Niti

NICKEL TITANIUMNICKEL TITANIUM
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Nickel Titanium AlloyNickel Titanium Alloy
– INTRODUCTIONINTRODUCTION
– HISTORYHISTORY
– EVOLUTION OF ARCHWIRE MATERIALSEVOLUTION OF ARCHWIRE MATERIALS
– METALLURGYMETALLURGY
– NICKEL-TITANIUM ALLOYS – GENERATIONSNICKEL-TITANIUM ALLOYS – GENERATIONS
– STRUCTURESTRUCTURE
– MECHANICAL PROPERTIES OF NITINOLMECHANICAL PROPERTIES OF NITINOL
– SHAPE MEMORY EFFECT AND NICKEL – TITANIUM ALLOYSHAPE MEMORY EFFECT AND NICKEL – TITANIUM ALLOY
– SUPERELASTICITYSUPERELASTICITY
– CLASSIFICATIONCLASSIFICATION
– CHINESE NITICHINESE NITI
– JAPANESE NITIJAPANESE NITI
– COPPER –NITICOPPER –NITI
– CV NITICV NITI
– REVERSE CURVE NITIREVERSE CURVE NITI
– GOLD NITIGOLD NITI
– DUAL FLEX ARCH WIRESDUAL FLEX ARCH WIRES
– SUPERCABLE WIRESUPERCABLE WIRE
– TURBO WIRE (BRAIDED PREFORMED NICKEL-TITANIUM)TURBO WIRE (BRAIDED PREFORMED NICKEL-TITANIUM)
– PLASTIC COATED NITIPLASTIC COATED NITI
– BIOFORCEBIOFORCE

– BIOCOMPATIBILITYBIOCOMPATIBILITY
– RECYCLINGRECYCLING
– ADVANTAGES OF NICKEL TITANIUM WIRESADVANTAGES OF NICKEL TITANIUM WIRES
– LIMITATIONS OF NITI WIRESLIMITATIONS OF NITI WIRES
– FRICTIONAL CHARACTERISTICS OF NICKEL TITANIUM WIRESFRICTIONAL CHARACTERISTICS OF NICKEL TITANIUM WIRES
– MODIFICATION OF ARCHWIRE SURFACEMODIFICATION OF ARCHWIRE SURFACE
– JOININGJOINING
– APPLYING ARCHWIRESAPPLYING ARCHWIRES
– FUTURE IN ORTHODONTIC ARCH WIRESFUTURE IN ORTHODONTIC ARCH WIRES
– CONCLUSIONCONCLUSION
– BIBILOGRAPHYBIBILOGRAPHY

IntroductionIntroduction
Titanium has been used as a structural metal ever since 1952 and itsTitanium has been used as a structural metal ever since 1952 and its
possible use in Orthodontics has been suggested periodically. Arch wirepossible use in Orthodontics has been suggested periodically. Arch wire
materials with a component of titanium became available to Orthodontics inmaterials with a component of titanium became available to Orthodontics in
the 1970’s. Nitinol, a Stochiometric nickel titanium alloy was first introducedthe 1970’s. Nitinol, a Stochiometric nickel titanium alloy was first introduced
for use in orthodontics in 1971, and is available asfor use in orthodontics in 1971, and is available as NiTi, Nitinol, Orthonol,NiTi, Nitinol, Orthonol,
Sentinol and TitanolSentinol and Titanol. Since their introduction, they became an integral part. Since their introduction, they became an integral part
of orthodontic mechanotherapy due to their unique characteristics ofof orthodontic mechanotherapy due to their unique characteristics of lowlow
stiffness, super elasticity and high reversibilitystiffness, super elasticity and high reversibility. They have substituted twisted. They have substituted twisted
steel wires for leveling because of its high resilience. The high spring back ofsteel wires for leveling because of its high resilience. The high spring back of
Nitinol is useful in circumstances that require large deflections but low forces.Nitinol is useful in circumstances that require large deflections but low forces.
This result in increased clinical efficiency of Nitinol and fewer archwireThis result in increased clinical efficiency of Nitinol and fewer archwire
changes or activations are required in routine orthodontic mechanicschanges or activations are required in routine orthodontic mechanics

HISTORYHISTORY
The alloy was developed byThe alloy was developed by William F BuehlerWilliam F Buehler, a research metallurgist at Naval, a research metallurgist at Naval
Ordinance Laboratory, now called as Naval Surface Weapons Center in SilverOrdinance Laboratory, now called as Naval Surface Weapons Center in Silver
Springs, Maryland in the year 1960, originally for space programme.Springs, Maryland in the year 1960, originally for space programme.
WILLIAM J. BUEHLER IN 1968, PICTURED WITH A DEMONSTRATION OF NITINOL WIRE. ELECTRICITYWAS PASSED THROUGH A STRAIGHTWILLIAM J. BUEHLER IN 1968, PICTURED WITH A DEMONSTRATION OF NITINOL WIRE. ELECTRICITYWAS PASSED THROUGH A STRAIGHT
PIECE OF WIRE, AND THE WIRE WOULD CHANGE INTO THE WORD “INNOVATIONS.” THE OAK LEAF, U.S. NAVAL ORDNANCEPIECE OF WIRE, AND THE WIRE WOULD CHANGE INTO THE WORD “INNOVATIONS.” THE OAK LEAF, U.S. NAVAL ORDNANCE
LABORATORY, WHITE OAK, MARYLANDLABORATORY, WHITE OAK, MARYLAND

The name Nitinol is an acronym derived from the elements, whichThe name Nitinol is an acronym derived from the elements, which
comprises the alloy (nitinol)comprises the alloy (nitinol)
NiNi-Nickel-Nickel
TiTi- titaniumtitanium
NolNol-Naval Ordinance Laboratory.-Naval Ordinance Laboratory.
This alloy had unique properties:This alloy had unique properties:
– it was non corrosiveit was non corrosive
– had the ability to change crystallinehad the ability to change crystalline
form with changes inform with changes in temperaturetemperature

Dr. Buehler termed the temperature at which this change took place theDr. Buehler termed the temperature at which this change took place the
““TEMPERATURE TRANSITION RANGETEMPERATURE TRANSITION RANGE”, or TTR”, or TTR..
Below the TTR, the alloy was aBelow the TTR, the alloy was a martensitemartensite
Above the TTR, it was anAbove the TTR, it was an austeniteaustenite..
The wire’s shape was formed at a very high temperature, far above the TTR. It couldThe wire’s shape was formed at a very high temperature, far above the TTR. It could
be then cooled below the TTR and deformed to any configuration. As the wire hasbe then cooled below the TTR and deformed to any configuration. As the wire has
warmed through the TTR, it would then recover its original shape completely.warmed through the TTR, it would then recover its original shape completely.
One of the first applications of nitinol was developed by NASA- antennae forOne of the first applications of nitinol was developed by NASA- antennae for
space capsules. The wire was preformed at a high temperature, cooled andspace capsules. The wire was preformed at a high temperature, cooled and
packaged. When the capsule was warmed by the sun in space, the packagepackaged. When the capsule was warmed by the sun in space, the package
opened and released the antenna as the wire passed through it TTR.opened and released the antenna as the wire passed through it TTR.

Dr. George AndreasenDr. George Andreasen thought of applying this wire to orthodonticsthought of applying this wire to orthodontics below andbelow and
above the mouth temperatureabove the mouth temperature. Mouth temperature would be the TTR. He. Mouth temperature would be the TTR. He
corresponded with Dr. Buehler about this idea. The first wires obtained from Dr.corresponded with Dr. Buehler about this idea. The first wires obtained from Dr.
Buehler were “55 % wt.” and “60 % wt” nitinol.Buehler were “55 % wt.” and “60 % wt” nitinol.
More the nickelMore the nickel →→ lower the TTRlower the TTR..
The 60% wt nitinol had a TTR of 16The 60% wt nitinol had a TTR of 16°°C to 27C to 27°°C, while the 50% wt nitinol had a TTR ofC, while the 50% wt nitinol had a TTR of
3232°°C to 42C to 42°°C.C.
Nitinol has excellentNitinol has excellent spring back propertyspring back property but itbut it does not possessdoes not possess shape memoryshape memory oror
super elasticitysuper elasticity as it was manufactured by a work hardening process.as it was manufactured by a work hardening process.
DR. GEORGE ANDREASEN DISPLAYING
NITINOL WIRE THAT HE ADAPTED FOR
ORTHODONTIC USE. NITINOL
ORTHODONTIC DEVICES REQUIRE
FEWER READJUSTMENTS THAN THEIR
STAINLESS STEEL COUNTERPARTS

After considerable experimentationAfter considerable experimentation,, Nitinol was marketed in the late 1970s forNitinol was marketed in the late 1970s for
orthodontic use in a stabilized martensitic form, with no application of phase transitionorthodontic use in a stabilized martensitic form, with no application of phase transition
effects. As provided for orthodontic use,effects. As provided for orthodontic use, Nitinol is exceptionallyNitinol is exceptionally springyspringy andand quitequite
strongstrong but hasbut has poor formabilitypoor formability. Other martensitic alloys marketed later (Titanol,. Other martensitic alloys marketed later (Titanol,
Lancer Pacific; Orthonol, Rocky Mountain) have similar strength and springiness toLancer Pacific; Orthonol, Rocky Mountain) have similar strength and springiness to
Nitinol but between formability. The family of stabilized martensitic alloys nowNitinol but between formability. The family of stabilized martensitic alloys now
commercially available are referred to as M-NiTicommercially available are referred to as M-NiTi

The new nickel – titanium alloys with active austenitic grain structure appeared in orthodonticsThe new nickel – titanium alloys with active austenitic grain structure appeared in orthodontics
by late 1980’s. These alloys exhibited super elasticity, which is manifested by very largeby late 1980’s. These alloys exhibited super elasticity, which is manifested by very large
reversible strains and a non-elastic stress strain or force deflection curve.reversible strains and a non-elastic stress strain or force deflection curve.
Chinese NiTiChinese NiTi reported byreported by BurstoneBurstone andand
Japanese NiTiJapanese NiTi byby MiuraMiura et alet al came to be known as A-NiTi.came to be known as A-NiTi.
HansonHanson introducedintroduced SupercableSupercable wire in 1993.wire in 1993.
In 1994In 1994 RohitRohit SachdevaSachdeva developeddeveloped copper NiTicopper NiTi, which forms the basis of variable, which forms the basis of variable
transformation temperature orthodontics.transformation temperature orthodontics.
LaterLater MaselMasel orthodontics introducedorthodontics introduced CV NiTiCV NiTi, the copper free NiTi as an alternative to copper, the copper free NiTi as an alternative to copper
NiTi.NiTi.

