Properties of Orthodontic
Wires
Part I

INDIAN DENTAL ACADEMY
Leader in continuing dental education
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Introduction
Moving teeth and craniofacial harmony
Forces and moments

Wires
Light continuous forces

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History
1. Material Scarcity, Abundance of Ideas
(1750-1930)
noble metals
Gold, platinum, iridium and silver alloys
good c...
History
Angle (1887)  German silver (a type of
brass)
Opposition Farrar
Neusilber brass (Cu 65%, Ni 14%, Zn 21%)
various...
History
Wood, rubber, vulcanite, piano wire and silk
thread
Steel - as ligature wire.

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History
Stainless steel (entered dentistry -1919)
Opposition  Emil Herbst

gold wire was stronger than stainless steel.
...
History
2. Abundance of materials, Refinement of
Procedures (1930 – 1975)
 Improvement in metallurgy and organic
chemistr...
History
3. The beginning of Selectivity (1975 to the
present)
Beta titanium (1980)
CAD/CAM
Composites and Ceramics
Iatroge...
Basic Properties of Materials
Elements – no simpler form
 Atoms
Electrons – orbits around nucleus
Electron shells
Electro...
Basic Properties of Materials
Molecules – 2 or more atoms
Amorphous – similar properties in all
directions – isotropy  Gl...
Basic Properties of Materials
anion – cation –anion – cation
extremely strong
Wiskers reinforce
If like ions are forced t...
Basic Properties of Materials
alloy crystals grow
anion – cation –anion – cation
Order is the dream of man,
and chaos the ...
Basic Properties of Materials
Crystals penetrate each other such that the
crystal shapes get deformed
Grains  microns to ...
Basic Properties of Materials

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Basic Properties of Materials
Vacancies – These are empty atom sites

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Interstitials – Smaller atoms that penetrate the
lattice Eg – Carbon, Hydrogen, Oxygen, Boron.

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Basic Properties of Materials

Substitutial Element – another metal atom can
substitute one of the same or similar size. E...
Basic Properties of Materials
The three dimensional arrangement of lines
that can be visualized as connecting the
atoms in...
Basic Properties of Materials

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Basic Properties of Materials
The atoms, which are represented as
points, are not static. Instead, they
oscillate about th...
Basic Properties of Materials
various defects  slip
planes

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Basic Properties of Materials
shear stress  atoms of the crystals
can glide
more the slip planes easier is it to
deform
...
Basic Properties of Materials
If the shearing force is:Small - atoms slip, and return back to their
original position (ela...
Basic Properties of Materials
During deformation - atomic bonds within the
crystal get stressed
 resistance to more defo...
Basic Properties of Materials
Strain hardening
 Hard and strong
Brittle.
Annealing – heat below melting point.
– More th...
Basic Properties of Materials
Recovery
Recrystallization
Grain Growth

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Basic Properties of Materials

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Before Annealing
Recovery – Relief of stresses
Recrystallization – New grains
from severely cold worked areas
Grain Growth...
Basic Properties of Materials
Recovery Heat Treatment
– Relief of internal stresses
– Heating to low temperatures (370 – 4...
Basic Properties of Materials
Various methods of obtaining smaller grain size
1. Enhancing crystal nucleation by adding fi...
Basic Properties of Materials
Twinning
Closed packed hexagonal type of crystals
Two symmetric halves
Fixed angle
NiTi
Subj...
Basic Properties of Materials

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Basic Properties of Materials
Polymorphism
Metals and alloys exist as more than one type of
structure
Transition from one ...
Basic Properties of Materials
Iron  FCC form
(austenite),
Lattice spaces
greater,
Carbon atom can
easily be
incorporated ...
Basic Properties of Materials
On Cooling
FCC  BCC
Carbon diffuses out
as FeC
FeC adds strength
to ferrite and
austenite
T...
Basic Properties of Materials
Rapidly cooled
(quenched)
– Carbon cannot
escape
Distorted body
centered tetragonal
lattice ...
Basic Properties of Materials
Grain boundaries are more in number
Alloy is stronger and more brittle
Interstitials are int...
Basic Properties of Materials
Cooled slowly
Other crystal structures are formed at
intermediate temperatures Softer
Some ...
Basic Properties of Materials
Tempering –
Reheat the alloy to intermediate temperature
Partial formation of the softer all...
Basic Properties of Materials
Some alloys
FCC to BCC by rearrangement of atoms
Diagonal plane of the BCC unit becomes the
...
Elastic Properties
Force applied to wire Deflection
External force Internal force
(equal and opposite)
Internal force = ...
Elastic Properties
Types of stress/strain
Tensile
Compressive
Shear
Complex force systems

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Elastic Properties

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Stress

Elastic Properties

Elastic Portion

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Strain
Elastic Properties
When the stress is removed, the wire returns
back to its original dimension.
Hooke’s law

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Elastic Properties

Stress

Yield strength

0.1%

Proportional Limit
Elastic Limit

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Strain
Stress

Elastic Properties
Ultimate Tensile
Strength

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Fracture Point

Strain
Elastic Properties
ultimate tensile strength is higher than the
yield strength
important clinically  maximum force that
t...
Stress

Elastic Properties

Slope α Stiffness
Stiffness α

1

.

Springiness
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Strain
Stress

Elastic Properties

Range

Springback
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Strain
Elastic Properties

Strength = Stiffness x Range

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Elastic Properties
Resiliency When a wire is stretched, the space between
the atoms increases. Within the elastic limit,
t...
Elastic Properties
Formability - amount of permanent
deformation that the wire can withstand
without breaking
Indication o...
Stress

Elastic Properties

Resilience

Formability

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Strain
Elastic Properties
Flexibility
large deformation (or large strain) with
minimal force, within its elastic limit.
Maximal f...
Elastic Properties
Toughness –force required to fracture a
material. Total area under the stress – strain
graph.
Brittlene...
Requirements of an ideal
archwire (Kusy
1.

Esthetics

7. Resiliency

2.

Stiffness

8. Coefficient of friction

3.

Stren...
1. Esthetics
Desirable
No compromise on mechanical properties
White coloured wires discolour
Destroyed by oral enzymes
Def...
2. Stiffness / Load deflection
Rate
Thurow - force:distance ratio, measure of
resistance to deformation.
Burstone – Stiffn...
Stiffness / Load deflection Rate
Magnitude of the force delivered by the appliance for a
particular amount of deflection.
...
Stiffness / Load deflection Rate
The shape and cross section of a wire have
an effect on the strength of the wire. The
eff...
3. Strength
Yield strength, proportional limit and ultimate
tensile/compressive strength
Kusy - force required to activate...
4. Range
Distance that the wire bends elastically,
before permanent deformation occurs
(Proffit).
Kusy – Distance to which...
5. Springback
Large springback
Activated to a large extent.
Hence it will mean fewer archwire changes.
Ratio – yield stren...
5. Springback
Kusy -- The extent to which a wire recovers
its shape after deactivation
Ingram et al – a measure of how far...
6. Formability
Kusy – the ease in which a material may be
permanently deformed.

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7. Resiliency
Amount of energy stored in a body.

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8. Coefficient of friction
Brackets (and teeth) must be able to slide
along the wire
High amounts of friction  anchor los...
9. Biohostability:- site for accumulation of
bacteria, spores or viruses. An ideal archwire
must have poor biohostability....
Properties of Wires
Before the titanium alloys were introduced
into orthodontics, the practitioners used
only steel wires....
Effects of Wire Cross Section
Wires of various dimensions and cross
sections.
Does the wire need to be move teeth over
lar...
Effects of Wire Cross Section
primary factor 
load deflection rate or stiffness
play of the wire not very significant
lig...
Effects of Wire Cross Section
Play in the second order –
0.016” wire in 0.022” slot is only 1.15 times
the play of a 0.018...
Effects of Wire Cross Section

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Effects of Wire Cross Section

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Effects of Wire Cross Section
Shape

Moment
of Inertia

Ratio to stiffness of
round wire

Пd4
64

1

s4
12

1.7

b3h
12

1...
Effects of Wire Cross Section
Stiffness of different dimensions of wires can
be related to each other.
Relative stiffness
...
Effects of Wire Cross Section

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Effects of Wire Cross Section

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A rough idea can be obtained clinically as well
Forming an arch wire with the thumb gives
an indication of the stiffness o...
Effects of Wire Cross Section
Rectangular wires  bending perpendicular
to the larger dimension (ribbon mode)
easier than ...
Effects of Wire Cross Section
The larger dimension  correction is needed.
The smaller dimension  the plane in which
more...
Effects of Wire Cross Section
> 1st order correction in anterior segment
> 2nd order in the posterior segment,
wire can be...
Effects of Wire Cross Section
If both, 1st & 2nd order corrections are required
to the same extent, then square or round
w...
Effects of Wire Cross Section
In torsion - absolute values of strength,
stiffness and range are different,
but the overall...
Effects of Length
Loops,
 the inter-bracket distance
For bending
1. Strength – decreases proportionately
2. Stiffness – d...
Effects of Length
In the case of torsion, the picture is slightly
different. Increase in length –

1. Stiffness decreases ...
Effects of Length
Way the beam is attached also affects the
values
cantilever, the stiffness of a wire is obviously
less
w...
Effects of Length

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Effects of Length
Stiffness is also affected by the method of
ligation of the wire into the brackets.
Loosely ligated, so ...
Clinical Implications
LIGHT CONTINUOUS FORCES
Stiff wires should be taboo to the
orthodontist?
Springier wire, can be easi...
Clinical Implications
Removable appliance cantilever spring
The material of choice is usually steel. (Stiff
material)
Suf...
Clinical Implications
In archwires of stiffer materials the same
principle can be used.
The length of wire between bracket...
Clinical Implications
Multi-stranded wires
Twisting of the two wires causes the strength
to increase, so that the wire can...
Clinical Implications
Variable cross-section orthodontics.

