United States Patent [19]
`Farzin-Nia et al.
`
`[11] (cid:9) Patent Number: (cid:9)
`[45] (cid:9) Date of Patent: (cid:9)
`
`6,149,501
`*Nov. 21, 2000
`
`[54] SUPERELASTIC ENDODONTIC
`INSTRUMENT, METHOD OF
`MANUFACTURE, AND APPARATUS
`THEREFOR
`
`[75] Inventors: Farrokh Farzin-Nia, Inglewood;
`William Otsen, Glendora; Gary
`Garman, La Verne, all of Calif.
`
`[73] Assignee: Kerr Corporation, Orange, Calif.
`
`[
`
`Notice: (cid:9)
`
`This patent is subject to a terminal dis-
`claimer.
`
`[21] Appl. No.: 09/014,139
`
`[22] Filed: (cid:9)
`
`Jan. 27, 1998
`
`Related U.S. Application Data
`
`[63] Continuation-in-part of application No. 08/938,507, Sep. 26,
`1997, Pat. No. 5,984,679.
`
`B24B 1/00
`[51] Int. Cl.7 ..... (cid:9)
`......... -....-.. ............ (cid:9)
`451/48; 451/540
`[52] U.S. Cl. (cid:9)
` 451/28, 48, 102,
`[58] Field of Search (cid:9)
`451/224, 165, 225, 540; 433/81, 102, 224,
`20
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4/1992 Heath et al. (cid:9)
`5,106,298
`4/1994 Heath et al. (cid:9)
`5,302,129
`7/1995 Farzin-Nia et al. (cid:9)
`5,429,501
`5,464,362 11/1995 Heath et al. (cid:9)
`5,527,205
`6/1996 Heath et al. (cid:9)
`5,628,674
`5/1997 Heath et al. (cid:9)
`5,655,950 8/1997 Ifeath et al. (cid:9)
`5,762,541
`6/1998 Heath et al. (cid:9)
`5,775,902
`7/1998 Matsutani et al. (cid:9)
`5,941,760
`8/1999 Heath et al. (cid:9)
`5,984,679 11/1999 Frazin-Nia et al. (cid:9)
`
` 433/102
` 433/244
` 433/21
` 451/48
` 451/48
` 451/48
` 451/48
` 451/48
` 433/102
` 451/28
` 433/102
`
`OTHER PUBLICATIONS
`
`Harmeel Walia et al., An Initial Investigation of the Bending
`and Torsional Properties of Nitinol Root Canal Files, Journal
`of Endodontics, vol. 14, No. 7, Jul. 1988.
`
`Primary Examiner—Derris H. Banks
`Attorney, Agent, or Firm—Wood, Herron & Evans, L.L.P.
`
`[57] (cid:9)
`
`ABSTRACT
`
`A superelastic endodontic instrument, such as a file, is
`formed by grinding a superelastic wire to form a file preform
`or blank, and rotating a first end of the blank while prevent-
`ing rotation of a second end of the blank. The file blank is
`maintained in the austenite phase at least until twisted to
`form a stress induced martensite which is plastically
`deformed by the twisting. A heat treatment step may be
`performed prior to twisting, during twisting or after twisting
`of the preform, The file blank may be heated by electrical
`heating methods or by submerging the blank in a heated
`liquid.
