Ni ti wires in orthodontics /certified fixed orthodontic courses by Indian dental academy

SEMINAR ONSEMINAR ON
SHAPE MEMORY ALLOYSSHAPE MEMORY ALLOYS
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INDIAN DENTAL ACADEMY
Leader in continuing dental education
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Introduction :-
It refers to the ability of the material to remember its
original shape after being plastically deformed while in
martensite form .
In typical application Certain shape is set when the alloy
is maintained at an elevated temperature, above
martensite – austenite transition temperature .
When the alloy is cooled below the transition
temperature it can be plastically deformed but when
heated again and the original shape is restored.

HISTORYHISTORY
• Classification – Orthodontic wires
• Stainless steel , titanium - Beta titanium , Nickel ti , co.
cr – nickel .
• In 1950 – 1st
material used are noble metals & alloys –
Gold , Platinum , Iridium , Silver alloy.
• They lacked flexibility & tensile strength hence they were
replaced by Stainless Steel.
• In 1919 –SS was introduced by “KRUPPS” dental clinic
in Germany by Dr. F.HAUPTMEYER.
• In 1930 – Angle used SS as ligature wire .
• In 1947 – SS was used as orthodontic material .

• In 1960 “ William F. Buehler” – developed nitinol in the
navel ordnance laboratory[Naval surface weapons
center] Ni – nickel, Ti – Titanium, Nol – Naval ordi. Lab. .
• In 1970 – “Andreasen “ – used NiTi wires for
orthodontics it was marketed in a stabilized martenstic
form with no application of phase transition effects .
• 1st
marketed by 3M Unitek corporation Monrovia ,U.S.A.
• In 1980 NiTi wires with active austensitic grain structure .
• Stabilized martenstitic alloy commercially available –
M -NiTi .
• NiTi alloys with super elasticity – A .NiTi ( sentinol)
• In 1990 NiTi wires – NEO SENTALLOY with shape
memory at oral environment – Intro.GAC –International .

In 1994 – ORMCO Corpo intro copper NiTi,wire was
available in 3 varients – Corresponding to austenitic
finish temp for the completion of martensite to austenite
transformation.
27* c – For mouth breathers
35* c – Activated at normal body temp.
40* c – Activation only after consuming hot food &
beverages.

NiTi wiresNiTi wires
• Titanium classi. Under light metals eg. AL , MG,Berllium
• Light metals – frequently used to reduce the weight of
components & structure .
• 1795 – GERMAN chemist “martin klaporth” named
titanium after the 1st
sons of earth titans .
• 1825 – An impure sample of Ti idendified .
• 1937 – Kroll reacted Ticl 4 with molten magnesium
under an atmosphere of argon.
• Basic reaction – Tio2+ 2cl2+ 2c = Ticl4 +2co .
• Briquette + tar+ chlorinate at 800 * c – fractional
distillation of Ticl4.
• Ticl4 +2mg = Ti + 2mgcl2 special atmospheric
conditions needed because alloys react with air.

• Sponge produced by reacting with mg is purified by
leaching with Hcl.
• With Na ,leaching is more efficient and Ti sponge
becomes more granular .
MANUFACTURING METHODS –
• Milling ,Powder metallurgy, injuc. Moulding .
• Advances – “Heroult” – Direct electric arc in furnace
• “Kjellin” – Induction method.
• Recent refinement – Argon decarburization & Widening
of alloying element , Consumable electrode arc furnace.
SOURCE – The mineral (rutile) – Tio2 , convenient source
found in beach sand.
• “ilmenite” –major source.

STRUCTURE & COMPOSITION –
• MARTENSITIC – form stable at low temperature .
• AUSTENITIC – form stable at higher temperature.
• The unit cells can rearrange themselves in a zig zag
pattern with congruent interfaces. Which results in a
reversible E.C. bain structure transformation which is
responsible for “Shape memory “ & “Super elastic”
properties .
• “BAIN DISTORTION” – In S.S the transformation is
diffusionless occuring from any chemical change & if
transition is as the result of specific crystallographic
relation ship between the parent phase & new phase,a
rearrangement of atoms in the unit cells occurs
– Bain distortion.
• Equiatomic phase is stable at higher temperature
austenite & is made of lattice in which units are cubic .

