Nickel titanium in orthodontics

Nickel Titanium in OrthodonticsNickel Titanium in Orthodontics
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Ni Ti alloy was discovered in early 1960sNi Ti alloy was discovered in early 1960s
byby William F. BuehlerWilliam F. Buehler, a research, a research
metallurgist at the Naval Ordnancemetallurgist at the Naval Ordnance
Laboratory in Silver springs, Maryland.Laboratory in Silver springs, Maryland.
key discovery occurred inkey discovery occurred in 1962,1962, when awhen a
binary alloy composed of equi-atomicbinary alloy composed of equi-atomic
nickel and titanium was found to exhibit anickel and titanium was found to exhibit a
shape recovery effect when heated aftershape recovery effect when heated after
being mechanically deformed.being mechanically deformed.

Although other reversible phase changeAlthough other reversible phase change
materials were known at the time, the Ni-Timaterials were known at the time, the Ni-Ti
alloys showed a large recoverable strain valuealloys showed a large recoverable strain value
when compared to other binary, ternary orwhen compared to other binary, ternary or
quaternary shape memory alloy systems.quaternary shape memory alloy systems.
Rumour has it that William Buehler, who wasRumour has it that William Buehler, who was
working with high nickel-bearing alloys for gasworking with high nickel-bearing alloys for gas
turbine components, left a small ingot of Ni-Titurbine components, left a small ingot of Ni-Ti
alloy made in a vacuum melt furnace on a deskalloy made in a vacuum melt furnace on a desk
in direct sunlight.in direct sunlight.

When Buehler and his colleagues came backWhen Buehler and his colleagues came back
from lunch, they noticed the ingot’s shape hadfrom lunch, they noticed the ingot’s shape had
changedchanged
The physical performance of the Ni-Ti alloyThe physical performance of the Ni-Ti alloy
made it a landmark discovery, and the range ofmade it a landmark discovery, and the range of
commercially viable applications that have beencommercially viable applications that have been
found for the materials is proof of the importancefound for the materials is proof of the importance
of the nickel-titanium shape memory alloys.of the nickel-titanium shape memory alloys.
Buehler’s preliminary results led to developmentBuehler’s preliminary results led to development
of the first Ni Ti orthodontic alloy 55% nickel andof the first Ni Ti orthodontic alloy 55% nickel and
45% titanium by pioneers such as45% titanium by pioneers such as AndreasenAndreasen
and his colleagues in 1972.and his colleagues in 1972.

TheThe Unitek CorporationUnitek Corporation licensed thelicensed the
patent [1974] and offered a stabilizedpatent [1974] and offered a stabilized
martensitic alloy (M-NiTi) that does notmartensitic alloy (M-NiTi) that does not
exhibit any shape memory effect (SME)exhibit any shape memory effect (SME)
under the name, Nitinol.under the name, Nitinol.
Nitinol – Ni Ti Naval ordnance laboratory.Nitinol – Ni Ti Naval ordnance laboratory.
It is a stabilized form of the alloy in whichIt is a stabilized form of the alloy in which
work hardening has abolished the phasework hardening has abolished the phase
transformationtransformation

This alloy hasThis alloy has low elastic moduluslow elastic modulus andand highhigh
rangerange
The nickel-titanium wires contain approximatelyThe nickel-titanium wires contain approximately
equiatomic proportionsequiatomic proportions of nickel and titanium,of nickel and titanium,
and are based upon the intermetallic com-poundand are based upon the intermetallic com-pound
NiTi (sometimes written as TiNi).NiTi (sometimes written as TiNi).
Examination of the binary phase diagramExamination of the binary phase diagram
reveals that some deviation from stoichiometryreveals that some deviation from stoichiometry
is possible for NiTi.is possible for NiTi.

BASIC CONCEPTS ABOUT NICKELBASIC CONCEPTS ABOUT NICKEL
TITANIUM ALLOYSTITANIUM ALLOYS
11. ACTIVE :-
A term that is used to describe an alloy that is
capable of undergoing its anticipated phase
transformation.
2. PASSIVE :- An alloy that is incapable of
undergoing its anticipated phase transformation
because extensive plastic deformation has
suppressed the transition.

AUSTENITEAUSTENITE :-:-
High temperature phase of Nickel titaniumHigh temperature phase of Nickel titanium alloys isalloys is
called Austenite . Like many ferrous alloys this austenitecalled Austenite . Like many ferrous alloys this austenite
can transform to Martensite. It has gotcan transform to Martensite. It has got Body centeredBody centered
cubic (BCC) structurecubic (BCC) structure. It is t. It is the stronger, higherhe stronger, higher
temperature phase present in NiTi.temperature phase present in NiTi.
MARTENSITIC TRASFORMATIONMARTENSITIC TRASFORMATION :-:-
Process of phase transformation which isProcess of phase transformation which is
DIFFUSIONLESS, occuring from within and without anyDIFFUSIONLESS, occuring from within and without any
chemical change which results in transformation ofchemical change which results in transformation of
Austenite (parent phase) to Martensite following rapidAustenite (parent phase) to Martensite following rapid
cooling. It has gotcooling. It has got distorted monoclinic, triclinic or HCPdistorted monoclinic, triclinic or HCP
structurestructure MMore deformable,ore deformable, lower temperature phaselower temperature phase
present in NiTi.present in NiTi.

TWINNING :- In certain metals that crystallize
in Hexagonal closed pack (HCP) structure,
deformation occurs by twinning.
It refers to a movement that divides the lattice
into two symmetric parts; these parts are no
longer in the same plane but rather at a certain
angle.
e.g., :- NiTi alloys are characterized by multiple
rather than single twining throughout the metal

The resulting structure is caused by aThe resulting structure is caused by a
reversible Bain transformationreversible Bain transformation [a[a
rearrangement of atoms in the newrearrangement of atoms in the new
phase], which is responsible for thephase], which is responsible for the
alloy’s “alloy’s “Shape MemoryShape Memory” and” and
SuperelasticitySuperelasticity, properties that derive, properties that derive
from the twinning-detwinningfrom the twinning-detwinning
mechanism.mechanism.

When these alloys areWhen these alloys are
subjected to highersubjected to higher
temperature.temperature.
⇓⇓
DETWINNINGDETWINNING
OCCURSOCCURS
⇓⇓
Alloy reverts to its originalAlloy reverts to its original
shape.shape.
(SHAPE(SHAPE
MEMORY EFFECT).MEMORY EFFECT).

Phase transformation terminologiesPhase transformation terminologies
Shape MemoryShape Memory: The ability of certain alloys to: The ability of certain alloys to
return to a predetermined shape upon heatingreturn to a predetermined shape upon heating
via a phase transformation.via a phase transformation.
Af TemperatureAf Temperature: The temperature at which a: The temperature at which a
shape memory alloy ( SMA ) finishesshape memory alloy ( SMA ) finishes
transforming to austenite upon heating.transforming to austenite upon heating.
Ap TemperatureAp Temperature: The temperature at which the: The temperature at which the
SMA is about 50% transformed to AusteniteSMA is about 50% transformed to Austenite
upon heating.upon heating.

As TemperatureAs Temperature: The temperature at which: The temperature at which
the SMA starts transforming to Austenitethe SMA starts transforming to Austenite
upon heating.upon heating.
Mf TemperatureMf Temperature: The temperature at which: The temperature at which
a SMA finishes transforming to Martensitea SMA finishes transforming to Martensite
upon cooling.upon cooling.
Mp TemperatureMp Temperature:: The temperature, at whichThe temperature, at which
a SMA is about 50% transformed toa SMA is about 50% transformed to
Martensite upon cooling.Martensite upon cooling.

Ms TemperatureMs Temperature: The temperature at which: The temperature at which
a SMA starts transforming to Martensitea SMA starts transforming to Martensite
upon cooling.upon cooling.
HysteresisHysteresis: The: The temperature differencetemperature difference
between a phase transformation uponbetween a phase transformation upon
heating and cooling. In NiTi alloys, it isheating and cooling. In NiTi alloys, it is
generally measured as the differencegenerally measured as the difference
between Ap and Mp.between Ap and Mp.

Af tempratureAf temprature : Most important marker.: Most important marker.
To exploit super elasticity to its fullestTo exploit super elasticity to its fullest
potential, the working temperature ofpotential, the working temperature of
orthodontic appliances should be greaterorthodontic appliances should be greater
than Af temperature.than Af temperature.

Phase TransformationPhase Transformation: The change from: The change from
one alloy phase to another with a changeone alloy phase to another with a change
in temperature, pressure, stress,in temperature, pressure, stress,
chemistry, and/or time.chemistry, and/or time.
R-phaseR-phase: A phase intermediate between: A phase intermediate between
Martensite and Austenite that can form inMartensite and Austenite that can form in
NiTi alloys under certain conditions.NiTi alloys under certain conditions.

Thermoelastic Martensitic TransformationThermoelastic Martensitic Transformation: A: A
diffusionless, thermally reversible phasediffusionless, thermally reversible phase
transformation characterized by a crystaltransformation characterized by a crystal
lattice distortion.lattice distortion.

SuperelasticitySuperelasticity:: The springy, “rubber like”The springy, “rubber like”
behaviour present in NiTi shape Memorybehaviour present in NiTi shape Memory
AlloysAlloys at temperatures above the Afat temperatures above the Af
temperature. The superelasticity arisestemperature. The superelasticity arises
from the formation and reversal of stressfrom the formation and reversal of stress
induced martensite.induced martensite.
MMdd:: It is the highest temperature at whichIt is the highest temperature at which
martensite formation can be induced bymartensite formation can be induced by
stress.stress.

Typical Loading And Unloading BehaviorTypical Loading And Unloading Behavior
Of Superelastic NiTi.Of Superelastic NiTi.
Part of the unusual nature of aPart of the unusual nature of a
superelastic material like A-NITI is that itssuperelastic material like A-NITI is that its
unloading curve differs from its loadingunloading curve differs from its loading
curve (i.e.,the reversibility has an energycurve (i.e.,the reversibility has an energy
loss associated with it [hysteresis]).loss associated with it [hysteresis]).