`
`4,443,193 4/1984 Roane (cid:9)
`5,044,947 9/1991 Sachdeva et al. (cid:9)
`
` 433/102
` 433/20
`
`112 Claims, 4 Drawing Sheets
`
`1PR2015-00632 — Ex. 1037
`US ENDODONTICS, LLC, Petitioner
`
`(cid:9)
`(cid:9)
`

`
`U.S. Patent (cid:9)
`
`Nov. 21, 2000 (cid:9)
`
`Sheet 1 of 4 (cid:9)
`
`6,149,501
`
`34
`
`FIG. I
`
`

`
`U.S. Patent (cid:9)
`
`Nov. 21, 2000 (cid:9)
`
`Sheet 2 of 4 (cid:9)
`
`6,149,501
`
`so
`
`•
`
`-8-
`
`FIG.2
`
`1.-
`_55.6 .$4
`
`FIG.2A
`-8
`14/e/
`/0:_k
`/0e64 (cid:9)
`
`/410!e
`
`FIG.2B
`/0/4 (cid:9)
`6,
`
`FIG.2C
`
`FIG.2D
`
`1
`
`5/
`
`8
`/d5
`
`FIG.34
`
`FIG.3B
`
`/0-5
`
`FIG.3C
`
`-54
`
`752
`L-5-56
`FIG.3
`
`

`
`U.S. Patent (cid:9)
`
`Nov. 21, 2000
`
`Sheet 3 of 4
`
`6,149,501
`
`FIG.5
`
`/D (cid:9)
`
`FIG.6
`
`(cid:9)
`(cid:9)
`

`
`U.S. Patent (cid:9)
`
`Nov. 21, 2000 (cid:9)
`
`Sheet 4 of 4 (cid:9)
`
`6,149,501
`
`.20D (cid:9)
`
`2/0
`
`.2.20
`
`,2a‘
`,z24.
`
`.2/26
`
`.2/.2
`
`FIG.8
`
`,e3Da
`
`zza
`
`.Z0.2
`
`.236
`
`,238
`
`FIG.7
`
`

`
`6,149,501
`
`1
`SUPERELASTIC ENDODONTIC
`INSTRUMENT, METHOD OF
`MANUFACTURE, AND APPARATUS
`THEREFOR
`
`RELATED APPLICATIONS
`
`This application is a continuation-in-part of U.S. patent
`application Ser. No. 08/938,507 filed on Sep, 26, 1997, the
`disclosure of which is hereby fully incorporated by reference
`herein now U.S. Pat. No. 5,984,679.
`
`FIELD OF THE INVEN'T'ION
`
`The present invention generally relates to superelaslic
`endodoritic instruments and, more specifically, to infra- 15
`merits such as tiles or reamers and methods and apparatus for
`manufacturing such instruments.
`
`2
`increased torsional and bending flexibility, as compared to
`conventional steel files, and manufactured by improved
`processes relative to prior superelastic file production tech-
`niques. Generally, the invention provides a process in which
`5 a superelastic endodontic instrument preform or blank may
`be ground and then twisted with plastic deformation, that is,
`maintenance of the twisted shape, without over-stressing the
`material into failure.
`The unique process of this invention involves maintaining
`10 the instrument blank in the austenite phase of the superelas-
`tic material at least prior to twisting and, preferably, prior to
`and during the twisting operation. To maintain the blank in
`the austenite phase, the blank is preferably maintained above
`the austenite finish temperature (Al) of the particular super-
`elastic material. The blank is more preferably maintained in
`the working temperature range 'I\v of the superelastic mate-
`rial. For a wide variety of superelastic alloys, this range
`would be between 200° F.-400° F. The material of the blank
`is converted from the austenite phase to the martensite phase
`20 by the stress applied during the twisting operation. The
`material undergoing stress induced martensite transforma-
`tion is plastically.deformed during twisting so that the fluted
`profile is retained after completion of the twisting process.
`Due to the ability to pregrind a file blank, for example, it is
`as passible to fabricate a superelastic endodontic file having
`many different transverse cross sectional shapes, such as
`those conventionally obtained with steel materials.
`In another aspect of this invention, the elevation in
`temperature In the austenite finish temperature Af of the
`30 superelastic blank may be accomplished through several
`different methods, such as ambient, induction, joulian, or
`radian! healing, or submersion within a heated liquid. Ambi-
`ent heating, for example, may be accomplished in an oven
`while induction heating may utilize an inductive heating coil
`35 surrounding the blank during the twisting operation.
`Submersion within a heated liquid can allow the blank to
`be heated in a rapid and controlled manner. The heated liquid
`may be oil or a salt solution, or other liquids that do not boil
`below or close to the Af of the particular superelastic metal.
