US007137815B2
`
`(12) United States Patent
`Matsutani et a1.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,137,815 B2
`Nov. 21, 2006
`
`(54) ROOT CANAL TREATMENT TOOL AND
`METHOD FOR MANUFACTURING THE
`
`4/1999 Buchanan ................. .. 433/102
`5,897,316 A *
`5,984,679 A * 11/1999 FarZin-Nia et a1. ....... .. 433/102
`
`SAME
`
`(75) Inventors, Kanji Matsutani’ Tochigi_ken (JP);
`Kaoru ohganea Tochigi_ken (1p);
`Toshiyuki Takase, Tochigi-ken (JP)
`
`(73) Assignee: Mani, Inc., Shioya-gun (JP)
`
`6,149,501 A * 11/2000 FarZin-Nia et a1. ......... .. 451/48
`
`6,299,445 B1* 10/2001 Garman .................... .. 433/102
`6,315,558 B1* 11/2001 FarZin-Nia et a1. ....... .. 433/102
`6,375,458 B1 *
`4/2002 Moorleghem et a1. ....... .. 433/2
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 120 days.
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`0 684 019 A1
`
`4/1995
`
`(21) Appl. No.2 10/855,492
`
`(22) Filed:
`
`May 28, 2004
`
`(65)
`
`(30)
`
`Prior Publication Data
`
`US 2005/0003325 A1
`
`Jan. 6, 2005
`
`Foreign Application Priority Data
`
`May 29, 2003
`
`(JP)
`
`........................... .. 2003-152564
`
`(51) Int. Cl.
`(2006.01)
`A61C 5/02
`(52) US. Cl. .................................................... .. 433/102
`(58) Field of Classi?cation Search .............. .. 433/ 102,
`433/81, 224
`See application ?le for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`* cited by examiner
`
`Primary ExamineriJohn J. Wilson
`Assistant ExamineriMeoghan E. MacPherson
`(74) Attorney, Agent, or F irmiToWnsend & Banta
`
`(57)
`
`ABSTRACT
`
`The present invention relates to a root canal treatment tool
`that is formed in a shape of a rod and has a Work portion
`formed in a predetermined length from a tip and a shank
`formed in a manner continuous With the Work portion. The
`Work portion has a shape memory characteristic in a range
`of a predetermined length from the tip and a superelastic
`characteristic in a remaining portion.
`
`5,775,902 A *
`
`7/1998 Matsutani et a1. ........ .. 433/102
`
`2 Claims, 4 Drawing Sheets
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`Nov. 21, 2006
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`US 7,137,815 B2
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`1
`ROOT CANAL TREATMENT TOOL AND
`METHOD FOR MANUFACTURING THE
`SAME
`
`FIELD OF THE INVENTION
`
`The present invention relates to a root canal treatment tool
`for dental treatment, and a method for manufacturing this
`root canal treatment tool.
`
`BACKGROUND OF THE INVENTION
`
`Various tools for treating the root canal of a tooth exist,
`including, for example, a reamer and a ?le that cut and form
`a root canal, a compactor, a ?ller, a spreader, and a plugger
`that ?ll the root canal With thermoplastic resin; a cleanser
`that removes remainders in the root canal; and a broach that
`?lls the root canal With cotton. The above-described reamer
`and ?le is constructed of a slender tapered rod having a Work
`portion provided With a cutting blade or piercing protrusion
`appropriate for a treatment object or a member having a
`Work portion formed by forming a tapered rod in a spiral
`shape. Moreover, the tools described above comprised of a
`handle or a grip integrated With the end of the member, so
`that the tool may be gripped or operated by a dentist, or is
`constructed of a shank, so that it may be gripped by a chuck
`of a hand piece or the like, or is directly operated by the
`dentist.
`The root canal is excessively thin and has a variety of
`shapes and siZes, and varies betWeen persons. For this
`reason, tools of many different siZes are needed, even for the
`same kind of root canal treatment tools. For example, in the
`case of cutting and forming a root canal by use of a reamer,
`the reamer 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 root canal. Japanese Patent
`No. 3375765 discloses a root canal treatment tool having
`extremely high elasticity and a shape restoration property as
`described above. This technology relates to a root canal
`treatment tool having a Work portion formed and manufac
`tured by applying a removing Work to a rod-shaped raW
`material that is subjected to shape memory heat treatment,
`and has a superelastic characteristic While holding it under
`a memory treatment temperature.
