General Properties of Dental Materials By Dr Rashid Hassan. This is a comprehensive lecture covering all the properties of Dental Materials.

1. PROPERTIES OF
DENTAL
MATERIALS
By
Dr. Rashid Hassan

2. PROPERTIES OF
DENTAL
MATERIALS

3. PROPERTIES OF DENTAL MATERIALS
Properties can be
Categorized into:
1) Properties of dental
material before
mixing.
2) Properties of dental
materials during
mixing & setting.
3) Properties of dental
materials after setting.

4. Properties Of
Dental Materials
Before Mixing
1) Shelf life.
2) Storage

5. PROPERTIES OF DENTAL MATERIALS
BEFORE MIXING (UNMIXED STATE)
In unmixed state dental
materials posses the
following properties
1) SHELF LIFE:
 It is the length of time a dental
material can be stored without
deterioration.
2) STORAGE:
 Must be stored as per
manufacturer’s
instructions.
 Over storage should be
avoided.

6. Properties Of Dental
Materials During
Mixing & Setting
1) Mixing time
2) Working time
3) Setting time

7. PROPERTIES OF DENTAL MATERIALS
DURING MIXING & SETTING
1) MIXING TIME:
 The recommended time
for mixing a material
until the required
consistency /
homogenous mixture is
achieved.
 It’s the time from the
addition of powder to
water until mixing is
completed.

8. PROPERTIES OF DENTAL MATERIALS
DURING MIXING & SETTING
2) WORKING TIME:
 It’s the time during
which a material can be
mixed/manipulated
ideally with no
thickening effect.
 Time available to use a
workable mix.

9. PROPERTIES OF DENTAL MATERIALS
DURING MIXING & SETTING
3) SETTING TIME:
 Time required for a
material to reach a
certain level of
rigidity/elasticity.
 Starts when the mixing
begins until the
material hardens
(Setting reaction is
complete)

10. Properties Of Dental
Materials
After Setting
1) Biological properties.
2) Chemical properties.
3) Electrical properties.
4) Thermal properties.
5) Physical properties.
6) Mechanical properties.

11. Properties Of Dental Materials
After Setting
BIOLOGICAL PROPERTIES
 Dental material should
be non toxic, non
irritant, non allergic,
non carcinogenic &
non mutagenic to oro-
dental tissues.
 Primarily the dental
material must be
harmless to
manufacturer,
assistant, dental
surgeon, patient and
any other relevant
person.

12. Properties Of Dental Materials
After Setting
BIOLOGICAL PROPERTIES
• The material is said to be
“biocompatible” when it
possesses the property of
being non destructive (non
toxic/non irritant) in a
biological system.
• Biocompatibility id defined
as,“The ability of a material
to elicit an appropriate
biological response in a
given application in the
body.”
12

13. 13
TESTS
FOR MEASURING
BIOCOMPATIBILITY

14. 1. IN VITRO TEST
• Performed outside the
organism.
• First screening test to
evaluate biological
response of a new
material.
• Conducted in test tube,
cell culture dish, flask
or other container.
• Contact may be
direct/indirect. 14

15. 15
1. IN VITRO TEST
ADVANTAGES
• Relatively fast.
• Inexpensive.
• Controlled
conditions.
• Large scale
testing.
DISADVANTAGES
• Lack of relevance
to in vivo
conditions.
• Lack of complex
systemic co-
ordinations.

16. 2. THE ANIMAL TEST
• Material placed into
an intact organism.
• Commonly used
animals are mice,
rats, hamsters or
guinea pigs.
• Other animals used
are cats, sheep's,
dogs, monkeys and
baboons 16

17. 17
2. THE ANIMAL TEST
ADVANTAGES
• Intact biological
system.
• Act as a bridge
between in vitro
and usage test.
DISADVANTAGES
• Expansive.
• Difficult to
control.
• May take months
or years.
• Ethical concerns.

18. 18
3. USAGE TEST
 Performed in animals
or humans.
 In case of humans it is
called as clinical trial.
 Choice of animal is
limited.
 Animals used should be
large, with anatomy
similar to the humans.
 Human clinical trial is
the “gold standard”.

19. 19
3. USAGE TEST
DISADVANTAGES:
• Very costly.
• Ethical permission required (In case
of humans)
• Prolonged time required for
results.
• Legal liabilities.

