0
Physical and Mechanical
Properties and its
application in
orthodontics
Prepared by
Dr.Hardik Lalakiya
Guided by
 Dr.Ajay Kubavat
 Dr.Chintan Agrawal
 Dr.Ketan Mashru
 Dr.Bhavik Patel
 Dr.M...
OUTLINE
 Introduction
 Crystal structure and
its arrangement
 Principal metal
structures and its
arrangement
 Classifi...
 Permanent Plastic
deformation
 Strain hardening
 Strength and its types
 Fatigue
 Static fatigue
 Brittleness
 Duc...
Mechanical properties are defined by the
laws of mechanics that is the physical science
that deals with the energy and fo...
The Plantonic Solids
CUBE DODECAHEDRON ICOSAHEDRON
OCTAHEDRON TETRAHEDRON
http://home.teleport.com/~tpgettys/platonic.shtml
 Atomic arrangements in crystalline solids can be
described with respect to a network of lines in three
dimensions.
 The...
 A particular
arrangement of atoms
in a crystal structure
can be described by
specifying the atom
positions in a
repeatin...
14 Bravais lattices
Principal metal crystal structures
 There are three principle crystal
 structures for metals:
 –(a) Body-centered cubic...
Principal structures
Body centered cubic (BCC)
(BCC)
Face centered cubic (FCC)
(FCC)
Hexagonal closed packed (HCP)
(HCP)
Classification
Definition:
When a force acts on a body
tending to produce deformation . A resistance
is developed to this external force ...
•Commonly expressed as Pascal 1Pa = 1N/m2. It is
common to report stress in units of Megapascals (MPa)
where 1 MPa = 106 P...
3 Types of stress
 Tensile
 Compressive Stress
 Shear stress
Tensile Stress
 A tensile Stress is caused by a load that tends
to stretch or elongate a body .
 for eg stress developed...
Compressive stress
 If a body is placed under a load that tends to
compress or shorten it,the internal resistance to such...
Shear stress
 A stress that tends to resist a twisting motion or
sliding of one portion of a body over another is
shearin...
Complex stress
 Complex stress those
produced by applied
forces that cause flexural
or torsional deformation
are called f...
STRAIN
o A force is applied to a body it undergoes
deformation.
o Strain is described as the change in length (Δ L = L –
L...
Strain has no units of measurement.
 It is a Dimensionless quantity.
 Reported as an absolute value or as a
percentage.
Facts
 The Average max sustainable biting force is 756N
(170 pounds) or (77kgs)
 The Guiness Book Of World records (1994...
 Each type of stress is capable of producing a
corresponding deformation in a body.
 Tensile stress produces tensile str...
Stress strain curve
 Represents energy storage capacity of the wire so
determines amount of work expected from a
particul...
True stress strain curve
 A stress strain curve based on stresses calculated
from a Non Constant Cross sectional area is ...
STRESS STRAIN CURVE
Mechanical Properties Based On Elastic
deformation
 Elastic Modulus
 Shear Modulus
 Flexibility
 Resilience
 Poisson’...
Elastic modulus
(young’s modulus or Elasticity)
 The term elastic modules describes the relative
STIFFNESS or RIGIDITY of...
Stress strain curve
 Modulus of elasticity is independent of the ductility
of a material and it is not a measure of its strength.
 It is an ...
 The Elastic modulus of a tensile test specimen can be
calculated as follows where
 E is elastic modulus
 P is the appl...
Flexibility
 The maximum flexibility is defined as the strain that
occurs when the material is stressed to its proportion...
Resilience
 Popularly the term Resilience is associated with
“springiness”.
 Definition: It is defined as the amount of ...
Poisson’s ratio
 Any material when subjected to a tensile or
compressive stress, there is simultaneous axial and
lateral ...
TOUGHNESS
 It is defined as energy required to fracture a material.
 It is measured as a total area under stress strain ...
Conventional Tensile Stress Strain Curve
IMPACT STRENGTH
 IMPACT:
 It is the reaction of a stationary object to a collision with a
moving object. Depending on th...
Impact Strength (continue)..
 It is the energy required
to fracture a material
under force.
 A charpey type tester
is us...
Strength properties
 Strength is the stress necessary to cause either
fracture(ultimate strength) or a specified amount o...
Proportional limit (PL)
 It is defined as the greatest stress that a material will
sustain without a deviation from the l...
