Orthodontic archwires

ORTHODONTIC ARCHWIRES
MATERIALS AND PROPERTIES.
www.indiandentalacademy.com

Contents
 Introduction
 Physical Properties of archwires
 Evolution of archwires
 Gold
 Stainless steel
 Cobalt chromium
 Nickel Titanium
 Alpha & Beta titanium
 Esthetic archwires
 Conclusion

Orthodontic wires which generate the biomechanical
forces communicated through brackets for tooth
movement ,are central to the practice of profession.
In the rational selection of wires for a particular
treatment ,the orthodontist should consider a variety of
factors ,including the amount of force delivery that is
desired ,the elastic range or springback ,formability and
the need for soldering and welding to assemble the
appliance

 With the need to maintain a relatively large
inventory ,orthodontists must be concerned with
the costs of wires ,which can vary considerably
among wire alloys as well as among companies

PROPERTIES OF
ORTHODONTIC WIRES
Physical properties of materials can be considered as
the ways that Materials respond to changes in their
environment
Physical properties : Descriptive of size, shape and appearance.
Material properties : Subdivided into
.
•Characteristics that are independent of external influences
simply termed “Material” properties.
•Those that are associated in someway with the
conditions of use or the use environment.
e.g : Mechanical, Chemical, Thermal and Magnetic

1. Elastic or reversible deformation
Proportional limit, Resilience, Modulus of
Elasticity.
2. Plastic or irreversible deformation
e.g :- Percent elongation.
3. Combination of Elastics Plastic deformation
e.g :- Toughness and Yield strength

STRESS :-
When a force acts on a body tending to produce
deformation a resistance is developed to this external
force application. The INTERNAL reaction is equal in
intensity and opposite in direction to the applied external
force and is called stress.
Stress( ) = Force/Area
Commonly expressed as Pascal 1Pa = 1N/m2
. It is
common to report stress in units of Megapascals (MPa)
where 1 MPa = 106
Pa.
TYPES OF STRESS :- tensile ,compressive & shear
6

STRAIN :-
Whenever a force is applied to a body it undergoes
deformation.
Strain is described as the change in length (Δ L = L –
LO) per unit length of the body when it is subjected to a
stress.
Change in length L – Lo ΔL
Strain (∈ ) = = =
Original length Lo Lo
• Strain has no units of measurement.
• It is a Dimensionless quantity.
• Reported as an absolute value or as a percentage.

Strain Elastic
Plastic
Each type of stress is capable of producing a
corresponding deformation in a body.
• Tensile stress produces tensile strain.
• Compressive stress produces compressive
strain.
• Shear stress produces shear strain.

 STRESS STRAIN CURVE:-
 Represents energy storage capacity of the wire so
determines amount of work expected from a particular
spring in moving a tooth.
 Engineering Stress-Strain Curve
 In the calculation of stress it is assumed that the
cross sectional area of the specimen remains constant
during the test. Stresses are calculated based on
original cross sectional area.


 True Stress Strain Curve :-
A stress strain curve based on stresses calculated from
a Non Constant Cross sectional area is called a true
stress strain Curve.
A true-stress strain curve may be quite different from an
engineering stress-strain curve at high loads because
significant changes in the area of specimen may occur.

 Poisson’s ratio –
When a tensile force is applied to an object ,the
object becomes longer & thinner ,the ratio of
accompanying strain in direction perpendicular
to force application to the strain in the force
direction is poisson’s ratio

Important mechanical properties based on Elastic or
reversible deformation are :-
 ELASTIC MODULUS
 FLEXIBILITY.
 RESILIENCE
Other properties that are determined from stresses at the
end of elastic region of stress -strain plot and at
beginning of plastic deformation region.
 PROPORTIONAL LIMIT.
 ELASTIC LIMIT.
 YIELD STRENGTH

ELASTIC MODULUS (Young’s Modulus or Modulus of
Elasticity)
• The term elastic modules describes the relative
STIFFNESS or rigidity of a material which is measured
by the elastic region of stress – strain diagram.
• It is denoted by letter E
• determined from stress stain curve by calculating ratio
of stress to strain or slope of linear portion of curve.
Stress
Elastic Modulus = =
Strain ∈
6

 • Modulus of elasticity is independent of the
ductility of a material and it is not a measure of
its strength.
 • it is an inherent property of a material and
cannot be altered appreciably by heat
treatment, work hardening or any other kind of
conditioning. This property is called
STRUCTURAL INSENSITIVITY.

FLEXIBILITY :-
The maximum flexibility is defined as the strain that
occurs when the material is stressed to its proportional
limit.
RESILIENCE :-
Popularly the term Resilience is associated with
“springiness”.
 It is defined as the amount of energy absorbed by a
structure when it is stressed to its proportional limit.
Area bounded by the elastic region is measure of
Resilience

SPRINGINESS :-
Proportional to slope of elastic portion stress-strain
curve.
More Horizontal the slope
Springier the wire having low stiffness
TOUGHNESS
Higher the strength and higher the ductility (total plastic
strain) greater the toughness.
The total area under the entire stress-strain curve is a
measure of the energy required to fracture the material
A tough material is generally strong although a strong
material is not necessarily tough

BRITTLENESS :-
It is the relative inability of a material to sustain plastic
deformation before fracture of a material occurs.
ULTIMATE STRENGTH :-
Ultimate tensile strength or stress is defined as the maximum
stress that a material can withstand before failure in tension.
YIELD STRENGTH
( Yield Stress, Proof Stress)
It is defined as the stress at which a material exhibits a
specified limiting deviation from proportionality of stress to
strain.
Amount of permanent strain is arbitrarily selected for material
being examined and may be indicated as 0.1%, 0.2% or 0.5%
(0.001, 0.002, 0.005) permanent strain
Amount of permanent strain may be referred to as PERCENT
OFFSET. Many specifications use 0.2% as convention.