Current Applications of Nitinol include:Current Applications of Nitinol include:
Orthodontic AppliancesOrthodontic Appliances
Scoliosis Treatment DevicesScoliosis Treatment Devices
Heat Shrink Hose CouplingsHeat Shrink Hose Couplings
AerospaceAerospace
Vascular CathetersVascular Catheters
Spring ActuatorsSpring Actuators

Underwire & BraUnderwire & Bra
SupportsSupports
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METALLURGYMETALLURGY
Titanium was discovered byTitanium was discovered by W. GregorW. Gregor ((English priest) in Cornwall in 1791.English priest) in Cornwall in 1791.
It was named byIt was named by KlaprothKlaproth in 1795.in 1795.
It has changed very rapidly from a rare metal in 1947 to an important structural metalIt has changed very rapidly from a rare metal in 1947 to an important structural metal
because of its lightweight, high strength and corrosion resistance.because of its lightweight, high strength and corrosion resistance.
Atomic number is 22Atomic number is 22 andand atomic weight 47.9atomic weight 47.9, occupies the, occupies the ninth placeninth place in abundancein abundance
of metals in the earth’s crust.of metals in the earth’s crust.
98% of all rocks examined contained titanium besides sand, slay and other soils.98% of all rocks examined contained titanium besides sand, slay and other soils.
Many minerals contain Titanium, the main ones beingMany minerals contain Titanium, the main ones being ilmeniteilmenite andand rutilerutile..
Ilmenite is an iron-titanium oxide ore or iron titanate that contains 32% titanium.Ilmenite is an iron-titanium oxide ore or iron titanate that contains 32% titanium.
Rutile is titanium dioxide, which is richer in titanium contentRutile is titanium dioxide, which is richer in titanium content..
U.S., Australia, Brazil, Norway, Russia, Sweden, Finland, Portugal, Africa andU.S., Australia, Brazil, Norway, Russia, Sweden, Finland, Portugal, Africa and IndiaIndia
are some of the countries in which titanium available.are some of the countries in which titanium available.
Travancore in IndiaTravancore in India is particularly important for its titanium ore content. Most of theis particularly important for its titanium ore content. Most of the
titanium ores imported by the U.S. come from India.titanium ores imported by the U.S. come from India.

Titanium is bright silvery metalTitanium is bright silvery metal
when polished resembles steel in appearancewhen polished resembles steel in appearance
it has got a low densityit has got a low density
is non-magneticis non-magnetic
its electrical and thermal conductivity can be considered almost near to stainless steelits electrical and thermal conductivity can be considered almost near to stainless steel
it is one of the metals that can be coupled with other metals without the fear of losing itsit is one of the metals that can be coupled with other metals without the fear of losing its
passivity.passivity.
When coupled with metals with greater corrosion potentials, the other metal may corrode by theWhen coupled with metals with greater corrosion potentials, the other metal may corrode by the
mechanism of galvanic corrosion.mechanism of galvanic corrosion.
Titanium’sTitanium’s
resistance to electrochemical degradation,resistance to electrochemical degradation,
benign biologic response elicited,benign biologic response elicited,
relatively lightweight and low density,relatively lightweight and low density,
low modulus and high strengthlow modulus and high strength
made titanium based materials attractive for use in dentistrymade titanium based materials attractive for use in dentistry..

Extraction of TitaniumExtraction of Titanium
Van Arkel processVan Arkel process Kroll processKroll process I.C.I. processI.C.I. process

Expensive process
Replaced with cheaper Chlorine, but
TiCl4 is much less decomposable
than Ti I4
Impure Ti
Iodide
170 0
TiI4
Deposition of
Ti crystals
Silica vessel
Decomposed
Van Arkel processVan Arkel process

Steel vessel
Rutile + CokeRutile + Coke
Magnesium
Chlorine gas passed
8000
Chloride is formed
TiO2 +2Cl2 + 2C = TiCl4 + 2CO
Fractional distillationFractional distillation
Purified by
Molten
magnesium
Magnesium + Ti Cl4 
Spongy Ti
Vapor is
passed over
Cleaned, compressed into
shape of an electrode
then melted and cast to ingot
under high temperature
Kroll processKroll process

Cleaned, compressed into
shape of an electrode
then melted and cast to
ingot under high
temperature

CRITERIA OF AN
IDEAL ARCH WIRE
Esthetic
Good range
Poor
Biohost
Tough
Good
Spring back
Low
Friction
Weldable
Springy
Formable
Biocompatible
Resilient
Strong

NICKEL-TITANIUM ALLOYS – GENERATIONS
First GenerationFirst Generation::
Reported byReported by AndreasenAndreasen in 1971.in 1971.
It was marketed asIt was marketed as NitinolNitinol by Unitek/3M.by Unitek/3M.
It did not exhibit superelastic behaviour, but possessed two features ofIt did not exhibit superelastic behaviour, but possessed two features of
considerable importance for clinical orthodontics:considerable importance for clinical orthodontics:
a very low elastic modulusa very low elastic modulus
an extremely wide working range.an extremely wide working range.
Second GenerationSecond Generation::
SuperelasticSuperelastic Chinese NiTiChinese NiTi marketed as “NiTi” by Ormco/ Sybron.marketed as “NiTi” by Ormco/ Sybron.
It exhibits non-linear loading and unloading characteristics more pronouncedIt exhibits non-linear loading and unloading characteristics more pronounced
than those of the original nitinol wire.than those of the original nitinol wire.

Third GenerationThird Generation::
Japanese NiTiJapanese NiTi marketed as “Sentalloy” by GAC international (superelastic behaviour).marketed as “Sentalloy” by GAC international (superelastic behaviour).
The unloading characteristics of this type of Ni-Ti alloys exhibit initial and final regionsThe unloading characteristics of this type of Ni-Ti alloys exhibit initial and final regions
of relatively steep slop, along with an extensive intermediate region where there is littleof relatively steep slop, along with an extensive intermediate region where there is little
or no change in stress.or no change in stress.
This superelastic behaviour and shape memory characteristics of these alloys areThis superelastic behaviour and shape memory characteristics of these alloys are
based on a reversible transformation between the austenitic and martensitic NiTibased on a reversible transformation between the austenitic and martensitic NiTi
phases.phases.
Fourth GenerationFourth Generation::
In early 1990s,In early 1990s, thermally activated nickel titanium wirethermally activated nickel titanium wire were introduced (e.g.were introduced (e.g. CopperCopper
NiTi, CV NiTiNiTi, CV NiTi), whose transition temperature is close to the level of body temperature.), whose transition temperature is close to the level of body temperature.

Thermal NitinolThermal Nitinol::
– The original composition comprised of a 1:1 atomic ratio of Nickel andThe original composition comprised of a 1:1 atomic ratio of Nickel and
Titanium.Titanium.
Nickel 55%Nickel 55%
Titanium 45%Titanium 45%
– However, in order to bring the transition temperature range down to 37ºC, theHowever, in order to bring the transition temperature range down to 37ºC, the
amount ofamount of cobalt added to the alloy is 1.6%.cobalt added to the alloy is 1.6%.
– The unique feature of this alloy was theThe unique feature of this alloy was the
– shape memory phenomenon.shape memory phenomenon.
– has a martensitic grain structurehas a martensitic grain structure
– transition brings about a change in the grain structuretransition brings about a change in the grain structure
from martensite to austenitefrom martensite to austenite..
Andreasen described Nitinol
1982
Thermal Nitinol Elastic Nitinol

The 50:50 compositions of nickel and titanium introduced by Andreasen was aThe 50:50 compositions of nickel and titanium introduced by Andreasen was a
shape memory alloy (SME) in composition only.shape memory alloy (SME) in composition only.
Indeed, this alloy was passive, as the SME had been suppressed by cold workingIndeed, this alloy was passive, as the SME had been suppressed by cold working
the wire during drawing to more than 8 to 10%.the wire during drawing to more than 8 to 10%.
The attractiveness was itsThe attractiveness was its low force per unit of deactivationlow force per unit of deactivation andand low stiffnesslow stiffness. This. This
wire used to deliver only one-fifth to one-seventh the force per unit of deactivationwire used to deliver only one-fifth to one-seventh the force per unit of deactivation
thereby meeting the criterion of light continuous force..thereby meeting the criterion of light continuous force..

Elastic NitinolElastic Nitinol::
– This consists of nickel and titanium alone and it became popular due toThis consists of nickel and titanium alone and it became popular due to
outstanding characteristics ofoutstanding characteristics of elasticity and flexibilityelasticity and flexibility

StructureStructure
Nickel-titanium system is theNickel-titanium system is the binary, equiatomic, intermetallic compound.binary, equiatomic, intermetallic compound.
The intermetallic compound is extraordinary because it has a moderate solubilityThe intermetallic compound is extraordinary because it has a moderate solubility
range for excess nickel or titanium, as well as most other metallic elements, and itrange for excess nickel or titanium, as well as most other metallic elements, and it
exhibits ductility comparable to most ordinary alloys.exhibits ductility comparable to most ordinary alloys.
This solubility allows alloying with many of the elements to modify both mechanicalThis solubility allows alloying with many of the elements to modify both mechanical
properties and the transformation properties of the system.properties and the transformation properties of the system.
Excess Ni in amount about upto 1%, is the most common alloying addition.Excess Ni in amount about upto 1%, is the most common alloying addition.
Excess Ni strongly depresses the transformation temperature and increases the yieldExcess Ni strongly depresses the transformation temperature and increases the yield
strength of the austenite.strength of the austenite.