`40 Flitting apparatus is provided generally above a vessel
`containing the liquid and includes a rotary motion mecha-
`nism for holding and rotating an instrument blank, such as
`a file blank, a clamping mechanism that receives a ground
`portion of the file blank and a linear or axial motion
`45 mechanism for moving the clamping mechanism along the
`longitudinal axis of the file blank at a rate which is propor-
`tional to the rate of rotation. According to this heating
`alternative, the twisting operation is preferably performed
`with the ground portion of the blank submerged in the heated
`50 liquid. After ihe twisting process is complete, the fluted,
`superelastic tile may then undergo subsequent quenching or
`heal treatment operations in order to achieve the desired
`physical properties.
`Additional objects and advantages of the invention will
`55 become more readily apparent to those of ordinary skill in
`the art upon review of the following detailed description of
`the preferred embodiment taken in conjunction with the
`drawings.
`
`60
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic perspective view of one type of
`apparatus used in fabricating a superelastic file in accor-
`dance with the present invention.
`FIG. lA is a side view of a file farmed on the apparatus
`
`BACKGROUND OF THE INVENTION
`
`Over the past several years, endodontic instruments such
`as root canal files have been manufactured by simulta-
`neously grinding and twisting thin carbon steel or stainless
`steel rods or wires. Specifically, steel wire blanks are first
`ground to the desired cross sectional shape, such as square,
`triangular or rhomboid, and to the appropriate size and taper.
`The ground blank is then gripped at one end and spring
`loaded jaws are brought into contact with the ground portion
`of the blank. As the blank is rotated from the gripped end,
`the jaws are moved axially away from ihai end. The jaws
`therefore twist the rotating blank and form helical flutes into
`the blank. The longitudinal, ground edges of the blank form
`helical cutting edges on the file. The axial jaw speed,
`twisting speed and spring force are controlled to obtain the
`desired helical configuration.
`With the emergence of superelastic materials, such as
`nickel titanium alloys, endodontic instrument manufacturers
`are now able to form endodontic root canal tiles with much
`more flexibility. This greatly assists the endodontic[ during
`use of the file in a root canal procedure. The use of
`superelastic material, however, causes some significant
`manufacturing concerns due to the tendency of the material
`to return to its original shape after the release of an applied
`force. File blanks manufactured of superelestic materials
`generally react in this manner to the conventional twisting
`methods employed for manufacturing carbon and stainless
`steel files. Moreover, if superelastic file blanks are over-
`stressed, such as by being twisted too much during the
`fluting procedure, the material is subject to failure. For
`reasons such as these, current manufacturers of endndontic
`files may resort to grinding the helical profile directly into
`the superelastic blanks while applying no twisting forces to
`the blanks. These direct grinding methods are lime consum-
`ing and expensive. They also limit the variety of cross
`sectional shapes that may be formed in the final product.
`With the above background in mind, it would be desirable
`to provide a method of manufacturing a wide variety of
`superelastic enduclontie appliances, such as tiles, using
`Iwisting and grinding techniques. ha short, it would he
`advantageous to retain the benefits of superelastic materials
`and the benefits of a twisting and grinding procedure that
`simplifies manufacture and allows the production of a wide
`variety of file cross sections.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides a superelastic endodontic
`instrument, which is preferably a file or reamer, having
`
`65 of FHIGG..11 is an enlarged cross-sectional view taken on line
`1B-1B of FIG. 1A.
`
`

`
`6,149,501
`
`3
`FIG. 2 is a schematic side view of one apparatus for
`forming a flat surface along the length of a file blank.
`FIGS. 2A, 2B, 2C and 2D are transverse cross-sectional
`views, perpendicular to the longitudinal axis of the finished
`file or the file blank using the apparatus of FIG. 2 or FIG. 6.
`.FIG. 3 is a schematic side view of an apparatus similar to
`FIG. 2 for forming a concave surface along the length of a
`file blank.
`FIGS. 3A, 3B and 3C are transverse cross-sectional
`views, perpendicular to the longitudinal axis of the finished
`file or the file blank, showing concave surfaces formed on
`file blanks, using the apparatus of FIG. 3.
`HO. 4 is a detail view of a rhomboidal file lip.
`FIG. 5 is a perspective view of another apparatus for
`forming flat surfaces along the length of a number of file
`blanks.
