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1. 1

2. ORTHODONTIC
ARCHWIRES
• Basic properties of
Orthodontic Wires
• Stainless steel wires

3. CONTENTS
1. Introduction
Definition
Wire dimensions
2. Evolution of Orthodontic Wires
3. Basic properties of Orthodontic Wires
4.Stainless steel wires
Austenitic Stainless steel wires (300series)
Properties of Stainless steel wires
Multistrand and coaxial wires

4. INTRODUCTION
Optimum orthodontic tooth movement is produced by light,
continuous force.
It is particularly important that these forces do not decrease rapidly.
 Also an ideal arch wire should have certain properties like esthetics,
biohostability, formability, resilience etc.
No wire is best for all stages, and no archwire is ideal.
For not abusing the material and for designing the appliance to its full
potential the proper understanding of the physical and mechanical
properties of orthodontic wires is required.

5. DEFINITION
• In orthodontic language, archwire refers to a wire
secured to two or more teeth through fixed
attachments to cause, guide or control orthodontic
tooth movement.
• ADA specification no. 32 includes orthodontic wires
excluding precious metals and ligature wires.
WIRE DIMENSIONS
• The wire dimension is expressed in terms of thousands
of an inch/mm, mil, gauge, judged by its cross-sectional
dimensions.

6. • Round wires- 0.010” to 0.022” (increment on 0.002”)
• Square wires- 0.016”×0.016”
• Rectangular wires- 0.016” ×0.022”
0.017” ×0.025”, 0.018” ×0.025”, 0.019×0.025”
0.0215” ×0.0275”

7. Evolution of Orthodontic Wires
Early era- Noble metals such as
Gold, Silver and Platinum
Wires in 1880s-’ Arch Bow’ : round,
threaded stiff wire drawn from Ni-
Ag or Pt-Au alloys – 0.032’’×0.036’’
Dr. Edward H Angle 1887-
Neusilver/ German Silver/ Nickle
Silver alloys.
7

8. The first true SS was melted on 13th august
1913 by Harry Brearley. (associated with
BROWN FIRTH LAB)
Within a year of Brearley’s invention, Krupp
in Germany was experimenting by adding
nickel to the melt. In 1919 entered dentistry
Brearley’s successor at Brown Firth
Laboratories, Dr. W.H. Hatfield is credited
with the invention of 18/8 SS in 1924.
1946- Mr. Claude Arthur J. Wilcock started
supplying orthodontic materials to Dr. Begg –
High Tensile wires/ Australian Wires
8

9. 1950- Elgin watch company (USA)
developed Elgiloy( Co-Cr-Ni)
1963- William Buehler developed Ni-
Ti alloy. Introduced in dentistry by
Geroge Andresen
1977 Burstone and Goldberg -
Titanium-Molybdenum alloy that had
a β-Ti structure
21st century-Tooth coloured wires like
Optiflex, Teflon coated wires, Shape
Memory Polymers
9

10. IDEAL ORTHODONTIC WIRE
Robert P.Kusy- 1997 (AO)
Kusy RP. A review of contemporary archwires: their properties and characteristics. The
Angle orthodontist. 1997 Jun;67(3):197-207.

11. • Aesthetics
• Biocompatibility and
environmental stability
• Biohostability
• Coefficient of friction
• Formability
• Range
• Resiliency
Basic properties of Metal
Orthodontic Wires
• Solderability
• Springback
• Stiffness
• Strength
• Toughness
• Weldability
• Zero stress relaxation

12. Aesthetics
• The wire should be least visible in the mouth.
• Important when using ceramic brackets.
• Desirable property but there should be no compromise on
mechanical properties.
Biocompatibility and environmental
stability
Biocompatibility - Resistance to corrosion and Tissue
tolerance to the elements in wire.
• Environmental stability - desirable properties of the wire
are maintained for extended periods of time
wire is not harmful when in use in the mouth.

