Umted States Patent [19]
`Heath et a1.
`
`[54] ENDODONTIC INSTRUMENT
`
`
`
`Inventors: Derek E. Heath; Jerry A. Mooneyhan’ both of JOhllSOll T6111].
`
`
`
`[73] Assignee: 'Iulsa Dental Products, L.L.C., 'Ihlsa,
`Okla.
`
`[21] APPL NO‘: 646,030
`
`[22] Filed:
`
`May 7, 1996
`
`Related US. Application Data
`
`[63] Continuation of Ser. N0. 76,367, Jun. 14, 1993, Pat N0.
`5,527,205, which is a continuation of Ser. No. 787,945, Nov.
`5, 1991, abandoned.
`
`[51] Int. Cl.6 ..................................................... .. A61C 3/00
`[52] U.S. c1. ................ ..
`451/48; 433/102; 433/224
`[58] Field of Search
`....... .. 451/28, 48; 433/165,
`433/102_ 224 225
`'
`’
`
`[56]
`
`References Cited
`
`U-S- PATENT DOCUMENTS
`7/1957 Jaffee et a1. .......................... .. 420/417
`2,797,996
`4,197,643 4/1980 Buistone et a1.
`.... .. 433/20
`4,611,509
`9/1986 Matsutani . . . . . . .
`. . . . .. 76/241
`4,871,312 10/1989 Heath ........................ .. 433/164
`4,934,934
`6/1990 Arpaio, Jr. et a1. .................. .. 433/102
`
`USO056286'74A
`[11] Patent Number: '
`[45] Date of Patent:
`
`5,628,674
`May 13, 1997
`
`3/1991 Speiser et a1.
`4,999,952
`5,065,549 11/1991 Speiser et a1.
`
`.......... .. 451/48
`451/48
`
`
`
`............................ .. OTHER PUBLICATIONS
`
`An Initial Investigation of the Bending and Torsional Prop
`erties of Nitinol Root Canal Files, Journal of Endodontics,
`Jul. 1988, vol. 14, No. 7, pp. 346-351.
`Superelastic Ni-Ti Wire, Wire Jounal International, Mar.
`1991, pp. 45-50.
`The Grinding Wheel, Lewis and Schleicher, Third Edition,
`The Grinding Wheel Institute, pp. 382-383.
`Primary Examiner-—Robert A. Rose
`Attorney, Age'"; of F inn-$611, Seltzer, Park& Gibson, PA
`[57]
`ABSTRACT
`
`A method of fabricating an endodontio instrument by a
`machining Operation is disclosed, and wherein a wire-like
`I°d cOmpmd of a titanium 411W is advanced Past *1 mating
`grinding wheel at a relatively slow feed rate, with a su?icient
`depth of cut to remove all of the material on a given surface
`without over grinding a previously ground surface, and with
`the grinding wheel rotating at a relatively slow surface
`speed. The disclosed method is able to e?iciently produce
`°nd°d°ntic instruments having a high degree °f ?exibility’
`high resistance to torsional breakage, and With shall) Cutting
`edges along the Working length.
`
`7 Claims, 3 Drawing Sheets
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`US. Patent
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`May 13, 1997
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`Sheet 3 of 3
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`5,628,674
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`1
`ENDODONTIC INSTRUMENT
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`5,628,674
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`2
`1. Feed Rate
`
`This application is a continuation of application Ser. No.
`08/076,367, ?led Jun. 14, 1993, now US. Pat No. 5,527,
`205, which in turn is a continuation of application Ser. No.
`07/7 87,945 ?led Nov. 5, 1991 and now abandoned.
`BACKGROUND OF THE INVENTION
`The present invention relates to a method of fabricating an
`endodontic instrument adapted for use in performing root
`canal therapy on teeth, and which is characterized by high
`?exibility and high resistance to torsional breakage.