Variable modulus orthodontics.

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Clinical Implications

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Clinical Implications
variable modulus orthodontics – Advantage– relatively constant dimension
– important for the third o...
Clinical Implications
Take into account the amount of force that
wire can deliver.
For example, a NiTi wire  efficient in...
Corrosion
Nickel 1. Carcinogenic,
2. mutagenic,
3. cytotoxic and
4. allergenic.
Stainless steels, Co-Cr-Ni alloys and NiTi...
Corrosion
Placement in the oral cavity

Greater peril than implanting

Implanted material gets surrounded by a
connectiv...
Corrosion
Passivating film  traces of Fe Ni and Mo.
Aqueous environment
– inner oxide layer
– outer hydroxide layer.

CrO...
Corrosion
1. Uniform attack –
the entire wire reacts with the environment,
hydroxides or organometallic compounds
detectab...
Corrosion
Steel

NiTi

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Corrosion
3. Crevice corrosion or gasket corrosion Parts of the wire exposed to corrosive environment
Sites of tying to th...
Corrosion
4. Galvanic corrosion
two metals are joined
or even the same metal after different type of
treatment (soldering ...
Corrosion
Anodic

Looses Electrons

Soluble ions

Leach out

Cathodic

Accepts electrons

Even less reactive

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Corrosion
5. Intergranular corrosion
Sensitization
6. Fretting corrosion
Wire and brackets contact
Friction  surface dest...
Corrosion
7. Microbiologically influenced corrosion
Adhersive
Craters at the base of brackets
Or wires directly bonded on ...
Corrosion

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Corrosion
8. Stress corrosion
Similar to galvanic corrosion
Bending of wires  different degress of
tension and compressio...
Corrosion
9. Fatigue corrosion –
Cyclic stressing of a wire
Accelerated in a corrosive medium such as
saliva

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Corrosion
Analysis of used wires also indicated that a
biofilm was formed on the wire.
Eliades et al
Calcification
– Shiel...
Corrosion
Ni and Cr
– impair phagocytosis of neutrophils and
– impair chemotaxis of WBCs.

Ni at conc. Released from denta...
rthOdOntic Arch Wire MAteriAl

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Precious Metals
Upto about the 1950s
Gold alloys
Only wire which would tolerate the oral
environment
Crozat appliance – ac...
Stainless Steel
1919 – Germany  used to make prostheses.
Extremely chemically stable
High resistance to corrosion.
Chromi...
Stainless Steel
Variety of stainless steels
Varying the degree of cold
work and annealing during
manufacture
Fully anneale...
Stainless Steel
stainless steel arch wires are cold worked to
varying extents,  yield strength increases, at
the cost of ...
Stainless Steel
Structure and composition
Chromium (11-26%)–improves the corrosion
resistance
Nickel(0-22%) – austenitic s...
Stainless Steel
Carbon (0.08-1.2%)– provides strength
Reduces the corrosion resistance
Sensitization.
Improper cooling aft...
Stainless Steel
Chromium carbides
Amount of chromium decreases
Chromium carbide is soluble, 
intergranular corrosion.
Sta...
Stainless Steel
Stabilization –
– Element which precipitates carbide more
easily than Chromium.
– Usu. Titanium.
– Ti 6x> ...
Stainless Steel
Silicon – (low concentrations) improves the
resistance to oxidation and carburization at high
temperatures...
Stainless Steel
Manufacture
Various steps –
1. Melting
2. Ingot Formation
3. Rolling
4. Drawing

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Stainless Steel
Melting
– Various metals of the alloy are melted
– Proportion influences the properties
Ingot formation
– ...
Stainless Steel
– Porosities due to dissolved gasses
(produced / trapped)
– Vacuum voids due to shrinking of late
cooling ...
Stainless Steel
Rolling –
– First mechanical process.
– Ingot reduced to thinner bars
– Finally form a wire
– Different wi...
Stainless Steel
– Altering of the shape of grains during rolling
– Grains get elongated, defects get rearranged
– Work har...
Stainless Steel
Drawing
– More precise
– Ingot  final size.
– Wire pulled through small hole in a die
– Progressively sma...
Stainless Steel
– Annealing at regular intervals.
– Exact number of drafts and annealing cycles
depends on the alloy.

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Stainless Steel
Classification
American Iron and Steel Institute (AISI)
Unified Number System (UNS)
German Standards (DIN)...
Stainless Steel
The AISI numbers used for stainless steel range
from 300 to 502
Numbers beginning with 3 are all austeniti...
Stainless Steel

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Stainless Steel
Austenitic steels (the 300 series)
Corrosion resistance
FCC structure,  non ferromagnetic
Not stable at r...
Stainless Steel
Martensitic steel
FCC  BCC
BCC structure is highly stressed.
More grain boundaries,
– Stronger
– Less cor...
Stainless Steel
Ferritic steels – (the 400 series)
Good corrosion resistance
Low strength.
Not hardenable by heat treatmen...
Stainless Steel
Austenitic steels more preferable :Greater ductility and ability to undergo more cold
work without breakin...
Stainless Steel
Duplex steels
Both austenite and ferrite grains
Increased toughness and ductility than
Ferritic steels
Twi...
Stainless Steel
Precipitation hardened steels
Certain elements added to them  precipitate
and increase the hardness on he...
Stainless Steel
General properties of steel
Relatively stiff material

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Stainless Steel

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Stainless Steel
Yield strength and stiffness can be varied
– Altering the carbon content and
– Cold working and
– Annealin...
Stainless Steel
Clinical terms:Loop - activated to a very small extent so as
to achieve optimal force
Deactivated by only ...
Stainless Steel
Force required to engage a steel wire into a
severely mal-aligned tooth.
– Either cause the bracket to pop...
Stainless Steel
High stiffness 
Maintain the positions of teeth
Hold the corrections achieved
Begg treatment, stiff archw...
Stainless Steel
Lowest frictional resistance
Ideal choice of wire during space closure
with sliding mechanics
Teeth be hel...
Stainless Steel
Ni is used as an austenite stabilizer.
Not strongly bonded to produce a chemical
compound.
 d likelihood ...
Stainless Steel
Nickel and chromium content in the steel
wires
Cause patients to be sensitized
Cause reactions in already ...
Stainless Steel
Passivating layer dissolved in areas of
plaque accumulation – Crevice corrosion.
Different degrees of cold...
High Tensile Australian Wires
History
Early part of Dr. Begg’s career
Arthur Wilcock Sr.
– Lock pins, brackets, bands, wir...
High Tensile Australian Wires
Beginners found it difficult to use the highest
tensile wires
Grading system
Late 1950s, the...
High Tensile Australian Wires
Newer grades were introduced after the 70s.
Raw materials directly from the suppliers
from o...
High Tensile Australian Wires
Highly brittle, and broke
easily
Straightening the wire 
softening and loss of
high tensile...
High Tensile Australian Wires
Bauschinger effect.
Described by dr. Bauschinger in 1886.
Material strained beyond its yield...
High Tensile Australian Wires

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High Tensile Australian Wires
Plastic prestrain increases the elastic limit of
deformation in the same direction as the pr...
High Tensile Australian Wires
Straightening a wire  pulling through a
series of rollers
Prestrain in a particular directi...
High Tensile Australian Wires
Special pulsing process.
This method :
1. Permits the straightening of high tensile
wires
2....
High Tensile Australian Wires
Higher yield strength 
more flexible.
Supreme grade
flexibility = β-titanium.
Higher resil...
High Tensile Australian Wires
Mollenhauer 
Supreme grade wire  faster and gentler
alignment of teeth.
Intrusion  simult...
High Tensile Australian Wires
Methods of increasing yield strength of
Australian wires.

