metallurgy and archwires

METALLURGY, PHYSICAL
PROPERTIES AND
MANUFACTURING OF ARCH
WIRES

CONTENTS
 Introduction
 Metallurgy
 History
 Development
 Extractive Metallurgy
 Properties and structure of metals
 Theories of metallic bond
 Wires
 History
 Classification
 Composition
 Manufacturing
 Annealing
 Forms of steel
 Stainless Steel

• Properties of orthodontic wires
– Stress
– Strain
– Elastic limit
– Proportional limit
– Modulus of elasticity
– Flexibility
– Toughness
– Brittleness
– Ductility
– Malleability
• Ideal properties of orthodontic wires
– Esthetics.
– Stiffness
– Strength
– Range
– Springback
– Formability
– Resiliency (Resilience)
– Coefficient of friction
– Biohostability
– Biocompatibility
– Weldability

• Bauschinger effect
• Australian Wire
• Composite Wire
• Cobalt chromium / elgiloy
• Nickel Titanium
• Alpha Titanium
• Beta Titanium
• Clinical Considerations
– Wire Fracture And Crack Propagation Theory
– Gauge Conversion
• Biblography

INTRODUCTION
 Man’s long history of technological development has been marked by a
continuing search for improved materials.
 Ideally arch wires are designed to move the teeth with light continuous force. It is
important that these forces do not decrease rapidly. Also an ideal arch wire
should have certain properties like esthetics, Biohostability, formability,
resilience etc. but the search of a arch wire which meets all this requirements
and is perfect is still not over and the search continuous…..
 Selection of improved material depends upon its physical and mechanical
properties which in turn depends upon the collective reaction of the atoms of the
material.
 For not abusing the material and for designing the appliance to its full potential
the proper understanding of its physical and mechanical properties is required.
The aim of this seminar is to provide this basic knowledge about orthodontic
wire.

BASIC METALLURGY
 Metallurgy is the science and technology of metals.
 Almost 80% of known elements are metals.
 In earth crust most metals are in compound form and not as
pure metal.
 Extractive metallurgy is concern with the extraction of metals
from their ores and subsequent refinement of these metals.
 Physical metallurgy concerns the physical and mechanical
properties of the metals and how metals may be shaped into
useful products by means of heat and mechanical process.

METAL THROUGH AGES
 5500 B.C. when Egyptian made and wore copper beads and their
rulers bathed in water conveyed by copper pipes from Nile River to their
private pool. Copper nugget, iron gold and silver were also used in that
time.
 3500 B.C. in ancient city of Ur in Mesopotamia Gold in the form of
nuggets
 2400B.C. Silver nuggets were used to make the ornaments
 Copper was used the most; new techniques of using it came and it
was probably the first industrial metal.
 older days molten metal was casted in molds made up of clays, or
were cut in solid blocks of stones
 late 4th millennium B.C. metallurgy became sophisticated.
 Smelting was discovered at the end of the Stone Age
 Iron age date back to 1500B.C. in this era iron ore was first known to
be smelted.
 Around 1300 A.D. the first Forge was developed in Spain

FROM ART TO SCIENCE
o Advance was more during beginning of power age
and beginning of industrial revolution in
England in 18th centaury.
o With industrial revolution came increase in demand of
metal, and various iron works were made. It marked
the beginning of rolling mills (1700’s)
o 18th century the scientists started appreciating the
complex chemistry of metallurgy
o 20th century modern processes like x-ray
diffraction for atomic structure of metals was
discovered.

MODERN TECHNIQUES
o Each metal requires specific process for separating from ore. Most
important is the pig iron from iron by smelting in blast furnace. From this
iron steel is produced by Bessemer process, open hearth
process, electric furnace process and oxygenation furnace
process.
o Alumina from bauxite by Bayers process from which aluminum is
made.
o One of the most important advances is of joining two pieces of
metals such that the junction is as strong as the parent metal. The
standard technique is electric arc and gas welding. Now electron
beam welding is also used in which heat is produced by bombarding
metal with dense beam of high velocity electron. Also laser welding
which allows excellent control of heat so good for delicate work.
o For strengthening or giving some special properties a process
known as solidification process is done in which the molten metal is
solidified with in seconds. Another process of zapping the metal with
charged ions of another element in a vacuum chamber can be
undertaken.

