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1. Orthodontic wires-I
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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2. Contents
Introduction
Evolution of materials
Basic properties of materials
Mechanical & Elastic properties
Physical properties
Requirements of an ideal arch wire
Properties of wires
Orthodontic arch wire materials
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3. Introduction
“All you can do is push, pull or turn a tooth. I have given
you an appliance and now for God’s sake use it”
Edward.H.Angle
The main components of an orthodontic appliance
-brackets and wires.
Active and reactive elements (Burstone)
Wires
Brackets
Bonding
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4. Introduction
Orthodontics involves correction of the position of teeth
–requiring moving teeth.
Forces and Moments
Optimum orthodontic tooth movement- light continuous
force.
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5. Introduction
The challenge –
Appliance which produces forces that are neither too
great nor variable.
Different materials and type of wires introduced to
provide forces.
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6. Evolution of Materials
1.
Material Scarcity, Abundance of Ideas (1750-1930)
Before Angle’s search;
Noble metals and their alloys.
- Gold (at least 75%), platinum, iridium and silver
alloys
Good corrosion resistance
Acceptable esthetics
Lacked flexibility and tensile strength
Inappropriate for complex machining and joining.
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7. Evolution of Materials
Angle listed few materials appropriate for work:
Strips of wire of precious metals.
Wood
Rubber
Vulcanite
Piano wire
Silk thread
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8. Evolution of Materials
Angle (1887) German silver (a type of brass)
“according to the use for which it was intended”-varying
the proportion of Cu, Ni & Zn and various degrees of cold
work.
Neusilber brass (Cu 65%, Ni 14%, Zn 21%)
jack screws (rigid)
expansion arches (elastic)
Bands (malleable)
Opposition by Farrar – discolored
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9. Evolution of Materials
Stainless steel (entered dentistry -1919).
Dumas ,Guillet and Portevin-(France), qualities
reported in Germany –Monnartz (1900-1910).
Discovered by chance before W W I.
1919 – Dr. F Hauptmeyer –Wipla (wie platin).
Simon, Schwarz, Korkhous, De Coster- orthodontic
material.
Angle used steel as ligature wire (1930).
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10. Evolution of Materials
Opposition
Emil Herbst
-Gold wire was stronger than stainless steel (1934).
“The Edgewater" tradition-1950-2 papers presented back to back-competition
between SS & gold.
- B/w Dr.Brusse (The management of stainless steel)
and Drs.Crozat & Gore (Precious metal removable
appliances).
Begg (1940s) with Wilcock-ultimately resilient arch
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wires-Australian SS.
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11. Evolution of Materials
2.
Abundance of materials, Refinement of
Procedures (1930 – 1975).
Kusy-after 1960s-proliferation abounds.
Improvement in metallurgy and organic chemistry –
mass production(1960).
Farrar’s dream(1878)-mass production of orthodontic
devices.
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12. Evolution of Materials
Cobalt chrome (1950s)-Elgin watch company
developed a complex alloyCobalt(40%),Chromium(20%),iron(16%)&nickel(15%).
Rocky Mountain Orthodontics- ElgiloyTM
1958-1961
various tempers
Red – hard & resilient
green – semi-resilient
Yellow – slightly less formable but ductile
Blue – soft & formable
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13. Evolution of Materials
Variable cross-section orthodonticsBurstone
To produce changes in load-deflection rate- wires of
various cross sections were used.
Load deflection rate varies with 4th power of the wire
diameter.
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14. Evolution of Materials
1962 - Buehler discovers nickel-titanium dubbed
NITINOL (Nickel Titanium Naval Ordnance Laboratory)
1970-Dr.George Andreason (Unitek) introduced NiTi to
orthodontics.
50:50 composition –excellent springback, no
superelasticity or shape memory (M-NiTi).
Late 1980s –NiTi with active austenitic grain structure.
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15. Evolution of Materials
Exhibited Superelasticity (pseudoelasticity in
engineering).
New NiTi by Dr.Tien Hua Cheng and associates at the
General Research Institute for non Ferrous Metals, in
Beijing, China.
Burstone et al–Chinese NiTi (1985).
In 1978 Furukawa electric co.ltd of Japan produced a
new type of alloy
1. High spring back.
2. Shape memory.
3. Super elasticity.
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Miura et al – Japanese NiTi (1986)
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16. Evolution of Materials
Variable – modulus orthodontics-Burstone
(1981)
Wire size was kept constant and material of the wire is
selected on the basis of clinical requirements.
Fewer wire changes.
Different materials-maintaining same cross-section.
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17. Evolution of Materials
Cu NiTi – (thermoelasticity) - Rohit Sachdeva.
•Quaternary metal – Nickel, Titanium, Copper,
Chromium.
•Copper enhances thermal reactive properties and creates a
consistent unloading force.
Variable transformation temperature
orthodontics
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18. Evolution of Materials
The beginning of Selectivity (1975 to the present)
Orthodontic manufacturers
CAD/CAM – larger production runs
Composites and Ceramics
Iatrogenic damage
Nickel and en-masse detachments
New productscontrol of government agencies, private organizations
3.
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19. Evolution of Materials
β titanium –Burstone and Goldberg-1980
β phase –stabilized at room temperature.
Early 1980s
Composition
Ti – 80%
Molybdenum – 11.5%
Zirconium – 6%
Tin – 4.5%
Burstone’s objective deactivation characteristics
1/3rd of SS or twice of conventional NiTi
TMA – Titanium Molybdenum alloy - ORMCO
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20. Evolution of Materials
Titanium-Niobium- M. Dalstra et al.
Nickel free Titanium alloy.
Finishing wire.
Ti-74%,Nb-13%,Zr-13%.
TiMolium wires (TP Lab)-Deva Devanathan (late 90s)
Ti - 82% ,Mo - 15% , Nb-3%
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21. Evolution of Materials
β III- Ravindra Nanda (2000-2001)
• Bendable,inc. force-low deflection
• Ni free
• Versatility of steel with memory of NiTi.
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22. Evolution of Materials
Fiber reinforced polymeric composites:
Next generation of esthetic archwires
Many orthodontic materials adapted-Aerospace industry
Pultrusion – round + rectangular
ADV – tooth colored enhanced esthetics
- reduced friction
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DISADV – difficult towww.indiandentalacademy.com once manufactured
change its shape
23. Basic Properties of Materials
To gain understanding of orthodontic wires – basic
knowledge of their atomic or molecular structure
and their behavior during handling and use in
the oral environment .
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24. Basic Properties of Materials
Atom - smallest piece of an element that keeps
its chemical properties.
Element - substance that cannot be broken
down by chemical reactions.
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25. Basic Properties of Materials
Electrons – orbit
around nucleus.
Floating in shells of diff
energy levels
Electrons form the
basis of bonds
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26. Basic Properties of Materials
Pure substances are rare-eg. Iron always contains carbon,
gold though occurs as a pure metal can be used only as an
alloy.