1. Work hardening
2. Dislocation ...
High Tensile Australian Wires
Clinical significance of high yield strength.
Flexibility – Yield strength
Elastic Modulus
R...
High Tensile Australian Wires
Zero Stress Relaxation
If a wire is deformed and held in a fixed
position, the stress in the...
High Tensile Australian Wires
external forces

particles slip over each other

activation of the wire is lost
Overcome

...
High Tensile Australian Wires
Zero stress relaxation in springs.
To avoid relaxation in the wire’s working
stress
Diameter...
High Tensile Australian Wires
Twelftree, Cocks and Sims (AJO 1977)
Premium plus, Premium and Special plus
wires showed min...
High Tensile Australian Wires
Hazel, Rohan & West (1984)
– Stress relaxation of Special plus wires after
28 days was less ...
High Tensile Australian Wires
Pulse straightened wires – Spinner
straightened
(Skaria 1991)
– Strength, stiffness and Rang...
High Tensile Australian Wires
Anuradha Acharya (2000)
– Super Plus (Ortho Organizers) – between
Special plus and Premium
–...
High Tensile Australian Wires
Highest yield strength and ultimate tensile strength
as compared to the corresponding wires....
High Tensile Australian Wires
Fracture of wires and crack propagation
Dislocation locking

High tensile wires have high d...
High Tensile Australian Wires
Small stress applied with the plier beaks

Crack propagation

Elastic energy is released
...
High Tensile Australian Wires
Ways of preventing fracture
1. Bending the wire around the flat beak of
the pliers.
Introduc...
High Tensile Australian Wires

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High Tensile Australian Wires
2. The wire should not be held tightly in the
beaks of the pliers.
Area of permanent deforma...
High Tensile Australian Wires

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High Tensile Australian Wires
3. The edges rounded  reduce the stress
concentration in the wire.
4. Ductile – brittle tra...
Multistranded Wires
2 or more wires of smaller diameter are
twisted together/coiled around a core wire.
Diameter - 0.0165 ...
Multistranded Wires
As the diameter of a wire decreases –
Stiffness – decreases as a function of the 4th
power
Range – inc...
Multistranded Wires
Elastic properties of multistranded archwires
depend on –
1. Material parameters – Modulus of elastici...
Multistranded Wires
Helical spring shape factor
Coils resemble the shape of a helical spring.
The helical spring shape fac...
Multistranded Wires

α = tan -1

l* .
π (D-d)
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Multistranded Wires
Bending shape factor
Complex property
– number of strands
– orientation of the strands
– diameter of t...
Multistranded Wires
Kusy (AJO 1984)
Triple stranded 0.0175” (3x0.008”) SS
GAC’s Wildcat
Compared the results to other wire...
Multistranded Wires

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Multistranded Wires

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Multistranded Wires
Did not resemble the 0.018” SS wire except Size
Wire-bracket relation.

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Multistranded Wires
Ingram, Gipe and Smith
(AJO 86)
Range independent of
wire size
Consistent for different
configurations...
Multistranded Wires
Nanda et al (AO 97)
Increase in No. of
strands  stiffness
Unlike single stranded
wires
– stiffness va...
Multistranded Wires
Kusy (AO 2002)
Interaction between individual strands was
negligible.
Range and strength Triple stran...
Multistranded Wires

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Friction
Two bodies in contact,
Relative motion
2 components :Frictional force –contact force between the sliding
surfaces...
Friction
Frictional force = Coefficient of friction x
normal force.
Coefficient of friction
– static
– kinetic

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Friction
Normal Force -

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Friction
Friction is determined by the relative
roughness of the two materials in contact.
This depends on :1. The materia...
Friction
Normal force –
1. Stiffness of the wire in bending.

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Friction
Friction is independent
of the area of contact
- Proffit
Rough at molecular
level – Asperities
Real contact only ...
Friction
Light loads can cause
plastic deformation.
Shearing of asperities.
“Stick-slip”
phenomenon.
Interlocking of
asper...
Friction
Frank and Nikoli (AJO-1980)
Friction depends on wire bracket angulation
– At lower angulations surface
– Higher ...
Friction
Rectangular wires > Round wires
– Greater area of contact.
At higher angulations  0.020” higher friction
than so...
Friction
Influence of wire material
NiTi wires - rougher surface than steel or
Elgiloy – more friction at low angulations
...
Friction
Stannard et al (AJO 1986)
surface layer of oxides - harder than the
material on the interior
unpredictability of ...
Friction
Before and after slidingSS had a smooth and polished structure
before sliding & surface roughness and wear
tracks...
Friction
Dry and wet conditions
Wet condition  the coefficient of friction
Except cobalt chromium
Liquid  the adhesion b...
Friction
Stainless steel and β titanium - lowest
friction.
NiTi
Cobalt Chrome. - Highest

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Friction
Tidy (AJO 1989)
stainless steel - lowest friction
NiTi second
TMA
TMA 5 times > stainless steel

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Friction
At high wire bracket angulations – normal
force more important.
– Initial stages – High friction of steel wires
–...
Friction
Round or Rectangular for sliding?
– After alignment, difference is negligible.
– Rect. Wire Better torque contro...
Welding of Steel
3 useful properties –
1. Comparatively low melting point,
2. High electrical resistance and
3. Low conduc...
Welding of Steel
Important to
– minimize the time of passing the current
– minimize the area of heating

Sensitization - b...
Welding of Steel
Join two thin sheets of metal
Same thickness
Joining tubes, wires and springs, soldering
is generally rec...
Cobalt Chromium
1950s the Elgin Watch
Rocky Mountain Orthodontics
Elgiloy
CoCr alloys - satellite alloys
– superior resist...
Cobalt Chromium
Cobalt – 40-45%
Chromium – 15-22%
Nickel – for strength and ductility
Iron, molybdenum, tungsten and titan...
Cobalt Chromium
Strength and formability modified by heat
treatment.
The alloy is highly formable, and can be
easily shape...
Cobalt Chromium

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Cobalt Chromium
Heat treated at 482oc for 7 to 12 mins
Precipitation hardening
  ultimate tensile strength of the alloy,...
Cobalt Chromium

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Cobalt Chromium
Blue – soft
Yellow – ductile
Green – semiresilient
Red – resilient

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Cobalt Chromium
Blue considerable bending, soldering or
welding
Red  most resilient and best used for
springs
– difficul...
Cobalt Chromium
After heat treatment 
Blue and yellow ≡ normal steel wire
Green and red tempers ≡ higher grade steel

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Cobalt Chromium
Heating above 650oC
– partial annealing, and softening of the wire

Optimum heat treatment  dark straw co...
Cobalt Chromium
Properties of Co-Cr are very similar to that of
stainless steel.
Force
– 2x of β titanium and
– 1/4th of n...
Cobalt Chromium
Frank and Nikoli (1980)
– Co-Cr alloys ≡ stainless steel.
Stannard et al (AJO 1986)
– Co-Cr highest fricti...
Cobalt Chromium
Ingram Gipe and Smith
(AJO 86)
Non heat treated
– Range < stainless
steel of comparable
sizes
But after he...
Cobalt Chromium
Kusy et al (AJO
2001)
The elastic modulus
did not vary
appreciably 
edgewise or ribbonwise configurations...
Cobalt Chromium
Round wires 
higher ductility than
square or
rectangular wires.

www.indiandentalacademy.com
Cobalt Chromium
As expected, the
modulus of elasticity
was independent of
temper of the wire.

www.indiandentalacademy.com
Cobalt Chromium
Elastic properties (yield strength and ultimate
tensile strength and ductility) were quite similar
for dif...
Cobalt Chromium

www.indiandentalacademy.com
Cobalt Chromium
Different tempers with different physical
properties – attractive
More care taken during the manufacture o...
Thank you
For more details please visit
www.indiandentalacademy.com
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Properties of orthodontic wire /certified fixed orthodontic courses by Indian dental academy

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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078

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Properties of orthodontic wire /certified fixed orthodontic courses by Indian dental academy