EXTRACTIVE
METTALURGY
 Mineral dressing
 Roasting
 Sintering
 Smelting
 Leeching/Hydrometallurgy
 Electrolysis

Amalgamation

PROPERTIES OF
METALS
 Physical properties
 Conduct electricity
 Conduction of heat
 Highly reflective surface
 Most deform and not shatter under
pressure

 Chemical properties
 Metal oxides along with water form basic solution .
 Metal combines with non-metals to form ionic
compound
 Properties of a pure metal are a lot different from
properties of a compound containing that metal.
PROPERTIES OF
METALS

 Atomic properties
 low affinity for the electrons.
 Have the lowest ionization potential.
 Lowest electro-negativity.
 As the ionization potential is lower the electrons are
not tightly bound to the atom hence greater range
of motion of the electrons, giving the atom a larger
atomic size.
PROPERTIES OF
METALS

STRUCTURE AND
BONDING IN METALS
 Metallic Bond
 As most atoms have few valance electrons
and many contacting neighbors in a solid
state it becomes clear that metallic crystals
cannot be held together by single electron
covalent bond between each pair of atoms.

THEORIES FOR METALLIC
BOND
 Free Electron Or Electron Gas Model.
• The metal atoms are imagined to be positive ions immersed in a
negatively charged gas or sea of valance electrons giving entire
structure electrical neutrality. The valance electrons in the sea
are not associated with any given atom and are free to move
through entire body of solid metal.
Gas Of Free Electrons
Atoms

BOND
 Model accounts for
 Conduction of electricity, due to the mobility of free
valance electrons. Electric resistance increases with
increase in temperature as vibration motion of metal atoms
increases impending the current flow.
 Layers of metal atoms can be shifted upon each other
without disrupting the electron sea, therefore are plastic
under pressure causing metal to be ductile and
malleable.
 Molten metal conducts electricity as well as solid
metal as positive metallic ions are still in the conducting free
electrons sea.

BOND
 Band Theory Of Solids
• All the electrons in a solid occupy the allowed energy levels that
are closely spaced and practically continuous. These energy
bands are separated by gaps of varying magnitude with in which
electrons are not allowed.
• Model accounts for
 Highly reflective surface: the incoming visible light photons
excites an electron from top level of its partially filled energy band to
one of the continuum of unoccupied higher level of the same band.
The excited electron then falls to the top filled level of band emitting
a visible photon of exactly the same energy, therefore reflecting the
light.
 Ferromagnetism: a property possessed by iron and few other
metals which allows them to become fully magnetized, is due to
electrons opposite spin, opposite magnetic polarity is distributed in
unequal amount in the energy band hence giving the metal a bulk
magnetic moment.

Lattice Structure
 Space Lattice
 Any arrangement of atoms in a space such
that every atom is situated similarly to
every other atom is called as space lattice.

Lattice Structure
 Body Centered Cubic (B.C.C.)

Iron below 910O
C

Face Centered Cubic (F.C.C.)

Iron above 910O
C, gold, silver
 Hexagonal Closed Packed Structure (H.C.P.)

Zinc, magnasium

HISTORY
 Early years appliances were constructed mainly of
precious metals.
 Around 1929 austenitic (18-8 stainless steel) was
introduced to orthodontics in the form of hard drawn
arch wire.
 Later in year 1946 Mr. Claude Arthur J. Wilcock
started supplying orthodontic materials to Dr. Begg.
 Around 1970’s due to price increase use of precious
metal became difficult and precious metal in
orthodontics became obsolete.

CLASSIFICATION OF
ORTHODONTIC WIRES
 Design
 Dimension
 Composition
 Austenitic stainless steel wire.
 Australian wire.
 Elgiloy
 Nickel Titanium wire.
 Beta Titanium wire.

COMPOSITION
Types
Chemical Composition Of Stainless Steel
Cr Ni C Mn Si P S
302
17-
19
8-10 0.15 2 1 0.045 0.030
304
18-
20
8-12 0.08 2 1 0.045 0.030
416
12-
14
None 0.15 1.25 1 0.06 0.15

COMPOSITION
 Composition of Elgiloy:
 Cobalt: 20-40%
 Nickel: 15%
 Molybdenum: 7%
 Manganese: 2%
 Copper: 15%
 Beryllium: 0.04%
 Iron: 15.8%
 Composition of Nitinol:
Originally the composition was
 Nickel: 55%
 Titanium: 45%
But now 1.6% cobalt is added to modify transition temperature and
mechanical properties.
 Compostion of Beta Titanium:
 Titanium: 11%
 Molybdenum: 6%
 Zirconium: 4%
 Tin

FUNCTION OF VARIOUS
COMPONENTS IN A STAINLESS STEEL
WIRE
 Chromium: gives resistance to tarnish and
corrosion.
 Nickel: for corrosion resistance and
increasing the strength of the alloy.
 Manganese: act as a scavenger for sulphor.
 Molybdenum, Silicon, Cobalt in traces.