20. 20
TESTS USED
TOGETHER
Usage
SECONDARY
PRIMARY
Progress of
testing
Number of materials

21. CHEMICAL PROPERTIES
OF
DENTAL MATERIALS
1) Sorption.
2) Adsorption.
3) Absorption.
4) Diffusion.
5) Osmosis.
6) Solubility.
7) Erosion.
8) Adhesion.
9) Cohesion.
10) Surface energy.
11) Wetting.
12) Contact angle of wetting.
13) Leaching.

22. CHEMICAL PROPERTIES OF
DENTAL MATERIALS
1) SORPTION:
 The taking up and holding of o
ne substance by another. Sorpt
ion is used especially as a gene
ral term for absorption
and adsorption
2) ADSORPTION:
 The process in which liquid or
gas molecules adheres firmly
to the surface of solid or
liquid.
3) ABSORPTION:
 The process in which a liquid
or gas molecules penetrate
into the solid material.

23. CHEMICAL PROPERTIES OF
DENTAL MATERIALS
4) DIFFUSION:
 The process by which
molecules intermingle as a
result of their kinetic energy
of random motion.
5) OSMOSIS:
 The diffusion of solute from
the region of low
concentration to the region
of high concentration
through semi permeable
membrane is called
osmosis.

24. CHEMICAL PROPERTIES OF
DENTAL MATERIALS
6) SOLUBILITY:
It is the
measurement of
the extent to
which a material
will dissolve in a
given fluid. e.g.
saliva or water.

25. CHEMICAL PROPERTIES OF
DENTAL MATERIALS
7) EROSSION:
 The process which
combines the chemical
process of dissolution
with a mild mechanical
action.
 In dentistry erosion is
used to describe the
destruction of natural
hard tissue by acids
(either occurring
naturally or present in
food/drinks)

26. CHEMICAL PROPERTIES OF
DENTAL MATERIALS
8) ADHESION:
 Force of attraction
between molecules of
different substances.
9) COHESION:
 Force of attraction
between molecules of
same substance.

27. 10) SURFACE ENERGY/SURFACE
TENSION:
 The increase in energy per
unit area is called as
surface energy or surface
tension.
 Interfacial tension that
exists between the two
surfaces due to unbalanced
intermolecular forces.
 For adhesion to exist the
surfaces must be attracted
to one another at their
interface. 27
CHEMICAL PROPERTIES OF
DENTAL MATERIALS

28. CHEMICAL PROPERTIES OF
DENTAL MATERIALS
11) WETTING/WETABILITY:
 Interfacial tension
between a liquid and a
solid resulting in a
contact angle of less
than 90°.
 Adhesion is negligible
when the surface
molecules of the two
materials are separated
by a distance greater
than 0.7nm.
28

29. CHEMICAL PROPERTIES OF
DENTAL MATERIALS
12) CONTACT ANGLE OF
WETTING:
 The extent to which an
adhesive can wet the
surface of adherend can be
determined by measuring
the contact angle between
the adhesive and the
adherend.
 If the molecules of
adhesive are attracted
more to the molecules of
the surface, the adhesive
will spread completely
over the surface of the
solid.
29
Complete wetting occurs
at 0° and no wetting
occurs at 180°.

30. ELECTRICAL PROPERTIES OF
DENTAL MATERIALS
1) Conductor
2) Insulator
3) Electric conductivity
4) Galvanism

31. ELECTRICAL PROPERTIES OF
DENTAL MATERIALS
1) CONDUCTOR:
A conductor is a
material that allow the
flow of electrical current
in one or more directions.
A metal wire is a common
electrical conductor.
2) INSULATOR:
The materials that
offer high resistance to
the flow of
electric current. Are called
insulators.

32. ELECTRICAL PROPERTIES OF
DENTAL MATERIALS
3) ELECTRICAL CONDUCTIVITY:
The ability of a
material to conduct an
electric current is called
electric conductivity.
4) GALVANISM:
Galvanic action occurs
when two
electrochemically
dissimilar metals are in
contact and a conductive
path occurs for electrons
and ions to move from
one metal to the other.