13. Weldability
• The ease to accumulate bacteria, spores or viruses.
• An ideal archwire should be a poor biohost
Biohostability
• It is the ease by which the wire can be joined to
other metals, by actually melting the work pieces in
the area of the bond.

14. Solderability
• The ease with which attachments can be soldered
to the wire.
• Both of the above properties - joinability
provides an additional advantage when
incorporating modifications to the appliance.

15. Coefficient of friction
 In an archwire - bracket couple,
it is the ratio of half the drawing
force that pulls the archwire
through the bracket slot to the
normal force that passes the
archwire into the bracket slot
 It is a constant , independent of
area of contact
µ= Ff / 2
N

16. • In orthodontics, Friction describes the ease of
movement of brackets over the wire.
If coefficient of friction is less
easier sliding with less strain over the anchor segments.
 High amounts of friction  anchor loss

17. Zero stress relaxation
• Stress relaxation- If a wire is deformed and held in a
fixed position, the stress in the wire diminishes with
time, but the strain remains constant.
• This occurs due to slippage of particles over each
other when subjected to forces, leading to loss of
activation in the wire.
• Zero stress relaxation is the property of a wire to
give constant light force, when subjected to external
forces. This property is desirable if a wire is to
provide constant forces for a longer period of time,
especially in springs and loops.

18. • The elastic behaviour of any material is defined in
terms of its stress-strain response to an external
load.
Basic properties of Elastic
Materials

19. 19
• Force applied to wire Deflection
• Internal force = Stress
Area of action
• change in length = Strain
Original length
Elastic - reversible
Plastic - permanent
 Three major properties that are critical for
defining the clinical usefulness of materials-
1. Strength
2. Stiffness ( inverse springiness)
3. Range

21. 21
Elastic Properties – strength analysis
3 points on the stress strain graph can be represented
to explain “STRENGTH”
1. Proportional limit
2. Yield strength
3. Ultimate tensile strength

22. 22
1. Proportional limit
It is the highest point till where
the stress and strain still have
a linear relationship
 At this point if the stress is
removed the wire returns
back to its original form
When a certain stress value
corresponding to point P is
exceeded, the line becomes
nonlinear and stress is no
longer proportional to strain

23. 23
2. Yield strength
 Experimentally it is difficult
to measure the proportional
Limit, a more practical indicator
Is Yield Strength.
This denotes the amount of stress on the stress strain graph
that causes a certain amount of permanent deformation
(usually 0.1%) is calculated.

24. 24
Strain
Stress
Elastic Portion
Wire returns back to original
dimension when stress is removed

25. 25
3. Ultimate tensile strength
 Max. load a wire can sustain before permanent
deformation
 Is greater than the yield
Strength & occurs after
Some plastic deformation
Clinically importance-
Determines Maximum force
a wire can deliver

26. 26
Strength
• Is defined as the force required to activate an
archwire to a specific distance
• The length and cross section of a wire have an effect
on the strength of the wire.
• The effects of these will be considered subsequently.

27. 27
Elastic Properties
Modulus of elasticity (Young’s modulus)
 Measures the relative stiffness or rigidity of the wire
Hooke’s law – stress and strain (elastic or compressive) are
proportional to each other
Modulus of elasticity – constant for a given material

28. 28
Elastic Properties
Represented by a straight line designated as ‘E’

29. 29
Stiffness and springiness
stiffness α E
springiness α 1/ E
stiffness = 1/ springiness
• Wilcock – Stiffness α Load
Deflection
The more horizontal the slope the
more springier the wire, the more
vertical the slope the more stiffer
the wire

30. 30
SPRINGBACK: Kusy - The extent to which a wire recovers its
shape after deactivation
• Large springback - wire will regain its original shape even
after being greatly deformed.
• Hence it will mean fewer archwire changes.

31. 31
Range – Distance the wire will bend elastically
before permanent deformation occurs
 Measured upto the yield strength.

