A comprehensive presentation covering basics of physical properties of dental materials.

1. Presented by:
Dr. Sahana Umesh
I MDS
Dept. of Cons &
Endo

2. o Introduction
o Structure of matter
o Adhesion and bonding
o Abrasion and abrasion resistance
o Hardness
• Brinell hardness test
• Knoop hardness test
• Vickers hardness test
• Rockwell hardness test
• Barcol hardness test
• Shore hardness test

3. o Rheology
• Viscosity
• Pseudoplastic behavior
• Plastic behavior
• Thixotropic behavior
o Stress and Strain
o Structural relaxation
• Stress relaxation
• Creep and flow
o Colour and optical effects
• Hue
• Value
• Chroma

4. o Measurement of colour
• Munsell colour system
• CIELAB system
o Factors affecting colour appearance and
selection
o Shade selection
o Thermal properties
• Thermal conductivity
• Thermal diffusivity
• Co-efficient of thermal expansion
• Heat of fusion & Latent heat of
solidification
• Melting and freezing temperature
• Specific Heat
o Conclusion

5. † The principal goal of dentistry is to
maintain and improve the quality of dental
health.
† This often requires replacement or
alteration of existing tooth structure.
† The main challenges for centuries have
been the selection and development of
good restorative materials that can
withstand the adverse conditions of the
oral environment.

6. What are physical properties?
Physical properties are based on the laws
of mechanics, acoustics, optics,
thermodynamics, elasticity, magnetism,
radiation, atomic structure, or nuclear
phenomena.

7. † Physical properties are the measures of a
material.
† The physical properties of a tooth set the
standard for materials attached to a tooth.
† Theory suggests that if a restorative
material can be made to hold properties
similar to those of natural tooth structure, it
should perform as well as original tooth*

8. † All matter is composed of invisible particles
called atoms.
† An atom consists of a nucleus, protons and
electrons*† An atom becomes a
negative ion when it
gains electron(s) or a
positive ion when it
loses electron(s).

9. † Two or more atoms can form an
electrically neutral entity called a
molecule.
† Atoms and molecules are held together by
atomic interactions*
† The forces that hold atoms together are
called cohesive forces.
† The strength of these bonds and their
ability to reform after breakage determine
the physical properties of a material.

10. Interatom
ic bonds
Primary
bonds
Ionic
bonds
Covalent
bonds
Metallic
bonds
Secondary
bonds
Hydrogen
bonds
van der
Waals
forces

11. Primary bonds:
1. Ionic bonds:
† Result from the mutual attraction of
positive and negative charges.
† The classic example is sodium chloride.
† Ionic bonds in dentistry - crystalline
phases of some dental materials - gypsum
and phosphate-based cements.

12. 2. Covalent bonds:
† Two valence electrons are shared by
adjacent atoms.
† Characterized by electron sharing and
very precise bond orientations.
† The hydrogen molecule, H2 is an
example of covalent bonding.

13. † The carbon atom has four
valence electrons forming an
sp3 hybrid configuration and
can be stabilized by
combining with hydrogen.
† Covalent bonding occurs in many organic
compounds - Dental resins - in which the
compounds link to form the backbone structure
of hydrocarbon chains.
† A typical characteristic of covalent bonds is
their directional orientation.

14. 3. Metallic bonds:
† Characterized by electron sharing and
formation of a “gas” or “cloud” of electrons
that bonds the atoms.
† Best understood by studying a metallic
crystal such as pure gold.

15. † Because of their ability to donate and
recover electrons, atoms in a metal crystal
exist as clusters of positive metal ions
surrounded by a cloud of electrons.
† Electrical and thermal conductivities of
metals - controlled by the ease with which
the free electrons can move through the
crystal.
† Deformability - slip of atoms along crystal
planes.
† During slip deformation, electrons easily
regroup to retain the cohesive nature of the

16. Combination of primary bonds:
† It is possible to find more than one type of
primary bond existing in one material.
† Calcium sulfate(CaSO4) – Main component of
gypsum products.