`HG. 6 is a perspective view of the apparatus used in
`straightening superelastic wire.
`FIG. 7 is a schematic devotional view of another type of
`apparatus used in fabricating a superelastic file of the present
`invention in.conjunction with a heated liquid.
`FIG, S is a bottom view of the apparatus shown in FIG.
`7.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`Superelastic materials are typically metal alloys which
`return to their original shape after substantial deformation.
`Superelastic alloys such as nickel titanium (Ni:Ti) can with-
`stand several times more strain than conventional materials,
`such as stainless steel, without becoming plastically
`deformed. Further, a superelastic material Will generally
`recover approximately 6% after twisting at ambient tem-
`perature while a stainless steel will recover only 1-2% after
`twisting. Typically, superelastic alloys undergo a stress
`induced martensitic transformation which allows for shape
`memory properties. Shape memory and superelasticity are
`found in stoichiometric NiTi, near-equiatornic (cid:9)
`for
`example, 50.8 atomic percent Ti and 49.2 atomic percent. Ni,
`Ni-Ti-Cu, Ni-Ti-Nb and Ni-Ti-Fe alloys as well as beta-
`phase titanium or other Ti based alloys. Examples of suitable
`nickel-titanium alloys in various stoichiometric ratios are
`disclosed in U.S. Pat. No. 5,044,947 (nickel-titanium-copper
`alloy) and U.S. patent application Ser. Nos. 08r221,638 and
`08/454,016, inventor Sachdeva et al., entitled "NiTiNb
`Alloy Processing Method and Articles Formed Thereby"
`(nickel-titanium-niobium-alloy). The disclosures of U.S.
`Pal. No. 5,044,947 and the aforesaid applications are hereby
`incorporated by reference.
`The specific alloy composition used for the endodoatic
`instrument of this invention is not critical as the invention
`may utilize many materials which exhibit superelastic char-
`acteristics. U.S. Pat. No. 5,429,501, which is hereby incor-
`porated in its entirety by reference herein, discloses super-
`elastic and shape memory beta-phase titanium. To form
`beta-phase titanium, metallic titanium may be alloyed with
`molybdenum, chromium, zirconium, tin, vanadium, iron or
`niobium. Other compositions such as Cu-Zn alloys are also
`known to be superelastic and are suitable for use in the
`present invention. Another material suitable for use in the
`present invention is a work hardened nickel titanium having
`a martensitic crystal structure, such as that sold under the
`tradename NITANOL for orthodontic wires by Unitek
`Corp., Arcadia Calif.
`Superelastic materials have a temperature range in which
`the material may be permanently deformed. This range is
`
`30
`
`4
`known as the working temperature range Tw. When a
`superelastic wire is heated to a temperature in the working
`temperature range Tw, the wire may be permanently
`deformed so that when the wire is cooled, the deformed
`5 shape is maintained. Typically, the superelastic wire is
`packaged in coils and should be straightened prior to grind-
`ing rind twisting. One method of straightening the wire 8 is
`to wrap the wire around a mandrel 160 as shown in FIG. 6.
`The mandrel 160 is then placed in a furnace and the wire 8
`10 is heated into the Tw. The wire 8 is then cooled, removed
`from the mandrel and the curved ends are trimmed.
`Superelastic alloys are in the martensitic phase when they
`arc below the austenitic transformation temperature Af, i.c.,
`the temperature at which the material is about 100% auste-
`15 rite, -these alloys retain their deformed shape when sub-
`jected to stress in the martensit le phase. However, the shape
`memory property returns the deformed material to its origi-
`nal predeformation configuration when heated above Af. In
`the present invention it is preferred to rise an alloy having an
`20 Af temperature lower than about 37° C. (i.e., body
`temperature) so that the instrument will be in the austeni tic
`phase during use in the human body.
`When the superelastic material is twisted, the material
`may form a stress induced martensite phase since less energy
`25 is necessary to stress induce and deform martensite than to
`deform austenite. If the file preform is deformed at room
`temperature and [here is not enough strain to induce plastic
`deformation of the martensite phase, the wire will spring
`back to its original shape once the twisting force is released.