An ore contains the compound of the metal and an
unwanted earthly material.
Compound - substance that can be broken into elements
by chemical reactions.
Molecule - smallest piece of a compound that keeps its
chemical properties (made of two or more atoms).
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27. Basic Properties of Materials
Cohesive forces-atoms held together.
Interatomic bonds
Primary
Ionic
Covalent
Metallic
Secondary
Hydrogen
Van der Waals
forces
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28. Basic Properties of Materials
Ionic-mutual attraction between positive and negative
ions-gypsum, phosphate based cements.
Covalent-2 valence electrons are shared by adjacent
atoms-dental resins.
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29. Basic Properties of Materials
Metallic –increased spatial extension of valence-electron
wave functions.
The energy levels are very closely spaced and the
electrons tend to belong to the entire assembly rather
than a single atom.
Array of positive ions in a “sea of electrons”
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30. Basic Properties of Materials
Electrons free to move
Electrical and thermal conductivity
Ductility and malleability
-electrons adjust to deformation
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31. Basic Properties of Materials
METALLIC BOND
IONIC BOND
Metallic bond
Ionic bond
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32. Basic Properties of Materials
Materials broadly subdivided into 2 categories Atomic arrangement
Crystalline structure
Regularly spaced
config-space lattice.
Non-crystalline structure
Possess short range
atomic order.
Anisotropic –diff in
mechanical prop due
directional arrangement
of atoms.
Isotropic-prop of material
remains same in all
directions.
Amorphous
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33. Characteristic properties of metals
An opaque lustrous chemical substance that is a good
conductor of heat and electricity & when polished is a
good reflector of light – Handbook of metals.
Metals are• Hard
• Lustrous
• Dense (lattice structure)
• Good conductors of heat & electricity
• Opaque (free e- absorb electromagnetic energy of
light)
• Ductile & Malleable
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34. Basic Properties of Materials
Crystals and Lattices
1665-Robert Hooke simulated crystal shapes –musket ball.
250 years later-exact model of a crystal with each
ball=atom.
Atoms combine-minimal internal energy.
Space lattice- Any arrangement of atoms in space in which
every atom is situated similarly to every other atom. May
be the result of primary or secondary bonds.
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35. Basic Properties of Materials
Crystal combination of unit cells, in which each shell
shares faces, edges or corners with the neighboring cells
There are 8 crystal systems:
Cubic system –Important as many metals belong to it.
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36. Basic Properties of Materials
There are 14 possible lattice forms.( Bravais lattices)
The unit cells of 3 kinds of space lattices of practical
importance –
1.Face-centered cubic:
Fe above 910°C & Ni.
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38. Basic Properties of Materials
3.Hexagonal close packed:
Co & Ti below 880°C
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39. Basic Properties of Materials
Perfect crystals - rare - atoms occupy well-defined
positions.
Cation-anion-cation-anionDistortion strongly opposed -similarly charged atoms
come together.
Single crystals- strong
Used as reinforcements –whiskers (single crystals- 10
times longer, than wide)
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40. Basic Properties of Materials
Crystal growth-atoms attach themselves in certain
directions.
Perfect crystals-atoms-correct direction.
In common metals the crystals penetrate each other such
that the crystal shapes get deformed.
Microscopic analysis of alloys-grains (microns to
centimeters).
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42. Basic Properties of Materials
Grain boundaries-area-crystals meet.
Atoms-irregular
Decrease mechanical strength
Increase corrosion
imperfections beneficial-interfere with movement along
slip planes
Dislocations cannot cross boundary- deformation
requires greater stress.
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43. Basic Properties of Materials
Usually crystals have imperfections- Lattice defects.
1.Point defects:
a. Impurities
•Interstitials – Smaller atoms that penetrate the lattice Eg –
Carbon, Hydrogen, Oxygen, Boron.
•Substitutial Element – Another metal atom of approx same
size can substitute . E.g. - Nickel or Chromium substituting iron in
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stainless steel.
44. Basic Properties of Materials
b.Vacancies: These are empty atom sites.
2.Line defects: Dislocations along a line. Plastic
deformations of metals occurs –motion of dislocations.
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45. Basic Properties of Materials
Edge dislocation
Sufficiently large forcebonds broken and new bonds
formed.
Slip plane
+
Slip direction
=
Slip system
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46. Basic Properties of Materials
Significance of slip planesShear stress atoms of the crystal can glide.
More the slip planes easier is it to deform.
Slip planes intercepted at grain boundaries.
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48. Basic Properties of Materials
Twinning – alt. mode of permanent deformation.
Seen in metals-few slip planes (NiTi & α-titanium)
Small atomic movements on either side of a twinning
plane results in atoms with mirror relationship
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49. Basic Properties of Materials
Also the mechanism for reversible transformationaustenite to martensite.
• A movement that
divides the lattice into 2
planes at a certain
angle.
•NiTi – multiple
twinning
•Subjected to a higher
temperature, stress
de - twinning
occurs (shape memory)
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50. Basic Properties of Materials
Cold working ( strain hardening or work
hardening)
• During deformation - atomic bonds within the crystal
get stressed
resistance to more deformation
•
Dislocations pile up along the grain boundaries.
•
Hardness & strength
•
Plastic deformation-difficult.
ductility
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51. Basic Properties of Materials
An interesting effect of cold work-crystallographic
orientation in the distorted grain structure.
Anisotropic (direction dependant) mechanical
properties.
Slip planes align with shear planes.
Wires – mechanical properties different when measured
parallel and perpendicular to wire axis.
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52. Basic Properties of Materials
Implications:
Fine grained metals with large no. of grains
- stronger
•Enhancing crystal nucleation by adding fine particles with a
higher melting point, around which the atoms gather.
•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
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slip planes.
53. Basic Properties of Materials
The effects of cold working can be reversed-heating the
metal to appropriate temperature- Annealing
• Relative process-heat below the melting temperature
•More the cold work, more rapid the annealing
•Higher melting point – higher annealing temp
•Rule of thumb-½ the melting temperature (°K)
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54. Basic Properties of Materials
Recovery-cold work disappears.
• Ortho appliances heat treated (recovery
temperature)• stabilizes the configuration of the appliance and
• reduces-fracture.
Recrystallization –severely cold worked-after recoveryradical change in microstructure.
• New stress free grains
• Consume original cold worked structure.
• Inc. ductility ,dec. resiliency
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55. Basic Properties of Materials
Grain growth - minimizes the grain boundary area.