  1. 1. Properties of Orthodontic Wires Part I INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. Introduction Moving teeth and craniofacial harmony Forces and moments Wires Light continuous forces www.indiandentalacademy.com
  3. 3. History 1. Material Scarcity, Abundance of Ideas (1750-1930) noble metals Gold, platinum, iridium and silver alloys good corrosion resistance acceptable esthetics lacked the flexibility and tensile strength www.indiandentalacademy.com
  4. 4. History Angle (1887)  German silver (a type of brass) Opposition Farrar Neusilber brass (Cu 65%, Ni 14%, Zn 21%) various degrees of cold work – jack screws, – expansion arches, – Bands www.indiandentalacademy.com
  5. 5. History Wood, rubber, vulcanite, piano wire and silk thread Steel - as ligature wire. www.indiandentalacademy.com
  6. 6. History Stainless steel (entered dentistry -1919) Opposition  Emil Herbst  gold wire was stronger than stainless steel. (1934) www.indiandentalacademy.com
  7. 7. History 2. Abundance of materials, Refinement of Procedures (1930 – 1975)  Improvement in metallurgy and organic chemistry Cobalt chrome (1950s) Nitinol (1970s) www.indiandentalacademy.com
  8. 8. History 3. The beginning of Selectivity (1975 to the present) Beta titanium (1980) CAD/CAM Composites and Ceramics Iatrogenic damage  Nickel and bis-GMA www.indiandentalacademy.com
  9. 9. Basic Properties of Materials Elements – no simpler form  Atoms Electrons – orbits around nucleus Electron shells Electrons form the basis of bonds In metals, the energy levels are very closely spaced and the electrons tend to belong to the entire assembly rather than a single atom. www.indiandentalacademy.com
  10. 10. Basic Properties of Materials Molecules – 2 or more atoms Amorphous – similar properties in all directions – isotropy  Glass atoms organize themselves into specific lattices  geometry CRYSTAL  anisotropy www.indiandentalacademy.com
  11. 11. Basic Properties of Materials anion – cation –anion – cation extremely strong Wiskers reinforce If like ions are forced together, breakage results. Unlike metals, crystals cannot deform. www.indiandentalacademy.com
  12. 12. Basic Properties of Materials alloy crystals grow anion – cation –anion – cation Order is the dream of man, and chaos the rule of nature www.indiandentalacademy.com
  13. 13. Basic Properties of Materials Crystals penetrate each other such that the crystal shapes get deformed Grains  microns to centimeters Grain boundaries Atoms are irregularly arranged, and this leads to a weaker amorphous type structure. Alloy  combination of crystalline (grains) and amorphous (grain boundaries) www.indiandentalacademy.com
  14. 14. Basic Properties of Materials www.indiandentalacademy.com
  15. 15. Basic Properties of Materials Vacancies – These are empty atom sites www.indiandentalacademy.com
  16. 16. Interstitials – Smaller atoms that penetrate the lattice Eg – Carbon, Hydrogen, Oxygen, Boron. www.indiandentalacademy.com
  17. 17. Basic Properties of Materials Substitutial Element – another metal atom can substitute one of the same or similar size. E.g. Nickel or Chromium substituting iron in stainless steel. www.indiandentalacademy.com
  18. 18. Basic Properties of Materials The three dimensional arrangement of lines that can be visualized as connecting the atoms in undisrupted crystals, is called a lattice. Unit cell Crystal  combination of unit cells, in which each shell shares faces, edges or corners with the neighboring cells 14 crystal lattices www.indiandentalacademy.com
  19. 19. Basic Properties of Materials www.indiandentalacademy.com
  20. 20. Basic Properties of Materials The atoms, which are represented as points, are not static. Instead, they oscillate about that point and are in dynamic equilibrium. www.indiandentalacademy.com
  21. 21. Basic Properties of Materials various defects  slip planes www.indiandentalacademy.com
  22. 22. Basic Properties of Materials shear stress  atoms of the crystals can glide more the slip planes easier is it to deform Slip planes intercepted at grain boundaries www.indiandentalacademy.com
  23. 23. Basic Properties of Materials If the shearing force is:Small - atoms slip, and return back to their original position (elastic deformation) Beyond the elastic limit crystal suffers a slight deformation permanent (plastic deformation) Greater stress - fracture www.indiandentalacademy.com
  24. 24. Basic Properties of Materials During deformation - atomic bonds within the crystal get stressed  resistance to more deformation Number of atoms that get stressed also increases  resistance to more deformation Strain or work hardening or cold work www.indiandentalacademy.com
  25. 25. Basic Properties of Materials Strain hardening  Hard and strong Brittle. Annealing – heat below melting point. – More the cold work, more rapid the annealing – Higher melting point – higher annealing temp. – ½ the melting temperature (oK) www.indiandentalacademy.com
  26. 26. Basic Properties of Materials Recovery Recrystallization Grain Growth www.indiandentalacademy.com
  27. 27. Basic Properties of Materials www.indiandentalacademy.com
  28. 28. Before Annealing Recovery – Relief of stresses Recrystallization – New grains from severely cold worked areas Grain Growth – large crystal “eat up” small ones www.indiandentalacademy.com
  29. 29. Basic Properties of Materials Recovery Heat Treatment – Relief of internal stresses – Heating to low temperatures (370 – 480oC) for 11 mins – Increase in measured elastic properties – Residual stresses + External stresses www.indiandentalacademy.com
  30. 30. Basic Properties of Materials Various methods of obtaining smaller grain size 1. Enhancing crystal nucleation by adding fine particles with a higher melting point, around which the atoms gather. 2. Preventing enlargement of existing grains. Abrupt cooling (quenching) of the metal. Dissolve specific elements at elevated temperatures. Metal is cooled Solute element precipitates barriers to the slip planes. www.indiandentalacademy.com
  31. 31. Basic Properties of Materials Twinning Closed packed hexagonal type of crystals Two symmetric halves Fixed angle NiTi Subjected to a higher temperature, de - twinning occurs www.indiandentalacademy.com
  32. 32. Basic Properties of Materials www.indiandentalacademy.com
  33. 33. Basic Properties of Materials Polymorphism Metals and alloys exist as more than one type of structure Transition from one to the other Allotropy At higher temperature, ironFCC structure (austenite) lower temperatures,  BCC structure (ferrite) www.indiandentalacademy.com
  34. 34. Basic Properties of Materials Iron  FCC form (austenite), Lattice spaces greater, Carbon atom can easily be incorporated into the unit cell www.indiandentalacademy.com
  35. 35. Basic Properties of Materials On Cooling FCC  BCC Carbon diffuses out as FeC FeC adds strength to ferrite and austenite TIME www.indiandentalacademy.com
  36. 36. Basic Properties of Materials Rapidly cooled (quenched) – Carbon cannot escape Distorted body centered tetragonal lattice called martensite www.indiandentalacademy.com
  37. 37. Basic Properties of Materials Grain boundaries are more in number Alloy is stronger and more brittle Interstitials are intentionally incorporated into the alloy to make it hard when it is quenched. www.indiandentalacademy.com
  38. 38. Basic Properties of Materials Cooled slowly Other crystal structures are formed at intermediate temperatures Softer Some are stable at room temperature Ultimately, the final structure is softer and more workable www.indiandentalacademy.com
  39. 39. Basic Properties of Materials Tempering – Reheat the alloy to intermediate temperature Partial formation of the softer alloys More workable www.indiandentalacademy.com
  40. 40. Basic Properties of Materials Some alloys FCC to BCC by rearrangement of atoms Diagonal plane of the BCC unit becomes the face of the FCC unit Shape memory alloys – Easy switching from one type of structure to another. Bain distortion Over a range of temperature {hysteresis} www.indiandentalacademy.com
  41. 41. Elastic Properties Force applied to wire Deflection External force Internal force (equal and opposite) Internal force = Stress Area of action Deflection change in length = Strain Original length www.indiandentalacademy.com
  42. 42. Elastic Properties Types of stress/strain Tensile Compressive Shear Complex force systems www.indiandentalacademy.com
  43. 43. Elastic Properties www.indiandentalacademy.com
  44. 44. Stress Elastic Properties Elastic Portion www.indiandentalacademy.com Strain
  45. 45. Elastic Properties When the stress is removed, the wire returns back to its original dimension. Hooke’s law www.indiandentalacademy.com
  46. 46. Elastic Properties Stress Yield strength 0.1% Proportional Limit Elastic Limit www.indiandentalacademy.com Strain
  47. 47. Stress Elastic Properties Ultimate Tensile Strength www.indiandentalacademy.com Fracture Point Strain
  48. 48. Elastic Properties ultimate tensile strength is higher than the yield strength important clinically  maximum force that the wire can deliver Ultimate tensile strength higher than the stress at the point of fracture – reduction in the diameter of the wire www.indiandentalacademy.com
  49. 49. Stress Elastic Properties Slope α Stiffness Stiffness α 1 . Springiness www.indiandentalacademy.com Strain
  50. 50. Stress Elastic Properties Range Springback www.indiandentalacademy.com Strain
  51. 51. Elastic Properties Strength = Stiffness x Range www.indiandentalacademy.com