• In each cell the Ni & Ti atoms are evenly distributed &
made up of self accommodating coherent twins.
• TWINNING – Is an angular movement of atoms parallel
& symmetric towards a specific plane .
• The unit cells can rearrange themselves in a zigzag
pattern with congruent interfaces
• Memory effect lasts only as long as the twinning &
detwinning phenomenon can take place .
• SHAPE MEMORY EFFECT – It refers to the ability of
the material to remember its original shape after being
plastically deformed in martensite form .( when the alloy
is cooled below the transition temperature it can be
plastically deformed & when heated again original temp.
is restored .

• SUPER ELASTICITY – Ability to withstand much higher
elastic strain than ordinary alloy before permanent set.
• This property is exploited in orthodontics at body temp.
to provide almost constant forces during long intervals of
deformation.
• COMPOSITION – Ni -55% Ti –45%
• For thermally activated purpose the third metal
commonly used are Cu because they reduce the
hysteresis & brings TTR close to oral temperature &
improves the strength of martensitic form .
• Addition of carbon improves control of arch wire spring
back properties .
• Small amount of impurities disrupt the matrices
( 0,N,&C)
• Copper - < 5% , Chromium O .3%.(cu NiTi)

CLASSIFICATION OF NiTi WIRES –
• In 1992 water’s review classified it into three groups –
Group I- Alloys with TTR bet. The room temp. & body
temp. ( martensitic active alloys)
Group II - TTR below the room temp. (austenitic)
Group III - TTR close to body temp. which by virtue of
shape memory effect spring back to their original shape
when activated by body heat .
Evans & Durning classification –
Phase I – Alloys of gold & stainless steel
Phase II – Original work hardened Nitinol.
Phase III – Predominantly austenitic at room temp. with
TTR below the intraoral temp.
Phase IV – Thermodynamic or active martensitic alloys .

• In this alloys the TTR is set close to the intraoral temp.
They have a great working range at room temp. because
they exist in a mixed or rhobohedral phase at room
temp. so they maintain the permanent deformation .
• Once exposed to higher intra oral temp. the martensite
form will be gradually converted into austenite with a
recovery of ideal preset arch form with an increased
force delivery. Eg .Cu NiTi .
• Phase V – Graded thermodynamic –
• Commercial Nitinol ortho. Wires contains 1.6 % Cobol to
modify the tranisition temp. & mechanical properties
• Shape memory phenomenon of NiTi alloys was investi.
By Andreasen & Barret in 1973 that resisted permanent
deformation .

• Forces developed as a result of contraction of pre
stretched .O2O NiTi wire when heated to room temp.
force ranging from 1.5 to 5 pounds is generated which
aids in space closure .
• Hence NiTi requires fewer arch wire changes & less
chair side time & shortens treatment time required to
accomplish correction of rotation & leveling.
• Andreasen & Morrow in1978 performed bending &
torsion test with new ADA spec. no. 32 on ortho. Wires
to compare NiTi & SS .OI8 round NiTi has stiffness
similar to .O14 SS. Until the deflection reaches 35 to 40 *
• Comparison of rectangular NiTi & Square SS wires were
done ,it was said that permanent set angle of NiTi wires
is 5 – 7 * .NiTi is said to exhibit superior characteristic in
torsion & stored energy in comparison with SS.

• NiTi wires can be used in cl.1 , cl.2 , cl.3 malocclusions
in both extraction & n.ext cases .
• Important benefits for NiTi rectangular wires is it can be
inserted early in the treatment for rotation, leveling ,
tipping & torquing
• Clinicians have been successful in beginning of the
treatment with Rectangular wires .017 X .O25 & .O19
x .O25 which nearly fill the bracket slot , in a few case
entire treatment can be done with just one arch wire .
• It is ideally suited for use with most pretorqed &
preangulated appliance becau.tipping & uprighiting can
be initated in early stages of treatment.
• Use of nitinol with pretorqued and preangulated brackets
require careful monitoring of tooth movement because of
wires high elasticity and more continuous force.

