NITI wires

A metal with mind….A metal with mind….
www.indiandentalacademy.com

Orthodontic therapy is a force management
procedure, largely based on the use of wires.
Wires are a mainstay in storing and distributing
the therapeutic force to the teeth thus bringing
them to the ideal function and esthetic position.
INTRODUCTION

Ideally, archwires are designed to move teeth
with light continuous forces. It is important that
the forces do not decrease rapidly.
Light forces reduce patient discomfort,avoid
tissue hyalinization and undermining resorption.

Recent advances in orthodontic wire alloys have
resulted in a wide array of wires that
demonstrate wide spectrum of properties and
have added versatility of orthodontic treatment.
The development of nitinol wire is another
improvement, which has emerged from the
orthodontists search for lighter force and
greater working range.

HISTORY
Father of NiTi - William F. Buehler, a research
metallurgist of Naval ordnance in Silver Springs,
Maryland in 1968.
NiTiNol derived from, Ni for nickel and Ti for
titanium, and Nol from naval ordnance laboratory.
Andreasen George F. et al first introduced
Nitinol, in orthodontics in 1971. The original alloy
contained 55% nickel and 45% titanium

Andreasen suggested that, the "memory"
phenomenon as a result of temperature induced
crystallographic transformations which helps in
shape changes, might be useful for the
orthodontist to apply forces.
Andreasen and Barrett demonstrated that nitinol
had a lower stiffness than stainless steel and
could be deflected further without permanent
deformation when tied into malaligned teeth.

Numerous nickel-titanium wires have been
introduced into the market like Chinese NiTi,
Japanese NiTi, Nitinol, Orthonol, Sentalloy,
Titanol etc. each claiming superb elastic property
and built in memory.
With the availability of wires with widely varying
property, it becomes possible for the clinician to
select wires for of early stages treatments and
increase to higher levels towards the finish of
treatment. This approach has been termed by
BURSTONE as "Variable modulus orthodontics".

PROPERTIES OF ARCHWIRE:PROPERTIES OF ARCHWIRE:
Assessment of orthodontic archwire properties
are essential to provide clinical meaning and
characteristics, which are desirable for optimum
performance during the treatment.

1. Proportional / elastic limit:
Point at which permanent deformation is 1st
Observed.
2. Yield strength:
The point at which deformation of 0.1% is
measured. Clinically useful spring back occurs if
the wire is deflected beyond the yield point.

STRAIN
Yield point
Proportional limit
Ultimate tensile strength
STRESS
Failure Point
Resilience Formability
Stiffness
Range
Spring back

3. Ultimate tensile strength:
This is a point which maximum load a wire can
sustain beyond which irreparable permanent
deformation occurs.
The max: load a wire can sustain

4. Stiffness (spring rate):
Stiffness is inversely proportional to springness
This relates to the force/deflection curve, more
horizontal the slope, Springer the wire and more
vertical the slope, stiffer the wire.
It represents the magnitude of force delivered
by the arch wire at a given deflection.

5. Spring back (range of action):
The spring back property is the portion of the
load deflection curve between the
proportional limit & ultimate tensile strength.
It is important in determining clinical
performance of a wire.
Distance a wire will bend elastically
before permanent deformation
Proffit 3rd
Ed

6. Resilience (Stored or spring energy):
It is the area under stress strain curve till the
proportional limit. It represents the energy
storage capacity of the wire, which is a
combination of strength and springiness.
Elasticity of the wire

7. Formability:
The amount of permanent deformation that a
wire can withstand before failing.
Maximimum bending before breaking
Yield point
Proportional limit
Ultimate tensile strength
STRESS
Failure Point
Resilience Formability
Stiffness
Range
Spring back

COMPARISION OF CLINICAL PROPERTIES OF ORTHODONTIC WIRES
WIRE BIOCOMPA
CTIBILITY
JOINABILITY FRICTION SPRING
BACK
STIFFNES
S
FORMABILI
TY
S.S GOOD SOLDERED /
WELDED
LOW LOW HIGH GOOD
COBALT
CROMIUM
GOOD SOLDERED /
WELDED
LOW LOW HIGH GOOD
NITI CORROSIO
N NOTED
NO LOW HIGH LOW POOR
TMA GOOD WELDED HIGH AVERAGE AVERAGE GOOD
MULTISTR
ANDED
GOOD SOLDERED /
WELDED
NOT
KNOWN
HIGH LOW POOR
AJO 1989 Aug Kapila and Sachdevawww.indiandentalacademy.com

