All about wires and their properties, usage, selection, advantages

1. Dr. DHANASEKARAN.R
FIRST YEAR MDS
Dept. of Orthodontics &
Dentofacial Orthopaedics
WIRES IN
ORTHODONTICS

2. Contents:-
• Introduction
• History
• Properties
• Ideal requirements
• Stainless steel
• High tensile Australian wires
• Multistranded wires
• Cobalt Chromium
• Nickel Titanium
• Chinese NiTi alloy
• Copper NiTi alloy
• β- Titanium
• α- Titanium
• Tooth colored wire (Opti
Flex)
• Conclusion
• References
2

3. INTRODUCTION
• Active components of fixed appliances.
• Bring about various tooth movements through the medium of
brackets and buccal tubes.
• The main components of an orthodontic appliance
• Brackets and Wires

4. History
• Before Angle’s era.
• Noble metals and their alloys. - Gold (at least 75%),
platinum, iridium and silver alloys.
• Good corrosion resistance.
• Acceptable esthetics.
• Lacked flexibility and tensile strength.
4

5. • Angle introduced German silver into orthodontics. (1887)
• Use prevailed up to 2nd half of the 20th century.
• Some of the other materials Angle used were wood, rubber,
vulcanite, piano wire and silk thread.
• In late 1930, stainless steel was introduced for appliance
fabrication.
• Angle used stainless steel in his last year, as ligature wire.
• By 1950s stainless steel alloy was used by most of the
orthodontist.

6. • Cobalt chrome alloys used as a spring in the watches.
• In 1950s cobalt chromium alloys drawn into wires available
for use in orthodontic appliances
• Marketed as Elgiloy.
• In 1970s, introduction of titanium alloys as orthodontic wire
materials.
• Beta titanium alloys were developed around 1980 by Charles
J. Burstone, marketed as TMA (titanium-molybdenum alloy).
6

7. • In 1985, Dr. C.J. Burstone reported the development of
Chinese Niti alloy and in 1986 Miura Fetal reported Japanese
Niti alloy.
• In 1992, the OPTIFLEX an aesthetic arch wire, was
introduced to orthodontics by Tallas.
• Recently in 2001, Dead Soft Security Arch wires has been
introduced by Binder and Scott. These arches are bend to lie
passively in all attachments.
7

8. Mechanical properties
• Stress & strain
• Elastic properties
• Young’s modulus (modulus of elasticity)
• Range
• Springback
• Formability
• Resiliency
• Flexibility
8

9. • Strength properties
• Proportional limit (elastic limit)
• Yield strength
• Plastic deformation
• stiffness/load deflection rate
9

10. Stress and strain
The elastic behavior of any material is defined in terms of its
stress–strain response to an external load.
• Stress - internal distribution of the load
Stress = force/area
• Strain - internal distortion produced by the load
Strain = deflection/unit length.
10

11. Types of stress/strain:-
• Tensile –stretch/pull
• Compressive – compress towards each other
• Shear – 2 non linear forces in opposite
direction which causes sliding of one part of
a body over another.
11

12. • Orthodontic archwires and springs can be considered as beams,
supported either only on one end (e.g., a spring projecting from a
removable appliance) or on both ends (the segment of an
archwire spanning between attachments on adjacent teeth)
12

13. • Three major properties of beam materials are critical in
defining their clinical usefulness:
• Strength,
• Stiffness,
• Range.
13

14. Three different points on
a stress–strain diagram
can be taken as
representative of the
STRENGTH
1. Proportional limit
2. Yield strength
3. Ultimate tensile strength
14

15. •Proportional limit
• The point at which first deformation
is seen.
• Highest point where stress and strain
still have a linear relationship
(Hooke’s law).
• At this point if the stress is removed
the wire returns back to its original
form.
15

16. •Yield strength
• The stress at which a material
exhibits a specified limiting
deviation from proportionality of
stress to strain.
• It is more practical indicator
• True elastic limit lies between
these two points.
16

17. 17
•Ultimate tensile strength
• Maximum load the wire can
sustain
• Reached after some permanent
deformation and is greater than
the yield strength.
Clinical implication:
• Determines the maximum force
the wire can deliver.