Proportional Limit :- (PL)
It is defined as the greatest stress that a
material will sustain without a deviation
from the linear proportionality of stress to
strain.
Hooke’s Law :- States that stress – strain
ratio is constant upto the proportional
limit, the constant in this linear stress-
strain relationship is Modulus of
Elasticity.
Below PL no permanent deformation
occurs in a structure.
Region of stress stain Curve.
Below PL – ELASTIC REGION
Above Pl – PLASTIC REGION

ELASTIC LIMIT :- (EL)
It is defined as maximum stress that a material can
withstand before it undergoes permanent deformation.
• For all practical purposes PL and EL represent same
stress. But they differ in fundamental concept :-
• PL deals with proportionality of strain to
stress in structure.
• EL describes elastic behavior of the material.
EL & PL limits are usually assumed to be identical
although their experimental values may differ slightly.

DUCTILITY AND MALLEABILITY :-
Ductility represents the ability of a material to sustain a large
permanent deformation under tensile load without rupture.
A material that may be drawn readily into a wire is said to be
DUCTILE.
Malleability :-
Ability of a material to sustain considerable permanent
deformation without rupture under compression as in hammering
or rolling into a sheet.
- Gold is most ductile and malleable pure metal
- Silver is second.
- Platinum ranks 3rd
in ductility.
Copper ranks 3rd
in malleability

Formability :-
It is defined as the amount of permanent
deformation that a wire can withstand before
failing.
Represents the amount of permanent bending
the wire will tolerate before it breaks.
Can be interpreted as area under plastic region
of stress – strain curve.

SPRING BACK
It represents the elastic strain recovered on unloading from
permanent deformation range.
Given by Expression :- YS/E. ( Yield strength / elastic modulus).
In many clinical situations, orthodontic wires are deformed
beyond their Elastic limit. Their spring back properties in portion
of load deflection curve between elastic limit and ultimate
strength are important in determining clinical performance.
Unloading curve from the permanent deformation range for well
behaved orthodontic wire alloys (i.e., other than NiTi wires) is
parallel to the elastic loading curve the value of YS/E represents
the approximately amount of elastic strain released by archwire
on unloading

. THREE BASIC ELASTIC PROPERTIES
Three basic properties of elastic materials and devices
follow :-
STIFFNESS
STENGTH
RANGE
STIFFNESS :- It is a force / distance ratio that is a
measure of resistance to deformation. It is a measure of
the force required to bend or otherwise deform the
material a definite distance.

STRENGTH : - It is a force value that is a measure of the maximum
possible load, the greatest force the wire or arch arrangement
can sustain or deliver if it is loaded to the limit to the material.
RANGE :- (WORKING RANGE) It is defined as the distance that
the wire will bend elastically before permanent deformation.
Relationship b/w three elastic properties :-
Strength = Stiffness x Range.
Factors that influence Strength Stiffness and Range :
• Mechanical arrangement by which force is applied to teeth e.g :-
bracket width, length of archwire, span and loops.
• Form of wire itself – size and shape of cross section.
Material including the alloy formula, its hardness etc

 BEHAVIOUR OF ARCHWIRE IN BENDING :-
 When an archwire is bent the metal is
stretched along the outside curvature and
compressed along the inside curvature.
 This combination of tension and compression
that resists bending and actually accomplishes
energy storage in the spring action of wire

Bending Moment :-
A measure of bending effort at any specified point in a
beam, measured in units of force times distance (Ounce
inches, grams-centimeters etc.)
critical (dangerous) section :-
Maximum bending moment in a cantilever is at the
supported end. In beam terminology the location of this
maximum bending moment is called CRITICAL or
DANGEROUS section

 NEUTRAL AXIS:
The part of a beam
that is neither
elongated nor
compressed in
bending. The neutral
axis is like a flat
ribbon through the
center of the wire,
midway between
outer and inner
curved sides.

. EFFECTS OF LENGTH AND CROSS SECTION ON ELASTIC
PROPERTIES:
EFFECTS OF LENGTH :-
IN BENDING :-
1
Stiffness
(Length)3
1
Strength
(Length)
Range (Length)2

BEHAVIOUR OF ARCHWIRE IN TORSION
TORSION :-
Torsion is the actual twisting (strain) that takes
place in the material as s result of the torque
Torque is the force (Stress) that causes twist.
In case of rectangular wire ”C” is the distance from
center of wire to an outer corner instead of to
one of the sides.

IN TORSION :-
There are no exponential
effects of length in torsion.
1. Strength :- Length has
absolutely no effect on
strength.
2. Range :- Range in torsion is
directly proportional to
length
3. Stiffness :- Stiffness in
torsion is inversely
proportional to length.

EFFECTS OF CROSS SECTION - Most potent single
factor available for control of orthodontic force
application.
IN BENDING
Round Wires
1. Range
‘C’ It is the distance b/w extreme fiber and neutral axis.
‘Index of working range of a bending wire
1
Range α
C
Therefore range is inversely proportional to diameter.