`Root canal therapy is a well-known procedure wherein the
`crown of a diseased tooth is opened so as to permit the canal
`to be cleaned and then ?lled. More particularly, a series of
`very delicate, ?exible, ?nger-held instruments or ?les are
`used to clean out and shape the root canal, and each ?le is
`manually rotated and reciprocated in the canal by the dentist
`Files of increasingly larger diameter are used in sequence, to
`achieve the desired cleaning and shaping. When the canal is
`thus prepared, it is solidly ?lled with a ?lling material, which
`typically comprises a waxy, rubbery compound known as
`gutta percha. In one procedure, the grtta percha is positioned
`on an instrument called a compactor, and the coated com
`pactor is inserted into the prepared canal and rotated and
`reciprocated to compact the gutta percha therein. The dentist
`thereafter ?lls the tooth above the gutta percha with a
`protective cement, and lastly, a crown is ?tted to the tooth.
`Endodontic instruments of the described type are conven
`tionally fabricated by permanently twisting a stainless steel
`rod of triangular or square cross section. The apices of the
`triangular or square cross section thus form cutting edges
`which spiral along the length of the instrument. More
`recently, such instruments have been produced by a machin
`ing process, and wherein a cylindrical rod of stainless steel
`is moved past a rotating grinding wheel, and while the rod
`is slowly rotated about its axis so as to impart a desired
`helical con?guration to the ground surface and form a spiral
`?ute on the surface. The rod is thereafter indexed and again
`moved past the wheel, and these steps are repeated as many
`times as are necessary to form the rod into a triangular or
`square cross section. By appropriate control of the process,
`helical lands may be formed between the spiral ?utes as
`illustrated in U.S. Pat. No. 4,871,312 to Heath.
`It is well-known by clinicians that inadvertent errors can
`occasionally arise during root canal therapy as described
`above. These errors can include the formation of a ledge in
`the wall of the canal, the perforation of the canal, and a
`separation or fracture of the instrument. Many of these errors
`which occur during the therapy of a canal have a common
`genesis, i.e. the basic stiffness of the stainless steel
`instruments, particularly with the respect to the instruments
`of larger size. Efforts have been made to improve the
`?exibility of stainless steel instruments based upon different
`cross sectional shapes, but without signi?cant success.
`Recently, a series of comparative tests of endodontic
`instruments made of nickel-titanium (Nitinol) alloy and
`stainless steel were conducted. The results of the tests were
`published in an article entitled “An Initial Investigation of
`the Bending and the Torsional Properties of Nitinol Root
`Canal Files”, Journal of Endodonn'cs, Volume 14, No. 7,
`July 1988, at pages 346-351.
`The Nitinol instruments involved in the above tests were
`machined in accordance with the procedure and operating
`parameters conventionally used in the machining of stainless
`steel endodontic instruments. More particularly, this stan
`dard procedure involves the following parameters:
`
`The rod from which the instrument is to be formed is
`moved axially past a rotating grinding wheel at a feed rate
`of about ten inches per minute. The rod is slowly rotated
`about its axis as it is axially advanced so as to impart a
`helical configuration to the ground surface.
`
`2. Depth of Cut
`
`10
`
`The depth of each cut is su?icient to remove all of the
`material on a given surface without over grinding a previ
`ously ground surface. For example, in the case of an
`instrument triangular cross-section, the rod is moved past
`the wheel three times, once for each surface, with about 25
`percent of the diameter being removed on each cut.
`
`3. Speed of Wheel
`An aluminum oxide grinding wheel is provided which is
`rotated at a surface speed of about 6000 feet per minute, and
`the wheel has a grit size of about 220.
`The above tests demonstrated that the Nitinol instruments
`produced by the described machining process exhibited
`superior ?exibility and torsional properties as compared to
`stainless steel instruments, but the cutting edges of the
`instruments exhibited heavily deformed metal deposits,
`which rendered the instruments generally unsatisfactory for
`use.
`It is accordingly an object of the present invention to
`provide a method of fabricating an endodontic instrument
`which is characterized by high ?exibility and high resistance
`to torsional breakage.
`It is another object of the present invention to provide a
`method of e?iciently fabricating an endodontic instrument
`which is composed of a titanium alloy, such as a nickel
`titanium alloy, and which exhibits high ?exibility and high
`resistance to torsional breakage, and which is also charac
`terized by sharp cutting edges.