  52. 52. Elastic Properties Resiliency When a wire is stretched, the space between the atoms increases. Within the elastic limit, there is an attractive force between the atoms. Energy stored within the wire. www.indiandentalacademy.com
  53. 53. Elastic Properties Formability - amount of permanent deformation that the wire can withstand without breaking Indication of the ability of the wire to take the shape Also an indication of the amount of cold work that they can withstand www.indiandentalacademy.com
  54. 54. Stress Elastic Properties Resilience Formability www.indiandentalacademy.com Strain
  55. 55. Elastic Properties Flexibility large deformation (or large strain) with minimal force, within its elastic limit. Maximal flexibility is the strain that occurs when a wire is stressed to its elastic limit. Max. flexibility = Proportional limit Modulus of elasticity. www.indiandentalacademy.com
  56. 56. Elastic Properties 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. Fatigue – Repeated cyclic stress of a magnitude below the fracture point of a wire can result in fracture. This is called fatigue. www.indiandentalacademy.com
  57. 57. Requirements of an ideal archwire (Kusy 1. Esthetics 7. Resiliency 2. Stiffness 8. Coefficient of friction 3. Strength 9. Biohostability 4. Range 10. Biocompatibility 5. Springback 11. Weldability 6. Formability www.indiandentalacademy.com
  58. 58. 1. Esthetics Desirable No compromise on mechanical properties White coloured wires discolour Destroyed by oral enzymes Deformed by masticatory loads Except the composite wires www.indiandentalacademy.com
  59. 59. 2. Stiffness / Load deflection Rate Thurow - force:distance ratio, measure of resistance to deformation. Burstone – Stiffness is related to – wire property & appliance design Wire property is related to – Material & cross section. Wilcock – Stiffness α Load Deflection www.indiandentalacademy.com
  60. 60. Stiffness / Load deflection Rate Magnitude of the force delivered by the appliance for a particular amount of deflection. Low stiffness or load deflection rate implies that:1) Low forces will be applied 2) The force will be more constant as the appliance deactivates 3) Greater ease and accuracy in applying a given force. www.indiandentalacademy.com
  61. 61. Stiffness / Load deflection Rate The shape and cross section of a wire have an effect on the strength of the wire. The effects of these will be considered subsequently. www.indiandentalacademy.com
  62. 62. 3. Strength Yield strength, proportional limit and ultimate tensile/compressive strength Kusy - force required to activate an archwire to a specific distance. Proffit - Strength = stiffness x range. Range limits the amount the wire can be bent, Stiffness is the indication of the force required to reach that limit. www.indiandentalacademy.com
  63. 63. 4. Range Distance that the wire bends elastically, before permanent deformation occurs (Proffit). Kusy – Distance to which an archwire can be activated Thurow – A linear measure of how far a wire or material can be deformed without exceeding the limits of the material. www.indiandentalacademy.com
  64. 64. 5. Springback Large springback Activated to a large extent. Hence it will mean fewer archwire changes. Ratio – yield strength Modulus of elasticity www.indiandentalacademy.com
  65. 65. 5. Springback Kusy -- The extent to which a wire recovers its shape after deactivation Ingram et al – a measure of how far a wire can be deflected without causing permanent deformation. (Contrast to Proffit). www.indiandentalacademy.com
  66. 66. 6. Formability Kusy – the ease in which a material may be permanently deformed. www.indiandentalacademy.com
  67. 67. 7. Resiliency Amount of energy stored in a body. www.indiandentalacademy.com
  68. 68. 8. Coefficient of friction Brackets (and teeth) must be able to slide along the wire High amounts of friction  anchor loss. www.indiandentalacademy.com
  69. 69. 9. Biohostability:- site for accumulation of bacteria, spores or viruses. An ideal archwire must have poor biohostability. 10. Biocompatibility:- Resistance of corrosion, and tissue tolerance to the wire. 11. Weldability:- the ease by which the wire can be joined to other metals, by actually melting the 2 metals in the area of the bond. (A filler metal may or may not be used.) www.indiandentalacademy.com
  70. 70. Properties of Wires Before the titanium alloys were introduced into orthodontics, the practitioners used only steel wires. So the way to control the stiffness of the wire was:1. Change the cross section of the wire 2. Increase the length of the wire ( inter bracket distance, incorporate loops.) www.indiandentalacademy.com
  71. 71. Effects of Wire Cross Section Wires of various dimensions and cross sections. Does the wire need to be move teeth over large distances, or does it need to correct the torque of the tooth? Is it primarily going to be used to correct first order irregularities, or second order? www.indiandentalacademy.com
  72. 72. Effects of Wire Cross Section primary factor  load deflection rate or stiffness play of the wire not very significant ligature ties minimizes the play in the first order www.indiandentalacademy.com
  73. 73. Effects of Wire Cross Section Play in the second order – 0.016” wire in 0.022” slot is only 1.15 times the play of a 0.018” wire. The play in the second order becomes significant if the wire dimensions are drastically different (0.010” and 0.020”) www.indiandentalacademy.com
  74. 74. Effects of Wire Cross Section www.indiandentalacademy.com
  75. 75. Effects of Wire Cross Section www.indiandentalacademy.com
  76. 76. Effects of Wire Cross Section Shape Moment of Inertia Ratio to stiffness of round wire Пd4 64 1 s4 12 1.7 b3h 12 1.7 b3h:d4 www.indiandentalacademy.com
  77. 77. Effects of Wire Cross Section Stiffness of different dimensions of wires can be related to each other. Relative stiffness Stiffness number (Burstone) 3500 3000 2500 2000 1500 1000 500 0 14 16 18 20 22 16x16 18x18 21x21 16x22 22x16 18x25 25x18 21x25 25x21 215x28 28x215 Wire dimension www.indiandentalacademy.com
  78. 78. Effects of Wire Cross Section www.indiandentalacademy.com
  79. 79. Effects of Wire Cross Section www.indiandentalacademy.com
  80. 80. A rough idea can be obtained clinically as well Forming an arch wire with the thumb gives an indication of the stiffness of the wire. Flexing the wires between the fingers, without deforming it, is a measure of flexibility Deflecting the ends of an archwire between the thumb and finger gives a measure of resiliency. www.indiandentalacademy.com
  81. 81. Effects of Wire Cross Section Rectangular wires  bending perpendicular to the larger dimension (ribbon mode) easier than bending perpendicular to the smaller dimension (edgewise). Relative stiffness 3000 (Burstone ) Stiffne ss numbe r 3500 2500 2000 1500 1000 500 0 14 16 18 20 22 16x16 18x18 21x21 16x22 22x16 Wire dime nsion 18x25 www.indiandentalacademy.com 25x18 21x25 25x21 215x28 28x215
  82. 82. Effects of Wire Cross Section The larger dimension  correction is needed. The smaller dimension  the plane in which more stiffness is needed. > first order, < second order – RIBBON > Second order, < first order - EDGEWISE www.indiandentalacademy.com
  83. 83. Effects of Wire Cross Section > 1st order correction in anterior segment > 2nd order in the posterior segment, wire can be twisted 90o ribbon mode in anterior region and edgewise in posterior region. www.indiandentalacademy.com
  84. 84. Effects of Wire Cross Section If both, 1st & 2nd order corrections are required to the same extent, then square or round wires. The square wires - advantage simultaneously control torque better orientation into a rectangular slot. (do not turn and no unwanted forces are created). www.indiandentalacademy.com
  85. 85. Effects of Wire Cross Section In torsion - absolute values of strength, stiffness and range are different, but the overall effect of changing the diameter of the wire is the same. 1. Strength – Increases with increase in diameter 2. Stiffness – increases 3. Range – decreases. www.indiandentalacademy.com
  86. 86. Effects of Length Loops,  the inter-bracket distance For bending 1. Strength – decreases proportionately 2. Stiffness – decreases as a cubic function 3. Range – increases as a square. www.indiandentalacademy.com
  87. 87. Effects of Length In the case of torsion, the picture is slightly different. Increase in length – 1. Stiffness decreases proportionately 2. Range increases proportionately 3. Strength remains unchanged. www.indiandentalacademy.com
  88. 88. Effects of Length Way the beam is attached also affects the values cantilever, the stiffness of a wire is obviously less wire is supported from both sides (as an archwire in brackets), again, the stiffness is affected www.indiandentalacademy.com
  89. 89. Effects of Length www.indiandentalacademy.com
  90. 90. Effects of Length Stiffness is also affected by the method of ligation of the wire into the brackets. Loosely ligated, so that it can slide through the brackets, it has ¼th the stiffness of a wire that is tightly ligated. www.indiandentalacademy.com
  91. 91. Clinical Implications LIGHT CONTINUOUS FORCES Stiff wires should be taboo to the orthodontist? Springier wire, can be easily distorted in the harsh oral environment. Aim at balance. www.indiandentalacademy.com
  92. 92. Clinical Implications Removable appliance cantilever spring The material of choice is usually steel. (Stiff material) Sufficiently thick steel wire Good strength to resist masticatory and other oral forces. Increase the length of the wire  – Proportionate decrease in strength, but the stiffness will decrease as a cubic function – Length is increase by either bending the wire over itself, or by winding helicals or loops into the spring www.indiandentalacademy.com