2. Stiffness :-
Stiffness of wires
depends on value called
the Moment of Inertia (I).
Moment of Inertia
Property of the cross
section of a beam that is
proportional to the effect
of the cross section on
resistance to bending or
twisting (Stiffness).
Stiffness α (diameter)4

3. Strength : -
Engineering term that
defines strength in terms of
wire’s cross section is
SECTION MODULUS –
Denoted by letter Z.
Z = I/C.
Strength α (Diameter)3


Rectangular wires:
In round wires → width and thickness are always same .
Both are called Diameter and treated as single
dimension.
Width & Thickness → Vary independently of one another
in rectangular wires.
Width:→ Used to describe dimension perpendicular to
direction of bending in plane of neutral axis.
Thickness: → dimension in plane of bend


1. Effect of width & thickness on range: Width has no
effect on bending range of wire. Range is inversely
related to thickness.
2. Effect of width on stiffness and strength: Width is
directly proportional to strength and stiffness in
rectangular wires.
3. Effect of thickness on stiffness and strength:
Stiffness α (Thickness)3
Strength α (Thickness)2

LABORATORY TESTS
In 1977, ADA specification No. 32 was published. This ADA
specification No. 32 for orthodontic wires not containing precious
metals contains directive on testing, packaging and marketing of
orthodontic arch wires.
Properties of orthodontic arch wires are commonly determined by
means of various laboratory tests.
Mechanical properties of orthodontic wires are determined from:-
- Tension test
- Bending test
- Torsion test.

Bending test: Considered more representative of clinical
conditions than the tension test.
Provides information on behaviour of wires when
subjected to 1st and 2nd
order bends.
Torsion tests: Reflect wire characteristics in third order
direction
Graphic descriptions:
- Stress against strain in tension
- Bending moment against angular deflection.
Torsional moment against torque angle.

Elastic Bending test:
Bending couple is applied at one end of specimen where
only rotation is permitted ; at the other end of test span
wire is held against fixed knife edge stop.
- Angular deformation measured is rotation of the shaft
(θ ).
- A typical plot of applied couple versus angular
deformation is done.
- Specified offset (2.9° according to ADA Sp. No. 32) is
used to determine yield strength.

MANUFACTURING OF
ORTHODONTIC WIRES
Metallic orthodontic wires are manufactured by a series of
proprietary steps, typically involving more than one company.
Sources:- Stainless steel orthodontic wires are procured by
suppliers from commercial sources of stainless steel.
Ingot:- Initially the wire alloy is cast in the form of an ingot which
must be subjected to successive deformation stages until cross
section becomes sufficiently small for wire drawing.
Rolling: The first mechanical step is rolling the ingot into a long bar.
This is done by series of rollers that gradually reduce the ingot to
a relatively small diameter.

Considerable work hardening of the alloy occurs during
rolling.
⇓
It may fracture if rolling is continued beyond this point.
⇓
TO PREVENT THIS:
 - Rolling process is interrupted
Metal is ANNEALED by heating to a suitably high
temperature

. Drawing:
After ingot has been reduced to a fairly small diameter
by rolling, it is further reduced to its final size by
drawing.
It is a forming process that is used to fabricate metal
wire and tubing. Deformation is accomplished by pulling
the material through a die by means of tensile force
applied to the exit side of a die.
Before it is reduced to orthodontic size, a wire is drawn
through many series of dies and annealed several times
along the way to relieve work hardening.

 Important proprietary details include:
 Rate of drawing.
 Amount of cross section reduction per pass.
 Nature of intermediate heat treatments.
 Die material.
Ambient atmosphere

RECTANGULAR WIRES:
 Rectangular cross section wires are fabricated
from round wires by a rolling process using
TURK’S HEAD which contains series of rolls.
 Rectangular or square cross section wires –
have some degree of rounding at corners
(EDGE BEVEL).

SPRING PROPERTIES OF WIRES:
Hardness and spring properties of most orthodontic
wires depend almost entirely on effects of work
hardening during manufacture.
 If metal is almost in need of another annealing at its
final size – it will have maximum work hardening and
spring properties.
 If drawing is carried too far enough after last annealing
– wire will be brittle.
If drawing is not carried far enough after last annealing –
too much residual softness and very low working range
and strength

STRUCTURE OF METALS AND ALLOYS
ALLOY: A solid mixture of a metal with one or more other
metals or with one or more non metals which are
mutually soluble in molten state is called an alloy.
e.g., Steel – Alloy of iron and carbon
Stainless steel alloy of iron, carbon and chromium.
PHASE: A phase is any physically distinct, homogenous
and mechanically separable portion of a system.
SOLID SOLUTION: An alloy phase in which one alloying
elements enters space lattice of the other.

GRAIN:- Metal is made up of
thousands of tiny crystals. Such
a metal is said to be
polycrystalline and each crystal
in a structure is called GRAIN.
UNIT CELL:- The smallest division
of the crystalline metal that
defines the unique packing is
called unit cell.

Crystal System Space Lattice
Cubic Simple cubic
Body-centered cubic
Face-centered cubic
Tetragonal Simple tetragonal
Body-centered tetragonal
Orthorhombic Simple orthorhombic
Body-centered orthorhombic
Face-centered orthorhombic
Base-centered orthorhombic
Rhombohedral (Trigonal) Simple rhombohedral
Hexagonal Simple hexagonal
Monoclinic Simple monoclinic
Base-centered monoclinic
Triclinic Simple triclinic

DEFORMATION IN METALS – ATOMIC LEVEL VIEW:
1. Elastic strain:
 Atoms are shifted from their equilibrium positions by fraction of
their atomic spacing.
 When stress is removed atoms return to equilibrium atomic
spacing.