`In the above-mentioned root canal treatment tool, the rod
`having the Work portion formed thereon is ?exibly deformed
`in response to an external force applied thereto, and is
`quickly restored to an original shape When the external force
`is removed. For this reason, this tool can conform Well to the
`shape of the root canal, and form the root canal With high
`accuracy.
`In the root canal treatment tool relating to the Japanese
`Patent No. 3375765, the Work portion has the superelastic
`characteristic uniformly along the Whole length and, hence,
`When the Work portion is bent, a tip portion of a free end also
`has an action of returning to an original shape. Accordingly,
`When the tip portion is inserted into the root canal for the
`treatment of the root canal and is bent, a repulsive force is
`generated to act on the Wall of the root canal. Thus, there is
`an undesirable possibility that, in the vicinity of a root sharp
`mouth (tip of the Work portion), the Work portion might cut
`the outside of a bent portion of the root canal more heavily,
`and might cut the inside in the center of the bent portion
`more heavily, so as to penetrate the root canal.
`Moreover, since the root canal treatment tool is rotated in
`a state Where the Work portion is bent almost along the
`Whole length from the tip at the time of forming the root
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`canal, a repeated bending stress is applied to the Work
`portion. This increases the possibility of breaking a slender
`tip portion of the Work portion. For this reason, although the
`root canal treatment tool relating to the Japanese Patent No.
`3375765 has sufficiently high durability as compared With a
`root canal treatment tool made of stainless steel, it lacks
`suf?cient durability.
`
`SUMMARY OF THE INVENTION
`
`The object of the present invention is to provide a root
`canal treatment tool that, unlike the conventional tool, is not
`apt to go out of the root canal and that is enhanced in
`durability by Weakening the action of returning to an origi
`nal shape of the tip portion of the Work portion, and a
`method for manufacturing the root canal treatment tool.
`In order to solve the above problems, a root canal treat
`ment tool according to the present invention is provided that
`is formed in the shape of a rod, has a Work portion formed
`in a predetermined length from a tip and a shank formed in
`a manner continuous With the Work portion, and is such that
`the Work portion has a shape memory characteristic in the
`range of a predetermined length from the tip and a super
`elastic characteristic in a remaining portion.
`In the root canal treatment tool of the present invention,
`the Work portion has the shape memory characteristic in the
`range of a predetermined length from the tip, and the
`superelastic characteristic in the remaining portion. For this
`reason, in a state Where the tip does not recover a memory
`shape, even When a small force is applied to the tip from the
`outside, it is easily deformed in response to this force. That
`is, the tip having the shape memory characteristic can be
`freely deformed by a small force as compared With the other
`portion having the superelastic characteristic.
`Therefore, the tip of the Work portion loses an action of
`returning to an original shape and hence conforms Well to
`the shape of the root canal, and does not deviate from the
`root canal at the time of forming the root canal. Furthermore,
`the tip portion becomes soft to improve durability When the
`Work portion is rotated at the time of forming the root canal.
`Further, a method for manufacturing a root canal treat
`ment tool according to the present invention is provided,
`comprising:
`subjecting a portion of a Wire provided With a superelastic
`characteristic by a memory heat treatment to a Working of
`removing metal;
`subjecting a portion of the portion of a Wire subjected to
`the Working of removing metal to heat treatment to provide
`the portion With a shape memory characteristic, or a portion
`of the Wire provided With the superelastic characteristic by
`the memory heat treatment is again subjected to heat treat
`ment to provide the portion With the shape memory char
`acteristic; and then
`subjecting the portion having the shape memory charac
`teristic and the portion that is continuous With the portion
`having the shape memory characteristic and that has the
`superelastic characteristic to the Working of removing metal.