`11 is also possible to permanently deform superelastic mate-
`rial by beating within the Tw range prior to and during
`twisting. A typical superelastic material will have a Tw range
`of 200° P.-400° E Another method of permanently deform-
`ing a preform or blank according to the invention is by
`35 performing a rapid twist step to heat the superelastic mate-
`rial by internal friction to a temperature at which the material
`forms a stress induced martensite.
`As used herein, the terms shape-memory alloy and super-
`40 elastic material or alloy or similar terms are intended to
`include all suitable alloy compositions which possess shape-
`memory and/or superelastic properties, respectively.
`Moreover, the term superelastic is intended to mean the
`ability of at material to withstand at least twice as much strain
`45 as stainless steel materials can withstand without plastic
`deformation. The term shape memory is intended to mean
`the ability of a wire to receiver to its original state by the use
`of temperature. The term rhombus or rhomboidal is intended
`to define a geometric shape, having four major sides, which
`50 is substantially a parallelogram. i.e., including four equal
`sides and no internal right angles.
`The files and file-forming processes of this invention are
`implemented, in one preferred embodiment, with an appa-
`ratus such as apparatus 10 depicted in FIG. 1. Prior to
`55 twisting, file preforms or blanks are ground to the desired
`shape, including length, transverse cross-section and taper,
`on any one of the devices shown in FIGS. 2, 3, or 5.
`Referring to FIG. 2, cylindrical superelastic rods or wires
`8 are ground to form file preforms or blanks 12 which are
`60 subsequently twisted to form helically fluted files 11. Cylin-
`drical rod or wire 8 is mounted into collet 52 which is fixedly
`mounted upon a stage 54 which is selectively horizontally
`movable in opposite directions as designated by arrows 55a
`and 556. Once rod 8 is mounted in the collet 52, grinding
`65 wheel 50 is lowered into contact with the rod 8. Stage 54 is
`then advanced horizontally rightwardly, as is seen in FIG. 2,
`to move collet 52 and rod 8 axially so that a flat surface 101
`
`

`
`6,149,501
`
`5
`
`15
`
`20
`
`25
`
`5
`is ground on one side of the rod 8. After one such flat, that
`is, flat surface, has been ground along the working length L
`(see FIG. 1A) of the rod, grinding wheel 50 is lifted
`vertically, and stage 54 is moved axially leftwardly to the
`initial or home position so that the grinding wheel 50 is
`aligned with the upper portion of the inner end of the
`working length of the partially ground rod.. Collet 52 is then
`indexed about its central axis by a predetermined angle, the
`magnitude of which depends on the number of flutes desired
`in the finished file. Indexing rotational angles of 180°, 120°
`and 90° are employed for 2, 3 and 4 flute files, respectively.
`It is also possible to rotate the collet by a series of angles
`(e.g. 60°, 120°, 60°) to obtain a file preform having a
`rhomboidal cross section. Grinding wheel 50 is then lowered
`to the desired depth of contact with the rod 8, and stage 54
`is then moved rightwardly to move rod 8 axially past
`grinding wheel 50 to grind the second flat surface on the file
`blank. The foregoing process is repeated until all the flats
`have been ground on the file blank.
`As noted, by varying the angle which collet 52 indexes
`rod 8, it is possible to form file blanks having three or more
`apices 103 shown generally in FIGS. 2A-2C. The apices L03
`of the preground file blank, once twisted, and permanently
`helically fluted, form the cutting edges of the helically fluted
`file. Typically, endodontic files include three or four apices
`or helical cutting edges 103.