Other frequently used elements areOther frequently used elements are
– iron and chromiumiron and chromium to lower the transformation temperatureto lower the transformation temperature
– coppercopper to decrease the hysteresis and lower the deformation stress ofto decrease the hysteresis and lower the deformation stress of
the martensitethe martensite
Because common contaminants such as oxygen, nitrogen and carbon canBecause common contaminants such as oxygen, nitrogen and carbon can
also shift the transformation temperature and degrade the mechanicalalso shift the transformation temperature and degrade the mechanical
properties, it is also desirable to minimize the amount of these elements.properties, it is also desirable to minimize the amount of these elements.
Oxygen forms TiOxygen forms Ti44NiNi22Ox inclusion, whichOx inclusion, which
– lowers the alloy elasticity,lowers the alloy elasticity,
– affects memory changesaffects memory changes
– reduces resistance to corrosionreduces resistance to corrosion
 Nitrogen also behaves in the same wayNitrogen also behaves in the same way

Selective work hardening which can exceed 50% reduction in some cases, andSelective work hardening which can exceed 50% reduction in some cases, and
proper heat treatment can greatly improve the ease with which the martensite isproper heat treatment can greatly improve the ease with which the martensite is
deformed, give an austenite with much greater strength, and create material thatdeformed, give an austenite with much greater strength, and create material that
spontaneouslyspontaneously moves itself both on heating and on coolingmoves itself both on heating and on cooling ((two-way shape memorytwo-way shape memory).).
One of the biggest challenges in using this family of alloys is in developing the properOne of the biggest challenges in using this family of alloys is in developing the proper
processing procedures to yield the properties desired.processing procedures to yield the properties desired.

Because of the reactivity of titanium in these alloys, all melting must be done in aBecause of the reactivity of titanium in these alloys, all melting must be done in a
vacuumvacuum or anor an inert atmosphereinert atmosphere..
Methods such asMethods such as
– plasma-arc meltingplasma-arc melting
– electron beam meltingelectron beam melting
– vacuum induction melting are all used commercially.vacuum induction melting are all used commercially.
After ingots are melted, standard hot forming processes such as forging, bar rolling,After ingots are melted, standard hot forming processes such as forging, bar rolling,
and extrusion can be used for initial breakdown.and extrusion can be used for initial breakdown.
The alloys react slowly with air, so hot working in air is quite successful. Most cold-The alloys react slowly with air, so hot working in air is quite successful. Most cold-
working processes can also be applied to these alloys, but they work hardenworking processes can also be applied to these alloys, but they work harden
extremely rapidly and frequent annealing is required. Wire drawing is probably theextremely rapidly and frequent annealing is required. Wire drawing is probably the
most widely used of the techniques, and excellent surface properties and sizes asmost widely used of the techniques, and excellent surface properties and sizes as
small as .05 mm (.002”) are made routinely.small as .05 mm (.002”) are made routinely.

Fabrication of articles from NiTi can usually be done with care, but some of theFabrication of articles from NiTi can usually be done with care, but some of the
normal processes are difficult.normal processes are difficult.
Machining by turning or milling is very difficult except with special tools and practices.Machining by turning or milling is very difficult except with special tools and practices.
Heat treating to impart the desired memory shape is often done at 500 to 800Heat treating to impart the desired memory shape is often done at 500 to 800°°C, butC, but
it can be done as low as 300 to 350it can be done as low as 300 to 350°°C, if sufficient time is allowed.C, if sufficient time is allowed.

Mechanical properties of NitinolMechanical properties of Nitinol
441276127693193171.771.7β-Titaniumβ-Titanium
221489148942742741.441.4NITINITI
552117211715791579179179SSSS
881682168214131413184184Co-Cr-NiCo-Cr-Ni
No. ofNo. of
9090 00
cold bendscold bends
withoutwithout
fracturefracture
UltimateUltimate
TensileTensile
StrengthStrength
(MPa)(MPa)
0.2 % Yield0.2 % Yield
strengthstrength
(MPa)(MPa)
Modulus ofModulus of
ElasticityElasticity
(GPa)(GPa)
AlloyAlloy

Important properties of orthodontic wire alloysImportant properties of orthodontic wire alloys
Property Stainless
steel
Cobalt
chromium
β - titanium
TMA
Nickel - titanium
Cost Low Low High High
Force delivery High High Intermediate Low
Spring back Low Low Intermediate High
Formability Excellent Excellent Excellent Poor
Ease of joining Welded
joints must
be reinforced
with solder
Welded joints
must be
reinforced with
solder
Only wire that
has true
weldability
Cannot be
soldered or
welded
Friction Low Low High High
Biocompatibility Some Some None Some

Shape Memory effect and Nickel – titanium alloyShape Memory effect and Nickel – titanium alloy
NiTi alloys have two remarkable properties that are unique in dentistry-NiTi alloys have two remarkable properties that are unique in dentistry-
– shape memoryshape memory
– super elasticity.super elasticity.
Both shape memory and super elasticity are related to phase transitions within theBoth shape memory and super elasticity are related to phase transitions within the
NiTi alloy between the martensitic and austenitic forms that occur at a relatively lowNiTi alloy between the martensitic and austenitic forms that occur at a relatively low
transition temperature.transition temperature.
Shape memory (“martensite memory” or “mechanical memory”) refers to the ability ofShape memory (“martensite memory” or “mechanical memory”) refers to the ability of
the materialthe material to remember its original shapeto remember its original shape after being plastically deformed while inafter being plastically deformed while in
the martensitic form. In a typical application, a certain shape is set while the alloy isthe martensitic form. In a typical application, a certain shape is set while the alloy is
maintained at an elevated temperature, above the martensite-austenite transitionmaintained at an elevated temperature, above the martensite-austenite transition
temperature. When the alloy is cooled below the transition temperature, it can betemperature. When the alloy is cooled below the transition temperature, it can be
plastically deformed, but when it is heated again the original shape is restored. Thisplastically deformed, but when it is heated again the original shape is restored. This
property,property, calledcalled thermoelasticitythermoelasticity,, was important to the original nitinol’s use in thewas important to the original nitinol’s use in the
space program but proved difficult to exploit in orthodontic applications.space program but proved difficult to exploit in orthodontic applications.www.indiandentalacademy.comwww.indiandentalacademy.com

Materials that exhibit shape memory only upon heating are referred to as having a one-way shape memory.Materials that exhibit shape memory only upon heating are referred to as having a one-way shape memory.
Some materials also undergo a change in shape upon recooling. These materials have a two-way shapeSome materials also undergo a change in shape upon recooling. These materials have a two-way shape
memory.memory.
There are two major NiTi phases in the nickel-titanium wires.There are two major NiTi phases in the nickel-titanium wires.
Austenitic NiTiAustenitic NiTi
– has an orderedhas an ordered bccbcc (CsCI -type) structure (sometimes termed B2)(CsCI -type) structure (sometimes termed B2)
– forms at high temperatures and low stresses.forms at high temperatures and low stresses.
Martensitic NiTMartensitic NiTii
– has been reported to have a distortedhas been reported to have a distorted monoclinicmonoclinic,, triclinictriclinic, or, or hexagonalhexagonal structurestructure,,
– forms at low temperatures and high stresses.forms at low temperatures and high stresses.
The shape-memory effect (SME) is associated with a reversible martensite – austenite transformation, whichThe shape-memory effect (SME) is associated with a reversible martensite – austenite transformation, which
occurs rapidly by crystallographicoccurs rapidly by crystallographic twinningtwinning at the atomic level. In some cases an intermediate R-phaseat the atomic level. In some cases an intermediate R-phase
having a rhombohedral crystal structure may form during this transformation processhaving a rhombohedral crystal structure may form during this transformation process

TwinningTwinning
is an angular movement of atoms parallel and symmetric towards a specific plane (twinningis an angular movement of atoms parallel and symmetric towards a specific plane (twinning
plane) that divides the lattice into two symmetric parts; these parts are no longer in theplane) that divides the lattice into two symmetric parts; these parts are no longer in the
same plane, but rather at a certain angle. NiTi is characterized by multiple twinningsame plane, but rather at a certain angle. NiTi is characterized by multiple twinning
throughout the metal. When these alloys are subjected to high temperature, detwinningthroughout the metal. When these alloys are subjected to high temperature, detwinning
occurs and the alloy reverts to its original shape or size.occurs and the alloy reverts to its original shape or size.

Thermoelastic martensitesThermoelastic martensites are characterized by their low energy and glissileare characterized by their low energy and glissile
interfaces, which can be driven by small temperature or stress changes. As sinterfaces, which can be driven by small temperature or stress changes. As s
consequence of this, and of the constraint due to the loss of symmetry duringconsequence of this, and of the constraint due to the loss of symmetry during
transformation, thermo elastic martensites aretransformation, thermo elastic martensites are crystallographically reversiblecrystallographically reversible. The. The
herringbone structure of a thermal martensite essentially consists of twin-related,herringbone structure of a thermal martensite essentially consists of twin-related,
self-accommodating variants. The interfaces between crystals remain perfectlyself-accommodating variants. The interfaces between crystals remain perfectly
coherent and mobile, but their assembly oscillates from a linear to a herringbonecoherent and mobile, but their assembly oscillates from a linear to a herringbone
shape congruent interfaces. The shape change among the variants tends to causeshape congruent interfaces. The shape change among the variants tends to cause
them to eliminate each other.them to eliminate each other.

As a result, little macroscopic strain is generated. In the case of stress-inducedAs a result, little macroscopic strain is generated. In the case of stress-induced
martensites, or when stressing a self-accommodating structure, the variant that canmartensites, or when stressing a self-accommodating structure, the variant that can
transform and yield the greatest shape change in the direction of the applied stress istransform and yield the greatest shape change in the direction of the applied stress is
stabilized and become dominant in the configuration. This process creates astabilized and become dominant in the configuration. This process creates a
macroscopic strain, which is recoverable as the crystal structure reverts to austenitemacroscopic strain, which is recoverable as the crystal structure reverts to austenite
during reverse transformation. This transformation occurs without diffusion orduring reverse transformation. This transformation occurs without diffusion or
chemical change, this transition is the result of a specific crystallographic relationshipchemical change, this transition is the result of a specific crystallographic relationship
between parent phase and new phase, a rearrangement of atoms in unit cells thatbetween parent phase and new phase, a rearrangement of atoms in unit cells that
has been termed reversiblehas been termed reversible E.C. Bain transformationE.C. Bain transformation, which is responsible for, which is responsible for
alloy’s shape memory and super elasticity.alloy’s shape memory and super elasticity.

