Nickel titanium in orthodontics /certified fixed orthodontic courses by Indian dental academy

Nickel Titanium in Orthodontics

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Ni Ti alloy was discovered in early 1960s
by William F. Buehler, a research
metallurgist at the Naval Ordnance
Laboratory in Silver springs, Maryland.
key discovery occurred in 1962, when a
binary alloy composed of equi-atomic
nickel and titanium was found to exhibit a
shape recovery effect when heated after
being mechanically deformed.


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


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

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

This alloy has low elastic modulus and high
range

The nickel-titanium wires contain approximately
equiatomic proportions of nickel and titanium,
and are based upon the intermetallic com-pound
NiTi (sometimes written as TiNi).
Examination of the binary phase diagram
reveals that some deviation from stoichiometry
is possible for NiTi.

BASIC CONCEPTS ABOUT NICKEL
TITANIUM ALLOYS
1. 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.


AUSTENITE :High temperature phase of Nickel titanium alloys is
called Austenite . Like many ferrous alloys this austenite
can transform to Martensite. It has got Body centered
cubic (BCC) structure. It is the stronger, higher
temperature phase present in NiTi.
MARTENSITIC TRASFORMATION :Process
of
phase
transformation
which
is
DIFFUSIONLESS, occuring from within and without any
chemical change which results in transformation of
Austenite (parent phase) to Martensite following rapid
cooling. It has got distorted monoclinic, triclinic or HCP
structure More deformable, lower temperature phase
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 a
reversible Bain transformation [a
rearrangement of atoms in the new
phase], which is responsible for the
alloy’s “Shape Memory” and
Superelasticity, properties that derive
from the twinning-detwinning
mechanism.

When these alloys are
subjected to higher
temperature.
⇓
DETWINNING
OCCURS
⇓
Alloy reverts to its original
shape.
(SHAPE
MEMORY EFFECT).


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

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


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


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


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

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


Superelasticity: The springy, “rubber like”
behaviour present in NiTi shape Memory
Alloys at temperatures above the Af
temperature. The superelasticity arises
from the formation and reversal of stress
induced martensite.
Md: It is the highest temperature at which
martensite formation can be induced by
stress.

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


Stress strain diagram of alloy with
superelastic behaviour

This means the
force that it delivers is
not the same as the
force applied to
activate it.


The different loading
and unloading curves
produce the even
more remarkable
effect that the force
delivered by an ANITI wire can be
changed during
clinical use merely by
releasing and retying
it .

Activation (to 80 degrees) and
reactivation
(to 40 degrees) curves for A-NiTi wire.


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

Stainless steel

Nickel Titanium


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


Hysteresis
There is a difference in the transformation
temperatures upon heating from martensite to
austenite and cooling from austenite to
martensite, resulting in a delay or “lag” in the
transformation.
This difference known as the transformation
temperature hysteresis, is generally defined as
the difference between the temperatures at
which the material is 50% transformed to
austenite upon heating and 50% transformed to
martensite upon cooling.

For NiTi Alloys, the difference between Mp
and Ap is 25-50°C.

Thus Nitinol transformations exhibit
thermal hysteresis, Ms ≠ Af and Mf ≠ As.


In addition to the hysteresis, the overall span of the
transformation may be important. Typical values for the
overall transformation temperature span are about 4070°C.
Both the hysteresis and the overall transformation
temperature span are slightly different for different NiTi
alloys. Further, alloying can greatly affect the
transformation hysteresis. Copper additions have shown
to reduce the hysteresis to about 10 to 15°C and
Niobium additions can expand the hysteresis over
100°C. ( Santaro AJO 2001)


Austenite and Martensite have different
crystal structure and mechanical
properties the most notable mechanical
properties of Nitinol wires i.e
superelasticity and shape memory are
result of reversible nature of Martensitic
transformation


Martensitic transformations do not occur at a
precise temperature but rather within a range
known as temperature transition range(TTR).
Range for most binary NiTi alloys → 40° - 60° C.
Transformation from Austenite to Martensite can
occur by.
→
Lowering the temperature.
→ Applying stress (Stress induced Martensite)
SIM.


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

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

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


Shape Memory is a
Combination of
Thermoelasticity and
Pseudoelasticity


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

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


Martensitic-active alloys - employ the
thermoelastic effect to achieve shape memory;
the oral environment raises the temperature of
the deformed arch wire with the martensitic
structure so that it transforms back to the
austenitic structure and returns to the starting
shape.

The clinician can observe this thermoelastic
shape memory if a deformed archwire segment
is warmed in the hands. These are the shapememory wire alloys such as Neo Sentalloy and
Copper Ni-Ti.

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

Nickel Titanium Wires
CONVENTIONAL NITINOL - Original alloy
- 55% Nickel, 45% Titanium ratio of
elements.
To modify mechanical properties and
transition temp. 1.6% Cobalt was added to
it


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

PROPERTIES
1. Springback and Flexibility
Most advantageous properties of
Good Springback and Flexibility.
Low force per unit of deactivation –
stiffness.