2. Plastic Deformation:
This mode of deformation requires that atoms be shifted to new
atomic sites on lattice.
Mechanism of plastic deformation is called “DISLOCATION
MOTION”.


LINE DEFECTS
(DISLOCAITONS):
e.g., Edge dislocation:
Dislocation line:- The
lattice is regular except
for one plane of atoms
which is discontinuous
forming a dislocation
line.
The plane along which
dislocation moves is
known as SLIP PLANE.

 POINT DEFECTS

STRAIN HARDENING / WORK HARDENING:-
Process resulting from cold working (i.e., deformation at room
temperature) as a result of which greater stress is required to
produce further slip and the metal becomes stronger, harder and
less ductile.
Ultimate result of strain hardening with further increase in cold
working is FRACTURE.
RESULTS OF STRAIN HARDENING:-
 Increased surface hardness, strength and PL.
 Decreased ductility and resistance to corrosion.

CAUSES OF STRAIN HARDENING:-
If dislocation during translation meets some other type of lattice
discontinuity, its gliding movement under stress might be
inhibited.
Such discontinuities are:-
 POINT DEFECTS.
 Collision of one dislocation with different type
 Foreign atom or group of atoms of different lattice
characteristics.
 GRAIN BOUNDARIES

. HEAT TREATMENT:
A process characterized by the transfer of energy in the
form of heat to a metallic material to alter its mechanical
and / or thermal properties.
Carried out in 3 Steps:-
1. System temperature is elevated by placing it in a high
temperature environment. (e.g., furnance or a hot salt
bath or by electric resistance/ induction heating).
2.Upon reaching desired temperature the system is
maintained there for a specific period of time.
3.System is returned to its initial state temperature.

TYPES OF HEAT TREATMENT:
1.Stress relief heat treatment.
2.Annealing heat treatment.
3.Hardening heat treatment.

1. Stress relief heat treatment:-
Releases the stresses incorporated in metal due to cold
working procedures.
Mechanism: Internal stresses are relieved by minute
slippages and readjustments in intergranular relations
without loss of hardening.
e.g., - Recommended temperature for stress relieving
stainless steel is 750°F (399°C) for 11min.

2.Annealing heat treatment:
A heat treatment process employing a relatively high
temperature that results in recrystallisation of
microstructure and produces marked changes in
mechanical properties.
Stages of annealing: Recovery
Recrystallisation
Grain growth.
 Temperature are substantially above that of stress relief
– Annealing of stainless steel requires few minutes at
1800-2000°F.

3. Hardening heat treatment (precipitation hardening):
Process by which a metal alloy is hardened and
strengthened by extremely small and uniformly
dispersed particles that precipitate from a
supersaturated solid solution.
- Also called Age hardening.
- Long term process (of several hours).
- Carried out at temperature somewhat below that
necessary to anneal followed by rapid quenching.
e.g., heat treatment of Co-Cr alloy to increase their
strength and resilience.

 CHEMICAL INFLUENCES:
 Oral cavity environment is inherently corrosive. The oral
fluids are strong, potential reactants toward oxidation of metals.
 CORROSION: A chemical or electrochemical process through
which a metal is attacked by natural agents such as air and
water, resulting in partial or complete dissolution, deterioration or
weakening of any solid substance.
 TARNISH: A process by which a metal surface is dulled in
brightness or discolored through formation of chemical film such
as sulfide and an oxide.
 Tarnish is often forerunner of corrosion

1.    Galvanic corrosion: An accelerated attack occurring on a less
noble metal when electrochemically dissimilar metals are in
electrical contact in presence of liquid corrosive environment.
-      Also known as Dissimilar metals corrosion.
2.    Stress corrosion:
Cold working of an alloy by bending, burnishing etc localizes
stresses in some parts of the structure.
⇓
A couple composed of stressed metal, saliva and unstressed metal
is formed.
⇓
Stressed area is more readily dissolved by the electrolyte

3. Concentration cell corrosion:
e.g., crevice corrosion.
Accelerated corrosion in narrow spaces caused by localized
electrochemical processes and chemistry changes such as
acidification and depletion of O2
content.
OTHER TYPES OF CORROSION:
Pitting corrosion.
Microbiologically induced corrosion.
Fretting corrosion

. WIRE CHARACTERISTICS OF CLINICAL RELEVANCE :-
Several characteristics of orthodontic wires are considered for
optimum performance during treatment which include :-
SPRING BACK
STIFFNESS / LOAD DEFLECTION RATE
FORMABILITY
MODULUS OF RESILIENCE OR STORED ENERGY
BIOCOMPATIBILITY AND ENVIRONMENTAL STABILITY
JOINABILITY
FRICITION

EVOLUTION OF ORTHODONTIC ARCHWIRES
 GOLD :-
Up until 1930’s the only orthodontic wires available were made
of Gold and their alloys.
1887 – Angle tried replacing noble metals with German silver
(Neusilber) a Brass (65% Cu, 14% Ni, 21% Zn).
Gold alloys Esthetically pleasing
Excellent Corrosion resistance
Low proportional limit.
The material that was to truly displace noble metals was stainless
steel.
1940’s :-
With the substantial rise in the cost of gold Austenitic stainless
steel began to displace gold.

In early 1940 s Begg partner with Wilcock to make what they
envisioned to the ultimate in resilient orthodontic wires –
AUSTRALIAN STAINLESS STEELS.
By 1960s gold was universally abandoned in favour of stainless
steel.
In 1960s :-
Cobalt –Chromium alloys were introduced. Their physical
properties were very similar to stainless steel. However they had
the advantage that they could be supplied in softer and more
formable state that could be hardened by heat treatment
. In 1962 :-
Buehler discovers Nitinol at Naval Ordinance laboratory.