Stress strain diagram of alloy with
superelastic behaviour

This means theThis means the
force that it delivers isforce that it delivers is
not the same as thenot the same as the
force applied toforce applied to
activate it.activate it.

The different loadingThe different loading
and unloading curvesand unloading curves
produce the evenproduce the even
more remarkablemore remarkable
effect that the forceeffect that the force
delivered by an A-delivered by an A-
NITI wire can beNITI wire can be
changed duringchanged during
clinical use merely byclinical use merely by
releasing and retyingreleasing and retying
it .it .
Activation (to 80 degrees) and
reactivation
(to 40 degrees) curves for A-NiTi wire.

Superelastic compounds generallySuperelastic compounds generally
present a high stiffness in the initialpresent a high stiffness in the initial
segment of the slope of the stress-strainsegment of the slope of the stress-strain
graph when the deflection of the wire isgraph when the deflection of the wire is
still minimum.still minimum.
The initial activation force required forThe initial activation force required for
autenitic NiTi can be 3 times greater thanautenitic NiTi can be 3 times greater than
the force required to deflect a classic workthe force required to deflect a classic work
hardened martensitic wire (nitinol).hardened martensitic wire (nitinol).

Stainless steel Nickel Titanium

INFLUENCE OF TREATMENT :-INFLUENCE OF TREATMENT :-
Memory effects lasts only as long as twinning -Memory effects lasts only as long as twinning -
detwinning phenomenon can take place.detwinning phenomenon can take place.
When atoms slide against each other with a fullWhen atoms slide against each other with a full
lattice unit – Irreversible transformationlattice unit – Irreversible transformation
(permanent set) takes place.(permanent set) takes place.
Consequently cold worked wires do not transformConsequently cold worked wires do not transform
b’ coz of their high elasticityb’ coz of their high elasticity

HysteresisHysteresis
There is a difference in the transformationThere is a difference in the transformation
temperatures upon heating from martensite totemperatures upon heating from martensite to
austenite and cooling from austenite toaustenite and cooling from austenite to
martensite, resulting in a delay or “lag” in themartensite, resulting in a delay or “lag” in the
transformation.transformation.
This difference known as the transformationThis difference known as the transformation
temperaturetemperature hysteresis,hysteresis, is generally defined asis generally defined as
the difference between the temperatures atthe difference between the temperatures at
which the material is 50% transformed towhich the material is 50% transformed to
austenite upon heating and 50% transformed toaustenite upon heating and 50% transformed to
martensite upon cooling.martensite upon cooling.

For NiTi Alloys, the difference between MpFor NiTi Alloys, the difference between Mp
and Ap is 25-50and Ap is 25-50°°C.C.
Thus Nitinol transformations exhibitThus Nitinol transformations exhibit
thermal hysteresis,thermal hysteresis, MsMs ≠≠ Af and MfAf and Mf ≠≠ As.As.

In addition to the hysteresis, the overall span of theIn addition to the hysteresis, the overall span of the
transformation may be important. Typical values for thetransformation may be important. Typical values for the
overall transformation temperature span are about 40-overall transformation temperature span are about 40-
7070°°C.C.
Both the hysteresis and the overall transformationBoth the hysteresis and the overall transformation
temperature span are slightly different for different NiTitemperature span are slightly different for different NiTi
alloys. Further, alloying can greatly affect thealloys. Further, alloying can greatly affect the
transformation hysteresis.transformation hysteresis. Copper additionsCopper additions have shownhave shown
toto reduce the hysteresisreduce the hysteresis to about 10 to 15to about 10 to 15°°C andC and
Niobium additions can expand the hysteresis overNiobium additions can expand the hysteresis over
100100°°C. ( Santaro AJO 2001)C. ( Santaro AJO 2001)

Austenite and Martensite have differentAustenite and Martensite have different
crystal structure and mechanicalcrystal structure and mechanical
properties the most notable mechanicalproperties the most notable mechanical
properties of Nitinol wires i.eproperties of Nitinol wires i.e
superelasticity and shape memory aresuperelasticity and shape memory are
result of reversible nature of Martensiticresult of reversible nature of Martensitic
transformationtransformation

Martensitic transformations do not occur at aMartensitic transformations do not occur at a
precise temperature but rather within a rangeprecise temperature but rather within a range
known asknown as temperature transition range(TTR)temperature transition range(TTR)..
Range for most binary NiTi alloysRange for most binary NiTi alloys →→ 4040°° - 60- 60°° C.C.
Transformation from Austenite to Martensite canTransformation from Austenite to Martensite can
occur by.occur by.
→→ Lowering the temperature.Lowering the temperature.
→→ Applying stressApplying stress (Stress induced Martensite)(Stress induced Martensite)
SIM.SIM.

Specific TTR is a function of :-Specific TTR is a function of :-
→→ Composition of the alloy.Composition of the alloy.
→→ Processing history.Processing history.
TTRS can be obtained from below roomTTRS can be obtained from below room
temperature upto 275temperature upto 275°°F or higher.F or higher.
e.g . Considering body temperature as referencee.g . Considering body temperature as reference
-- TTR above that temperature – Alloy isTTR above that temperature – Alloy is
Austentic (Rigid).Austentic (Rigid).
TTR below that temperature – Alloys is MartensiticTTR below that temperature – Alloys is Martensitic
(Superelastic)(Superelastic)

EFFECTS OF ADDITIONS AND IMPURITIES ONEFFECTS OF ADDITIONS AND IMPURITIES ON
TTR :-TTR :-
Adding a third metal can lower the TTRAdding a third metal can lower the TTR
→→ to as low as - 330to as low as - 330°° F ( - 200F ( - 200°° C).C).
→→ Narrow the difference b/w cooling and heatingNarrow the difference b/w cooling and heating
(Narrow Hysteresis).(Narrow Hysteresis).
For thermally activated purposes mostFor thermally activated purposes most
common third metals are Cu and Cocommon third metals are Cu and Co
because.because.
→→ Reduce the hysteresisReduce the hysteresis
→→ Bring TTR close to body temperature.Bring TTR close to body temperature.

Dissolved interstitial elements (small atomsDissolved interstitial elements (small atoms
such as O, N and C) disrupt the matricessuch as O, N and C) disrupt the matrices
which affects alloy shape memory andwhich affects alloy shape memory and
super elasticity.super elasticity.
Thermally respondent wires – designed soThermally respondent wires – designed so
that composition , Annealing and coldthat composition , Annealing and cold
working match Ms to temperature ofworking match Ms to temperature of
human bodyhuman body

Shape Memory is aShape Memory is a
Combination ofCombination of
Thermoelasticity andThermoelasticity and
PseudoelasticityPseudoelasticity

CLASSIFICATION OF NITI COMPOUNDSCLASSIFICATION OF NITI COMPOUNDS::
II.. Based on Transformation TemperatureBased on Transformation Temperature
Ranges ( Waters,1992)Ranges ( Waters,1992)
Group 1Group 1: Alloys with TTRs between room: Alloys with TTRs between room
temperature and body temperature [Activetemperature and body temperature [Active
Martensite].Martensite].
Group 2:Group 2: Alloys with TTR below roomAlloys with TTR below room
temperature [Austenite active]temperature [Austenite active]
GroupGroup 3: Alloys with TTR close to body3: Alloys with TTR close to body
temperature, “which by virtue of the shapetemperature, “which by virtue of the shape
memory effect spring back to their original shapememory effect spring back to their original shape
when activated by body heat”.when activated by body heat”.

Kusy ( 1991)Kusy ( 1991) classified NiTi into :classified NiTi into :
Martensitic-stabilized alloysMartensitic-stabilized alloys - do not- do not
possess shape memory or superpossess shape memory or super
elasticity, because the processing of theelasticity, because the processing of the
wire creates a stable martensitic structure.wire creates a stable martensitic structure.
These are the non superelastic wire alloysThese are the non superelastic wire alloys
such as originally developed Nitinol.such as originally developed Nitinol.

Martensitic-active alloysMartensitic-active alloys - employ the- employ the
thermoelastic effect to achieve shape memory;thermoelastic effect to achieve shape memory;
the oral environment raises the temperature ofthe oral environment raises the temperature of
the deformed arch wire with the martensiticthe deformed arch wire with the martensitic
structure so that it transforms back to thestructure so that it transforms back to the
austenitic structure and returns to the startingaustenitic structure and returns to the starting
shape.shape.
The clinician can observe this thermoelasticThe clinician can observe this thermoelastic
shape memory if a deformed archwire segmentshape memory if a deformed archwire segment
is warmed in the hands. These are the shape-is warmed in the hands. These are the shape-
memory wire alloys such asmemory wire alloys such as Neo Sentalloy andNeo Sentalloy and
Copper Ni-Ti.Copper Ni-Ti.

Austenitic-active alloysAustenitic-active alloys - undergo a stress-- undergo a stress-
induced martensitic (SIM) transformation wheninduced martensitic (SIM) transformation when
activated. These alloys display superelasticactivated. These alloys display superelastic
behavior , which is the mechanical analogue ofbehavior , which is the mechanical analogue of
the thermoelastic shape-memory effect (SME).the thermoelastic shape-memory effect (SME).
An austenitic-active alloy does not exhibitAn austenitic-active alloy does not exhibit
thermoelastic behavior when a deformed wirethermoelastic behavior when a deformed wire
segment is warmed in the hands. These alloyssegment is warmed in the hands. These alloys
are the superelastic wires that do not possessare the superelastic wires that do not possess
thermoelastic shape memory at the temperaturethermoelastic shape memory at the temperature
of the oral environment, such asof the oral environment, such as Nitinol SE.Nitinol SE.