`According to the above method for manufacturing a root
`canal treatment tool, the Wire provided With the superelastic
`characteristic is previously subjected to the Working of
`removing metal, thereby being formed into the shape of an
`objective root canal treatment tool, and then the tip portion
`of the Work portion is again subjected to heat treatment. In
`this manner, it is possible to manufacture the root canal
`treatment tool having the Work portion that is provided With
`the shape memory characteristic in the tip and the super
`elastic characteristic in the remaining portion. Moreover, a
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`US 7,137,815 B2
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`3
`portion of the Wire provided With the superelastic charac
`teristic is previously again subjected to heat treatment,
`thereby being provided With the shape memory character
`istic, and then is subjected to the Working of removing metal,
`thereby being formed into the shape of the objective root
`canal treatment tool. In this manner, it is possible to manu
`facture the root canal treatment tool of the present invention
`having the Work portion that is provided With the shape
`memory characteristic in the tip and the superelastic char
`acteristic in the remaining portion.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a side vieW of a the root canal treatment tool of
`the present invention.
`FIG. 2A is an illustration of a side vieW of NiiTi Wire
`used to form the rod-shaped raW material used to manufac
`ture the root canal treatment tool of the present invention.
`FIG. 2B is a side vieW of the needle portion 1 of the root
`canal treatment tool shoWn in FIG. 1, illustrating the con
`struction of the tapered Work portion after Working of the
`raW material shoWn in FIG. 2 according to the method of the
`present invention.
`FIG. 2C is a side vieW of the needle portion 1 of the root
`canal treatment tool shoWn in FIG. 1, illustrating the super
`elastic portion 7 and shape memory portion 6 formed after
`heat treatment of the needle portion 1 according to the
`method of the present invention.
`FIG. 3 is a partial schematic vieW illustrating the appli
`cation of a fatigue fracture test on the tip portion of a root
`canal treatment tool according to the present invention.
`FIG. 4(a) is an illustration of a partial heating method of
`the Work portion by hot air of the present invention.
`FIG. 4(b) is an illustration of a partial heating method of
`the Work portion by a furnace of the present invention.
`FIG. 4(c) is an illustration of a partial heating method of
`the Work portion by liquid of the present invention.
`FIG. 4(d) is an illustration of a partial heating method of
`the Work portion by solid of the present invention.
`FIG. 4(e) is an illustration of a partial heating method of
`the Work portion by heating pod of the present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The preferred embodiment of a root canal treatment tool
`according to the invention Will be described beloW With
`reference to draWings and the preferred method for manu
`facturing the same.
`The root canal treatment tool according to the present
`invention is a tool for treating a root canal, and includes all
`tools formed by use of a rod-shaped material. In this root
`canal treatment tool, a Work portion having a shape capable
`of performing an objective treatment most reasonably is
`formed at one end portion, and an operation portion operated
`by a dentist is formed at an opposite end portion. When the
`dentist directly operates the tool, this operation portion is
`formed into a handle, and When a tool such as a hand piece
`is used, the operation portion is provided With a grip formed
`in a shape suitable for the structure of the grip of the tool.
`The shape of a reamer A Will be described as an example
`of the root canal treatment tool With reference to FIG. 1. The
`reamer A is a tool for cutting a Wall of the root canal, and is
`constructed of a needle portion 1 and a grip 2. In the needle
`portion 1, a tapered Work portion 4 extending a predeter
`mined length from a tip 3 is formed, and a straight shank 5
`is formed in a manner continuous With the Work portion 4.
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`The Work portion 4 is provided in various cross sections
`according to the kind of reamer, such as rectangle, triangle,
`or square, so as to perform its unique function.
`In the reamer in this embodiment, a rectangular cross
`section is formed in the shape of a spiral along the Work
`portion 4, to form a groove 4a and a cutting edge 4b along
`the groove 4a. The shank 5 has a function of being mounted
`in the grip 2. The grip 2, as shoWn in FIG. 1, is formed so
`as to be gripped in the chuck of a handle piece, or so as to
`be gripped and operated by a dentist, thereby being formed
`in the shape and of material corresponding to the respective
`functions.