`
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`SUMMARY OF THE lNVENI'ION
`The above and other objects and advantages of the present
`invention are achieved in the embodiments illustrated herein
`by the discovery that when an endodontic instrument of
`titanium alloy is machined under certain speci?c operating
`parameters, a totally satisfactory instrument, having high
`?exibility, high resistance to torsion breakage, and sharp
`cutting edges, may be produced. The speci?c operating
`parameters are not suggested by the lmown procedure for
`machining stainless steel instruments as summarized above,
`and indeed, the parameters which are effective in producing
`a satisfactory instrument are directly contrary to accepted
`practices for machining titanium alloys as presented in
`authoritative literature, note for example the brochure
`entitled “RMI Titanium”, published by RMI Company of
`Niles, Ohio.
`More particularly, the present invention involves the steps
`of (a) providing a cylindrical rod of metallic material which
`is composed of at least about 40% titanium and which has
`a diameter less than about 0.06 inches, and (b) axially
`moving the rod past a rotating grinding wheel at a feed rate
`of not more than about 5 inches per minute, while rotating
`the rod about its axis, and so that the wheel removes at least
`about 25% of the diameter of the rod at the point of
`maximum removal and forms a helical surface on the rod.
`The grinding wheel is rotated at a relatively slow surface
`speed of not more than about 3000 feet per minute, and
`preferably not more than about 2200 feet per minute. Also,
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`the grinding wheel has a relatively ?ne grit size which is
`greater than about 200 grit, and preferably greater than about
`220 grit. In the preferred embodiment, the rod is composed
`of an alloy comprising at least about 40% titanium and about
`50% nickel.
`It is often preferred to form the rod into a triangular or
`square cross sectional con?guration, and in such
`embodiments, the rod is rotatably indexed about a rotational
`axis of not more than 180 degrees, and speci?cally either
`120 degrees or 90 degrees, and step (b) is repeated so as to
`form a second helical surface on the rod. The indexing and
`grinding steps are again repeated as many times as are
`necessary to form the desired number of sides on the
`instrument.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Some of the objects and advantages of the present inven
`tion having been stated, others will appear as the description
`proceeds, when taken in conjunction with the accompanying
`drawings, in which
`FIG. 1 is a cross sectional view of a tooth have two roots,
`with an endodontic instrument manufactured in accordance
`with the present invention being positioned in one of the
`roots;
`FIG. 2 is an enlarged perspective vieW of the lower
`portion of the instrument shown in FIG. 1;
`FIG. 3 is a transverse sectional view taken substantially
`along the line 3-3 of FIG. 2;
`FIG. 4 is a view similar to FIG. 2, but illustrating a second
`embodiment of the instrument;
`FIG. 5 is a transverse sectional view taken substantially
`along the line 5—5 of FIG. 4;
`FIG. 6 is a schematic side elevation view of a machining
`apparatus which is adapted to fabricate endodontic instru
`ments in accordance with the present invention; and
`FIG. 7 is a top plan view of the apparatus shown in FIG.
`6, and illustrating certain of the steps of the fabrication
`process.
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`4
`FIGS. 4-5 illustrate a second embodiment of an endo
`dontic instrument 10' which may be fabricated in accordance
`with the present invention. In this embodiment, the outer
`peripheral surface of the Working length 18' is tapered at an
`included angle of about one degree, and the working length
`18' includes two continuous helical ?utes 21, 22 formed in
`the peripheral surface. The ?utes have an arcuate curvature
`as best seen in FIG. 5, and they have a pitch so as to de?ne
`helical lands 24 on the outer periphery of the instrument. An
`instrument of this general construction is further described
`in US. Pat. No. 4,871,3 12 to Heath, and pending application
`Ser. No. 07/679,628, ?led Apr. 3, 1991.
`FIGS. 6 and 7 schematically illustrate a machining appa
`ratus for practicing the method of the present invention. As
`will be further described below, the method involves a
`unique machining process which has been found to effi
`ciently produce endodontic instruments of the type
`described, from a rod 30 composed of titanium alloy. Such
`alloys typically have a titanium content of at least about 40
`percent. Nickel-titanium alloys are preferred, which typi
`cally consist of about 40 percent titanium and about 50
`percent nickel. In one preferred speci?c embodiment, the
`alloy consists of 44 percent titanium and 56 percent nickel
`and no appreciable amount of other ingredients which could
`adversely effect the purity required for endodontic instru
`ments.
