(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0115786 A1
`Matsutani et al.
`(43) Pub. Date:
`Jun. 1, 2006
`
`US 20060115786A1
`
`(54) ROOT CANAL TREATMENT TOOL
`
`(30)
`
`Foreign Application Priority Data
`
`(76) Inventors: Kanji Matsutani, Tochigi-ken (JP);
`Kaoru Ohgane, Tochigi-ken (JP);
`Toshiyuki Takase, Tochigi-ken (JP)
`
`Correspondence Address:
`
`Law O?ice of Townsend & Banta
`c/o PortfolioIP
`P_()_ BOX 52050
`Minneapolis, MN 55402 (Us)
`
`(21) App1_ NQ;
`
`11/287,771
`
`(22) Filed:
`
`Nov. 28, 2005
`
`Nov. 29, 2004 (JP) ......................... .. 2004-344717(PAT.)
`
`Publication Classi?cation
`
`(51) Int. Cl.
`(2006.01)
`A61C 5/02
`(52) U.S. Cl. ............................................................ .. 433/102
`
`(57)
`
`ABSTRACT
`
`A ?leA acting as a root canal treatment tool has a rod-shaped
`needle portion 1 that includes a Working portion 4 of a
`predetermined length from a tip 3 and a shank 5 formed
`continuously to the Working portion 4 and is composed of
`NiiTi alloy, Wherein at a part of the Working portion or the
`entire Working portion is subjected to heat treatment paying
`attention to durability to rotation fatigue.
`
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`Patent Application Publication Jun. 1, 2006 Sheet 3 0f 3
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`US 2006/0115786 A1
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`US 2006/0115786 A1
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`Jun. 1, 2006
`
`ROOT CANAL TREATMENT TOOL
`
`BACKGROUND OF THE INVENTION
`
`[0001] 1. Field of the Invention
`
`[0002] The present invention relates to a root canal treat
`ment tool for dental use, and more particularly, to a root
`canal treatment tool having improved durability against
`fatigue caused by the rotation of the root canal treatment tool
`that performs a treatment purpose by being rotated, inserted
`and extracted in a lengthWise direction, and repeatedly
`rotated forWard and rearWard about 1A.
`
`[0003] 2. Description of the Related Art
`
`[0004] Tools for treating the root canal of a tooth While
`being rotated include a ?le and reamer that cut and form a
`root canal. These root canal treatment tools are composed of
`a member having a Working portion provided With a cutting
`blade or piercing protrusion formed to a slender tapered rod
`so as to be appropriate for a treatment purpose or composed
`of a member having a Working portion formed by molding
`a tapered rod in a spiral shape. Further, some kind of tool
`includes a handle or a grip Which is integrated With an end
`of the member and gripped and manipulated by a dentist so
`that it is gripped by a chuck of a hand piece and the like or
`directly manipulated by the dentist.
`
`[0005] The root canal is excessively thin and has a variety
`of shapes and siZes and is very different betWeen persons.
`For this reason, many tools of different siZes are provided
`even for the same kind of root canal treatment tools. For
`example, in the case of cutting and forming a root canal by
`using a ?le, the ?le is required to be deformed along the
`shape of the root canal, that is, to have appropriate elasticity
`so that it should not hurt the surrounding of the root canal.
`
`[0006] A technology disclosed in Japanese Patent No.
`3375765 is proposed as a root canal treatment tool having
`extremely high elasticity and shape restoration property as
`described above. This technology relates to a root canal
`treatment tool having a Working portion formed and manu
`factured by applying a removing process to a rod-shaped
`raW material that is subjected to shape memory heat treat
`ment and has a superelastic characteristic While holding it
`under a memory treatment temperature.
`
`[0007] In the above root canal treatment tool, the rod
`having the Working portion formed thereon is ?exibly
`deformed in response to an external force applied thereto
`and is quickly restored to an original shape With the removal
`of the external force. For this reason, this tool can extremely
`folloW up the shape of the root canal With an extremely high
`folloW-up property and form the root canal With high
`accuracy.