Nickel Titanium WiresNickel Titanium Wires
CONVENTIONAL NITINOLCONVENTIONAL NITINOL -- Original alloyOriginal alloy
-- 55% Nickel55% Nickel,, 45% Titanium45% Titanium ratio ofratio of
elements.elements.
To modify mechanical properties andTo modify mechanical properties and
transition temp. 1.6% Cobalt was added totransition temp. 1.6% Cobalt was added to
itit

CRYSTAL STRUCTURE:CRYSTAL STRUCTURE:
-- Stabilized Martensitic formStabilized Martensitic form..
-- No application of phase transition effects.No application of phase transition effects.
The family of Stabilized Martensitic alloysThe family of Stabilized Martensitic alloys
now commercially available are referred tonow commercially available are referred to
asas M – NiTiM – NiTi..

PROPERTIESPROPERTIES
1.1. Springback and FlexibilitySpringback and Flexibility
Most advantageous properties of Nitinol areMost advantageous properties of Nitinol are
Good Springback and Flexibility.Good Springback and Flexibility.
Low force per unit of deactivation – that is lowLow force per unit of deactivation – that is low
stiffness.stiffness.
Nitinol wires have greater springback and largerNitinol wires have greater springback and larger
recoverable energy than Stainless Steel orrecoverable energy than Stainless Steel or ββ-Ti-Ti
when activated to same extent. High spring backwhen activated to same extent. High spring back
is useful in circumstances that require largeis useful in circumstances that require large
deflections but low forces.deflections but low forces.
Delivers 1/5Delivers 1/5thth
– 1/6– 1/6thth
force per unit of deactivationforce per unit of deactivation

2.2. Spring Rate / Load Deflection RateSpring Rate / Load Deflection Rate::
Load deflection rate of Stainless Steel is twiceLoad deflection rate of Stainless Steel is twice
that of Nitinol.that of Nitinol.
Clinically this means that for any givenClinically this means that for any given
malocclusion nitinol wire will produce a lower,malocclusion nitinol wire will produce a lower,
more constant and continuous force on teethmore constant and continuous force on teeth
than would a stainless steel wire of equivalentthan would a stainless steel wire of equivalent
sizesize

3.3. Formability :Formability : Nitinol has poor formability.Nitinol has poor formability.
Therefore best suited for preadjusted systems.Therefore best suited for preadjusted systems.
-Bending also adversely effects springback-Bending also adversely effects springback
property of this wire.property of this wire.
-Bending of loops and stops in nitinol is not-Bending of loops and stops in nitinol is not
recommended.recommended.
- Any 1- Any 1stst
, 2, 2ndnd
and 3and 3rdrd
order bends have to be overorder bends have to be over
prescribed to obtain desired permanent bend.prescribed to obtain desired permanent bend.

Cinch backs distal to molar tubes can be obtainedCinch backs distal to molar tubes can be obtained
by flame annealing the end of wire. This makesby flame annealing the end of wire. This makes
the wire dead soft and it can be bent into thethe wire dead soft and it can be bent into the
preferred configuration.preferred configuration.
A dark blue color indicates the desired annealingA dark blue color indicates the desired annealing
temperature. Care should be taken not totemperature. Care should be taken not to
overheat the wire because this makes it brittle.overheat the wire because this makes it brittle.

4.4. Shape MemoryShape Memory::
Andreasen and MorrowAndreasen and Morrow described the “shapedescribed the “shape
memory” phenomenon as capability of wire tomemory” phenomenon as capability of wire to
return to a previously manufactured shape whenreturn to a previously manufactured shape when
it is heated through TTR.it is heated through TTR.
Ironically the first 50 : 50 composition of Ni andIronically the first 50 : 50 composition of Ni and
Ti was shape memory alloy (SMA) inTi was shape memory alloy (SMA) in
composition only.composition only.
Nitinol alloy isNitinol alloy is passivepassive..
SME had been suppressed by cold working theSME had been suppressed by cold working the
wire during drawing to more than 8 – 10%.wire during drawing to more than 8 – 10%.

5.5. Joinability:Joinability:
Not joinableNot joinable
Since hooks cannot be bent or attached to Nitinol,Since hooks cannot be bent or attached to Nitinol,
crimpable hooks and stops are recommended for use.crimpable hooks and stops are recommended for use.
6.6. FrictionFriction::
Garner, Allai and Moore (1986)Garner, Allai and Moore (1986) andand Kapila et al (1990):Kapila et al (1990):
Noted that bracket wire frictional forces with nitinol wiresNoted that bracket wire frictional forces with nitinol wires
are higher than those with SS wires and lower thanare higher than those with SS wires and lower than
those withthose with ββ-Ti, in 0.018 inch slot.-Ti, in 0.018 inch slot.
In 0.022 inch slot – NiTi andIn 0.022 inch slot – NiTi and ββ-Ti wires demonstrated-Ti wires demonstrated
similar levels of friction.similar levels of friction.
Although NiTi has greater surface roughness Beta –Ti hasAlthough NiTi has greater surface roughness Beta –Ti has
greater frictional resistancegreater frictional resistance

CLINICAL APPLICATIONS:CLINICAL APPLICATIONS:
Levelling and Aligning:Levelling and Aligning:
Nitinol wire is much more difficult to deform duringNitinol wire is much more difficult to deform during
handling and seating into bracket slots is easier thanhandling and seating into bracket slots is easier than
Stainless Steel arch wires.Stainless Steel arch wires.
- Reduces loops formerly needed to level dentition.Reduces loops formerly needed to level dentition.
- Can be used for longer periods of time without changing.- Can be used for longer periods of time without changing.
--

Torque can be controlled early in treatment becauseTorque can be controlled early in treatment because
successive arch wires fit with precision and case.successive arch wires fit with precision and case.
The deactivation force released by superelastic NiTi forThe deactivation force released by superelastic NiTi for
torque control is definitely lower than that released by antorque control is definitely lower than that released by an
equivalent rectangular stainless steel wire, but theequivalent rectangular stainless steel wire, but the
property is due more to the intrinsic elastic properties ofproperty is due more to the intrinsic elastic properties of
NiTi compounds than to the presence of a phaseNiTi compounds than to the presence of a phase
transformation.transformation.
- Rectangular Nitinol inserted early in R- Rectangular Nitinol inserted early in Rxx – accomplishes– accomplishes
simultaneous leveling, torquing and correction ofsimultaneous leveling, torquing and correction of
rotations.rotations.
--

Bite opening usingBite opening using
RCS. (Reverse CurveRCS. (Reverse Curve
of Spee)of Spee)

ADVANTAGES :ADVANTAGES :
- Fewer arch wire changes.- Fewer arch wire changes.
- Less chair side time.- Less chair side time.
- Less patient discomfort.- Less patient discomfort.
Reduction in time to accomplish rotations.Reduction in time to accomplish rotations.

LIMITATIONS:LIMITATIONS:
- Poor formability.- Poor formability.
- Poor joinability.- Poor joinability.
- By its very nature nitinol is not a stiff wire- By its very nature nitinol is not a stiff wire
which means that it can easily be deflected. Lowwhich means that it can easily be deflected. Low
stiffness of nitinol provides inadequate stabilitystiffness of nitinol provides inadequate stability
at completion of treatment. Such stability is oftenat completion of treatment. Such stability is often
best maintained by using stiffer Stainless Steelbest maintained by using stiffer Stainless Steel
wires tailored to the desired finished occlusion.wires tailored to the desired finished occlusion.
- Tendency for dentoalveolar expansion.- Tendency for dentoalveolar expansion.
- Expensive.- Expensive.

Conventional Nitinol is available asConventional Nitinol is available as
-- Nitinol classicNitinol classic -- UnitekUnitek
corporationcorporation..
-- TitanalTitanal -- Lancer pacificLancer pacific..
-- OrthonolOrthonol -- Rocky mountainRocky mountain
orthodontics.orthodontics.

PSEUDOELASTIC NITINOLPSEUDOELASTIC NITINOL::
In the late 1980s, new Nickel titanium wires withIn the late 1980s, new Nickel titanium wires with
anan Active Austenitic grain structureActive Austenitic grain structure appeared.appeared.
These wires exhibited the remarkable propertyThese wires exhibited the remarkable property
of NiTi alloys – SUPERELASTICITY.of NiTi alloys – SUPERELASTICITY.
SUPERELASTICITY:SUPERELASTICITY: Manifested by very largeManifested by very large
reversible strains and a non elastic stress strainreversible strains and a non elastic stress strain
or force deflection curve.or force deflection curve.

This group is also referred to asThis group is also referred to as A-NiTiA-NiTi..
This group includes :This group includes :
--            Chinese NiTi.Chinese NiTi.
--            Japanese NiTi (Sentinol)Japanese NiTi (Sentinol)
--            2727°°C superelasticC superelastic Cu-NiTiCu-NiTi..
In Austenitic active alloy both MartensiteIn Austenitic active alloy both Martensite
and Austenitic phases play an importantand Austenitic phases play an important
role during its mechanical deformationrole during its mechanical deformation

MECHANISM OF SUPERELASTICITY:MECHANISM OF SUPERELASTICITY:
Stress Induced Martensitic Transformation : (SIM)Stress Induced Martensitic Transformation : (SIM)
Unique force deflection curve for A-NiTi occurs becauseUnique force deflection curve for A-NiTi occurs because
of phase transition in grain structure from Austenite toof phase transition in grain structure from Austenite to
Martensite, in response not to temperature change butMartensite, in response not to temperature change but
applied force.applied force.
This transformation is mechanical analogue of thermallyThis transformation is mechanical analogue of thermally
induced shape memory effect. ,the Austenitic alloyinduced shape memory effect. ,the Austenitic alloy
undergoes a transition in internal structure in response toundergoes a transition in internal structure in response to
stress without requiring a significant temperaturestress without requiring a significant temperature
change.change.

It is possible for these materials as their TTR isIt is possible for these materials as their TTR is
close to room temperature.close to room temperature.
MMdd of A-NiTi group is above mouth temperatureof A-NiTi group is above mouth temperature
allowing formation of SIM at oral temperature.allowing formation of SIM at oral temperature.

