General properties of orthodontics wire

1. General Properties of Orthodontic
wire
Guided BY:
• Prof.Dr. Hemant kumar Halwai
• Assist .Prof. Dr kishor Dutta
• Assist .Proff. Dr. Sandeep Gupta
Presented by:
Dr. Madhurendra Prasad
Sah
Junior Resident(1st year)
Orthodontics and
Dentofacial Orthopedics

2. Content
• Introduction
• Atomic arrangement
• Mechanical properties
• Work hardening
• Heat treatment
• comparsion different properties of
orthodontic wire
• Refernces

3. Introduction
• The fundamental knowledge in relationship
between composition , structure, properties is
necesssary to understanding of orthodontic
material .
• commonly used material are metallic , cerami
, polymeric material etc

4. Atomic arrangements for metallic
materials
In general, materials can be subdivided into
two categories according to their atomic
arrangements.
• crystalline material
• Non crystalline material

5. • There are seven crystal systems, with
lattice parameters
• Inherently, a space lattice is a geometric
construct wherein each point has identical
surroundings.
• Crystal structures of real material are
based upon space lattices, where there is
a single atom or a group of atoms at each
space lattice point.

7. • The hexagonal close-packed (hcp) structures
can be considered as formed from two
interpenetrating simple hexagonal structures.
• Pure metal used for orthodontic achwire and
bracket have following space lactice
fcc Fe(above~910degree celsius) Ni
bcc Fe ( below ~910 degree celsius and above
~1400 degree celsius)
Cr, Ti ( above~880degree celsius)
hcp Co ,Ti ( below ~880 degree celsius)

8. • nickel and chromium have body centered
cubic and face centered cubic structures,
respectively, all temperatures below their
melting points, iron and titanium have
crystal structures that depend upon
temperature.
• The different crystal structure of a given
metal are called polymorphic or allotropic
form

10. Mechanical properties
Stress
stress is the internal distribution of the load
,defined as force per unit area.
stess= force/area
It can be expressed as pasacal
stress –tensile
-compressive
-shear

11. • Tensile stress: It is caused by a load that
tends to stretch or elongate a body
• compressive stress: if a body is placed
under a load to compress or shorten it.
• shear stress: It tends to resist the sliding
or twisting of one portion of a body over
another.

12. strain
• strain is the internal distortion produced by
the load ,defined as deflection per unit
length
• strain = change in length/original length
• Strain can be elastic or plastic depending
upon ability of material to regain the
original shape after removing the stress

13. Elastic properties
• Elasticity:
-Ability of the stressed material to return to it’s original form.
• Elastic limit:
- The greatest stress to which a material can be subjected
so that it will return to it’s original dimension when the
forces are released.
• Hookes law:
-Stress is proportional to strain within the proportional limit i.e
if the tensile stress is introduced into the wire,the resulting
strain is proportional to the increments of stress

14. • Proportional limit:
-Greatest possible
stress that can
be induced in a
material such
that stress is
directly
proportional to
strain.
-It is the point at
which the stress
strain curves
begin to bent

15. • Yield Strength - It is defined as the stress
at which a material exhibits a specified
limiting
deviation from proportionality of stress to
strain. It is a more practical indicator , at
which a plastic deformation of 0.1% is
seen
• Ultimate strength-it is the strength at
which the material fracture.

16. Modulus of elasticity
(young’s
modulus,elastic
modulus)
Modulus of elasticity describes
the relative stiffiness or rigidity of a
material ,which is measured by the
slope of elastic region of the strain-
stress graph.
• modulus of elasticity (E)=
stess/strain

17. • Stiffness-It is s a measure of resistance to deformation .it is
measure of force required to bend or otherwise deform the
material over a definite distance .Stiffness determines the
force acting on the tooth.
• Spring back -Condition that occurs when a flat-rolled metal or
alloy is cold-worked; upon release of the forming force, the
material has a tendency to return to its original shape
because of the elastic recovery of the material. Measure of
how far a wire can be deflected without causing permanent
deformation .
• Clinically significant spring back will occur beyond if wire is
deflected beyond the range .

18. • Springiness-proportional to the slope of
elastic portion of stress strain curve
• Stiffness and springiness are reciprocal
properties :springiness=1/stifness
• Springer the wire lower is the stiffness.

19. • Each is proportional to
the slope of elastic
portion of force deflection
curve , more horizontal
the slope ,the springier
the wire and vice versa
• i.e in springer wire
slight force cause large
deflection.

20. Resilience
• Itcan be defined as the amount of energy
absorbed within a unit volume of a stnlcture
when it is stressed to its proportional limit.
• Maximum amount of energy a material can
absorb without undergoing permanent
deformation.
• A highly resilient wire will be able to exert force
for larger range and sustain the activation for a
longer peroid of time.

22. Formability:
• it is the amount of permanent deformation
that a wire will withstand before failing i.e.
before breaking or fracture.
• It allows the wire to bend a wire into
desired configutation such as loops, coils
and stops without facturing the wire.