`
`[0008] In the root canal treatment tool relating to Japanese
`Patent No. 3375765, the Working portion has a uniform
`superelastic characteristic along the Whole length. Accord
`ingly, When the Working portion is bent, a tip of a free end
`also has an action of returning to an original shape, thereby
`stress is generated When the tip is inserted into and bent in
`the root canal for the treatment of the root canal. In particu
`lar, When the root canal is to be formed, the tool is rotated
`in a state that a tip portion of the Working portion is mainly
`bent, from Which a problem arises in that there is a high
`
`possibility that the slender tip portion is damaged because
`stress acts on the Working portion repeatedly.
`
`SUMMARY OF THE INVENTION
`
`[0009] Accordingly, an object of the present invention is to
`provide a root canal treatment tool Which has a less possi
`bility of being damaged even if it is bent repeatedly by being
`rotated to form a root canal, that is, Which has high dura
`bility.
`[0010] To solve the above problem, there is provided a
`rod-shaped root canal treatment tool composed of NiiTi
`alloy and having a Working portion of a predetermined
`length from a tip as Well as a shank formed continuously to
`the Working portion, Wherein at least a part of the Working
`portion or the entire Working portion is subjected to heat
`treatment at predetermined treating temperature and treating
`time decided by paying attention to durability against rota
`tion fatigue.
`[0011] Since the root canal treatment tool of the present
`invention is subjected to the heat treatment paying attention
`to the rotation fatigue at least in a part of the Working portion
`or in the entire Working portion, the treatment tool can
`exhibit high durability against repeated bending caused
`When it is rotated to treat a root canal.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0012] FIG. 1 is a vieW shoWing a ?le as an example
`representative of a root canal treatment tool;
`
`[0013] FIG. 2 is a schematic vieW explaining an arrange
`ment of the ?le When a fatigue breakage test of a tip portion
`of the ?le is performed; and
`
`[0014] FIG. 3 is a graph shoWing a result of test of a
`fatigue breakage time When the same material is subjected to
`heat treatment at different temperatures.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`[0015] Aroot canal treatment tool according to the present
`invention is a tool for treating a root canal by being rotated
`and includes all the tools formed of a rod-shaped material
`composed of nickel-titanium (NiiTi) alloy. In this root
`canal treatment tool, a Working portion having a shape
`capable of performing a treatment purpose most reasonably
`is formed at one end portion and a manipulating portion
`manipulated by a dentist is formed at the other end portion.
`When the dentist directly manipulates the tool, this manipu
`lating portion is formed of a handle and When a tool such as
`a hand piece is used, the manipulating portion is provided
`With a grip formed in a shape suitable for the structure of a
`handle of the tool.
`[0016] In particular, heat treatment is performed paying
`attention to the durability of a part of the Working portion or
`the entire Working portion to thereby eliminate a possibility
`of breakage of the tool by improving the durability of the
`portion thereof repeatedly bent When a root canal is treated
`by the tool.
`
`Embodiment l
`
`[0017] A preferable embodiment of a root canal treatment
`tool according to the present invention Will be explained
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`US 2006/0115786 A1
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`Jun. 1, 2006
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`below with reference to the drawings. FIG. 1 is a view
`showing a ?le as an example representative of the root canal
`treatment tool. FIG. 2 is a schematic view explaining an
`arrangement of the ?le when a fatigue breakage test of the
`tip of the ?le is performed.
`[0018] A shape of a ?le A, which is representative of the
`root canal treatment tool, will be explained with reference to
`FIG. 1. The ?le A is a tool for cutting a wall in a root canal
`and composed of a needle portion 1 and a grip 2.
`[0019] A tapered working portion 4 extending in a prede
`termined length from a tip 3 is formed to the needle portion
`1, and a straight shank 5 is formed continuously to the
`working portion 4. The working portion 4 is con?gured to
`have various cross sections according to a kind of the ?le,
`such as rectangle, triangle, or square so as to exert its unique
`function.
`
`[0020] In the ?le A of the embodiment, a rectangular cross
`section is formed in a spiral shape along the working portion
`4 to thereby form a groove 4a and a cutting edge 4b along
`the groove 4a.
`
`[0021] The shank 5 has a function of being mounted in the
`grip 2. As shown in the drawing, the grip 2 is con?gured so
`as to be gripped by a chuck of a handle piece or so as to be
`gripped and manipulated by a dentist, thereby being formed
`in a shape and of a material corresponding to the respective
`functions.