MANUFACTURE OF
ORTHODONTIC WIRES
 Various steps involved in the
manufacture of orthodontic wires are as
follows:
 Melting.
 Ingot formation.
 Rolling.
 Drawing.

PROCESS OF
MANUFACTURE
 Spinner Straightening
o It is the mechanical process of straightening
resistant materials, usually in the cold drawn
condition. The wire is pulled through rotating bronze
rollers that torsionally twist it into straight condition.
 Pulse Straightening
o The wire is pulsed in special machines that permit
high tensile wires to be straightened.

• The advantages of this method over other straightening methods
are:
– It permits the highest tensile wire to be straightened,
– The material tensile yield stress is not suppressed in any way,
– The wire has a much smoother appearance and hence less bracket
friction.
• The significance of this in the production of orthodontic springs is:
– Greater flexibility.
– Greater resiliency.
– It permits the usage of a smaller diameter wire resulting in a lighter and
more constant force with minimal or no relaxation.

STRESS RELIEF OF
STAINLESS STEEL
 It is a level of heat treatment at which internal
stresses are relieved by minute slippages and
readjustments in intergranular relations; without the
loss of hardening that accompanies the higher
temperature process of annealing.

WORK HARDENING /
STRAIN HARDENING
 In a polycrystalline metal there is a build up of
dislocations at the grain boundaries and occurs on
intersecting slip planes. Later point defect increases
and entire grain gets distorted leading to increased
stress required to cause further slip, leading to
stronger, harder and less ductile metal with less
resistance to tarnish and corrosion.
 Increases: - Hardness
Yield stress
Tensile stress
 Decreases: - Resistance to tarnish and corrosion
Ductility

•Cold Working
It is the process of deforming a metal at room
temperature.
•Annealing
It is the process in which the effects associated
with cold working (for example: strain hardening,
lowered ductility and distorted grains) can be
reversed by simply heating the metal.

ANNEALING
 Recovery
 Recrystallization
 Grain growth

Reduction
in area
Grain Size
Recovery Recrystallization Grain Growth
P
HY
S
I
C
AL
P
R
O
P
E
R
T
I
E
S Electric Conductivity
Elongation
Strength
Annealed Cold Worked Recovery Recrystallized Grain Growth

HARDENING AND HEAT
TREATMENT / STRESS RELIEF
ANNEAL
 The key to controlling the important internal structure of steel is
heat treatment. It makes the material soft when it must be
worked and hard or tough when required.
 Points in consideration while heat treating:
 Heat treating the wire before giving it the final shape does not
enhance the physical properties.
 When the wire is formed into arches loops etc. stress is induced at
the points of bending. These additional stresses are removed by
heat treatment. The loops, arches etc. acquire the new shape and
resist deformation towards previous form greater then it would have
had when it was untreated.
 For orthodontic wires heat treatment is done by placing in a heat
controlled oven over a specified time period. It has been found out
that 500o
C for 20 min and 750o
C for 10 min is adequate for stainless
steel wires.

FORMS OF STEEL
 At high temperatures (more than 1400 to 1500°F / 750 to 800°C) steel
is a homogenous material with all of the carbon in solid solution in the
iron. At this temperature, the iron carbide is completely decomposed.
This form of steel is called “Austenite”.
 At low temperatures (less than 450°F / 225°C), an almost pure
cementite, the hardest and most brittle form of iron-carbon combination
called “Martensite” is formed. This form of steel begins to form as the
mass of cooling metal reaches the 450°F (225°C) range and complete
transformation occurs at about 200°F (90°C).
 Between these high and low extremes of temperature many
intermediate phases are formed. These are various mixtures of ferrite
and cementite.

Slowly Cooled Ferrite + Cementite
Austenite Tempering
(heating to
200
o
C-450
o
C and
then
quenching)
Rapidly Cooled Martensite

• Tempering
It is the process of reheating steel to
intermediate temperature ranges usually below
1000°F [525 °C] under carefully controlled
conditions to permit a partial transformation into
softer forms. This is done to remedy steel which
when quenched in water results in very brittle
martensite that is unsuitable for most
mechanical applications.

STAINLESS STEEL
 Stainless Steel is defined as a alloy of
iron that is resistant to corrosion.
 It was discovered accidentally in U.K.
during second world was by a Sheffield
metallurgist BREARLEY. It was
patented in 1917.