Nitinol are
that is low

Nitinol wires have greater springback and larger
recoverable energy than Stainless Steel or β-Ti
when activated to same extent. High spring back
is useful in circumstances that require large
deflections but low forces.
Delivers 1/5th – 1/6th force per unit of deactivation

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

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


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


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

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

CLINICAL APPLICATIONS:
Levelling and Aligning:
Nitinol wire is much more difficult to deform during
handling and seating into bracket slots is easier than
Stainless Steel arch wires.
- Reduces loops formerly needed to level dentition.

- Can be used for longer periods of time without changing.
-


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

Bite
opening
using
RCS. (Reverse Curve
of Spee)


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


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


Conventional Nitinol is available as
Nitinol
classic
Unitek
corporation.
- Titanal
Lancer pacific.
Orthonol
Rocky
mountain
orthodontics.


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


This group is also referred to as A-NiTi.
This group includes :
-      Chinese NiTi.
-      Japanese NiTi (Sentinol)
-      27°C superelastic Cu-NiTi.
In Austenitic active alloy both Martensite
and Austenitic phases play an important
role during its mechanical deformation

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


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


Af (Austenitic finish) of these alloys is below mouth
temperature.
                                ⇓
•      Formation of SIM is reversible when stress is
reduced.
•      These alloys cannot be easily cooled down
below their Ms.
                                ⇓
Do not display clinically useful shape memory

To exploit superelasticity to its fullest potential
the working temperature of orthodontic
appliances should be greater than the A f
temperature.
• It is the differential between Af temperature and
mouth temperature that determines the force
generated by NiTi alloys.
Af can be controlled over wide range by affecting
composition, thermomechanical treatment and
manufacturing process of alloy

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

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


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


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

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

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


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

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


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

CHARACTERISTICS
OF
AN
IDEAL
THERMODYNAMIC NITINOL WIRE:
1. Dead soft at room temperature so that it can
be tied easily.
2.

Instantaneously activated by heat of mouth.

3.

Able to apply clinically acceptable orthodontic
forces.


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

Thermoelastic Nitinol – formable at ice water temperatures.
⇓
Ice water is below Ms of thermoelastic wires
⇓
Martensite while engaging
When warmed above Af by mouth temp.
⇓
Transformation is reversed to from Austenite
⇓
Wire returns to its original shape thus displaying shape
memory.


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

Chromium : to compensate for the above
mentioned unwanted effect 0.5%
chromium is added to return TTR close to
oral temperature


TYPES OF CU-NITI:
1. Type I
Af 15°C.
2. Type II
Af 27°C
3. Type III
Af 35°C
4. Type IV
Af 40°C


Chill Spray
Facilitates adjustments or
fitting of Ni Ti orthodontic
archwires,
springs,appliances, etc.
Ideal for Niti Memory
Expanders and Rotators
such as the Tandem
Loop Arndt Memory
Expander and Arndt
Memory Rotator.
Chills to -620º F/-520
ºC.... puts Niti into its soft
martensitic state

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

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

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

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

Similar manufacturing procedures have been
perfected to produce wires such as Bioforce
Sentalloy (GAC) that are able to deliver selective
forces according to the needs of the individual
dental arch segments

BioForce (GAC) offers 80 grams of force for
anteriors and up to 320 grams for molars


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

The IONGUARD process actually alters the wire’s
surface to provide a dramatically reduced
coefficient of friction for sliding mechanics that
are better than the same size stainless steel wire
and half the friction of competitive NiTi wire.
It also seals the occlusal surface of the wire to
eliminate breakage and reduce nickel leaching.
While the IONGUARD process alters the surface
of the wire, none of the wire’s unique properties
is changed.


Nitinol Total Control .A new
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.
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 .

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

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


HU-FRIEDY’S Hammerhead NiTi Tie Back
Plier
Reduce a multi-step
process down to one,
simple squeeze — no
heat required
Bends NiTi wire
intraorally with no heat
treating
Designed to tie back NiTi
distal to the buccal tube,
gabel bends, omega
loops

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


The pliers are
available in a set of
two, featuring a long
and thin design to
reach behind the
molar tube for easier
cinch-back purposes
and wire activations in
the four mouth
quadrants.

Recycling & Sterilization of Nickel Titanium
Archwires

Recycling of nitinol wires is often practiced
because of their favorable physical
properties and the high cost of the wire.
The ability to recycle these archwire relies
on effective sterilization of the wire prior to
re-use without resulting in deterioration of
clinical properties.

For effective sterilization, steam autoclaving
(ideally at 134ºC, 32 psi for 3 minutes) is
the method recommended.

For instruments unable to withstand
autoclaving, an effective cold disinfection
solution such as 2% glutaraldehyde is an
alternative.

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

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


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


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

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

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

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

Clinical Performance
Evans et al (1998) clinically evaluated three
commonly used orthodontic tooth aligning arch
wires: 0.016 x 0.022 inch active martensitic
medium force nickel titanium, 0.016 x 0.022 inch
graded force active martensitic nickel titanium ,
and 0.015 inch multistrand stainless steel. It was
a prospective randomized clinical trial
Heat activated nickel titanium arch wires failed to
demonstrate a better performance than the
cheaper multistrand stainless steel wires in this
randomized clinical trial.