32. 32
Clinical implication
Relationship b/w strength, stiffness & range
• Clinically optimal springback occurs when the wire
is bent b/w its elastic limit and ultimate strength
• The greater the springback, the more the wire can
be activated
Ultimate strength = stiffness x range

33. 33
Resiliency & formability
 Resiliency – represents the energy storage capacity
of the wire when it is elastically deformed.
Strength + springiness
 wire is stretched- space between the atoms
increases.
 Within the elastic limit, there is an attractive force
between the atoms.

34. 34
Strain
Stress
Resilience Formability
Proportional limit
Yield strength
 It is represented by the area under the stress
strain graph upto the proportional limit.

35. 35
Formability
• Amount of permanent deformation that the wire can
withstand before breaking
• Indication of the permanent bending the wire will
tolerate while bent into springs , archforms etc
• Also an indication of the amount of cold work that a
wire can withstand

36. 36
Strain
Stress
Resilience Formability
Proportional limit
Yield strength
It is represented by the area under the stress strain
graph b/w the yield strength and fracture point.
Fracture point

37. 37
Other mechanical properties
1. Flexibility
2. Toughness
3. Brittleness
4. Fatigue
Flexibility
• large deformation (or large strain) with minimal force, within its
elastic limit FLEXIBLE
• Maximal flexibility is the strain that occurs when a wire is stressed
to its elastic limit.
Max. flexibility = Proportional limit
Modulus of elasticity.

38. 38
• Toughness –force required to fracture a material. Total area
under the stress – strain graph.
• Brittleness –opposite of toughness. A brittle material, is
elastic, but cannot undergo plastic deformation.
• Cyclic fatigue- If there is repeated cyclic stress of a
magnitude below the fracture point of a wire, then fracture
of the wire can occur. This is due to cyclic fatigue

39. 39
Mechanical properties
• Assessed by tensile, bending and torsional test
Specimen
Universal testing machine

40. 40
Effects of size and shape on elastic
properties
• Each of the major elastic properties strength ,
stiffness and range are affected by the geometry of
the beam
• Two such variables
1. Change in cross section
2. Change in length

41. 41
Effects of Wire Cross Section
• Cantilever spring – round wire – double the diameter

42. 42
Rectangular wires
• Torsion is of practical importance in orthodontics only
for rectangular wires that can be twisted into rectangular
slots
• In torsion, more shear stress rather than bending stress
in encountered
• However the principle is same

43. 43
• Increase in diameter – increase in stiffness
threshold point – too stiff for orthodontic use
• Decrease in diameter – decrease in stiffness
threshold point – too soft for orthodontic use
Ideally wire should be in b/w these two extremes

44. 44
Cantilever beam – double the length
L 2L

45. 45
 Supporting a beam on both ends makes it much stronger but
also much less springy than supporting it on only one end.
• If a beam is rigidly attached on both ends, it is twice as strong
but only one fourth as springy as a beam of the same material
and length that can slide over the abutments.
The elastic properties of an orthodontic arch wire are affected
by whether it is tied tightly or held loosely in a bracket.

46. 46
Nomograms
• Developed by Kusy
• Provide comparison of stiffness , strength and range
of wires of different materials and dimensions
• A reference wire is chosen (0.012”SS) and given a
value of 1 . The strength , stiffness and range of other
wires are calculated to this reference

47. 47
Nomograms are helpful in allowing one to assess at a glance a
whole set of relationships that would require pages of tables
3
6
0.7
1.9

48. Stainless Steel
archwires

49. CARBON STEEL
Steels are iron based alloys that contain less
than 1.2% carbon ( More than 2% carbon
containing alloys are called PIG IRON).
STAINLESS STEEL
When the chromium (generally 12 to 30% )is
added to steel, alloy is commonly defined as
stainless steel.
49

50. AISI grades of stainless steel
alloys

51. 51

52. Manufacturing of stainless steel
MELTING
INGOT
FORMATI
ON
ROLLING
DRAWIN
G
MELTING
The selection and melting of the components of alloys
influence the physical properties of wire .