AAff (Austenitic finish) of these alloys is below mouth(Austenitic finish) of these alloys is below mouth
                                                                ⇓⇓
••           Formation ofFormation of SIMSIM is reversible when stress isis reversible when stress is
reduced.reduced.
••           These alloys cannot be easily cooled downThese alloys cannot be easily cooled down
below their Ms.below their Ms.
                                                                ⇓⇓
Do not display clinically useful shape memoryDo not display clinically useful shape memory

To exploit superelasticity to its fullest potentialTo exploit superelasticity to its fullest potential
the working temperature of orthodonticthe working temperature of orthodontic
appliances should be greater than the Aappliances should be greater than the Aff
•• It is the differential between AIt is the differential between Aff temperature andtemperature and
mouth temperature that determines the forcemouth temperature that determines the force
generated by NiTi alloys.generated by NiTi alloys.
AAff can be controlled over wide range by affectingcan be controlled over wide range by affecting
composition, thermomechanical treatment andcomposition, thermomechanical treatment and
manufacturing process of alloymanufacturing process of alloy

A superelastic material will not be superelastic atA superelastic material will not be superelastic at
all temperatures, but will exhibit goodall temperatures, but will exhibit good
superelastic properties in a temperature windowsuperelastic properties in a temperature window
extending from the Active Af temperature upto aextending from the Active Af temperature upto a
temperature which is about 50temperature which is about 50°°C above activeC above active
Af.Af.
A material with an Active Af of about 15A material with an Active Af of about 15°°C willC will
exhibit good superelasticity upto about 65exhibit good superelasticity upto about 65°°CC
which means that the material will exhibit goodwhich means that the material will exhibit good
superelasticity at both room temperature andsuperelasticity at both room temperature and
body temperaturebody temperature

CHINESE NI TICHINESE NI TI
Developed byDeveloped by Dr. Tien Hua ChengDr. Tien Hua Cheng and associatesand associates
for orthodontic applications at the Generalfor orthodontic applications at the General
Research Institute for Non ferrous metals inResearch Institute for Non ferrous metals in
Beijing, China. Reported byBeijing, China. Reported by BurstoneBurstone in 1985in 1985..
Spring Back :Spring Back :
At 80At 80°° of activation.of activation.
Chinese NiTi wire has :Chinese NiTi wire has :
-- 1.4 times the springback of Nitinol wire.1.4 times the springback of Nitinol wire.
-- 4.6 times the springback of SS wire.4.6 times the springback of SS wire.

Stiffness of Chinese NiTi is 36% that of NitinolStiffness of Chinese NiTi is 36% that of Nitinol
wire.wire.
TTemperature dependent effects are clinicallyemperature dependent effects are clinically
insignificant.insignificant.
Chinese NiTi deformation is not particularly time Chinese NiTi deformation is not particularly time
dependent unlike nitinol wire, will not continue to dependent unlike nitinol wire, will not continue to
deform a significant amount in mouth between deform a significant amount in mouth between
adjustments.adjustments.
The initial activation force required for austeniticThe initial activation force required for austenitic
NiTi can be 3 times greater than the forceNiTi can be 3 times greater than the force
required to deflect a classic work hardenedrequired to deflect a classic work hardened
martensitic wire (Nitinol).martensitic wire (Nitinol).

JAPANESE NITIJAPANESE NITI
In 1978In 1978 : Furukawa Electric Co. Ltd. of Japan: Furukawa Electric Co. Ltd. of Japan
produced a new type of Japanese NiTi alloy.produced a new type of Japanese NiTi alloy.
In 1986In 1986 :: Miura et alMiura et al reported on Japanese NiTireported on Japanese NiTi
Superelasticity is produced by stress, not bySuperelasticity is produced by stress, not by
temperature change and is calledtemperature change and is called stress inducedstress induced
Martensitic transformation (SIM)Martensitic transformation (SIM)..
Provides light continuous force for physiologicProvides light continuous force for physiologic
tooth movementtooth movement

Japanese NiTi is marketed as Sentalloy.
The relationship between the temperature andThe relationship between the temperature and
time of the heat treatment of the Japanese NiTitime of the heat treatment of the Japanese NiTi
alloy wire was studied to optimize the super-alloy wire was studied to optimize the super-
elastic properties of the alloy.elastic properties of the alloy.
When the heat application was raised to 500° C,When the heat application was raised to 500° C,
the force level indicating the super-elasticthe force level indicating the super-elastic
property could be reduced.property could be reduced.

Other Super Elastic NiTi wiresOther Super Elastic NiTi wires
3M Unitek: Nitinol Super Elastic3M Unitek: Nitinol Super Elastic
American Orthodontics: TitaniumAmerican Orthodontics: Titanium
Memory Wire:Memory Wire: Available in two forceAvailable in two force
levels :levels : Force IForce I – low force,– low force,Force IIForce II – high– high
force.force.
Ortho Organizers: NitaniumOrtho Organizers: Nitanium
Masel Orthodontics: ElastinolMasel Orthodontics: Elastinol

ADVANTAGES:ADVANTAGES:
Constant force over wide range of deflection.Constant force over wide range of deflection.
Low stiffness.Low stiffness.
High springback.High springback.
More effective in initial tooth alignment.More effective in initial tooth alignment.
Less patient discomfort.Less patient discomfort.

LIMITATIONS OF SUPERELASTIC NiTi:LIMITATIONS OF SUPERELASTIC NiTi:
Cannot be soldered or welded.Cannot be soldered or welded.
Poor formability.Poor formability.
Tendency for dentoalveolar expansion.Tendency for dentoalveolar expansion.
““Travels” around the arch.Travels” around the arch.
Expensive.Expensive.

Thermoelastic nitinolThermoelastic nitinol
Thermal analog of pseudoelasticity in whichThermal analog of pseudoelasticity in which
martensitic phase transformation occursmartensitic phase transformation occurs
from Austenite as temperature isfrom Austenite as temperature is
decreased.decreased.
This phase transformation can beThis phase transformation can be
reversed by increasing the temperature toreversed by increasing the temperature to
its original value.its original value.

CHARACTERISTICS OF AN IDEALCHARACTERISTICS OF AN IDEAL
THERMODYNAMIC NITINOL WIRE:THERMODYNAMIC NITINOL WIRE:
1. Dead soft at room temperature so that it can1. Dead soft at room temperature so that it can
be tied easily.be tied easily.
2. Instantaneously activated by heat of mouth.2. Instantaneously activated by heat of mouth.
3. Able to apply clinically acceptable orthodontic3. Able to apply clinically acceptable orthodontic
forces.forces.


4.4. Once fully activated would not be affectedOnce fully activated would not be affected
further by increased heat in the mouth.further by increased heat in the mouth.
5.5. A fairly narrow TTR i.e., it should beA fairly narrow TTR i.e., it should be
completely active at mouth temperature yetcompletely active at mouth temperature yet
completely passive at lower temperature.completely passive at lower temperature.
This property would allow the clinician sufficientThis property would allow the clinician sufficient
time to tie archwire into the bracket slots beforetime to tie archwire into the bracket slots before
heat of mouth activates the wire.heat of mouth activates the wire.

Thermoelastic NitinolThermoelastic Nitinol – formable at ice water temperatures.– formable at ice water temperatures.
⇓⇓
Ice water is belowIce water is below MsMs of thermoelastic wiresof thermoelastic wires
⇓⇓
Martensite while engagingMartensite while engaging
When warmed aboveWhen warmed above AAff by mouth temp.by mouth temp.
⇓⇓
Transformation is reversed to from AusteniteTransformation is reversed to from Austenite
⇓⇓
Wire returns to its original shape thus displaying shapeWire returns to its original shape thus displaying shape
memory.memory.

COPPER NiTiCOPPER NiTi
Invented byInvented by Dr. Rohit Sachdeva & Suchio MiyazakiDr. Rohit Sachdeva & Suchio Miyazaki ..
COMPOSITION :COMPOSITION : Quaternary alloy containing.Quaternary alloy containing.
* Nickel* Nickel * Copper (5 – 6%)* Copper (5 – 6%)
• TitaniumTitanium * Chromium (0.2 – 0.5%)* Chromium (0.2 – 0.5%)
CopperCopper::
--            Increases strengthIncreases strength
--            Reduces hysteresisReduces hysteresis
--        these benefits occur at expense of increasing TTRthese benefits occur at expense of increasing TTR
above that of oral cavity.above that of oral cavity.

ChromiumChromium :: to compensate for the aboveto compensate for the above
mentioned unwanted effect 0.5%mentioned unwanted effect 0.5%
chromium is added to return TTR close tochromium is added to return TTR close to
oral temperatureoral temperature

TYPES OF CU-NITITYPES OF CU-NITI::
1.1. Type IType I AfAf 1515°°C.C.
2.2. Type IIType II AfAf 2727°°CC
3.3. Type IIIType III AfAf 3535°°CC
4.4. Type IV AfType IV Af 4040°°CC

Chill SprayChill Spray
Facilitates adjustments orFacilitates adjustments or
fitting of Ni Ti orthodonticfitting of Ni Ti orthodontic
archwires,archwires,
springs,appliances, etc.springs,appliances, etc.
Ideal for Niti MemoryIdeal for Niti Memory
Expanders and RotatorsExpanders and Rotators
such as the Tandemsuch as the Tandem
Loop Arndt MemoryLoop Arndt Memory
Expander and ArndtExpander and Arndt
Memory Rotator.Memory Rotator.
Chills to -620Chills to -620ºº F/-520F/-520
ººC.... puts Niti into its softC.... puts Niti into its soft
martensitic statemartensitic state

Active Martensite Thermodynamic WireActive Martensite Thermodynamic Wire::
Included in the active martensitic group are wiresIncluded in the active martensitic group are wires
with an Af set at a temperature at or above 37with an Af set at a temperature at or above 37°°CC
[CuNiTi 37[CuNiTi 37°°C and CuNiTi 40C and CuNiTi 40°°C], which is almostC], which is almost
complete, transformed into martensite duringcomplete, transformed into martensite during
clinical application.clinical application.
Martensitic alloy has a greater working rangeMartensitic alloy has a greater working range
than austenite, and it may therefore provethan austenite, and it may therefore prove
advantageous during the process of alignmentadvantageous during the process of alignment
and leveling.and leveling.