Hooke’s Law :- States that stress – strain ratio is
constant upto the proportional limit, the constant in
this linear stre...
Elastic limit (EL)
Definition: It is defined as maximum stress that a
material can withstand before it undergoes
permanent...
 PL deals with proportionality of strain to
stress in structure.
 EL describe elastic behavior of the material.
 EL & P...
Yield Strength
(yield stress or proof stress)
 It is defined as the stress at which a material exhibits
a specified limit...
 Amount of permanent strain may be referred to as
PERCENT OFFSET. Many specifications use 0.2% as
convention.
Permanent (Plastic) deformation
 If the material is deformed by a stress at a point
above the proportional limit before f...
Strain hardening
 Strengthening by increase of dislocation density
 (Strain Hardening = Work Hardening = Cold Working)
...
 Average distance between dislocations decreases and
dislocations start blocking the motion of each other.
 The percent ...
Strength
 It is the maximal stress required to fracture a structure.
 Strength is not a measure of individual atom to at...
Tensile strength
 Tensile Strength is
determined by
subjecting a rod , wire
or a dumbbell shaped
specimen to a tensile
lo...
Diametral Tensile Strength
 Brittle material an
indirect tensile test
called Diametral
compression test or
Brazillian tes...
Compressive strength
 Crushing strength is
determined by subjecting a
cylindrical specimen to a
compressive load.
 The s...
SHEAR SRENGTH
 Maximum stress a
material can withstand
before failure in a shear
mode of loading. It is
tested using punc...
FLEXURE STRENGTH
 Transverse strength or modulus of
rupture or flexure strength
Obtained using a beam supported
at each e...
Fatigue
 A Structure subjected to repeated or cyclic stress below its
proportional limit can produce abrupt failure of th...
Static fatigue
 Some material support a static load for a long period
of time and fail abruptly. This type of failure may...
Brittleness
 A brittle material fractures at or near its proportional
limit.
 It is opposite of toughness.
 Brittle mat...
Ductility
 Ability of a material to withstand permanent
deformation under a tensile load without rupture.
 It is the abi...
MEASUREMENT OF DUCTILITY
 1.Percentage elongation after fracture
 Gauge length = 51 mm( STANDARD GAUGE
LENGTH FOR DENTAL...
Malleability
 It is the ability of a material to withstand rupture under
compression.
 It is seen in hammering or rollin...
Stress concentration factors
 THESE INCLUDES
 Surface flaws
 Internal voids
 air bubbles.
 Inclusions of other materi...
Some clinical relations with orthodontic
wire
 Tension Test Results; UTS and E for stainless steel
and titanium material....
Stress-Strain curve of stainless steel specimen the
x-axis the strain in the specimen
and the y-axis stress (MP/mm2). By w...
Physical Properties
Abrasion and abrasion resistance
 Phenomenon of wearing/ removal process that occurs
whenever surfaces slide against each...
 Hardness is one of the common index of a material to resist
abrasion or wear but not the only index.
 Other factor whic...
hardness
 Resistance to surface penetration / surface scratching /ability
to resist indentation.
 Indentation is produce...
 Common tests are
 Barcol
 Brinell (BH)
 Rockwell (RH)
 Shore
 Vickers (HV)
 Knoop (KH) Microhardness test
Macrohar...
Brinell hardness number (BHN)
 Oldest, simplest , convenient &
extensively used
 Hardened steel ball pressed with
standa...
Rockwell hardness number (RHN)
 Conical diamond point is
used.
 Depth of penetration is
measured directly by the
dial ga...
Vickers hardness test
 HV test employs square based
pyramid of 136 Degrees
 Method of computation is the load
divided by...
Knoop hardness number (KHN)
 Uses diamond tip tool.
 Rhombohedral pyramid diamond
tip is used of dimension 130
degree an...
 KHN and HV are called as micro hardness test.
BHN and RHN are macro hardness test.
 Shore and Barcol test are sometimes...
Viscosity
 Resistance of a liquid to flow Study of flow
character of a material is the basis
for Rheology
 Importance of...
Change in Viscosity
 Whenever a force is applied to a material it will
deform.
 The force / area is called stress.
 The...
 Viscosity of most liquids decreases with increase in
temperature i.e. its flow increases
 To explain viscous nature of ...
 Based on Rheologic
 behavior fluids are
classified in to four types
 Newtonian fluid
 Pseudoplastic
 Dilatant fluid
...