  93. 93. Clinical Implications In archwires of stiffer materials the same principle can be used. The length of wire between brackets can be increased – loops, or smaller brackets, or special bracket designs. Also, the use of flexible wires www.indiandentalacademy.com
  94. 94. Clinical Implications Multi-stranded wires Twisting of the two wires causes the strength to increase, so that the wire can withstand masticatory forces. The properties of multistranded wires depend on the individual wires that are coiled, and on how tightly they are coiled together. www.indiandentalacademy.com
  95. 95. Clinical Implications Variable cross-section orthodontics. Variable modulus orthodontics. www.indiandentalacademy.com
  96. 96. Clinical Implications www.indiandentalacademy.com
  97. 97. Clinical Implications variable modulus orthodontics – Advantage– relatively constant dimension – important for the third order control variable stiffness approach, – compromise control for getting a wire with adequate stiffness, – had to spend clinical time bending loops into stiffer archwires, which would offer less play. www.indiandentalacademy.com
  98. 98. Clinical Implications Take into account the amount of force that wire can deliver. For example, a NiTi wire  efficient in tipping teeth to get them into alignment, but may not be able to achieve third order corrections. After using rectangular NiTi wires for alignment, rectangular steel wire must always be used to achieve the correct torque of the tooth. www.indiandentalacademy.com
  99. 99. Corrosion Nickel 1. Carcinogenic, 2. mutagenic, 3. cytotoxic and 4. allergenic. Stainless steels, Co-Cr-Ni alloys and NiTi are all rich in Ni www.indiandentalacademy.com
  100. 100. Corrosion Placement in the oral cavity  Greater peril than implanting  Implanted material gets surrounded by a connective tissue capsule  In the oral cavity, the alloy is free to react with the environment. www.indiandentalacademy.com
  101. 101. Corrosion Passivating film  traces of Fe Ni and Mo. Aqueous environment – inner oxide layer – outer hydroxide layer. CrO is not as efficient as TiO in resisting corrosion some Ni release Improper handling  sensitization www.indiandentalacademy.com
  102. 102. Corrosion 1. Uniform attack – the entire wire reacts with the environment, hydroxides or organometallic compounds detectable after a large amount of metal is dissolved. 2. Pitting Corrosion – manufacturing defects sites of easy attack www.indiandentalacademy.com
  103. 103. Corrosion Steel NiTi www.indiandentalacademy.com
  104. 104. Corrosion 3. Crevice corrosion or gasket corrosion Parts of the wire exposed to corrosive environment Sites of tying to the brackets Plaque build up  disturbs the regeneration of the passivating layer Reach upto 2-5 mm High amount of metals can be dissolved in the mouth. www.indiandentalacademy.com
  105. 105. Corrosion 4. Galvanic corrosion two metals are joined or even the same metal after different type of treatment (soldering etc) difference in the reactivity  Galvanic cell.  Less Reactive (Cathodic)  More Reactive (Anodic) www.indiandentalacademy.com
  106. 106. Corrosion Anodic  Looses Electrons  Soluble ions  Leach out Cathodic  Accepts electrons  Even less reactive www.indiandentalacademy.com
  107. 107. Corrosion 5. Intergranular corrosion Sensitization 6. Fretting corrosion Wire and brackets contact Friction  surface destruction Pressure  rupture of the oxide layer Debris get deposited at grain boundaries, grain structure is disturbed. www.indiandentalacademy.com
  108. 108. Corrosion 7. Microbiologically influenced corrosion Adhersive Craters at the base of brackets Or wires directly bonded on to teeth shown by matasa. Certain bacteria dissolve metals directly form the wires. Others affect surface structure. www.indiandentalacademy.com
  109. 109. Corrosion www.indiandentalacademy.com
  110. 110. Corrosion 8. Stress corrosion Similar to galvanic corrosion Bending of wires  different degress of tension and compression. Alter the electrochemical behavior   anode cathode www.indiandentalacademy.com
  111. 111. Corrosion 9. Fatigue corrosion – Cyclic stressing of a wire Accelerated in a corrosive medium such as saliva www.indiandentalacademy.com
  112. 112. Corrosion Analysis of used wires also indicated that a biofilm was formed on the wire. Eliades et al Calcification – Shielding the wire – Protecting the patient form the alloy www.indiandentalacademy.com
  113. 113. Corrosion Ni and Cr – impair phagocytosis of neutrophils and – impair chemotaxis of WBCs. Ni at conc. Released from dental alloys – activating monocytes and endothelial cells, – promote intracellular adhesion. – This promotes inflammatory response in soft tissues. Arsenides and sulfides of Ni - carcinogens and mutagens. Ni at non toxic levels - DNA damage. www.indiandentalacademy.com
  114. 114. rthOdOntic Arch Wire MAteriAl www.indiandentalacademy.com
  115. 115. Precious Metals Upto about the 1950s Gold alloys Only wire which would tolerate the oral environment Crozat appliance – according to original design www.indiandentalacademy.com
  116. 116. Stainless Steel 1919 – Germany  used to make prostheses. Extremely chemically stable High resistance to corrosion. Chromium content. The chromium gets oxidized,  Impermeable, corrosion resistant layer. www.indiandentalacademy.com
  117. 117. Stainless Steel Variety of stainless steels Varying the degree of cold work and annealing during manufacture Fully annealed stainless steel  extremely soft, and highly formable Ligature wire “Dead soft” www.indiandentalacademy.com
  118. 118. Stainless Steel stainless steel arch wires are cold worked to varying extents,  yield strength increases, at the cost of their formability The steel with the highest yield strength, the Supreme grade steels, are also very brittle, and break easily when bent sharply. www.indiandentalacademy.com
  119. 119. Stainless Steel Structure and composition Chromium (11-26%)–improves the corrosion resistance Nickel(0-22%) – austenitic stabilizer copper, manganese and nitrogen - similar – amount of nickel added to the alloy – adversely affect the corrosion resistance. www.indiandentalacademy.com
  120. 120. Stainless Steel Carbon (0.08-1.2%)– provides strength Reduces the corrosion resistance Sensitization. Improper cooling after heat treatment – During soldering or welding – 400-900oc Chromium diffuses towards the carbon rich areas (usually the grain boundaries) www.indiandentalacademy.com
  121. 121. Stainless Steel Chromium carbides Amount of chromium decreases Chromium carbide is soluble,  intergranular corrosion. Stabilization www.indiandentalacademy.com
  122. 122. Stainless Steel Stabilization – – Element which precipitates carbide more easily than Chromium. – Usu. Titanium. – Ti 6x> Carbon – No sensitization during soldering. – Most steels used in orthodontics are not stabilized. www.indiandentalacademy.com
  123. 123. 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. www.indiandentalacademy.com
  124. 124. Stainless Steel Manufacture Various steps – 1. Melting 2. Ingot Formation 3. Rolling 4. Drawing www.indiandentalacademy.com
  125. 125. Stainless Steel Melting – Various metals of the alloy are melted – Proportion influences the properties Ingot formation – Molten alloy into mold. – Non uniform in compositon – Porosities and slag. – Grains seen in the ingot – control of grain size. www.indiandentalacademy.com
  126. 126. Stainless Steel – Porosities due to dissolved gasses (produced / trapped) – Vacuum voids due to shrinking of late cooling interior. – Important to control microstructure at this stage. www.indiandentalacademy.com
  127. 127. Stainless Steel Rolling – – First mechanical process. – Ingot reduced to thinner bars – Finally form a wire – Different wires, slightly different composition. www.indiandentalacademy.com
  128. 128. Stainless Steel – Altering of the shape of grains during rolling – Grains get elongated, defects get rearranged – Work hardening. – Wires starts to crack if rolling continues – Annealing is done – Rolling continued www.indiandentalacademy.com
  129. 129. Stainless Steel Drawing – More precise – Ingot  final size. – Wire pulled through small hole in a die – Progressively smaller diameter. – Same pressure all around, instead of from 2 opposite sides. www.indiandentalacademy.com
  130. 130. Stainless Steel – Annealing at regular intervals. – Exact number of drafts and annealing cycles depends on the alloy. www.indiandentalacademy.com
  131. 131. Stainless Steel Classification American Iron and Steel Institute (AISI) Unified Number System (UNS) German Standards (DIN). www.indiandentalacademy.com
  132. 132. Stainless Steel The AISI numbers used for stainless steel range from 300 to 502 Numbers beginning with 3 are all austenitic Higher the number  – More the iron content – More expensive the alloy – Numbers having a letter L signify a low carbon content www.indiandentalacademy.com
  133. 133. Stainless Steel www.indiandentalacademy.com
  134. 134. Stainless Steel Austenitic steels (the 300 series) Corrosion resistance FCC structure,  non ferromagnetic Not stable at room temperature, Austenite stabalizers Ni, Mn and N Known as the 18-8 stainless steels. www.indiandentalacademy.com
  135. 135. Stainless Steel Martensitic steel FCC  BCC BCC structure is highly stressed. More grain boundaries, – Stronger – Less corrosion resistant Making instrument edges which need to be sharp and wear resistant. www.indiandentalacademy.com