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


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


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

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


Coil Springs With Eyelets
Adjustable force and
superelastic closed
coil springs are
available with eyelets.
These stainless steel
eyelets attach to each
end of adjustable
force or superelastic
closing (closed coil)
springs.

This allows to easily
engage a bracket hook,
sliding hook, buccal
tube hook and/or posted
arch wire hooks


Place one eyelet over
the distal hook and
gripping the leading
edge of the front
eyelet with pliers, pull
gently forward to
engage your anterior
hook.


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


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

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

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


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

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

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


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


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


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

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

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

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

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


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

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

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

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


When the appliance begins to stiffen in the
mouth, it may cause some discomfort at first.
The patient can alleviate this by sipping a cold
liquid, which will temporarily make the nickel
titanium slightly more flexible. Many of my
patients have delighted in showing this effect to
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 distalization
Superelastic NiTi wire: Locatelli et al (1992) used a 100
gm NeoSentalloy wire (superelastic Nickel-titanium wire)
with shape memory for molar distalization .
Crimp stops just distal to first premolar bracket are
placed 5 – 7 mm distal to anterior opening of molar tube
and hooks between lateral incisors and canines.
Excess wire is deflected gingivally into buccal fold. As
wire returns to original shape, it exerts 100 gm distal
force against molars.


Super elastic 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.

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

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


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

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

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


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


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


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


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


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


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

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


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

Generally it has been shown that intra oral
exposure of Ni Ti wires alter the topography &
structure of the alloy surface through surface
attack in form of pitting, crevice corrosion, or
formation of integuments.
Retrieved Ni Ti wires demonstrated signs of
corrosion after more than 2 months of in vivo
placement.
Signs of pitting corrosion have been detected in
retrieved wires after at least 6months exposure.

Adsorption of intraoral integuments might greatly
reduce the coefficient of friction ( salivary protein
adsorption, plaque accumulation) .
Alternatively calcified integuments might
increase surface resistance & resistance to
shear forces.
Also intraorally exposed Ni Ti wires do break
more frequently than expected : Variations in
intra oral temprature might affect their properties
& fracture resistance.


Also the force delivery of superelastic coil
springs can be substantially affected by
small changes in temprature.


CONCLUSION
Properties of Nickel Titanium alloy have
made them preferred material in
Orthodontic treatment.
However their use should be done
keeping all treatment goals in mind.


References
Denny JP, Valiathan Ashima, Surendra Shetty
V : Wires in orthodontics. JIOS : 1993;24:6065.
Kapila Sunil, Sachdeva Rohit: Mechanical
properties and clinical application of
orthodontic wires. AJODO 1989; 96:100-109.
Miura, F.; Mogi, M.; and Ohura, Y.: Japanese
NiTi alloy wire:Use of the direct electric
resistance heat treatment method, Eur.J.
Orthod. 10:187-191, 1988.

Theodore Eliades, Christopher Bourauel : Intra
oral aging of Orthodontic materials: the picture
we miss & its clinical relevance. AJODO
2005,127 ; 403-412.
Brantley WA, Eliades T.: Orthodontic
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York: Thieme;2001. Page – 80 - 103
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super-elastic property of the Japanese NiTi
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Andreasen GF, Hilleman TB: An evaluation of
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Andreasen GF, Morrow RE.: Laboratory and
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Waters NE: Orthodontic products update.
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Kusy RP : Nitinol alloys: so, who’s on first?
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Hurst CL, Duncanson MG Jr, Nanda RS,
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orthodontic wires. AJO 1990; 98: 72-76.

Santoro M, Nicolay OF, Cangialosi TJ.:
Pseudoelasticity and thermoelasticity of nickel
titanium alloys: A clinically oriented review.
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Segner D, Ibe D.: Properties of superelastic
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treatment. EJO 1995; 17:395-402
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West AE, Jones Ml, Newcombe RG. : Multiflex versus
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trial of aligning archwires. EJO 1990; 12:380-384.
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nickel titanium archwires. Angle Orthod 2002; 72:302309.


Agaoglu G, Arun T, Izagu B, Yarat A: Nickel
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Kim H, Johnson J: Corrosion of stainless
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Eliades T, Eliades G, Athanasiou AE, Bradley
TG: Surface characterization of retrieved NiTi
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Buckthal, J.E. Mayhew, M.J. Kusy, R.P.
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Buckthal, J.E. and Kusy, R.P: Effects of cold
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WatanakeL G: Effects of clinical recycling on
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Puneet Batra,Ritu Duggal, Hari Prakash:
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Arndt WV: Nickel Titanium Palatal expander.
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Gianelly A , Bednar J, Dietz V.S.: Japanese Ni Ti
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1991,99;564-566.
Jebby Jacob, H.S. Divakar Karanth,
K.Sadashiva Shetty : Force characteristics of
NiTi open & closed coil springs in a simulated
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