~merican Journal of
`ORTHODONTIC
`and
`DENTOFACIAL
`ORTHOPEDICS
`
`Volume 99
`
`• APRIL 1991
`
`• Number 4
`
`ORIGINAL ARTICLES
`Fracture resistance of ceramic brackets during arch wire torsion Holt, Nanda, and
`Duncanson, Jr.
`Conservative approach to unerupted teeth within cystic lesions Peled, Kahn, and
`Laufer
`Biochemical analysis of bite force Oyen and Tsay
`Bending properties of superelastic and nonsuperelastic NiTi wires Khier, Brantley,
`and Fournelle
`Horizontal rotation of condyle after sagittal split osteotomy Carter, Leonard,
`Cavanaugh, and Brand
`Use of vertical loops in retraction systems Faulkner, Lipsett, EI-Rayes, and
`Haberstock
`Centers of rotation with transverse forces Nager/, Burstone, Becker, and
`Kubein-Messenburg
`Nasal airway impairment Warren, Hairfield, and Dalston
`Diagnostic tests for impaired and respiration Vig, Spalding, and Lints
`Muscle activity during first year of activator treatment
`lngerva/1 and Thiler
`Bonding of ceramic brackets to enamel Eliades, Viazis, and Eliades
`SPECIAL ARTICLE Waldman
`
`LEGAL ASPECTS OF ORTHODONTIC PRACTICE
`REVIEWS AND ABSTRACTS
`
`DIRECTORY: AAO OFFICERS AND ORGANIZATIONS
`
`NEWS, COMMENTS, AND SERVICE ANNOUNCEMENTS
`
`Complete contents begin on page 5A
`
`Official publication of the
`American Association of Orthodontists, its constituent societies,
`and the American Board of Orthodontics
`
`Published by
`Mosby- Year Book, Inc.
`
`ISSN 0889-5406
`
`"Dentistry's oldest specialty"
`
`1 of 10
`
`IPR2015-00632 - Ex. 1018
`US ENDODONTICS, LLC., Petitioner
`
`

`

`Bending properties of superelastic and
`nonsuperelastic nickel-titanium orthodontic wires
`
`Salwa E. Khier,* William A. Brantley,** and Raymond A. Fournelle***
`Milwaukee, Wis.
`
`Cantilever bending properties were evaluated for several clinically popular sizes of three superelastic
`and three nonsuperelastic brands of nickel-titanium orthodontic wires in the as-received condition,
`and for 0.016-inch diameter wires after heat treatment at 500° and at 600° C, for 1 0 minutes and for
`2 hours. A torque· meter apparatus was used for the bending experiments, and the specimen
`test-span length was 1 I 4 inch (6 mm). In general, the bending properties were similar for the three
`brands of superelastic wires and for the three brands of nonsuperelastic wires. For the three brands
`of superelastic wires, heat treatment at 500° C for 1 0 minutes had minimal effect on the bending
`plots, whereas heat treatment at 500° C for 2 hours caused decreases in the average superelastic
`bending moment during deactivation; heat treatment at 600° C resulted in loss of superelasticity. The
`bending properties for the three brands of nonsuperelastic wires were only slightly affected by these
`heat treatments. The differences in the bending properties and heat treatment responses are
`attributed to the relative proportions of the austenitic and martensitic forms of nickel-titanium alloy
`(NiTi) in the microstructures of the wire alloys. (AM J 0RTHOD DENTOFAC 0RTHOP 1991 ;99:31 0-8.)
`
`Nickel-titanium orthodontic wires have
`been of considerable interest to the specialty since the
`introduction of the originaP Nitinol alloy somewhat
`more than a decade ago. The very low modulus of
`elasticity, considerable elastic force delivery range, and
`high springback of this alloy provide the orthodontist
`with unique advantages compared with the stainless
`steel, cobalt-chromium-nickel, and f3-titanium wires.
`Within the last few years many new nickel-titanium
`orthodontic wire alloys have been introduced, and some
`of these new brands possess the property of superelas(cid:173)
`ticity. Superelastic behavior was first specifically noted
`in the orthodontic literature for the Japanese2 NiTi alloy.
`When the wire is subjected to tensile loading, appre(cid:173)
`ciable activation and deactivation take place at nearly
`constant values of stress. Under bending conditions,
`this superelastic behavior is less evident, although there
`is a substantial region of nearly constant bending mo(cid:173)
`ment during deactivation. Although the term super-
`
`From Marquette University.
`Based on a dissertation submitted by Dr. Khier in partial fulfillment of the
`requirements for the PhD degree at Marquette University.
`*Former graduate student in materials science program, College of Engineering.
`Now at Mansoura University, Mansoura, Egypt.
`**Formerly Professor and Chairman, Department of Dental Materials, School
`of Dentistry. Now Professor, Section of Restorative and Prosthetic Dentistry,
`College of Dentistry, The Ohio State University, Columbus, Ohio.
`***Professor, Department of Mechanical and Industrial Engineering, College
`of Engineering.
`8/1119762
`
`310
`
`elasticity was not explicitly used in the article intro(cid:173)
`ducing the Chinese3 NiTi wire alloy, the bending test
`plots for Chinese and Japanese NiTi were very similar,
`indicating that the former alloy also showed superelastic
`behavior.
`The superelastic property of some nickel-titanium
`wire brands has been attributed to a phase transfor(cid:173)
`mation from the body-centered cubic austenitic form to
`the hexagonal close-packed martensitic form of NiTi
`when the stress reaches a certain level during activa(cid:173)
`tion. 2 Upon deactivation, the reverse-phase transfor(cid:173)
`mation from the martensitic to the austenitic structure
`takes place when the stress is decreased to an appro(cid:173)
`priate level, which is somewhat less than that required
`to cause the forward transformation. It is thus necessary
`for the proprietary wire manufacturing processes to
`leave the nickel-titanium alloys largely in the austenitic
`structure for superelastic behavior to occur, whereas the
`original Nitinol alloy and other nonsuperelastic nickel(cid:173)
`titanium wires havf1 principally a work-hardened mar(cid:173)
`tensitic structure.
`A clinically useful consequence of superelastic be(cid:173)
`havior is that variations in heat treatment by the man(cid:173)
`ufacturer can result in differing stress levels to initiate
`the phase transformations in the same nickel-titanium
`wires. For Japanese NiTi, 2 heat treatment at 400° Chad
`no affect on the bending plots. However, heat treatment
`at 500° C for periods of 5 minutes to 2 hours caused
`considerable differences in the constant force levels for
`
`2 of 10
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`IPR2015-00632 - Ex. 1018
`US ENDODONTICS, LLC., Petitioner
`
`

