111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20110271529Al
`
`(19) United States
`c12) Patent Application Publication
`Gao et al.
`
`(10) Pub. No.: US 2011/0271529 A1
`Nov. 10, 2011
`(43) Pub. Date:
`
`(54)
`
`ENDODONTIC ROTARY INSTRUMENTS
`MADE OF SHAPE MEMORY ALLOYS IN
`THEIR MARTENSITIC STATE AND
`MANUFACTURING METHODS
`
`(75)
`
`Inventors:
`
`(73)
`
`Assignee:
`
`Yong Gao, Broken Arrow, OK
`(US); Randall Maxwell, Broken
`Arrow, OK (US)
`
`DENTSPLY International Inc.,
`York, PA (US)
`
`(21)
`
`Appl. No.:
`
`13/102,439
`
`(22)
`
`Filed:
`
`May 6, 2011
`
`Related U.S. Application Data
`
`(60) Provisional application No. 61/332,954, filed on May
`10, 2010.
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`B23P 17100
`
`(2006.01)
`
`(52) U.S. Cl. ....................................................... 29/896.1
`
`(57)
`
`ABSTRACT
`
`A method for manufacturing a non-superelastic rotary file
`comprising the steps of: providing a superelastic rotary file
`having an austenite finish temperature; and heating the super(cid:173)
`elastic rotary file to a temperature of at least about 300° C. for
`a time period of at least about 5 minutes to alter the austenite
`finish temperature thereby forming the non-superelastic
`rotary file; wherein the altered austenite finish temperature of
`the non-superelastic rotary file is greater than about 25° C.
`
`10
`
`l I ;·
`
`18
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`Patent Application Publication Nov. 10, 2011 Sheet 1 of 10
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`US 2011/0271529 A1
`
`Fig.2
`
`18
`
`Fig.l
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`Patent Application Publication Nov. 10, 2011 Sheet 2 of 10
`
`US 2011/0271529 A1
`
`too . .--------------.....,------------.....,__,
`
`Cooling
`~
`
`0'
`
`'
`...._ _________ ,.::::· --1-~-~-------- --~'------
`. · '
`Mf
`-~__........_ ____ _
`.
`Ms
`
`1
`
`~
`fieating
`
`0
`
`·50
`
`FIG. 3
`
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`Patent Application Publication Nov. 10, 2011 Sheet 3 of 10
`
`US 2011/0271529 A1
`
`1 .
`
`.
`
`i
`
`"'t
`
`2 '
`
`3 '
`
`, .
`
`•••• W~Jil ......
`
`··~
`
`•
`
`. : ~
`
`.Key
`
`revelrsibl·e· gea:r, m:otot
`stop
`to.rque~measuring· devloe·
`C\Btqh. pi1r11.
`
`FIG. 4
`
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`Patent Application Publication Nov. 10, 2011 Sheet 4 of 10
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`US 2011/0271529 A1
`
`Flexibility (Stiffness)
`
`1 ~-------------------------------------------------.
`
`0.8
`
`N' q
`g
`g: 0.6
`~
`
`tT
`
`.:00:
`Ill
`Ql
`g. 0.4
`
`0.69
`
`0.2
`
`0
`
`Regular SuperEiastic (Af=l7°C)
`
`Martensitic (Af=37°C)
`
`FIG. 5
`
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`Patent Application Publication Nov. 10, 2011 Sheet 5 of 10
`
`US 2011/0271529 A1
`
`WARM WATER
`OR
`COMPRESSED AIR
`
`94
`
`118
`
`92
`88
`
`FIG. 6
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`Patent Application Publication Nov. 10, 2011 Sheet 6 of 10
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`US 2011/0271529 A1
`
`,---------------------------------------,
`Resistance against cyclic fatigue
`
`...
`Ql 1400
`
`:::1 ... ... I'll 1200
`
`800
`
`600
`
`.:::
`0 ....
`"' OJ 1000
`~ ...
`.... 0
`... Ql
`.0
`E
`:::1
`.::::
`iii ....