The shape memory effect of Nitinol can effectively be exploited in orthodontics byThe shape memory effect of Nitinol can effectively be exploited in orthodontics by
forming the archwire in desired shape in the martensitic form. The formed archwireforming the archwire in desired shape in the martensitic form. The formed archwire
then is passed through the transition temperature range to the austenitic grainthen is passed through the transition temperature range to the austenitic grain
structure. Keeping the wire in austenitic form, the wire is deformed to confirm to thestructure. Keeping the wire in austenitic form, the wire is deformed to confirm to the
irregularities in the arch form. Taking the wire again through TTR will result in originalirregularities in the arch form. Taking the wire again through TTR will result in original
shape in martensitic form.shape in martensitic form. WasilewskiWasilewski on describing the optimal conditionson describing the optimal conditions
facilitating a complete shape recovery explained thatfacilitating a complete shape recovery explained that

A low homologous temperatureA low homologous temperature MsMs, Preferably well below recovery temperature is, Preferably well below recovery temperature is
needed.needed.
Absence of plastic flow during the memory inducing deformation and this requiresAbsence of plastic flow during the memory inducing deformation and this requires
high yield strength of the initial matrix - whether martensitic or parent structure,high yield strength of the initial matrix - whether martensitic or parent structure,
and low stress levels required to affect the stress induced transformation.and low stress levels required to affect the stress induced transformation.
The optimum temperature for memory inducing deformation is close toThe optimum temperature for memory inducing deformation is close to Mf.Mf.
Increasing the plastic yield strength of NiTi by pre straining will lead to moreIncreasing the plastic yield strength of NiTi by pre straining will lead to more
complete shape recovery but at the same time lowers the maximum recoverablecomplete shape recovery but at the same time lowers the maximum recoverable
strain levels.strain levels.

HursHurstt evaluated the percentage recovery of five commercially available Nitinol wiresevaluated the percentage recovery of five commercially available Nitinol wires
after subjecting to tensile deformation followed by heating beyond their transformationafter subjecting to tensile deformation followed by heating beyond their transformation
temperature range (TTR). He could observe a 90% recovery in all the wires studiedtemperature range (TTR). He could observe a 90% recovery in all the wires studied
and suggested some clinical uses of shape memory phenomena, also which includeand suggested some clinical uses of shape memory phenomena, also which include
possible consolidation of extraction spaces and alignment of crowded teeth.possible consolidation of extraction spaces and alignment of crowded teeth.
The transformation from austenite to martensite and reverse do not take place at theThe transformation from austenite to martensite and reverse do not take place at the
same temperature; this difference is known assame temperature; this difference is known as hysteresishysteresis, and the range for most, and the range for most
binary NiTi alloys is 40ºC to 60ºC.binary NiTi alloys is 40ºC to 60ºC.
There are several important phase transformation temperatures for the nickel-titaniumThere are several important phase transformation temperatures for the nickel-titanium
alloys.alloys.
Hysteresis is generally defined as the difference between the
temperatures at which the material is 50 % transformed to austenite upon
heating and 50 % transformed to martensite upon cooling. This
difference can be up to 20-30 °C (Buehler et al. 1967, Funakubo 1987).
In practice, this means that an alloy designed to be completely
transformed by body temperature upon heating (Af < 37 °C) would
require cooling to about +5 °C to fully retransform into martensite (Mf).

On coolingOn cooling thethe Ms (Ms (martensite-start) andmartensite-start) and MfMf (martensite-finish) temperatures are the(martensite-finish) temperatures are the
temperatures at which the transformation to martensite begins and is completed, respectively.temperatures at which the transformation to martensite begins and is completed, respectively.
Analogously,Analogously, on heatingon heating, the, the AsAs (austenite-start) and(austenite-start) and AfAf (austenite-finish) temperatures are the(austenite-finish) temperatures are the
temperatures at which the transformation to austenite begins and is completed, respectively.temperatures at which the transformation to austenite begins and is completed, respectively.
Similar transformation temperatures ofSimilar transformation temperatures of Rs and RfRs and Rf may be defined for the R-phase. Themay be defined for the R-phase. The
transformation temperature range (TTR) for each of the three structures (austenite, R-phase,transformation temperature range (TTR) for each of the three structures (austenite, R-phase,
and martensite) refers to the temperature range for the start and completion of theand martensite) refers to the temperature range for the start and completion of the
transformation to that particular structure.transformation to that particular structure.

For the stress-induced formation of martensite, an additionalFor the stress-induced formation of martensite, an additional MdMd (martensite-(martensite-
deformation) temperature is defined as the highest temperature at which it is possibledeformation) temperature is defined as the highest temperature at which it is possible
to have martensite. Above theto have martensite. Above the MdMd temperature the stress to form martensite bytemperature the stress to form martensite by
twinning is greater than the stress for the irreversible movement of dislocations bytwinning is greater than the stress for the irreversible movement of dislocations by
slip.slip.

SuperelasticitySuperelasticity
The unique force-deflection curve for A-NiTi wire occurs because of a phaseThe unique force-deflection curve for A-NiTi wire occurs because of a phase
transition in grain structure from austenite to martensite, in response not to atransition in grain structure from austenite to martensite, in response not to a
temperature change but to applied force. The transformation is a mechanicaltemperature change but to applied force. The transformation is a mechanical
analogue to the thermally induced shape memory effect. In other words, theanalogue to the thermally induced shape memory effect. In other words, the
austenitic alloy undergoes a transition in internal structure in response to stress,austenitic alloy undergoes a transition in internal structure in response to stress,
without requiring a significant temperature change (which is possible because forwithout requiring a significant temperature change (which is possible because for
these materials, the transition temperature is very close to room temperature). Thusthese materials, the transition temperature is very close to room temperature). Thus
inducing austenite to martensite transition by stress can produce superelasticity,inducing austenite to martensite transition by stress can produce superelasticity,
which results from twinning-detwinning mechanism. It results in low forces and awhich results from twinning-detwinning mechanism. It results in low forces and a
large working range.large working range.

The following figure shows a stress-strain curve illustrating superelasticityThe following figure shows a stress-strain curve illustrating superelasticity due to thedue to the
stress-induced transformation from the austenitic to the martensitic phase, as in A-stress-induced transformation from the austenitic to the martensitic phase, as in A-
NiTi. SectionNiTi. Section
A-BA-B represents purely elastic deformation of the austenitic phase (note in figure that in this phase A-NiTi is stiffer than M-NiTi).represents purely elastic deformation of the austenitic phase (note in figure that in this phase A-NiTi is stiffer than M-NiTi).
The stress corresponding to point B is the minimum stress at which transformation to the martensitic phase starts to occur.The stress corresponding to point B is the minimum stress at which transformation to the martensitic phase starts to occur.
A-BA-B represents purely elastic deformationrepresents purely elastic deformation
of the austenitic phaseof the austenitic phase
The stress corresponding to point B is the minimumThe stress corresponding to point B is the minimum
stress at which transformation to the martensiticstress at which transformation to the martensitic
phase starts to occurphase starts to occur
At point C, the transformation is completed.At point C, the transformation is completed.

The difference between the slopes of A-B and B-C indicates the ease with which transformationThe difference between the slopes of A-B and B-C indicates the ease with which transformation
occurs. This increase in strain is due to volume changes that results from change in crystaloccurs. This increase in strain is due to volume changes that results from change in crystal
structure.structure.
After the transformation is completed, the martensitic structure deforms elastically, representedAfter the transformation is completed, the martensitic structure deforms elastically, represented
by section C-D.by section C-D.
if the stress is released before reaching point D (as at point C1 in the diagram), elasticif the stress is released before reaching point D (as at point C1 in the diagram), elastic
unloading of the martensitic structure occurs along the line C1-F. Point F indicates theunloading of the martensitic structure occurs along the line C1-F. Point F indicates the
maximum stress on which the stress-induced martensitic structure on unloading can exist, andmaximum stress on which the stress-induced martensitic structure on unloading can exist, and
at that point the reverse transformation to austenite begins, continuing to point G, where theat that point the reverse transformation to austenite begins, continuing to point G, where the
austenitic structure is completely restored. G-H represents the elastic unloading of the austeniteaustenitic structure is completely restored. G-H represents the elastic unloading of the austenite
phase. A small portion of the total strain may not be recovered because of irreversible changesphase. A small portion of the total strain may not be recovered because of irreversible changes
during loading or unloading.during loading or unloading.
the martensitic structure deforms elastically,the martensitic structure deforms elastically,
represented by section C-D.represented by section C-D.
At point D the yield stress of theAt point D the yield stress of the
martensitic phase is reached, andmartensitic phase is reached, and
the material deforms plasticallythe material deforms plastically
until failure occurs at E.until failure occurs at E.
G-H represents theG-H represents the
elastic unloading ofelastic unloading of
the austenite phasethe austenite phase
Point F indicates the maximum stressPoint F indicates the maximum stress
on which the stress-inducedon which the stress-induced
martensitic structure on unloading canmartensitic structure on unloading can
exist, and at that point the reverseexist, and at that point the reverse
transformation to austenite begins,transformation to austenite begins,
continuing to point G, where thecontinuing to point G, where the
austenitic structure is completelyaustenitic structure is completely
restoredrestored
elastic unloading of the martensiticelastic unloading of the martensitic
structurestructure
occurs along the line C1-Foccurs along the line C1-F

the martensitic structure deformsthe martensitic structure deforms
elastically, represented by section C-D.elastically, represented by section C-D.
At point D the yield stress of theAt point D the yield stress of the
martensitic phase is reached, andmartensitic phase is reached, and
the material deforms plasticallythe material deforms plastically
until failure occurs at E.until failure occurs at E.
G-H represents theG-H represents the
elastic unloading ofelastic unloading of
the austenite phasethe austenite phase
Point F indicates the maximum stressPoint F indicates the maximum stress
on which the stress-inducedon which the stress-induced
martensitic structure on unloadingmartensitic structure on unloading
can exist, and at that point thecan exist, and at that point the
reverse transformation to austenitereverse transformation to austenite
begins, continuing to point G, wherebegins, continuing to point G, where
the austenitic structure is completelythe austenitic structure is completely
restoredrestored
elastic unloading of the martensiticelastic unloading of the martensitic
structurestructure
occurs along the line C1-Foccurs along the line C1-F

Part of the unusual nature of a superelastic material like A-NiTi is that itsPart of the unusual nature of a superelastic material like A-NiTi is that its
unloading curve differs from its loading curve (i.e. the reversibility has an energy lossunloading curve differs from its loading curve (i.e. the reversibility has an energy loss
associated with it [hysteresis]). This means the force that is delivers is not the sameassociated with it [hysteresis]). This means the force that is delivers is not the same
as the force applied to activate it. The different loading and unloading curves produceas the force applied to activate it. The different loading and unloading curves produce
the even more remarkable effect that the force delivered by an A-NiTi wire can bethe even more remarkable effect that the force delivered by an A-NiTi wire can be
changed during clinical use merely by releasing and retying it.changed during clinical use merely by releasing and retying it.