`

`Volume 99
`Number 4
`
`Bending properties of superelastic and nonsuperelastic NiTi wires 311
`
`Table I. Summary of orthodontic wires used in
`present investigation
`
`Wire brand
`
`Size (inch)
`
`Manufacturer
`
`superelastic behavior, and the superelastic property of
`this alloy was lost after heat treatment at 600° C. By
`using appropriate heat treatments, the manufacturer is
`able to offer the Japanese NiTi alloy (commercially
`marketed as Sentinol) in three different superelastic
`force ranges of light, medium, and heavy for individual
`wire sizes. This responsiveness to heat treatment ap(cid:173)
`pears to be possible for other superelastic wire brands,
`in principle, but vacuum or inert atmosphere conditions
`are required because the nickel-titanium alloys react
`quickly with air at elevated temperatures.
`This investigation compares the bending properties
`of several superelastic and nonsuperelastic nickel(cid:173)
`titanium wire brands in the size range of principal clin(cid:173)
`ical interest, and it investigates the effects of heat treat(cid:173)
`ment on the bending plots and superelastic behavior.
`Extensive studies of the metallurgical structure of the
`alloys have been performed by means of x-ray diffrac(cid:173)
`tion,4 and these results will be presented in a separate
`article.
`
`MATERIALS AND METHODS
`The six brands of nickel-titanium orthodontic wires
`and the sizes selected for this investigation are sum(cid:173)
`marized in Table I. From product information literature
`and private communication with the manufacturers, it
`was found that the Nitinol SE, Sentinol, and Ni-Ti
`alloys show superelastic behavior, whereas the Nitinol,
`Titanal, and Orthonol alloys are not superelastic. The
`sizes of round and rectangular wires listed in Table I
`encompass a variety of the most common clinical ap(cid:173)
`pliances.
`A torque meter apparatus previously used for several
`8 in our laboratory provided accurate and re(cid:173)
`studies5
`-
`producible measurements of the bending moment and
`angular deflection. A cantilever test span of 0.25 inch
`(6 mm) was selected, and the bending apparatus was
`based on the design recommended in the original
`version9 of American Dental Association specification
`No. 28. Two torque meters (Models 783-C-2 and 783-
`C-10, Power Instruments, Skokie, Ill.), with ranges of
`0.05 to 2 inches · ounces and 0.5 to 10 inches per
`ounce, were used, depending on the maximum moment
`levels developed by a given group of specimens. The
`torque meter was operated manually, and the specimens
`were bent at room temperature (22° C ± 2° C) to an(cid:173)
`gular deflections of approximately 80° and then un(cid:173)
`loaded. The rectangular wire specimens were subjected
`to second-order activation because of greater conve(cid:173)
`nience with the design9 of the specimen-gripping fixture
`and the direction of bending in the horizontal plane
`with the apparatus. The pointers on the torque meters
`obscured the position of zero bending moment and the
`
`Nitinol SE
`
`Sentinol
`(medium)
`
`Ni-Ti
`
`Nitinol
`
`Titanal
`
`Orthonol
`
`0.016, 0.018,
`Unitek
`0.018 X 0.025, Monrovia, Calif.
`0.021 X 0.025
`0.016, 0.018,
`0.018 X 0.025,
`0.0215 X 0.028
`0.016, 0.018*
`
`GAC International
`Central Islip, N.Y.
`
`Ormco/Div. of Sybron
`Glendora, Calif.
`0.016, 0.018,
`Unitek
`0.018 X 0.025, Monrovia, Calif.
`0.021 X 0.025
`0.016, 0.018,
`0.018 X 0.025,
`0.021 X 0.025
`0.016, 0.018,
`0.018 X 0.025,
`0.021 X 0.025
`
`Lancer Orthodontics
`Carlsbad, Calif.
`
`Rocky Mountain Orthodontics
`Denver, Colo.
`
`*Only these two round wire sizes were available at the time of this
`investigation.
`
`initial ranges to 0.05 or 0.5 inch · ounce, and it was
`not possible to establish the portions of the bending
`deformation plots near the origin. Consequently, the
`graphic plots in the following section are presented as
`relative values of angular position or bend angle, and
`the horizontal axes have been shifted and labeled so
`that the bending curves begin approximately at the or(cid:173)
`igin. These torque meters are reported by the manu(cid:173)
`facturer to be accurate to within 2%, and values of
`bending moment were obtained at 5° increments of an(cid:173)
`gular position. Values of the relative angular deflection
`could be read to approximately the nearest 0.25° to 0.5°
`from a protractor mounted on the base of the test
`apparatus. There were three replications for each wire
`brand-size combination, and the three bending mo(cid:173)
`ment values at each increment of angular position
`were averaged and converted from inches · ounces to
`grams · millimeters in the preparation of a single bend(cid:173)
`ing plot.
`Heat treatments were performed in a dental furnace
`(Big Brute, K.H. Huppert, South Holland, Ill.) at 500°
`and 600° C for 10 minutes and 2 hours on 0.016-inch(cid:173)
`diameter segments of the six wire brands. The speci(cid:173)
`mens were sealed in evacuated (approximately 0.01 to
`0.1 torr) quartz capsules and placed in ceramic boats.
`Each capsule also contained a small piece of pure ti(cid:173)
`tanium that served as a "getter" of residual atmospheric
`gases to suppress any oxidation of· the wire or incor(cid:173)
`poration of other impurities from the air. After com(cid:173)
`pletion of the heat treatments, the quartz capsules were
`
`3 of 10
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`US ENDODONTICS, LLC., Petitioner
`
`