`For example, the grip 2 is made of metal such as stainless
`steel or the like, and has a shank 5 inserted into a hole made
`in its center and ?xed thereto With adhesive. Moreover, in
`the case of forming a grip to be gripped and operated by
`hand by the dentist, the grip may be also molded by the
`injection molding of synthetic resin, so as to have the shank
`5 inserted therein, thereby being integrated With and ?xed to
`the shank 5.
`The needle portion 1 is made of metal having a shape
`memory characteristic, for example, nickel-titanium (Nii
`Ti) alloy, and is formed of a Wire having a diameter
`corresponding to the diameter of the needle portion 1
`constructing the reamer A. A portion extending a predeter
`mined length from the tip 3 of the Work portion 4 is formed
`as a shape memory portion 6 having the shape memory
`characteristic, and a portion on the shank 5 side nearer to the
`shape memory portion 6 in the Work portion 4 is formed as
`a superelastic portion 7 having a superelastic characteristic.
`The shape memory portion 6 in the needle portion 1 is
`provided With such a characteristic by performing heat
`treatment on the NiiTi alloy, so as to cause the NiiTi
`alloy to not recover a memory shape in the range of a room
`temperature or a body temperature. When the shape memory
`portion 6 reaches a shape recovery temperature, it recovers
`a previously stored shape, and exerts high strength. HoW
`ever, When an external force is applied to the shape memory
`portion 6 in a state Where it does not reach the shape
`recovery temperature, the shape memory portion 6 is easily
`deformed in shape in response to the external force applied
`thereto. Therefore, the shape memory portion 6 does not
`exhibit the characteristic of returning to its original shape,
`but can be deformed in a preferable shape.
`For this reason, the dentist can bend (pre-curve) the shape
`memory portion 6 in correspondence With the shape of root
`canal or the root sharp mouth of a patient at the time of
`treatment. This pre-curving of the shape memory portion 6
`enables the tip 3 and the shape memory portion 6 to folloW
`the root canal With high ?delity at the time of inserting the
`tip 3 into the root canal and performing treatment on the root
`canal. Then, When the dentist takes the root canal treatment
`tool out of the root canal after ?nishing the treatment, he can
`deform it to the original shape by applying a force to the
`shape memory portion 6, or can recover its memory shape
`by increasing its temperature to the shape recovery tempera
`ture.
`As described above, the shape memory portion 6 that does
`not recover the memory shape has high ?exibility and a high
`fatigue resistance characteristic. For this reason, When the
`Work portion 4 is bent and rotated in a state Where the tip 3
`is inserted into the root canal, a fatigue fracture time can be
`elongated as compared With a tool Whose Work portion has
`a superelastic characteristic along the Whole length.
`The superelastic portion 7 memoriZes the shape of a
`straight needle and keeps a state Where a memory shape is
`formed in the shape of the straight needle in the range of
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`room temperature. This superelastic portion 7 has extremely
`high ?exibility and high restorability. That is, the superelas
`tic portion 7 is easily deformed (bent) in response to an
`external force applied thereto, but is easily restored to an
`original shape When the application of the external force is
`removed.
`In particular, because the Work portion 4 is formed in the
`shape of a taper, When the Work portion 4 is bent With a
`fulcrum at the tip 3, the shank 5 is kept nearly in a straight
`line, and the superelastic portion 7 is bent into the shape of
`an arc having a small curvature on the shank 5 side and is
`heavily bent into the shape of an arc that increases a
`curvature as its portion is closer to the shape memory portion
`6 side and the shape memory portion 6 is further heavily
`bent. That is, the Work portion 4 is not uniformly bent, but
`rather is bent in response to the taper. When the bending of
`the Work portion 4 is released, the superelastic portion 7 is
`restored to the original shape (in the shape of a straight
`needle), and the shape memory portion 6 keeps a bent shape.
`The length of the shape memory portion 6 in the Work
`portion 4 is not limited to a special value. According to the
`tests performed by the present inventors, in the Work portion
`having a superelastic characteristic along the Whole length,
`in many cases, the Work portion Was broken in a portion at
`2 mm to 3 mm from the tip. For this reason, the length of the
`shape memory portion 6 in the Work portion 4 needs to be
`at least 2 mm from the tip 3. Although the maximum length
`is not limited to a special length, the maximum length is
`about 3A of the Whole length of the Work portion 4. More
`over, When the length of the Work portion 6 is 16 mm, the
`particularly preferable length range of the shape memory
`portion 6 is from about 3 mm to 6 mm from the tip 3, and
`more preferably about 3 mm or 4 mm.