Newtonian fluid
 Ideal fluid which
demonstrates a shear strain
proportional to the shear
stress
 The plot on the graph i...
Pseudoplastic fluid
 When the viscosity of a
material decreases with
increasing strain rate
until it reaches the
constant...
Dilatant fluid
 These are the liquids that
becomes more rigid as the
rate of deformation
increases.
These liquids show
op...
Plastic
Some classes of material
behave like a rigid body until
some minimum value of
shear stress is reached (off
set val...
Thixotrophic material
 Viscosity of liquid also depends on previous
deformation of liquid
 A liquid of this type that be...
Importance of Viscosity Properties
 Teaches us the best way to manipulate the materials
 Guides as on the best use of th...
Creep and flow
 If the metal is held at the temperature near its
melting point and subjected to constant applied
stress, ...
Creep and flow (continue…)
 A filling material called “Amalgam” has low
melting range. So when in mouth it is close to th...
Creep and flow (continue…)
 Flow is measured using compressive forces mostly.
 Testing flow: A cylinder prescribed dimen...
Thermophysical properties
 Heat transfer through solid substances most
commonly occur by means of conduction.
 The condu...
Thermoconductivity Properties
 The Thermal conductivity or coefficient of thermal
conductivity is the quantity of heat in...
Thermoconductivity Properties
(Cont..)
 The international system (SI) unit or measure for
thermal conductivity is watt / ...
Thermal Diffusivity
 The value of thermal diffusivity of a material controls
the time rate of temperature change as heat ...
Thermal Diffusivity (cont)..
 The formula that related thermal diffusivity to
 thermal conductivity is
 h = k / cpρ
 h...
Thermal Diffusivity (cont)..
 Square root of thermal diffusivity is indirectly
proportional to thermal insulation ability...
Coefficient of thermal expansion
 Coefficient of thermal expansion, is defined as the
change in length / unit of the orig...
Color and color perception (cont)..
 Sensation induced from color of various wavelength
reaching the eye.
 Eye is sensit...
Color and color perception (cont)..
Color and color perception (cont)..
 Thus,
 Light from object
 Incident on eyes
 Focused in retina →rods and cones
 C...
Color and color perception (cont)..
 Three dimension of color are:
 1. Hue
 2. Value
 3. Chroma
Color and color perception (cont)..
 Hue:
 Dominant color of an object
 E.g. red, blue, green (dominant wavelength).
 ...
Color and color perception (cont)..
 Value
 Relative lightness or
darkness of color.
 The human teeth have a
value in t...
Color and color perception (cont)..
 CHROMA
 Degree of saturation of particular hue.
 Higher the chroma, more intense a...
Color and color perception (cont)..
 Color Solid:
 Central rod = value
 Spikes = hue
 Volume = chroma
Color and color perception (cont)..
 CIE SYSTEM:
 Commission
International Eclairage.
 Based on Adam system
 Colour in...
Color and color perception (cont)..
 Shade Guide :
 In the dental laboratory, color matching is usually
performed by the...
Color and color perception (cont)..
 Metamerism:
 Object that appear to be color matched under one
type of light may app...
Metamerism
Color and color perception (cont)..
 Near ultraviolet radiation:
 Natural tooth structure absorbs light at wave
lengths ...
Color and color perception (cont)..
 Fluorescence:
 Energy that the tooth absorbs is converted into light
with longer wa...
Fluorescence
Color and color perception (cont)..
 BEZOLD BRUCKE EFFECT:
 At low light levels, rods of human eye are dominant
and colo...
BEZOLD BRUCKE EFFECT
BEZOLD BRUCKE EFFECT
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
Physical and mechanical properties and its application in orthodontics
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Physical and mechanical properties and its application in orthodontics

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Hai this is very interesting topic for the dental students and also for the PG of orthodontics .So just have a glance over it and always your suggestions are heartly welcome.please free to suggest and make necessary suggestions.