CHINESE NiTi:-
• At mouth temperature this wire is work hardened
martensite and hence does not reply on shape memory
characteristics in clinical application.
• Its very high springback and low stiffness characteristics
have won wide clinical acceptance.
• Chinese NiTi alloy wires was originally developed by
Dr.Hua Cheng Tien and colleagues at research institute
for non-ferrous metal in Beijing china in 1978.
• Chinese NiTi wires posses super elasticity and shape
memory. The possible use of chinese NiTi are many in
that it offers low siffness and high spring back for tooth
alignment.
• High range of action of spring back chinese NiTi is
applicable where large defection for uprighting, labial and
lingual movements is needed.

• super elasticity among various NiTi wires is seen.
• A flag shaped curve is formed when the stress deforms
the alloy wire, inducing the martensite stage of
transformation. In body temperature the alloy is easily
transformed to martensite state in the mouth.The wire
becomes activated thus using the shape memory effect.
• Ex: Chinese NiTi
• Burstone in 1985 – chinese Ni-Ti - Properties.
• The wire has spring back that of 4.4 times that
comparable stainless steel wire and is 1.6 that of NiTi. –
5mm span cantilever test.

• At 80 degrees of activation the average stiffness of
chinese NiTi wire is 73% that stainless steel wire and
36% of NiTi wire.
• A significant design feature for constant force application
is seen.
• The load deformation rate at small activations is
considerably higher than that at large activations.
• Chinese NiTi wire is highly suitable if low stiffness is
required and large deflections are needed.
• Higher stiffness at small activations make it more
effective than wires of traditional alloys.

JAPANESE NICKEL TITANIUM ALLOYS:-
• In 1978 Furu Kawa electric company of Japan produced
Japanese NiTi alloy possessing all there properties
(excellent spring back, shape memory and super
elasticity).
• Honma and takei have reported on martenstic
temperature range changes in relation to the electrical
resistance present in the NiTi alloy. Heat treatment was
made to study the effect of temperature and time on
super elasticity of the japanese NiTi alloy wire.
• Up to 500o
C in the linear portion, elastic deformation
was indicted and the super elasticity level was lowered.

• Individualized force can be preformed in an arch wire of
same diameter without fabrication of any loops.
• It is possible to modify the amount of orthodontic force in
an individualized segment of arch wire. Ex: by applying
controlled heat with adequate temperature and time on
the anterior segment of arch wire, the amount of force
within anterior segment can be increased & posterior
arch wires are not disturbed.
Arch wire charact:
• Japanese NiTi alloy wire exhibit superelastic properties
indicating an area of definite amount of stress in spite of
changes in strain rate.
• Three point bending tests indicate that Nitinol wire
provides a light force and a lesser amount of permanent
deformation.
• They possesses super elastic properties whereby the
load deflection decreases.

• The relationship between the temperature and time of
the heat treatment of the japanese NiTi alloy wire
optimizes the super elastic properties of the alloy. It
delivers a relatively constant force for a long period of
time.
NiTi in cross bite correction:
Progressive first order offsets in the buccal segment of
nitinol wire so that each tooth will be loaded in
approximately equal amounts and then expands and
contracts the two arch wires opposite the direction of
crossbite. It produce a direction of force having a low
load deflection rate that is more desirable that cross
elastics.

Uprighting the impacted canines:-
• Uprighting of impacted canines by the use of couple or
torque in the second order . Torque is accomplished by
inserting an auxillary nitinol wire into the bracket slot of
canine.
• This in turn produces a tipping action above the bracket
and produces an uprighting force on the canine roots.
• Also used as a sectional arch for bringing lingually
displaced canines into position.

Opening the bite:
• For opening the bite either by intruding the maxillary and
mandibular anterior segments or by extruding the
posterior segments.
• For opening a deep bite & for complete anterior maxillary
retraction one can place first order steps in the anterior
segment to produce intruding forces on the anterior
segment and extruding forces on the premolars and
molars.
NiTi in Beggs:
A.J.Wilcock S.S wires are replaced by NiTi wires.
• Alloy of NiTi with its flexibility and resistance to
deformation hence facilitates and simplifies begg
treatment by replacing looped stainles steel arch wires
with plain arch wires and also used where Bite opening
is not critical.