COMPARISION OF MECHANICAL PROPERTIES OF ORTHODONTIC WIRES
S.S ELGILOY NITI TMA GOLD ALLOY
Mod: of
elasticity
179 184 41.4 71.7 100
Yield strength 1579 1413 427 931 862
Ultimate tensile
strength
2117 1687 1489 1276 931
Hardness 600 420 89 RB 91 RB 145
Heat Rx 400 0
- 900 0
260 0
- 650 0
482 0
1625 0
871 0
- 955 0
1998 AJO Mar Asgharnia and Brantleywww.indiandentalacademy.com

Ideal Orthodontic Alloys:
The ideal orthodontic wire is one that gives a
high maximal elastic load and a low load
deflection rate.
The mechanical properties that determine these
characteristics are elastic limit and modulus of
elasticity.
ADA specification No: 32 , 1977

PROPERTIES OF NITI WIRE:
Various outstanding properties have been
attributed to Ni-Ti such as:
1. Shape memory
2. Super elasticity
3. Corrosion resistance
4. Bio compatibility
5. Resistance to torsional fracture

Structure of NiTi:Structure of NiTi:
Ni & Ti have several valance and can generate
different combination, ( NiTi, Ti2Ni3 ) which can
transform to each other segregating an excess
of one metal in the process. This along with
propensity of alloy component crystallize in
different system.
Niti – epitome of transformation

The surface characteristics of the nickel-
titanium alloy wires are a result of its complex
manufacturing process and surface treatments.
Nickel and titanium are most commonly
manufactured into the niti alloy by the process of
vacuum induction melting or vacuum arc melting.
Segregation is often a problem because there is a
relatively wide disparity of melting points.
AJO 1991 Oct

Vacuum melting
rolling
Press forging
Rotaryswaging

Several remelts are often needed to improve
homogeneity of the niti alloy. Alloy is then
made into powders. The process of hot
isostatically pressing is used by the
manufacturer to form the powders into wires.
Voids occur in areas where the powders are not
completely pressed together. The wires obtain
their final shape by the process of drawing or
rolling. The process of drawing or rolling may
leave scratch marks on the surface.

Niti can exist in more than one form or crystal
structure. Martensite form exist in lower temp:
and austenite form exist in higher temp:
Shape memory – ability of the material to
remember its original shape after being
plastically deformed while in martensitic form.
Alloy is set in a shape above TTR and when its
cooled below, it can be plastically deformed. Now
when its re heated it regains its original shape.
This property is called thermoelasticity.

Ni & Ti atoms
are distributed
evenly (austenite)
External
influence
Tetragonal (martensitic)
structure made up of self
accommodating coherent twins
Twinning – angular movements of
atom to a specific plane.
Crystalline structure remains
coherent but their assembly
oscillates from one plane to other.
Bain transformation
is responsible for
shape memory & super
elasticity
Unit cell can rearrange themselves

Martensitic
Distorted monoclinic
Austenitic
Body centered
cubic lattice
R – phase
Rhomboidal structurewww.indiandentalacademy.com

During twinning the stress strain curve takes the
shape of a plateau and a minor increase in stress
may produce as much as 8% deformation.
Within the plateau the rearrangement of the
atoms is reversible. How ever if the material is
deformed below a certain yield point, permanent
deformation results.

A
B
C
C1
F
D
G
H
E
STRAIN
STRESS A-B = elastic deformation (A)
B = Ms
C = Mf
C-D = elastic deformation (M)
C1 = unloading
D = deformation
E = failure
F = max: stress (As)
G = Af
Proffit 3rd
Ed

In the 1 st stage the preexisting austenite
deforms elastically from 0 – 2 % . Above this
level, a martensitic, super elastic
transformation occurs that is completed at 8 -
10% strain levels and the structure becomes
stretched, detwinned martensite.
With a further increase in stress, the atomic
planes slip and an irreversible change occurs.
How ever if the remains below this point and is
later removed, the stretched detwinned
structure regains its former shape.