`

`312 Khier, Brantley, and Fournelle
`
`E
`E
`
`0>
`rt)
`
`-E
`0 ,.. --s::
`0> s:: =a s::
`(]) co
`
`(])
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`0
`:ia:
`
`NITINOL SE WIRES (As-received)
`• 0.016 in.
`• 0.018 in.
`4 0.0 18x0.025 in.
`v 0.021 x0.025 in.
`
`span: 6mm
`
`2
`
`30
`
`60
`
`90
`
`Angular Position (deg)
`
`Am. J. Ortlwd. Demofac. Orthop.
`Apri/1991
`
`Ni:ri WIRES (As-received)
`• 0.016 in.
`• 0.018 in.
`
`span: 6mm
`
`2
`
`0
`
`30
`
`60
`
`90
`
`Angular Position (deg)
`
`E
`E
`
`0>
`rt)
`
`-E
`0 ,.. --s::
`
`(])
`E
`0
`~
`0> s::
`=t5 s::
`(]) co
`
`Fig. 1. Bending plots for as-received Nitinol SE wires.
`
`Fig. 3. Bending plots for as-received Ni-Ti wires.
`
`SENTINOL WIRES (As-received)
`•0.016 in.
`• 0.018 in.
`6
`4 0.018x0.025 in. span: mm
`v 0.0215 x0.028 in.
`
`30
`
`60
`
`90
`
`Angular Position (deg)
`
`Fig. 2. Bending plots for as-received Sentinol wires.
`
`immersed in water at room temperature and broken to
`quench the specimens.
`
`RESULTS
`
`The bending plots for the as-received superelastic
`alloys, Nitinol SE, Sentinol, and Ni-Ti, are shown in
`
`Figs. 1 to 3, and the bending plots for the as-received
`nonsuperelastic alloys, Nitinol, Titanal, and Orthonol,
`are shown in Figs. 4 to 6. Examination of these two
`sets of figures reveals that the bending curves for the
`three superelastic alloys were similar and that the three
`nonsuperelastic alloys also had similar bending curves.
`However, it is evident that there were considerable gen(cid:173)
`eral differences in the bending deformation behavior
`for the superelastic and nonsuperelastic wires. Although
`it was not as apparent in the loading or activation por(cid:173)
`tions of the curves, the unloading portions of the bend(cid:173)
`ing plots for the superelastic wires generally contained
`a nearly horizontal region or plateau where deactivation
`took place at almost constant moment values. An ex(cid:173)
`ception was found for the two rectangular sizes of Sen(cid:173)
`tinol (Fig. 2), where the major portion of each deac(cid:173)
`tivation plot had a linear region with a relatively small
`slope. In contrast, the activation and deactivation
`curves shown in Figs. 4 to 6 for the nonsuperelastic
`wires had much greater slopes compared to the bending
`plots for the supere.lastic wires. Another distinguishing
`feature of superelastic and nonsuperelastic alloys was
`the difference in elastic springback, which follows from
`the differences for the residual permanent deformation
`after unloading. The permanent set for the 1 I 4-inch test
`span specimens was approximately 10° to 15° for the
`three superelastic wires, whereas approximate values
`of 35° to 40° permanent deformation for Nitinol and
`Titanal and 20° to 30° for Orthonol correspond to much
`less spring back for nonsuperelastic wires.
`
`4 of 10
`
`IPR2015-00632 - Ex. 1018
`US ENDODONTICS, LLC., Petitioner
`
`

`

`Volume 99
`Number 4
`
`4
`
`.,.....
`E
`E
`E 3
`
`2
`
`0')
`r<>
`0
`"F'
`"'-"
`......
`c:
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`0') c:
`=t5 c:
`CD
`OJ
`
`Bending properties of superelastic and nonsuperelastic NiTi wires 313 .
`
