files of the present
13 invention. Finally, since the files of the present invention gradually
14 expand the taper created in the root canal (instead of creating the
tapered enlarged root canal area in nine or ten segments virtually
16 guaranteed to be anything but smooth), the taper created in the root
17 canal is perfectly smooth, and will exactly fit the selected tapered
18 filling material corresponding to the last file used. Tbe present
19 invention brings with it no attendant disadvantages, and therefore
represents a highly desirable improvement in the art.
21 Although there have been described above specific arrangemen~s of
22 an anti-curvature dental root canal shaping file in accordance with the
23 invention for the purpose of illustrating the ~anner in which the
24 invention may be used to advantage, it will be appreciated that the
invention is not limited thereto. Accordingly, any and all
26 modifications, variations or equivalent arrangements which may occur to
27 those skilled in the art should be considered to be within the scope of
28 the invention as defined in the annexed claims.
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