53. • The molten alloy is poured
into the mold.
• A non uniform chunk of
metal is produced c/d ingot
• The mechanical properties
of the ingot is controlled by
its granular structure.
• When the ingot is cooled,
different grains form at
once.
• These growing crystals
crowd and surround each
other.
Ingot
formation INGOT — colony of
irregularly shaped
grains of different
materials.

54. ROLLING
•First mechanical step in process.
•Ingot is rolled in series of rollers to reduce its
diameter.
•. Now the wire is actually a "distorted ingot".
•The squeezing and rolling of ingot alters the shape
and arrangement of the crystals
•Rolling will cause the elongation of crystals into a
finger like process, closely meshed with each other..
•Hardness/ brittleness increases as the grain
positions and arrangements are altered
•The metal is annealed by heating into high
temperature, which relives the internal stress
formed by rolling.
•On cooling ,it resembles an original casting.

55. DRAWING
The wire is reduced to its final
size by drawing.
This is a more precise process
in which the wire is pulled
through a small hole in a die.
Before it is reduced to orthodontic
size, a wire is drawn through many
series of dies and annealed several
times along the way to relieve work
hardening.

56. Chromium is added to increase tarnish
and corrosion resistance. It also increases
hardness, tensile strength and proportional
limit.
Nickel  strengthens the alloy and helps in
increasing the tarnish and corrosion
resistance.
Cobalt  decreases the hardness
Manganese  acts a scavenger and increases
the hardness during quenching.
Silicon  acts as a deoxidizer and also as
scavenger
Tantalum  inhibits the precipitation of
chromium carbide.
Based on lattice
structure
56
Crystal Space Lattice
• The formed crystals in a metal are arranged in an
orderly pattern – layer by layer in regular stacks.
• The crystals of a metal is in the form of a space
lattice.
• The type of space lattice varies from metal to
metal.

57. • At high temperatures (912 to 1394°C) steel is a homogenous
material with all of the carbon in solid solution in the iron. At this
temperature, the iron carbide is completely decomposed. This
form of steel is called "Austenite".
 The stable form of iron is a face
centered cubic structure (FCC) called
austenite.
Austenitic stainless steels (300 series)
orthodontic wires and bands.

58. • If the austenite is cooled rapidly (quenched), it will undergo a
spontaneous diffusionless transformation to a body centered
tetragonal structure (BCT) called martensite
 The hardest and most brittle form of iron- carbon combination
• This form of steel begins to form as the
mass of cooling metal reaches 225°C
and complete transformation occurs at
about 90°C.

60.  Pure iron at room temperature
has a body centered cubic (BCC)
structure and is referred to as
ferrite; this phase is stable in
temperatures as high as 9120 C.
Between these high and low extremes of temperature many
intermediate phases are formed. These are various mixtures of
ferrite and cementite

61. MECHANICAL PROPERTIES
• Modulus of elasticity: It has large modulus of
elasticity thus showing a steep slope which
indicate a rigid material.
• Spring back: It has low spring back than those
of titanium based alloys. The stored energy of
activated stainless steel is substantially less.
• Friction: It has low friction so it offers lower
resistance to tooth movement than other
alloys.
• Formability: It has good formability.
• Resiliency: It has low resiliency.
• Biocompatibility: It has good biocompatibility.
• Joinability: It can be soldered and wires welded.
• Corrosion resistance: Good corrosion resistance.

62. • AISI Series 400.
 Ferritic stainless steels provide good corrosion resistance at low cost,
but low strength.
 These steels can not hardened by heat treatment because
temperature change induces no phase change in the solid state.
 Also they are not readily work-hardened.
 Therefore, the ferritic stainless steels have numerous industrial uses,
they have no application in dentistry.
FERRITIC STAINLESS STEEL

63.  AISI Series 400
 Can be heat treated.
 Because of their high strength and
hardness, they used for surgical
and cutting instruments.
 Their corrosion resistance is less
than that of the other two types
and is reduced further following
hardening heat treatment.
MARTENSITIC STAINLESS STEEL