17. Secondary bonds
† Secondary bonds do not share electrons.
† Instead, charge variations among atomic
groups of the molecules induce dipole
forces that attract adjacent molecules/
parts of a large molecule.

18. 1. Hydrogen bonds:
† Special case of dipole attraction of polar
compounds.
† Ex: Water molecule.
† Oxygen atom is attached
to 2 hydrogen atoms by
covalent bonds.
† Protons pointing away
from the oxygen atom
become +vely charged.

19. † Opposite side of the H2O molecule,
electrons that fill the outer shell of
oxygen provide -ve charge.
† The +ve H2 nucleus is
attracted to the unshared
electrons of neighboring
water molecules –
Hydrogen bridge.
† This accounts for
intermolecular reactions
in many organic
compounds – sorption of
water by synthetic dental
resins.

20. 2. van der Waals forces:
† Arise from dipole interactions.
† Polar molecules – Dipoles are induced
by an unequal sharing of electrons.
† Nonpolar molecules – random
movement of electrons within the
molecule created fluctuating dipoles.

21. † All materials we use consist of trillions of atoms.
† ROBERT HOOKE, 1665 – Explained crystal shapes
in terms of packing of their component parts,
like stacking musket balls in piles.
† This is an exact model of the atomic structure of
many familiar metals, with each ball
representing an atom.
† They form a regularly spaced configuration
known as a crystal.

22. † A space lattice is defined as any arrangement
of atoms in space in which every atom is
situated similarly to every other atom.
† There are 14 possible space lattice types.
† Simplest and most regular – Cubic type.
† Characterized by axes of equal length and
meet at 90º
- Anusavice, Phillips
12th ed
Crystalline Structure

23. † Simple cubic type –
• Atoms present at each corner of the
cube.
• Leaves enough space for additional
atoms to fit per unit cell.
• Most metals used in dentistry belong
to the cubic system.

24. † Body centered cubic type –
• An atom at each corner of the cube
and an atom at the body center of
the cube.
• Ex: Iron at room temperature.

25. † Face centered cubic type –
• It has an additional atom at the centre of
each face of the unit cell but none at the
center of the cube

26. Other space lattice types of dental
interest:
• Hexagonal close packed
arrangement – Ti, Zn, Zr• All metallic based dental
materials – Crystalline.
• Pure ceramics – alumina and
zirconia core materials –
entirely crystalline.

27. Non crystalline structure
† Structures other than crystalline forms can
occur in the solid state.
† Ex: Waxes - solidify as amorphous
materials.
† Glass - non crystalline solid.

28. † The ordered arrangement of the glass is
more or less locally interspersed with a
considerable number of disordered units.
† Because this arrangement is also typical of
liquids, such solids are sometimes called
supercooled liquids.
† Super cooled liquid - A liquid that has been
cooled at a sufficiently rapid rate to a point
below the temperature at which an
equilibrium phase change can occur.- Anusavice, Phillips
12th ed

29. † The temp. at which there is an abrupt in
the thermal expansion coefficient, indicating
increased molecular mobility, is called the
glass transition temperature (Tg)
† < Tg – material loses its fluid characteristic
and gains significant resistance to shear
deformation.
† Set synthetic dental resins, Tg > body temp.
† Dental materials – consist of non crystalline
glassy matrix and crystalline inclusions.
† Crystalline inclusions – color, opacity,
thermal expansion coefficients.

30. Interatomic Bond Distance And
Thermal Energy
† Between any two atoms, there are forces of
attraction drawing them together and forces
of repulsion pushing them apart.
† Both forces increase as the distance between
the atoms decreases. The force of repulsion
increases much more than the force of
attraction as the atoms get closer.
† Bond Distance - The position at which both
forces are equal in magnitude (but opposite
in direction) is considered the equilibrium
position of the atoms.

31. The interatomic distance at equilibrium
represents the distance between the centers of
the two adjacent atoms.

32. † Bonding Energy- Amount of energy that
has to be supplied to separate the two
atoms.
† Energy is defined as the product of force
and distance.† Integration of the
interatomic force over the
interatomic distance
yields the interatomic
energy.
† Generally covalent bonds
are the strongest,
followed by the iconic
bonds, then metallic

33. † Thermal Energy - The atoms in a crystal at
temperatures above absolute zero are in a
constant state of vibration, and the average
amplitude is dependent on the temperature.
† temperature - amplitude of the atomic
vibration† It follows that the mean
interatomic distance
increases as well as the
internal energy. The
overall effect is the
phenomenon known as
thermal expansion.