`NITINOL WIRES (As-received)
`• 0.016 in.
`. span: 6mm
`1111 0.0 18 in.
`• 0.0 18x0.025 m.
`v 0.021 x0.025 in.
`
`TIT ANAL WIRES (As-received)
`• 0.016 in.
`1111 0.018 in.
`_. 0.0 18x0.025 in. span: 6mm
`v 0.021 x0.025 in .
`
`4
`
`3
`
`2
`
`.......
`E
`E
`E
`
`0>
`1'0
`0
`or-
`"""
`......
`c:
`<:D
`E
`0
`~
`0> c:
`::0 c:
`<:D
`Cil
`
`30
`
`60
`
`90
`
`Angular Position (deg)
`
`Fig. 4. Bending plots for as-received Nitinol wires.
`
`30
`
`60
`
`90
`
`Angular Position (deg)
`
`Fig. 5. Bending plots for as-receiv13d Titanal wires.
`
`The maximum bending moment at goo activation
`for the three superelastic alloys ranged from about 1200
`to 2000 gm · mm as the diameter varied from 0. 016
`inch to rectangular specimens of either 0. 021 x 0. 025
`inch or 0.0215 x 0.02g inch (Figs. 1 to 3). During
`deactivation, the bending moment for the region of
`superelasticity correspondingly ranged from about 400
`to 1200 gm · mm. For the three nonsuperelastic alloys,
`the maximum bending moment at goo activation ranged
`from nearly 2000 gm · mm for the 0.016-inch-diameter
`specimens to approximately 3goo gm · mm for the
`0.021 x 0.025-inch rectangular specimens. While
`there were only small differences in the bending plots
`for the Nitinol (Fig. 4) and Titanal (Fig. 5) specimens
`of the same wire size, the Orthonol specimens (Fig. 6)
`displayed -greater differences with respect to the other
`two nonsuperelastic alloys. The maximum bending mo(cid:173)
`ment delivered by the 0.021 X 0.025-inch Orthonol
`specimens was about 3000 gm · mm, a value consid(cid:173)
`erably less than that for the corresponding Nitinol and
`Titanal specimens. In addition, the maximum moment
`for the 0.01g-inch-diameter segments of Orthonol ex(cid:173)
`ceeded that for the 0.01g x 0.025-inch rectangular
`
`segments of this alloy in second-order activation; the
`maximum moment was greater for these rectangular
`segments of Nitinol and Titanal, compared to Orthonol.
`For the 0.016-inch-diameter specimens, the maximum
`bending moment was similar for the three nonsuper(cid:173)
`elastic alloys.
`The effects of the heat treatments on the bending
`properties of the 0.016-inch-diameter specimens of the
`three superelastic alloys were very similar, as shown in
`Figs. 7 to 9. There was little difference between the
`bending plots for these wires in the as-received con(cid:173)
`dition and after heat treatment at 500° C for 10 minutes.
`Heat treatment at 500° C for 2 hours resulted in de(cid:173)
`creases in both the maximum moment at goo activation
`and the average moment for the central or superelastic
`portion of the deactivation curve; there was little change
`in the value of springback. The superelastic behavior
`was lost for all three alloys after the heat treatments at
`600° C for 10 minutes or for 2 hours. The criteria for
`the loss of superelasticity were the disappearance of the
`plateau region in the deactivation curve and the de(cid:173)
`crease in spring back. For the heat treatments of 10
`minutes and 2 hours at 600° C, the permanent set for
`
`5 of 10
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`US ENDODONTICS, LLC., Petitioner
`
`