Force produced by niti wire does not vary over a
considerable range of deflection. So the initial arch
wire can exert about the same force when it is
deflected over a range of distance.
deflection
force
S.S
C-NiTi
NiTi
Proffit 3rd
Edwww.indiandentalacademy.com

This is because of the phase transition in grain
structure from austenite to martensite. The
austenite alloy undergo a transition in initial
structure in response to stress without requiring a
significant temp: change. ( TTR – room temp )
Niti’s unloading curve differs from its loading
curve because of energy loss associated with it –
hysteresis. Force delivers is not same as force
applied to activate it.
Martensite phase resembles elastomers
& austenite phase resembles S.Swww.indiandentalacademy.com

H1
H2
C3
C2
C1
Temp:
Energy The transformation from austenite to martensite
and its reverse does not take place in same temp:,
this difference is called hysteresis.
Brantley 2nd
Ed

Normally TTR of niti is too elevated to respond to
the body temp & so more complex metals are so
to that the TTR can be lowered to as much as
-200o
c.
Fe, Al, Co, Cr, etc may be added to increase the
stiffness of the alloy. For thermally activated
purpose Cu & Co may be added to so that they
bring down the TTR close to oral temp:
Vanarsdall 4th
Ed

The addition of Cu helps in easier engagement of
the wire and deliver higher forces while the
addition of Carbon improves spring back property
of the wire.
Dissolve interstitial elements may disrupt the
structural matrix. Oxygen forms a Ti4Ni2Ox
inclusion which lowers alloy elasticity.

1) Stabilized Nickel Titanium Alloys
2) Super Elastic Nickel Titanium
Alloys (active austenitic)
3) Thermodyanimic Nickel Titanium
Alloys ( active martensitic)
4) Graded Thermodynamic Nickel Titanium4) Graded Thermodynamic Nickel Titanium
(bioforce archwires)(bioforce archwires)
A) Chinese Niti Alloy wire
B) Japanese NiTi alloy wire
Copper Niti wire
5) Teflon Coated (Esthetic) Nitinol Archwires
TYPESOFNITI

1) STABILIZED NICKEL TITANIUM ALLOYS1) STABILIZED NICKEL TITANIUM ALLOYS
Andreasen and Hilleman (1971)
55 % nickel + 45 % titanium =
stabilized martensite crystal structure
JCO 1978www.indiandentalacademy.com

The stabilized martensitic alloy do not
possess shape memory or super elasticity,
because the processing of the wire creates a
stable martensitic structure.
Moderately high ultimate strength of 250,000
psi, with low modulus of elasticity at 4,800,000
psi. These give 'Nitinol' its good spring back or
working range.

2)2) Superelastic nickel titanium alloysSuperelastic nickel titanium alloys
(active austenitic)(active austenitic)
A) Chinese Niti Alloy wire
General Research Institutes
for Non-Ferrous metals
Beijing, China 1978
Dr. Tien Hue Cheng
AJO 1985 Burstone, Qin and Mortonwww.indiandentalacademy.com

It has more than 4.4 times the springback of S.S
wire and more than 1.6 times the spring back of
nitinol wire in all modes of deformation, tension,
bending and torsion.
It has lower transition temperature.
It exerts constant force regardless of the
amount of deflection. Deformation is not
particularly time-dependent and its efficient in
moving teeth into alignment from extreme
positions.

At 80° of activation the average stiffness of
Chinese NiTi wire is 73% that of stainless steel
wire and 36% that of nitinol wire.
Chinese NiTi shows low stiffness when large
deflections are needed and high stiffness at
small activations, which make it more effective
than wires of traditional alloys.