The ability to vary transition temperatures inThe ability to vary transition temperatures in
martensitic wires of identical dimensions, allowsmartensitic wires of identical dimensions, allows
the clinician to apply appropriate levels ofthe clinician to apply appropriate levels of
physiological force during alignment, whilstphysiological force during alignment, whilst
maintaining archwire size.maintaining archwire size.
This wire combines greater heat sensitivity, highThis wire combines greater heat sensitivity, high
shape memory, and extremely low, constantshape memory, and extremely low, constant
forces to provide a full-size wire that can beforces to provide a full-size wire that can be
inserted early in treatmentinserted early in treatment

ADVANTAGES OF Cu-NiTi OVER OTHER NiTiADVANTAGES OF Cu-NiTi OVER OTHER NiTi
AlloysAlloys::
1.1. Cu – NiTi generates more constant force overCu – NiTi generates more constant force over
long activation spans.long activation spans.
2. More resistant to permanent deformation.2. More resistant to permanent deformation.
3.3. Exhibits better springback properties.Exhibits better springback properties.
4. Exhibits smaller drop in unloading forces4. Exhibits smaller drop in unloading forces
(reduced hysteresis).(reduced hysteresis).
Provides precise TTRs at 4 different levels –Provides precise TTRs at 4 different levels –
Enables Clinician to select archwires on a caseEnables Clinician to select archwires on a case
specificspecific

Bioforce SentalloyBioforce Sentalloy ––
A Graded Thermodynamic WireA Graded Thermodynamic Wire The heatThe heat
treatment of selected sections of the archwire bytreatment of selected sections of the archwire by
means of different electric current delivered bymeans of different electric current delivered by
electric pliers modified the values of theelectric pliers modified the values of the
deactivation forces by varying the amount ofdeactivation forces by varying the amount of
austenite present in the alloy.austenite present in the alloy.
After heating the anterior segment for 60After heating the anterior segment for 60
minutes, the linear plateau of the deactivationminutes, the linear plateau of the deactivation
force dropped to 80 g in a 3-point bending test atforce dropped to 80 g in a 3-point bending test at
room temperature.room temperature.

Similar manufacturing procedures have beenSimilar manufacturing procedures have been
perfected to produce wires such as Bioforceperfected to produce wires such as Bioforce
Sentalloy (GAC) that are able to deliver selectiveSentalloy (GAC) that are able to deliver selective
forces according to the needs of the individualforces according to the needs of the individual
dental arch segmentsdental arch segments
BioForce (GAC) offers 80 grams of force forBioForce (GAC) offers 80 grams of force for
anteriors and up to 320 grams for molarsanteriors and up to 320 grams for molars

NITROGEN COATED ARCHWIRES:NITROGEN COATED ARCHWIRES:
Implanting Nitrogen on surface of NiTi alloys byImplanting Nitrogen on surface of NiTi alloys by
Ion implantation process –Ion implantation process – NITRIDINGNITRIDING..
Advantages:Advantages:
--        Make Titanium more esthetically pleasing givingMake Titanium more esthetically pleasing giving
it gold like aspect.it gold like aspect.
--            Hardens surface.Hardens surface.
--            Reduces friction.Reduces friction.
--            Reduces Nickel release into mouth.Reduces Nickel release into mouth.
e.g :e.g : Bioforce IonguardBioforce Ionguard - 3- 3µµm Nitrogen coating.m Nitrogen coating.

TheThe IONGUARDIONGUARD process actually alters the wire’sprocess actually alters the wire’s
surface to provide a dramaticallysurface to provide a dramatically reducedreduced
coefficient of friction for sliding mechanicscoefficient of friction for sliding mechanics thatthat
are better than the same size stainless steel wireare better than the same size stainless steel wire
and half the friction of competitive NiTi wire.and half the friction of competitive NiTi wire.
It also seals the occlusal surface of the wire toIt also seals the occlusal surface of the wire to
eliminate breakage and reduce nickel leaching.eliminate breakage and reduce nickel leaching.
While the IONGUARD process alters the surfaceWhile the IONGUARD process alters the surface
of the wire, none of the wire’s unique propertiesof the wire, none of the wire’s unique properties
is changed.is changed.

Nitinol Total Control .A newNitinol Total Control .A new
Orthodontic alloy.Orthodontic alloy.
TODD A. THAYER, KARL FOX,ERIC
MEYER ( JCO1999) developed a new
pseudo-superelastic nickel titanium,alloy,
Nitinol Total Control,
Accepts specific 1st-, 2nd-, and 3rd-order
bends while maintaining its desirable
superelastic properties.

Combines the ability of superelastic nickel
titanium to deliver light, continuous forces over a
desired treatment range with the bend ability
required to account for variations in tooth
morphology, archform, and bracket
prescriptions.
Frictional and bending tests verify that the force
levels produced by them are within accepted
ranges for optimal tooth movement.
Furthermore,wire properties are not
temperaturedependent.

Because of relatively low stiffness, it should not be used
for space closure.
It can avoid the need to change archwires, , int he
following situations:
Repositioning due to improper bracket placement
• Repositioning brackets to maintain torque control
•

Placement of extrusion, intrusion, or utilityarches
•Functional finishing with detailing bends thataddress
variations in tooth morphology and interarch occlusal
relationships
• Filling the bracket slot with controlled, lightforce (torque
without shearing the bracket)
Reduces archwire inventory without compromising
treatment mechanics. Lower forces are generally
associated with less patient discomfort. In addition, by
reducing the number of archwire changes required,
allows the clinician to treat more patients effectively and
efficiently.

NiTi wire bending pliers.NiTi wire bending pliers.
In 1988, Miura, Mogi, and Ohura demonstrated
the use of electrical-resistance heat treatment to
introduce permanent bends in their nickel
titanium wires. The technique requires special
pliers attached to an electric power supply.
Although the authors claimed that the
superelastic force of the wire was not affected by
the treatment, heating the wire does alter the
crystalline structure of the nickel titanium lattice.

MaselMasel offers two “V”offers two “V”
Notch Stop pliers thatNotch Stop pliers that
place precise “V” bendsplace precise “V” bends
in NiTi wire.in NiTi wire.
The newly designedThe newly designed
Extraoral “V” Notch StopExtraoral “V” Notch Stop
Plier #649 forms aPlier #649 forms a
precise 1-mm “V” stopprecise 1-mm “V” stop
that prevents wire fromthat prevents wire from
disengaging from thedisengaging from the
buccal tube. Bends roundbuccal tube. Bends round
wire from 0.012 to 0.020wire from 0.012 to 0.020
inches, and rectangularinches, and rectangular
wire up to 0.017 x 0.022wire up to 0.017 x 0.022
inches.inches.

The Intraoral “V” Notch Stop Plier makesThe Intraoral “V” Notch Stop Plier makes
“V” stops right in the mouth with one“V” stops right in the mouth with one
squeeze. It bends round wire up to 0.016squeeze. It bends round wire up to 0.016
inches and rectangular wire up to 0.016 xinches and rectangular wire up to 0.016 x
0.022 inches.0.022 inches.

HU-FRIEDY’S Hammerhead NiTi Tie BackHU-FRIEDY’S Hammerhead NiTi Tie Back
PlierPlier
Reduce a multi-stepReduce a multi-step
process down to one,process down to one,
simple squeeze —simple squeeze — nono
heat requiredheat required
Bends NiTi wireBends NiTi wire
intraorally with no heatintraorally with no heat
treatingtreating
Designed to tie back NiTiDesigned to tie back NiTi
distal to the buccal tube,distal to the buccal tube,
gabel bends, omegagabel bends, omega
loopsloops

Bendistal PliersBendistal Pliers
Allow orthodontists to NiTi wires intraorally usingAllow orthodontists to NiTi wires intraorally using
a V-bend technique that corrects manya V-bend technique that corrects many
challenging orthodontic problems with single-challenging orthodontic problems with single-
squeeze adjustments.squeeze adjustments.
The pliers’ tiny tips fit between brackets to allowThe pliers’ tiny tips fit between brackets to allow
placement of intraoral activating bends on tiedplacement of intraoral activating bends on tied
archwires without breaking the wire or thearchwires without breaking the wire or the
brackets.brackets.

The pliers areThe pliers are
available in a set ofavailable in a set of
two, featuring a longtwo, featuring a long
and thin design toand thin design to
reach behind thereach behind the
molar tube for easiermolar tube for easier
cinch-back purposescinch-back purposes
and wire activations inand wire activations in
the four mouththe four mouth
quadrants.quadrants.

Recycling & Sterilization of Nickel TitaniumRecycling & Sterilization of Nickel Titanium
ArchwiresArchwires
Recycling of nitinol wires is often practicedRecycling of nitinol wires is often practiced
because of their favorable physicalbecause of their favorable physical
properties and the high cost of the wire.properties and the high cost of the wire.
The ability to recycle these archwire reliesThe ability to recycle these archwire relies
on effective sterilization of the wire prior toon effective sterilization of the wire prior to
re-use without resulting in deterioration ofre-use without resulting in deterioration of
clinical properties.clinical properties.

For effective sterilization, steam autoclavingFor effective sterilization, steam autoclaving
(ideally at(ideally at 134ºC, 32 psi for 3 minutes134ºC, 32 psi for 3 minutes) is) is
the method recommended.the method recommended.
For instruments unable to withstandFor instruments unable to withstand
autoclaving, an effective cold disinfectionautoclaving, an effective cold disinfection
solution such as 2% glutaraldehyde is ansolution such as 2% glutaraldehyde is an
alternative.alternative.