`If the length of the shape memory portion 6 is smaller than
`2 mm, durability is not substantially different as compared
`With a reamer having a superelastic characteristic along the
`Whole length of the Work portion. Moreover, if the length of
`the shape memory portion 6 is larger than 3/4 of the Work
`portion, at the time of inserting the tip 3 into the root canal
`and rotating it, a problem may occur in that the position of
`a rotational axis is not ?xed, but is made eccentric to make
`it di?icult to cut the root canal Well.
`Although the memory shape in the shape memory portion
`6 is not limited to a special one, the shape memory portion
`6 is preferably formed in the shape of a straight needle as an
`extension of the superelastic portion 7. Moreover, it is
`preferable that the shape recovery temperature of the shape
`memory portion 6 is suf?ciently higher than room tempera
`ture and body temperature. That is, When the shape recovery
`temperature is as high as the body temperature, there might
`be a possibility that While the root canal is treated, the
`memory shape is recovered, thereby presenting the same
`problem encountered When the Work portion 4 has the
`superelastic characteristic along the Whole length. Hence, it
`is necessary that the shape recovery temperature of the shape
`memory portion 6 is su?iciently higher than the room
`temperature or the body temperature. Such a temperature
`includes a processing temperature at the time of autoclave
`sterilization but, needless to say, it is not intended to limit the
`shape recovery temperature to this temperature.
`In the case of using the above reamer A, as illustrated in
`FIG. 1, it is possible to cut the Wall of the root canal and to
`form the root canal in the folloWing manner: a dentist makes
`the chuck of a hand piece (not shoWn) grip the grip 2, holds
`the hand piece, bends the shape memory portion 6 formed on
`the tip 3 side of the Work portion 4 in correspondence to the
`shape of the patient’s root canal, and then inserts the tip 3
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`into the root canal and moves it in the axial direction While
`rotating it in a direction of the cutting edge 4b.
`Incidentally, because the reamer A as a root canal treat
`ment tool is taken as an example in this embodiment, the
`cutting edge 4b is formed on the reamer A. HoWever, all of
`the root canal treatment tools do not necessarily have the
`cutting edge 4b formed on their Work portions 4 but some of
`them have a needle-shaped protrusion or a tapered coil
`formed on the Work portions. Even in such a root canal
`treatment tool, by forming the shape memory portion 6
`Within a predetermined range from the tip 3 of the Work
`portion 4, and by forming the remaining portion of the
`superelastic portion 7, it is possible to prevent the tool from
`being WithdraWn from the root canal and to improve dura
`bility.
`Next, a ?rst manufacturing method for manufacturing the
`reamer A Will be described With reference to FIGS. 2A, 2B,
`and 2C. The ?rst manufacturing method is a method by
`Which a raW material previously provided With a superelastic
`characteristic is subjected to a Working of removing metal to
`form a Work portion, and by Which the tip side of the Work
`portion is again subjected to a heat treatment to provide the
`tip side With a shape memory characteristic.
`As shoWn in FIG. 2A, a Wire made of a NiiTi alloy
`previously provided With a superelastic characteristic and
`having a diameter corresponding to the siZe of the objective
`reamer A is cut in correspondence With the length of the
`reamer A to form a rod-shaped raW material 11.
`As shoWn in FIG. 2B, the raW material 11 is Worked into
`the shape of a taper, is Worked to form the groove 4a and the
`cutting edge 4b, and is further Worked to form the tip 3,
`Whereby the Work portion 4 and the shank 5 are formed. In
`this manner, the needle portion 1 is formed. At the time of
`Working the raW material 11, the raW material 11 can not be
`plastically Worked because it has a superelastic characteris
`tic. For this reason, the Workings of tapering the raW material
`11 and forming the groove 4a and the cutting edge 4b are
`performed by a Working of removing metal, including a
`cutting Working. The Work portion 4 formed in this manner
`has the superelastic characteristic along the Whole length
`thereof.