`
`1201
`
`389
`
`0
`1-
`
`400
`
`200
`
`0
`
`Regular SuperEiastic (Af=17"C)
`
`Ma rtensltic (Af=37"C)
`
`FIG. 7
`
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`Patent Application Publication Nov. 10, 2011 Sheet 7 of 10
`
`US 2011/0271529 A1
`
`1
`
`2
`
`\ \
`\
`5
`
`·~
`
`..
`
`l
`
`·~
`
`,....
`
`.,_
`
`:;1
`
`4
`\
`
`-,
`
`·.~
`
`I ~·--E ·-·- ..,..
`7
`I
`
`-
`
`3
`
`1
`
`I
`
`2
`
`3
`
`Key
`
`1
`2
`
`chuck with hardened steel jaws
`soft brass Jaws
`
`Details oftest chuck
`
`.reversible gear motor
`chuck with hardened steel jaws
`clu.ick With soft brass jaws:
`torque measuring devJce
`linear ball-bearing
`
`2
`3
`4
`5
`
`Af.)paratus for torque test
`
`FIG. 8
`
`8 of 17
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`Patent Application Publication
`
`Nov. 10, 2011 Sheet 8 of 10
`
`US 2011/0271529 A1
`
`Torsional Property
`
`503
`
`520
`
`:!!
`~
`E
`... 500
`.s
`c
`0 :;:;
`~ 480
`0::
`
`Q)
`
`bJ)
`
`:!! 460
`Q) c
`E
`~ 440
`·x
`1'0
`:lE
`
`...................................... .
`
`440
`
`420
`
`f-····················-········-····
`
`400
`
`Regular SuperEiastic (Af=l?"C)
`
`Martensitic (Af=37"C)
`
`FIG. 9
`
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`Patent Application Publication Nov. 10, 2011 Sheet 9 of 10
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`US 2011/0271529 A1
`
`Torsional Resistance
`
`1.8
`
`1.75
`
`'N
`0
`:§. 1.7
`
`Ill
`::J
`tT
`~ 1.65
`
`,:,(.
`<G
`Ill
`Q.
`
`1.6
`
`1.55
`
`1.5
`
`Regular SuperEiastic (Af=17•C)
`
`Martensitic (Af=37"C)
`
`FIG. 10
`
`10 of 17
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`Patent Application Publication Nov. 10, 2011 Sheet 10 of 10
`
`US 2011/0271529 A1
`
`FIG. 11
`
`11 of 17
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`US 2011/0271529 AI
`
`Nov. 10, 2011
`
`1
`
`ENDODONTIC ROTARY INSTRUMENTS
`MADE OF SHAPE MEMORY ALLOYS IN
`THEIR MARTENSITIC STATE AND
`MANUFACTURING METHODS
`
`FIELD OF INVENTION
`
`[0001] The present invention is directed to a method for
`treating a dental instrument, and specifically to a rotary file
`useful for shaping and cleaning root canals with severe cur(cid:173)
`vature.
`
`BACKGROUND OF THE INVENTION
`
`[0002] The endodontic instruments (including files and
`reamers) are used for cleaning and shaping the root canals of
`infected teeth. They may be in mode of either rotation or
`reciprocation in the canal by dentists, either manually or with
`the aid of dental handpieces onto which the instruments are
`mounted. Instruments are generally used in sequence (de(cid:173)
`pending on different root canal surgery techniques) in order to
`achieve the desired outcome of cleaning and shaping. The
`endodontic instrument is subjected to substantial cyclic bend(cid:173)
`ing and torsional stresses as it is used in the process of clean(cid:173)
`ing and shaping a root canal. Because of the complex curva(cid:173)
`ture of root canals, a variety of unwanted procedural accidents
`such as !edging, transportation, perforation, or instrument
`separation, can be encountered in the practice of endodontics.
`[0003] Currently, endodontic rotary instruments made of
`Shape Memory Alloys (SMA) have shown better overall per(cid:173)
`formance than stainless steel counterparts. However, the
`occurrence of unwanted procedural accidents mentioned
`above has not been drastically reduced. Therefore, it neces(cid:173)
`sitates new endodontic instruments with improved overall
`properties, especially flexibility and resistance to fracture
`either due to cyclic fatigue and torsional overload.
