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2. STRUCTURE OF MATTER
Study of dental materials and its
properties particularily of solids.
Basic materials used in the field of
Dentistry.
Collective reaction of these atoms,
whether physical or chemical determine
the effectiveness of an material.
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5. EQUILIBRIUM INTER ATOMIC
DISTANCE
Limiting factor for the atoms & molecules
from approaching each other too closely.
Boundaries & volumes of an atom are not
discrete instead they are vague determined
by their electrostatic fields.
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6. Forces of
attraction versus
forces of repulsion
dictating the
equilibrium
position of the
atoms.
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7. CRYSTAL STRUCTURE
UnitCell-smallest
repeating unit that is
contained in a crystal.
SpaceLattice-any
arrangement of atoms
in space such that
every atom is situated
similarly to every
other atom.
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10. Line defects (dislocations)
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11. Planar defects (grain boundaries in
metals)
Orientation of space lattice of each grain.
Structure of grain proper & grain
boundaries are they same?
Grain boundaries a region of transition.
Non crystalline.
High energy.
Tendency towards amorphism.
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12. SURFACE ENERGY
The increase in the energy per unit area of
surface is referred as the surface energy
or surface tension.
Surface energy of a solid is greater than
its interior.
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13. Factors affecting the surface energy
Available functional groups.
Type of crystal plane of a space lattice
present at the surface.
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14. Adhesion & Bonding
Adhesive force - like molecules.
Cohesive force - unlike molecules.
Adhesive.
Adherend.
Chemisorption.
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15. BASIC METALLURGICAL TERMS
What is a metal?
Any chemical element that ionises (+vely )
in solution is known as metal.
What is an alloy?
A solid mixture of two or more metals.
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16. What is an cast
metal?
Solidification of pure
metal.
What is an wrought
metal?
Wires are made from
castings by drawing
a cast metal through
die.
certain metallurgical
characteristics not
associated with cast
structure.
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17. HISTORY OF STAINLESS STEEL
In the year 1740 Beryamin Huntsman.
In the year 1913,a break through came
when Brearly of Shiffield.
Introduction of chromium steel to the field
of orthodontics by Friel of Ireland in 1933.
Steel is an iron based alloy that contains
carbon less than 1.2%.
When chromium is added to steel the alloy
is called stainless steel(12%-30%).
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18. CLASSIFICATION
Based on lattice arrangements
Ferritic (bcc)
Austenitic (fcc)
Martenistic (bct)
Based on carbon content(0.8%)
Hypo-eutectoid
Hyper-eutectoid
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19. Acc to American iron and steel institute
300 – 502
Acc to Andereson
Soft
Half-hard
Hard
ANSI/ADA specification no 32
Type 1 (low-resilience)
Type 2 (high-resilience)
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20. PROPERTIES BASED ON
LATTICE ARRANGEMENTS
Ferritic (AISI-400)
Good corrosion
resistance.
Not hardenable by
heat treatment.
Not readily work
hardenable.
Finds little application
in dentistry.
Martensitic(AISI-400)
Can be heat treated.
High strength &
hardness.
Used in surgical &
cutting instruments.
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21. Austenitic(AISI-302),18-8 stainless steel.
Type 304(0.08%),Type 316L(0.03%).
Greater ductility and ability.
Substantial strengthening.
Ease of welding
Readily over comes sensitization
Less critical grain growth
Ease in forming
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22. SENSITIZATION (weld decay)
When 18-8 stainless steel is heated to
4000
-9000
c.
Formation of chromium carbide at grain
boundaries highest at 6500
c.
An inter- granular corrosion occurs and a
partial disintegration of the metal may
occur.
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23. STABILIZATION
Theoretical stand point reduce the carbon
content such that carbide precipitation
does not occur.
The method most commonly employed is
introduction of titanium approximately 6
times the carbon content.
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24. DEFORMATION OF METALS
From the physical properties of the metals
two types of deformation may exist.
Stresses below the proportional limit.
Stresses above the proportional limit.