18. Stiffness
• Stiffness is proportional to the
slope of the elastic portion of
the force–deflection curve.
• The more vertical the slope,
the stiffer the wire, the more
horizontal the slope, the more
flexible the wire.
18

19. Range
• The distance that the wire
will bend elastically before
permanent deformation
occurs.
• If the wire is deflected
beyond this point, it will not
return to its original shape,
but clinically useful
springback will still occur
unless the failure point is
reached.
• Strength = × Stiffness Range
19

20. Resilience and Formability
• Two other important characteristics
also can be illustrated with a stress–
strain graph
• Resilience is the area under the
stress–strain curve out to the
proportional limit.
• Represents the energy storage
capacity of the wire.
• Strength and springiness.
20

21. Formability
• The amount of permanent
deformation that a wire can
withstand before failing.
• It represents the amount of
permanent bending the wire
will tolerate before it breaks.
21

22. Ideal Requirements
22

23. Stainless steel
23

24. Stainless Steel
3 major types are present
Ferretic SS Martensitic SS Austenitic SS
400 series
Good corrosion
resistance , < strength
Share 400 series
Have high strength &
hardness
300 series
Most corrosion
resistant
Not hardenable by
heat treatment or cold
work
Can be heat treated Contain approx
18 – 20 % Cr
8 – 12% Ni
18-8 steel
Industrial purposes Surgical and cutting
instruments
Type 302 & 304
Orthodontic wires and
bands
24

25. Stainless Steel
Other elements
• Nickel – stabilizes the crystal into a homogenous austenitic
phase
• adversely affect the corrosion resistance.
• Other elements like Mb, Mn , Cu are added to in steels used for
implants
25

26. Stainless Steel
• Silicon – (low concentrations) improves the resistance to
oxidation and carburization at high temperatures.
• Sulfur (0.015%) increases ease of machining
• Phosphorous – allows sintering at lower temperatures.
• But both sulfur and phosphorous reduce the corrosion
resistance.
26

27. Austenitic steels more preferable :-
1. Greater ductility and ability to undergo more cold work
without breaking.
2. Substantial strengthening during cold work. Easy to weld
3. Easily overcome sensitization
4. Ease in forming.
27

28. Duplex steels
• Both austenite and ferrite grains
• Increased toughness and ductility than Ferritic steels
• Twice the yield strength of austenitic steels
• Lower nickel content
• Manufacture of one piece brackets (eg Bioline ‘low nickel’
brackets)
28

29. Properties of Stainless Steel
1. Relatively stiff material
• Yield strength and stiffness can be varied
• Altering diameter/cross section
• Altering the carbon content and
• Cold working and
• Annealing
• High forces - dissipate over a very short amount of
deactivation (high load deflection rate).
29

30. Properties of Stainless Steel
Clinically:-
Loop - activated to a very small extent so as to achieve optimal
force
• Once deactivated by only a small amount (0.1 mm) Force level
will drop tremendously
• Not physiologic
• More activations
30

31. Properties of Stainless Steel
• Difficult to engage a steel wire into a severely mal-aligned tooth
• bracket to pops out,
• pain.
• Overcome by using thinner wires, which have a lower stiffness.
• Fit poorly loss of control on the teeth.
31

32. Properties of Stainless Steel
High stiffness can be advantageous 
• Maintain the positions of teeth & hold the corrections achieved
• Begg treatment, stiff archwire, to dissipate the adverse effects of
third stage auxiliaries
32

33. Properties of Stainless Steel
2. Lowest frictional resistance
• Ideal choice of wire during space closure with sliding
mechanics
• Teeth will be held in their corrected relation
• Minimum resistance to sliding
33

34. Properties of Stainless Steel
Sensitization
• During soldering or welding, 400 - 900 oc
• Reduces the corrosion resistance -Sensitization.
• Diffusion of Chromium carbide towards the carbon rich areas
(usually the grain boundaries)
34

35. Properties of Stainless Steel
Stabilization – methods to overcome sensitiztion
• One or two elements that form carbide precipitates more
easily than Chromium are added
• Eg titanium, tantalum or niobium
• Expensive – not used for orthodontic wires
35

36. High Tensile Australian Wires
History
• Early part of Dr. Begg’s career
• Arthur Wilcock Sr.
• Lock pins, brackets, bands, wires, etc
• Wires which would remain active for long
• No frequent visits
• This lead Wilcock to develop steel wires of high tensile strength.
36

37. High Tensile Australian Wires
• Beginners found it difficult to use the highest tensile wires
• H D Kesling – US - Grading system
• Late 1950s, the grades available were –
• Regular
• Regular plus
• Special
• Special plus
37