`Next, the shape memory portion 6 is formed in a range of
`a predetermined length from the tip 3 of the Work portion 4.
`This process, as shoWn in FIG. 2C, is performed as folloWs:
`portions other than a portion corresponding to the shape
`memory portion 6 in the needle portion 1 are cooled by a
`cooling agent 12, and the shape memory portion 6 is heated
`on the basis of heat treatment conditions set for the raW
`material 11 in a state Where the shape memory portion 6 is
`kept in an objective shape (in the shape of a straight needle
`in this embodiment). Any one of the folloWing methods can
`be selected as a speci?c example of a method for forming the
`shape memory portion 6.
`(A) Partial heating method by hot air (see FIG. 4A)
`A portion 1B not to be heat-treated is partially dipped in
`Water 21 as a cooling agent so as to prevent a temperature
`increase or is bloWn by cool air and, at the same time, a
`portion 1A to be heat-treated is bloWn by hot air 22, thereby
`being partially heated.
`(B) Partial heating method by a fumace (see FIG. 4B)
`A furnace 23 is partitioned into tWo layers and a portion
`1A to be heat-treated is partitioned by heat insulating
`material 24 so as to prevent a portion 1B not to be heat
`treated from being increased in temperature and is heated in
`the furnace 23. Here, if a portion 1A can be surely insulated
`from heat, the furnace 23 is not required to be partitioned.
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`(C) Partial heating method by liquid (see FIG. 4C)
`A portion IE not to be heat-treated is held by a clip 25
`provided With a cooling function, and a portion 1A to be
`heat-treated is dipped in liquid in a salt bath 26 at high
`temperatures, thereby being heated.
`(D) Partial heating method by solid (see FIG. 4D)
`A portion IE not to be heat-treated is dipped in a cooling
`agent 27, such as Water, to prevent a temperature increase,
`and a portion 1A to be heat-treated is brought into contact
`With or close to a heating body 28 at high temperatures,
`thereby being heated.
`(E) Partial heating method by heating pod (see FIG. 4E)
`A small hole 30 through Which a Work piece (Wire) can be
`inserted is made in a heating pod 29, and only a portion 1A
`to be heat-treated is inserted into this small hole 30, thereby
`being partially heated. Here, a portion not to be inserted into
`the heating pod 29 (portion not to be heat-treated) 1B may
`be bloWn by cool air, thereby being actively cooled.
`The cooling agent 12 for cooling a portion other than the
`shape memory portion 6 at the time of heat-treating the
`shape memory portion 6 is not limited to a special one but,
`for example, Water can be used.
`The shank 5 of the needle portion 1 provided With the
`shape memory portion 6 in the range of a predetermined
`length from the tip 3 is inserted into and bonded to a grip
`(not shoWn), Whereby the objective reamer A can be manu
`factured.
`A second manufacturing method according to the present
`invention is a method by Which the raW material 11 shoWn
`in FIG. 2A is heat-treated in the range of a predetermined
`length from a tip on one side at the step of forming the raW
`material 11 to provide it With the shape memory character
`istic, and by Which the raW material 11 is then subjected to
`a Working including the removal of metal to form the Work
`portion 4 having the groove 4a and the cutting edge 4b to
`manufacture an objective reamer A.
`According to the above second manufacturing method, at
`the step of the raW material 11, a portion having the shape
`memory characteristic and a portion having the superelastic
`characteristic are formed, and then the raW material 11 is
`subjected to the Working of removing metal to form the Work
`portion 4. Therefore, in the shape memory portion 6, the
`shape of a straight needle is memoriZed, and groove 4a and
`the cutting edge 4b are formed continuous With the super
`elastic portion 7 formed thereon.
`As described above, the raW material 11 having the
`portion corresponding to the shape memory portion and the
`portion corresponding to the superelastic portion is sub
`jected to the Working, including the removal of metal, to
`form the needle portion 1, including the Work portion 4 and
`the shank 5. Then, the shank 5 is inserted into and bonded
`to the grip (not shoWn), Whereby the objective reamer A can
`be manufactured.