`The rod 30 from which the instrument is to be fabricated
`is conventionally supplied from the producer in a selected
`diameter, which closely conforms to the diameter of the
`instrument being produced. In this regard, endodontic instru
`ments are sized in accordance with established standards,
`which range from a diameter at the pilot end 16 of 1.4 mm
`(0.062 inches-size 140) to a diameter at the pilot end 16 of
`0.06 mm (0.0024 inches-size 06).
`In accordance with the illustrated embodiment of the
`present invention, the continuous rod 30 is positioned to
`extend through an axial feed block 32 and an indexing block
`34 of conventional well-known construction. A work hold
`ing ?xture 36 is positioned to support the forward end of the
`rod 30 adjacent the periphery of a rotating grinding wheel
`38. The two blocks 32, 34 are then advanced so that the rod
`30 is axially moved past the rotating grinding wheel 36 at a
`slow feed rate of between about 3 to 8 inches per minute, and
`preferably not more than about 5 inches per minute. Con
`currently with this axial movement, the indexing block 34
`serves to slowly rotate the rod 30 about its axis at a
`controlled speed, which causes the ground surface 19 to
`assume a helical con?guration as described above with
`respect to FIGS. 2 and 3.
`The rod preferably moves past the wheel only once for
`each ground surface 19, and thus the rod is positioned with
`respect to the wheel 38 such that the full depth of the cut is
`removed in a single pass. As best seen in FIG. 3, the wheel
`preferably removes at least about 25 percent of the diameter
`of the rod at the point of maximum removal, which is along
`a diameter which extends perpendicular to the surface 19
`being formed.
`As a further aspect of the present invention, the grinding
`wheel 38 is rotated at a relatively slow surface speed of not
`more than about 3000 feet per minute, and preferably not
`more than about 2200 feet per minute. Frn'ther, the wheel 38
`is composed of a relatively ?ne grit, which is greater than
`about 200 and preferably about 220 grit. A wheel of the
`above gn't size and which is fabricated from silicon carbide
`has been found to be very satisfactory.
`To produce an instrument of the construction illustrated in
`FIGS. 1-3, the grinding wheel 38 is oriented to rotate about
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`Referring more particularly to FIGS. 1-3, an endodontic
`instrument 10 is illustrated which comprises a shank 12
`which is composed of a titanium alloy as further described
`below. The shank 12 typically has a length of about 30 mm
`(1.2 inches), and it includes an outer or proximate end which
`mounts a conventional handle 14. The portion of the shank
`immediately below the handle is cylindrical and has a
`diameter of between about 0.5 and 1.6 mm (0.02 and 0.07
`inches), and this shank portion includes calibrated depth
`markings 15 of conventional design. The shank further
`includes an opposite distal or pilot end 16, and a working
`length 18 is de?ned adjacent the pilot end 16. The working
`length may be cylindrical as illustrated, or it may be slightly
`tapered toward the pilot end 16 at an included angle of about
`one degree. The working length 18 may have a length of
`about 2 mm (0.08 inches) up to the full length of the shank
`12, Le. about 30 mm (1.2 inches). However, in the illustrated
`embodiment, the working length 18 has a length suf?cient to
`extend substantially the full depth of a tooth root canal as
`illustrated in FIG. 1, which is about 16 mm (0.63 inches).
`Also, the cross sectional con?guration of the working length
`18 is triangular and is composed of three linear surfaces 19,
`as best seen in FIG. 3, and so that the apices of the triangle
`form cutting edges.
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`5
`an axis generally parallel to the axis of the advancing rod 30,
`and the wheel 38 thus forms a generally ?at surface 19. Also,
`by reason of the slow rotation of the rod about its axis, this
`?at surface assumes a helical con?guration. Where the
`instrument is to have a tapered working length, the axis of
`the index block 34 is slightly inclined with respect to the
`rotational axis of the wheel 38, so as to provide a controlled
`and variable depth of cut along the working length.