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25. COLD WORKING
Also known as strain hardening/work hardening.
In a poly crystalline material.
Over a period of time greater stress is required
to produce the further slip.
Metal becomes stronger and harder.
As a result surface hardness, strength &
proportional limit are increased, where as the
ductility & resistance to corrosion are decreased.
Elastic modulus remains the same.
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26. ANNEALING
Effects associated with cold working can
be reversed by heating the metal.
Severe the cold working ,more readily
does annealing occur.
In general comprises of three stages
recovery, recrystallisation and grain
growth.
Higher the melting point of the metal
higher is the temp needed for annealing.
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29. DESIRABLE PROPERTIES
Wires should have good modulus of
elasticity.
low constant forces.
Large elastic deflections.
Ease of joining.
Good tarnish & corrosion resistance.
Good formability.
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30. MECHANICAL PROPPERTIES
Stress and strain.
The internal force divided by the area over which
it acts within the body is the resultant stress.
The deformation is called strain.
Depending on their direction they are classified
into three types,
Tensile stress
Compressive stress
Shear stress
Complex stress
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32. MODULUS OF ELASTICITY :
YOUNGS MODULUS(ELASTIC
MODULE)
Ratio of stress to strain.
The slope of this ratio indicates the
relative stiffness and the springiness of a
wire.
Wire with low modulus of elasticity has
increased flexibility as compared to a wire
of high modulus of elasticity.
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34. Hardness
Property used to predict the wear
resistance of a material.
Toughness
Property of being difficult to break.
Brittleness
Opposite of toughness, indicates the
material is apt to fracture at or near its
proportional limit.
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35. Stress relaxation
Change in the stress over a period of time.
Zero stress relaxation
In a deflected wire ,if the stress does not
reduce and wire still exists a constant
force.
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36. Ductility
Ability to with stand
under a tensile load.
The relative ease in
which a metal can be
drawn into wire.
Dependent on tensile
strength.
Malleability
Ability to with stand
under compression.
Increases with
increase in temp.
The relative ease in
which a metal can be
drawn into sheet.
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37. HEAT TREATMENT OF ALLOYS
Softening.
Electric furnace for 10
mins at 7000
c &
quenched in water.
Indicated for
structures that are to
be ground, shaped or
cold worked.
Hardening.
Heated for 15-30
mins.
Temp depends upon
the alloy composition.
Generally ranges
from 2000
c-4500
c.
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40. FLUX
Latin word means to flow.
Purpose is to remove any oxide layer on
the parent metal.
Based on their action
Protective
Reducing
Solvent
Type1 (low temp glass)
Type 2(reducing)
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42. TYPES OF SOLDERS
Soft
Lead-tin alloys.
Low melting point.
Lack corrosion
resistance.
Hard
Silver, copper, zinc,
cadmium.
High melting point.
Gold & silver solders.
Have good tarnish &
corrosion resistance.
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43. PROPERTIES OF A SOLDER
Appropriate flow temperature.
Ability to wet the parent metal.
Sufficient fluidity.
Good contrast.
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44. HEAT SOURCE
A gas-air or gas-oxygen torch.
Gases commonly used,
Hydrogen.
Natural gas.
Propane.
Acetylene.
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45. OVEN(FURNACE BRAZING)
Provides an heated surroundings.
Less heat is lost as compared to torch
brazing.
Transmission of heat from the heating
elements to the working area.
Convection.
Conduction.
Radiant heat.
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46. METHODS OF SOLDERING
Free hand soldering.
Investment soldering.
Infra red soldering.
1000 watt tungsten filament quartz iodine
bulb.
Mounted at the primary focal point of a
gold plated elliptical reflector.www.indiandentalacademy.com
47. WELDING
A portion of metal being joined is melted &
flowed together.
Joining of flat structures.
A nugget of re-solidified cast structure.
Strength of the joint depends on the area
of weld.
Pioneer work in this field was done by
Friel1933&McKeag1939.
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48. PARTS OF A TYPICAL WELDER
Heat generated=KI2
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49. THANK YOU
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