38. High Tensile Australian Wires
• Newer grades were introduced after the 70s.
• Premium, premium +, supreme
• Disadvantages:
• Brittle.
• Softening , loss of high tensile properties
38

39. High Tensile Australian Wires
BAUSCHINGER EFFECT
• Described by Dr. Bauschinger in 1886.
• Material strained beyond its yield point in one direction & then
strained in the reverse direction, its yield strength in the reverse
direction is reduced.
39

40. High Tensile Australian Wires
• Imp during manufacturing processes.
• Wire is subjected to plastic deformation during Straightening
processes.
• Prestrain in a particular direction.
• Yield strength for bending in the opposite direction will
decrease.
• Premium wire  special plus or special wire.
40

41. Fracture of wires & Crack propagation
High tensile wires have high density of dislocations and
crystal defects

Pile up, and form a minute crack

Stress concentration

sensitization
41

42. High Tensile Australian Wires
Small stress applied with the plier beaks

Crack propagation

Fracture of wire
42

43. High Tensile Australian Wires
Ways of preventing fracture
1. Bending the wire around the flat beak of the pliers.
Introduces a moment about the thumb and wire gripping
point, which reduces the applied stress on the wire.
43

44. High Tensile Australian Wires
44

45. High Tensile Australian Wires
2. The wire should not be held tightly in the beaks of the
pliers.
Area of permanent deformation to be slightly enlarged,
Nicking and scarring avoided.
The tips of the pliers should not be of tungsten carbide.
45

46. High Tensile Australian Wires
3. The edges rounded  reduce the stress concentration in the
wire.
4. Ductile – brittle transition temperature slightly above room
temperature.
Wire should be warmed.
Spools kept in oven at about 40o, so that the wire remains
slightly warm.
46

47. Multi stranded Wires
• Two or more wires of smaller diameter are twisted
together/coiled around a core wire.
• Individual diameter - 0.0165 or 0.0178
final diameter – 0.016" – 0.025",
rectangular or round
• On bending  individual strands slip over each other and the
core wire, making bending easy. (elastic limit)
47

48. Multi stranded wires
48
Co-axial
Twisted wire
Multi braided

49. Multistranded Wires – general considerations
49
Implies that the wire delivers lighter forces per unit
activation over a greater distance
strength – distortion + fracture
Twisting of wires
Result - high elastic modulus wire behaving like a low
stiffness wire

50. Multistranded Wires
Elastic properties of multistranded archwires depend on –
1. Material parameters – Modulus of elasticity
2. Geometric factors – wire dimension
3. Constants:
• Number of strands coiled
• The distance from the neutral axis to the outer most fiber
of a strand
• Plane of bending
• Poisson’s ratio
50

51. Cobalt Chromium
51

52. Cobalt Chromium
• 1950s the Elgin Watch
“The heart that never breaks”
• Rocky Mountain Orthodontics - Elgiloy
• CoCr alloys - stellite alloys
• Superior resistance to corrosion, comparable to that of gold
alloys.
52

53. Cobalt Chromium
• Cobalt – 40-45%
• Chromium – 15-22%
• Nickel – for strength and ductility
• Iron, molybdenum, tungsten and titanium to form stable
carbides and enhance hardenability.
53

54. Cobalt Chromium properties
• Strength and formability modified by heat treatment.
• Before heat treatment - highly formable and can be easily
shaped.
• Heat treated.
• Strength 
• Formability 
54

55. Cobalt Chromium
• Heat treated at 482oc for 7 to 12 mins -Precipitation
hardening
•  ultimate tensile strength of the alloy, without hampering
the resiliency.
• After heat treatment, elgiloy has elastic properties similar to
steel.
55

56. Cobalt Chromium
56

57. Cobalt Chromium
57
various tempers
Red – hard & resilient
green – semi-resilient
Yellow – slightly less
formable but ductile
Blue – soft & formable

58. Cobalt Chromium
• Blue considerable bending, soldering or welding
• Red  most resilient and best used for springs
• difficult to form, (brittle)
• After heat treatment , no adjustments can be made to the wire,
and it becomes extremely resilient.
After heat treatment 
• Blue and yellow ≡ normal steel wire
• Green and red tempers ≡ higher grade steel
58