`When the rod 30 has advanced past the rotating wheel 38
`a distance suf?cient to form the ?rst surface 19 along the
`desired working length on the instrument, the table 39
`supporting the feed block 32, the index block 34, and the
`?xture 36 is moved laterally, then axially rearwardly, and
`then laterally back to its original position as illustrated
`schematically in FIG. 7. Concurrently, the rod 30 is rotatably
`indexed about its axis. The angular extent of this rod
`indexing will depend upon the number of surfaces 19
`desired on the ?nished instrument, and where three surfaces
`are to be formed as seen in FIG. 3, the rod is indexed 120
`degrees. The rod is then again axially advanced while being
`slowly rotated, and so as to form the second surface 19. The
`table 39 is then again moved laterally and rearwardly in the
`manner described above, and the rod 30 is rotatably indexed
`another 120 degrees. The grinding process is then repeated
`to form the third surface 19 of the instrument. The rod 30
`may then be severed by conventional techniques, such as by
`axially advancing the rod and then moving the grinding
`wheel laterally through the rod. The severed rod is then
`further processed in a conventional manner to form the
`completed instrument as illustrated for example in FIG. 1.
`As a modi?cation of the illustrated process, the rod 30
`may be initially severed into appropriate lengths, and each
`length may be separately mounted in a collet at the forward
`end of the indexing block 34, and then machined in the
`manner described above.
`The process as described above has been found to produce
`instruments of consistently high quality, and at cormner
`cially acceptable production rates. Of particular
`signi?cance, the process results in the formation of cutting
`edges at the apices of the triangular cross section, which are
`sharp, and substantially free of burrs and rolled edges which
`characterized the early instruments of titanium alloys as
`described above.
`While an instrument of triangular cross section is illus
`trated in FIGS. 1-3, it will be understood that other con
`?gurations are possible. For example, the instrument could
`have four sides which form a square in cross section. In the
`embodiment of FIGS. 4-5, the working length 18‘ of the
`instrument is tapered and is composed of two helical ?utes
`21, 22 of arcuate con?guration. To fabricate this
`embodiment, substantially the same procedure as described
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`above is followed. However, the taper of the working length
`18' is preferably initially formed on a separate grinding
`machine, and the tapered blank is then mounted on a
`machine as shown in FIG. 6, and the axis of the wheel 38 is
`oriented so that the wheel lies in a plane which follows the
`desired helical con?guration of the ?utes 21, 22. Also, the
`outer periphery of the wheel is curved in cross section as
`opposed to being ?at, and so as to form the desired arcuate
`con?guration of the ?utes 21, 22. Since the instrument as
`illustrated has two ?utes, the rod is indexed 180° between
`the two machining operations.
`In the drawings and speci?cation, there has been set forth
`preferred embodiments of the invention, and although spe
`ci?c terms are employed, they are used in a generic and
`descriptive sense only and not for purposes of limitation.
`That which is claimed is:
`1. An endodontic instrument that is ?exible and resistant
`to torsional breakage and that is adapted for use in perform
`ing root canal therapy on a tooth, comprising:
`a cylindrical elongate shank composed of an alloy com
`prising at least about 40% titanium and having a
`diameter not greater than about 0.07 inches, said elon
`gate shank further having a proximate end and an
`opposite pilot end so as to de?ne a working length
`adjacent said pilot end; and
`at least one ground ?ute extending helically around said
`shank working length, said one ?ute de?ning at least
`one cutting edge, and with the cutting edge being
`formed by moving the shank past a grinding wheel only
`once and which de?nes an as-ground condition of said
`cutting edge which is sharp and substantially free of
`rolled deformed metal.
`2. The endodontic instrument as defined in claim 1
`wherein said shank is composed of an alloy comprised of at
`least about 40% titanium and at least about 50% nickel.
`3. The endodontic instrument as de?ned in claim 1,
`wherein the shank is tapered.
`4. The endodontic instrument as de?ned in claim 1
`wherein said one ?ute is ground to form a surface that is
`linear when viewed in transverse cross section.
`5. The endodontic instrument as de?ned in claim 1
`wherein said one ?ute is ground to form a surface that is
`arcuate when viewed in transverse cross section.
`6. The endodontic instrument as de?ned in claim 5
`wherein a helical land is positioned between axially adjacent
`?ute segments.
`7. The endodontic instrument as de?ned in claim 1 further
`comprising a handle mounted at said proximate end of said
`shank.
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