`

`314 Khier, Brantley, and Fournelle
`
`-E
`~ --c:
`
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`
`ORTHONOL WIRES (As-received)
`• 0.016 in.
`11110.018 in.
`"' 0.0 18x0.025 in. span: 6mm
`v0.021x0.025 in.
`
`30
`
`60
`
`90
`
`Angular Position (deg)
`
`3
`
`2
`
`0
`
`Fig. 6. Bending plots for as-received Orthonol wires.
`
`NITINOL SE WIRE <o.o16in.,Heat:...treated>
`-
`--o- -
`500°C, 1Om in
`- - .e- - - 500°C,120min
`---e--- 600°C, 1 Omin
`- • - - •- 600°C, 120min
`
`span=6mm
`
`E
`E
`:?> 2
`0
`
`-E
`~ --c:
`
`CD
`E
`~ 1
`0) c:
`~ c:
`CD co
`
`60
`30
`Angular Position (deg)
`
`90
`
`Fig. 7. Bending plots for 0.016-inch-diameter Nitinol SE wires
`after heat treatments.
`
`Nitinol SE, Sentinel, and Ni-Ti increased to values of
`approximately 20-35°. For the three nonsuperelastic al(cid:173)
`loys, these heat treatments had only minor effects on
`the bending plots, compared to the as-received condi-
`
`Am. J. Orthod. Dentofac. Orthop.
`· Apri/199!
`
`SENTINOL WIRE <o.o16in.,Heat-treatect>
`--e-- 500°C, 1Om in
`-- -o--- 500°C 120min
`- - - - 600°C: 1Om in
`• e-- • 600°C, 120min
`
`span=6mm
`
`-E
`~ --c:
`
`E
`E
`:?> 2
`0
`
`CD
`E
`~ 1
`0) c:
`~ c:
`CD co
`
`60
`30
`Angular Position (deg)
`
`90
`
`Fig. 8. Bending plots for 0.016-inch-diameter Sentinel wires
`after heat treatments.
`
`rl')
`
`0
`
`E
`~ 2
`
`-E
`~ --c:
`CD 5 1
`::;!
`0) c:
`~ c:
`CD co
`
`NFri WIRE (0.016in.,Heat-treated)
`
`500°C, 1Om in
`..._ -
`-
`-- -o- - -500°C, 120min
`--G-..-,- 600°C, 1 Omin
`-
`•e-- • 600°C, 120min
`
`span=6mm
`
`60
`30
`Angular Position (deg)
`
`Fig. 9. Bending plots for 0.016-inch-diameter Ni-Ti wires after
`heat treatments.
`
`tion, as shown in Figs. 10 to 12 for Nitinol, Titanal,
`and Orthonol.
`
`DISCUSSION
`
`The results of this investigation agree with the pre(cid:173)
`vious studies by Miura et al. 2 for Japanese NiTi and
`Burs tone et al. 3 for Chinese NiTi. The 6 mm cantilever
`test spans used in the present study were chosen to be
`intermediate in length between the equivalent 7 mm
`cantilever specimens used2 to evaluate Japcmese NiTi.
`
`6 of 10
`
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`US ENDODONTICS, LLC., Petitioner
`
`