B) Japanese NiTi alloy wire (super elastic):
Fujio Miura et al in 1986
Furukawa electric Co. Ltd., of Japan in 1978
These have three main properties - Excel1ent
spring back, shape memory, and Super elasticity &
was the least likely to undergo permanent
deformation during activation.
1986 Jul Miura, Mogi, Ohura, and Hamanakawww.indiandentalacademy.com

The super elastic nature is because of their
crystal structures which are able to vary under
different environmental conditions. The material
is capable of phase transformation under
conditions of stress and temperature, and is
termed 'active' .
Because of super elastic nature its used as
aligning arch wire. super elasticity results from
stress induction during archwire ligation.

at room temperature - austenitic phase
with body centered cubic lattice structure
stress
Transformation into martensitic phase
with hexagonal close packed structure
S.I.M
When stress is diminished, returns to the
previous shape without retaining the permanent
deformation because of the characteristics of
returning to the austenite phase within a given
temperature range.
Mech: analogue of shape memorywww.indiandentalacademy.com

3)3) ThermodynamicThermodynamic Nickel Titanium AlloysNickel Titanium Alloys
( active martensitic):( active martensitic):
Heat treatment can result in different stress
level to initial phase transformation in niti wires.
Using heat treatment in vacuum condition,
manufacture are able to vary the percentage of
austenite present in room temp: there by changing
the degree of force delivery for identical
archwire dimension.

Scientist are able to control the transition
temperature (TTR) of nickel titanium alloys and
now it can be set around the internal
temperatures.
Incorporation of copper in the nickel-titanium
wire (copper-NiTi) increases the sensitivity to
changes in mouth temperature by allowing
greater precision in the setting of
transformation temperatures.

ligation of the malleable
martensitic archwire
reverts to its predetermined
ideal austenitic archform
body heat
increases the ratio of
austenite present
Thermodynamic
Shape memory
An active martensitic wire will deliver 25-30% of
the force / unit area.
Thermal analogue of shape memorywww.indiandentalacademy.com

Copper Niti wire:
Quaternary alloy
nickel, titanium, copper & chromium
Dr.Rohit Sachdeva in 1994
Orthodontic archwires fabricated from this alloy
have been developed for specific clinical
situations. These four alloys form the basis for
“Variable transformation temperature
orthodontics"

For very small activations, copper Ni- Ti
generates near constant force over a long
activation spans than other niti alloys.
Copper NiTi is more resistant to permanent
deformation, exhibits better springback
characteristics and a smaller drop in unloading
force than other nickel titanium alloys.

The addition of copper to nickel titanium
enhances the thermal-reactive properties of the
wire, thereby enabling the clinician to provide
optimal forces for consistent tooth movement.
Ormco offers three different Copper Ni-Ti
archwires with precise and consistent
transformation temperatures: 27°C, 35°C, and
40°C.

27°C Superelastic Copper NiTi – Round and
Rectangular
27°C Copper Ni-Ti generates forces in the high
range of physiological force limits and produces
constant unloading forces that can result in
rapid tooth movement.

27°C
Superelastic
Copper NiTi
35°C Thermo
Active Copper
NiTi
40°C Thermo-
Active Copper
NiTi
Low loading
force
Low loading
force
Low loading
force
Unloading forces
are high
Unloading force
are high &
sustained
Unloading force
are intermittent

35°C Thermo Active Copper NiTi – Round,
Rectangular and Square
35°C Copper NiTi generates mid-range constant
force levels when the wire reaches mouth
temperature. Early ligation is easier with full-
size archwires due to the lower loading forces.
Unloading forces are higher and more sustained
than other shape memory wires when the wire
reaches body temperature.

40°C Thermo-Active Copper NiTi –
Rectangular
40°C Copper Ni-Ti provides intermittent forces
that are activated when the mouth temperature
exceeds 40°C. It is useful as an initial wire and
can be used to engage severely malaligned teeth
(such as high cuspids) without creating damaging
or painful levels of force or unwanted side
effects. It is also the wire of choice for
patients scheduled for long intervals between
visits when control of tooth movement is a
concern.

Copper Ni-Ti demonstrates a smaller loading
force for the same degree of deformation,
making it possible to engage severely malposed
teeth with less patient discomfort and potential
for root resorption.
The decreased hysteresis and flatter unloading
curve result in more consistent forces that are
active longer within the optimal range for tooth
movement.