33. THERMAL PROPERTIES OF
DENTAL MATERIALS
1) Boiling point.
2) Melting point.
3) Freezing point.
4) Dew point.
5) Heat of fusion.
6) Heat of vaporization.
7) Thermal conductivity.
8) Thermal diffusivity.
9) Specific heat.
10)Coefficient of thermal expansion.

34. THERMAL PROPERTIES OF
DENTAL MATERIALS
BOILING POINT:
 The temperature at which
a liquid boils and turns to
vapour..
MELTING POINT:
 The temperature at which
a given solid will melt.
FREEZING POINT:
 The temperature at which
a liquid turns into a solid
when cooled.

35. THERMAL PROPERTIES OF
DENTAL MATERIALS
DEW POINT:
 The atmospheric temperature
(varying according to pressure
and humidity) below which water
droplets begin to condense and
dew can form.
 A higher dew point indicates
more moisture in the air.
 Dew point greater than 20 °C
(68 °F) is considered
uncomfortable and greater than
22 °C (72 °F) is considered to be
extremely humid.
Frost point is the dew point
when temperatures are below
freezing.

36. THERMAL PROPERTIES OF
DENTAL MATERIALS
HEAT OF FUSION:
Heat of fusion is the energy
required to change a gram
of a substance from the
solid to the liquid state at
melting temperature.
HEAT OF VAPOURIZATION:
Heat of vaporization is the
energy required to change a
gram of a liquid into the
gaseous state at the boiling
point Is called the "heat of
vaporization"

37. THERMAL PROPERTIES OF
DENTAL MATERIALS
THERMAL CONDUCTIVITY:
It is the measure of the
ability of a material to allow
the flow of heat.
THERMAL DIFFUSIVITY:
Thermal conductivity of a
substance divided by the
product of its density and its
specific heat capacity.
SPECIFIC HEAT:
The specific heat is the
amount of heat per unit
mass required to raise the
temperature by one degree
Celsius.
COEFFICIENT OF THERMAL
EXPANSION:
Change in length per unit
original length per degree
rise in temperature is called
coefficient of thermal
expansion.

38. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
A. OPTICAL PROPERTIES
1) Colour.
2) Hue.
3) Value.
4) Chroma.
5) Transparency.
6) Translucency.
7) Opacity.
8) Fluorescence.
B. RHEOLOGICAL
PROPERTIES
1) Viscosity.
2) Creep & Flow.
3) Viscoelasticity.
4) Newtonian behavior.
5) Pseudoplastic behavior.
6) Thixotrophic behavior.
7) Dilatant

39. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
A. OPTICAL PROPERTIES
COLOUR:
Combined intensities of the
wavelengths present in the
beam of light determine the
property calour.
HUE:
The property associated
with colour of an object (i.e.
Red, Green, Blue)
VALUE:
The amount of lightness or
darkness of a colour is called
value (i.e. from bright to
dull)
CHROMA:
Degree of saturation of a
particular hue.
Highe the chroma = more
intense the colour.

40. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
A. OPTICAL PROPERTIES
TRANSPARENCY:
The property of a material
that allows the passage of
light in such a manner that
the object may be clearly
seen through.
TRANSLUCENCY:
The property of a material
that permits passage of light
but disperses the light so
the object cannot be seen
through.

41. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
A. OPTICAL PROPERTIES
OPACITY:
The property of a material
that prevents the passage of
light.
FLUORESCENCE:
The phenomenon of
emission of light by a
substance that has absorbed
light or other
electromagnetic radiations.

42. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
B. RHEOLOGICAL PROPERTIES
The study of flow of a material is
called “Rheology”

43. VISCOSITY
Resistance of a liquid to flow
43
Viscosity is dependent upon
interatomic bonding
Water molecules has weak
interatomic bonding thus flows
easily as compared to oil/honey

44. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
B. RHEOLOGICAL PROPERTIES
CREEP AND FLOW
“Creep is defined as
the time dependent
plastic strain of a
material under static
load or constant
stress”
“Flow describes the
rheology of the
amorphous
materials in
dentistry” 44

45. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
B. RHEOLOGICAL PROPERTIES
VISCOELASTICITY
The behavior that is
intermediate between
viscous liquid and elastic
solid.
e.g. Elastomeric
impression materials.
The more rapidly the
material is loaded or
unloaded the more
elastically the material
will behave.
45

46. PHYSICAL PROPERTIES OF
DENTAL MATERIALS
B. RHEOLOGICAL PROPERTIES
NEWTONIAN BEHAVIOR
When shear strain rate is
proportional to shear stress,
the behavior is called
Newtonian behavior.
PSEUDOPLASTIC BEHAVIOR
Material is called
pseudoplastic when
viscosity decreases with
increase in shear rate.
THIXOTROPIC BEHAVIOR
Material is called thixotropic
when it exhibit a different
viscosity after deformation.
DILATANT
Behavior seen in liquids that
show higher viscosity with
increase in shear rate.