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  • Indian Dental Academy Now offers comprehensive online Orthodontics course Course includes: 1.whiteboard lecture presentations 2.access and support @ 350 USD only. For Demo please visit :www.idalectures.com/preview/ For more details visit: www.idalectures.com Please contact us for any clarifications: idalectures@gmail.com indiandentalacademy@gmail.com Thanks & Regards Indian Dental Academy
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Transcript of "Physical and mechanical properties and its application in orthodontics"

  1. 1. Physical and Mechanical Properties and its application in orthodontics
  2. 2. Prepared by Dr.Hardik Lalakiya Guided by  Dr.Ajay Kubavat  Dr.Chintan Agrawal  Dr.Ketan Mashru  Dr.Bhavik Patel  Dr.Manish Desai  Dr.Vishal Patel Department of Orthodontics and Dentofacial Orthopaedics
  3. 3. OUTLINE  Introduction  Crystal structure and its arrangement  Principal metal structures and its arrangement  Classification  Stress and its types  Strain  True Stress strain curve  Poisson’s ratio  Mechanical properties based on elastic deformation  Toughness  Impact strength  Proportional limit  Elastic limit  Yield strength
  4. 4.  Permanent Plastic deformation  Strain hardening  Strength and its types  Fatigue  Static fatigue  Brittleness  Ductility  Malleability  Physical Properties  Abrasion and abrasion resistance.  Hardness  Viscosity  Creep and flow  Color and color perception  Bezold brucke effect
  5. 5. Mechanical properties are defined by the laws of mechanics that is the physical science that deals with the energy and forces and their effects on bodies the discussion centers primarily on the static bodies –those at rest-rather than on dynamic bodies. Many factors must be taken into account when considering which properties are relevant to the successful performance of the material used in dentistry
  6. 6. The Plantonic Solids CUBE DODECAHEDRON ICOSAHEDRON OCTAHEDRON TETRAHEDRON http://home.teleport.com/~tpgettys/platonic.shtml
  7. 7.  Atomic arrangements in crystalline solids can be described with respect to a network of lines in three dimensions.  The intersections of the lines are called “lattice sites” (or lattice points). Each lattice site has the same environment in the same direction.
  8. 8.  A particular arrangement of atoms in a crystal structure can be described by specifying the atom positions in a repeating “unit cell”.
  9. 9. 14 Bravais lattices
  10. 10. Principal metal crystal structures  There are three principle crystal  structures for metals:  –(a) Body-centered cubic (BCC)  –(b) Face-centered cubic (FCC)  –(c) Hexagonal close-packed (HCP)
  11. 11. Principal structures
  12. 12. Body centered cubic (BCC)
  13. 13. (BCC)
  14. 14. Face centered cubic (FCC)
  15. 15. (FCC)
  16. 16. Hexagonal closed packed (HCP)
  17. 17. (HCP)
  18. 18. Classification
  19. 19. Definition: 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 STRESS
  20. 20. •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 In english system of measurement ,the stress is usually expressed in pounds per square inch.
  21. 21. 3 Types of stress  Tensile  Compressive Stress  Shear stress
  22. 22. Tensile Stress  A tensile Stress is caused by a load that tends to stretch or elongate a body .  for eg stress developed on the gingival side of 3 unit bridge bridge
  23. 23. Compressive stress  If a body is placed under a load that tends to compress or shorten it,the internal resistance to such a load is called compressive stress.
  24. 24. Shear stress  A stress that tends to resist a twisting motion or sliding of one portion of a body over another is shearing stress  For eg If a force is applied along the surface of tooth enamel by a sharp edged instrument parallel to the interface between the enamel and an orthodontic bracket may debond by shear stress failure of the resin luting cement
  25. 25. Complex stress  Complex stress those produced by applied forces that cause flexural or torsional deformation are called flexural stress  More than two  They are also called as  bending stress.
  26. 26. STRAIN o A force is applied to a body it undergoes deformation. o 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. Strain ( ) = Change in length = L – Lo = Δ L Original length Lo Lo
  27. 27. Strain has no units of measurement.  It is a Dimensionless quantity.  Reported as an absolute value or as a percentage.
  28. 28. Facts  The Average max sustainable biting force is 756N (170 pounds) or (77kgs)  The Guiness Book Of World records (1994) lists the highest biting force as 4337N (975 pounds).
  29. 29.  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.
  30. 30. Stress strain curve  Represents energy storage capacity of the wire so determines amount of work expected from a particular spring in moving a tooth.
  31. 31. 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.
  32. 32. STRESS STRAIN CURVE
  33. 33. Mechanical Properties Based On Elastic deformation  Elastic Modulus  Shear Modulus  Flexibility  Resilience  Poisson’s ratio.