`[0022] For example, the grip 2 shown in the drawing is
`made of metal such as stainless steel or the like and has the
`shank 5 inserted into a hole formed at its center and ?xed
`thereto with adhesive. Further, when a grip is formed such
`that it is gripped and manipulated by a hand of the dentist,
`the grip may be molded by injection molding of synthetic
`resin so as to have the shank 5 inserted therein, thereby being
`integrated with and ?xed to the shank 5.
`
`[0023] The needle portion 1 is composed of nickel-tita
`nium (NiiTi) alloy and is formed of a wire having a
`diameter corresponding to the diameter of the needle portion
`1 constituting the ?le A. The needle portion 1 is subjected to
`heat treatment paying attention to durability against rotation
`fatigue in a portion 6 as a part of the working portion 4
`(hereinafter, referred to as “durable heat treatment”).
`[0024] Note that although the durable heat treatment to the
`?le A is applied only from the tip 3 to the portion 6 of the
`working portion 4, it is needless to say that the durable heat
`treatment may be applied to the working portion 4 in its
`entirety in the present invention.
`[0025] The length of the portion 6 of the working portion
`4 is not particularly limited. According to the experiment
`performed by the inventors of the present invention, when
`the working portion was provided with a superelastic char
`acteristic in its entirety, breakage occurred in a portion 2 mm
`to 3 mm apart from a tip in many examples. Thus, the
`portion 6 of the working portion 4 requires at least 2 mm
`from the tip 3 and requires the entire length of the working
`portion 4 at maximum. Further, when the working portion 4
`has a length of 16 mm, the particularly preferable range of
`length of the portion 6 is about 3 mm to 10 mm from the tip
`3 and a length of about 3 mm or 4 mm is more preferable.
`
`[0026] Further, the length of the portion 6 may be changed
`in correspondence to the taper of the ?le A. When the taper
`
`is, for example, 2/ 100, the portion apart from the tip 3 of the
`working portion 4 (grip side portion) does not have a large
`diameter. Therefore, strength can be maintained on the grip
`side by forming the portion 6 in a predetermined range
`extending from the tip 3 and providing the other portion with
`the superelastic characteristic. When the taper is 4/100 or
`6/100, since the diameter on the grip side increases, even if
`the durable heat treatment is applied to the working portion
`4 in its entirety, strength is maintained on the grip side with
`excellent operability.
`
`[0027] The portion 6 of the working portion 4 can be
`subjected to the durable heat treatment by increasing the
`temperature of the portion (the portion 6 or the entire
`working portion 4) to be subjected to the treatment to the
`temperature obtained by a test described later as well as
`keeping the increased temperature for a time obtained by the
`test. In the durable heat treatment, the Af temperature of the
`nickel-titanium alloy used as the material of the ?le is
`increased to a temperature higher than normal temperatures
`so that the portion 6 is arranged as a portion that can exhibit
`a shape memory function.
`
`[0028] In the ?le A arranged as described above, the
`dentist can previously curve the portion 6 in correspondence
`to the shape of a root canal or an apical foramen of a patient
`(precurve) in treatment. The thus formed precurve permits
`the tip 3 and the portion 6 to exhibit an excellent follow-up
`property to the root canal when treatment is performed by
`inserting the tip 3 into the root canal. After the treatment is
`?nished and the tip 3 is extracted from the root canal, the
`portion 6 can be returned to its original shape by force
`applied thereto by the dentist or the original shape of the
`portion 6 can be recovered by increasing the temperature
`thereof to a temperature higher than the Af temperature set
`by the durable heat treatment.
`
`[0029] Since the portion 6 has high ?exibility, a period of
`time until it is broken can be extended when the working
`portion 4 is bent and rotated while inserting the tip 3 into the
`root canal, inserted and extracted in a lengthwise direction,
`and repeatedly rotated about 1A forward and rearward.
`
`[0030] In particular, because the working portion 4 is
`formed in the shape of a taper, when the working portion 4
`is bent with a fulcrum at the tip 3, the shank 5 is kept nearly
`in a straight line and the working portion 4 is bent to an arc
`shape having a small curvature on the shank 5 side and is
`greatly bent to an arc shape that increases a curvature as its
`portion is closer to the portion 6 side and the portion 6 is
`further greatly bent. That is, the working portion 4 is not
`uniformly bent but is bent in response to the taper. When the
`bending of the working portion 4 is released, the portions
`other than the portion 6 are restored to the original shape (in,
`for example, a straight needle shape) and the portion 6 keeps
`a bent shape.