• Ferritic stainless steel (400 series):
– It has good corrosion resistance, is cheaply made.
– Disadvantage of this type of stainless steel is that it is not hard nor can it be
hardened.
• Martensitic stainless steels (400 series):
– Alloys in the 400 series contain little or no Nickel and are primarily alloys of Iron
and Chromium.
– They can be heat treated much the same as carbon steel to form martensite at
room temperature.
– The low resistance to fracture and high corrosion resistance of these alloys
render them useful in the construction of orthodontic instruments.
– The disadvantage in such type of steel is its brittle nature.
• Austenitic stainless steel / 18-8 stainless steels (300 series):
– They contain Iron, Chromium 18%, Nickel 8% and 0.15% Carbon.
– The Nickel content has a stabilizing effect on austenite only at high
temperatures, but in the Chromium-Nickel steels, the austenite is stable even at
room temperature. Hence these alloys are called "Austenitic stainless steel".
– Presence of Chromium in the alloy provides the austenite with the necessary
strength and high resistance to corrosion.
– Commonly used in orthodontic appliances.

• The advantages of austenitic stainless
steel are:
– Most corrosion resistant form.
– Greater ductility.
– Strengthening during cold working.
– Ease of welding.
– Readily overcome sensitization.
– Less critical grain growth.
– Ease of forming.

• Sensitization of 18-8 Stainless Steel:
– The resistance to corrosion of stainless steel
reduces at temperature between 400o
C and 900o
C
due to precipitation of chromium carbide at the grain
boundaries. This is reduced by three methods:
• Reduce the carbon content so that carbide
precipitation does not occur.
• Introduction of some elements that precipitates as
carbide in preference to chromium. Titanium was
added approx six times the carbon content.
• Stainless steel is cold worked such that the
carbide precipitates along the slip planes and gets
more distributed, hence more resistant. This
method is used in orthodontic wires.

• Stabilization of Stainless Steel
– Austenitic form of steel is found at temperatures
between 912o
C to 1394o
C but due to its preferred
physical properties like greater ductility, ease of
welding etc. it is preferred over the other forms. To
make it stable at room temperature Nickel is added.
– Nickel, Carbon and Iron when quenched from 1000o
C
we get a austenitic structure which is a solid solution
of Chromium, Nickel, Carbon and Iron. Due to the
presence of nickel the conversion from austenitic to
martensitic state is sluggish and martensitic formation
temperature goes below the room temperature. This
austenitic solution can not be heat treated but can be
cold worked to increase the physical properties, this is
done while rolling into sheets or drawing into wires.

PROPERTIES OF
ORTHODONTIC WIRES
 Stress
 It is the force applied to a
mechanical part.
 It is measured in units of force such
as ounces/grams per unit area.
 Mathematically
 STRESS = FORCE / AREA

PROPERTIES OF
ORTHODONTIC WIRES
 Types of Stress
 Tension stress

PROPERTIES OF
ORTHODONTIC WIRES
 Types of Stress
 Compressive stress

PROPERTIES OF
ORTHODONTIC WIRES
 Types of Stress
 Shear stress

PROPERTIES OF
ORTHODONTIC WIRES
 Types of Stress
 Complex stress

A single type of pure stress does not occur in a
wire. Like when a wire is stretched along with
the tensile strength the diameter of the wire
decreases telling about the compressive stress
also some shear stress occurs.

PROPERTIES OF
ORTHODONTIC WIRES
 Strain
 Change of shape (deformation) of a material when
subjected to stress.
 Strain is measured in units of length such as
inches or millimeters.
 By definition strain is change in length per unit
length

STRAIN = l / L
 Strain can be elastic or plastic.

Elastic strain can be reversible

Plastic strain is due to the permanent displacement of
atoms inside the material.

PROPERTIES OF
ORTHODONTIC WIRES
Ultimate Tensile Strength
Yield Strength
STRAIN
b
Proportional Limit
Failure Point
S
T
R
E
S
S

PROPERTIES OF
ORTHODONTIC WIRES
 Proportional limit
 Defined as the greatest stress which
may be produced in a material such
that the stress is directly proportional to
the strain.

PROPERTIES OF
ORTHODONTIC WIRES
 Modulus of elasticity
 If any stress value equal or less than the
proportional limit is divided by its corresponding
strain value, a constant of proportionality will
result, this constant is called as Modulus of
elasticity.

Modulus of elasticity = Stress/Strain
 Unit for modulus of elasticity is force per unit area
(Mpa or psi)
 Modulus of elasticity of
 Nitinol 10X106
psi
 Beta Titanium 15X106
psi
 Gold Alloys 20X106
psi
 Stainless Steel 28X106
psi

PROPERTIES OF
ORTHODONTIC WIRES
 Elastic limits
 The elastic limit of a material is the
greatest stress to which a material can be
subjected, such that it will return to its
original dimensions when the forces are
released.