•Coarse grains
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56. Basic Properties of Materials
Before Annealing
Recovery – Relief of stresses
Recrystallization – New grains from severely cold
worked areas
Grain Growth – large crystal “eat up” small ones
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57. Basic Properties of Materials
Polymorphism
Metals and alloys exist as more than one type of
structure
Transition from one to the other-reversible- Allotropy
Steel and NiTi
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58. Basic Properties of Materials
Steel -alloy of iron and carbon
Iron – 2 forms• FCC-above 910°c
• BCC-below-Carbon practically insoluble.(0.02%)
•Iron FCC form
(austenite)
•Lattice spaces greater
•Carbon atom can easily
be incorporated into the
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unit cell
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59. Basic Properties of Materials
On Cooling
FCC BCC
Carbon diffuses out
as Fe3C
Cementite adds
strength to ferrite
and austenite
Rapidly
cooled (quenched)
Carbon
cannot escape
Distorted
body centered
tetragonal lattice called
martensite
Too
brittle-tempered-heat b/w
200-450°C –held at a given temp
for known length of time-cooled
rapidly.
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62. Basic Properties of Materials
NiTi•
•
•
Transformations –temperature & stress.
Austenite (BCC)
Martensitic (Distorted monoclinic, triclinic,
hexagonal structure.
Austenite- high temperature & low stress.
Martensite –low temperature & high stress.
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hysteresis
63. Basic Properties of Materials
Bain distortion
• Transformations occur without chemical change or
diffusion
•
Result-crystallographic reln b/w parent and new
phase
•
Rearrangement of atoms-minor movements
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64. Evolution of Materials
Gold
1887-Neusilber brass (Cu,Ni,Zn)
1919-Stainless steel
1950s-Cobalt chromium
1962-NiTiNOL-1970-Orthodontia
Early 1980s-β-titanium
1985,86-superelastic NiTi
1989-α-Titanium
1990s- Cu NiTi, Ti Nb and Timolium
2000-β-III
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66. Making an orthodontic wire
Sources
Stainless steel- based on standard formulas of AISI.
After manufacture –further selection to surpass the
basic commercial standard
Orthodontists –small yet demanding customers
Chrome – cobalt and titanium alloys- fixed formulas
Gold –supplier’s own specification.
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67. Making an orthodontic wire
4 steps in wire production
1. Melting
2.The Ingot
3.Rolling
4.Drawimg
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68. Making an orthodontic wire
Melting
-Selection and melting of alloy materials-important
-Physical properties influenced
-Fixes the general properties of the metal
The Ingot
-Critical step- pouring the molten alloy into mold
- Non –uniform chunk of metal
- Varying degrees of porosities and inclusions of slag.
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69. Making an orthodontic wire
-Microscopy –grains –influence mechanical properties.
-Size and distribution of grains –rate of cooling and the
size of ingot.
-Porosity -2 sources
o Gases dissolved or produced
o Cooling and shrinking –interior cools late
-Ingot – trimmed
Important to control microstructure at this stage –
basis of its physical properties and mechanical
performance
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70. Making an orthodontic wire
Rolling
- 1st mechanical step-rolling ingot –long bars
-Series of rollers – reduced to small diameter
-Different parts of ingot never completely lose identity
-Metal on outside of ingot-outside the finest wire,
likewise ends
- Different pieces of wire same ingot differ depending on
the part they came from
-Individual grains also retain identity
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71. Making an orthodontic wire
-Each grain elongated in the same proportion as the ingot
-Mechanical rolling-forces crystals into long finger-like
shapes –meshed into one another
-Work hardening-increases the hardness and brittleness
-if excess rolling-small cracks
-Annealing –atoms become mobile-internal stresses
relieved
-More uniform than original casting
-Grain size controlled
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72. Making an orthodontic wire
Drawing
-Further reduced to final size
-Precise process –wire pulled
through a small hole in a die
- Hole slightly smaller than
the starting diameter of the
wire – uniformly squeezed
-Wire reduced to the size of
die
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73. Making an orthodontic wire
- Many series of dies
- Annealed several times at regular intervals
- Exact number of drafts and annealing cycles depends
on the alloy (gold <carbon steel<stainless steel)
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74. Making an orthodontic wire
Rectangular wires
-Draw through rectangular die or roll round wires to
rectangular shape
-Little difference in the wires formed by the 2 processes
-Drawing –produces sharper corners –advantageous in
application of torque
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75. Making an orthodontic wire
Hardness and spring properties depend–entirely on the
effects of work hardening during manufacture
Drawing –Annealing schedule –planned carefully with
final properties & size in mind
Metal almost in need of annealing at final size-maximum
spring prop.
Drawing carried too far-brittle, not enough-residual
softness.
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77. Mechanical properties
Strength-ability to resist stress without fracture or
strain (permanent deformation).
Stress & strain-internal state of the material.
Stress-internal distribution of load – force/ unit area
(Internal force intensity resisting the applied load)
Strain- internal distortion produced by the loaddeflection/unit length
(change in length/original length)
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78. Mechanical properties
Material can be stressed in 4 ways• Compression
•
Tensile
•
Shear
•
Complex force systems
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79. Mechanical properties
Evaluation of mechanical properties –
• Bending tests
• Tension tests
• Torsional tests
•
•
•
Bending tests : 3 types
A cantilever bending test-Oslen stiffness tester (ADA32)
3 point
4 point
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82. Mechanical properties
The modulus of elasticity calculated
from the force-deflection plot, using
equations from solid mechanics.
Cantilever bending test-incompatible
with flexible wires-(NiTi and
multistranded).
Disadvantage of 3 point-bending
moment-maximum at loading point
to zero at the 2 supports.
4 point –uniform bending momentspecimen fails at the weakest point.
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83. Mechanical properties
Nikolai et al proposed a 5 point bending test:
-2 loading points at each end-simulate a couple.
-simulates engagement of arch wire in bracket.
Tensile testing-strain - rate mechanical testing machine
is used.
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85. Elastic properties
STRESS
Wire returns back to original
dimension when stress is
removed
Elastic portion
(Hooke’s law)
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STRAIN
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87. Elastic properties
Elastic /Proportional limit-used interchangeably
Proportional limit –determined by placing a straight
edge on the stress-strain plot.
Elastic limit -determined with aid of precise strain
measurement apparatus in the lab.
Yield strength (Proof stress) -PL-subjective ,YS used to
for designating onset of permanent deformation.0.1% is
reported.
Determined by intersection of curved portion with 0.1%
strain on horizontal axis.
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89. Elastic properties
Ultimate tensile strength -the maximum load the wire
can sustain (or)
maximum force that the wire can deliver.
Permanent (plastic) deformation -before fractureremoval of load-stress-zero, strain = zero.
Fracture -Ultimate tensile strength higher than the
stress at the point of fracture
reduction in the diameter of the wire (necking)
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91. Elastic properties
Slope of initial linear region- modulus of elasticity (E).
(Young’s modulus)
•
Corresponds to the elastic stiffness or rigidity of
the material
•
Amount of stress required for unit strain
•
E = σ/ε where σ does not exceed PL (Hookean
elasticity)
•
The more horizontal the slope-springier the wire;
vertical-stiffer
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94. Elastic properties of metals
Range-
•
Proffit-Distance that the wire bends elastically, before
permanent deformation occurs
•
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.