`In order to form a file blank having a square transverse
`cross section as shown in FIG. 2A, rod 8 is indexed 90° after
`each fiat surface 101 is ground. In order to form a file blank
`having three apices and a triangular transverse cross section,
`the rod is indexed 120° after each fiat surface is formed (as
`shown in F1G. 2B). Using the method of the present inven-
`tion it is also possible to form a file haVing a rhomboidal
`transverse cross section (FIG. 2C). This is accomplished by
`grinding a first flat surface 101c1; indexing the rod 60° 35
`clockwise as viewed in FIG. 2C and grinding a second flat
`surface 101c2; indexing the rod 120° clockwise as viewed M
`FIG. 2C and grinding a third flat surface 101c3; and indexing
`the rod 60° clockwise as viewed in FIG. 2C and grinding the
`fourth flat surface 101c4. It is not necessary to change the
`initial depth of cut of the wheel to fabricate the square,
`triangular and rhomboidal preforms shown in FIGS. 2A-2C,
`respectively. However, in order to fabricate a preform hav-
`ing a rectangular cross-section, as shown in FIG. 21), the
`initial depth of cut may be adjusted prior to forming each flat
`side or may be adjusted after opposing pairs of edges are
`ground. For example, as seen in FIG. 21), a first flat side
`101d1, is ground; the rod 8 is then indexed 90°, the initial
`depth of cut reduced and a second flat side 101d„ is gEnund;
`rod 8 is then indexed 90°, the initial depth of cut is increased
`to the depth used for the cut of side 101d1 and a third flat side
`101d3 is ground; rod 8 is then indexed 90°, the initial depth
`of cut is reduced to the depth used for the cut of side 101d,
`and fourth side 101d,, is ground. It is also possible to grind
`flat side 1014 index the rod I.80°, and grind'flat side 1014
`index the rod 91? and decrease the initial depth of cut and
`grind flat side 101d2; and finally index the rod 180° and
`grinding the final flat side 101d3.
`It is possible to form a variety of different cross sectional
`shapes by varying the surface of the grinding wheel and/or 60
`the index angles. For example, by dressing the surface of
`grinding wheel 50 so that the surface is convexcd, as shown
`in FIG. 3, it is possible to form ground surfaces 105 having
`the concave shapes shown in FIGS. 3A, 3B and 3C, rather
`than the flat shapes of the surfaces 101 shown in FIGS. 2A, 65
`2B and 2C. When the surface of the grinding wheel 50 is
`convexed, the angle A of the apices 107 (FIG. 3A) is more
`
`6
`acute for a file having the same index angle and number of
`sides than is angle N of the apices 103 (FIG. 2A) when the
`surface of the grinding wheel 50 is flat (FIG. 2). While angle
`A is more acute and provides a sharper cutting edge, that
`edge is weaker due to the lower amount of material at the
`apex. Thus, the apices shown in FIGS. 2A-2C are more
`rugged to maintain a usable edge and provide for a longer
`working life.
`Another device for grinding cylindrical rods 8 is shown in
`FIG. 5. FIG. 5 shows a wide grinding wheel 120 which
`moves transversely to the longitudinal axes of a large
`number of rods 8 to grind a flat surface onto the rods. The
`cylindrical rods 8 are placed upon rest 122. The rods 8 are
`disposed in parallel and extend along substantially the entire
`width of the rest 122. The parallel rods 8 are held by retainer
`124 which is movable along the length of rest 122 as shown
`by opposing arrows 128a and 128b. Movable retainer 124
`includes lateral projection 124a which extends over an end
`portion of rods 8 to secure the rods to rest 122 and prevent
`the rotation of the rods during grinding. Once rods 8 are
`retained between the lateral projection 124a and the rest 122,
`grinding wheel 120 moves back and forth across the width
`of rest 122 to grind a flat surface on the entire working length
`of each rod 8. Typically, the grinding 120 wheel moves
`across each rod twice, once while traveling away from
`projection 124a and once while traveling toward projection
`124a. During grinding, the wheel 120 may he moved
`straight across the rods or may move in a figure eight or
`zigzag pattern. The grinding wheel is preferably a porous
`wheel such as an ANSI standard C-60/ V wheel rotating at
`rate between 3,000 and 8,000 surface feet per minute and
`preferably about 5,000 surface feet per minute. The material
`is passed under the wheel at a feed rate between about 50 and
`100 lineal feet per minute, and preferably about 75 lineal
`feet per minute.