  136. 136. Stainless Steel Ferritic steels – (the 400 series) Good corrosion resistance Low strength. Not hardenable by heat treatment. Not readily cold worked. www.indiandentalacademy.com
  137. 137. Stainless Steel Austenitic steels more preferable :Greater ductility and ability to undergo more cold work without breaking. Substantial strengthening during cold work. (Cannot be strengthened by heat treatment). Strengthening effect is due partial conversion to martensite. Easy to weld Easily overcome sensitization Ease in forming. www.indiandentalacademy.com
  138. 138. Stainless Steel Duplex steels Both austenite and ferrite grains Increased toughness and ductility than Ferritic steels Twice the yield strength of austenitic steels Lower nickel content Manufacturing low nickel attachments www.indiandentalacademy.com
  139. 139. Stainless Steel Precipitation hardened steels Certain elements added to them  precipitate and increase the hardness on heat treatment. The strength is very high Resistance to corrosion is low. Used to make mini-brackets. www.indiandentalacademy.com
  140. 140. Stainless Steel General properties of steel Relatively stiff material www.indiandentalacademy.com
  141. 141. Stainless Steel www.indiandentalacademy.com
  142. 142. Stainless Steel Yield strength and stiffness can be varied – Altering the carbon content and – Cold working and – Annealing High forces - dissipate over a very short amount of deactivation (high load deflection rate). www.indiandentalacademy.com
  143. 143. Stainless Steel Clinical terms:Loop - activated to a very small extent so as to achieve optimal force Deactivated by only a small amount (0.1 mm) Force level will drop tremendously Not physiologic More activations www.indiandentalacademy.com
  144. 144. Stainless Steel Force required to engage a steel wire into a severely mal-aligned tooth. – Either cause the bracket to pop out, – Or the patient to experience pain. Overcome by using thinner wires, which have a lower stiffness. Fit poorly loss of control on the teeth. www.indiandentalacademy.com
  145. 145. Stainless Steel High stiffness  Maintain the positions of teeth Hold the corrections achieved Begg treatment, stiff archwire, to dissipate the adverse effects of third stage auxiliaries www.indiandentalacademy.com
  146. 146. Stainless Steel Lowest frictional resistance Ideal choice of wire during space closure with sliding mechanics Teeth be held in their corrected relation Minimum resistance to sliding www.indiandentalacademy.com
  147. 147. Stainless Steel Ni is used as an austenite stabilizer. Not strongly bonded to produce a chemical compound.  d likelihood of slow release of Ni www.indiandentalacademy.com
  148. 148. Stainless Steel Nickel and chromium content in the steel wires Cause patients to be sensitized Cause reactions in already sensitized patients www.indiandentalacademy.com
  149. 149. Stainless Steel Passivating layer dissolved in areas of plaque accumulation – Crevice corrosion. Different degrees of cold work – Galvanic corrosion Different stages of regeneration of passivating layer – Galvanic corrosion Sensitization – Inter-granular corrosion www.indiandentalacademy.com
  150. 150. 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. www.indiandentalacademy.com
  151. 151. High Tensile Australian Wires Beginners found it difficult to use the highest tensile wires Grading system Late 1950s, the grades available were – – Regular – Regular plus – Special – Special plus www.indiandentalacademy.com
  152. 152. High Tensile Australian Wires Newer grades were introduced after the 70s. Raw materials directly from the suppliers from out of Australia More specific ordering and obtaining better raw materials Higher tensile strength wires – premium www.indiandentalacademy.com
  153. 153. High Tensile Australian Wires Highly brittle, and broke easily Straightening the wire  softening and loss of high tensile properties. www.indiandentalacademy.com
  154. 154. 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. www.indiandentalacademy.com
  155. 155. High Tensile Australian Wires www.indiandentalacademy.com
  156. 156. High Tensile Australian Wires Plastic prestrain increases the elastic limit of deformation in the same direction as the prestrain. Plastic prestrain decreases the elastic limit of deformation in the direction opposite to the prestrain. If the magnitude of the prestrain is increased, the elastic limit in the reverse direction can reduce to zero. www.indiandentalacademy.com
  157. 157. High Tensile Australian Wires Straightening a wire  pulling through a series of rollers Prestrain in a particular direction. Yield strength for bending in the opposite direction will decrease. Premium wire  special plus or special wire www.indiandentalacademy.com
  158. 158. High Tensile Australian Wires Special pulsing process. This method : 1. Permits the straightening of high tensile wires 2. Does not reduce the yield strength of the wire 3. Results in a smoother wire, hence less wire – bracket friction. www.indiandentalacademy.com
  159. 159. High Tensile Australian Wires Higher yield strength  more flexible. Supreme grade flexibility = β-titanium. Higher resiliency  nearly three times. NiTi  higher flexibility but it lacks formability www.indiandentalacademy.com
  160. 160. High Tensile Australian Wires Mollenhauer  Supreme grade wire  faster and gentler alignment of teeth. Intrusion  simultaneously with the base wires Gingival health seemed better Originally in lingual orthodontics Equally good for labial orthodontics as well. www.indiandentalacademy.com
  161. 161. High Tensile Australian Wires Methods of increasing yield strength of Australian wires. 1. Work hardening 2. Dislocation locking 3. Solid solution strengthening 4. Grain refinement and orientation www.indiandentalacademy.com
  162. 162. High Tensile Australian Wires Clinical significance of high yield strength. Flexibility – Yield strength Elastic Modulus Resilience - (Yield strength)2 Elastic Modulus Plastic portion of the stress-strain graph is smaller  wires are more brittle. www.indiandentalacademy.com
  163. 163. High Tensile Australian Wires Zero Stress Relaxation If a wire is deformed and held in a fixed position, the stress in the wire may diminish with time, but the strain remains constant. Property of a wire to give constant light force, when subjected to external forces (like occlusal forces). www.indiandentalacademy.com
  164. 164. High Tensile Australian Wires external forces  particles slip over each other  activation of the wire is lost Overcome  Internal friction Between particles   yield strength www.indiandentalacademy.com
  165. 165. High Tensile Australian Wires Zero stress relaxation in springs. To avoid relaxation in the wire’s working stress Diameter of coil : Diameter of wire = 4 smaller diameter of wires  smaller diameter springs (like the mini springs) Higher grade wires, ratio can be 2 www.indiandentalacademy.com
  166. 166. High Tensile Australian Wires Twelftree, Cocks and Sims (AJO 1977) Premium plus, Premium and Special plus wires showed minimal stress relaxation. Special, Remanit, Yellow Elgiloy, Unisil. www.indiandentalacademy.com
  167. 167. High Tensile Australian Wires Hazel, Rohan & West (1984) – Stress relaxation of Special plus wires after 28 days was less than Dentaurum SS and Elgiloy wires. Barrowes (82) & Jyothindra Kumar (89) – Higher working range among steel wires. www.indiandentalacademy.com
  168. 168. High Tensile Australian Wires Pulse straightened wires – Spinner straightened (Skaria 1991) – Strength, stiffness and Range higher – Coeff. of friction higher – Similar surface topography, stress relaxation and Elemental makeup. www.indiandentalacademy.com
  169. 169. High Tensile Australian Wires Anuradha Acharya (2000) – Super Plus (Ortho Organizers) – between Special plus and Premium – Premier (TP) – Comparable to Special – Premier Plus – Special Plus – Bowflex – Premium www.indiandentalacademy.com
  170. 170. High Tensile Australian Wires Highest yield strength and ultimate tensile strength as compared to the corresponding wires. Higher range Lesser coefficient of friction – Surface area seems to be rougher than that of the other manufacturers’ wires. Lowest stress relaxation. www.indiandentalacademy.com
  171. 171. High Tensile Australian Wires Fracture of wires and crack propagation Dislocation locking  High tensile wires have high density of dislocations and crystal defects  Pile up, and form a minute crack  Stress concentration www.indiandentalacademy.com
  172. 172. High Tensile Australian Wires Small stress applied with the plier beaks  Crack propagation  Elastic energy is released  Propagation accelerates to the nearest grain boundary www.indiandentalacademy.com
  173. 173. 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. www.indiandentalacademy.com
  174. 174. High Tensile Australian Wires www.indiandentalacademy.com
  175. 175. 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. www.indiandentalacademy.com
  176. 176. High Tensile Australian Wires www.indiandentalacademy.com
  177. 177. 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. www.indiandentalacademy.com
  178. 178. Multistranded Wires 2 or more wires of smaller diameter are twisted together/coiled around a core wire. Diameter - 0.0165 or 0.0175, but the stiffness is much less. On bending  individual strands slip over each other and the core wire, making bending easy. www.indiandentalacademy.com