As copper is an efficient conductor of heat,
Copper Ni-Ti demonstrates consistent
transformation temperatures that ensure
consistency of force from batch to batch.
This equates to consistent effectiveness in
moving teeth.

GRADED THERMODYNAMIC NICKELGRADED THERMODYNAMIC NICKEL
TITANIUM (BIOFORCE ARCHWIRES)TITANIUM (BIOFORCE ARCHWIRES)
4)4)
The response of a tooth to force application and
the rate of tooth movement is dependent on the
amount of a constant and low force with the area
of periodontium involved.
Bioforce archwire is able to produce variation in
archwire force by variable transition of
temperatures within the same archwire.

This graded force delivery within the same
aligning archwire providing light forces of
approximately 80g anteriorly, and a heavier force
of 300g posteriorly.
The level of force applied is therefore graded
throughout the arch length according to tooth
size.

TEFLON COATED ( ESTHETIC ) NITINOLTEFLON COATED ( ESTHETIC ) NITINOL
ARCHWIRES:ARCHWIRES:
5)5)
There has been a continuing search for materials
that are esthetically acceptable to help improve
the smile of orthodontic patients.
The coated wires currently available basically
consist of a parent wire, which is either stainless
steel or nickel titanium alloy, on which organic
coating is placed.
Teflon - PUNKEIT (1938) USAwww.indiandentalacademy.com

These wires are available in standard sizes and in
round or rectangular shapes. The introduction of
a coating material on to the parent wire could
significantly alter the force delivery
characteristics.
Advantages:
Esthetics & Low friction between Teflon and the
bracket, which enhances sliding mechanics.

Surface treatment of the wire is essential to
improve the adhesion of the coating. The
resultant cosmetic wire is therefore a composite
of two materials that individually have diverse
physical properties.
The size of the parent wire, for a given slot size
is less, to accommodate for the thickness of the
coating. Surface treatment of the wire is
essential to improve the adhesion of the coating.

Advantage of niti wire over the other types when
used in case of a malalignment arch form is that,
the more the wire has to deflect from the ideal
arch form when ligated into the bracket; the
greater benefit niti wire has over stainless steel
wire.
CLINICAL IMPLICATIONS OF NITI:CLINICAL IMPLICATIONS OF NITI:

The important benefits from niti wire is, when a
rectangular wire is inserted early in treatment
simultaneous rotation, leveling, tipping and
torquing can be accomplished earlier with a
resilient rectangular wire, such as nitinol.
Nitinol wire can be used in class I, II or III
malocclusion, in both extraction and non-
extraction cases.

Turbo Wire is a nine-strand rectangular braided
Ni-Ti, with low stiffness and great flexibility.
Turbo Wire is recommended as an initial wire to
unravel and level while controlling torque
and engaging brackets fully.
It is also effective as a finishing wire, retaining
torque but allowing vertical elastic use.

Align nickel titanium archwires are available in
two popular arch forms, Tru-Arch and Damon.
The Align archwires come with the option of a
permanent midline “dimple.” This vertical dimple
prevents archwire “walking” and eliminates the
need to cinch the archwire behind the buccal
tube.

Niti wires facilitate and simplify Beggs, because
unraveling and leveling to attain good tooth
alignment occurs faster than with s.s looped
arches & so treatment time is diminished.
Nitinol archwires were 25% faster for rotation or
aligning and leveling. Also no need to change the
archwire in stage I.
Patient response is good and less discomfort is
reported.

AJO 1996 Jan Clemens and Walter
NiTi coil springs are used extensively in today's
orthodontics. Niti spring offers a low constant
force delivery in relation to time of use and
activation and achieves rapid space closure.
Closed coil springs are used for space closure
and distalization of impacted canines.
Opening coil springs are mainly used for opening
spaces to unravel the teeth or for the
distalization of the molars.