In 1970 :- Andreasen brought this intermetallic composition of 50%
Ni and 50% Ti to orthodontics through University of Iowa.
Unitek company licensed the patent (!974) and offered a
stabilized martensitic alloy that doesn’t exhibit shape memory
effect under the name NITINOL.
In 1977 :
Beta titanium was introduced to orthodontic profession by C.J
Burstone and Jon Goldberg. This beta titanium alloy had a
modulus closest to that of traditional gold along with good
springback, formability and weldability.

In 1984 :
Mr. A.J Wilcock Jr. as per request of Dr. Mallenhauer of
Melbourne Australia resulted in production of Ultra high tensile
stainless steel round wires – The SUPREME GRADE.
In 1985 :-
Burstone reported of an alloy, Chinese NiTi developed by Dr.
Tien Hua Cheng and associates at the General Research
Institute for nonferrous metals in Beijing china.
In 1986 :
Miura et al reported on Japanese NiTi, an alloy developed at
Furukawa Electric Company Limited Japan in 1978. Both of
these alloys i.e Chinese NiTi and Japanese NiTi are active
austenitic alloys that form Stress Induced Martensite (SIM)

In 1988 :
Mr. A.J Wilcock Jr. develops much harder. Alpha Titanium
archwires.
In 1990 :
Neo-Sentalloy is introduced as a true active martensitic alloy.
In 1992 :
Optiflex a new Orthodontic archwire – developed by M.F Talass.
Combined unique mechanical properties with a highly esthetic
appearance.
In 1994 :-
Copper NiTi, a new quaternary alloy containing Ni, Ti, Cu and Cr
was invented by Dr. Rohit Sachdeva. Display phase transition at
27° C, 35° C, 40°C.

In 2000 :-
Titanium Niobium – an innovative new arch wire
designed for precision tooth to tooth finishing reported
by Dalstra et al.
Additional progress in orthodontic arch wire materials
including composite “plastic” wires is being made.

GOLD ALLOYS
I
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. COMPOSITION :-
Similar to type IV gold casting alloys. Two types
of gold wires are recognized in ADA Sp. No. 7
Type I wire (75% gold) High noble or
Type II wire (65% gold) Noble Metal
alloys

Wire type Gold
Platinu
m
Palladiu
m
Silve
r
Coppe
r
Nicke
l
Zin
c
ADA
Type I
54-63 7-18 0-8 9-12 10-15 0-2
0-
0.6
ADA
Type II
60-67 0-7 0-10 8-21 10-20 0-6
0-
1.7
P-G-P
25-30 40-50 25-30 16-17
P-S-C
0-1 42-44
38-
41

General effects of Constituents
Pt and Pd → ↑ the fusion temperature.
Copper → Contributes to ability of alloy to
AGE HARDEN
Nickel→ Strengthens the alloy.
Zinc → Scavenger agent.

. MECHANICAL PROPERTIES : -
Yield strength - 50 x 103
– 160 x 103
p.s.i
Elongation - 3 – 16%.
Modulus of Elasticity - 15 x 106
p.s.I
. HEAT TREATMENT:-
Strengthened to variable stiffnesses with proper heat
treatment, although they are typically used in the as –
drawn condition.
Accomplished by :-
Heating at 450° C (842° F) for 2 min.
Cooling to 250° C (482° F) over a period of 30 min .
Quenching to room temp.

ADVANTAGES :-
• Good formability.
• Capable of delivering lower forces than stainless steel.
• Easily joined by soldering.
• Excellent corrosion resistance.
DISADVANTAGES :-
• High Cost.
• Low proportional limit / yield strength.
USES :-
Only the Crozat appliance is still occasionally made
from gold following original design of early 1900s.

STAINLESS STEEL

. HISTORICAL BACKGROUND :-
→ The corrosion resisting steel was reported by
Berno Strauss and Edward Maurer of Germany in
Journal Stahl Undeisen in 1914.
→ Stainless steel (SS) entered dentistry in 1919
Introduced at Krupp’s Dental Polyclinic in Germany by the
company’s dentist Dr. F. Hauptmeyer.
He first used it to make a prosthesis and called it Wipla
(Wieplatin ; In German like platinum).
By 1937 – value of SS as an orthodontic material had
been confirmed.

. METALLURGICAL ASPECTS :-
Steels – Iron based alloys that usually contain less that 1.2%
carbon.
Lattice arrangements of Iron Ferrite
Austentite
Martensite
Ferrite :- (α - iron)
• Pure iron has BCC structure at room temp
• Stable upto 912° C.
• Carbon has a very low solubility in ferrite (0.02 wt %) – because
spaces between atoms in BCC structure are small and oblate.
Austenite :- (γ - Iron )
• Face centred Cubic (FCC) structure.
• Exists between 912° C - 1394°C.
Maximum carbon solubility of 2.1 weight %.

Martensite :
• It Austenite is cooled rapidly (quenched).
⇓
Undergoes a spontaneous DIFFUSIONLESS
transformation to Body
Centered tetragonal (BCT) structure.
• Highly distorted and strained lattice.
• Hard, strong, brittle.