59. Cobalt Chromium
• Heating above 650oC
• partial annealing, and softening of the wire
• Optimum heat treatment  dark straw color of the wire
Advantage of Co-Cr over SS
• Greater resistance to fatigue and distortion
• longer function as a resilient spring
59

60. Cobalt Chromium
• Kusy et al (AJO 2001)
• Evaluated round , rectangular ,square Cs wires of sizes ranging
from 14 mils to 21 x 25 mils of the 4 tempers available
• They evaluated the yield strength, ultimate tensile strength ,
ductility and elastic modulus
60

61. Cobalt Chromium
1. The elastic modulus did not vary appreciably  edgewise or
ribbon-wise configurations.
2. Round wire had significantly higher ductility than square or
rectangular wires
3. The modulus of elasticity was independent of the temper of
the wire
4. The yield strength . ultimate tensile strength & ductilty -
differed from diff cross sectional areas and tempers
• Diff tempers – diff mechanical properties – care during
manufacturing
61

62. Nickel titanium alloy
• William F. Buehler in 1960’s invented Nitinol
Ni – Nickel
ti-titanium
Nol-Naval Ordinance Laboratory,U.S.A.
• Andreasen G.F. and co-workers introduced the use of nickel-
titanium alloys for orthodontic use in the 1970’s.
62

63. • 55% nickel, 45% titanium resulting in a stoichiometric ratio
of these elements.
• 1.6% cobalt is added to obtain desirable properties.
63

64. Properties
• Transition Temperature Range (TTR)
• Shape Memory
• Super elasticity
64

65. Transition Temperature Range (TTR)
• Transition temperature range is a specific temperature range
when the alloy nickel titanium on cooling undergoes
martensitic transformation from cubic crystallographic
lattice.( Austenitic phase of the alloy.)
• In martensitic phase, the alloy cannot be plastically
deformed.
65

66. • At higher temperatures the alloy is found to be in cubic
crystallographic lattice consisting of body centered cubic
crystallographic structures.
• It is also known as Austenitic phase of the alloy.
• Plastic deformation can be induced, in austenitic phase of the
alloy.
66

67. • The same plastic deformation induced at the higher
temperature returns back when the alloy is heated through a
temperature range known as reverse transformation
(transition) temperature range, RTTR.
• Any plastic deformation below or in the TTR is recoverable
when the wire is heated through RTTR.
67

68. Shape memory
• Shape memory refers to the ability of the material to
"remember” its original shape after being plastically deform
while in martesitic form.
68

69. Super elasticity
• It is the property of the wire
explained as even when the
strain is added, the rate of
stress increase levels off, due
to the progressive deformation
produced by the stress induced
martinsitic transformation.
69

70. Chinese Niti Alloy
• Another nickel titanium alloy introduced by Burstone and
developed by Dr Tien Hua Cheng is called as Chinese Niti
alloy in1985
• It has a springback that is 4.4 times that of comparable
stainless steel wire and 1.6 times that of nitinol wire
• At 80° of activation the average stiffness of Chinese NiTi
wire is 73% that of stainless steel wire and 36% that of
nitinol wire.
70

71. Copper Niti alloy
• In 1994 Ormco Corporation introduced a new orthodontic
wire alloy, Copper NiTi.
• Copper Ni Ti is a new quaternary ( nickel, Titanium copper
and chromium ) alloy.
71

72. 72
• Orthodontic archwires fabricated from this alloy have been
developed for specific clinical situations and are classified as
follows:
• Type I Af 15℃
• Type II Af 27℃
• Type III Af 35℃
• Type IV Af 40℃

73. • These variants would be useful for different types of
orthodontic patients.
• For example,
The 27℃ variant would be useful for mouth breathers;
The 35℃ variant is activated at normal body
temperature; and the 40℃ variant would provide activation
only after consuming hot food and beverages.
73

74. β – Titanium (Titanium Molybdenum Alloy)
• In the 1960’s an entirely different “high temperature” form
of titanium alloy became available.
• At temperature above 1625°F pure titanium rearranges into a
body centered cubic lattice(BCC), referred to as ‘Beta’ phase.
• With the addition of such elements as molybdenum or
columbium, a titanium based alloy can maintain its beta
structure even when cooled to room temperature.
74