`The present inventors manufactured ?ve samples (con
`ventional samples), each of Which Was a No. 30 reamer
`formed of a raW material of about 1.0 mm in diameter and
`having a tip portion of about 0.3 mm in diameter, a taper of
`4/100, a rectangular cross section, a needle portion protruding
`from the grip 2 and having a length of about 25 mm, and a
`Work portion having a length of about 15 mm, Wherein the
`Work portion had a superelastic characteristic along the
`Whole length thereof; ?ve samples (?rst method samples)
`each of Which had the shape memory portion 6 formed in the
`range of about 4 mm from the tip 3 and had the superelastic
`portion 7 formed in the remaining Work portion 4 by the ?rst
`manufacturing method; and ?ve samples (second method
`
`40
`
`45
`
`20
`
`25
`
`30
`
`35
`
`50
`
`55
`
`60
`
`65
`
`8
`samples) each of Which had the shape memory portion 6
`formed in the range of about 4 mm from the tip 3 and had
`the superelastic portion 7 formed in the remaining Work
`portion 4 by the second manufacturing method, and then
`conducted tests of bending tests and fatigue fracture tests.
`Incidentally, the heat treatment for forming the shape
`memory portion 6 in the Work portion 4 is performed on the
`thin rod Within a limited range, and hence a boundary is not
`clearly produced betWeen the shape memory 6 and the
`superelastic portion 7. For this reason, it is dif?cult to
`express the range of length from the tip 3 of the shape
`memory portion 6 by an exact numerical value, but there is
`no other choice but to express that the shape memory portion
`6 is formed in the range of about 4 mm.
`In the bending test, the Work portion 4 Was gripped at a
`position of about 3 mm from the tip 3, and torque When the
`Work portion 4 Was bent about 45 degrees in this state Was
`measured. As a result, the average value of the conventional
`samples Was about 51 gf-cm, the average value of the ?rst
`method samples Was about 43 gf-cm, and the average value
`of the second method samples Was about 45 gf-cm.
`From the above measurement results, it can be said that
`the reamerAhaving the shape memory portion 6 in the range
`of about 4 mm from the tip 3 of the Work portion 4 can be
`bent by smaller torque, as compared With a reamer having
`the superelastic characteristic along the Whole length. That
`is, the reamer A according to the present invention has
`higher ?exibility in the range of about 4 mm from the tip 3,
`as compared With the conventional reamer.
`Therefore, even if the shape memory portion 6 is forcibly
`bent, and then the bending force is released, the bent shape
`of the shape memory portion 6 can be maintained. For this
`reason, at the time of treating the root canal, it is possible to
`bend the shape memory portion 6 previously according to
`the shape of the patient’s root canal, to insert the tip 3 into
`the root canal, and to perform treatment With this maintained
`bent shape. That is, it is possible to make the shape memory
`portion 6 conform to the shape of the root canal before and
`during treatment.
`Moreover, even When treatment for the root canal
`progresses, and Where the tip 3 reaches the root sharp mouth,
`because the shape memory portion 6 is easily bent, the shape
`memory portion 6 does not apply a repulsive force to the
`Wall of the root canal. This prevents the shape memory
`portion 6 from cutting the Wall of the root canal more
`heavily near the root sharp mouth, and in the center of curve
`and deviating from the root canal.
`The fatigue fracture tests Were conducted by use of an
`apparatus shoWn in FIG. 3. That is, by use of the apparatus
`having a pair of pins 21, 22 having grooves 21a, 22a capable
`of receiving the tip 3 side of the Work portion 4, the Work
`portion 4 Was set such that a position of 4 mm from the tip
`3 of the Work portion 4 corresponded to the center of one pin
`21 and that the tip 3 Was inserted into the groove 22a of the
`other pin 22 to bend the shape memory portion 6 in the Work
`portion 4 about 45 degrees. Then, the Work portion 4 Was
`rotated at 200 rpm While keeping this state of bending, and
`the time elapsed before the shape memory portion 6 frac
`tured Was measured.
`As a result of the above fatigue fracture tests, the con
`ventional samples Were fo