`

`Volume 99
`Number 4
`
`Bending properties of superelastic and nonsuperelastic NiTi wires 315
`
`NITINOL WIRE <o.o16in.,Heat-treated>
`
`-e- -
`-
`500°C, 1Om in
`-- ...._- -500°C,120min
`-e---:--- 600°C, 1Om in
`- · - • 600°C, 120min
`
`span ~6mm
`
`3
`
`2
`
`1
`
`TITANAL WIRE <o.o16in.,Heat-treated>
`-e- -:-- 500°C, 1Om in
`-
`---e---500°C,120min
`- - e - - 600°C, 1Om in
`- · - • 600°C, 120min
`
`span=6mm
`
`3
`
`2
`
`1
`
`E
`E
`,..,
`0>
`
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`0 ,... --c:
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`0
`:!
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`
`60
`30
`Angular Position (deg)
`
`90
`
`Fig. 10. Bending plots for 0.016-inch-diameter Nitinol wires after
`heat treatments.
`
`60
`30
`Angular Position (deg)
`
`90
`
`Fig. 11. Bending plots for 0.016-inch-diameter Titanal wires
`after heat treatments.
`
`where three-point bending and 14 mm test spans were
`employed, and the 5 mm cantilever test spans used3 to
`evaluate the Chinese alloy. The bending plots for the
`three superelastic wire alloys in Figs. 1 to 3 have the
`distinctive appearance originally observed for the
`Chinese and Japanese alloys, and the values of bending
`moment and permanent deformation after unloading
`for 0.016-inch-diameter specimens of the superelastic
`wires and Nitinol were very similar to those reported
`by Burs tone et al. 3
`For the superelastic wires, short cantilevered spec(cid:173)
`imen lengths are necessary to achieve adequately high
`bending-moment values during testing. 3 Such test spans
`provide the additional advantage of relevance to clinical
`interbracket distances, in contrast to the longer 0 .5-inch
`and l-inch test spans used in some earlier studies I.Io,
`11
`of the bending properties of Nitinol cantilevered wires.
`The bending curves for the superelastic alloys have
`pronounced nonlinear appearances, and it is not pos(cid:173)
`sible to define a single value of stiffness or slope of the
`bending plot for a particular wire. 3 The dramatic effects
`of decreasing the cantilever test -span length from 0. 5
`inch (12.5 mm) to 5 or 6 mm for the nonsuperelastic
`Nitinol can be seen in a comparison between the original
`bending plots charted by Andreasen and Morrow 1 for
`0.018-inch-diameter wires and the results Burstone
`et al. 3 found for 0. 016-inch-diameter wires and the pres(cid:173)
`ent study. With the shorter test spans, the bending
`curves for Nitinol were considerably more nonlinear,
`
`ORTHONOL WIRE <o.o1ein.,Heat-treated>
`-
`-e- -
`500°C, {Omin
`-- -e--- 500°C, 120min
`_ ___...,_ 600oC, 1Om in
`-
`....... - 600°C, 120min
`
`span~ 6mm
`
`3 -·
`E
`E
`E 0)
`,..,
`0 ,... 2 --c:
`
`Q)
`E
`0
`::E
`0> 1
`c:
`:.0 c:
`Q) c:c
`
`60
`30
`Angular Position (deg)
`
`90
`
`Fig. 12. Bending plots for 0.016-inch-diameter Orthonol wires
`after heat treatments.
`
`and the permanent deformation after unloading was
`30° to 35°, compared with about 5° for the 0.5-inch
`(12.5 mm) test spans.
`Under the well-defined and relatively simple load(cid:173)
`ing conditions of the tension test, the existence of su-
`
`7 of 10
`
`IPR2015-00632 - Ex. 1018
`US ENDODONTICS, LLC., Petitioner
`
`