At larger activations, part of unloading curve is relatively flat. Clinical significance isAt larger activations, part of unloading curve is relatively flat. Clinical significance is
that more constant forces delivered to tooth during deactivation. Also, stiffness isthat more constant forces delivered to tooth during deactivation. Also, stiffness is
greater for small activations than for large activations.greater for small activations than for large activations.
The wires can be shaped and their properties can be altered, however, by heat-The wires can be shaped and their properties can be altered, however, by heat-
treatment. This can be done in the orthodontic office by passing an electric currenttreatment. This can be done in the orthodontic office by passing an electric current
between electrodes attached to the wire or a segment of it.between electrodes attached to the wire or a segment of it.
MiuraMiura et alet al have shown that it is possible to reposition the teeth on a dental cast tohave shown that it is possible to reposition the teeth on a dental cast to
the desired post treatment occlusion, bond brackets to the setup, Force an A-NiTithe desired post treatment occlusion, bond brackets to the setup, Force an A-NiTi
wire into the brackets, and then heat-treat the wire so that it memorizes it s shapewire into the brackets, and then heat-treat the wire so that it memorizes it s shape
with the teeth in the desired position.with the teeth in the desired position.

The properties of A-NiTi have quickly made it the preferred material for orthodonticThe properties of A-NiTi have quickly made it the preferred material for orthodontic
applications in which a long range of activation with relatively constant force isapplications in which a long range of activation with relatively constant force is
needed (i.e. for initial Arch wires and coil springs). M-NiTi remains useful, primarilyneeded (i.e. for initial Arch wires and coil springs). M-NiTi remains useful, primarily
in the later stages of treatment when flexible but larger and somewhat stiffer wiresin the later stages of treatment when flexible but larger and somewhat stiffer wires
are needed.are needed.
GarattiniGarattini et alet al showed that some areas in the oral cavity appear to be moreshowed that some areas in the oral cavity appear to be more
sensitive than others to thermal variations due to swallowing liquids; the uppersensitive than others to thermal variations due to swallowing liquids; the upper
interincisor area, the lower premolar area and the middle portion of the palate. Itinterincisor area, the lower premolar area and the middle portion of the palate. It
may be presumed that the force applied by the NiTi devices in these areas maymay be presumed that the force applied by the NiTi devices in these areas may
also be subject to even more consistent variationsalso be subject to even more consistent variations

If on one hand the thermal variations can modify the forces applied by nickel titaniumIf on one hand the thermal variations can modify the forces applied by nickel titanium
alloys, on the other, not all wires sold as superelastic, possess the characteristicsalloys, on the other, not all wires sold as superelastic, possess the characteristics
claimed by the manufacturers. In addition to this, the force applied by the NiTi archesclaimed by the manufacturers. In addition to this, the force applied by the NiTi arches
in clinical practice, depends also on the friction developed inside the slots of thein clinical practice, depends also on the friction developed inside the slots of the
brackets. From all these factors it is clear that in actual fact it is difficult to believe thatbrackets. From all these factors it is clear that in actual fact it is difficult to believe that
NiTi devices in general can apply a constant force in time.NiTi devices in general can apply a constant force in time.

Classification of NITIClassification of NITI
Nonsuperelastic alloys
e.g. Nitinol
Superelastic alloys
e.g. Japanese NiTi
True shape memory alloys
e.g. Copper NiTi

Nitinol and other nonsuperelastic nickel-titaniumNitinol and other nonsuperelastic nickel-titanium orthodontic wire alloys containorthodontic wire alloys contain
substantial quantities of heavily cold-worked and stable martensite. Thesubstantial quantities of heavily cold-worked and stable martensite. The AsAs
temperatures for these alloys are much higher than room temperature and thetemperatures for these alloys are much higher than room temperature and the
temperature of the oral environment.temperature of the oral environment.
TheThe superelastic (but not true shape memory) alloyssuperelastic (but not true shape memory) alloys have microstructures that arehave microstructures that are
incompletely transformed to austenite at the temperature of the oral environment.incompletely transformed to austenite at the temperature of the oral environment.
TheThe AfAf temperatures for these wires can be much greater than 37temperatures for these wires can be much greater than 37oo
C.C.
TheThe shape-memory wire alloysshape-memory wire alloys havehave AfAf temperatures that are below the temperaturetemperatures that are below the temperature
of the oral environment, so that the wires have essentially the completely austeniticof the oral environment, so that the wires have essentially the completely austenitic
structure in vivo.structure in vivo.

KusyKusy classifiedclassified
NITINITI
martensitic-stabilized alloysmartensitic-stabilized alloys
(Conventional nitinol)(Conventional nitinol)
martensitic-active alloysmartensitic-active alloys
(thermoelastic)(thermoelastic)
austenitic-active alloysaustenitic-active alloys
(pseudoelastic)(pseudoelastic)

The martensitic-stabilized alloys (Conventional nitinol)The martensitic-stabilized alloys (Conventional nitinol) do not possess shapedo not possess shape
memory or superelasticity, because the processing of the wire creates a stablememory or superelasticity, because the processing of the wire creates a stable
martensitic structure. These are the nonsuperelastic wire alloys such as Nitinol.martensitic structure. These are the nonsuperelastic wire alloys such as Nitinol.

The martensitic-active alloys (thermoelastic)The martensitic-active alloys (thermoelastic) employ the thermoelastic effect toemploy the thermoelastic effect to
achieve shape memory; the oral environment raises the temperature of the deformedachieve shape memory; the oral environment raises the temperature of the deformed
arch wire with the martensitic structure so that it transforms back to the austeniticarch wire with the martensitic structure so that it transforms back to the austenitic
structure and returns to the starting shape. This is the long-awaited nitinol alloy thatstructure and returns to the starting shape. This is the long-awaited nitinol alloy that
Dr. Andreasen hoped to someday employ in orthodontics. This thermoelastic shapeDr. Andreasen hoped to someday employ in orthodontics. This thermoelastic shape
memory can be observed by the clinician if a deformed archwire segment is warmedmemory can be observed by the clinician if a deformed archwire segment is warmed
in the hands.in the hands.

For many years the alloy composition simply could not be controlled preciselyFor many years the alloy composition simply could not be controlled precisely
enough to make a uniform wire product. Transition temperatures from martensite toenough to make a uniform wire product. Transition temperatures from martensite to
austenite had to occur in the region of ambient oral temperature, and yet it wasaustenite had to occur in the region of ambient oral temperature, and yet it was
known that for every 150 parts per million (ppm) variation in composition, a 1 °Cknown that for every 150 parts per million (ppm) variation in composition, a 1 °C
change in the transition temperature occurred.change in the transition temperature occurred.
MiuraMiura was the one who developed upon this concept and showed a series of caseswas the one who developed upon this concept and showed a series of cases
treated by preparing a series of arches in desired shape, which was set by heat.treated by preparing a series of arches in desired shape, which was set by heat.
Upon distortion and insertion into patient’s mouth, the appliance would be activatedUpon distortion and insertion into patient’s mouth, the appliance would be activated
by warmth of oral cavity and regain its predetermined shape. By using this property ofby warmth of oral cavity and regain its predetermined shape. By using this property of
thermo elasticity, a series of arches can be produced enabling practitioner tothermo elasticity, a series of arches can be produced enabling practitioner to
maintain control of tooth movement.maintain control of tooth movement.

This has got major applications in medical field especially in treatment ofThis has got major applications in medical field especially in treatment of
scoliosis and in the next few years orthodontists will hopefully achievescoliosis and in the next few years orthodontists will hopefully achieve
dramatic results with this type of alloy wire reducing the undesirable effectsdramatic results with this type of alloy wire reducing the undesirable effects
of round-tripping. Today this thermo elastic effect demonstrated inof round-tripping. Today this thermo elastic effect demonstrated in
SentalloyTM light of GAC International.SentalloyTM light of GAC International.

The austenitic-active alloys (pseudoelasticThe austenitic-active alloys (pseudoelastic)) undergo a stress induced martensiticundergo a stress induced martensitic
transformation when activated. These alloys display super elastic behaviortransformation when activated. These alloys display super elastic behavior
(psuedoelastic), which is the mechanical analogue of the thermo elastic shape-(psuedoelastic), which is the mechanical analogue of the thermo elastic shape-
memory effect. An austenitic active alloy does not exhibit thermo elastic behaviormemory effect. An austenitic active alloy does not exhibit thermo elastic behavior
when a deformed wire segment is warmed in the hands. These alloys are the superwhen a deformed wire segment is warmed in the hands. These alloys are the super
elastic wires that do not posses thermo elastic shape memory at the temperature ofelastic wires that do not posses thermo elastic shape memory at the temperature of
the oral environment, such as Nitinol SE.the oral environment, such as Nitinol SE.

In the austenitic active alloy, both the martensitic and austenitic phases play anIn the austenitic active alloy, both the martensitic and austenitic phases play an
important role during permanent deformation.important role during permanent deformation. Martensite represents the lowMartensite represents the low
stiffness phase having elastic modulus of 4.7×10stiffness phase having elastic modulus of 4.7×1066
psi and ultimate tensile strength ofpsi and ultimate tensile strength of
231×10231×1033
psi whereas the high stiffness phase austenite exhibits an elastic moduluspsi whereas the high stiffness phase austenite exhibits an elastic modulus
of 13×10of 13×1066
psi and ultimate tensile strength of 121×10psi and ultimate tensile strength of 121×1033
psi.psi. Thus on loading the activeThus on loading the active
austenitic alloy starts with a slope that produces some three times the forceaustenitic alloy starts with a slope that produces some three times the force
activation of conventional martensitic stabilized Nitinol alloy. Fortunately this effectactivation of conventional martensitic stabilized Nitinol alloy. Fortunately this effect
is short-lived and gives way to long plateau like area.is short-lived and gives way to long plateau like area.