  34. 34. Elastic modulus (young’s modulus or 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 o Determined from stress stain curve by calculating ratio of stress to strain or slope of linear portion of curve. Stress 6 Elastic Modulus = = Strain 
  35. 35. Stress strain curve
  36. 36.  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.
  37. 37.  The Elastic modulus of a tensile test specimen can be calculated as follows where  E is elastic modulus  P is the applied force or load  A is the cross sectional area of material under stress  ^l is the increase in length  Lo is the original length
  38. 38. Flexibility  The maximum flexibility is defined as the strain that occurs when the material is stressed to its proportional limit.  For example in an orthodontic appliance, a spring is often bent a considerable distance with a small stress resulting in such a case structure is said to be flexible.
  39. 39. Resilience  Popularly the term Resilience is associated with “springiness”.  Definition: 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.
  40. 40. Poisson’s ratio  Any material when subjected to a tensile or compressive stress, there is simultaneous axial and lateral strain.  Within elastic range the ratio of lateral to axial strain is known as poisson’s ratio.  Dental materials have poisson’s ratio in the range of 0.3 to 0.5.
  41. 41. TOUGHNESS  It is defined as energy required to fracture a material.  It is measured as a total area under stress strain curve.  Toughness of the material is dependent on the ductility and malleability of the material than upon the flexibility or elastic modulus.
  42. 42. Conventional Tensile Stress Strain Curve
  43. 43. IMPACT STRENGTH  IMPACT:  It is the reaction of a stationary object to a collision with a moving object. Depending on the resilience of the object , energy is stored in the body without causing deformation or with deformation.  Impact resistance decreases with increase in stiffness.  Resilient material have high impact strength. Increase in volume leads to increase in impact resistance.
  44. 44. Impact Strength (continue)..  It is the energy required to fracture a material under force.  A charpey type tester is used. It has a heavy pendulum which swings down to fracture the specimen.  Another instrument called Izod impact tester can also be used.
  45. 45. Strength properties  Strength is the stress necessary to cause either fracture(ultimate strength) or a specified amount of plastic deformation(yields strength).  The strength of a material can be described by  Proportional limit  Elastic strain  Yield strength  Ultimate tensile strength, shear ,compressive and flexural strength.
  46. 46. 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.
  47. 47. 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
  48. 48. Elastic limit (EL) Definition: 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 :-
  49. 49.  PL deals with proportionality of strain to stress in structure.  EL describe elastic behavior of the material.  EL & PL limits are usually assumed to be identical although their experimental values may differ slightly.
  50. 50. Yield Strength (yield stress or 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
  51. 51.  Amount of permanent strain may be referred to as PERCENT OFFSET. Many specifications use 0.2% as convention.
  52. 52. Permanent (Plastic) deformation  If the material is deformed by a stress at a point above the proportional limit before fracture,the removal of applied force will reduce the stress to zero,but the strain does not decrease to zero because the plastic deformation has occurred .  Thus the object does not return to its original dimension when the force is removed.It remains bent,streched,compressed or otherwise plastically deformed.
  53. 53. Strain hardening  Strengthening by increase of dislocation density  (Strain Hardening = Work Hardening = Cold Working)  Ductile metals become stronger when they are deformed plastically at temperatures well below the melting point.  The reason for strain hardening is the increase of dislocation density with plastic deformation.
  54. 54.  Average distance between dislocations decreases and dislocations start blocking the motion of each other.  The percent cold work (% CW) is often used to express the degree of plastic deformation:  %CW is just another measure of the degree of plastic deformation, in addition to strain.
  55. 55. Strength  It is the maximal stress required to fracture a structure.  Strength is not a measure of individual atom to atom attraction or repulsion , but rather it is a measure of the interatomic forces collectively over the material which is stressed.  STRENGTH IS BASICALLY OF FOUR TYPES:  Tensile  Compressive  Shear  Flexure
  56. 56. Tensile strength  Tensile Strength is determined by subjecting a rod , wire or a dumbbell shaped specimen to a tensile loading.  It is defined as the maximal stress the structure will withstand before rupture.
  57. 57. Diametral Tensile Strength  Brittle material an indirect tensile test called Diametral compression test or Brazillian test is used .  A compressive load is placed on the diameter of a short cylindrical material .