Use of Nitinol Archwire
• Cases with severe crowding 0.16 NiTi arch wires are
used.
• Anchor bends or tipbends more accentuated when SS is
used in compared to NiTi.
• Step up bends distal to the lateral brackets aid in
intruding the four anterior teeth.
• In 25 patients were treated with .016 maxillary and
mandibular NiTi arch wires and SS arch wires-Compar..
• Time taken for tooth alignment in NiTi – 42 days,for SS
is 49 days. NiTi arches showed 25% faster response for
rotation, tipping and leveling when comp.. With SS .
• Bite opening responded better to stainless steel arch
wires than to NiTi arch wires, because relatively low
force level is generated by NiTi than SS arch wires.

• Time for space opening with NiTi – 44 days, SS was 53
days.
Limitations:
• NiTi wires when compared to SS – has resistance to
take a bend.
• Hence the placement of desire in and out bends
becomes difficult – It will rapidly break when bent over a
sharp edge. Closing loops in particular are not practical
for nitinol wire.
• NiTi cannot be soldered or successfully welded to itself
without annealing the wire and because the bending of
tie back hooks entails a high risk of failure, crimpable
hooks and stops a successful alternative.
• Use of auxillary retraction forces will have the effect of
opening the patient’s posterior bite, can be managed by
remove the auxillary force mechanism at the completion
of treatment and going to conventional posterior bite
closing mechanics with SS arch wires.

Neo Sentalloy:
• New super elastic NiTi rectangular wire can be used with
extremely light force in the initial phase of treatment.
• Three point bending and torque tests have shown the
wire to exert light, continuous force regardless of
deflection or wire size.
• Three dimensional tooth control can be effected at the
same time as horizontal and vertical leveling and root
torquing.
• They also provide greater arch wire flexibility and less
patient discomfort than other NiTi wires.

Copper NiTi:
• The NiTi in the alloy has been partially replaced by
copper to produce ternary alloys.
• Copper NiTi at the room temperature is in martensitic
phase, it is possible to introduce relatively sharp bends
on the wire. The original archform will be regained simply
be heating the wire at a temperature above austenitic
phase (i.e) has TTR of 40 degrees.
• Forces exerted on the dento alveolar structure are
remarkably low therefore the alloy is recommended for
the treatment of patients with periodontal problems.
• Disadvantage is the low stiffness of this wire of not
allowing for complete dental alignment or full control of
transverse dimensions.

Nickel Hypersensitivity :
• Nickel is one of the most common causes of allergic
contact dermatitis.
• Nickel is a strong biological sensitizer and consquently
may induce a delayed hypersensitivity reaction (type IV
immune response). It is estimated that 4.5 % of the
population have a hyper senstitivity to nickel with a higher
prevalence in females.
• This delayed allergic reaction can be verified by “Epi
cutaneous test”, this is performed by taping to skin the
suspected substance ,dissloved in an adequate medium
like water, alcohol. After a period of time – 48 hours
erthmatous reactions are evaluated according to a scale
ranking.

RECENT DEVELOPMENTS:
• NiTi wires with epoxy and nitride coatings have been
recently marketed.
• Nitride coatings were originally added to orthodontics
wires to aid in surface hardending, epoxy electro coating
provides improved esthetics.
• Coated wires may be an important addition to the
orthodontic armamentarium if corrosion can be inhibited
and nickel release into the oral cavity can be prevented.
• Epoxy coated NiTi exhibited low corrosive potential as
compared to the regular NiTi.
• NiTi – arch wires with ion-implanted surfaces to obtain
reduced bracket friction have been introduced.

Conclusion:
• Findings indicate that nitinol wires do facilitate and
simplify Begg mechanotherapy, because unraveling and
leveling for attaining good tooth alignment occurs faster
than stainless steel looped arches & treatment time
diminished.
• They provide a good spring back effect and flexibility,
which allows for large elastic deflections, with low forces.
• Patient response is good and less discomfort is reported.

BIBLIOGRAPHY
Contemporary orthodontics – Profit
Orthodontics – Graber
Clinical Handling of Dental materials
Orthodontic Materials – William. A . Brantley
A.J.O – 1990 sep,1995 jul,1998 aug.

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Ni ti wires in orthodontics /certified fixed orthodontic courses by Indian dental academy

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Ni ti wires in orthodontics /certified fixed orthodontic courses by Indian dental academy