`
`SUMMARY OF THE INVENTION
`
`[0004] The present invention seeks to improve upon prior
`endodontic instruments by providing an improved, process
`for manufacturing endodontic instruments. In one aspect, the
`present invention provides a method for manufacturing a
`non-superelastic rotary file comprising the steps of: providing
`a superelastic rotary file having an austenite finish tempera(cid:173)
`ture; and heating the superelastic rotary file to a temperature
`of at least about 300° C. for a time period of at least about 5
`minutes to alter the austenite finish temperature thereby form(cid:173)
`ing the non-superelastic rotary file; wherein the altered aus(cid:173)
`tenite finish temperature of the non-superelastic rotary file is
`greater than about 25° C.
`[0005]
`In another aspect, the present invention contem(cid:173)
`plates a method for manufacturing a non-superelastic rotary
`file comprising the steps of: providing a non-superelastic wire
`having an austenite finish temperature greater than about 25°
`C.; heating the non-superelastic wire to a manufacturing tem(cid:173)
`perature that is higher that the austenite finish temperature;
`and forming flutes, grooves, or a combination of both about
`the superelastic wire to form a rotary file; wherein the rotary
`file is non-superelastic at a temperature that ranges from
`about 25° C. to about the austenite finish temperature
`[0006]
`In yet another aspect, any of the aspects of the
`present invention may be further characterized by one or any
`combination of the following features: the austenite finish
`temperature of the non-superelastic rotary file is greater than
`27° C.; the altered austenite finish temperature of the non-
`
`superelastic rotary file is greater than 30° C.; the altered
`austenite finish temperature of the non-superelastic rotary file
`is greater than 3 7° C.; the heating step, the temperature ranges
`from about 300° C. to about 600° C.; the heating step, the
`heating step, the manufacturing temperature ranges from
`about so C. to about 200° C.; the time period ranges from
`about 5 minutes and about 120 minutes; the superelastic
`rotary file includes a shape memory alloy; the shape memory
`alloy includes nickel and titanium; the shape memory alloy
`includes a copper based alloy, an iron based alloy or a com(cid:173)
`bination of both; the shape memory alloy is a nickel-titanium
`based ternary alloy; the nickel-titanium based ternary alloy of
`the formula Ni-Ti-X wherein X is Co, Cr, Fe, or Nb; a ratio
`of peak torque of the non-superelastic rotary file to the super(cid:173)
`elastic rotary file is less than about 8:9 at about 25° C.; a ratio
`of total number of cycles to fatigue of the non-superelastic
`rotary file to the superelastic rotary file is at least about 1.25: 1
`at about 25° C.; or any combination thereof.
`[0007]
`It should be appreciated that the above referenced
`aspects and examples are non-limiting as others exist with the
`present invention, as shown and described herein. For
`example, any of the above mentioned aspects or features of
`the invention may be combined to form other unique configu(cid:173)
`rations, as described herein, demonstrated in the drawings, or
`otherwise.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0008] FIG. 1 is an elevational view of a typical endodontic
`instrument.
`[0009] FIG. 2 is an elevational cross-sectional view of a
`molar human tooth showing the root system and the coronal
`area penetrated by a hole to expose the root canal system.
`[0010] FIG. 3 is a Differential Scanning calorimetry (DSC)
`curve showing phase transformation temperatures of the
`present invention.
`[0011] FIG. 4 is a diagrammatic representation of a bending
`test apparatus to measure stiffness or root canal instruments
`as described in ISO 3630-1:2008, Dentistry-Root-canal
`instrument-Part I: General requirements and test methods).
`[0012] FIG. 5 is a chart showing the testing results of the
`test method shown in FIG. 4.
`[0013] FIG. 6 is diagrammatic representation of a test appa(cid:173)
`ratus used to test the bending-rotation fatigue resistance of
`endodontic instruments.
`[0014] FIG. 7 is a schematic graph of the relationship
`between different NiTi microstructures (austenic vs. marten(cid:173)
`sitic) and average cyclic fatigue life of endodontic rotary
`instruments made ofNiTi shape memory alloy.