Distalization of
impacted canines
opening spaces for
the distalization
of the molars

Nickel titanium coil springs can be used for
partially impacted second molars.
JCO 2003 Aksoy, Aras

Niti Connecticut Intrusion Arch (CTA) is used
for absolute intrusion of anterior teeth. It has
many other applications, including molar tipback
for Class II correction, correction of minor open
bites, leveling of anterior occlusal cants, and
finishing.
When the arch is activated, a simple force
system results, consisting of a vertical force in
the anterior region and a moment in the
posterior region
JCO 1998 Nanda, Marzban, Kuhlberg

Intrusion of
anterior teeth
Leveling of anterior
occlusal cants
Molar tipback for
Class II correction

The CTA’s basic mechanism for force delivery is a
V-bend calibrated to deliver approximately 40
-60g of force. Upon insertion, the V-bend lies just
anterior to the molar brackets.
About 1mm of intrusion can be expected every 6
weeks. It is important to use headgear to
counteract side effects on the molars and correct
molar root positions as needed.
Two wire sizes - .016x.022 and .017x.025

Nickel titanium double-loop system can be used
for simultaneous distalization of molars.
Superelastic nickel titanium wires have been
found as effective as other means in producing
distal movement of the maxillary first molars.
When the distalization is carried out before the
second molars have erupted, it can reliably
produce 1-2mm of space.
JCO 1998, 35 : 4 (255-260) Giancotti, cozza

The .018" nickel titanium stop for prevention of
archwire crawl.
Stops crimped on niti archwire
distal to central incisor
brackets. Rectangular tubes cut
in half to make 2.5mm stops.
JCO April 1999 John J. Baccelli
Midline bend in niti archwire
helps reduce archwire crawl

Slow maxillary expansion with niti.
The TTR of niti at room temperature is 94°F. The
expander is too stiff to bend for insertion.
Chilling the expander softens the central
component, allowing easy manipulation. Once
placed, the expander warms to body temperature,
stiffens, and begins to return to its original
shape.
3mm of expansion -350g of force
JCO August 1999, Nanda

Nitinol total control: A new orthodontic alloy.
JCO October 1999 Thayer, Fox
A new pseudo-superelastic nickel titanium
Alloy - Nitinol Total Control, accepts specific
1st
, 2nd
, and 3rd
order bends while maintaining
its desirable superelastic properties. NTC
combines the ability of superelastic niti to
deliver light, continuous forces over a desired
range with the flexibility required to account for
variations in archform.

NTC 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, NTC
allows the clinician to treat more patients
effectively and efficiently.
Because of NTC’s relatively low stiffness, it
should not be used for space closure. NTC’s
properties are not temperature dependent.

If greater degree of tipping is present after
retraction, in case of an 018 slot a 17x25 niti wire
may be used initially to obtain proper root
movements and to attain final root position.
In case of a 022 slot a 21x25 niti wire is used
initially, followed by beta-ti for finishing.
In edge wise mech: where brackets have a built in
torque, tipping of incisors can be prevented
during space closure by using a full size niti wire.

In case if brackets are poorly positioned, during
the final stages of treatment, true inclinations
are not attained and so brackets have to be
repositioned and a flexible 21x25 M-Niti wire is
required (022 slot) for proper root positioning.

ADVANTAGES OF NITI:ADVANTAGES OF NITI:
The most advantageous properties of nitinol are
the low load deflection rate, good springback
and flexibility, which allow for large elastic
deflections.
Nitinol wire has a low modulus of elasticity that
gives it wide range and flexibility and its
resistances to deformation.

O.18 NiTi would engage the rotation wings better
and there will not be any distortion of the wire as
S.S.
Early bracket engagement with rectangular Nitinol.
Early / rapid alignment, and rotation & leveling of
the arches.
Dr. Creekmore Thomas D, AJO 93 julwww.indiandentalacademy.com

It is very efficient for bracket-to-bracket
leveling in preparation for the final leveling and
finishing archwire.
You can recycle & no breakage problem in
patient’s mouth.
The .016 Nitinol wire is very flexible with a long
working range and produces very little patient
discomfort either initially or on activation.

DISADVANTAGES OF NITI:DISADVANTAGES OF NITI:
Nitinol cannot used for major corrections of
torque, root paralleling or closing of extraction
spaces as reasonable amounts of stiffness cannot
be accomplished with Nitinol.
Leveling curve of spee and moderate torque is
difficult to accomplish with Nitinol.