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95. Springback• Proffit- Portion of the loading curve b/w elastic limit and
ultimate tensile strength.
•Kusy -- The extent to which the range recovers upon
deactivation
•Ingram et al – a measure of how far a wire can be
deflected without causing permanent deformation.
•Kapila & Sachdeva- YS/E
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97. Elastic properties
Resiliency-Area under stress-strain curve till
proportional limit.
-Maximum amount of energy a material can absorb
without undergoing permanent deformation.
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.
Strength + springiness
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98. Elastic properties
Work = f x d
•
When work is done on a body-energy imparted to
it.
•
If the stress not greater than the PL elastic energy
is stored in the structure.
•
Unloading occurs-energy stored is given out
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99. Elastic properties
It depends on –
Stiffness and Working Range
Independent of –
Nature of the material
Size (or)
Form
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100. Elastic properties
Formability –
•
Amount of permanent deformation that the wire can
withstand before failing.
•
Indication of the ability of the wire to take the shape
•
Also an indication of the amount of cold work that it can
withstand
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101. Elastic properties
•
Flexibility –
Amount a wire can be strained without undergoing
plastic deformation.
•
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.
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103. Elastic properties
Toughness –Amount of elastic & plastic deformation
required to fracture a material. Total area under the
stress – strain graph.
Brittleness –Inability to sustain plastic deformation
before fracture occurs.
Fatigue – Repeated cyclic stress of a magnitude below
the fracture point of a wire can result in fracture. Fatigue
behavior determined by the number of cycles required to
produce fracture. www.indiandentalacademy.com
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104. Elastic properties
Poisson’s ratio (ν)
ν = - εx/ εy = -εy / εz
Axial tensile stress (z axis) produces elastic tensile strain
and accompanying elastic contractions in x in y axis.
The ratio of x,y or x,z gives the Poissons ratio of the material
It is the ratio of the strain along the length and along the
diameter of the wire.
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105. Elastic properties
Ductility –ability to sustain large permanent
deformation under tensile load before fracturing.
Wires can be drawn
Malleability –sustain deformation under compressionhammered into sheets.
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106. Requirements of an ideal arch wire
Robert P.Kusy- 1997 (AO)
1. Esthetics
2. Stiffness
3. Strength
4. Range
5. Springback
6. Formability
7.Resiliency
8.Coefficient of friction
9.Biohostability
10.Biocompatibility
11.Weldability
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107. Requirements of an ideal arch wire
Esthetic
•Desirable
•Manufacturers tried-coating -White coloured wires
• Deformed by masticatory loads
•Destroyed by oral enzymes
•Uncoated-transparent wires-poor mechanical properties
•Function>Esthetics
•Except the composite wires
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108. Requirements of an ideal arch wire
Stiffness / Load –Deflection Rate
•Proffit: - Slope of stress-strain curve
•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
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109. Requirements of an ideal arch wire
Magnitude of the force delivered by the appliance for a
particular amount of deflection.
Low stiffness or Low LDR 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.
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110. Requirements of an ideal arch wire
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.
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111. Requirements of an ideal arch wire
Range
•Distance to which an archwire can be activated
• Distance wire bends elastically before permanent
deformation.
•Measured in millimeters.
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112. Requirements of an ideal arch wire
Springback
• The extent to which the range recovers upon deactivation
•Clinically useful-many wires deformed
-wire performance-EL & Ultimate strength
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113. Requirements of an ideal arch wire
Formability
•
Kusy – The ease in which a material may be permanently
deformed.
•
Clinically- Ease of forming a spring or archwire
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114. Requirements of an ideal arch wire
Resiliency
•
Store/absorb more strain energy /unit volume before
they get permanently deformed
•
Greater resistance to permanent deformation
•
Release of greater amount of energy on deactivation
High work availability to move the teeth
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115. Requirements of an ideal arch wire
Coefficient of Friction
•
Brackets (and teeth) must be able to slide along the wire
•
Independent of saliva-hydrodynamic boundary layer
•
High amounts of friction anchor loss.
•
Titanium wires inferior to SS
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116. Requirements of an ideal arch wire
Biohostability-
•Site for accumulation of bacteria, spores or viruses.
• An ideal archwire must have poor biohostability.
•Should not-actively nurture nor passively act as a substrate
for micro-organisms/spores/viruses
•Foul smell, discolouration, build up of material-compromise
mechanical properties.
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117. Requirements of an ideal arch wire
Biocompatability
•
Ability of a material to elicit an appropriate biological
response in a given application in the body
•
Wires-resist corrosion –products – harmful
•
Allergies
•
Tissue tolerance
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118. Requirements of an ideal arch wire
Weldability –
•
Process of fusing 2 or more metal parts though
application of heat, pressure or both with/out a filler
metal to produce a localized union across an interface.
•
Wires –should be easily weldable with other metals
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119. Elastic properties
Thurow
- 3 characteristics of utmost importance
- Important for the orthodontist –selection of the
material and design-any change in 1 will require
compensatory change in others.
Strength = Stiffness x Range
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120. Elastic properties
•
Clinical implications:
The properties can be expressed in absolute terms -in
orthodontics-simple comparison.
•
Main concern-change in response – if there is change
in material, wire size or bracket arrangement.
•
Knowledge- force and movement can be increased or
decreased in certain circumstances
Comparing the 3 properties
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121. Elastic properties
Stiffness indicates rate of force delivery
how much force
how much distance can be covered
Strength –measures the load or force that carried at its
maximum capacity
Range-amount of displacement under maximum load
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122. Elastic properties
Factors effecting the 3 components
- Mechanical arrangement-includes bracket width,
length of arch wire.
-Form of wire-size, shape & cross-section
- Alloy formula, hardness, state of heat treatment
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123. Optimal Forces & Wire Stiffness
Varying force levels produced during deactivation of a
wire: excessive, optimal, suboptimal, & subthreshold.
During treatment by a wire with high load deflection
rate the optimal zone is present only over a small
range
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124. Optimal Forces & Wire Stiffness
Overbent wire with low load-deflection rate (Burstone)
Tooth will reach desired position before subthreshold force
zone is reached.
Replacement of wires is not required
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125. Effects of wire cross-section
Variable-cross section orthodontics
How does change in size and shape of wire effect
stiffness, strength & springiness?
Considering a cantilever beam;
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126. Effects of wire cross-section
Doubling diameter makes beam 8 times stronger
But only 1/16 times springy
½ the range.
Strength changes as a cubic fn of the ratio of the 2 cross
sections.
Springiness-4th power
Range-direct proportion
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127. Effects of wire cross-section
Rectangular wire
The principle is same
In torsion more shear stress rather than bending stress
in encountered
However the principle is same
Increase in diameter – increase in stiffness & strength
rapidly– too stiff for orthodontic use & vice-versa
Ideally wire should be in b/w these two extremes
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128. Effects of wire cross-section
Wire selection-based on
load -deflection rate requirement
-magnitude of forces and moments required
Is play a factor?