`
`[0031] Next, a test method of setting a heat treatment
`temperature and a keeping time (heat treatment conditions)
`when heat treatment is performed to the portion 6 as a part
`of the working portion 4 or the entire working portion 4
`paying attention to the durability against the rotation fatigue
`and a result of the test will be explained.
`
`[0032] An object of the test is to investigate heat treatment
`conditions in which the ?le A can exhibit highest durability
`as well as to investigate heat treatment conditions common
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`to different types of nickel-titanium alloy assuming a case
`that a root canal is treated by most harshly rotating the root
`canal treatment tool among the treatments performed by
`rotating the tool, inserting and extracting it in the lengthWise
`direction, or repeatedly rotating it about 1A forWard and
`rearWard.
`[0033] For this purpose, in the experiment, ?les A having
`the same speci?cation Were formed of a plurality of types of
`nickel-titanium alloy Wires, a plurality of samples Were
`subjected to heat treatment at different temperatures for
`different keeping times, and then the fatigue breakage
`thereof Was tested using an apparatus shoWn in FIG. 2,
`thereby times passed until they Were broken Were measured,
`and heat treatment conditions in consideration of durability
`against rotation fatigue Were obtained by comparing the
`results of measurement.
`
`[0034] Although a time that passes until the ?le A is
`broken due to fatigue is preferably as long as possible,
`Whether or not the time is long cannot be determined unless
`a certain reference is set. Thus, in the test, about 20 minutes,
`during Which breakage due to fatigue does not occur in a test
`performed using a fatigue breakage tester to be described
`later, are set as the reference.
`
`[0035] Used as raW materials constituting ?les A Were
`Wires having a diameter of about 1.0 mm and composed of
`a material 1 having a composition of Ni: 55.76 Wt % and the
`balance being Ti, a material 2 having a composition of Ni:
`55.91 Wt % and the balance being Ti, a material 3 having a
`composition of Ni: 55.97 Wt % and the balance being Ti, a
`material 4 having a composition of Ni: 55.90 Wt % and the
`balance being Ti, and a material 5 having a composition of
`Ni: 55.89 Wt % and the balance being Ti Were used as the
`material for forming the ?les A, and a plurality of pieces of
`?les #30 Were formed of these Wires. Each ?le had a tip
`portion having a tip diameter of about 0.3 mm, a taper of
`4/100, a cross section formed in a rectangular shape, a
`needle portion extending from a grip 2 and having a length
`of about 25 mm, and a Working portion having a length of
`about 15 mm.
`
`[0036] Next, samples, Which Were not subjected to heat
`treatment (untreated), samples, Which Were subjected to heat
`treatment at 300° for 30 minutes (heat treatment condition
`1), samples, Which Were subjected to heat treatment at 400°
`for 30 minutes (heat treatment condition 2) and then,
`samples, Which Were subjected to heat treatment at 5000 for
`30 minutes (heat treatment condition 3), samples, Which
`Were subjected to heat treatment at 600° for 15 minutes (heat
`treatment condition 4) Were made from the ?les A composed
`of the materials 1 to 5. Then, these samples Were subjected
`to a fatigue breakage (durability) test and additionally sub
`jected to a bend test and a tWist test.
`[0037] It should be noted that, in the respective tests, the
`heat treatment included a case in Which the entire Working
`portion 4 Was subjected to the heat treatment by inserting the
`needle portion 1 composed of NiiTi alloy into an electric
`furnace and a case in Which the heat treatment Was per
`formed in correspondence to the portion 6 from the tip 3.
`Further, the number of the samples to be tested in the same
`condition Was set to 5 pieces. Further, numerical values
`shoWn summarize test data.
`
`[0038] First, a method of a bend test and a result of it Will
`be explained. The bend test Was performed by using samples
`
`Whose needle portions 1 Were entirely subjected to the heat
`treatment and by measuring maximum torque When the
`samples Were bent up to 45° While gripping them at a
`position 3 mm apart from the tip 3 of the Working portion 4.