TEMPERING :-
Heat
Martensite Ferrite + Carbide
Treatment (525° C)
This process results in
- ↓ The hardness
↑ toughness

COMPOSITION AND TYPES OF STAINLESS STEEL :-
Steel + 12-30% Chromium → STAINLESS STEEL
• When at least 10-12% Chromium is present.
⇓
• A Coherent oxide layer formed that passivated the surface
rendering the alloy ‘STAINLESS’
CLASSIFICATION :
Steels are classified according to the American Iron and Steel
Institute (AISI) system.
Ferritic
Three types of stainless steel Austenitic
Martensitic

TYPE
(Space lattice)
CHROMIUM NICKEL CARBON
Ferritic (BCC)
11.5 – 27 0 0.20 max.
Austenitic (FCC)
16 –26 7 – 22 0.25 max.
Martensitic (BCT)
11.5 – 17 0 – 2.5 0.15 – 1.20
BALANCE is Iron

Ferritic Stainless steels – AISI 400 series
• Provide good corrosion resistance at a low cost
provided that high strength is not required.
• Not readily work hardenable.
• Finds little application in dentistry.
Martensitic Stainless steels – AISI 400 Series
• High strength and hardness.
• Less corrosion resistant and less ductile.
Used for surgical and cutting instruments

Austenitic Stainless Steel – AISI 300 series
Most commonly used for orthodontic materials. Most
corrosion resistant of the stainless steels.
AISI 302
Three Types AISI 304
AISI 316 L
18% Chromium.
AISI 302 8% Nickel.
0.15% Carbon.
Balance iron

Function of Nickel - Stabilizes Austenite phase at room temp so it
is an “AUSTENIZING ELEMENT”. Other e.g :- Mn and N.
Mechanism : Makes diffusion of carbon so low that Austenite
cannot decompose to pearlite and temperature is too low to allow
formation of Martensite.
AISI 304 :- Similar Composition
Chief difference → Carbon content (0.08%)
Both 302 and 304 stainless steel are designated as 18-8
stainless steel
Type 316 L – ‘L’ → Low Carbon Content
Carbon content → 0.03% max. carbon
Used for implants.

Austenitic stainless steel is preferable to
Ferritic SS b’coz
• Greater ductility and ability to undergo more
cold work without fracturing.
• Substantial strengthening during cold working
• Greater ease of welding.
• Ability to fairly readily overcome sensitization.
•

1. STIFFNESS :- High stiffness demonstrated by large values of
Modulus of Elasticity.
→ Necessitate use of smaller wires for alignment of
moderately or severely displaced teeth.
→ Advantageous in resisting deformation caused by extra
and intraoral tractional forces.
160-180 GPa
2. SPRING BACK :-
SS has lower spring back than those of newer titanium based
alloys.- .0060-.0094

3. RESILIENCE OR STORED ENERGY :-
Represents work available to move teeth.
Resilience of activated SS wires is substantially less than that of
Beta titanium and Nitinol wires.
Clinical Relevance : Implies that stainless steel wires produce higher
forces that dissipate over shorter periods of time than either beta
titanium or nitinol wires, thus requiring more frequent activation or
archwire changes.
4. FORMABILITY :-
Excellent formability,yield strength- 1100-1500MPa
5. JOINABILITY :-
SS wires can be soldered and welded. Stainless steel wires can
be fused together by welding but this generally requires
reinforcement with solder.

Important Considerations in Soldering SS :-
•     SS wire should not be heated to too high temp
→           To minimize Carbide precipitation.
→           To Prevent excessive softening of wire.
•      Use of low fusing sliver solders (620° C - 665° C). Silver
solders corrode in use because they are anodic to stainless steel.
•      Fluoride containing fluxes should be used because they
dissolve the passivating film formed by chromium.  Solder does
not wet the metal when such a film is present.
Welding :
Needs reinforcement by solder
Bands and Brackets are usually welded.

BIOCOMPATIBILITY AND ENVIRONMENTAL STABILITY :-
CORROSION RESISTANCE :-
SS owes it corrosion resistance to Chromium – a highly reactive
base metal .
A thin transparent but tough and impervious oxide layer ( Cr2
O3

forms [PASSIVATION] on surface of alloy when it is subjected to
oxidizing atmosphere such as room air.
O2
is necessary to form and maintain the film.
Causes of Corrosion of Stainless Steel :-
• Any surface roughness or unevenness.
• Incorporation of bits of Carbon steel or similar metal in its
surface.

• Stress Corrosion.
Severe strain hardening may produce localized electric
couples in presence of an electrolyte such as saliva.
• Soldered joints.
Attack by solutions containing chlorine


Classification Example
Acetic acid Vinegar
Copper chloride Certain appliance cleansers
Fatty acids By - products of the micro-organism, Streptococcus mutans
General foods Beet juice
Hydrogen sulfide Effluent of mouth air
Lactic acid Spoiled milk
Phosphoric acid Colas
Salt water Saliva
Sodium hypochlorite Certain appliance cleansers
Sulfite solution Wine
Zinc chloride Certain mouth washes and certain appliance cleansers

SENSITIZATION OF 18-8 SS :-
18–8 stainless steel may loose its resistance to corrosion if it is
heated b/w 400° C-900°C. The reason for decrease in
corrosion resistance is :
⇒ Precipitation of Chromium Carbide (Cr3
C) at the grain
boundaries.
⇒ Formation of Cr3-
C is  most rapid at 650°C. Chromium is depleted
adjacent to grain boundaries.
    When chromium combines with carbon its passivating qualities
are lost
⇓
    Chromium is depleted adjacent to grain boundaries.
⇓
   Alloy becomes susceptible to INTERGRANULAR CORROSION.