`[0015] FIG. 8 is a diagrammatic representation of a torque
`test apparatus used to measure the resistance to fracture by
`twisting and angular deflection as described in ISO 3630-1:
`2008, Dentistry-Root-canal instrument-Part I: General
`requirements and test methods).
`[0016] FIG. 9 is a schematic graph of the relationship
`between different metallurgical structures and average
`"maximum degree of rotation to fracture" of endodontic
`rotary instruments made ofNiTi shape memory alloy.
`[0017] FIG. 10 is a schematic graph of the relationship
`between different metallurgical structures and average "peak
`torque" of endodontic rotary instruments made ofNiTi shape
`memory alloy.
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`2
`
`[0018] FIG.ll shows a root with a highly curved canal and
`a complex canal shape.
`
`DETAILED DESCRIPTION OF INVENTION
`
`[0019] Superelastic materials are typically metal alloys
`which return to their original shape after substantial deforma(cid:173)
`tion. Examples of efforts in the art towards superelastic mate(cid:173)
`rials are found in U.S. Pat. No. 6,149,501, which is herein
`incorporated by reference for all purposes.
`[0020] The endodontic rotary instrument made of shape
`memory alloys (e.g., NiTi based, Cu based, Fe based, or
`combinations thereof) in their martensitic state of the present
`invention may provide more flexibility and increase fatigue
`resistance by optimized microstructure, which is particularly
`effective in shaping and cleaning canals with severe curva(cid:173)
`tures. Superelastic alloys such as nickel titanium (NiTi) or
`otherwise can withstand several times more strain than con(cid:173)
`ventional materials, such as stainless steel, without becoming
`plastically deformed.
`[0021] This invention relates to dental instruments in gen(cid:173)
`eral. Specifically, this invention relates to endodontic rotary
`instruments for use in root canal cleaning and shaping proce(cid:173)
`dures. The present invention provides an innovation of endo(cid:173)
`dontic instrument that is made of shape memory alloys
`(SMA) such as Nickel-Titanium (NiTi) based systems, Cu
`based systems Fe based systems, or any combination thereof
`(e.g., materials selected from a group consisting of near(cid:173)
`equiatomic Ni-Ti, Ni-Ti-Nb alloys, Ni-Ti-Fe alloys,
`Ni-Ti---Cu alloys, beta-phase titanium and combinations
`thereof).
`[0022] The present invention comprises rotary instruments
`made ofNiTi Shape Memory Alloys, which provide one or
`more of the following novel aspects:
`[0023] Primary metallurgical phase in microstructure: mar(cid:173)
`tensite is the primary metallurgical phase in the present inven(cid:173)
`tion instrument, which is different from standard NiTi rotary
`instruments with predominant austenite structure at ambient
`temperature;
`[0024] Higher austenite finish temperature (the final
`A.sub.f temperature measured by Differential Scanning calo(cid:173)
`rimetry): the austenite finish temperature is preferably higher
`(e.g., at least about 3° C.) than the ambient temperature (25°
`C.); in contrast, most standard superelastic NiTi rotary instru(cid:173)
`ments have austenite finish temperatures lower than ambient
`temperature;
`[0025] Due to higher austenite finish temperature, the
`present invention instrument would not return to the original
`complete straight state after being bent or deflected; in con(cid:173)
`trast, most standard superelastic NiTi rotary instruments can
`return to the original straight form via reverse phase transfor(cid:173)
`mation (martensite-to-austenite) upon unloading.
`[0026] Endodontic
`instruments made of NiTi shape
`memory alloys in their martensitic state have significantly
`improved overall performance than their austenitic counter(cid:173)
`parts (regular superelastic NiTi instruments), especially on
`flexibility and resistance against cyclic fatigue.
`[0027] The strength and cutting efficiency of endodontic
`instruments can also be improved by using ternary shape
`memory alloys NiTiX (X: Co, Cr, Fe, Nb, etc) based on the
`mechanism of alloy strengthening.