`As a result of the bend test, the materials 1 to 5 of the
`non-treatment condition Were Within the range of 40 gf-cm
`to 50 gf-cm, the materials 1 to 5 of the treatment condition
`1 Were Within the range of 40 gf-cm to 55 gf-cm, the
`materials 1 to 5 of the treatment condition 2 Were Within the
`range of 35 gf-cm to 40 gf-cm, the materials 1 to 5 of the
`treatment condition 3 Were Within the range of 30 gf-cm to
`40 gf-cm, and the materials 1 to 5 of the treatment condition
`4 Were Within the range of 35 gf-cm to 40 gf-cm, Which
`results in that no signi?cant difference cannot be admitted.
`
`[0039] Next, a method of the tWist test and a result of it
`Will be explained. The tWist test Was performed by using
`samples Whose needle portions 1 Were entirely subjected to
`the heat treatment and by measuring maximum torque and
`angles When the samples Were rotated and broken While
`gripping them at a position 3 mm apart from the tip 3 of the
`Working portion 4. As a result of the tWist test, the materials
`1 to 5 of the non-treatment condition Were Within the range
`of maximum torque 70 gf-cm to 80 gf-cm, angle: 400° to
`500°, the materials 1 to 5 of the treatment condition 1 Were
`Within the range of maximum torque 70 gf-cm to 80 gf-cm,
`angle: 400° to 500°, the materials 1 to 5 of the treatment
`condition 2 Were Within the range of maximum torque 80
`gf-cm to 120 gf-cm, angle: 400° to 600°, the materials 1 to
`5 of the treatment condition 3 Were Within the range of
`maximum torque 70 gf-cm to 100 gf-cm, angle: 450° to
`700°, and the materials 1 to 5 of the treatment condition 4
`Were Within the range of maximum torque 70 gf-cm to 90
`gf-cm, angle: 800° to 1100°, Which results in that although
`the result of test of the samples of the heat treatment
`condition 4 are more advantageous than the samples of the
`other heat treatment conditions, it cannot be admitted that
`the samples of the other heat treatment conditions have a
`signi?cant difference.
`
`[0040] Next, a method of the fatigue breakage test and a
`result of it Will be explained. The fatigue breakage test Was
`performed using the needle portions 1 entirely subjected to
`the heat treatment and the apparatus shoWn in FIG. 2. More
`speci?cally, the apparatus used for the test had a pair of pins
`21, 22 disposed therein, and the pins 21, 22 had grooves 21a,
`22a capable of receiving the tip 3 side of the Working portion
`4. The Working portion 4 Was set to the apparatus such that
`the position thereof apart 4 mm from the tip 3 Was located
`at the center of the pin 21 on one hand as Well as the tip 3
`Was inserted into the groove 22a of the pin 22 on the other
`hand. Then, a time passed until the Working portion 4 Was
`broken Was measured in a state that the Working portion 4
`Was rotated at a speed of 200 rpm While bending the portion
`6 of the Working portion 4 at approximately 45°.
`
`[0041] As a result of the fatigue breakage test, it can be
`found that the time passed until fatigue breakage occurs
`greatly changes depending on the heat treatment conditions.
`More speci?cally, in the non-treatment condition, the time
`Was about 18 minutes even in the most durable material 2,
`Within the range of 5 to 10 minutes in the heat treatment
`condition 1, Within the range of 4 to 11 minutes in the heat
`treatment condition 3, and Within the range of 4 to 5 minutes
`in the heat treatment condition 4. Whereas, in the heat
`treatment condition 2 (400° C. for 30 minutes), it Was Within
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`the range of about 8 to 56 minutes Which Were greatly longer
`than the times of the samples Which Were fatigue broken in
`the other heat treatment conditions.
`
`[0042] More speci?cally, When the heat treatment is per
`formed in the heat treatment condition 2, an effect of greatly
`extending the fatigue breakage time can be obtained, from
`Which it can be said that the heat treatment can exhibit high
`durability.
`[0043] As described above, it can be found that the dura
`bility of the root canal treatment tool can be improved by
`performing the heat treatment While keeping the raW mate
`rial of NiiTi alloy at 400° C. for 30 minutes. However, it
`is not apparent Whether or not the condition of 400° C. for
`30 minutes is an optimum condition. Accordingly, the
`fatigue breakage test Was performed by changing tempera
`ture While specifying a material and employing a constant
`treatment time.
`
`[0044] The above material 2 having the composition of Ni:
`55.91 Wt % and the balance being Ti Was used in the test.