Methods to Minimize Sensitization :-
1.    Keeping out of sensitizing temp range (425° - 650° C)
2.    Controlling the Carbon.
1. Controlling temp to prevent intergranular
corrosion :-
Speed in handling metal in sensitizing temp range –
effective means  of minimizing sensitization.
e.g Quenching immediately after soldering.

2. Stabilization of stainless steel :-
Objective
→            To make Carbon unavailable for sensitizing
action Introduction  of some element that precipitates
as a carbide in  preference to chromium. e.g :- Titanium
and Columbium.
→            Titanium is introduced in an amount approx 6
times the carbon content. Steel that has been treated in
any of the foregoing ways to reduce the available
Carbon is called STABILIZED STEEL.
→            Stabilized steel is less susceptible to
Intergranular corrosion, but it is still not 100% safe.

 FRICTION :-
Low levels of bracket / wire friction have
been reported with experiments using
stainless steel wires. This signifies that
stainless steel arch wires offer lower
resistance to tooth movement than other
orthodontic alloys

 . HEAT TREAMENT :-
STRESS RELIEVING HEAT TREATMENT
Only heat treatment used with stainless steel after bending
wire into an arch, loops or coils.
Purpose :-
→ Causes significant decrease in residual stress.
→ Enhances elastic properties of wire – slight ↑
resilience.
Temperature :- Recommended temperature time
schedule is
750° F (399° C) for 11 min

 Funk (1951) :-
Recommends use of color Index to determine when
adequate heat treatment is achieved. He suggests a
straw colored wire indicates that optimum heat
treatment has been attained.
 METHODS OF HEATING :-
1. Oven is most reliable medium for heat Rx because of
its relatively uniform temperature.
2. Heating the wire with Electric current from a welder or
special heat treating power source.
Disadvantage: Lack of uniform temperature.

 I. SOLID STAINLESS STEEL ARCH WIRES
Are available in :-
1. Various sizes and cross sections
Round → 0.012, 0.014, 0.016, 0.018, 0.020 etc.
Rectangular → 0.016x 0.022, 0.017x 0.025, 0.018x 0.025,
0.019x 0.025 etc.
Square → 0.016 x 0.016 , 0.017 x 0.017


 2. Various Grades :-
American Orthodontics Standard
Gold tone
Super Gold tone
Dentaurum Super special spring hard
                            Extra spring hard
                            Spring hard
Unitek Standard
                                                         Resilient
RMO Resilient arch wire temper
Retainer wire temper
Clasp wire temper
Ligature wire temper
Available in Spooled forms
Straight lengths
Preformed archeswww.indiandentalacademy.com

 Preformed arches :-
•     Tru – Arch arch forms (A company)
•     Natural arches (American Orthodontics)
•     Preformed Anatomically Refined arches (Ormco)
•     Pentamorphic arches (RMO)
•     Standard and Proform (Ortho Organizers).


 . MULTISTRANED STAINLESS STEEL WIRES :-
 Composed of specified numbers of thin wire
sections coiled around each other to provide round or
rectangular cross section.
 Idea behind Multistranded Wires :-
 To improve strength and at the same time to
maintain desirable stiffness and Range properties,
many small wires are twisted together and even swaged
or spot welded.
 Result is an inherently high elastic modulus
material behaving as a low stiffness member because of
its Co-axial spring like nature.

overall stiffness of the orthodontic appliance (S) is
determined by the wire stiffness (Ws) and design
stiffness (As) as represented by:
S = Ws x As
Design stiffness (As) is dependent on factors such as
interbracket distance and the incorporation of loops
and coils into the wire. Altering the cross-sectional
stiffness (Cs) and/or the material stiffness (MS) as
designated by the formula, on the other hand, can
bring about changes in wire stiffness (Ws).
Ws = Ms x Cs

PROPERTIES :
Kusy and Dilley (1984) :-
Investigated strength, stiffness and spring back properties of
Multistranded SS wires in a bending mode of stress. They noted
that
→ Stiffness of triple stranded 0.0175 inch (3 x 0.008 inch) SS
arch wire was similar to that of 0.010 inch single stranded SS
wire.
→ 25 % stronger than 0.010 inch SS wire.
→ 0.0175 inch triple stranded wire and 0.016 Nitinol
demonstrated similar stiffness. Nitinol tolerated more than 50%
greater activation than multistranded wire.
Triple stranded wire – half as stiff as 0.016 inch Beta titanium
wire.

Ingram, Gipe and Smith (1986)
• Titanium alloy wires and multistranded SS wires have
low stiffness when compared with solid SS wires.
• Multistranded wires – spring back similar to Nitinol but
greater as compared to solid SS or Beta titanium wires.
• Multistranded and titanium wires have spring back
properties that are relatively independent of wire size
unlike solid stainless steel wires in which springback
decreases with increasing thickness.


Clinical applications
- Compare favourably with titanium wires.
- Provide a viable alternative to more expensive
titanium wires for initial leveling.
- Braided rectangular steel wires are available
in variety of stiffnesses and the stiffest of these
is 0.021 x 0.025 – useful in 0.022 slot for
finishing.