`[0028] Specifically, the present invention instrument has
`essential and most desired characteristics for successful root
`canal surgery, including higher flexibility and lower stiffness,
`improved resistance to cyclic fatigue, higher degree of rota-
`
`tion against torsional fracture, more conforming to the shape
`of highly curved canals (less likely for !edging or perfora(cid:173)
`tion), and minimum possibility of instrument separation in
`comparison against conventional endodontic instruments
`made ofNiTi shape memory alloy in superelastic condition
`with fully austenitic phase in microstructure.
`
`Methods of Manufacturing Martensitic Endodontic Instru(cid:173)
`ments
`
`[0029]
`In one embodiment of the present invention, endo(cid:173)
`dontic instruments made ofNiTi shape memory alloys in their
`martensitic state may be fabricated by the following method:
`[0030] Method 1: Post heat treatment after the flutes of a file
`have been manufactured according to mechanical design (i.e.,
`after the flute grinding process in a typical file manufacturing
`process).
`[0031] This method may include a post heat treatment hav(cid:173)
`ing a heating step at temperature of at least 300° C. Preferably
`the heating step includes a temperature ranging from about
`300° C. to about 600° C., and more preferably from about
`370° C. to about 510° C. The heat treatment step may be
`present for a time period of at least 5 minutes. Preferably, the
`heating step may be present for a time period that ranges from
`about 5 minutes to about 120 minutes, and more preferably
`from about 10 minutes to about 60 minutes (typically under a
`controlled atmosphere).
`[0032] For example, the additional thermal process of
`Method 1 may be employed in after the traditional NiTi rotary
`file manufacturing process (e.g., grinding of the flutes) using
`regular superelastic NiTi wires. More particularly, an addi(cid:173)
`tional thermal process may be performed after the flute grind(cid:173)
`ing process (of a traditional NiTi rotary file manufacturing
`process) so that a post heat treatment occurs at a temperature
`range of370-510° C. for a period of time (typically 10-60
`min, depending on file size, taper, and/or file design require(cid:173)
`ment). It is appreciated that Nickel-rich precipitates may form
`during this post heat treatment process. Correspondingly, the
`ratio of Ti/Ni may increase and a desired austenite finish
`temperature (the final Aftemperature) will be achieved. After
`post heat treatment, a file handle (e.g., brass, steel, the like, or
`otherwise may be installed.
`[0033]
`In another embodiment of the present invention,
`endodontic instruments made ofNiTi shape memory alloys in
`their martensitic state may be fabricated by the following
`method:
`[0034] Method 2: Heat treatment during the manufacturing
`process of the file (e.g., during the grinding process) to ensure
`the temperature on the NiTi materials is higher than their
`austenite finish temperatures:
`[0035] This method may include (concurrent) heat treat(cid:173)
`ment to wires prior to and/or during the grinding process so
`that grinding will be directly applied to martensitic SMA
`(e.g., NiTi) wires. However, it is appreciated that martensitic
`SMA (e.g., NiTi) wires may be heated to a temperature higher
`than their austenite finish temperatures during grinding pro(cid:173)
`cess. Therefore, martensitic SMA (e.g., NiTi) wires may tem(cid:173)
`porarily transform to superelastic wires (a stiffer structure in
`the austenitic state) to facilitate the grinding process during
`the instrument manufacturing process. Advantageously, the
`instruments will transform back to martensitic state at ambi(cid:173)
`ent temperature after the flute grinding process.
`[0036] For example, in one embodiment, Method 2 may
`include a non-superelastic wire. The non-superelastic wire
`may be provided in a manufacturing environment with a
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`Nov. 10, 2011
`
`3
`
`temperature higher than its austenite finish temperature (at
`least 25 degree C.). The non-superelastic wire may transform
`to superelastic at this higher temperature). Then forming
`flutes and grooves about the file to form the (semi finished)
`rotary file. Furthermore, the (semi-finished) rotary file may be
`removed from the manufacturing environment with higher
`(warmer) temperature. The non-superelastic wire may form a
`non-superelastic rotary file at (or above) room temperature
`about 25° C.