Wire ligature minimizes the play in I order direction as
wires can seat fully.
Narrow edgewise brackets-ligature tie tends to minimize
No point-0.018” over 0.016-diffrence in play.
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129. Effects of wire cross-section
Should a smaller wire be chosen to obtain greater elastic
deflection?
Elastic deflection varies inversely with diameter of
wire but differences are negligible 0.016 has 1.15 times maximum elastic deflection as 0.018
wire.
Major reason- load deflection rate
Small changes in the wire produce large changes in L-D
rate
Determined by moment of inertia.
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130. 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 b3hd4
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131. Effects of wire cross-section
The clinician needs a simplified system to determine the
stiffness of the wire he uses.
Cross-sectional stiffness number (CS)-relative stiffness
0.1mm(0.004in) round wire-base of 1.
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132. Effects of wire cross-section
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134. Effects of wire cross-section
•
•
Rectangular wires
Bending perpendicular to the larger dimension (ribbon
mode)
Easier than bending perpendicular to the smaller
dimension (edgewise).
•The larger dimension correction is needed.
•The smaller dimension the plane in which more stiffness
is needed.
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135. Effects of wire cross-section
> first order, < second order – RIBBON
> Second order, < first order - EDGEWISE
•> 1st order correction in anterior segment
•> 2nd order in the posterior segment, wire can be
twisted 90°
•Ribbon mode in anterior region and edgewise in posterior
region.
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136. Effects of wire cross-section
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).
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137. Orthodontic wires
Mechanical & Elastic properties
Ideal requirements of an arch wires
Strength, stiffness & range
Optimal forces and wire stiffness
Effects of cross-section
Strength changes as a cubic fn of the ratio of the 2 cross
sections.
Springiness-4th power
Range-direct proportion
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138. Effects of length
Changing the length-dramatically affects properties
Considering a cantilever ;
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139. Effects of length
If length is doubled• Strength – cut by half-(decreases proportionately)
• Springiness – inc. 8 times ( as a cubic function)
• Range – inc 4 times (increases as a square.)
In the case of torsion, the picture is slightly different.
Increase in length –
•Stiffness decreases proportionately
•Range increases proportionately
•Strength remains unchanged.
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140. 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
• 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.
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141. Effects of material
Modulus of elasticity varied by changing the material
Material stiffness number-relative stiffness of the
material
Steel -1.0(Ms)
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143. Nomograms
Developed by Kusy
Graphic representation-comparing wire materials and
sizes
Fixed charts that display mathematical relationshipsscales
Nomograms of each set drawn to same base, any wire on
1 of 3 can be compared to any other.
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144. Nomograms
A
reference wire is
chosen (0.012”SS) and
given a value of 1 . The
strength , stiffness and
range of other wires are
calculated to this
reference
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147. Clinical implications
Balance between stiffness, strength & range
Vary - material ,cross-section or length as the
situation demands.
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148. Clinical implications
Variation in Cross-Section
Wires with less cross-section-low stiffness (changes by
4th power)
Used initial part of treatment
Thicker-stiffer wires used later
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149. Clinical implications
Multi-stranded wires
2 or more wires of smaller diameter are twisted
together/coiled around a core wire
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.
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150. Clinical implications
Variation in length
•Removable appliance -cantilever spring
•The material of choice is usually steel. (Stiff material)
•Good strength to resist masticatory and other oral
forces.
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151. Clinical implications
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 helices or loops into the spring
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152. Clinical implications
Fixed appliance
The length of wire between brackets can be increased
Loops, or Smaller brackets,
or Special bracket designs –Mini-unitwin bracket,Delta
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153. Clinical implications
Variation in the material
Relatively constant dimension important for the third
order control
Titanium wires-low stiffness-used initial part of
treatment
Steel-when rigidity-control and torque expression
required
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155. Clinical implications
Stage
Wires
Reason
Aligning
Multistranded SS,
NiTi
Great range and light
forces are reqd
Space closure
Β-Ti (frictionless),
SS – if sliding
mechanics is
needed
Increased formability,
springback , range and
modest forces per unit
activation are needed
Finishing
SS , preferably
rectangular
More stability & less
tooth movement reqd
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156. Clinical implications
Stage
Wires
Reason
Aligning
Multistranded SS,
Low LDR-SS
Great range and light
forces are reqd
Space closure
SS(high resilience
aust.wire) –
sliding mechanics
Increased formability,
springback , range and
modest forces per unit
activation are needed
Finishing
SS , α-titanium
More stability & less
tooth movement reqd
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157. Clinical implications
A rough idea can be obtained clinically
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.
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158. Physical properties
Corrosion
Chemical or electrochemical process in
which a solid, usually a metal, is attacked by an
environmental agent, resulting in partial or complete
dissolution.
Not merely a surface deposit –deterioration of metal
Localized corrosion-mechanical failure
Biological effects-corrosion products
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159. Physical properties
Nickel 1. Carcinogenic,
2. Mutagenic,
3. Cytotoxic and
4. Allergenic.
Stainless steels, Co-Cr-Ni alloys and NiTi are all rich in
Ni
Co & Cr can also cause allergies.
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160. Physical properties
Studies-Ni alloy implanted in the tissue
Although-more invasive –reactivity of the implanted
material is decreased –connective tissue capsule
Intraoral placement-continuous reaction with
environment
Corrosion resistance of steel SS- passivating layer-Cr-also contains Fe, Ni, Mo
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161. Physical properties
Passivating film-inner oxide layer-mainly-Cr oxide
outer- hydroxide layer
Elgiloy-similar mechanism of corrosion resistance
Titanium oxides-more stable
Corrosion resistance of SS inferior to Ti alloys
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162. Physical properties
-Forms of corrosion
1.
2.
Uniform attack –
Commonest type
The entire wire reacts with the environment
Hydroxides or organometallic compounds
Detectable after a large amount of metal is dissolved.
Pitting Corrosion –
Manufacturing defects
Sites of easy attack
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164. Physical properties
3. Crevice corrosion or gasket corrosion
Parts of the wire exposed to corrosive environment
Non-metallic parts to metal (sites of tying)
Difference in metal ion or oxygen concentration
Plaque build up disturbs the regeneration of the
passivating layer
Depth of crevice-reach upto 2-5 mm
High amount of metals can be dissolved in the mouth.
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166. Physical properties
4.Galvanic /Electrochemical Corrosion
Two metals are joined
Or even the same metal after different type of treatment
are joined
Difference in the reactivity
Galvanic cell.