64. Most corrosion-resistant of three
Used for orthodontic wires, endodontic instruments,
and crowns in pediatric dentistry.
AISI Series 300 is achieved by addition of nickel to the
iron-chromium-carbon composition.
The lower cost AISI Series 200 substitute manganese
and nitrogen for nickel and are not used for dental
applications.
AUSTENITIC STAINLESS STEEL

65. • Type 302 and 304 stainless steel are often given the
designation of 18-8 stainless steel, based on the
percentages of chromium and nickel in their
composition.
These types are most commonly used in
orthodontic wires and bands.

66.  Greater ductility and ability to undergo more cold working
without fracturing
 Substantial strengthening during cold working
 Greater ease of welding
 Ability to overcome sensitization
 Comparative ease in forming
Properties of austenitic stainless steel
( compared to ferritic stainless steel)

67. Austenitic stainless steel may loose its resistance to corrosion due
to prolonged heating or improper slow cooling between ( critical
temperature) 425 to 815 degrees Celsius.
SENSITIZATION
• This decrease in corrosion
resistance is caused by
precipitation of chromium-
iron carbide at the grain
boundaries.

68.  To reduce the carbon content of the steel to such an extent
that carbide precipitation cannot occur, but not feasible.
 Stainless steel is severely cold worked and heated within the
sensitization temperature range. So, the chromium-iron
carbides precipitate at dislocations along the slip planes and,
as a result, are more uniformly distributed throughout the alloy.
 STABILIZATION Introduction of some elements, Ti, Niobium
and Tantalum, that precipitates as carbide in preference to
chromium.
 Titanium - added six times the carbon content.
METHODS TO REDUCE SENSITIZATION

69. Heat Treatment
• General process using thermal energy to change
the characteristics of metallic alloys as in
tempering, precipitation hardening or annealing.
Robert P Kusy 1997
• At optimum temperature - results in rearrangement
of the dislocation which restores the resiliency of
wire
• It reduces the magnitude of residual stresses
induced by inelastic deformation

70. Heat Treatment
1. Tempering- Heat treatment at low
temperature(200-650 degree celcius) that
enhances toughness and ductility.
2. Precipitation Hardening-
also called ‘’age hardening’’ as it requires time to
harden alloy.
• Metal alloy is hardened or strengthened by
extremely small and uniformly dispersed particles
that precipitate from a supersaturated solid
solution

71. Annealing
The process by which the stresses (effects associated with
cold working) reversed simply by heating the metal to an
appropriate elevated temperature known as Annealing.
 A rule of thumb is to use a temperature
approximately half the melting point of a pure metal or the
fusion temperature of an alloy .
The higher the melting point of the metal, the higher is the
temperature needed for annealing

72. • Annealing can take place in three
successive stages:
1. Recovery
2. Recrystallization
3.Grain growth.

73.  The properties of the cold-worked metal begin to
disappear
 No significant changes are observed under microscopic
examination
 Decrease in dislocation density with rearrangement of the
dislocations
 CLINICAL APPLICATION:
 Elimination of residual stresses
 Reduces the likelihood of fracture during clinical
adjustments
Recovery

74. Temperature
 Heat treatment be performed in the recovery temperature
range and not at higher temperatures
 Heat treatment is best at 850 F for a period of 3 minutes
The temperature between 700-950 degree F (Funk)
 Kemler: 700-8000F for 5-15 minutes
 Backofen and Gales: 750-8200F for 10 minutes
 The most practical index for heat treatment for everyday
purpose is straw colour appearance
 Too much heat - wire becomes dark chocolate colour
Funk AC. The heat-treatment of stainless steel. The Angle Orthodontist. 1951 Jul;21(3):129-38.