`[0037] With respect to FIGS. 1 and 2, an endodontic instru(cid:173)
`ment is shown positioned within one of the root canals is the
`endodontic instrument. While in this position, the endodontic
`instrument is typically subjected to substantial cyclic bending
`and torsional stresses as it is used in the process of cleaning
`and shaping a root canal.
`It is believed that a shape memory alloy like NiTi
`[0038]
`alloy generally has two primary crystallographic structures,
`which are temperature dependent, (i.e. austenite at higher
`temperatures and martensite at lower temperatures). This
`temperature-dependent diffusionless phase transformation
`will be from martensite (M) to austenite (A) (e.g., M~A)
`during heating. Furthermore, it is appreciated that a reverse
`transformation from austenite to martensite (A~M) may be
`initiated upon cooling. In another embodiment, an interme(cid:173)
`diate phase (R) may appear during phase transformations i.e.,
`either (M)~(R)~(A) during heating or (A)~(R)~(M) dur(cid:173)
`ing cooling. The R-phase being defined as an intermediate
`phase between the austenite phase (A) and the martensite
`phase (M).
`[0039] The phase transformation temperatures can be
`determined using Differential Scanning calorimetry (DSC)
`curve as shown in the FIG. 3. For example, Af( austenite finish
`temperature) may be obtained from the graphical intersection
`of the baseline with the extension of the line of maximum
`inclination of the peak of the heating curve. The final Af
`temperature of endodontic instrument made of shape memory
`alloys was measured in DSC test with general accordance
`with ASTM Standard F2004-05 "Standard Test Method for
`Transformation Temperature of Nickel-Titanium Alloys by
`Thermal Analysis", such as using heating or cooling rates of
`1 0±0.5° C./min with purge gas of either helium or nitrogen,
`except that the fluted segment cut from rotary instrument
`sample does not need any further thermal annealing process
`(i.e., 850° C. for 30 min in vacuum), which is typically used
`for measuring ingot transition temperatures at fully austenitic
`condition.
`[0040] More particularly, FIG. 3 provides a schematic dif(cid:173)
`ferential scanning calorimetry (DSC) curve of a shape
`memory alloy (nickel-titanium) in both heating and cooling
`cycle. Af (austenite finish temperature), As (austenite start
`temperature), Mf (martensite finish temperature), Ms (mar(cid:173)
`tensite start temperature) may be obtained from the graphical
`intersection of the baseline with the extension of the line of
`maximum inclination of the appropriate peak of the curve.
`The martensite start temperature (MJ being defined as the
`temperature at which the transformation from austenite to
`martensite begins on cooling. The martensite finish tempera(cid:173)
`ture (Mf): the temperature at which the transformation from
`austenite to martensite finishes on cooling; Austenite start
`temperature (As) being defined as the temperature at which
`the transformation from martensite to austenite begins on
`heating. The austenite finish temperature, (Af) being defined
`as the temperature at which the transformation from marten(cid:173)
`site to austenite finishes on heating.
`
`[0041] Experimental results have shown that the present
`invention (e.g., an additional heat treatment process for the
`formation of endodontic instruments) results in desirable
`characteristics. More particularly, the endodontic instru(cid:173)
`ments made ofNiTi shape memory alloys in their martensitic
`state may include one or more of the following desired char(cid:173)
`acteristics for root canal surgery: (1) higher flexibility and
`lower stiffness; (2) improved resistance to cyclic fatigue; (3)
`higher degree of rotation against torsional fracture; ( 4) more
`conforming to the curved canal profile, especially for the root
`canals with considerable curvature and complex profile, and
`combinations thereof.
`[0042] For example in order to compare the impact of dif(cid:173)
`ferent metallurgical structures (austenite vs. martensite), two
`different instrument samples were made utilizing different
`thermal processing in order to represent two distinct struc(cid:173)
`tures: (1) superelastic instruments with fully austenitic micro(cid:173)
`structure and (2) instrument with martensitic microstructure.