Mayhew and Kusy (1988)Mayhew and Kusy (1988) andand Buckthal andBuckthal and
Kusy(1986)Kusy(1986) have demonstrated no appreciablehave demonstrated no appreciable
loss in properties of nitinol wires after as manyloss in properties of nitinol wires after as many
as three cycles of various forms of heatas three cycles of various forms of heat
sterilization or chemical disinfection .sterilization or chemical disinfection .
In a recent in vitro investigation on the effects ofIn a recent in vitro investigation on the effects of
a simulated oral environment on 0.016” nickela simulated oral environment on 0.016” nickel
titanium wires,titanium wires, Harris et al(1988)Harris et al(1988) noted anoted a
significant decrease in yield strength of thesesignificant decrease in yield strength of these
wires over a period of four months.wires over a period of four months.

The testing procedure involved a staticThe testing procedure involved a static
environment in which thermal changesenvironment in which thermal changes
were not taken into account and in whichwere not taken into account and in which
the dynamic changes in forces, such asthe dynamic changes in forces, such as
those of mastication and occlusion, werethose of mastication and occlusion, were
nonexistent.nonexistent.

Burstone et al (1985)Burstone et al (1985) andand Miura et alMiura et al
(1986)(1986) noted that temperatures greaternoted that temperatures greater
than 60ºC increased the susceptibility ofthan 60ºC increased the susceptibility of
these austenitic nickel titanium wires tothese austenitic nickel titanium wires to
plastic deformation and decreased theirplastic deformation and decreased their
springback.springback.

Corrosion SusceptibilityCorrosion Susceptibility
Corrosion in wire alloys becomes a factorCorrosion in wire alloys becomes a factor
in the quality of the wire performance inin the quality of the wire performance in
Orthodontics.Orthodontics.
Corrosion phenomena are increased byCorrosion phenomena are increased by
internal stresses in the metal appliances,internal stresses in the metal appliances,
by the inhomogeneous structure of theby the inhomogeneous structure of the
alloy, and by different metals coming intoalloy, and by different metals coming into
contact.contact.

When the in vivo and in vitro corrosionWhen the in vivo and in vitro corrosion
behaviour of stainless steel, Elgiloy, nitinolbehaviour of stainless steel, Elgiloy, nitinol
and TMA wires were compared,and TMA wires were compared,
It was found that the stainless steel,It was found that the stainless steel,
Elgiloy and TMA exhibited no appreciableElgiloy and TMA exhibited no appreciable
corrosion damage, but the pitting due tocorrosion damage, but the pitting due to
corrosion was observed on the surface ofcorrosion was observed on the surface of
nitinol.(nitinol.( Clinard , JDR 1981Clinard , JDR 1981))

A study byA study by Kim and Johnson(1999)Kim and Johnson(1999) determined ifdetermined if
there is a significant difference in the corrosivethere is a significant difference in the corrosive
potential of stainless steel, nickel titanium,potential of stainless steel, nickel titanium,
nitride-coated nickel titanium, epoxy-coatednitride-coated nickel titanium, epoxy-coated
nickel titanium, and titanium orthodontic wires.nickel titanium, and titanium orthodontic wires.
SEM photographs revealed that some nickelSEM photographs revealed that some nickel
titanium and stainless steel wires weretitanium and stainless steel wires were
susceptible to pitting and localized corrosion.susceptible to pitting and localized corrosion.
The nitrides coating did not affect the corrosionThe nitrides coating did not affect the corrosion
of the alloy, but epoxy coating decreasedof the alloy, but epoxy coating decreased
corrosion. Titanium wires and epoxy-coatedcorrosion. Titanium wires and epoxy-coated
nickel titanium wires exhibited the least corrosivenickel titanium wires exhibited the least corrosive
potential.potential.

Study byStudy by Eliades et al (2000)Eliades et al (2000) evaluating theevaluating the
structure and morphological condition ofstructure and morphological condition of
retrieved NiTi orthodontic arch wires reportedretrieved NiTi orthodontic arch wires reported
that intra-oral exposure of NiTi wires alters thethat intra-oral exposure of NiTi wires alters the
topography and structure of the alloy surfacetopography and structure of the alloy surface
through surface attack in the form of pitting orthrough surface attack in the form of pitting or
crevice corrosion or formation of integuments.crevice corrosion or formation of integuments.
NiTi wires were coated by intra-orally formedNiTi wires were coated by intra-orally formed
proteinaceous integuments that masked theproteinaceous integuments that masked the
alloy surface topography to an extent dependentalloy surface topography to an extent dependent
on the individual patient’s oral environmentalon the individual patient’s oral environmental
conditions and the intra-oral exposure period.conditions and the intra-oral exposure period.

Clinical PerformanceClinical Performance
Evans et al (1998)Evans et al (1998) clinically evaluated threeclinically evaluated three
commonly used orthodontic tooth aligning archcommonly used orthodontic tooth aligning arch
wires:wires: 0.016 x 0.022 inch active martensitic0.016 x 0.022 inch active martensitic
medium force nickel titanium,medium force nickel titanium, 0.016 x 0.022 inch0.016 x 0.022 inch
graded force active martensitic nickel titaniumgraded force active martensitic nickel titanium,,
andand 0.015 inch multistrand stainless steel0.015 inch multistrand stainless steel. It was. It was
a prospective randomized clinical triala prospective randomized clinical trial
Heat activated nickel titanium arch wires failed toHeat activated nickel titanium arch wires failed to
demonstrate a better performance than thedemonstrate a better performance than the
cheaper multistrand stainless steel wires in thischeaper multistrand stainless steel wires in this
randomized clinical trial.randomized clinical trial.

The failure to demonstrate in vivo superiority atThe failure to demonstrate in vivo superiority at
the clinical level may be due to the confoundingthe clinical level may be due to the confounding
effects of large variations in individual metaboliceffects of large variations in individual metabolic
response.response.
Alternatively, it may be that in routine clinicalAlternatively, it may be that in routine clinical
practice NiTi-type wires are not sufficientlypractice NiTi-type wires are not sufficiently
deformed to allow their full superelasticdeformed to allow their full superelastic
properties to come in to play during initialproperties to come in to play during initial
alignment.alignment.

According to data, under conditions of minimumAccording to data, under conditions of minimum
crowding there is no special reason to use acrowding there is no special reason to use a
superelastic alloy wire rather than an establishedsuperelastic alloy wire rather than an established
multistranded stainless steel wire, because themultistranded stainless steel wire, because the
range of force delivered by the multistrandedrange of force delivered by the multistranded
stainless steel is considered acceptable.stainless steel is considered acceptable.
Superelastic NiTi may represent the electiveSuperelastic NiTi may represent the elective
choice when moderate crowding is present andchoice when moderate crowding is present and
when arch form and torque control are requiredwhen arch form and torque control are required
in the initial stages of treatment because anin the initial stages of treatment because an
equivalent rectangular multistranded stainlessequivalent rectangular multistranded stainless
steel wire presents rather higher stiffness and issteel wire presents rather higher stiffness and is
subject to permanent deformationsubject to permanent deformation..

NiTi Coil SpringsNiTi Coil Springs
Compression & tension springs made of Ni TiCompression & tension springs made of Ni Ti
have been recommended-have been recommended-
a) Minimum of permanent deformation.a) Minimum of permanent deformation.
b) More constant force during unloading.b) More constant force during unloading.
Closed coil springs – used for space closure.Closed coil springs – used for space closure.
Open coil springs- Mainly for opening space toOpen coil springs- Mainly for opening space to
unravel the teeth for distalization of molars.unravel the teeth for distalization of molars.

The superelastic coil springs were designed andThe superelastic coil springs were designed and
manufactured to produce a specific forcemanufactured to produce a specific force
throughout the working range of the spring.throughout the working range of the spring.
Like the adjustable force springs, ourLike the adjustable force springs, our
superelastic coil springs will not take asuperelastic coil springs will not take a
permanent set. They return to their originalpermanent set. They return to their original
length after normal deflection.length after normal deflection.

Coil Springs With EyeletsCoil Springs With Eyelets
Adjustable force andAdjustable force and
superelastic closedsuperelastic closed
coil springs arecoil springs are
available with eyelets.available with eyelets.
These stainless steelThese stainless steel
eyelets attach to eacheyelets attach to each
end of adjustableend of adjustable
force or superelasticforce or superelastic
closing (closed coil)closing (closed coil)
springs.springs.
This allows to easilyThis allows to easily
engage a bracket hook,engage a bracket hook,
sliding hook, buccalsliding hook, buccal
tube hook and/or postedtube hook and/or posted
arch wire hooksarch wire hooks

Place one eyelet overPlace one eyelet over
the distal hook andthe distal hook and
gripping the leadinggripping the leading
edge of the frontedge of the front
eyelet with pliers, pulleyelet with pliers, pull
gently forward togently forward to
engage your anteriorengage your anterior
hook.hook.

A study was designed byA study was designed by Heinz et al ( AJO 1999)Heinz et al ( AJO 1999)
to determine whether relatively constant forcesto determine whether relatively constant forces
can be delivered and whether the forcecan be delivered and whether the force
magnitudes approach the manufacturer’smagnitudes approach the manufacturer’s
targeted force values.targeted force values.
Heavy, medium, and light springs were activatedHeavy, medium, and light springs were activated
15 mm at temperatures that ranged from 15°C to15 mm at temperatures that ranged from 15°C to
60°C. The forces were measured during60°C. The forces were measured during
deactivation with a specially constructed forcedeactivation with a specially constructed force
transducer temperature chamber.transducer temperature chamber.

Relatively constant forces can be achieved with anRelatively constant forces can be achieved with an
over-activation procedure that allows relaxationover-activation procedure that allows relaxation
to the desired activation.to the desired activation.
The light springs delivered forces that were nearThe light springs delivered forces that were near
the targeted force; no difference was foundthe targeted force; no difference was found
between the heavy and medium springs in thebetween the heavy and medium springs in the
constant force range.constant force range.
The force magnitudes varied markedly dependingThe force magnitudes varied markedly depending
on mouth temperature.on mouth temperature.

