The intelligent archwire

Introduction
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.
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•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,
tissue hyalinization and undermining
resorption.

Evolution of NI-TI alloys
Buehler’s preliminary results led to
the development of the first Ni-Ti
orthodontic alloy by pioneers such as
ANDREASEN and his colleagues.
The engineering of nickel- titanium
alloys has made remarkable progress
since the original work of BUEHLER
for the Naval Ordinance Laborotory
in the early 1960’s.

Further research led to the advent of
Superelastic and Thermodynamic Ni-Ti
alloys.
• Chinese Ni-TI – the General Research
Institute for Non-ferrous Metals – Beijing.
• Japanese Ni-TI – the Furukawa Electric
Company Ltd – Japan.
• Copper Ni-Ti – Rohit Sachdeva.
These more advanced alloys have different
transition temperatures and present a phase
transformation.www.indiandentalacademy.com

Wire characteristics & clinical
relevance.
• Several characteristics of orthodontic wires are
considered desirable for optimum performance
during treatment.
• These include a large springback,low
stiffness,high formability,high stored
energy,biocompatibility and environmental
stability,low surface friction and the capability to
be welded or soldered to auxiliaries and
attachments.

Atomic structure of Ni-Ti
The crystallographic,tri-dimensional lattice of the
ni-ti alloy is present in 2 phases:
Martensite phase:the lattice is body-centered
(cubic or tetragonal)
Austenitic phase: the lattice is face –centered
(hexagonal close packed)
An intermediate rhombohedral ‘R’phase with a
simple hexagonal lattice has also been identified.

• Ni-Ti alloys has a specific temperature
range in which the phase transition takes
place from the austenite to the martensitic
phase(reversible change) and this TTR
contributes to the shape memory effect of
Ni-Ti alloys.
• Shape memory is a phenomenon whereby
the alloy is soft and readily formable at a
low temp.,but can easily be returned to its
original configuration when heated to a
suitable TTR.

…An interesting feature of shape
memory
• Through deflection and repeated temp. cycles, the
wire in the austenitic phase is able to “memorize”a
preformed shape.
• By lowering the temp.,the alloy is transformed
into martensite and becomes pliable and easily
deformed.
• However, every time the temp. rises above
austenitic phase,the wire will remember and
recover the ideal arch-form.

• Superelasticity is a phenomenon where in
the stress remained nearly constant despite
the strain change within a specific range.
• This allows a constant force to be delivered
over an extended portion of the deactivation
range,and is therefore more likely to
generate physiologic tooth movement and
greater patient comfort.

Pseudoelasticity –stress-related
behavior of Ni-Ti
• The deflection in an austenitic archwire at oral
temp. generates a local martensitic transformation
and produce stress induced martensite-SIM.
• SIM is unstable and undergoes reverse
transformation as soon as stress is removed.
• In clinical application SIM forms where the wire
is tied to brackets on misaligned teeth so that the
wire becomes pliable ,with seemingly permanent
deformation.

Cu Ni-Ti…Advancing towards
ideal archwire
• Cu Ni-Ti alloy wire
represents a major
advancement in shape
memory wires by
reducing hysteresis
and by providing
precise transformation
temperature at four
different levels.

Role of Copper :-
• Cu enhances the thermal reactive properties
of Ni-Ti alloys thus providing equal loading
(engaging) and unloading (tooth driving)
forces.
• Cu gives precise control of the
transformation temperature.
• Cu produces lubricants to the system and
decreases friction.

Recycling of Ni-Ti
Recycling involves
• Repeated exposure of the wire for several
weeks or months to mechanical stresses and
elements of the oral environment
• Sterilization between uses

Advantages of Ni-Ti
Fewer archwire changes
Less chair side time
Reduction in time required to accomplish
rotations and leveling
Less patient discomfort

Limitations to use of Ni-Ti
Poor formability
Fractures readily when bent over sharp edge
and effects springback property
Bending loops and stops in ni-ti is therefore
not recommended.(cinch-backs can be
obtained by flame –annealing the end of
wire)

…and to conclude
In contempory practice no one
archwire material meets all ideal
requirements and the best results are
obtained by using specific archwire
material for specific purposes

The intelligent archwire

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