Less Reactive
(Cathodic)
More Reactive
(Anodic) less noble metal
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167. Physical properties
Less noble metal-oxidizes-anodic-soluble
Nobler metal-cathodic-corrosion resistant
“Galvanic series”
SS-can be passive or active depending on the nobility of
the brazing material
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168. Physical properties
5.Intergranular corrosion
Sensitization - Precipitation of CrC-grain boundaries
-Solubility of chromium carbide
6.Fretting corrosion
Material under load
Wire and brackets contact –slot – archwire interface
Friction
surface destruction
Cold welding -pressure rupture at contact pointswww.indiandentalacademy.com
wear oxidation pattern
168
169. Physical properties
7.Microbiologically influenced corrosion (MIC)
Sulfate reducing-Bacteroides corrodens
Matasa – Ist to show attack on adhesives in
orthodontics
Craters in the bracket
Certain bacteria dissolve metals directly form the wires.
Or by products alter the microenvironment-accelerating
corrosion
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171. Physical properties
8.Stress corrosion
Similar to galvanic corrosion-electrochemical potential
difference-specific sites
Bending of wires - different degrees of tension and
compression develops locally
Sites-act as anodes and cathodes.
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172. Physical properties
9.Corrosion Fatigue:
Cyclic stressing of a wire-aging
Resistance to fracture decreases
Accelerated in a corrosive medium such as saliva
Wires left intraorally-extended periods of time under
load
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173. Physical properties
Corrosion – Studies
In vitro Vs In vivo
Never simulate the oral environment
Retrieval studies
Biofilm-masks alloy topography
Organic and inorganic components
Mineralized –protective esp. low pH
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174. Physical properties
Ni hypersensitivity-case reports-very scarce
Insertion of NiTi wires –
rashes
swelling
Erythymatous lesions
Ni and Cr
impair phagocytosis of neutrophils and
impair chemotaxis of WBCs.
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175. Physical properties
Ni at conc. released from dental alloys
Activating monocytes and endothelial cells,
Promote intercellular adhesion(molecule 1)
Promotes inflammatory response in soft tissues.
Arsenides and sulfides of Ni - carcinogens and mutagens.
Ni at non toxic levels - DNA damage.
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177. Stainless steel
Gold
1960s-Abandoned in favour of stainless steel
Crozat appliance –original design
1919 – Dr. F Hauptmeyer –Wipla (wie platin).
•Extremely chemically stable
•Better strength and springiness
• High resistance to corrosion-Chromium
content.
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178. Stainless steel
Properties of SS controlled-varying the degree of cold
work and annealing during manufacture
Steel wires-offered in a range of partially annealed states
–yield strength progressively enhanced at the cost of
formability compromised
Fully annealed stainless steel extremely soft, and highly
formable
Ligature wire-“Dead soft”
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179. Stainless steel
Steel wires with high yield strength- “Super” grade wiresbrittle-used when sharp bends are not needed
High formability- “regular” wires-bent into desired
shapes
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180. Stainless steel
Structure and composition
Iron –always contains carbon-(2.1%)
When aprrox 12%-30% Cr added- stainless
Cr2O3-thin transparent, adherent layer when exposed to
oxidizing atm.
Passivating layer-ruptured by chemical/mechanical
means-protective layer reforms
Favours the stability of ferrite (BCC)
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181. Stainless steel
Nickel(0-22%) – Austenitic stabilizer (FCC)
Loosly bound
Copper, manganese and nitrogen – similar function
Mn-dec corrosion resistance
Carbon (0.08-1.2%)– provides strength
Reduces the corrosion resistance
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182. Stainless steel
Sensitization.
400-900oC-looses corrosion resistance
During soldering or welding
Chromium diffuses towards the carbon rich areas
(usually the grain boundaries)-chromium carbide-most
rapid 650°C
Chromium carbide is soluble- intergranular corrosion.
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183. Stainless steel
3 methods to prevent sensitization-
1.
Reduce carbon content-precipitation cannot occur-not
economically feasible
2.
Severely cold work the alloy-Cr carbide ppts at
dislocations-more uniform
Stabilization
Addition of an element which precipitates carbide more
easily than Chromium.
Niobium, tantalum & titanium
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184. Stainless steel
Usually- Titanium.
Ti 6x> Carbon
No sensitization during soldering.
Most steels used in orthodontics are not stabilizedadditional cost
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185. Stainless steel
Other additions and impurities-
Silicon – (low concentrations) improves the resistance
to oxidation and carburization at high temperatures and
corrosion resistance
Sulfur (0.015%) increases ease of machining
Phosphorous – allows sintering at lower temperatures.
But both sulfur and phosphorous reduce the corrosion
resistance.
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187. Stainless steel
The AISI numbers used for stainless steel range from
300 to 502
Numbers beginning with 3 are all austenitic
Higher the number
Less the non-ferrous content
More expensive the alloy
Numbers having a letter L signify a low carbon
content
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190. Stainless steel
Austenitic steels (the 300 series)
Most corrosion resistance
FCC structure, non ferromagnetic
Not stable at room temperature,
Austenite stabalizers Ni, Mn and N
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191. Stainless steel
Type 302-basic alloy -17-19%
Cr,8-10% Ni,0.15%-C
304- 18-20%-Cr, 8-12%Ni,0.08%-C
Known as the 18-8 stainless
steels- most common in
orthodontics
316L-10-14%-Ni,2-3%Mo,16-18%-Cr,O.03%-Cimplants
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192. Stainless steel
The following properties Greater ductility and malleability
More cold work-strengthened
Ease –welding
Dec. sensitization
Less critical grain growth
Ease in forming
X-ray diffraction-not always single phase-Bcc
martensitic phase present
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194. Stainless steel
Martensitic steel (400)
FCC BCC
BCC structure is highly stressed. (BCT)
More grain boundaries,
Stronger
Dec. ductulity-2%
Less corrosion resistant
Making instrument edges which need to be sharp and
wear resistant.
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196. Stainless steel
Ferritic steels – (the 400 series)
Name derived from the fact-microstr (BCC) same as iron
Difference-Cr
“super ferritics”-19-30% Cr-used Ni free brackets
Good corrosion resistance, low strength.
Not hardenable by heat treatment-no phase change
Not readily cold worked.
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197. Stainless steel
Duplex steels
Both austenite and ferrite grains
Fe,Mo,Cr, lower nickel content
Increased toughness and ductility than ferritic steels
Twice the yield strength of austenitic steels
High corrosion resistant-heat treated –sigma-dec
corrosion resistance
Manufacturing low nickel attachments-one piece
brackets
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198. 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.
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199. Stainless steel
-General properties
1. Relatively stiff material
Yield strength and stiffness can be varied
Altering the carbon content and
Cold working and
Altering diameter/cross section
Annealing
High forces - dissipate over a very short amount of
deactivation (high load deflection rate).
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200. Stainless steel
In clinical terms•Loop - activated to a very small extent so as to
achieve optimal force but
•Deactivated by only a small amount (0.1 mm)
force level will drop tremendously
•Type of force-Not physiologic
•More activations
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201. Stainless steel
Force required to engage a steel wire into a severely malaligned tooth.
Either cause the bracket to pop out,
Or the patient to experience pain.
Overcome by using thinner wires, which have a lower
stiffness.
Not much control.