You can not use intramaxillary elastics with
Nitinol wire as wire is not stiff enough to hold a
good arch form and prevent unwanted tipping
adjacent to extraction sites.
Have poor formability and so cannot bend loops &
stops.

Does not really produce a 2nd & 3rd order bends,
might have to overprescribe to obtain the desired
bend .
The major disadvantage of the wire is its
limitation of adjustment. In orthodontics putting
a preformed wire and expecting the teeth to
assume some exact preset positions is not true.

The association of different metals in the oral
environment, where saliva is the connecting
medium may produce electro galvanic currents
which results in discharge of ions and metallic
compounds.
Masticatory forces may also produce a discharge
of these ions as a result of wearing restorations.
These products may be swallowed or may become
attached to the mucosal or dental surfaces.
NICKEL HYPERSENSITIVITY:NICKEL HYPERSENSITIVITY:

The discharge of nickel ions, which is a strong
immunologic sensitizer, may result in contact
hypersensitivity.
It is estimated that 4.5% to 28.5% of the
population have hypersensitivity to nickel, with a
higher prevalence in females.
A high association between the allergic reaction
to nickel and personal history of allergy was also
observed, evidencing an early manifestation of
this reaction in subjects with hypersensitivity to
this metal.
AJO 1998 Junwww.indiandentalacademy.com

Most causes for nickel allergies have been
attributed to dermatologic exposures to these
metals or to compounds containing these metals.
Pierced earrings, occupational exposures,
wristwatches, detergents, jewelry, etc have been
found to be responsible for a significant number
of nickel hypersensitivity cases in both men &
women.

Patch testing for nickel allergy:
The most frequently used method. False negative
reactions have been reported.
Should not be used indiscriminately since these
tests may induce sensitivity in persons who
before testing were not sensitive.

Normal blood concentrations for nickel have been
reported to be between 2.4 ± 0.5 mg/ml.
The primary route for elimination of absorbed
nickel from the body is through the urine.
According to Silness and Löe, gingival and plaque
indices can also be measured for the amount of
inflammation as displayed by clinical features
such as bleeding, edema, and hypertrophy.

Nickel carcinogenicity:
Nickel induced carcinoma have occurred from
occupational exposures to inhaled metal
compounds. The primary tumor locations are the
lung and the nasal mucosa. Not all nickel
compounds have carcinogenic potential. The
average latency period from the time of exposure
to the development of cancer has been reported
to be between 20 and 25 years.
AJO 1993 Feb

Symptoms of allergic reactions from Ni included
severely inflamed hyperplastic gingival tissue,
alveolar bone loss and edema of the throat,
palate, & gums.
In addition, osteomyelitis was reported when
stainless steel bone fixation wires were used in
the jaws of a patient who was sensitive to nickel.
Nickel allergy reactions to orthodontic appliances
have been reported after the use of facebows
and also after the insertion of nickel-titanium
orthodontic arch wires.

Why is it that persons with marked sensitivity
to nickel do not manifest any intra oral
reaction?
Perhaps higher concentrations of nickel are
necessary to elicit an intra oral reaction.
Spiechowicz attempted to explain the lack of an
intra oral response by four different
mechanisms.

1. Formation of salivary glycoprotein films that
act as diffusion barriers.
2. Differences in the permeability of the skin
and the oral mucosa.
3. Cellular hypersensitivity mechanisms differ
between the skin and the oral mucosa.
4. Differences in the distribution and function
of Langerhans cells.

Orthodontic appliances used in their "as-
received" condition corrode in the oral
environment releasing nickel, but in amounts
significantly below the average dietary intake.
Furthermore, the biodegradation of orthodontic
appliances during the initial 5 months of
treatment does not result in an increase in the
blood level of nickel in patients undergoing
orthodontic treatment.
CORROSION BEHAVIOUR OF NITINOLCORROSION BEHAVIOUR OF NITINOL
WIRES :WIRES :

The corrosion behavior of Niti wires was
compared with s.s, cobalt - chrome and B-titanium
by Sarkar et al (1979). The wires were exposed to
a 1% Nacl solution via an electrochemical cyclic
polarization technique.
SEM and energy dispersive X-ray analysis was
used to determine differences between pre and
post polarized surfaces. The Nitinol alloy
exhibited a pitting type corrosion attack.