75. • Such alloys are referred as beta stabilized titaniums.
• Goldberg and Burstone demonstrated that with proper
processing of an 11% molybdenum, 6% Zirconium and 4%
tin in beta titanium alloy, it is possible to develop an
orthodontic wire with a modulus of elasticity of 9.4 x 106 psi
and yield strength of 17 x 104 psi.
• The resulting YS/E ratio (springback) of 1.8 x 10-2 is superior
to 1.1 x 10-2 for stainless steel.
75

76. • The low elastic modulus yields large deflections for low
forces.
• The high ratio of yield strength to elastic modulus produces
orthodontic appliances that can sustain large elastic
activations when compared with stainless steel devices of the
same geometry.
76

77. • β- titanium can be highly cold worked . The wrought wire
can be bent into various orthodontic configurations and has
formability comparable to that of austenitic stainless steel .
• Clinically satisfactory joints can be made by electrical
resistance welding of β- titanium (light-capacitance weld).
Such joints need not be reinforced with solder.
77

78. • Beta titanium wire possesses a unique balance of high spring
back & formability with low stiffness ,making it particularly
suitable for a number of treatment modalities.
78

79. Alpha Titanium Alloy
• The alpha titanium alloy is attained by adding 6% aluminium
and 4% vanadium to titanium
• Because of its hexagonal lattice, it possesses fewer slip
planes making it less ductile from β- titanium.
• The hexagonal closed packed structures of Alpha-Titanium
has only one active slip plane along its base rendering it less
ductile.
79

80. • Composotion
• Alpha-Beta alloy with titanium, aluminum, vadadium
• A smooth surface structure
• Less friction at the archwire bracket inter
• Better strength than existing titanium based alloy
• Poor in its weld characteristics
80

81. Tooth Colored Wire (OPTIFLEX)
• Optiflex is a new orthodontic archwire that is designed to
combine unique mechanical properties with a highly esthetic
appearance.
81

82. • Made of three clear optical fiber
• A silicon dioxide core that provides the force for moving
teeth
• A silicon resin middle layer that protect the core from
moisture & adds strength
• A strain resistant nylon layer that prevent the damage to the
wire
82

83. • It is used in adult patients with high aesthetic requirements.
• It can be used as an initial wire in cases with moderate
amounts of crowding in one or both arches.
• The wire can be round or rectangular & is manufactured in
various sizes.
• Mechanical properties includes a wide range of action &
ability to apply light continuous force.
83

84. • Sharp bends must be avoided ,since they could fracture the
core.
• Highly resilient wire that is especially effective in the
alignment of crowded teeth.
84

85. Applying archwires
Stage Wires Reason
I aligning Multistranded SS,
NiTi
Great range and light
forces are reqd
II stage Β-Ti , larger size NiTi ,
SS – if sliding
mechanics is needed
Increased formability,
springback , range and
modest forces per unit
activation are needed
III stage SS , preferably
rectangular
More stability & less
tooth movement reqd
85

86. Conclusion
• It is important to know the properties of the arch wires as it is
widely used in orthodontics.
• Proper handling of the material gives the best result.
• Material with excellent aesthetics and strength expected to
replace metals in orthodontics in the near future.
86

87. References
• Proffit – Contemporary orthodontics
• Graber vanarsdall – orthodontics – current principles and
techniques
• Kusy & Greenberg. Effects of composition and cress section on
the elastic properties of orthodontic wires. Angle Orthod
1981;51:325-341
• Kapila & Sachdeva. Mechanical properties and clinical
applications of orthodontic wires. AJO 89;96:100-109.
• Burstone. Variable modulus orthodontics. AJO 81; 80:1-16
• Kusy. A review of contemporary archwires: Their properties and
characteristics. Angle orthodontist 97;67:197-208
87

88. • Ingram, Gipe, Smith. Comparative range of orthodontic wires
AJO 1986;90:296-307
• Tidy. Frictional forces in fixed appliances. AJO 89; 96:249-54
• Twelftree, Cocks, Sims. Tensile properties of Orthodontic wires.
AJO 89;72:682-687
• Kusy and Dilley. Elastic property ratios of a triple stranded
stainless steel archwire. AJO 84;86:177-188
• Arthur J Wilcock. JCO interviews. JCO 1988;22:484-489
• Frank and Nikolai. A comparative study of frictional resistance
between orthodontic brackets and archwires. AJO 80;78:593-
609
• Arthur Wilcock. Applied materials engineering for orthodontic
wires. Aust. Orthod J. 1989;11:22-29.
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