`

`316 Khier, Brantley, and Fournelle
`
`Am. J. Orthod. Dentofac. Orthop.
`Apri/1991
`
`perelastic behavior for an orthodontic wire is proved
`unambiguously when extensive horizontal regions of
`constant elastic strain occur on the loading and un(cid:173)
`loading portions of the stress-strain curve. 2 It can be
`seen from Figs. 1 to 3 that similar superelastic regions
`of nearly constant bending moment were more evident
`for the deactivation portions of the bending plots than
`during activation. For the rectangular wire sizes of two
`superelastic alloys, these horizontal regions or plateaus
`were not as evident or present on the deactivation
`curves, but the slopes of tpe bending plots were still
`much less than those for the nonsuperelastic alloys in
`Figs.· 4 to 6. The value of spring back provides a com(cid:173)
`plementary and probably superior criterion for assessing
`the presence of superelasticity in bending. For the pres(cid:173)
`ent 6 mm cantilever test spans and approximately 80°
`activation, the as-received superelastic alloys and wire
`sizes had springback values ranging from about 65° to
`70°, whereas the as-received nonsuperelastic wire spec(cid:173)
`imens had values of springback ranging from about 40°
`to 60°. (We obtained these data by subtracting the values
`of permanent set given in the previous section from the
`maximum activation of 80° before unloading.) In prin(cid:173)
`ciple, it would be possible theoretically to derive the
`cantilevered bending moment -angular deflection plot
`from the experimental tensile stress-strain curve. 12
`However, this is a formidable task for the nickel(cid:173)
`titanium wires because of several factors: the variation
`in strain across the specimen cross section during bend(cid:173)
`ing; the occurrence of both elastic deformation and per(cid:173)
`manent deformation, where the former may include
`superelastic strain; and the complexity of the bending
`mechanics analysis for large deflections, 13 which would
`be particularly important with the use of short test span
`lengths.
`Because of these considerations, we anticipate prob(cid:173)
`lems in the determination of traditional11 mechanical
`properties of elastic modulus and yield strength for the
`nickel-titanium wires when short cantilevered test spans
`are used. Following the approach of Burstone et al. ,3
`researchers can make quantitative measurements of the
`moment at yielding, the maximum moment developed
`at the greatest angular deflection, the average moment
`for the superelastic region of deactivation, and the per(cid:173)
`manent deformation that remains after unloading. The
`average unloading stiffness during deactivation is an
`important characteristic for the nonsuperelastic wires,
`and values of unloading stiffness that correspond to
`the different regions on the bending curves for the
`supereiastic wires can be determined. With the excep(cid:173)
`tion of the moment at yielding, all of these foregoing
`measurements can be obtained with facility from the
`cantilevered bending plots. Determination of the mo-
`
`ment value for some small amount of permanent
`deformation-e.g., in the range of 1 o to 3° -requires
`additional experiments in which nominally identical test
`segments are subjected to increasing amounts of angular
`deflection and then unloaded. Thus the standardized
`testing procedures, which appear in ADA specification
`No. 32 for orthodontic wires, 14 should be modified
`for the nickel-titanium alloys. This specification was
`originally developed for longer l-inch test spans of
`high-stiffness alloys (stainless steel, cobalt-chromium(cid:173)
`nickel) where the cantilevered bending plots are well
`behaved and very similar for loading and unloading.
`Our complementary research with the techniques of
`x-ray diffraction (XRD), differential scapning calori(cid:173)
`metry (DSC), and optical microscopy has shown that
`the metallurgical structures of the as-received super(cid:173)
`elastic wires are complex. Although the XRD spectra
`confirm that these wires consist largely of an austenitic
`matrix of nickel-titanium, some martensitic NiTi is also
`present. 4 The DSC thermograms 15 provide clear evi(cid:173)
`dence of an additional metastable rhombohedral struc(cid:173)
`ture (termed the R structure), 16 which is an intermediate
`phase for the austenite-to-martensite transformation in
`NiTi. The microstructural phases present in the super(cid:173)
`elastic wires depend on the transformation temperatures
`for the austenitic phase. For example, if the tempera(cid:173)
`tures for the transformations from austenite to the R
`structure and martensite are below room temperature,
`the superelastic wires will have an austenitic matrix at
`room temperature. In contrast, the as-received nonsu(cid:173)
`perelastic wires have microstructures consisting of cold(cid:173)
`worked martensitic NiTi and R structure. 4
`15
`•
`The heat treatment temperatures and times used in
`this study were chosen on the basis of the previously
`published results reported by Miura et al. 2 for Japanese
`NiTi. The objectives were to ascertain whether the heat(cid:173)
`treatment responses of the other commercial superelas(cid:173)
`tic alloys would be similar, as confirmed in Figs. 7 to
`9, and to investigate the effects of such heat-treatment
`conditions for the nonsuperelastic alloys (Figs. 10 to
`12). The heat treatments at 500° and 600° C result in
`some loss of internal stresses in the wires and cause
`transformation of the martensitic NiTi and R phase in
`the microstructure to austenitic NiTi. 4 During subse(cid:173)
`quent cooling to room temperature, the austenitic NiTi
`may be retained or may undergo transformation. The
`relative proportions of austenitic NiTi, R structure, and
`martensitic NiTi in the wire microstructures depend on
`the phase-transformation temperatures, which, in turn,
`depend on both the heat-treatment temperature and the
`18 A more complete description
`amount of cold work. 17
`•
`of these relatively complex metallurgical processes will
`be published separately.
`
`8 of 10
`
`IPR2015-00632 - Ex. 1018
`US ENDODONTICS, LLC., Petitioner
`
`