`Further, a heat treatment temperature Was set to 250° C.,
`300° C., 350° C., 375° C., 400° C., 410° C., 420° C., 425°
`C., 430° C., 440° C., 450° C., 475° C., 500° C., and 550° C.,
`and the fatigue breakage test Was performed to the samples
`subjected to the heat treatment at the respective tempera
`tures.
`
`[0045] FIG. 3 shoWs a result of the fatigue breakage test.
`As shoWn in the draWing, When the heat treatment tempera
`ture is Within the range of 400° C. to 450° C., the time passed
`until the fatigue breakage occurs exceeds 15 minutes and
`exceeds 20 minutes at 430° C. and 440° C. It can be said
`from the result of the test that the heat treatment paying
`attention to the durability against the rotation fatigue in the
`entire Working portion can be performed by the heat treat
`ment executed at the temperature Within the range of 400° C.
`to 450° C. for 30 minutes.
`
`[0046] Next, the fatigue breakage test Was also performed
`using a partial heat apparatus (not shoWn) to samples each
`formed of the above material 2 having the composition of
`Ni: 55.91 Wt % and the balance being Ti and subjected to the
`heat treatment Within the range of about 5 mm and about 10
`mm from the tip 3 of the Working portion 4. In the test, a
`keeping time Was set to 45 minutes (?xed) and heat treat
`ment temperatureitemperature set to the partial heat appa
`ratus Were selected from 400° C. (350° C., 340° C.), 425° C.
`(37020 C., 360° C.), 450° C. (390° C, 375° C.), 475° C.
`(410° C., 390° C.), 500° C. (440° C., 420° C.), 525° C. (460°
`C., 430° C.), and 550° C. (480° C., 440° C.). Further, the
`fatigue breakage test Was also performed to samples sub
`jected to the heat treatment at 400° C. for 40 minutes using
`a drier as a comparative example.
`
`[0047] Note that since the heat treatment to sample in the
`ranges of about 5 mm and about 10 mm from the tip of the
`Working portion 4 is performed to a very thin rod by
`restricting the range thereof, the siZe of the range cannot be
`accurately regulated. Thus, since it is dif?cult to shoW the
`range of the lengths from the tip 3 by accurate numerals, the
`range cannot help being shoWn as about 5 mm and about 10
`mm.
`
`[0048] When the heat treatment is performed using the
`partial heat apparatus, it cannot be guaranteed that the
`temperature set to the partial heat apparatus accurately
`
`corresponds the actual temperature of the sample. When the
`surface temperatures of the samples Were measured at the
`time the heat treatment Was actually performed by the partial
`heat apparatus, there Were differences betWeen the surface
`temperatures and the temperature set to the apparatus. More
`speci?cally, the former temperatures in parentheses Were the
`surface temperatures of the samples When they Were heated
`Within the range of about 5 mm from the tip and the latter
`temperatures in parentheses Were the surface temperatures
`of the samples When they Were heated Within the range of
`about 10 mm from the tip With respect to the temperature set
`to the partial heat apparatus. As described above, the surface
`temperatures of the samples being subjected to the heat
`treatment are loWer than the temperature set to the partial
`heat apparatus.
`
`[0049] As a result of the above test, When the heat treat
`ment Was performed Within the range of about 5 mm, the
`time until the fatigue breakage occurred Was about 29
`minutes When the heat treatment temperature Was set to 425°
`C., and, in the other heat treatment conditions, the fatigue
`breakage occurred in a time shorter than 20 minutes.
`
`[0050] When the range of the heat treatment Was Within
`about 10 mm, the time until the fatigue breakage occurred
`exceeded 20 minutes at the heat treatment temperature set
`Within the range of 425° C. to 500° C. Further, the fatigue
`breakage occurs in about 19 minutes at the heat treatment
`temperature set to 525° C.
`
`[0051] Further, in the comparative example, the time until
`the fatigue breakage occurred Was about 35 minutes.
`
`[0052] In practical application, it is su?icient that the time
`until the fatigue breakage occurs be at least about 20
`minutes. Accordingly, it can be said that the heat treatment
`can be performed paying attention to the durability against
`the rotation fatigue in a part of the Working portion by heat
`treating the ?le A Whose range of about 5 mm from the tip
`is to be heat treated in the heat treatment condition of 425°
`C. for 45 minutes and by heat treating the ?le A Whose range
`of about 10 mm from the tip is to be heat treated in the heat
`treatment condition of 425° C. for 45 minutes to 525° C. for
`45 minutes.