`After grinding a first flat side, the movable retainers 124
`is translated with respect to the rest 122. The lateral projec-
`tion 124a of the retainers 124 remains in contact with rods
`8 so that the movement of the retainer along the direction
`shown by arrows 128a, 1286 causes each rod to rotate by a
`predetermined angle about the longitudinal axis of the rods
`8. Once the rotation is complete, a second flat surface is
`ground across the working length of the rod. Depending
`uixm Ilse desired cross section of the file 11, the rods 8 are
`typically rotated and ground one or more times.
`After the superelastic file blanks have been ground to the
`desired cross-sectional file preform shape they are prefer-
`ably heated to a temperature above ambient temperature
`so prior to, during and subsequent to the twisting operation
`using thermal or frictional energy or a combination thereof.
`This temperature is preferably above the nustenite finish
`temperature Al of the particular superelastic material and
`can be as high as the working temperature range TW of the
`material.
`The heating process may externally heat the wire preform
`in the collet 14 by the provision of induction coils, radiant
`heating elements or electrodes to provide for joulian heating.
`The temperature to which the preform is heated is based
`upon the specific alloy used. A temperature range of 200°
`F.-400° F. is contemplated to be typical. Alternatively, the
`files can be heated without the application of heat from an
`external heat source by twisting rapidly so that internal
`friction heats the file.
`Once the file preforms are formed, they are twisted or
`heated and twisted on a device such as that shown in FIG.
`1. The twisting apparatus 10, shown in FIG. 1, includes a
`
`30
`
`40
`
`45
`
`55
`
`

`
`6,149,501
`
`7
`drive head 9 which rotates about a horizontal axis. Extend-
`ing from the drive head 9 is a collet 14 which circumfer-
`entially grips and secures the proximal or inner end of a
`preformed ground file blank 12 for rotation about the
`longitudinal axis thereof. The distal or outer end portion of 5
`the file blank 12 is secured by opposing jaws 20, 22, which
`are mounted on a stage 28 which moves parallel to the
`longitudinal axis of the file blank (horizontally as shown in
`FIG. 1), away from collet 14 at a predetermined rate as the
`collet rotates to twist the file blank 12. At least one of the 10
`jaws includes a spring or air cylinder 16 so that it may be
`compressed against the opposing jaw with a constant force.
`Each jaw includes a protectant layer 24, 26 which is mal-
`leable and able to withstand the working temperature of the 15
`file blank 12. Brass is one material known to be suitable.
`With each subsequent file formed, the jaws 20, 22 are
`provided with a new protectant layer 24, 26 from strips 29,
`30 from a source 32, 34 such as take-off reels. The protectant
`layer may optionally be contacted by a heating element 25, 20
`27 which may heat by any suitable process, such as an
`electrical heating process of joulian, radiant or induction
`heating or may be supplied with a heated fluid such as steam
`or oil.
`
`In order to optimize the superelastic properties of the
`finished file it is desirable, although not essential, to heat
`treat the twisted files. The heat treatment may be performed
`in any furnace with air circulation. The radiant heating
`elements or electrodes to provide for joulian heating can be
`used for the post twist heat treatment.
`
`25
`
`30
`
`Typically the files are made in a variety of working
`lengths varying from 19-30 mm. The specific variables
`which are typically controlled in fabricating such files are set
`forth in the Tables 1 and 2. In Tables 1 and 2 the variables 35
`A and B represent the minimum thickness of the transverse
`cross section at 16.00 mm and 3.00 mm, respectively, from
`the tip. The variables C and D represent the maximum
`thickness of the transverse cross section at 16.00 mm and
`3.00 mm, respectively, from the tip. (cid:9)
`
`40
`
`8
`linear or axial motion mechanism 206 similar to apparatus
`10 of FIG. 1. Each mechanism 204, 206 is connected to file
`blank 202 for purposes to be described. Rotary motion
`mechanism 204 and linear motion mechanism 206 may be
`conventional mechanisms known in the art for forming
`helical flutes on endodontic files. Each mechanism 204, 206
`is operated by a suitable electric motor 210. A ge ar drive 212
`is connected in a conventional manner between an output
`210a of motor 210 and linear motion mechanism 206 to
`convert the rotary motion of motor 210 into linear motion.