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202. Stainless steel
High stiffness can be advantageous
Maintain the positions of teeth & hold the corrections
achieved
Begg treatment, stiff archwire, to dissipate the adverse
effects of third stage auxiliaries
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203. Stainless steel
2. Lowest frictional resistance
Ideal choice of wire during space closure with sliding
mechanics
Teeth will be held in their corrected relation
Minimum resistance to sliding
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204. Stainless steel
3.High corrosion resistance
Ni is used as an austenite stabilizer.
Not strongly bonded to produce a chemical compound.
Likelihood of slow release of Ni
Symptoms in sensitized patients
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205. 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
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208. High Tensile Australian Wires
Claude Arthur J. Wilcock started association with dental
profession-1936-37
Around 1946-asssociation with Dr.Begg
Flux, silver solder, lock pins, brackets, bands, ligature
wires, pliers & high tensile wire
Needed-wires that were active for long
Dr Begg-progressively harder wires
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209. 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
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210. High Tensile Australian Wires
Demand-very high-1970s
Raw materials overseas
Higher grades-Premium
Preformed appliances, torquing auxiliaries, springs
Problems-impossibility in straightening for appliances
-work softening-straightening
-breaking
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211. High Tensile Australian Wires
•Higher working range- E
(same) But inc. YS
Range=YS/E
•Higher resiliency
ResilαYS2/E
•Zero stress relaxation
•Reduced formability
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212. 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 deliver a constant light elastic
force, when subjected to external forces (like occlusal
forces).
Only wires with high yield strength-possess this desirable
property
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213. High Tensile Australian Wires
Relaxation in material- Slip dislocation
Materials with high YS-resist such dislocations-internal
frictional force.
New wires-maintain their configuration-forces generated
are unaffected
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214. 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 (spring index)
smaller diameter of wires smaller diameter springs (like
the mini springs)
Higher grade wires (high YS), ratio can be =2, much
lighter force
Bite opening anchor bendszero stress relaxation –infrequent reactivation
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215. High Tensile Australian Wires
Spinner straightening
It is mechanical process of straightening resistant
materials in the cold-hard drawn condition
The wire is pulled through rotating bronze rollers that
torsionally twist it into straight condition
Wire subjected to tension-reverse straining.
Disadv:
Decreases yield strength (strain softened)
Creates rougher surface
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216. 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.
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217. 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.
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219. 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.
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220. High Tensile Australian Wires
JCO,1991 Jun(364 - 369): Clinical Considerations in the
Use of Retraction Mechanics - Julie Ann Staggers,
Nicholas Germane
The range of action will be greatest in the direction of the
last bend
With open loop, activation unbends loop; but with closed
loop, activation is in the direction of the last bend
-increases range of activation.
Premium wire special plus or special wire
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222. High Tensile Australian Wires
Pulse straightening
Placed in special machines that permits high tensile
wires to be straightened.
This method :
Permits the straightening of high tensile wires
1. Does not reduce the yield strength of the wire
2. Results in a smoother wire, hence less wire – bracket
friction.
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223. High Tensile Australian Wires
Dr.Mollenhauer requested –ultra high tensile SS
round wire.
Supreme grade wire –lingual orthodontics-initial faster
and gentler alignment of teeth-brackets close
Labial Begg brackets-reduces tenderness
Intrusion simultaneously with the base wires
Gingival health seemed better
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224. 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
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225. 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
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226. High Tensile Australian Wires
Twelftree, Cocks and Sims (AJO 1977)
Wires-0.016-7 wires
Premium plus, Premium and Special plus wires showed
minimal stress relaxation-no relaxation -3 days
Special,
Remanit,
Yellow Elgiloy,
Unisil.
Special plus maintained original coil size, Unisil-inc.
curvature
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227. 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)
Sp.plus greater working range than stnd. SS but
NiTi,TMA & multistranded-greater
Jyothindra Kumar (89) -evluated working range
Australian wires-better recovery than Remanuim
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228. High Tensile Australian Wires
Pulse straightened wires – Spinner
straightened
(Skaria 1991)
Strength, stiffness and Range higher than spinner
staightened wires
Coeff. of friction higher-almost double
Similar- surface topography, stress relaxation and
Elemental makeup.
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229. High Tensile Australian Wires
Anuradha Acharya (2000)
Super Plus (Ortho Organizers) – between Special plus
and Premium
Premier (TP) – Comparable to Special
Premier Plus (TP)– Special Plus
Bowflex (TP) – Premium
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230. 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.
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231. High Tensile Australian Wires
High and sharp yield points-freeing of dislocations and
effective shear stress to move these dislocations.
Flow stress dependent on Temperature
Density of dislocations in the material
Resulting structure-hard-high flow stress
Plastic deformation absence of dislocation locking-low
YS
Internal stress=applied stress x density of dislocations
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232. 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
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233. High Tensile Australian Wires
Small stress applied with the plier beaks
Crack propagation
Elastic energy is released
Propagation accelerates to the nearest grain boundary
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234. 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.
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236. 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
3.Wilcock-Begg light wire pliers, preferably not tungsten
carbide tipped
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238. High Tensile Australian Wires
4. The edges rounded reduce the stress concentration in
the wire. –sandpaper & polish if sharp.
5.Ductile – brittle transition temperature slightly above
room temperature.
Wire should be warmed – pull though fingers
Spools kept in oven at about 40o, so that the wire
remains slightly warm.
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239. Multistranded wires
They are composed of specified numbers of thin wire
sections coiled around each other to provide round or
rectangular cross section
The wires-twisted or braided
When twisted around a core wire-coaxial wire
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241. Multistranded wires
Individual diameter - 0.0165 or 0.0178
final diameter – 0.016" – 0.025“
On bending - individual strands slip over each other ,
making bending easy.
Strands of .007 inch twisted into .017 inch-(3 wires)
stiffness comparable to a solid wire of .010 inch
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242. Multistranded wires
Stiffness – decreases as a function of the 4th
power
Range – increases proportionately
Strength – decreases as a function of the 3rd power
Result - high elastic modulus wire behaving like a low
stiffness wire
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243. Multistranded wires
Elastic properties of multistranded archwires depend on –
1.Material parameters – Modulus of elasticity
2.Geometric factors – moment of inertia & wire dimension
3.Twisting or braiding or coaxial
4.Dimensionless constants
Number of strands coiled
Helical spring shape factor
Bending plane shape factor
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244. 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)
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246. Multistranded wires
Schematic definition of the helix angle (a). If one revolution of a wire
strand is unfurled and its base length [p(D-d)] and corresponding
distance traversed along the original wire axis (S*) are determined,
then a ratio of these two distances equals tan a. Everything else
being equal, the greater p(D-d) or the less S* is, the more compliant
a wire will be.