Examples :-
1. Ormco Corporation :-
→ Triple flex (Triple stranded  twisted wire).
→ Respond    (Coaxial – 6 stranded).
→ D-rect (Braided Rectangular – 8
stranded)
→ Force 9 (Braided Rectangular – 9
stranded).
2. TP Orthodontics :- Co-Ax wire ( 5 strands)
3. Unitek :-  Twist flex (Triple stranded)
4. RMO :- Triflex (3 strands, twisted

. AUSTRALIAN ARCH WIRES
Historical Background :-
Wilcock archwires have been the mainstay of Begg technique.
In 1940 S :-
Dr. Begg met Mr. Arthur J. Wilicok Sr. of Whittlesea, Victoria
who was directing metallurgical research projects at University of
Melbourne. After many years of research and development
introducing high tensile wires Mr. Wilcock produced cold drawn
heat treated wire that combined the balance between hardness
and resiliency with unique property of zero stress relaxation.
Different grades of Australian wires formerly used

Regular Grade :-
Lowest grade and easiest to bend.
Used  for practice bending.
Regular plus : Used for auxiliaries and archwires when more
pressure and resistance  to deformation is required.
Special Grade :-
0.016  is  often used for starting archwires in many techniques.
Special plus :-
Routinely used by experienced operators Hardness and
resiliency of 0.016 is excellent for supporting anchorage and
reducing deep overbites.  Must be bent with care.
Extra Special plus grade (ESP) :
→   This grade is unequalled in resiliency and hardness
→   Difficult to bend and brittle.

RECENT ADVANCES IN AUSTRALIAN WIRES
A.J Wilcock scientific and Engineering Company. Announced
new series of wire grades and sizes.
The fundamental difference for the superior properties for these
new wires is use of new manufacturing process called PULSE
STRAIGHTENING.
   Wires are straightened by use of 2 processes :-
1.    SPINNER STRAIGHTENING.
2.    PULSE STRAIGHTENING.

 1. SPINNER STRAIGHTENING :-
Mechanical process of straightening materials usually in cold
drawn condition. Wires are straightened by process of
REVERSE STRAINING.
Flexing in a direction opposite to that of original bend (This is
what is done manually in clinical setting). In conventional
manufacturing wire is pulled through high speed rotating Bronze
rollers which torsionally twist the wire into straight condition.
Disadvantage :-
→ Resultant deformation.
→ Decreased yield strength in tension and compression as
compared to that of the “as drawn” material.

 2. PLUSE STRAIGHTENING :
This process was developed to overcome above
mentioned difficulties.
Has several advantages over other straightening
methods :-
• Permits higher tensile wires to be straightened.
• Material yield strength is not diminished in any way.
Wire has smoother surface and hence less bracket friction.

NEWER GRADES OF WILCOCK WIRES :-
3 more grades have been introduced :
→           Premium
→           Premium plus
→           Supreme
PROPERTIES :-
Higher yield strength of newer grade wires influences
following properties :-


1. SPRINGBACK - (YS/E) :–
Newer grade wires have better springback than lower grade wires.
2. RESILIENCY – (YS2
/2E) :-
For the same material (ie with same modulus of elasticity) higher
yield strength results in greater resiliency. This means that
higher grade wires store or absorb more energy per unit volume
before they get permanently deformed.
Higher YS results in greater resiliency.
3. ZERO STRESS RELAXATION :-
Ability of wire to deliver over long periods a constant force when
subjected to an external load. Newer wires maintain their
configuration over long periods against deforming forces (forces
of occlusion).
Forces generated by them remain practically unaffected over
long periods.

4. FORMABILITY :- For the same material
greater resiliency lesser the formability.
Theses wires are more brittle than lower
grade wires and need to be bent in
specific way.
→                         Warm the wire by pulling
through fingers before  bending because
these wires have a ductile brittle transition
temp. slightly above room  temp.
    →      Bend the wire around square beak
of pliers.


CLINICAL USAGE OF NEW GRADES OF AUSTRALIAN WIRES :-
Their specific  applications are :-
1.    When relatively high load deflection rate is required :-
a)        For generating relatively lighter forces in stage I (for incisor
intrusion and lateral contraction or expansion of post teeth).
       → 0.016 or 0.018 Premium + or P wires are used.
b)    Large resistance   to deformation  is required  e.g., :-
        Maintaining arch from
      → 0.018 P or P + or 0.020 P wires are indicated.
   → Similarly for overcoming undesired reactions of a
   torquing auxiliary or uprighting springs in IIIrd stage –
       0.020 P wire is employed

2. When a low load deflection rate is required.
Supreme  grade arch wires of sizes 0.008 – 0.011
are used for :-
→           Unravelling of crowded anterior teeth.
→           MAA (Mollenhauer aligning auxiliary)
→           Miniuprighting springs.
0.010 Supreme :-
•     Used to form Reciprocal torquing auxiliaries.
•     Best indicated for incisially activated mouse traps
and Minisprings.
0.011 /0.012 supreme :
Used for aligning second molars towards and of stage
III.
0.012 Supreme – Torquing Auxiliary in Stage III
because of its high resiliency and springback

IV. RECENT ADVANCES IN STAINLESS STEEL
METALLURAGY :-
1. NICKEL FREE STAINLESS STEEL :-
The steel Din 1.4456 with its variations is one of them.
COMPOSITION :-
15 – 18% Chromium.
3 – 4% Molybdenum
10 - 14% Manganese.
0.9 % Nitrogen – To compensate for Ni.
Nickel is no more an alloying element (but only an impurity).
Orthodontic wires
→Menzamium (Scheu Dental)
→Noninium (Dentaurum

Menzanium Wire :-
→                               SS is fabricated in a patented high
pressure melting process where Manganese and
Nitrogen replace allergic components of Ni.
•     Ideal for Ni sensitive patient.
•     Corrosion  resistant and durable.
Availability :-
Supplied by Great lakes orthodontics.
Grade :- Hard and spring Hard.
Sizes :- 0.028, 0.032, 0.036.

Orthodontic archwires

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