34. † Adhesion - A molecular or atomic attraction
between two contacting surfaces promoted
by the interfacial force of attraction between
the molecules or atoms of two different
species.
† Cohesion - Force of molecular attraction
between molecules or atoms of the same
species.

36. Surface And Surface Energy
† Solids or liquids are made up of a finite
number of atoms or molecules bonded by
primary and/or secondary bonds.
† This means that their surface is populated
by atoms or molecules that are ready to
attract other atoms or molecules
approaching the surface.

37. † When primary bonding is involved, the
adhesion is termed chemisorption, as
compared with physical bonding by van
der Waals forces.
† In chemisorption, a chemical bond is
formed between the adhesive and the
adherend.† Adhesive – Substance that
promotes adhesion of one
substance or material to
another.
† Adherend – A material
substrate that is bonded to
another material by means

38. † The increase in energy per unit area of surface
is referred to as the surface energy or surface
tension.
† Surface tension - Interfacial tension, usually
between a liquid and a solid surface, which
occurs because of unbalanced intermolecular
forces.
† Any acquired surface
impurity- such as an
adsorbed gas, an oxide, or
human secretions-can
cause a reduction in the
surface energy and
adhesive qualities of a
given solid as these

39. † To produce adhesion on any targeted surface,
the liquid must flow easily over the entire
surface and adhere to the solid. This
characteristic is known as wetting.
† The ability to wet the substrate is the
dominating contributor to the adhesive bond
when the adhesive sets from liquid to solid.
† The ability of an adhesive to wet the surface of
the adherend is influenced by a number of
factors.
• The cleanliness of the surface.
• Surface energy.
• Impurity-free metal surfaces.

40. † The tangent line drawn relative to the
curvature of the liquid profile and the solid
surface constitute an angle; this is called the
contact angle.

41. † A small contact
angle indicates that
the adhesive forces
at the interface are
stronger than the
cohesive forces
holding the
molecules of the
adhesive together.
† Complete wetting
occurs at a contact
angle of 0° and no
wetting occurs at an

42. † Wetting must occur between gypsum and the
impression to ensure good surface quality of
the gypsum model.
† To improve the wettability of the set
elastomeric impression material by a gypsum-
water mixture, the operator usually sprays a
surfactant (also called debubblizer).
† The wetting agent
migrates to the solid
surface and
accommodates surface
wetting by the aqueous
gypsum forming mixture.

43. † Abrasion is the process of scraping or wearing.
† Hardness - index of the ability of a material to
resist abrasion or wear.
† Hardness of a material is only one of many
factors that affect the wear of the contacting
enamel surfaces.
† Other major factors - biting force, frequency of
chewing, abrasiveness of the diet, composition
of intraoral liquids, temperature changes,
surface roughness, physical properties of the
materials, and surface irregularities

44. † The excessive wear of tooth enamel by an
opposing ceramic crown is more likely to
occur in the presence of high biting forces
and a rough ceramic surface.
† Dentists cannot control the bite force of a
patient.
† They can adjust the occlusion
• Create broader contact areas in order to
reduce localized stresses
• Polish the abrading ceramic surface to
reduce the rate of destructive enamel
wear.

45. † The property of hardness is one of the major
properties in the comparison of restorative
materials.
† Hardness may be defined as “the resistance
to permanent surface indentation or
penetration”.
† The most common concept of hard and soft
substances is their relative resistance to
indentation.
† Hardness is a measure of resistance to
plastic deformation and is measured as a

46. † Micro Hardness Tests:
• Knoop hardness test
• Vickers hardness test
† Macro Hardness Tests:
• Brinell hardness test
• Rockwell hardness test
† Others:
• Barcol hardness test
• Shore hardness test

47. † These tests depends on the penetration of
some small, symmetrically shaped indenter
into the surface of the material being tested.
† The various hardness tests differ in the
indenter material, geometry and load.
† The indenter may be made of steel, tungsten
carbide or diamond and be shaped as a
sphere cone, pyramid or needle.
† Loads typically range from 1-3000 kg.