`In one specific example based on the DSC measurements, the
`final Af temperatures for these two instruments with distinct
`microstructures are 1 7° C. (for instrument ( 1) having the fully
`austenitic microstructure) and 37° C. (for instrument (2) hav(cid:173)
`ing the martensitic microstructure), respectively. All instru(cid:173)
`ment samples were of the same geometric design. All tests
`were performed at ambient temperature -23° C.
`I. Stiffness test: Showing higher flexibility and
`[0043]
`lower stiffness on endodontic instruments made ofNiTi shape
`memory alloys in their martensitic state as compared to NiTi
`shape memory alloys in their austenitic state.
`In this stiffness test, the stiffness of all sample
`[0044]
`instruments have been determined by twisting the root canal
`instrument through 45° using the testing apparatus as shown
`in FIG. 4.
`[0045] As shown in the testing results in FIG. 5, the rotary
`instruments with martensitic microstructure at ambient tem(cid:173)
`perature exhibit higher flexibility and lower stiffness (as indi(cid:173)
`cated by lower peak torque on bending). In comparison with
`the regular superelastic instrument with the final Aftempera(cid:173)
`ture 17° C., the instruments with the martensitic microstruc(cid:173)
`ture (the final Af temperature -37° C.) have shown 23%
`reduction in bending torque. The lower stiffness of martensi(cid:173)
`tic instruments can be attributed to the lower Young's modu(cid:173)
`lus of martensite (about 30-40 GPa) whereas austenite is
`about 80-90 GPa at ambient temperature.
`[0046] FIG. 5 shows a schematic graph of the relationship
`between different NiTi microstructures (regular superelastic
`or austenic vs. martensitic) and average peak torque of endo(cid:173)
`dontic rotary instruments made ofNiTi shape memory alloy
`in bending test. As can gleemed from FIG. 5, lower peak
`torque (less stiff or more flexible) may be achieved by a
`martensitic microstructure, which is indicated by the higher
`Af (austenite finish temperatures). In one embodiment, the
`ratio of peak torque (flexibility/stiffness) of the non-super(cid:173)
`elastic rotary file to the superelastic rotary file may be less
`than about 1:0.9 (e.g., less than about 1:0.85, and preferably
`less than about 1:0.8) at about 25° C.
`II. Bending rotation fatigue test: Showing higher
`[0047]
`fatigue life on endodontic instruments made of NiTi shape
`memory alloys in their martensitic state
`In this bending test, the fatigue resistance of all
`[0048]
`sample instruments is measured by bending rotation fatigue
`tester as shown in FIG. 6. According to the testing results
`shown in FIG. 7, the average cyclic fatigue life of instruments
`
`14 of 17
`
`IPR2015-00632 - Ex. 1014
`US ENDODONTICS, LLC., Petitioner
`
`

`
`US 2011/0271529 AI
`
`Nov. 10, 2011
`
`4
`
`in the martensitic state (A.sub.ftemperature 37° C.) is about
`3 times of its austenitic counterpart (Af temperature 17° C.).
`[0049] As shown in the diagrammatic representation of
`FIG. 6, a test apparatus may be used to test the bending(cid:173)
`rotation fatigue resistance of endodontic instruments. The
`endodontic rotary instrument sample may be generally rotat(cid:173)
`ing freely within a simulated stainless steel canal with con(cid:173)
`trolled radius and curvature.
`[0050] The schematic graph of FIG. 7 shows the relation(cid:173)
`ship between different NiTi microstructures (austenic vs.
`martensitic) and average cyclic fatigue life of endodontic
`rotary instruments made ofNiTi shape memory alloy. More
`particularly, FIG. 7 shows that longer cyclic fatigue life may
`be achieved by a martensitic microstructure at ambient tem(cid:173)
`perature, which is indicated by the higher Af(austenite finish
`temperature). It is appreciated that the ratio of total number of
`cycles to fatigue (resistance against cyclic fatigue) of the
`non-superelastic rotary file to the superelastic rotary file may
`be at least about 1.25:1 (e.g., at least about 1.5:1, preferably at
`least about 2: 1) at about 25° C.