PROPERTIES OF
ORTHODONTIC WIRES
 Flexibility
 When a material can be bent considerably with small stress,
then the material is known as flexible.
 The flexibility according to Mr. Arthur J. Wilcock can be
found out by flexing the wires between the fingers.
Stress
Strain
Stress
Strain

PROPERTIES OF
ORTHODONTIC WIRES
 Toughness
 Is the property of being difficult to break.
 It is defined as energy required to fracture
a material.
 It is dependent upon the ductility of the
material; also the tough materials are
generally strong.

PROPERTIES OF
ORTHODONTIC WIRES
 Brittleness
 Brittleness is opposite of toughness. Brittle
materials are apt to fracture at or near its
proportional limit. Brittle materials not necessarily
lack in strength.

PROPERTIES OF
ORTHODONTIC WIRES
 Ductility
 It is the ability of the material to withstand
permanent deformation under tensile load without
rupture. It depends on the tensile strength and
plasticity.

PROPERTIES OF
ORTHODONTIC WIRES
 Malleability
 Is the ability of the material to withstand
permanent deformation under
compression, without rupture. It increases
with increase in temperature.

PROPERTIES OF
ORTHODONTIC WIRES
 According to Proffit are:

High strength.

Low stiffness.

High range.

High formability.

PROPERTIES OF
ORTHODONTIC WIRES
 According to Kusy (1997) a few ideal characteristics
desired in an archwire as follows:
 Esthetics.
 Stiffness
 Strength
 Range
 Springback
 Formability
 Resiliency (Resilience)
 Coefficient of friction
 Biohostability
 Biocompatibility
 Weldability

Esthetics
 No wire today meets this criterion.
 When coated, white-colored wires have
routinely succumbed to the forces of
mastication and/or enzyme activity of the oral
cavity. When uncoated, transparent wires
have had such poor mechanical properties
that they merely function as a placebo.
 The use of composites is one promising
approach toward achieving an esthetic
archwire with excellent overall properties.

Stiffness
 Thurow defines stiffness as a force/distance ratio that is a
measure of resistance to deformation (rate of force delivery).
 Stiffness is defined as the ratio of force to deflection of a
member.
Stiffness ∞ load
deflection
 Burstone determined stiffness as:
a) Stiffness (S) = Ws X As
i.e. Appliance stiffness = Wire stiffness X Design stiffness.
b) Stiffness (Ws)= Ms X Cs
This is wire stiffness = material stiffness number X cross -
sectional stiffness number.
 A quick way of finding stiffness according to A.J. Wilcock is by
forming an arch with the thumb which gives some indication of
the force required to deform the material.

Stiffness
 Stiffness of a wire can be varied by three
ways:
 The first and the traditional approach is vary the
second moment of area about the axis of bending,
which can be bought about by changing the
dimension of the wire.
 By changing the elastic modulus; various arch
wires have different modulus of elasticity which
can be used .
 Build up strand of stainless steel, example take a
core of stainless steel wrap wires around it. The
strand becomes more flexible as there is contact
slip between adjacent wrap wires and the core of
the wire.

Strength
 It is a force value that is measure of the maximum possible load.
 Kusy (1997) defines it as the force required to activate an archwire to a
specific distance.
 Strength depends on a combination of working range and stiffness.
 Proffit defines strength as the product of stiffness and range.

Strength = Stiffness X Range.
 The size and shape of the cross section of a wire have profound effects
on the stiffness, strength and working range of a wire.
 Tensile strength: It is the definite maximum value for a particular
material, beyond which if stressed the material undergoes very
localized plastic deformation and finally breaks.
 Yield strength: Stress at which a material exhibits a specified limiting
deviation from proportionality of stress to strain.

Range / Working Range
 Thurow defines it as a linear measure of how far a
wire or material can be deformed without exceeding
the limits of the material.
 Kusy defines it as the distance that an archwire can
be activated by a specific activation. He terms this
distance as "Working" range, when an orthodontist
defines the limit of activation.
 Proffit defines range as the distance that the wire will
bend elastically before permanent deformation
occurs.

Effects Of Length Of The Beam
And Cross-section On It’s
Properties
 Strength is inversely proportional to L.
 Working range is directly proportional to L2.
 Changing the diameter of a beam, no matter how it is supported,
greatly affects its properties.
 The parts of the wire farthest from the neutral axis take the brunt of any
bending action. They are stretched and compressed the most, so they
accomplish most force storage. These sections of the wire are called
the extreme fibers, a term that is descriptive of the shape and action of
this section of the wire and nothing more. The greater the distance
between the extreme fibers and the neutral axis, the more it will be
stretched or compressed in bending. This distance (usually abbreviated
"c") is the index of the working range of a bending wire. Working range
(or maximum acceptable bend) is inversely proportional to c.
 When beams of any type made from two sizes of wire are compared,
strength changes as a cubic function of the ratio of the two cross -
sections, springiness changes as the fourth power of the ratios and
range changes as a direct proportion. Thus, as the diameter of a wire
decreases, its strength and stiffness decrease.