  179. 179. Multistranded Wires As the diameter of a wire decreases – Stiffness – decreases as a function of the 4th power Range – increases proportionately Strength – decreases as a function of the 3rd power Multistranded wires  Small diameter wires, High strength www.indiandentalacademy.com
  180. 180. Multistranded Wires Elastic properties of multistranded archwires depend on – 1. Material parameters – Modulus of elasticity 2. Geometric factors – moment of inertia & wire dimension 3. Dimensionless constants – Number of strands coiled – Helical spring shape factor – Bending plane shape factor www.indiandentalacademy.com
  181. 181. Multistranded Wires Helical spring shape factor Coils resemble the shape of a helical spring. The helical spring shape factor is given as – 2sin α 2+ v cos α α - helix angle and v - Poisson’s ratio (lateral strain/axial strain) Angle α can be seen in the following diagram :www.indiandentalacademy.com
  182. 182. Multistranded Wires α = tan -1 l* . π (D-d) www.indiandentalacademy.com
  183. 183. Multistranded Wires Bending shape factor Complex property – number of strands – orientation of the strands – diameter of the strands and the entire wire – helix angle etc. Different for different types of multistranded wires www.indiandentalacademy.com
  184. 184. Multistranded Wires Kusy (AJO 1984) Triple stranded 0.0175” (3x0.008”) SS GAC’s Wildcat Compared the results to other wires commonly used by orthodontists. www.indiandentalacademy.com
  185. 185. Multistranded Wires www.indiandentalacademy.com
  186. 186. Multistranded Wires www.indiandentalacademy.com
  187. 187. Multistranded Wires Did not resemble the 0.018” SS wire except Size Wire-bracket relation. www.indiandentalacademy.com
  188. 188. Multistranded Wires Ingram, Gipe and Smith (AJO 86) Range independent of wire size Consistent for different configurations of wires. For round as well as rectangular multistranded wires. www.indiandentalacademy.com
  189. 189. Multistranded Wires Nanda et al (AO 97) Increase in No. of strands  stiffness Unlike single stranded wires – stiffness varied as deflection varied. www.indiandentalacademy.com
  190. 190. Multistranded Wires Kusy (AO 2002) Interaction between individual strands was negligible. Range and strength Triple stranded Ξ Coaxial (six stranded) Stiffness  Coaxial < Triple stranded Range of small dimension single stranded SS wire was similar. www.indiandentalacademy.com
  191. 191. Multistranded Wires www.indiandentalacademy.com
  192. 192. Friction Two bodies in contact, Relative motion 2 components :Frictional force –contact force between the sliding surfaces and is opposite to it. Normal (perpendicular force) – forces that arise which are normal (perpendicular) to the two surfaces in contact www.indiandentalacademy.com
  193. 193. Friction Frictional force = Coefficient of friction x normal force. Coefficient of friction – static – kinetic www.indiandentalacademy.com
  194. 194. Friction Normal Force - www.indiandentalacademy.com
  195. 195. Friction Friction is determined by the relative roughness of the two materials in contact. This depends on :1. The material itself 2. manufacturing process (polishing, heat treatment etc.) 3. Shelf and/or use time.(due to corrosion, creep etc) www.indiandentalacademy.com
  196. 196. Friction Normal force – 1. Stiffness of the wire in bending. www.indiandentalacademy.com
  197. 197. Friction Friction is independent of the area of contact - Proffit Rough at molecular level – Asperities Real contact only at these spots. www.indiandentalacademy.com
  198. 198. Friction Light loads can cause plastic deformation. Shearing of asperities. “Stick-slip” phenomenon. Interlocking of asperities. Harder materials plow into softer materials. www.indiandentalacademy.com
  199. 199. Friction Frank and Nikoli (AJO-1980) Friction depends on wire bracket angulation – At lower angulations surface – Higher angulations Normal force www.indiandentalacademy.com
  200. 200. Friction Rectangular wires > Round wires – Greater area of contact. At higher angulations  0.020” higher friction than some rectangular wires (17x25) www.indiandentalacademy.com
  201. 201. Friction Influence of wire material NiTi wires - rougher surface than steel or Elgiloy – more friction at low angulations at high angulations - normal force – NiTi  lower stiffness than steel or Elgiloy  lower frictional resistance. www.indiandentalacademy.com
  202. 202. Friction Stannard et al (AJO 1986) surface layer of oxides - harder than the material on the interior unpredictability of the exact area of contact Friction cannot be determined accurately every time. www.indiandentalacademy.com
  203. 203. Friction Before and after slidingSS had a smooth and polished structure before sliding & surface roughness and wear tracks were seen after sliding β titanium had a grainy surface before and a smoother surface after sliding. NiTi and cobalt chrome had a fibrous surface before and no change after sliding. www.indiandentalacademy.com
  204. 204. Friction Dry and wet conditions Wet condition  the coefficient of friction Except cobalt chromium Liquid  the adhesion b/w molecules of the wire and bracket Saliva does not act as a lubricant www.indiandentalacademy.com
  205. 205. Friction Stainless steel and β titanium - lowest friction. NiTi Cobalt Chrome. - Highest www.indiandentalacademy.com
  206. 206. Friction Tidy (AJO 1989) stainless steel - lowest friction NiTi second TMA TMA 5 times > stainless steel www.indiandentalacademy.com
  207. 207. Friction At high wire bracket angulations – normal force more important. – Initial stages – High friction of steel wires – NiTi and β titanium have lower friction. (lower stiffness) After alignment, surface characteristics more important – Steel has smoother surface. www.indiandentalacademy.com
  208. 208. Friction Round or Rectangular for sliding? – After alignment, difference is negligible. – Rect. Wire Better torque control Leave rect. Wire in place for final corrections Start sliding after 1 visit. www.indiandentalacademy.com
  209. 209. Welding of Steel 3 useful properties – 1. Comparatively low melting point, 2. High electrical resistance and 3. Low conductivity of heat. www.indiandentalacademy.com
  210. 210. Welding of Steel Important to – minimize the time of passing the current – minimize the area of heating Sensitization - between 400 and 900oC Chromium carbides need time for their formation. www.indiandentalacademy.com
  211. 211. Welding of Steel Join two thin sheets of metal Same thickness Joining tubes, wires and springs, soldering is generally recommended. Electrodes - small tips, not exceeding 1 mm in diameter. www.indiandentalacademy.com
  212. 212. Cobalt Chromium 1950s the Elgin Watch Rocky Mountain Orthodontics Elgiloy CoCr alloys - satellite alloys – superior resistance to corrosion, comparable to that of gold alloys. www.indiandentalacademy.com
  213. 213. 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. www.indiandentalacademy.com
  214. 214. Cobalt Chromium Strength and formability modified by heat treatment. The alloy is highly formable, and can be easily shaped. Heat treated. – Strength  – Formability  www.indiandentalacademy.com
  215. 215. Cobalt Chromium www.indiandentalacademy.com
  216. 216. Cobalt Chromium Heat treated at 482oc for 7 to 12 mins Precipitation hardening   ultimate tensile strength of the alloy, without hampering the resilience. After heat treatment, elgiloy had elastic properties similar to steel. www.indiandentalacademy.com
  217. 217. Cobalt Chromium www.indiandentalacademy.com
  218. 218. Cobalt Chromium Blue – soft Yellow – ductile Green – semiresilient Red – resilient www.indiandentalacademy.com
  219. 219. 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. www.indiandentalacademy.com
  220. 220. Cobalt Chromium After heat treatment  Blue and yellow ≡ normal steel wire Green and red tempers ≡ higher grade steel www.indiandentalacademy.com
  221. 221. 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 is – – Greater resistance to fatigue and distortion – longer function as a resilient spring www.indiandentalacademy.com
  222. 222. Cobalt Chromium Properties of Co-Cr are very similar to that of stainless steel. Force – 2x of β titanium and – 1/4th of niti. www.indiandentalacademy.com
  223. 223. Cobalt Chromium Frank and Nikoli (1980) – Co-Cr alloys ≡ stainless steel. Stannard et al (AJO 1986) – Co-Cr highest frictional resistance in wet and dry conditions. www.indiandentalacademy.com
  224. 224. Cobalt Chromium Ingram Gipe and Smith (AJO 86) Non heat treated – Range < stainless steel of comparable sizes But after heat treatment, the range was considerably increased. www.indiandentalacademy.com
  225. 225. Cobalt Chromium Kusy et al (AJO 2001) The elastic modulus did not vary appreciably  edgewise or ribbonwise configurations. www.indiandentalacademy.com
  226. 226. Cobalt Chromium Round wires  higher ductility than square or rectangular wires. www.indiandentalacademy.com
  227. 227. Cobalt Chromium As expected, the modulus of elasticity was independent of temper of the wire. www.indiandentalacademy.com
  228. 228. Cobalt Chromium Elastic properties (yield strength and ultimate tensile strength and ductility) were quite similar for different cross sectional areas and tempers. This does not seem to agree with what is expected of the wires. www.indiandentalacademy.com
  229. 229. Cobalt Chromium www.indiandentalacademy.com
  230. 230. Cobalt Chromium Different tempers with different physical properties – attractive More care taken during the manufacture of the wires. www.indiandentalacademy.com
  231. 231. Thank you For more details please visit www.indiandentalacademy.com

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