Nicholson James A. (1983), examined the effects
of corrosion and stress on the mechanical
properties of Nitinol. This study suggests
clinically that, orthodontists who attempt to
reuse Nitinol wires may face a decrease from the
expected mechanical properties of the wire.
Examination of the statistical and graphic
results indicates that this decrease occurred
gradually throughout the 4 months period of
investigation.

This change is evident by the fourth month, but
this does not make the wire unacceptable. It
merely means that a decreased performance may
be seen.
Interstitial oxygen causes NiTi alloy to become
susceptible to pitting and crevice attack of
halides such as salt sol:

RECYCLING & STERILIZATION:RECYCLING & STERILIZATION:
The relatively high cost of Nitinol wires and
their ability to return to their original form has
prompted many clinicians to recycle these wires.
This raises concern about the treatment of the
wires between patients for prevention of cross
infection.

Recycling involves repeated exposure of the wire
for several weeks or months to mechanical
stresses and elements of the oral environment,
as well as sterilization between uses.
The combined effects of repeated clinical use
and sterilization may subject the wire to
corrosion and cold working, with a resultant
alteration in its properties.

Heat sterilization is the most reliable method of
destroying pathogens on wires before reuse.
Schwaninger et al. noted that corrosion does not
affect the flexural properties of niti wires, some
reports indicate an increase in permanent
deformation and a decrease in elasticity of these
wires caused by corrosion or the cumulative
effects of cold working.
A.O 1991www.indiandentalacademy.com

Buckthal J.E et al & Kusy RP (1988) detected no
detrimental effects in the fundamental
stiffness or inherent strength of the wires
after multiple disinfectant cycles using three
disinfectants approved by the ADA i.e 2 %
acidic gluteraldehyde, chlorine dioxide and
Iodophor on straight lengths of Nitinol
archwires. Besides there was no additional
surface pitting or corrosion as assessed by
laser-spectroscopy was detected.

Mayhew & Kusy (1988) examined the effects of
dry heat, formaldehyde - alcohol vapor and
steam autoclave sterilization on the mechanical
properties and surface topography of niti
archwires.
After sterilization, the elastic modulus and
tensile properties were determined for Niti
wire. Laser scanning was employed to detect
surface alterations caused by tarnish, corrosion
or pitting.
No detrimental effects were noted, and the niti
archwires maintained all their properties.

Effects of dry heat sterilization:
Dry heat sterilization produced significant changes
in the loading and unloading forces associated with
NiTi wires.
The mean forces on loading and unloading of Niti
wires after two cycles of DHS were greater than
those required to deflect the normal wires and
wires subjected to one cycle of sterilization. These
differences in force levels were primarily seen in
the 1 to 2 mm range of deflection for both loading
and unloading.

Effects of clinical recycling
The mean forces on loading and unloading of Niti
wires after one cycle and two cycles of clinical
use and DHS were significantly greater than
those associated with normal wires. The
increased levels of forces in recycled wires as
compared with normal wires were noted primarily
between 1 and 2 mm on loading, and from
approximately 2.0 to 0.4 mm on unloading.

• Requires fewer archwire changes.
• Requires less chair side time.
• Produce less patient discomfort.
• Shortens the treatment time required to
accomplish rotations and leveling.
Conclusion:Conclusion:
Niti orthodontic wire has been evaluated by both
clinicians and researchers and the results have
been quite similar. We can concluded that during
long term orthodontic application NiTi :

So when applied with skill and professional
judgment, Niti archwire represents a significant
improvement over conventional orthodontic
archwire and is a valuable addition to the
orthodontist's armamentarium.

THANK YOUTHANK YOU

27°C Superelastic Copper NiTi – Round and
Rectangular
27°C Copper Ni-Ti generates forces in the high
range of physiological force limits and produces
constant unloading forces that can result in
rapid tooth movement. Engagement force is
lower than with other superelastic wires
because of the lower loading forces built into
the copper alloy; at the same time, unloading
force levels are comparable to traditional
superelastic nickel titanium wires.

NITI wires

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