`
`[0053] As described above, it can be said that the heat
`treatment can be performed paying attention to the durability
`against the rotation fatigue in a part of the Working portion
`or in the entire Working portion by performing the heat
`treatment at the heat treatment temperature Within the range
`of 400° C. to 450° C. for a keeping time of 30 minutes to 45
`minutes comprehensively judging from a result of the
`fatigue breakage test of the samples Whose Working portion
`4 Was entirely heat-treated and from a result the fatigue
`breakage of the samples Whose ranges of 5 mm and 10 mm
`from the extreme end of the Working portion Were heat
`treated.
`
`[0054] In the ?le A described above, the grip 2 is gripped
`by a chuck of a hand piece (not shoWn) as Well as the hand
`piece is held by the dentist, the portion 6 formed to the
`Working portion 4 is previously bent in correspondence to
`the shape of the root canal of the patient, and then the tip 3
`is inserted into the root canal and moved in an axial direction
`While being rotated in the direction of the cutting edge 4b,
`thereby the root canal can be formed by cutting the Wall of
`the root canal.
`
`8 of 9
`
`PGR2015-00019 - Ex. 1025
`US ENDODONTICS, LLC., Petitioner
`
`

`
`US 2006/0115786 A1
`
`Jun. 1, 2006
`
`[0055] Note that, in the embodiment, since the ?le A as the
`root canal treatment tool is exempli?ed, the cutting edge 4b
`is formed thereto. However, the cutting edge 4b is not
`necessarily formed to the Working portion 4 of all the root
`canal treatment tools, and the tools may be formed in a coil
`shape With a piercing protrusion and a taper. Even the root
`canal treatment tools arranged as described above can
`exhibit high durability by subjecting the portion 6 of the
`Working portion 4 or the entire Working portion 4 to the
`durable heat treatment as long as they are root canal treat
`ment tools for treating the root canal by being rotated.
`
`[0056] Although a method of manufacturing the ?le A is
`not particularly limited, typical methods Will be brie?y
`explained. In a ?rst manufacturing method, the Working
`portion is made from a material, Which is previously pro
`vided With a superelastic characteristic, by being subjected
`to a process of removal metal, and then a part of the Working
`portion on an extreme end side or the entire Working portion
`is subjected to the durable heat treatment.
`
`[0057] More speci?cally, a rod-shaped raW material is
`formed by cutting an NiiTi alloy Wire previously provided
`With the superelastic characteristic and having a diameter
`corresponding to a siZe of a target ?le to a length of the ?le.
`Then, the raW material is processed into the shape of a taper,
`is processed to form a groove and a cutting edge, and is
`further processed to form a tip, the Working portion, and a
`shank, thereby a needle portion is formed. At the time, since
`the raW material cannot be plastically processed because it
`has the superelastic characteristic, the respective processes
`to the raW material are performed by the process of remov
`ing metal, including a cutting process.
`[0058] Next, a portion subjected to the durable heat treat
`ment is formed Within the range having a predetermined
`length from the tip of the Working portion or in the entire
`Working portion 4. This process is performed in such a
`manner that the portions other than a portion corresponding
`to the part in a needle portion previously formed into the
`predetermined shape, to Which the durable heat treatment is
`applied, are cooled by a cooling agent, and heated based on
`heat treatment conditions having a preset temperature and
`keeping time. The cooling agent used at the time is not
`particularly limited, and, for example, Water can be used.
`
`[0059] A target ?le can be manufactured by inserting a
`shank of the needle portion, Which is provided With the
`portion 6 composed of the range of a predetermined length
`from the tip of the Working portion or the entire Working
`
`portion to Which the durable heat treatment is applied, into
`a grip as Well as bonding them each other.
`
`[0060] In a second manufacturing method, the range of a
`predetermined length corresponding to a portion subjected
`to the durable heat treatment from a tip on one side of a raW
`material or a portion corresponding to an entire Working
`portion of the raW material is subjected to the durable heat
`treatment and then subjected to the process including the
`removal of metal, thereby the target ?le is manufactured by
`forming the Workin