The actual thing happened here is the stress induced phase transformation throughThe actual thing happened here is the stress induced phase transformation through
which the wire has transformed to martensitic phase. Upon deactivation the reversewhich the wire has transformed to martensitic phase. Upon deactivation the reverse
occurs, as the linear region that is associated with the martensitic phase of aoccurs, as the linear region that is associated with the martensitic phase of a
conventional alloy gives way to a second plateau region at a lower force and theconventional alloy gives way to a second plateau region at a lower force and the
martensitic phase is gradually transformed to austenitic phase. When the stress-martensitic phase is gradually transformed to austenitic phase. When the stress-
induced transformation is complete, the initial high slope associated with aninduced transformation is complete, the initial high slope associated with an
austenitic phase is revisited. The second plateau region, in which the martensiteaustenitic phase is revisited. The second plateau region, in which the martensite
reversibly transforms to austenite and thereby changes shape to maintain force,reversibly transforms to austenite and thereby changes shape to maintain force,
represents the key attribute of this non-linear but nonetheless elastic alloy and isrepresents the key attribute of this non-linear but nonetheless elastic alloy and is
calledcalled pseudo elasticitypseudo elasticity. This feature of stress induced active austenitic arch wires. This feature of stress induced active austenitic arch wires
makes them unique within the orthodontist’s armamentarium.makes them unique within the orthodontist’s armamentarium.

CHINESE NiTiCHINESE NiTi
BurstoneBurstone reported of a new nickel-titanium alloy developed especially forreported of a new nickel-titanium alloy developed especially for
orthodontic applications byorthodontic applications by Dr. Hua Cheng TienDr. Hua Cheng Tien and associates at the Generaland associates at the General
Research Institute for Non-Ferrous Metals in Beijing, China in 1978. This alloy hasResearch Institute for Non-Ferrous Metals in Beijing, China in 1978. This alloy has
unique characteristics and offers significant potential in the design of orthodonticunique characteristics and offers significant potential in the design of orthodontic
appliances. Its history of little work hardening and a parent phase which is austeniteappliances. Its history of little work hardening and a parent phase which is austenite
yield mechanical properties that differ significantly from nitinol wire. In addition,yield mechanical properties that differ significantly from nitinol wire. In addition,
Chinese NiTi wire has a much lower transition temperature than nitinol wire. The newChinese NiTi wire has a much lower transition temperature than nitinol wire. The new
nickel-titanium alloy has the following unique mechanical properties:nickel-titanium alloy has the following unique mechanical properties:

1.1. The wire has a springback that is 4.4 times that of comparable stainless steel wire andThe wire has a springback that is 4.4 times that of comparable stainless steel wire and
1.6 times that of nitinol wire, if springback is measured at yield based on a 5-mm1.6 times that of nitinol wire, if springback is measured at yield based on a 5-mm
span cantilever test. Because of its high range of action or spring back, these wiresspan cantilever test. Because of its high range of action or spring back, these wires
are applicable inare applicable in situations where large deflections are required.situations where large deflections are required.
2. At 80° of activation the average stiffness of Chinese NiTi wire is 73% that of stainless2. At 80° of activation the average stiffness of Chinese NiTi wire is 73% that of stainless
steel wire and 36% that of nitinol wire.steel wire and 36% that of nitinol wire.
3. The unusual nonlinear loading curve builds into the NiTi wire provide a constant force3. The unusual nonlinear loading curve builds into the NiTi wire provide a constant force
mechanism low load deflection rate in the middle range of deactivation. This ismechanism low load deflection rate in the middle range of deactivation. This is
potentially a significant design feature for constant-force appliances. The higherpotentially a significant design feature for constant-force appliances. The higher
stiffness found in this wire during the final stage of unloading helps assure that notstiffness found in this wire during the final stage of unloading helps assure that not
only the forces delivered are at a more constant rate but a higher magnitude of forceonly the forces delivered are at a more constant rate but a higher magnitude of force
level is maintained.level is maintained.

4.4. Unlike wires of other orthodontic alloys, the characteristic stiffness is determined byUnlike wires of other orthodontic alloys, the characteristic stiffness is determined by
the amount of activation. The load-deformation rate at small activations isthe amount of activation. The load-deformation rate at small activations is
considerably higher than that at large activations.considerably higher than that at large activations.
5. NiTi wire deformation is not particularly time dependent and, unlike nitinol wire, will not5. NiTi wire deformation is not particularly time dependent and, unlike nitinol wire, will not
continue to deform a significant amount in the mouth between adjustments.continue to deform a significant amount in the mouth between adjustments.
6. Chinese NiTi wire is highly suitable if6. Chinese NiTi wire is highly suitable if low stiffness is required and large deflectionslow stiffness is required and large deflections areare
needed. Its higher stiffness at small activations make it more effective than wires ofneeded. Its higher stiffness at small activations make it more effective than wires of
traditional alloys whose force levels may be too low (as teeth approach the passivetraditional alloys whose force levels may be too low (as teeth approach the passive
shape of the wire).shape of the wire).
7. In addition, if large cross-sections of Chinese NiTi wires are used, they are capable of7. In addition, if large cross-sections of Chinese NiTi wires are used, they are capable of
delivering the larger moments required for major tooth movement such as rootdelivering the larger moments required for major tooth movement such as root
movement and translationmovement and translation

JAPANESE NiTiJAPANESE NiTi
In 1986,In 1986, MiuraMiura et alet al reported of a new Japanese nickel-titanium (NiTi) alloy wirereported of a new Japanese nickel-titanium (NiTi) alloy wire
developed by thedeveloped by the Furukawa Electric Co.Ltd. of JapanFurukawa Electric Co.Ltd. of Japan..
It is a nearly equiatomic intermetallic compound, that incorporates a variety ofIt is a nearly equiatomic intermetallic compound, that incorporates a variety of
properties, which can be controlled by manufacturing method.properties, which can be controlled by manufacturing method.
At high temperature range, the crystal structure of Japanese NiTi is in austeniticAt high temperature range, the crystal structure of Japanese NiTi is in austenitic
phase, which is body centered cubic lattice and at low temperatures, a martensiticphase, which is body centered cubic lattice and at low temperatures, a martensitic
phase or close packed hexagonal lattice. By controlling the low and high temperaturephase or close packed hexagonal lattice. By controlling the low and high temperature
ranges, a change in crystal structure called martensitic transformation is produced.ranges, a change in crystal structure called martensitic transformation is produced.
This phenomenon is said to cause change in physical properties of the alloy.This phenomenon is said to cause change in physical properties of the alloy.
In the martensitic phase, which has a low temperature range, this metal is ductileIn the martensitic phase, which has a low temperature range, this metal is ductile
and acts like a safety fuse to readily induce a change of shape and in austeniticand acts like a safety fuse to readily induce a change of shape and in austenitic
phase, it is more difficult to induce deformationphase, it is more difficult to induce deformation

This alloy possesses excellentThis alloy possesses excellent
springback property,springback property,
shape memory,shape memory,
super elasticity.super elasticity.

Three-point bending test results indicated that Nitinol wire provides a light force andThree-point bending test results indicated that Nitinol wire provides a light force and
a lesser amount of permanent deformation in comparison with stainless steel and Co-a lesser amount of permanent deformation in comparison with stainless steel and Co-
Cr-Ni wires. The Japanese NiTi alloy wire possessed super-elastic propertiesCr-Ni wires. The Japanese NiTi alloy wire possessed super-elastic properties
whereby the load became almost even when the deflection was decreased in thewhereby the load became almost even when the deflection was decreased in the
bending test. This feature provides a light continuous force so that an effectivebending test. This feature provides a light continuous force so that an effective
physiologic tooth movement can be delivered. Super-elasticity is especially desirablephysiologic tooth movement can be delivered. Super-elasticity is especially desirable
because it delivers a relatively light continuous constant force, which is considered abecause it delivers a relatively light continuous constant force, which is considered a
physiologically desirable force for tooth movement.physiologically desirable force for tooth movement.

Although two alloys, Nitinol and Japanese NiTi belongs to the same class of Nickel –Although two alloys, Nitinol and Japanese NiTi belongs to the same class of Nickel –
titanium alloys theytitanium alloys they differ in manufacturing process and physical propertiesdiffer in manufacturing process and physical properties..
Japanese NiTi is manufactured by a different process than Nitinol and has got anJapanese NiTi is manufactured by a different process than Nitinol and has got an
active austenitic grain structure to demonstrate super elastic property. The tensileactive austenitic grain structure to demonstrate super elastic property. The tensile
test diagram for the metallurgical evaluation of the material will clearly indicate thetest diagram for the metallurgical evaluation of the material will clearly indicate the
above findingabove finding

The relationship between the temperature and time of the heat treatment of theThe relationship between the temperature and time of the heat treatment of the
Japanese NiTi alloy wire was studied to optimize the super-elastic properties of theJapanese NiTi alloy wire was studied to optimize the super-elastic properties of the
alloy.alloy.
After subjecting Japanese NiTi to heat treatment,After subjecting Japanese NiTi to heat treatment, Honma and TakeiHonma and Takei reported thatreported that
when the heat application was raised to 500° C, the force level indicating the super-when the heat application was raised to 500° C, the force level indicating the super-
elastic property could be reduced.elastic property could be reduced.
It was also observed that heat treatment at 600ºC eliminated the superelastic behaviorIt was also observed that heat treatment at 600ºC eliminated the superelastic behavior.
They proved that the martensitic transformation temperature could be changed withouThey proved that the martensitic transformation temperature could be changed withou
affecting the integrity of wire by heat treatment thus lowering the amount of forceaffecting the integrity of wire by heat treatment thus lowering the amount of force
indicating super elasticity. By this property archwire providing a different magnitude ofindicating super elasticity. By this property archwire providing a different magnitude of
force can be fabricated from the wires of same diameter. In addition, in the preformedforce can be fabricated from the wires of same diameter. In addition, in the preformed
arch wire, different magnitudes of force can be produced by controlling the temperaturearch wire, different magnitudes of force can be produced by controlling the temperature
and time in the desired section of the arch wire.and time in the desired section of the arch wire.