23. • Range : defined as the distance the wire
will bend elastically before causing
permanent deformation . If the wire is
deflected beyond the range it will not
return to its original position but clinically
useful springback will occur unless the
failure point is reached .
• strength= stiffness x range

24. • Load deflection rate:
–For a given load the deflection
observed within the elastic limit.
–Low load deflection rate provides ability
to apply low forces, a more constant
force over time while deactivation,
greater ease and accuracy in applying a
given force.
• LDR-load/deflection

25. • Toughness-Ability of a material to absorb the eastic energy
and to deform plastically before fracturing.
• Ductility-It is the ability of a material to be plastically strained
in tension i.e., ability of a material to withstand permanent
deformation under a tensile load without rupture it decreases
with increase in temperature.
• Malleability -The ability of a material to withstand permanent
deformation without rupture under compression ,as in
hammering or rolling into sheet is termed as malleability
Malleability increases with increase in temperature

26. FLEXIBILITY :- The maximum flexibility is
defined as the strain that occurs when the
material is stressed to its proportional
limit.for example, in an orthodontic
appliance,a spring is often bent a
considerable distance under the influence
of a small stress.In such a case, the stucture
is said to be flexible and it possesses the
property of flexibility

27. • superelastic: It is the ability of a wire to sustain or deliver a
near constant force over a wide range of activation
• Joinability: this donotes the ability to attach auxilliaries to
orthodontic wire by welding and soldering.
• sensitisation: when stainless steels are heated up to
temperatures between 800 -12000F carbon reacts with
chromium carbide, hence chromium tied up as the carbide
cannot contributes to the corrosion resistance of the metal.
This phenomenon is callled sensitisation. The carbon
inactivates the chromium at the grain boundaries opening
them to corrosion.

28. • stabilisation: This is the process by which
carbon is made unavailable for the
sensitisation.steel that has been treated to
reduce the available carbon is called
stabilised steel.
• Brittleness: This is considered being the
opposite of toughness.A brittle material
cannot undergo plastic deformation.

29. • Bauschinger effect: This donotes the
phenomena when the material is strained
beyond its yield point in one direction, and
then strained in the reverse direction , iits
yield stength in the reverse direction is
reduced.
• Biocompatibility: Biocompability refers to
resistance to corrosion and tissue
tolerance to element in the wire.

30. • Biohostability: The ease with which a wire
tends to accumulates bacteria, spores or
viruses is called biohostability wire. an
ideal archwire should be a poor biohost.
• hystresis: the difference between the
energy required to activates the wire by
deflection and that released by it during
deactivation is called engergy loss or
hysteresis

31. • Coefficient of friction: Friction is resistance
to motion of one material with respect to
another closely aproximated material.In
orthodontics friction describe the ease of
movement of brackets over the wire .
• if the coeffficient of friction is less

32. Cold working and work hardening
• The deformation of the space lattice of the metals by
mechanical manipulation at room temperatures is cold
working . It alters certain physical properties such as ductility .
• If the metal is continually stressed it becomes stiffer and
harder. Hardening of metal by cold working is called strain
hardening or work hardening.
• During strain hardening dislocations tend to build up at grain
boundaries. The barrier effect of grain boundaries will cause further
hardness.

33. • Consequences:
• Increased surface hardness.
• Greater yield and ultimate strength.
• Less ductility.
• Proportional limit is increased.
• Reduced resistance to corrosion.
• No change in elastic modulus

34. Heat treatment –Annealing(softening heat
treatment
• The effects associated with cold working ,strain
hardening decreased ductilitty and distorted
grain can be reveresed simply by heating the
metal to an appropriate elevated temprature-
annealing
• 3 succesive stages
-recovery
-recrystallization
-grain growth
• The annealing process is intended to soften
metals, to increase their plastic deformation
potential, to stabilize shape, and to increase
machinability.

35. Annealing –softening heat
treatment
• Recovery:
– Cold work properties begin to disappear.
– Slight decrease in tensile strength and no change in
ductility.
– All the residual stress is relaxed.
• Recrystallisation:
– Old grains disappear totally and are replaced with
strain free grains.
– Occurs mostly in regions where defects have
accumulated.
– It attains it’s soft and ductile condition at the end of
this stage.
•

36. • Grain Growth:
–The Grain size and number of the
recrystallised structure depends on the
amount of prior cold working.
–On repeated annealing larger grains
consume smaller grains. At the end of
annealing the number of grains
decrease and size increases.

37. • In general, an orthodontist should
consider the following aspects in the
selection of wires: force delivery
characteristics, elastic working range,
ease of joining individual segments to
fabricate more complex appliances,
corrosion resistance and biocompatibility
in the oral environment and cost.

38. • Requirements of an ideal archwire
1. Esthetics
2. Resilient
3. Stiffness
4. Strength
5. Range
6. Biohostability
7 . Springback
8. Biocompatibility
9. Formability
10.Weldability

39. commly used materials for archwire:
• stainless steel alloy
• Elgiloy
• Nickel-titanium alloy
• Beta titanium alloy
• multistrand stainless steel

40. • Stiffness
• sprin
• Springback
• Resiliency
• Formability
Stainless steel beta titanium M-NiTi, A-NiTi Cu-NiTi
Elgiloy Multistranded SS
Cu-NiTi A-NiTi M-NiTi , Multistrand SS beta titanium SS, Elgiloy
A-NiTi, Cu NiTi M-NiTi, Multistrand SS beta titanium Stainless Steel
Elgiloy Stainless steel , beta titanium M-NiTi, A-NiTi , Cu-NiTi
Multistrand SS

41. • Joinability
• Biocompatibility
• Friction
Beta titanium SS M-NiTi, A-NiTi
Elgiloy Cu-Niti
Beta titanium Stainless steel M-NiTi, Cu-NiTi
Elgiloy A-Niti
Multistrand SS
Beta titanium M-NiTi, A-NiTi , Elgiloy Stainless steel
Cu-Niti

42. reference
1 Orthodontic material scientific and clinical
aspect: william A. brantely
2.Contemporary Orthodontics – William R.
Proffit
3.Orthodontics Diagnosis and Management
of
Malocclusion and Dentofacial Deformities-
Om Prakash Kharbanda 2nd edition
4.philips science of dental material (eleventh
edition)