  58. 58. Compressive strength  Crushing strength is determined by subjecting a cylindrical specimen to a compressive load.  The strength is obtained from the cross sectional area and force applied.  Complex failure
  59. 59. SHEAR SRENGTH  Maximum stress a material can withstand before failure in a shear mode of loading. It is tested using punch or pushout method.  Shear strength = Force/ Π punch dia * thickness
  60. 60. FLEXURE STRENGTH  Transverse strength or modulus of rupture or flexure strength Obtained using a beam supported at each end and load applied in the middle.  Also called three point  bending test.  Used in long span bridges.  Neutral Axis
  61. 61. Fatigue  A Structure subjected to repeated or cyclic stress below its proportional limit can produce abrupt failure of these structure.  Fatigue behavior is determined by subjecting a material to a cyclic stress of known value and determining the number of cycles that are required to produce failure.
  62. 62. Static fatigue  Some material support a static load for a long period of time and fail abruptly. This type of failure may occur in wet environment.  Eg ceramic materials.
  63. 63. Brittleness  A brittle material fractures at or near its proportional limit.  It is opposite of toughness.  Brittle material will not bend appreciably without breaking.  Though a brittle material may have a very high compressive strength. E.g. glass.
  64. 64. Ductility  Ability of a material to withstand permanent deformation under a tensile load without rupture.  It is the ability of the metal to be drawn into wires.  Ductility depends on tensile strength.  It decreases with increase in temperature.
  65. 65. MEASUREMENT OF DUCTILITY  1.Percentage elongation after fracture  Gauge length = 51 mm( STANDARD GAUGE LENGTH FOR DENTAL MATERIALS)  2.Measuring reduction in cross sectional areas of fractured ends in comparison to the original area of the wire. This is also called as reduction in area method.  3. cold bend test
  66. 66. Malleability  It is the ability of a material to withstand rupture under compression.  It is seen in hammering or rolling of a material into sheets.  It is not dependent on the strength of the material  It increases with temperature.  Gold is most ductile and malleable and silver stands the second.  Platinum is third most ductile and copper ranks third in malleability.
  67. 67. Stress concentration factors  THESE INCLUDES  Surface flaws  Internal voids  air bubbles.  Inclusions of other materials  Hertzian load  Sharp angles  Notches  Thermal mismatch
  68. 68. Some clinical relations with orthodontic wire  Tension Test Results; UTS and E for stainless steel and titanium material.  Material Type UTS (MPa) E (GPa)  Stainless steel 1300 193  titanium 1615 179
  69. 69. Stress-Strain curve of stainless steel specimen the x-axis the strain in the specimen and the y-axis stress (MP/mm2). By wp 300 tensile testing machine
  70. 70. Physical Properties
  71. 71. Abrasion and abrasion resistance  Phenomenon of wearing/ removal process that occurs whenever surfaces slide against each other  The material which causes wearing is called abrasive  The material which is worn is called substrate.
  72. 72.  Hardness is one of the common index of a material to resist abrasion or wear but not the only index.  Other factor which cause and influence abrasion / abrasion resistance are  Biting force  Frequency of chewing,  Abrasiveness of diet,  Intra oral liquid, temperature changes,  Surface roughness,  Impurities and irregularities (Pits and grooves)
  73. 73. hardness  Resistance to surface penetration / surface scratching /ability to resist indentation.  Indentation is produced on the surface of the material from a applied force of a sharp point or an abrasive particle.  Most hardness test are based on ability of a surface of a material to resist penetration by diamond point or a steel ball under a specified
  74. 74.  Common tests are  Barcol  Brinell (BH)  Rockwell (RH)  Shore  Vickers (HV)  Knoop (KH) Microhardness test Macrohardness test
  75. 75. Brinell hardness number (BHN)  Oldest, simplest , convenient & extensively used  Hardened steel ball pressed with standard load on polished surface of material .  Load is divided by the area of projected surface of indentation .  Thus for a given load smaller the indentation, larger is the number and the harder is the material
  76. 76. Rockwell hardness number (RHN)  Conical diamond point is used.  Depth of penetration is measured directly by the dial gauge on the Instrument  RHN and BHN are used for measuring hardness of metal and alloys and they are not suitable for brittle materials.
  77. 77. Vickers hardness test  HV test employs square based pyramid of 136 Degrees  Method of computation is the load divided by the projected area of Indentation.  The length of the diagonals are measured and averaged.  Can be used for brittle materials.  also called 136 degree diamond pyramid test.