75.  This heat treatment stabilizes the configuration of an
appliance and allows a constant force that an
appliance will be able to deliver in the mouth.
 Increases resiliency of wire
 Elimination of residual stresses in an appliance also
reduces the likelihood of fracture during clinical
adjustments
Clinical application

76.  Recrystallization occurs after the recovery stage.
 This involves a radical change in the microstructure, old,
deformed grains disappear completely and are replaced by
new strain-free grains.
 These new grains nucleate in the most severely cold-
worked regions in the metal
 After completion of recrystallization, the metal essentially
attains its original soft and ductile condition therefore
during heat treatment it should be avoided
Recrystallization

77.  If the recrystallized metal is further annealed, grain
growth, occurs in such a way to minimize the grain
boundary area (energy), with large grains consuming
small grains.
 The average grain size of the recrystallized structure
depends on the initial number of nuclei.
 The more severe the cold working, the greater the
number of such nuclei, and the grain size for the
recrystallized metal
Grain Growth

79. Grain size after cold working and annealing

80. Hardening heat treatment
 There is no hardening heat treatment for
austenitic steel due to it’s stability.
 It can only be hardened by cold working.

81. 81
An increase in the elastic properties of a stainless steel wire
can be obtained by heat treating to temperatures between
400 and 500 degrees Celsius after it has been cold worked.
This heat treatment removes residual stresses introduced
during manipulation of the wire, and thus stabilizes the
shape of the appliance.
This is important clinically because such residual stresses
might cause fracture when the appliance is being adjusted by
the clinician for the patient.
RECOVERY HEAT TREATMENT

83. MODIFICATIONS OF
STAINLESS STEEL :
1)DUPLEX STEELS
2)PRECIPITATION HARDENED
(PH) STEELS

84. Consist of an assembly of both austenite and ferrite grains.
Contains Mo and Cr and a lower Ni content.
Properties :
 Improved strength and toughness
 Yield strength twice of austenitic steel
 High stress –corrosion resistance
 Improved mechanical properties due to lower Ni content.
The high strength which has been achieved opens the possibility for
reduction of implant sizes where limited anatomical space is often
an issue.
DUPLEX STEELS

85. Unlike most stainless steels the PH steels can be
hardened by heat treatment.
Because of its high tensile strength, it is widely
used for “mini” brackets.
It can be used to make edge lock brackets.
However, The added metals lower their corrosion
resistance.
PRECIPITATION HARDENED (PH) STEELS

86. • Very small diameter stainless steel
wires that have been braided or
twisted together to form larger
multistranded wires, are used for
clinical orthodontics.
• These braided or twisted wires are
able to sustain large elastic
deflections in bending, and they
apply much lower forces for a given
deflection, compared with solid
stainless steel wires with the same
cross-section.
BRAIDED AND TWISTED WIRES

87. CONCLUSION
 It can be seen that there is no archwire that meets all
the requirements of the orthodontist. We still have a
long way to go, in terms of finding the ‘ideal’ archwire.
But, with such rapid progress being made in science
and technology, we surely will see significant
improvements in archwires in the near future.

88. REFERENCES
1.Thurow RC. Edgewise Orthodontics. St Louis, Mosby 1982:21–68.
2.Kusy RP. Orthodontic biomaterials: from the past to the present. Angle
Orthod 2002;72(6):501–12.
3.Kenneth J. Anusavice - Philips’ Science Of Dental Materials, 10th edition
W.B. Sounders Company, 1996.
4. William R. Proffit – Contemporary Orthodontics, 5rd edition
5. A review of contemporary arch wires: Their properties and
characteristics. Robert P. Kusy, Angle Orthodontics; 1997; 197-207.
6. Interviews on orthodontic wires. Wilcock A.J. Jr.; JCO; 1988; XXII (8):484-
489.
7. Heat treatment of stainless steel. Funk.
8. Kapila S, Sachdeva R. Mechanical properties and clinical applications of
orthodontic wires. Am J Orthod Dentofacial Orthop 1989;96:100e9
9. Structure, composition, and mechanical properties of australian
orthodontic wire. Pelsue BM et all. Angle Orthod. 2009 ;79(1):97-101

89. THANK YOU