Effects Dimensions Of A
Rectangular Wire On It’s Properties
 The width is defined as the dimension perpendicular to the
direction of bending in the plane of the neutral axis. Thickness is
the dimension in the plane of the bend.
Effect of width and thickness of range :
 Width has no effect on the range, while increase in thickness is
inversely related to range.
Effect of width on stiffness and strength :
 Width has a simple proportional relationship to the stiffness and
strength of rectangular wires. Doubling the width will double
both the stiffness and the strength.

Effects Of Of A Rectangular Wire
On It’s Properties
 Effect of thickness on stiffness and strength:
 Stiffness of a rectangular wire is proportional to
the cube of thickness.

Effects Of Of A Rectangular Wire
On It’s Properties
 Strength of a rectangular wire is
proportional to the square of the thickness.

Springback
 Kusy defines it as the extent to which the range recovers upon
deactivation of an activated arch wire. Springiness is inversely
proportional to stiffness.
 Kapila, Sachdeva (1989) referred to Springback as the
maximum elastic deflection.
Springback = YS
E
where; YS = yield strength and E = modulus of elasticity.
 It is a measure of how far a wire can be deflected without
causing permanent deformation or exceeding the limits of the
material.

Formability
 Kusy defines it as the ease with which a material
maybe permanent deformed as measured by the
magnitude of the difference between the elastic
range (which occurs as the proportional limit) and the
range failure.
 It can be related to the percentage elongation a wire
can undergo before fracture. Wires with high and
sharp yield points possess low elongation values.

STRAIN
b
S
T
R
E
S
S
F
o
r
m
a
b
i
l
i
t
y

Resiliency (Resilience)
 It is the amount of energy stored in a body when one unit
volume of the material is stressed not to exceed its proportional
limit.
 It is the capacity of a material for the elastic storage of
energy. The term resilience is associated with springiness. It
depends on the combined effects of stiffness and working range
and is independent of the nature of material , its size or form.
 Resiliency ∞ (Yield Stress)2
Elastic Modulus
R = P2
2E
where, R = modulus of resilience, P = proportional limit and, E
= modulus of elasticity.
 Resiliency can be found out by measuring how much is the
spring in the arch by deflecting between the thumb and the
index finger, according to Mr. A. J. Wilcock.

Resilience
STRAIN
b
S
T
R
E
S
S
RANGE

Coefficient of friction
 Stmulard, Gait, Haima (1966) calculated
kinetic coefficient friction µ as:
µ= T/2
N
 where, µ=coefficient of friction, T=frictional
force measured (this value is divided by two
as each wire had two surfaces in contact with
the binding grips) and N=normal force applied
to each binding grip surface.

Biohostability
 Is the ease with which a material will
culture bacteria, spores or viruses.

Biocompatibility
 It is achievement of compatibility of
non-living implant material with the
body.

Weldability
 The ease by which metals may be
joined by actually melting the work
pieces in the vicinity of the bond. A filler
metal may/may not be used to join the
work pieces.

BAUSCHINGER EFFECT
 This phenomenon was discovered by Dr. Bauschinger in
1886.
 He observed the relationship between permanent deformation
and loss of yield strength and found that if the metal was
permanently deformed in one direction then, it reduced its yield
strength in the opposite direction.
 If a straight peice of wire is bent so that permanent deformation
occurs and an attempt is made to increase the magnitude,
bending in the same direction as had originally be done, the
wire is more resistant to permanent deformation than if an
attempt had been made to bend in the opposite direction.
 The wire is more resistant to permanent deformation because a
certain residual stress remains in it, after placement of first
bend.
 If a bend is made in an orthodontic appliance the maximum
elastic load is not the same in all direction: it is greatest in the
direction identical to the original direction of bending or twisting.

BAUSCHINGER EFFECT
 Two noteworthy points about this effect are
 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 reverse to prestrain.
If the magnitude of prestrain is increased, the
elastic limit in the reverse direction can reduce to
zero.