`[0051]
`III. Torque test: Showing higher degree of rotation
`against torsional fracture on endodontic instruments made of
`NiTi shape memory alloys in their martensitic state
`[0052]
`In this torque test, the resistance to fracture of root
`canal instruments is performed to measure the average maxi(cid:173)
`mum degree of rotation against torsional fracture using the
`testing apparatus as shown in FIG. 8. According to the testing
`results in FIGS. 9 and 10, the instruments with a martensitic
`microstructure exhibit a higher degree of rotation and peak
`torque against torsional fracture than their austenitic counter(cid:173)
`parts.
`[0053]
`It is appreciated that most instrument separation
`may have been caused by either cyclic fatigue or torsional
`fracture; therefore, the separation of instruments made of
`shape memory alloys with martensitic microstructure may be
`significantly reduced according to the testing results in (II)
`bending rotation fatigue test and (III) torque test.
`[0054] The schematic graph of FIG. 9 shows the relation(cid:173)
`ship between different metallurgical structures and average
`"maximum degree of rotation to fracture" of endodontic
`rotary instruments made ofNiTi shape memory alloy. More
`particularly, FIG. 9, shows that a higher degree of rotation
`may be achieved by martensitic microstructure. It is appreci(cid:173)
`ated that the ratio of the maximum degree of rotation to
`fracture (torsional property) of the non -superelastic rotary file
`to the superelastic rotary file may be at least about 1.05:1
`(e.g., at least about 1.075:1, preferably at least about 1.1:1) at
`about 25° C.
`[0055] The schematic graph of FIG. 10 shows the relation(cid:173)
`ship between different metallurgical structures and average
`"peak torque" of endodontic rotary instruments made ofNiTi
`shape memory alloy. More particularly, FIG. 10, shows that
`higher torque resistance may be achieved by a martensitic
`microstructure. It is appreciated that the ratio of peak torque
`(torsional resistance) of the non -superelastic rotary file to the
`superelastic rotary file may be at least about 1.05:1 (e.g., at
`least about 1.075:1, preferably at least about 1.09:1) at about
`25° C.
`[0056]
`IV. Endodontic instruments made of NiTi shape
`memory alloys in their martensitic state show increased con(cid:173)
`forming to a curved canal profile
`[0057] Without introducing !edging, transportation, and/or
`perforation, it is appreciated that instruments formed of shape
`memory alloys in their martensitic microstructure may be
`
`used in cleaning and shaping the highly curved canal as
`shown in FIG. 11. Advantageously, these instruments tend to
`be more conforming to the curvature of the root canal because
`of (1) high flexibility due to the presence of martensite; (2)
`better reorientation and self-accommodation capability of the
`martensitic variants due to the low symmetry of monoclinic
`crystal structure of martensite relative to the cubic crystal
`structure of austenite under applied dynamic stresses during
`root canal surgery.
`[0058] Superelasticity may be generally defined as a com(cid:173)
`plete rebound to the original position. However, in the indus(cid:173)
`try, it is appreciated that less than 0.5% permanent set (after
`stretch to 6% elongation) would be acceptable. For example,
`if the file does not reverse to its original position, it may no
`longer be considered a Superelastic Shape Memory Alloy
`(SMA) (e.g., it may not be considered a superelastic SMA if
`it does not return to a generally straight position).
`[0059] For NiTi based alloys in the "shape memory" form
`(or martensitic state), a desirable characteristic may be the
`temperature above which the bent materials will become
`straight again. For example, you may need to heat the material
`above its austenite finish temperature (Af) to achieve a com(cid:173)
`pletely straight position.
`[0060]
`It is appreciated that for shape memory alloys, once
`they are capable of returning to a straight position, they may
`be considered superelastic at this "application" temperature.
`However, it is further appreciated that if cooling occurs using
`dry ice or liquid nitrogen and the material is bent, the material
`may remain in the deformed position. Once the material is
`removed from the cold environment, the material will return
`to a straight form at room temperature.
`[0061]
`It can be seen that the invention can also be
`described with reference to one or more of the following
`combinations.
`[0062] A. A method for manufacturing a non-superelastic
`rotary file comprising the steps of: (i) providing a superelastic
`rotary file having an austeni