Angolkar, RS Nanda (AJO1992)Angolkar, RS Nanda (AJO1992) designed a indesigned a in
vitro study to determine the force degradation ofvitro study to determine the force degradation of
closed coil springs made of stainless steel (SS),closed coil springs made of stainless steel (SS),
cobalt-chromium-nickel (Co-Cr-Ni) and nickel-cobalt-chromium-nickel (Co-Cr-Ni) and nickel-
titanium (Niti) alloys, when they were extendedtitanium (Niti) alloys, when they were extended
to generate an initial force value in the range ofto generate an initial force value in the range of
150 to 160 gm.150 to 160 gm.
The specimens were divided into two groups.The specimens were divided into two groups.
Group IGroup I included SS, Co-Cr-Ni, and two nickel-included SS, Co-Cr-Ni, and two nickel-
titanium spring types (Niti 1 and Niti 2), 0.010 ´titanium spring types (Niti 1 and Niti 2), 0.010 ´
0.030 inch with an initial length of 12 mm.0.030 inch with an initial length of 12 mm.

Group llGroup ll was comprised of SS, Co-Cr-Ni, and Ni Ti 3was comprised of SS, Co-Cr-Ni, and Ni Ti 3
0.010 ´ 0.036-inch springs, with an initial length of 6 mm.0.010 ´ 0.036-inch springs, with an initial length of 6 mm.
A universal testing machine was used to measure force.A universal testing machine was used to measure force.
Initial force was recorded, and then the springs wereInitial force was recorded, and then the springs were
extended to the respective distances at 4 hours, 24extended to the respective distances at 4 hours, 24
hours, 3 days, 7 days, 14 days, 21 days, and 28 dayshours, 3 days, 7 days, 14 days, 21 days, and 28 days
resulting in a total of eight time periods.resulting in a total of eight time periods.
Between the time intervals, all springs were extended toBetween the time intervals, all springs were extended to
the same initial extension on specially designed racksthe same initial extension on specially designed racks
and stored in a salivary substitute at 37° C.and stored in a salivary substitute at 37° C.

All springs showed a force loss over time. Of theAll springs showed a force loss over time. Of the
total, the major force loss for most springs wastotal, the major force loss for most springs was
found to occur in the first 24 hours.found to occur in the first 24 hours.
The SS and Co-Cr-Ni springs showed relativelyThe SS and Co-Cr-Ni springs showed relatively
higher force decay in group I (0.010 ´ 0.030higher force decay in group I (0.010 ´ 0.030
inch) compared with Niti 1 and Niti 2.inch) compared with Niti 1 and Niti 2.
The Niti 3 springs of group II (0.010 ´ 0.036 inch)The Niti 3 springs of group II (0.010 ´ 0.036 inch)
showed higher force degradation than the SSshowed higher force degradation than the SS
and Co-Cr-Ni springs of this group.and Co-Cr-Ni springs of this group.

The least force decay was found in the NitiThe least force decay was found in the Niti
1 springs. In general, the total force loss1 springs. In general, the total force loss
after 28 days was in the range of 8% toafter 28 days was in the range of 8% to
20% for all springs tested.20% for all springs tested.
This was considered to be relatively lessThis was considered to be relatively less
compared with force loss shown by latexcompared with force loss shown by latex
elastics and synthetic elastic modules aselastics and synthetic elastic modules as
reported in the literature.reported in the literature.

Jebby Jacob, K.Sadashiva Shetty (JIOS 2002)Jebby Jacob, K.Sadashiva Shetty (JIOS 2002)
conducted a study to evaluate the force characteristics ofconducted a study to evaluate the force characteristics of
NiTi open & closed coil springs of different length,NiTi open & closed coil springs of different length,
diameter, lumen size to determine the effect of staticdiameter, lumen size to determine the effect of static
simulated oral environment on spring properties .simulated oral environment on spring properties .
Results showed-Results showed-
Increase in size of lumenIncrease in size of lumen : decreased force.: decreased force.
Increasing wire diameterIncreasing wire diameter : increases force.: increases force.
Increasing open coil spring lengthIncreasing open coil spring length : range of: range of
superelaticity increased significantly.superelaticity increased significantly.

Closed coil springs with shorter length &Closed coil springs with shorter length &
smaller diameter showed good supersmaller diameter showed good super
elastic range.elastic range.
Spring properties showed very minorSpring properties showed very minor
changes over a period of 4 weeks in staticchanges over a period of 4 weeks in static
stimulated oral enviornment.stimulated oral enviornment.

Nattrass (EJO1998)Nattrass (EJO1998) conducted a study on 9mmconducted a study on 9mm
closed coil spring & found that increase inclosed coil spring & found that increase in
temprature increased the force level.temprature increased the force level.
In same study elastomeric chains were alsoIn same study elastomeric chains were also
tested & it was found that they were effectedtested & it was found that they were effected
both by temprature & oral environment.both by temprature & oral environment.
Increase in temprature & exposure to soft drinkIncrease in temprature & exposure to soft drink
& turmeric solution lead to a more force loss in& turmeric solution lead to a more force loss in
elastomeric chains.elastomeric chains.

Han et al (Angle 1993)Han et al (Angle 1993) conducted a studyconducted a study
of Ni Ti closed coil springs, Stainless steelof Ni Ti closed coil springs, Stainless steel
springs,& polyurethane elastics in asprings,& polyurethane elastics in a
simulated oral environment for 4 weeks.simulated oral environment for 4 weeks.
Results showed degradation of physicalResults showed degradation of physical
properties of stainless steel springs &properties of stainless steel springs &
elastics, but Ni Ti remained relativelyelastics, but Ni Ti remained relatively
stable.stable.

In a in vivo study byIn a in vivo study by Sonis AL ( JCO 1994)Sonis AL ( JCO 1994)
Ni Ti closed coil springs produced nearlyNi Ti closed coil springs produced nearly
twice as rapid a rate of tooth movement astwice as rapid a rate of tooth movement as
conventional elastic at same force level.conventional elastic at same force level.
Miura et al ( 1988)Miura et al ( 1988) compared mechanicalcompared mechanical
properties of Japanese Ni Ti & stainlessproperties of Japanese Ni Ti & stainless
steel coil springs in both closed & opensteel coil springs in both closed & open
types.types.

Japanese Ni Ti coil springs exhibitedJapanese Ni Ti coil springs exhibited
superior spring back, super elasticsuperior spring back, super elastic
properties.properties.
Most important characteristic of Ni Ti coilMost important characteristic of Ni Ti coil
spring was the ability to exert a very longspring was the ability to exert a very long
range of constant ,light & continuousrange of constant ,light & continuous
force.force.

Ni Ti Palatal expanderNi Ti Palatal expander
Conventional rapid palatal expanders are uncomfortable,Conventional rapid palatal expanders are uncomfortable,
require patient cooperation, and rely on labor-intensiverequire patient cooperation, and rely on labor-intensive
laboratory production.laboratory production.
They are inefficient because of the intermittent nature ofThey are inefficient because of the intermittent nature of
their force application. Also, they are often soldered totheir force application. Also, they are often soldered to
maxillary first molars with pre-existing mesiolingualmaxillary first molars with pre-existing mesiolingual
rotations that the devices are unable to correct.rotations that the devices are unable to correct.
These rotations can distort the appliances into ineffectiveThese rotations can distort the appliances into ineffective
shapes, and until the rotations are corrected, much ofshapes, and until the rotations are corrected, much of
the potential expansion time can be wasted.the potential expansion time can be wasted.

To overcome the limitations of conventionalTo overcome the limitations of conventional
expansion appliances,expansion appliances, William Arndt ( JCOWilliam Arndt ( JCO
1993)1993) developed a tandem-loop, nickel titanium,developed a tandem-loop, nickel titanium,
temperature-activated palatal expander with thetemperature-activated palatal expander with the
ability to produce light, continuous pressure onability to produce light, continuous pressure on
the midpalatal suture while simultaneouslythe midpalatal suture while simultaneously
uprighting, rotating, and distalizing the maxillaryuprighting, rotating, and distalizing the maxillary
first molars.first molars.
The action of the appliance is a consequence ofThe action of the appliance is a consequence of
nickel titanium's shape memory and transitionnickel titanium's shape memory and transition
temperature effects. Nickel titanium can betemperature effects. Nickel titanium can be
processed into a set shape to which it constantlyprocessed into a set shape to which it constantly
tends to return after deformationtends to return after deformation

In addition, it can be alloyed to produce a metalIn addition, it can be alloyed to produce a metal
with a specific transition temperature.with a specific transition temperature.
At temperatures below the transitionAt temperatures below the transition
temperature, the interatomic forces weaken,temperature, the interatomic forces weaken,
making the metal much more flexible.making the metal much more flexible.
Above the transition temperature, theAbove the transition temperature, the
interatomic forces bind the atoms tighter and theinteratomic forces bind the atoms tighter and the
metal stiffens.metal stiffens.

The nickel titanium expander has aThe nickel titanium expander has a transitiontransition
temperature of 94°Ftemperature of 94°F. When it is chilled before. When it is chilled before
insertion, it becomes flexible and can easily beinsertion, it becomes flexible and can easily be
bent to facilitate placement .bent to facilitate placement .
As the mouth begins to warm the appliance, theAs the mouth begins to warm the appliance, the
metal stiffens, the shape memory is restored,metal stiffens, the shape memory is restored,
and the expander begins to exert a light,and the expander begins to exert a light,
continuous force on the teeth and the midpalatalcontinuous force on the teeth and the midpalatal
suture .suture .

Nickel titanium expanders come in eight differentNickel titanium expanders come in eight different
intermolar widths, ranging fromintermolar widths, ranging from 26mm to 47mm26mm to 47mm,,
that generate forces ofthat generate forces of 180-300g180-300g..
The 26-32mm sizes have softer wires thatThe 26-32mm sizes have softer wires that
produce lower force levels for younger patients.produce lower force levels for younger patients.
The clinician determines the appropriate size byThe clinician determines the appropriate size by
measuring the amount of expansion needed,measuring the amount of expansion needed,
then adding 3mm for overcorrection.then adding 3mm for overcorrection.