BAUSCHINGER EFFECT
Reverse Strain
Yield Point
Yield Point
Yield Point
Forward Strain
Compressive
Stress
Tensile
Stress

PROPERTIES OF
AUSTRALIAN WIRES
 The Australian wires were developed by the late Mr.
Arthur J. Wilcock in order to meet the demands
made by Dr. Raymond Begg for his light wire
technique. The arch wire is a round austenitic
stainless steel wire that has been heat treated and
cold drawn to its proper diameter from round wires of
larger dimensions. These wires were known for their
high tensile strength, resiliency and toughness.
 The wires are marked in various sizes and grades.
The pulse straightening process rather than the
spinner straightening process was used in the
manufacture of the newer grades.

Composite Arch Wires (Zufall
and Kusy)
 Composition:
 (Zufall and Kusy)Matrix material is a network
copolymer, which consisted 61% by weight
bisphenol-A diglycidyl methacrylate, 39% by
weight triethylene glycol dimethacrylate
(TEGDMA) and 0.4% by weight benzoin ethyl
ether as the ultraviolet initiator for
polymerization.

Composite Arch Wires
 Composite Arch wires made of optical fiber,
it comprise of three layers.
I. Silicon dioxide core that provides the force for
moving teeth.
II. Silicon resin middle layer that protects the core
from moisture and adds strength.
III. A stain resistant nylon outer layer that prevents
damage to the wire and further increases its
strength.

Silicon
Dioxide Core Nylon Outer Layer
Silicon
Dioxide
Middle
Layer

Composite Arch Wires
 Advantages:
 Aesthetics.
 Complete stain resistant.
 Effective light continuous force.
 Very flexible has a wide range of action.
 Favorable mechanical properties.
 The stiffness could be varied by controlling the
reinforcement and matrix composition.

Cobalt Chromium Nickel
Alloys / Elgiloy
 Was developed in Elgin National Company for
modern precision time pieces.
 It is available in different temper and is color coded.
 Blue is easily bent even with fingers.
 Yellow is relatively ductile and more resilient.
 Green is more resilient and can be shaped with pliers.
 Red is most resilient elgiloy with high spring qualities.
 Its advantages are:
 Easier to bend then stainless steel and Ni-Ti. Wires.
 Can be heat treated after manipulation to achieve the
hardness.

Nickel-Titanium Wires
 Was invented in early 60’s by William F.
Buchler, a researcher metallurgist of the
Naval Ordinance Laboratory in Silver Springs,
Maryland.
 The name Nitinol is given for NI for nickel, TI
for titanium and NOL for Naval Ordinance
Laboratory.
 It was initially developed for space programs
but was first introduced into dentistry by
Unitek cooperation in 1970’s .

 NiTi wires have two remarkable properties which makes its use
in dentistry:
 Shape memory:
 The material remembers its original shape after being plastically
deformed while in martensitic phase. It is the phenomenon where
the alloy is soft and readily formable at low temperatures, but can
be easily returned to its original configuration when heated to a
suitable transition temperature.
 It is generally an accepted fact that NiTi alloy is a nearly
equiatomic intermetallic compound. A given zone lies between
the high and low temperature ranges. At high temperature range,
the crystal structure of NiTi alloy is in the austenitic phase. The
martensitic phase is at a low temperature range. By controlling the
low and high temperature ranges, a change in crystal structure
called martensitic transformation can be produced.

 When an external force is applied, the deformation of most
metals is induced with a slip of lattice; the deformation
of Niti alloy is induced with martensitic transformation.
The martensitic transformation can be reversed by
heating the alloy to return to its austenite phase and it is
gradually transformed by reversing back into the energy
stable condition. This means that the alloy can return to the
previous shape. This phenomenon is called shape
memory.
 This phenomenon is said to cause a change in its physical
properties.

In the martensitic phase which has a low temperature
range, the metal is ductile and acts like a safety fuse to
readily induce a change of shape.

In the austenite phase in the high temperature range, it

 Superelasticity:
 Superelasticity means the ability of the wire to exert the same
force whether it is deflected a relatively small or a large
distance.
 This can be produced by stress, not by temperature difference
and is called stress induced martensitic transformation.
 Martensitic transformation begins when an external force is
applied in such a manner that the stress exceeds a given
amount.
 Even when strain is added, the rate of stress increase; levels
off due to the progressive deformation produced by stress
induced martensitic transformation, indicating a movement
similar to slip deformation.
 On the other hand if the stress is diminished the NiTi alloy
returns to the previous shape without retaining the permanent
deformation because of the characteristic of returning to the
austenite phase within the given temperature range.

Alpha Titanium
 At temperatures below 815o
C titanium is stable in
hexagonal closed packed lattice also called as alpha
lattice, while at higher temperature metal is stable in
body centered cubic or Beta lattice.
 The alpha titanium is attained by adding 6%
aluminum and 4% vanadium to titanium.
 Due to its hexagonal structure it has lesser slip
planes, less is the number of slip planes the easier is
it to deform the metal, hence Alpha titanium which
has only one active slip plane is less ductile.