`

`Volume 99
`Number 4
`
`Bending properties of superelastic and nonsuperelastic NiTi wires 317
`
`In closing, one must be careful not to draw un(cid:173)
`warranted conclusions for orthodontic practice from this
`laboratory study of bending properties, in particular
`about the relative merits of superelastic versus nonsu(cid:173)
`perelastic wires, which can be established only after
`clinical research. It may also be noted that the minor
`effects of the 500° and 600° C heat treatments on the
`bending properties of the nonsuperelastic wires are con(cid:173)
`sistent with the results reported by Mayhew and Kusy. 19
`These investigators found that the mechanical proper(cid:173)
`ties of Nitinol and Titanal arch wires were not affected
`by approved heat -sterilization methods performed at
`temperatures below 180° C. Future research in this area
`has been recommended 19 for the superelastic NiTi
`wires.
`
`CONCLUSIONS
`From an extensive series of cantilever bending ex(cid:173)
`periments performed on several popular sizes of six
`brands of nickel-titanium orthodontic wires, the follow(cid:173)
`ing conclusions are drawn:
`1. The bending deformation plots for the three
`brands of superelastic wires were similar, but differed
`substantially from the bending plots for the three brands
`of nonsuperelastic wires, which were also similar. For
`example, the maximum bending moment at 80° acti(cid:173)
`vation for 11 4-inch (6 mm) cantilevered test spans of
`the superelastic wires ranged from about 1200 to 2000
`gm · mm when the cross-section varied from 0.016
`inch in diameter to 0.021 X 0.025 or 0.0215 X 0.028
`inch. The corresponding maximum moment values for
`the nonsuperelastic wires were nearly twice as great,
`ranging from about 2000 to 3800 gm · mm. Permanent
`deformation of the test spans after unloading from 80°
`activation was about 10° to 15° for the superelastic wires
`and at least twice as great for the nonsuperelastic wires.
`2. A superelastic region of nearly constant bending
`moment was observed for deactivation of the round
`wires but was less evident during deactivation for the
`rectangular superelastic wires tested. The slopes of the
`nonlinear bending plots (stiffness values) were always
`considerably less for the superelastic wires, compared
`to the nonsuperelastic wires. The present results indi(cid:173)
`cate that the value of springback in bending is an ex(cid:173)
`cellent criterion to distinguish between the existence
`or absence of superelastic behavior for these nickel(cid:173)
`titanium alloys. Unambiguous proof of superelastic be(cid:173)
`havior requires use of the tension test where extensive
`horizontal regions appear on both the loading and un(cid:173)
`loading portions of the stress-strain curve.
`3. While heat treatment at 500° and 600° C caused
`only small changes in the bending plots for the non(cid:173)
`superelastic wires, the superelastic wires showed con-
`
`siderable response to heat treatment. For all three su(cid:173)
`perelastic brands, the maximum moment at 80° acti(cid:173)
`vation and the average superelastic moment during
`deactivation were decreased by heat treatment at
`500° C for 2 hours, although there was little change in
`spring back. Heat treatment at 500° C for 10 minutes
`caused minimal changes in the bending plots for the
`three superelastic alloys, while heat treatment at
`600° C for as little as 10 minutes resulted in complete
`loss of superelastic behavior. The differences in the
`bending properties and heat -treatment responses for the
`sup