Freeze-gel packs, provided in the expander kits,Freeze-gel packs, provided in the expander kits,
can be placed around the expander assemblycan be placed around the expander assembly
while the band cement is being prepared. Thiswhile the band cement is being prepared. This
will cool the appliance enough to allow easywill cool the appliance enough to allow easy
insertion into the lingual sheaths.insertion into the lingual sheaths.
The expander should be handled by the molarThe expander should be handled by the molar
attachments during placement to avoid warmingattachments during placement to avoid warming
the nickel titanium.the nickel titanium.

When the appliance begins to stiffen in theWhen the appliance begins to stiffen in the
mouth, it may cause some discomfort at first.mouth, it may cause some discomfort at first.
The patient can alleviate this by sipping a coldThe patient can alleviate this by sipping a cold
liquid, which will temporarily make the nickelliquid, which will temporarily make the nickel
titanium slightly more flexible. Many of mytitanium slightly more flexible. Many of my
patients have delighted in showing this effect topatients have delighted in showing this effect to
their friends.their friends.

Maurice Corbett (JCO 1997) Described a
modification called the Nickel palatal expander
2, that delivers a uniform, slow continuous force
for maxillary expansion, molar distalization and
rotation.
Puneet Batra,Ritu Duggal, Hari Prakash (JIOS
2003): studied the efficacy of nitinol expander in
cleft and non cleft patients and they concluded
that it would be effective in both type of patients
requiring transverse expansion of the maxilla.

Donohue V, Marshman, WinchesterL EJO
2004 compared maxillary expansion using
either a quadhelix appliance or a nickel
titanium expander in 28 patients.
There was no significant difference in the
efficacy or rate of expansion between the
two appliances. The quad helix however
appeared to exert a more controlled rate
of expansion.

Molar distalizationMolar distalization
Superelastic NiTi wire:Superelastic NiTi wire: Locatelli et alLocatelli et al ((19921992) used a 100) used a 100
gm NeoSentalloy wire (superelastic Nickel-titanium wire)gm NeoSentalloy wire (superelastic Nickel-titanium wire)
with shape memory for molar distalization .with shape memory for molar distalization .
Crimp stops just distal to first premolar bracket areCrimp stops just distal to first premolar bracket are
placed 5 – 7 mm distal to anterior opening of molar tubeplaced 5 – 7 mm distal to anterior opening of molar tube
and hooks between lateral incisors and canines.and hooks between lateral incisors and canines.
Excess wire is deflected gingivally into buccal fold. AsExcess wire is deflected gingivally into buccal fold. As
wire returns to original shape, it exerts 100 gm distalwire returns to original shape, it exerts 100 gm distal
force against molars.force against molars.

Super elastic nickel titanium wires haveSuper elastic nickel titanium wires have
been found as effective as other means inbeen found as effective as other means in
producing distal movement of theproducing distal movement of the
maxillary first molars.maxillary first molars.
When the distalization is carried out beforeWhen the distalization is carried out before
the second molars have erupted, it canthe second molars have erupted, it can
reliably produce 1-2mm of space.reliably produce 1-2mm of space.

The concept of using coil springs for distalizationThe concept of using coil springs for distalization
was introduced bywas introduced by Miura (1988)Miura (1988) who used 100who used 100
gms superelastic coils.gms superelastic coils.
Gianelly ( AJO1991)Gianelly ( AJO1991) used Japanese NiTi coilused Japanese NiTi coil
springs exerting 100 gms of force to movesprings exerting 100 gms of force to move
maxillary molars distally.maxillary molars distally.

Movement achieved is 1-1.5 mm perMovement achieved is 1-1.5 mm per
month.month.
NiTi molar distalizing springs are also aNiTi molar distalizing springs are also a
part of appliances like Jones jig, Distal jetpart of appliances like Jones jig, Distal jet
etc.etc.

Erverdi et al ( BJO 1997)Erverdi et al ( BJO 1997) compared Ni Ticompared Ni Ti
coil springs & repelling magnets as 2coil springs & repelling magnets as 2
methods of intra oral molar distalizers for amethods of intra oral molar distalizers for a
period of 3 months.period of 3 months.
Although upper molar distalization wasAlthough upper molar distalization was
achieved with ease in both techniques, Niachieved with ease in both techniques, Ni
Ti coil springs were found to be moreTi coil springs were found to be more
effective in terms of movement achieved.effective in terms of movement achieved.

Neet Separating SpringsNeet Separating Springs
The Neet Separating Springs are manufacturedThe Neet Separating Springs are manufactured
from Nickel Titanium. These innovativefrom Nickel Titanium. These innovative
separators provide light continous forces that willseparators provide light continous forces that will
separate stubborn molars while maintainingseparate stubborn molars while maintaining
patient comfort.patient comfort.
Inserting the separator into any contact is easyInserting the separator into any contact is easy
and will provide generous space for banding.and will provide generous space for banding.
The clinician no longer has to struggle trying toThe clinician no longer has to struggle trying to
"saw" through the contact with an elastomeric"saw" through the contact with an elastomeric
separator.separator.

Nickel allergyNickel allergy
Nickel is the most common metal to causeNickel is the most common metal to cause
contact dermatitis in orthodontics.contact dermatitis in orthodontics.
Nickel-titanium alloys may have nickel content inNickel-titanium alloys may have nickel content in
excess of 50 per cent and can thus potentiallyexcess of 50 per cent and can thus potentially
release enough nickel in the oral environment torelease enough nickel in the oral environment to
elicit manifestations of an allergic reaction.elicit manifestations of an allergic reaction.
Nickel elicits contact dermatitis, which is a TypeNickel elicits contact dermatitis, which is a Type
IV delayed hypersensitivity immune response.IV delayed hypersensitivity immune response.

It has been shown that the level of nickelIt has been shown that the level of nickel
in saliva and serum increases significantlyin saliva and serum increases significantly
after the insertion of fixed orthodonticafter the insertion of fixed orthodontic
appliances.appliances. ( Agaoglu,2001).( Agaoglu,2001).
It has been suggested that a thresholdIt has been suggested that a threshold
concentration of approximately 30 ppm ofconcentration of approximately 30 ppm of
nickel may be sufficient to elicit a cytotoxicnickel may be sufficient to elicit a cytotoxic
response.response. (Bour ,1994).(Bour ,1994).

Barrett et al ( AJO,1993)Barrett et al ( AJO,1993) reported that thereported that the
release rate for nickel from stainless steelrelease rate for nickel from stainless steel
or nickel titanium wires are notor nickel titanium wires are not
significantly differentsignificantly different
Possible risks associated with nickelPossible risks associated with nickel
toxicity : Risk of nephrotoxicity,toxicity : Risk of nephrotoxicity,
Carcinogenicity, risk of immune changesCarcinogenicity, risk of immune changes
& alveolar bone loss.& alveolar bone loss.

: Flexile nickel-titanium wires release increased: Flexile nickel-titanium wires release increased
amounts of nickel and are thought to inductamounts of nickel and are thought to induct
nickel sensitivity; there may be up to 20 per centnickel sensitivity; there may be up to 20 per cent
conversion rate.conversion rate. (Jia ,1999)(Jia ,1999) These high nickelThese high nickel
content wires should be avoided in nickelcontent wires should be avoided in nickel
sensitive patients.sensitive patients.
Alternatives include twistflex stainless steel,Alternatives include twistflex stainless steel,
fibre-reinforced composite archwires. Wiresfibre-reinforced composite archwires. Wires
such as TMA, pure titanium, and gold-platedsuch as TMA, pure titanium, and gold-plated
wires may also be used without risk.wires may also be used without risk.

Altered nickel-titanium archwires also existAltered nickel-titanium archwires also exist
and include plastic/resin-coated nickel-and include plastic/resin-coated nickel-
titanium archwires.titanium archwires.

Ion-implanted nickel-titanium archwires haveIon-implanted nickel-titanium archwires have
their surface bombarded with nitrogen ions,their surface bombarded with nitrogen ions,
which forms an amorphous surface layer,which forms an amorphous surface layer,
conferring corrosion resistance and displacingconferring corrosion resistance and displacing
nickel atoms.nickel atoms.
Manufacturers claim that these altered nickel-Manufacturers claim that these altered nickel-
titanium archwires exhibit less corrosion thantitanium archwires exhibit less corrosion than
stainless steel or non-coated nickel-titaniumstainless steel or non-coated nickel-titanium
wires, which results in a reduction of the releasewires, which results in a reduction of the release
of nickel and decrease the risk of an allergicof nickel and decrease the risk of an allergic
response.response.

Diagnosis of nickel allergyDiagnosis of nickel allergy
It is important to make a correct diagnosis ofIt is important to make a correct diagnosis of
nickel allergy, symptoms of which may occurnickel allergy, symptoms of which may occur
either within or remote to the oral environment.either within or remote to the oral environment.
The following patient history would suggest aThe following patient history would suggest a
diagnosis of nickel allergy:diagnosis of nickel allergy:
previous allergic response after wearing earringsprevious allergic response after wearing earrings
or a metal watchstrap;or a metal watchstrap;

appearance of allergy symptoms shortlyappearance of allergy symptoms shortly
after the initial insertion of orthodonticafter the initial insertion of orthodontic
components containing nickel;components containing nickel;
confined extra-oral rash adjacent toconfined extra-oral rash adjacent to
headgear studs.headgear studs.

Intra oral agingIntra oral aging
For brackets & archwires, issue of interest is theFor brackets & archwires, issue of interest is the
in vivo alteration of material due to the expectedin vivo alteration of material due to the expected
long period of performance, with possible effectslong period of performance, with possible effects
on mechanical properties.on mechanical properties.
Main focus of the alterations induced onMain focus of the alterations induced on
orthodontic wires is on Ni Ti archwires becauseorthodontic wires is on Ni Ti archwires because
stainless steel & Co-Cr-Ni archwires are usuallystainless steel & Co-Cr-Ni archwires are usually
replaced in an escalating stepwise process asreplaced in an escalating stepwise process as
treatment progresses.treatment progresses.

Nickel titanium in orthodontics

Nickel titanium in orthodontics

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