CA1286128C - Anti-curvature dental root canal shaping file - Google Patents

Abstract

ANTI-CURVATURE DENTAL ROOT CANAL SHAPING FILE

Abstract of the Disclosure A series of instruments for use in cleaning and shaping the root canal of a tooth is disclosed. The instruments are files having increasing tapers on sequentially-used files, with all of the files having the same, or nearly the same, small diameter at the tip of the cutting surface. The files create an increasingly tapered aperture in the root canal, which is exactly sized to admit a selected one of a set of variable taper filling materials available for filling a prepared root canal. Each file also has a safe edge to eliminate perforating the root canal, a rounded tip to eliminate ledging, and a handle shaped to provide a tactile reference to the orientation of the safe edge.

Description

~Z86128 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 -1- ~

12~361Z8 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 lZ861Z8 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 ~ 12t~61,>8 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.

I 12861~8 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 12~612~

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;

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 .

12t~6128 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 12~61~ 1 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.

_g_ ~286128 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.

Claims (19)

WHAT IS CLAIMED IS:

1. An endodontic instrument for cleaning and shaping a root canal in a tooth, comprising:
a first file having thereon a tapered portion, said tapered portion having a larger diameter at one end thereof and a smaller diameter at the other end thereof, said first file having a tip at the end of said tapered portion having said smaller diameter;
cutting edges disposed on said tapered portion about the circumference thereof, with the cutting edges being altered along substantially the entire extent of one longitudinal side of said tapered portion; and a rounded surface disposed at said tip of said first file.

2. An endodontic instrument as defined in claim 1 comprising a plurality of files, each having a tapered portion with cutting edges disposed thereon about the circumference and the cutting edges being altered along substantially the entire extent of one longitudinal side of the tapered portion, each file of said plurality having a different taper from the others, said files increasing in taper from the first to the last of said plurality.

3. An endodontic instrument as defined in claim 2 wherein the taper of said tapered portion of each file corresponds respectively to the taper of a series of variable taper filling materials available to fill a prepared root canal.

4. An endodontic instrument as defined in claim 1 additionally comprising:

a handle mounted on said file at the end of said tapered portion having the larger diameter, said handle having a tactile identifying element thereon, which identifying element is oriented relative to said longitudinal side of said tapered portion with said cutting edges being altered.

5. An endodontic instrument as defined in claim 4 wherein said handle is essentially round in cross-section, and said identifying element comprises a flat side on said handle.

6. An endodontic instrument as defined in claim 3 further comprising in combination therewith:
a template having a plurality of shapes therein corresponding to the sizes of variable taper filling materials, said template being for use as a reference in selecting the size of the taper of the corresponding file.

7. An endodontic instrument as defined in claim 3 wherein the files having the smaller taper are for use prior to use of the files having a larger taper.

8. A file for cleaning and shaping a root canal in a tooth, comprising:
a tapered shaft having a smaller diameter at one end thereof and a larger diameter at the other end thereof, a plurality of cutting surfaces located in said tapered shaft from said larger diameter end nearly to said smaller diameter end;

a safe edge on said file resulting from the dulling of said cutting surfaces along one entire longitudinal side of said tapered shaft; and a rounded surface machined onto the tip of said shaft at the end of said shaft having said smaller diameter.

9. A plurality of files as defined in claim 8, each file having a different degree of taper from the others, the degree of taper of the files corresponding respectively to the sizes of variable taper filling materials available for filling root canals.

10. A series of files for use in succession in cleaning and shaping a root canal in a tooth, comprising:
a first shaft having a first taper, said first shaft having a smaller diameter at one end thereof and a larger diameter at the other end thereof, said first shaft having cutting surfaces located therein from said larger diameter end nearly to said smaller diameter end, said cutting surfaces having been dulled along one longitudinal side of said first shaft, said first shaft having a rounded tip at the end of said first shaft having said smaller diameter; and a second shaft having a second taper, said second taper being greater than said first taper, said second shaft having a smaller diameter at one end thereof and a larger diameter at the other end thereof, said second shaft having cutting surfaces located therein from said larger diameter end nearly to said smaller diameter end, said cutting surfaces having been dulled along one longitudinal side of said second shaft, said second shaft having a rounded tip at the end of said second shaft having said smaller diameter.

11. A series of files as defined in claim 10 wherein the one of said first and second shafts having the smaller taper is used before the other of said first and second shafts.

12. A set of instruments for cleaning and shaping a root canal of a tooth, comprising:
a plurality of files, each including a shaft having a different taper from the others, said files all having cutting surfaces located in their shafts, said cutting surfaces having been dulled along one longitudinal side of each of said files, said files having a rounded tip at the smaller end of their shafts, the files being for use in succession from the smaller tapers to the larger tapers.

13. An endodontic file for cleaning and shaping a root canal, comprising:
a tapered shaft which is axially twisted, said tapered shaft having a plurality of spiral cutting surfaces along the length thereof and a conical tapered tip on the smaller end thereof, said tapered tip having a rounded end to prevent ledging, said cutting surfaces being dulled along one full side of said tapered shaft, thereby producing a safe edge.

14. A file as defined in claim 13 further including a handle mounted on said file, the handle having tactile reference means for locating the alignment of said safe edge.

15. A file as defined in claim 14 wherein the tactile reference means comprise a flat side on a generally round handle, the flat side being oriented in alignment with said safe edge.

16. An endodontic file for cleaning and shaping a root canal, comprising:
a round tapered shaft having cutting surfaces machined into said shaft along the length of said shaft all the way nearly to the smaller end of said shaft, a portion of said cutting surfaces being absent along one full side of said shaft; and a rounded tip at said smaller end of said shaft.

17. A method of making a file for cleaning and shaping a root canal in a tooth, comprising:
(a) providing a tapered shaft having a smaller diameter at one end thereof and a larger diameter at the other end thereof;
(b) forming cutting surfaces in said tapered shaft from said larger end nearly to said smaller end;
(c) dulling said cutting surfaces along the full extent of one longitudinal side of said tapered shaft to develop a safe edge which is free of cutting surfaces; and (d) machining a rounded surface onto the tip of said shaft at the end having said smaller diameter.

18. The method of claim 17 comprising:
providing a plurality of tapered shafts for making a plurality of said files, each of said shafts having a different degree of taper from the next; and repeating steps (b), (c) and (d) for each individual file.

19. The method of claim 18 further comprising selecting the degree of taper of each shaft to be substantially equal to a corresponding one of a set of variable taper filling materials available for filling prepared root canals.