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247. 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
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248. Multistranded wires
Deflection of multi stranded wire
= KPL3
knEI
K – load/support constant
P – applied force
L – length of the beam
K – helical spring shape factor
n- no of strands
E – modulus of elasticity
I – moment of inertia
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249. 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- SS,NiTi & β-Ti
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250. Multistranded wires
The multistranded wire did not resemble the 0.018 wire
in any way except for the size and & slot engagement
Stiffness was comparable to 0.010 SS wire but strength
was 20% higher
0.016
NiTi-equal in stiffness, considerably stronger and
50% more activation
0.016
β-Ti –twice as stiff, comparable to 0.012 SS
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253. Multistranded wires
Ingram, Gipe and Smith (AJO
86)
Range independent of wire
size
Range seems to increase
with increase in diameter
It varies only from 11.2-10.0largest size having slightly
greater range than smallest
wire.
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254. Multistranded wires
Oltjen,Duncanson,Nanda,Currier (AO-1997)
Wire stiffness can be altered by not only changing the
Increase in but of strands
size or alloy compositionNo. by varying the number of
strands. stiffness
Unlike single stranded
wires
Increase in No. of strands stiffness
stiffness varied as
deflection varied.
Unlike single stranded wires
stiffness varied as deflection varied.
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255. Multistranded wires
Rucker & Kusy (AO 2002)
Interaction between individual strands was negligible.
Range and strength Triple stranded = Co-axial (six
stranded)
Stiffness Coaxial < Triple stranded
Range of small dimension single stranded SS wire was
similar.
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257. Cobalt chromium
1950s the Elgin Watch
“The heart that never breaks”
Rocky Mountain Orthodontics - Elgiloy
CoCr alloys –belong to stellite alloys
superior resistance to corrosion (Cr oxide),
comparable to that of gold alloys exceeding SS.
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259. Cobalt chromium
Advantages over SS
1. Delivered in different degrees of hardening or tempers
2. High formability
3.Further hardened by heat treatment
4.Greater resistance to fatigue and distortion
5.Longer function as a resilient spring
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260. Cobalt chromium
The alloy as received
is highly formable,
and can be easily
shaped.
Heat treatedConsiderable strength
and resiliency
Strength
Formability
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261. Cobalt chromium
Ideal temperature- 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
. Heating above 650oC
partial annealing, and softening of the wire
Optimum heat treatment dark straw color of the wire or
temperature indicating paste
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262. Cobalt chromium
1958-1961-4 tempers
Red – hard & resilient
Green – semi-resilient
Yellow – slightly less formable
but ductile
Blue – soft & formable
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263. Cobalt chromium
Blue-bent easily -fingers or pliers
Recommended –considerable bending, soldering or
welding required
Yellow -bent with ease-more resilient
-inc. in resiliency and spring performance-heat
Green –more resilient than yellow,can be shaped to
some extent-pliers
Red- most resilient –high spring qualities,minimal
working
Heat treatment-inc. resilient but fractures easily.
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264. Cobalt chromium
After heat treatment
Blue and yellow =normal steel wire
Green and red tempers =higher grade steel
E very similar –SS & blue elgiloy (10% inc in E)
Similar force delivery and joining characters
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266. Cobalt chromium
Comparable amount of Ni
Coefficient of friction higher than steel -recent studycomparable to steel-zero torque brackets are used.
The high modulus of elasticity of Co-Cr and SSDeliver twice the force of β-Ti and 4times NiTi for equal
amounts of activation.
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267. Cobalt chromium
Stannard et al (AJO 1986)
Co-Cr highest frictional resistance in wet and dry
conditions.
Ingram
Gipe and Smith
(AJO 86)
•Non heat treated
•Range < stainless steel
of comparable sizes
•But after heat treatment,
the range was
considerably increased.
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268. Cobalt chromium
Kusy et al (AJO 2001)
16 mil (0.4mm or .016 inch) evaluated
E values –identical
-red –highest- YS & UTS
-blue-most ductile
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269. Cobalt chromium
The elastic modulus did not vary appreciably edgewise
or ribbon-wise configurations.
Round wires higher ductility than square or rectangular wires
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270. Cobalt chromium
The averages of E,YS,UTS and ductility plotted against
specific cross-sec area.
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.
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272. Cobalt chromium
Conclusion- based on force-deactivation
characteristics- interchangeably – SS
Can choose different tempers and amounts of formability
Inc the YS by heat treating
Fine in principle-but-lack of control of the processing
variables in the as received state.
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273. To strive, to seek to find ,and not to yield
- Lord Tennyson ( Ulyssess)
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274. References
Proffit – Contemporary orthodontics-3rd ed
Graber vanarsdall – orthodontics – current principles
and techniques-3rd ed
Phillips’ science of dental materials-Anusavice -11th ed
Orthodontic materials-scientific and clinical aspectsBrantly and Eliades
Edgewise orthodontics-R.C. Thurow-4th ed
Notes on dental materials-E.C.Combe-6th ed
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275. References
Frank and Nikolai. A comparative study of frictional
resistance between orthodontic brackets and archwires.
AJO 80;78:593-609
Burstone. Variable modulus orthodontics. AJO 81; 80:116
Kusy and Dilley. Elastic property ratios of a triple
stranded stainless steel archwire. AJO 84;86:177-188
Stannard, Gau, Hanna. Comparative friction of
orthodontic wires under dry and wet conditions. AJO
86;89:485-491Ingram, Gipe, Smith. Comparative range
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of orthodontic wires AJO 1986;90:296-307
276. References
Ingram, Gipe, Smith. Comparative range of orthodontic
wires AJO 1986;90:296-30
Arthur J Wilcock. JCO interviews. JCO 1988;22:484-489
Khier, Brantley, Fournelle,Structure and mechanical
properties of as received and heat treated stainless steel
orthodontic wires. AJO March 1988, 93, 3, 206-212
Twelftree, Cocks, Sims. Tensile properties of Orthodontic
wires. AJO 89;72:682-687
Kapila & Sachdeva. Mechanical properties and clinical
applications of orthodontic wires. AJO 89;96:100-109.
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277. References
Arthur Wilcock. Applied materials engineering for
orthodontic wires. Aust. Orthod J. 1989;11:22-29.
Julie Ann Staggers, Nicolas ,Clinical considerations in the
use of retraction mechanics.. JCO June 1991
Klump, Duncanson, Nanda, Currier ,Elastic energy/
Stiffness ratios for selected orthodontic wires.. AJO 1994,
106, 6, 588-596
A study of the metallurgical properties of newly introduced
high tensile wires in comparison to the high tensile
Australian wires for various applications in orthodontic
treatment. – Anuradha Acharya, MDS Dissertation
September 2000.
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278. References
Kusy, Mims, whitley ,Mechanical characteristics of
various tempers of as received Co-Cr archwires.. AJO
March 2001, 119, 3, 274-289
Eliades, Athanasios- In vivo aging of orthodontic alloys:
implications for corrosion potential, nickel release, &
biocompatibility –AO, 72,3,2002
Kusy.Orthodontic biomaterials: From the past to the
present-AJO May 2002
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279. Thank you
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