MiyazakiMiyazaki et alet al found super elasticity to be greatly dependent on thermal history offound super elasticity to be greatly dependent on thermal history of
material and showed various heat treatments can produce or eliminate super elasticmaterial and showed various heat treatments can produce or eliminate super elastic
behavior.behavior.
BrantleyBrantley et. al.et. al. studied the phase transformation behavior for the three major typesstudied the phase transformation behavior for the three major types
of nickel-titanium orthodontic wiresof nickel-titanium orthodontic wires (superelastic, nonsuperelastic and true shape(superelastic, nonsuperelastic and true shape
memory)memory) usingusing differential scanning calorimetric (DSC) analysesdifferential scanning calorimetric (DSC) analyses..
For theFor the superelastic alloy Nitinolsuperelastic alloy Nitinol SESE, they found that there is only a small amount of, they found that there is only a small amount of
hysteresis (difference in TTR) for the forward and reverse transformation between R-hysteresis (difference in TTR) for the forward and reverse transformation between R-
phase and austenite, but considerable hysteresis occurs for the forward and reversephase and austenite, but considerable hysteresis occurs for the forward and reverse
transformations between martensite and the R-phase. It can be seen that the Aftransformations between martensite and the R-phase. It can be seen that the Af
temperature on heating is about 60ºC, so that this alloy will be a mixture of R-phasetemperature on heating is about 60ºC, so that this alloy will be a mixture of R-phase
and austenite at the temperature of the oral environment.and austenite at the temperature of the oral environment.

For theFor the superelastic nickel-titanium alloysuperelastic nickel-titanium alloy Ni-TiNi-Ti, complete transformation to austenite, complete transformation to austenite
occurs only slightly above the temperature of the oral environment, since the Afoccurs only slightly above the temperature of the oral environment, since the Af
temperature on heating is about 40ºC. Under in vivo conditions, this alloy istemperature on heating is about 40ºC. Under in vivo conditions, this alloy is
predominantly austenite with some R-phase. This alloy has heating and cooling DSCpredominantly austenite with some R-phase. This alloy has heating and cooling DSC
curves that are similar to and contain two peaks for the forward and reversecurves that are similar to and contain two peaks for the forward and reverse
martensite – austenite transformations.martensite – austenite transformations.

For the shape-memory alloy (Neo SentalloyFor the shape-memory alloy (Neo Sentalloy)) there is athere is a single peak on the heatingsingle peak on the heating
DSC curve that corresponds to the direct transformation from martensite to austenite.DSC curve that corresponds to the direct transformation from martensite to austenite.
There areThere are two peaks on the cooling curvetwo peaks on the cooling curve; one for the transformation from austenite; one for the transformation from austenite
to R-phase and the other for the transformation from R-phase to martensite. There isto R-phase and the other for the transformation from R-phase to martensite. There is
again considerable hysteresis for the TTR in the forward and reverse directions foragain considerable hysteresis for the TTR in the forward and reverse directions for
the complete transformation between the martensite and austenite. Neo sentalloythe complete transformation between the martensite and austenite. Neo sentalloy
has essentially a completely austenitic structure at the temperature of the oralhas essentially a completely austenitic structure at the temperature of the oral
environment. Similar heating and cooling DSC curves were also observed for theenvironment. Similar heating and cooling DSC curves were also observed for the
shape-memory alloy Titanal LT (Lancer Orthodontics, Carlsbad, CA, USA).shape-memory alloy Titanal LT (Lancer Orthodontics, Carlsbad, CA, USA).

For theFor the nonsuperelastic alloy Nitinolnonsuperelastic alloy Nitinol there is a weak and broadthere is a weak and broad single peak on thesingle peak on the
heatingheating DSC curve that corresponds to the direct transformation from martensite toDSC curve that corresponds to the direct transformation from martensite to
austenite. Theaustenite. The cooling curve contains two peakscooling curve contains two peaks; one for the transformation from; one for the transformation from
austenite to R-phase and the other for the transformation from R-phase toaustenite to R-phase and the other for the transformation from R-phase to
martensite. There is considerable hysteresis between the TTR on the heating andmartensite. There is considerable hysteresis between the TTR on the heating and
cooling curves for the overall transformation between the martensitic and austeniticcooling curves for the overall transformation between the martensitic and austenitic
phases. This alloy is composed of martensite, austenite and perhaps R-phase at thephases. This alloy is composed of martensite, austenite and perhaps R-phase at the
temperature of the oral environment.temperature of the oral environment.

COPPER –Ni TiCOPPER –Ni Ti
Copper NiTi is the most recent introduction to the family of NiTi alloy wires and theCopper NiTi is the most recent introduction to the family of NiTi alloy wires and the
credit goes tocredit goes to Rohit SachdevaRohit Sachdeva andand Suichi MiyaskiSuichi Miyaski (1994).(1994).
Copper NiTi is a quaternary alloy, which has distinct advantages over the formerlyCopper NiTi is a quaternary alloy, which has distinct advantages over the formerly
available nickel-titanium alloys.available nickel-titanium alloys.
It generates aIt generates a more constant forcemore constant force over long activation span and that too on aover long activation span and that too on a
consistent basis.consistent basis.
For very small activations, it will generate a near constant force.For very small activations, it will generate a near constant force.
It is more resistant to permanent deformation and exhibits excellent spring backIt is more resistant to permanent deformation and exhibits excellent spring back
characteristics.characteristics.
It exhibits a small drop in unloading force than is true with other nickel titanium alloys.It exhibits a small drop in unloading force than is true with other nickel titanium alloys.
Addition of Copper combined with more sophisticated manufacturing and thermalAddition of Copper combined with more sophisticated manufacturing and thermal
treatment make possible four different types of Copper – NiTi wires with precise andtreatment make possible four different types of Copper – NiTi wires with precise and
consistent transformation temperatures i.e.,consistent transformation temperatures i.e., 1515oo
C, 27C, 27oo
C, 35C, 35oo
C and 40C and 40oo
C.C.www.indiandentalacademy.comwww.indiandentalacademy.com

The last property of the alloy brought to orthodontics a very useful phenomenon –The last property of the alloy brought to orthodontics a very useful phenomenon –
variable transformation temperature orthodonticsvariable transformation temperature orthodontics..
Stress–induced martensite is responsible for the Super elastic characteristics ofStress–induced martensite is responsible for the Super elastic characteristics of
Nickel titanium alloys. However martensitic transformation is also temperatureNickel titanium alloys. However martensitic transformation is also temperature
dependent. According to Sachdeva, the stability of the martensite and/or austeniticdependent. According to Sachdeva, the stability of the martensite and/or austenitic
phase at a given temperature is based upon the transformation temperature of thephase at a given temperature is based upon the transformation temperature of the
alloy and one of the most important markers is the material’s austenitic finish (Af)alloy and one of the most important markers is the material’s austenitic finish (Af)
temperature. It is the differential between Af temperature and mouth temperature thattemperature. It is the differential between Af temperature and mouth temperature that
determines the force generated by Nickel titanium alloys. This temperature (Af) candetermines the force generated by Nickel titanium alloys. This temperature (Af) can
be controlled over a wide range by affecting the composition, thermo mechanicalbe controlled over a wide range by affecting the composition, thermo mechanical
treatment and manufacturing process of the alloy. This property of Nickel titaniumtreatment and manufacturing process of the alloy. This property of Nickel titanium
alloys are made use in manufacturing process of copper-Ni alloy which demonstratesalloys are made use in manufacturing process of copper-Ni alloy which demonstrates
a smaller mechanical hysteresis i.e., It does not lose its recovery load at do othera smaller mechanical hysteresis i.e., It does not lose its recovery load at do other
Nickel titanium alloys.Nickel titanium alloys. www.indiandentalacademy.comwww.indiandentalacademy.com

CompositionComposition
Atomic wt% Wt %Atomic wt% Wt %
TitaniumTitanium 42.9942.99 48.0848.08
NickelNickel 49.8749.87 45.3945.39
ChromiumChromium 0.500.50 0.960.96
CopperCopper 5.64 5.575.64 5.57
KusyKusy reportedreported
5-6 wt% copper5-6 wt% copper
0.2 – 0.5 wt% chromium0.2 – 0.5 wt% chromium..
2727oo
C variant contains 0.5 % chromium to compensate for the effect of copper in raisingC variant contains 0.5 % chromium to compensate for the effect of copper in raising
the Af temperature above that of the oral environmentthe Af temperature above that of the oral environment
4040oo
C variant contains 0.2% chromium.C variant contains 0.2% chromium.

The reasons for adding copper to the alloy areThe reasons for adding copper to the alloy are
– More accurate control of TTRMore accurate control of TTR
– More energy efficient, i.e., the force to tie in a rotationMore energy efficient, i.e., the force to tie in a rotation
closely approximates the force required to rotate aclosely approximates the force required to rotate a
tooth. The difference between the two is scientificallytooth. The difference between the two is scientifically
termed “hysteresis”termed “hysteresis”
– It lowers the friction of the wire to make it slip easierIt lowers the friction of the wire to make it slip easier
along a bracket.along a bracket.
– Increase the strength.Increase the strength.

Depending on Af temperature, copper NiTi can be classified asDepending on Af temperature, copper NiTi can be classified as
Type I – Af -15Type I – Af -15oo
CC
– Not used for clinical applications due to its high force level.Not used for clinical applications due to its high force level.
Type II – Af – 27Type II – Af – 27oo
CC
– This generates heavy force than type III, IV wiresThis generates heavy force than type III, IV wires
– Best used in patients withBest used in patients with average or high pain thresholdaverage or high pain threshold..
– Patients withPatients with normal periodontal healthnormal periodontal health
– Patients in whomPatients in whom rapid tooth movementrapid tooth movement is required.is required.
Type III- Af - 35Type III- Af - 35oo
CC
– This generates mid range of forces and best used inThis generates mid range of forces and best used in
– Periodontally compromised patientsPeriodontally compromised patients
– Patients with low to normal pain thresholdPatients with low to normal pain threshold
– When relativelyWhen relatively low forces arelow forces are requested.requested.
Type IV- Af - 40Type IV- Af - 40oo
CC
– This generates tooth-moving forces when mouth temperature exceeds 40This generates tooth-moving forces when mouth temperature exceeds 40oo
C.C.
These wires are best used inThese wires are best used in
– Patients who are sensitive to painPatients who are sensitive to pain
– Periodontally compromised patientsPeriodontally compromised patients..
– Where tooth movement is deliberately slowed down.Where tooth movement is deliberately slowed down.
– This wire is very beneficial as an initial rectangular wire.This wire is very beneficial as an initial rectangular wire.