47. MECHANICAL PROPERTIES
OF
DENTAL MATERIALS
1) Stress.
2) Strain.
3) Proportional limit.
4) Yield point.
5) Modulus of elasticity.
6) Poision’s ratio.
7) Toughness.
8) Brittleness.
9) Strength.
10) Resilience.
11) Hardness.
12) Relaxation.
13) Permanent deformation.
14) Ductility.
15) Maleability.

48. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
• Defined by the laws of
mechanics.
• The physical science
that deals with energy
and forces and their
effects on the bodies.
• Mechanical properties
need to be considered
collectively.
• Intended application of
a material is important.
 Failure or success
potential of any
prosthesis /
restoration is
dependent upon the
mechanical properties
of the material.
 The material response
may be,
1. Elastic …. reversible
on force removal.
2. Plastic …… Irreversible
/ non-elastic.

49. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
 Generally, the force
applied may be
1. Axial (tensile or
compressive)
2. Shear (sliding,
rubbing)
3. Tortional (twisting
movement)
4. Bending (bending
movement)
TENSION
• Tension results when a
body is subjected to
two sets of forces
directed away from
each other in a straight
line.
• Causes the material to
elongate/Stretch.

50. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
COMPRESSION
• Compression results
when the body is
subjected to two sets of
forces directed towards
each other in a straight
line.
• Causes the material to
shorten.
SHEAR FORCE
• Shear is a result of two
sets of forces directed
parallel to each other ,
but not along the same
straight line.

51. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
TORSION
Torsion results from the
twisting of the body.
BENDING
• Bending results by
applying bending
movement.

52. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
STRESS
• When a force acts on the
body, a resistance is
developed to the external
force applied which is
equal in
magnitude/intensity and
opposite in direction to
the applied force and is
called as “STRESS”
• Denoted by “S” or “σ”
• Designated as force per
unit area (σ=N/m²)
• Pascal = 1 N / m².
STRAIN
• Relative deformation of
an object due to stress.
• It is change in length per
unit length.
• It may be elastic, plastic
or both elastic and
plastic.
• It is denoted by “ε”
• Designated as ∆L / L.

53. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
PROPORTIONAL LIMIT
• It is the maximum stress
at which the stress is
equivalent/proportional
to strain and above this
limit the plastic
deformation of a
material occurs.
• The material may be
subjected to any type of
applied force.
53

54. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
YIELD POINT
The point beyond which stress
causes a material to undergo
permanent deformation.
Yield point is always slightly
higher than proportional limit.
Eg: Gold alloy
(Proportional limit = 276 Mpa
& Yield point = 324 Mpa)
Material does not recover
elastically when stress is
removed.

55. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
MODULUS OF
ELASTICITY
• It is relative stiffness or rigidity
of a material.
• Measured by the slope of the
elastic region Also called as
Young ‘s modulus.
• It is measured by the slope of
stress strain curve.
• If a tensile or compressive
stress (below the proportional
limit) is divided by
corresponding strain value, a
constant of proportionality will
be obtained.
• Unaffected by the amount of
elastic or plastic stress induced
in the material.
• Independent of ductility of a
material.
• The lower the strain for a
given stress, greater will be
the elastic modulus.
• E.g. two wires of same shape
and size.
• Polyether impression
materials.
• Unit is Giganewtons/m² (GPa).
55

56. STRESS STRAIN
CURVE
MECHANICAL PROPERTIES
OF
DENTAL MATERIALS
56
For materials in which strain
is independent of the length
of time that a load is applied
“ STRESS STRAIN CURVES“
are important.

57. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
STIFFNESS & FLEXIBILITY
1) If longitudinal portion
of the curve is closer
to the long axis the
material is stiff & not
flexible.
2) If it is away from the
long axis the material
is flexible.
TOUGHNESS & BRITTLENESS
1) If material fractures after
a long concave portion of
the curve, it donates that
the material is tough &
ductile.
2) If elastic portion of the
curve is minimal, it shows
the brittleness of the
material 57
ANALYSIS FOR A STRESS STRAIN CURVE

58. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
STRNGTH & WEAKNESS
• If longitudinal portion of
curve is longer, means that
the material is strong.
• If longitudinal portion is
short the material is weak.
HENCE FROM THE ANALYSIS
OF THE STRESS STRAIN
CURVE IT IS POSSIBLE TO
HAVE AN IDEA ABOUT THE
PROPERTIES OF A
MATERIAL.
58
ANALYSIS FOR A STRESS STRAIN CURVE

59. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
ANALYSIS FOR A STRESS STRAIN CURVE

60. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
POISION’S RATIO
• If a cylinder is subjected
to a tensile or
compressive stress,
there will be
simultaneously an axial
or lateral strain.
• Within the elastic
range, the ratio of
letaral to axial strain is
known as Poision’s
Ratio.
60

61. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
STRENGTH
Strength is the maximum
stress that a material can
withstand without
sustaining a specific
amount of plastic strain.
OR
Stress at the point of
fracture.
SHEAR STRENGTH:
Maximum shear stress at
the point of fracture.
FLEXURAL STRENGTH:
Defined as “force per unit
area at the point of
fracture when a material
is subjected to flexural
loading”
Also called as “BENDING
STRENGTH” or
“MODULUS OF RUPTURE”
61

62. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
FATIGUE STRENGTH
• Determined by subjecting
a material to cyclic stress
of maximum known value
and determining the
number of cycles required
to cause failure of the
material.
• Maximum service stress
(endurance limit) can be
maintained without
failure over an infinite
number of cycles.
• Endurance limit is lower
for materials with brittle
and rough surface.
IMPACT STRENGTH
• Impact is the reaction of a
stationary object to a
collusion with a moving
body.
• Impact strength is defined
as energy required to
fracture a material under
an impact force.
• The energy units are
joules.

63. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
TOUGHNESS
 The energy required to
fracture a material is
called toughness.
 Also determined by the
total area under stress
strain curve.
 Toughness describes
how difficult it is to
break a material.

64. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
BRITTLENESS
• It is opposite of
toughness.
• When a material fractures
at or near its proportional
limit.
• Should not be confused
with the lack of strength.
• Porcelain, Dental stone &
Cements are examples of
a brittle material.

65. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
RESILIENCE
(Springiness)
• It is the amount of energy
absorbed by a material
when it is stressed not to
exceed its proportional
limit.
• Measured in terms of
modulus of resilience
(amount of energy stored in
the body)
• Modulus of
resilience=Proportional
limit/Modulus of elasticity

66. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
CLASSIFICATION OF
HARDNESS TESTS
HARDNESS
• In mineralogy, relative
hardness of a substance is
based upon its ability to
resist scratching.
• In metallurgy and mostly
in all other disciplines,
hardness is defined as
resistance to indentation.
• Higher hardness number =
more hardness.
66

67. MECHANICAL PROPERTIES OF
DENTAL MATERIALS

68. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
68
KNOOP HARDNESS
TEST
BRINELL &
ROCKWELL
HARDNESS TEST
VICKERS
HARDNESS
TEST
Shapes produced by indenters
On materials

69. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
RELAXATION
 Change in shape due to
release of stresses is
referred as relaxation.
Example:
 Dental waxes & other
thermoplastic materials.

70. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
PERMANENT
DEFORMATION
• After crossing the elastic
limit with continuous
stress the resulting
change in strain
(dimension) is
permanent.
For example:
Elastic impression materials

71. MECHANICAL PROPERTIES OF
DENTAL MATERIALS
DUCTILITY
• Ability of a material to
deform plastically under a
tensile stress before
fracture. e.g. metal drawn
readily into long thin
wires.
MALLEABILITY
• The ability of a material
to sustain plastic
deformation, without
fracture under
compression.
• Gold is the most ductile
and malleable pure metal,
followed by silver.
• Platinum is ranked third
in ductility.
• Copper ranks third in
malleability.
71

73. THANK YOU