Molybdenum Alloy /
T.M.A
 The normally available titanium had a hexagonal closed packed
crystal form at temperatures below 1625o
F and has a elastic
deflection of one third that of stainless steel.
 In the 1960’s the new high temperature from of titanium alloy
became available which at high temperatures; this is at
temperatures above 1625o
F gets converted into a body centric
cubic lattice called as Beta Phase. If molybdenum was added to
it the titanium remained in its Beta Phase even when it was
cooled to room temperature. Such alloys were called as Beta
Stabilized Titanium or simply Beta Titanium.
 Advantages:
 High deflection without permanent deformation, almost twice to that
of stainless steel.
 Low force value, almost half of that of stainless steel.
 Highly formable, can be readily bent into loops etc.
 Can be welded together without much loss of its mechanical
properties.

Wire Fracture And Crack
Propagation Theory In Relation To
Appliance Forming
 This theory states that there exists a relationship between the applied
stresses and the internal stress at the head of dislocation pile-ups as
seen in high and sharp yield point materials.
 The presence of point defect/defects at the head of a dislocation may
form a minute crack. The stress concentration at this point is so high
that only a small amount of applied stress could initiate transgranular
crack propagation. The presence of carbide precipitations along the
highly elongated grain boundaries would require only a small amount of
surface energy to split the grains and the elastic energy thus released
would cause the crack to continue until the crack head is blunted by its
own plastic deformation and stops. This explains why a crack at times
travels up to half an inch from the point of bending, thus giving the
appearance of the wire skin splitting from the main wire.
 A few methods to avoid wire fracture are:
 Bending around the flat of the pliers,
 Rounding off the edges of the flat beak.
 Warming the wire between the fingers before bending

Gauge Conversion
 mm to Inch and Visa Versa
One meter = 39.37 inches
One mm = 0.03937 inches
If approximately accepted
1 mm = 0.040 inches
Or
1 mm = 40 / 1000 inch = 1 / 25 of an inch
Or
1 inch = 25 mm
 Inch Into Mils and mm Into Mils
Thousand of an inch = one mils
i.e. 1 / 1000 inch = one mils
1 inch = 1000 mils
0.04 inch = 0.04 X 1000 mils = 40 mils
Or
1 mm = 40 mils
 mm Into Gauge
Gauge of the wire = 29 – (amount in mm X 10)
Example
Gauge of 0.1 mm wire = 29 – (0.1 X 10) = 29 – 1 = 28gauge

BIBLOGRAPHY
 Craig Robert G. – Restorative Dental Materials, 9th edition C.V.
Mosby Company, 1993.
 Kenneth J. Anusavice - Philips’ Science Of Dental Materials,
10th edition W.B. Sounders Company, 1996.
 Thurow Raymond C. – Edgewise Orthodontics, 3rd edition, C.V.
 Graber Thomas M., Vanarsdall. Jr. Robert L. – Orthodontics,
Current Principles and techniques, 2nd edition, Mosby
Company, 1994.
 William R. Proffit – Contemporary Orthodontics, 3rd edition,
 Richard Van Noort –
 E.H. Greener –
 C.P. Adams –
 Lexicon Encyclopedia –
 World Encyclopedia –

BIBLOGRAPHY
 A review of contemporary arch wires: Their properties and
characteristics. Robert P. Kusy, Angle Orthodontics; 1997; 197-207.
 Some metallurgical aspects of orthodontic stainless steel. John V.
Wilkinson, Am. J. Orth.;1962; 48:192-200.
 Mechanical properties and clinical application of orthodontic wires.
Sunil Kapila and Rohit Sachdeva; Am. J. of Dentofacial Orthopedics.;
1989; 96:100-109.
 Stress relaxation and recovery behavior of composite archwire
bending. Scott W. Zufall and Robert P. Kusy; European Journal of
Orth.; 2000; 1-12.
 Applied materials engineering for orthodontic wires. Wilcock A. J. Jr.;
Australian Orth. J.; 1989; 11(1):22-29.
 Some metallurgical aspects of orthodontic stainless steel. Wilkinson
J.V.; Am. J. Of Orth.; 1962; 48(3):192-206.
 Interviews on orthodontic wires. Wilcock A.J. Jr.; JCO; 1988; XXII
(8):484-489.
 Comparative friction of wires under dry and wet conditions.
Stannard, Gau, and Hanna; AJO; 1986; 89(6) :485-491.

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