In a recent study the 27In a recent study the 27oo
C Copper Ni-Ti wire alloy contained aC Copper Ni-Ti wire alloy contained a single peak on both thesingle peak on both the
heating and coolingheating and cooling DSC curves, indicating direct transformation from martensite toDSC curves, indicating direct transformation from martensite to
austenite on heating and from austenite to martensite on cooling, without anaustenite on heating and from austenite to martensite on cooling, without an
intermediate R-phase.intermediate R-phase.
In contrast, the 35In contrast, the 35oo
C Copper Ni-Ti and 40C Copper Ni-Ti and 40oo
C Copper Ni-Ti wire alloys exhibited twoC Copper Ni-Ti wire alloys exhibited two
overlapping peaks on heating, corresponding to transformation from martensite to R-overlapping peaks on heating, corresponding to transformation from martensite to R-
phase followed by transformation from R-phase to austenite. All three Copper Ni-Tiphase followed by transformation from R-phase to austenite. All three Copper Ni-Ti
variants had a single peak on the cooling DSC curve, corresponding to directvariants had a single peak on the cooling DSC curve, corresponding to direct
transformation from austenite to martensite.transformation from austenite to martensite.

Copper Ni-Ti is supplied in both small and large sizes, upper and lower, in the
broad arch form.
27ºC: .014, .016, .018, .016 x .022, .017 x .025, .019 x .025
35ºC: .016”, .018, .016x.022, .017x.025, .019x.025
40ºC: .016x.022, .017x.025, .019x.025

Masel introduced CV NiTi wiresMasel introduced CV NiTi wires, as an alternative to the copper NiTi wires used in, as an alternative to the copper NiTi wires used in
many orthodontic procedures. When cold, CV NiTi is very soft and workable.many orthodontic procedures. When cold, CV NiTi is very soft and workable.
However, as CV NiTi warms up in a patient’s mouth, CV NiTi returns to its perfect-However, as CV NiTi warms up in a patient’s mouth, CV NiTi returns to its perfect-
arch shape, moving teeth along the way (“Shape Memory Effect”).arch shape, moving teeth along the way (“Shape Memory Effect”).
CV NiTi comes in three types:CV NiTi comes in three types:
2727oo
C CV NiTi For maximum force activationC CV NiTi For maximum force activation
3535oCoC
CV NiTi For moderate force activationCV NiTi For moderate force activation
4040oCoC
CV NiTi For the most gentle activationCV NiTi For the most gentle activation
CV NiTiCV NiTi

2727oo
C CV NiTiC CV NiTi
2727oo
C CV NiTi is a high activation force wire used to move a severely malpositionedC CV NiTi is a high activation force wire used to move a severely malpositioned
tooth.tooth.
2727oo
C can be readily deformed when the wire is colder than about 10C can be readily deformed when the wire is colder than about 10oo
C, but the wireC, but the wire
recovers its original shape after the wire has been in patients’ mouth for about 2recovers its original shape after the wire has been in patients’ mouth for about 2
weeks. Because the wire is set far below body temperature, it starts to workweeks. Because the wire is set far below body temperature, it starts to work
immediately.immediately.
The result is that when the wire is cold, you can bend the wire enough to reach aThe result is that when the wire is cold, you can bend the wire enough to reach a
severely malpositioned tooth. Yet the wire will return back to its original shape, afterseverely malpositioned tooth. Yet the wire will return back to its original shape, after
the wire warms up to body temperature.the wire warms up to body temperature.

To use 27To use 27oo
C CV NiTi, cool the wire either by storing the wire in aC CV NiTi, cool the wire either by storing the wire in a
freezer for an hour or more, or cooling the wire with Endo-ice. Makefreezer for an hour or more, or cooling the wire with Endo-ice. Make
sure that the wire stays cold while handling it. Bend the wire so thatsure that the wire stays cold while handling it. Bend the wire so that
it can reach the malpositioned tooth. Cool the wire again to makeit can reach the malpositioned tooth. Cool the wire again to make
sure that the wire does not deform while ligating it. Then ligate thesure that the wire does not deform while ligating it. Then ligate the
wire in patient’s mouth as any other wirewire in patient’s mouth as any other wire

3535oo
C CV NiTiC CV NiTi
3535oo
C CV NiTi is a moderate force activation wire used to level, align and rotate teeth.C CV NiTi is a moderate force activation wire used to level, align and rotate teeth.
3535oo
C CV NiTi can be readily deformed when the wire is colder than about 20C CV NiTi can be readily deformed when the wire is colder than about 20oo
C, butC, but
the wire recovers its original shape when the wire warms up in patient’s mouth. Thethe wire recovers its original shape when the wire warms up in patient’s mouth. The
wire is set at body temperature, so the patient needs to drink warm fluids to activatewire is set at body temperature, so the patient needs to drink warm fluids to activate
the wire. Again, it is possible to bend the wire enough to ligate a rotated tooth whenthe wire. Again, it is possible to bend the wire enough to ligate a rotated tooth when
the wire is cool. Yet, the wire will return back to its original shape, after the wirethe wire is cool. Yet, the wire will return back to its original shape, after the wire
warms up to body temperature.warms up to body temperature.
C CV NiTi, cool the wire either by storing the wire in a refrigerator for an hourC CV NiTi, cool the wire either by storing the wire in a refrigerator for an hour
or more, or cooling the wire with Endo-ice. Make sure that the wire stays below roomor more, or cooling the wire with Endo-ice. Make sure that the wire stays below room
temperature while handling it. Then ligate the wire in patient’s mouth as any other wire. The wiretemperature while handling it. Then ligate the wire in patient’s mouth as any other wire. The wire
activates slowly. And the effects can be seen after it is in patient’s mouth for a month.activates slowly. And the effects can be seen after it is in patient’s mouth for a month.

4040oo
C CV NiTiC CV NiTi
4040oo
C CV NiTi is used as an initial archwire. It is designed to level and alignC CV NiTi is used as an initial archwire. It is designed to level and align
malpositioned teeth with minimal, gentle force. 40malpositioned teeth with minimal, gentle force. 40oo
C CV NiTi is body heat activateC CV NiTi is body heat activate
and is stimulated by hot liquids. Therefore, patients need to drink hot fluids to activateand is stimulated by hot liquids. Therefore, patients need to drink hot fluids to activate
the wire.the wire.
C CV NiTi, cool the wire either by storing the wire in a freezer for anC CV NiTi, cool the wire either by storing the wire in a freezer for an
hour or more, or cooling the wire with Endo-ice. Make sure that the wire stays belowhour or more, or cooling the wire with Endo-ice. Make sure that the wire stays below
body temperature while handling it. Ligate the wire in patient’s mouth as any otherbody temperature while handling it. Ligate the wire in patient’s mouth as any other
wire. Be sure to instruct patients to drink hot fluids to activate the wire.wire. Be sure to instruct patients to drink hot fluids to activate the wire.

Chemically, how is CV NiTi different than Copper NiTi?Chemically, how is CV NiTi different than Copper NiTi?
CV NiTi and copper NiTi are very similar, chemically. Both contain mainly nickel andCV NiTi and copper NiTi are very similar, chemically. Both contain mainly nickel and
titanium. Both have been especially formulated and heat treated to have atitanium. Both have been especially formulated and heat treated to have a
superelastic phase transition at 27, 35 or 40 °C. Both have similar corrosionsuperelastic phase transition at 27, 35 or 40 °C. Both have similar corrosion
resistance.resistance.
The only significant chemical difference is that copper NiTi has aThe only significant chemical difference is that copper NiTi has a minor amount ofminor amount of
copper (up to 5%) added to the nickel and titaniumcopper (up to 5%) added to the nickel and titanium..
Both CV NiTi and copper NiTi can be deformed at room temperature and below, andBoth CV NiTi and copper NiTi can be deformed at room temperature and below, and
both recover at body temperature. The standard stress/strain curves are almost theboth recover at body temperature. The standard stress/strain curves are almost the
same. Some studies have shown that copper NiTi recovered its shape somewhatsame. Some studies have shown that copper NiTi recovered its shape somewhat
more quickly than CV NiTi did.more quickly than CV NiTi did.

How Are The Mechanical Properties Of CV NiTi andHow Are The Mechanical Properties Of CV NiTi and
Copper NiTi different?Copper NiTi different?
The 5% copper in the copper NiTi changes its'The 5% copper in the copper NiTi changes its'
mechanical properties a little bit. However, with only 5%mechanical properties a little bit. However, with only 5%
copper, the effects of the mechanical properties of thecopper, the effects of the mechanical properties of the
alloy are relatively small. The figure on the rightalloy are relatively small. The figure on the right
compares the performance ofcompares the performance of 353500
C copper NiTi andC copper NiTi and
353500
C CV NiTi at body temperatureC CV NiTi at body temperature. Notice that the. Notice that the
curves are very similar. Both CV NiTi and copper NiTicurves are very similar. Both CV NiTi and copper NiTi
can be deformed at room temperature and below, andcan be deformed at room temperature and below, and
both recover at body temperature. The standardboth recover at body temperature. The standard
stress/strain curves are almost the same.stress/strain curves are almost the same.
In tests conducted , copper NiTi recovered its shapeIn tests conducted , copper NiTi recovered its shape
somewhat more quickly than CV NiTi which somesomewhat more quickly than CV NiTi which some
people might think of as an advantage. However, wepeople might think of as an advantage. However, we
think that it is an advantage for the shape to recoverthink that it is an advantage for the shape to recover
more slowly, since it is more comfortable for the patientmore slowly, since it is more comfortable for the patient
that way.that way.

Niti

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