`Gear drive 212 is shown to simply include two gears 212a,
`212b, for simplicity, but it will be understood that idler gears
`may be used between gears 212a, 212b. Such idler gears are
`conventionally used to set the material feed rate. A support
`plate 220 is provided generally for connecting rotary motion
`mechanism 204 to linear motion mechanism 206. Support
`plate 220 can also serve as a mounting plate for a mechanism
`(not shown) used to raise and lower apparatus 200, for
`reasons to be described.
`
`Rotary motion mechanism 204 further comprises a rotary
`shaft 222 which may be directly coupled to output shaft
`210a of motor 210. A conventional collet 224 is provided for
`holding a proximal end of superelastic file blank 202.
`Superelastic file blank 202 further has its ground portion or
`working length held between a pair of spring-loaded clamp-
`ing jaws 226, 228, as best shown in FIG. 8. Clamping jaws
`226, 228 are held at a relative lower end 230a of a clamping
`jaw support 230. Clamping jaw support 230 preferably has
`a conventional biasing mechanism to force jaws 226, 228
`toward one another with a desired clamping force. Further,
`clamping jaw support 230 holds a helical threaded shaft 232
`for rotation at a relative upper end 230b. Helical threaded
`shaft 232 is also held within internal threads of gear member
`212a of gear drive 212 such that, upon operation of gear
`drive 212 by motor 210, gear member 212a will rotate and
`also rotate helical threaded shaft 232. This will move shaft
`232 linearly along its longitudinal axis thereby moving jaw
`support 230 and jaws 226, 228 along the length of the
`pre-ground superelastic file blank 202.
`
`Table 1 describes the characteristics of a twisted rhom-
`boidal file. In observing the longitudinal cross section of a
`rhomboidal file there are alternating large flutes 153, result-
`ing from the major axis of the rhombus, and small flutes 151,
`resulting from the minor axis of the rhombus. In Table 1 the
`column entitled Tight Flute Limit includes two values. The
`first value is the minimum acceptable length of a small flute
`151 resulting from the twisting of the minor axis of the
`rhombus. The second value is the minimum acceptable
`length of a large flute 153 resulting from the twisting of the
`major axis of the rhombus. Similarly, the column entitled
`Loose Flute Limit includes two values. The first value is the
`maximum acceptable length of a small flute 151 resulting
`from the twisting of the minor axis of the rhombus. The
`second value is the maximum acceptable length of a large
`flute 153 resulting from the twisting of the major axis of the
`rhombus. In Table 1 the column labeled T max represents the
`maximum acceptable length of the untwisted portion at the
`distal tip of the file. In Table 2 the value L is the length of
`the ground portion of the rod.
`
`45
`
`50
`
`55
`
`60
`
`Referring now to FIG. 7, an apparatus 200 is shown for
`forming a superelastic endodontic file blank 202 into a
`fluted, superelastic file. File blank 202 has been ground, such
`as in accordance with the above descriptions, before being 65
`fluted by apparatus 200. Apparatus 200 generally comprises
`a rotary motion mechanism 204 operatively connected to a
`
`In accordance with one aspect of the invention, a heated
`liquid 234 contained in a vessel 236 receives the ground
`portion of file blank 202 during a twisting and fluting
`operation. The heated liquid media 234 may, for example,
`comprise a salt solution or other suitable liquids such as oil.
`Preferably, the chosen liquid will have a boiling temperature
`preferably above the Af temperature or even above the Tw
`of the particular superelastic material. Presently, it is con-
`templated that a suitable operating temperature for liquid
`234 is approximately 500° C. or above. Again, it is prefer-
`able that the liquid does boil at the chosen operating tem-
`perature. Liquid 234 may be heated by any conventional
`manner, such as with an electrical heating element 238 or a
`heating jacket.
`
`For purposes of describing the operation of the apparatus
`200 shown in FIGS. 7 and 8, one contemplated example
`involves placing a ground file blank 202, formed of a
`superelastic metallic alloy and formed with a rhomboid
`cross section as generally described above, within collet
`224. Clamping j