  78. 78. Knoop hardness number (KHN)  Uses diamond tip tool.  Rhombohedral pyramid diamond tip is used of dimension 130 degree and 172.30 degree  The length of the largest diagonal is measured .  The projected area is divided in to the load to give KHN  Can be used for extremely hard and soft materials.
  79. 79.  KHN and HV are called as micro hardness test. BHN and RHN are macro hardness test.  Shore and Barcol test are sometimes employed to measure hardness of rubber and plastic type of dental materials.  These have spring loaded metal indenter point.
  80. 80. Viscosity  Resistance of a liquid to flow Study of flow character of a material is the basis for Rheology  Importance of knowing flow:  impressions, Gypsum products, cements, waxes.  Resistance to flow is controlled by internal frictional forces. Thus viscosity is the measure of consistency of a medium and its inability to flow.
  81. 81. Change in Viscosity  Whenever a force is applied to a material it will deform.  The force / area is called stress.  The calculation of deformation is the strain.  Strain = change in length / initial length.  Unit of viscosity is MPa / second or CETIPOISE
  82. 82.  Viscosity of most liquids decreases with increase in temperature i.e. its flow increases  To explain viscous nature of some materials , shear stress / shear strain rate curve is plotted .
  83. 83.  Based on Rheologic  behavior fluids are classified in to four types  Newtonian fluid  Pseudoplastic  Dilatant fluid  Plastics
  84. 84. Newtonian fluid  Ideal fluid which demonstrates a shear strain proportional to the shear stress  The plot on the graph is a straight line  Newtonian fluids has a constant viscosity and is independent of the shear strain rate.
  85. 85. Pseudoplastic fluid  When the viscosity of a material decreases with increasing strain rate until it reaches the constant value such a material is called Pseudoplastic materials or fluid.
  86. 86. Dilatant fluid  These are the liquids that becomes more rigid as the rate of deformation increases. These liquids show opposite tendency as described for pseudoplastic
  87. 87. Plastic Some classes of material behave like a rigid body until some minimum value of shear stress is reached (off set value) These fluids which exhibits rigid behavior initially and then attend constant viscosity are referred to as plastic. Ketchup is a familiar example .
  88. 88. Thixotrophic material  Viscosity of liquid also depends on previous deformation of liquid  A liquid of this type that becomes less viscous and more fluid under more repeated application of pressure is called as Thixotrophic materials  Examples: Dental polishing paste, plaster of paris,  impression materials, resins and cements
  89. 89. Importance of Viscosity Properties  Teaches us the best way to manipulate the materials  Guides as on the best use of the materials  Measure of working time  Thixotropic materials stays on tray but on applying pressure in the mouth the material flows
  90. 90. Creep and flow  If the metal is held at the temperature near its melting point and subjected to constant applied stress, the resulting strain will increases over time.  Creep is defined as the time dependant plastic strain of a materials under static / constant load.  Sag is same as creep but the load is the mass of the same material .
  91. 91. Creep and flow (continue…)  A filling material called “Amalgam” has low melting range. So when in mouth it is close to the melting point and is subjected to constant biting forces. It gets get deformed. Here the biting forces keep changing and continuous Dyanamic creep.  For waxes term flow rather than creep is used as it is amorphous. The flow of wax is its potential to deform under small static load / or its own mass.
  92. 92. Creep and flow (continue…)  Flow is measured using compressive forces mostly.  Testing flow: A cylinder prescribed dimension is subjected to a given compressive stress for a specified time and temperature.  The creep or flow is measured as percentage decrease in length.  Significance of creep / sag.
  93. 93. Thermophysical properties  Heat transfer through solid substances most commonly occur by means of conduction.  The conduction of heat through metals occurs through the interaction with atoms.  Thermal conductivity (k) is the thermophysical measure of how well heat is transferred through a material by conductive flow.  The measurement of thermal conductivity is performed under steady state conditions.
  94. 94. Thermoconductivity Properties  The Thermal conductivity or coefficient of thermal conductivity is the quantity of heat in calories per second that passes through a specimen 1 cm thick having a cross sectional area of 1cm2 ,when the temperature difference between the surfaces Thermoconductivity Properties perpendicular to the heat flow of the specimen is 10 K.  Materials that have a high thermal conductivity are called conductors, whereas materials of low thermal conductivity are called insulators.
  95. 95. Thermoconductivity Properties (Cont..)  The international system (SI) unit or measure for thermal conductivity is watt / meter / second /o Kelvin  Increase in thermal conductivity , greater is the ability to transfer thermal energy.  Metal restoration – increase conductivity compared to other materials.
  96. 96. Thermal Diffusivity  The value of thermal diffusivity of a material controls the time rate of temperature change as heat passes through a material.  It is a measure of the rate at which a body with a nonuniform temperature reaches a state of thermal equilibrium.  For a given volume of material, the heat required to raise the temperature , to a given amount depends on its heat capacity or specific heat and the density.
  97. 97. Thermal Diffusivity (cont)..  The formula that related thermal diffusivity to  thermal conductivity is  h = k / cpρ  h = Thermal diffusivity  k = Thermal conductivity  cp = Heat capacity  ρ = temperature dependent density
  98. 98. Thermal Diffusivity (cont)..  Square root of thermal diffusivity is indirectly proportional to thermal insulation ability.  SI unit is square meter per second commonly used.
  99. 99. Coefficient of thermal expansion  Coefficient of thermal expansion, is defined as the change in length / unit of the original length of a material when its temperature is raised 1degree K.  SI unit μm /m0 K or ppm / k0  A tooth restoration may contract or expand more than the tooth during the change in temp which may cause micro leakage or debond of restoration of teeth.  To reduce this, selection of material whose expansion or contraction coefficient should be matched approximately within 4%.  PFM
  100. 100. Color and color perception (cont)..  Sensation induced from color of various wavelength reaching the eye.  Eye is sensitive to wavelength of 400nm(violet) to 700nm(dark red).  For an object to be visible, it must reflect and transmit incident light at certain wavelength.  Color is measured using munsell system.
  101. 101. Color and color perception (cont)..
  102. 102. Color and color perception (cont)..  Thus,  Light from object  Incident on eyes  Focused in retina →rods and cones  Converted into nerve impulses  Transmitted to brain
  103. 103. Color and color perception (cont)..  Three dimension of color are:  1. Hue  2. Value  3. Chroma
  104. 104. Color and color perception (cont)..  Hue:  Dominant color of an object  E.g. red, blue, green (dominant wavelength).  The normal human teeth have hue range of 6.3  yellow red to 9.3 yellow red.
  105. 105. Color and color perception (cont)..  Value  Relative lightness or darkness of color.  The human teeth have a value in the range of 0- 7.
  106. 106. Color and color perception (cont)..  CHROMA  Degree of saturation of particular hue.  Higher the chroma, more intense and mature the color.  Chroma cannot exist itself and it is always associated with hue and value.  Normal human teeth has chroma of 4 to 7.
  107. 107. Color and color perception (cont)..  Color Solid:  Central rod = value  Spikes = hue  Volume = chroma
  108. 108. Color and color perception (cont)..  CIE SYSTEM:  Commission International Eclairage.  Based on Adam system  Colour in L*a*b  L = value  a = measure along r-g  axis  b= measure along y-b axis
  109. 109. Color and color perception (cont)..  Shade Guide :  In the dental laboratory, color matching is usually performed by the shade guide.  The most commonly used guide is VITA shade guide.  The range is from A1 to D4 .From left to right the darkness increase.
  110. 110. Color and color perception (cont)..  Metamerism:  Object that appear to be color matched under one type of light may appear different under another light source.  Day light, incandescent lamps, fluorescent lamps are most common source of light in dental operatory.  Two or more sources of light should be used to prevent metamerism causing wrong selection of
  111. 111. Metamerism
  112. 112. Color and color perception (cont)..  Near ultraviolet radiation:  Natural tooth structure absorbs light at wave lengths too short to be visible at human eye.  These wave lengths between between 300nm- 400nm are referred as near ultraviolet radiation.  Sources are natural sunlight, photoflash lamps, UV light
  113. 113. Color and color perception (cont)..  Fluorescence:  Energy that the tooth absorbs is converted into light with longer wavelength in which case the tooth actually becomes a light source.  The phenomenon is called Fluorescence.  Ceramics, composites – fluorescent agents are added.
  114. 114. Fluorescence
  115. 115. Color and color perception (cont)..  BEZOLD BRUCKE EFFECT:  At low light levels, rods of human eye are dominant and color perception is lost. As the brightness becomes more intense , color appears to change.
  116. 116. BEZOLD BRUCKE EFFECT
  117. 117. BEZOLD BRUCKE EFFECT
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