48. † A load is applied to a
carefully prepared
diamond indenting tool
with a pyramid shape.
† The lengths of the
diagonals of the resulting
indentation in the material
are measured.
† The Knoop hardness test was developed to
fulfill the needs of a micro indentation test
method.
KNOOP HARDNESS TEST:

49. VICKERS HARDNESS TEST:
† This hardness test uses a 136 diamond
pyramid.
† A squarish indentation is produced.
† Standard testing for dental casting gold
alloys.† Suitable for brittle
materials – cast
dental alloys as
well as tooth
structure.

50. BRINELL HARDNESS TEST:
† This is among the oldest methods used to
test metals and alloys used in dentistry.
† Method depends on resistance to the
penetration of a small steel or tungsten
carbide ball, typically 1.6 mm in diameter,
when subjected to a weight of 123 N.† The indentation diameter is
measured.
† Because BH test yields relatively
large indentation area, this test is
good for determining average
hardness values and poor
determining very localized

51. ROCKWELL HARDNESS TEST:
† Similar to BH, instead of diameter the depth of
penetration is measured directly by a dial gauge
on the instrument.
† Depth of indentation is measured with a
sensitive micrometer.
† Good for testing viscoelastic materials. Not
suitable for brittle materials.

52. SHORE & BARCOL HARDNESS TESTS:
† Used to study the depth of cure of resin
composites.
† Has a spring loaded needle with a diameter
of 1 mm that is pressed against the surface.
† If no penetration occurs, needle reads 0.
† Reading decreases as indentation increases.

53. NANOINDENTATION:
† Traditional tests used high loads and
indentation areas were large.
† Many materials have microstructural
constituents and to accurately measure
these microphases, it is necessary to be
able to create indentations of a smaller
size scale and also to be able to control
the location of indentations.
† Therefore nanoindentation has recently
been introduced and are able to apply
loads in the range of 0.1-5000 mg.

54. † Indentations are of 1µm in size.
† Studies compared the efficacy by
comparing values obtained earlier.
N.H. KHN
Dentin 71 kg/mm2 68
kg/mm2
Enamel 457 kg/mm2 343
kg/mm2† This method of testing
can be employed to
examine materials that
vary in hardness over an
area of interest.

55. Journal of Biomedical Materials Research, Vol. 27,
747-755 (1993) 1993 John Wiley & Sons, Inc.

60. † The term rheology was coined by Eugene C.
Bingham.
† Rheology is the study of the deformation and
flow characteristics of matter, whether liquid
or solid.
† Viscosity is the resistance of a fluid to flow
which is controlled by internal frictional forces
within the liquid.
† Thus viscosity is a
measure of the
consistency of a fluid
and its inability to
flow.

61. † Most dental materials are initially in a fluid
state so that they can be placed and shaped
as required.
† Cements and impression materials undergo
fluid-to-solid transformation in the mouth.
Gypsum products are transformed extra-
orally.† Curves depicting shear
stress versus shear
strain rate are used to
characterize the viscous
behavior of fluids.

62. † An “ideal” fluid produces a shear stress
proportional to the strain rate.
† That is, the greater the force applied, the
faster the fluid flows and the plot is a
straight line. This is known as Newtonian
viscosity.
† Newtonian fluid has a constant viscosity
and exhibits a constant slope of shear
stress plotted against strain rate.

63. † Many dental materials exhibit pseudoplastic
behavior – their viscosity decreases with
increasing shear rate until it reaches a nearly
constant value.
• E.g. Rubber impression materials.
† The viscosity of a dilatant liquid increases with
increasing shear rate.
• E.g. Fluid denture base resins.
† These liquids become more liquid as the rate
of deformation increases.

64. † Fluids which exhibit rigid behavior initially
and then attain constant viscosity is referred
to as plastic.
• E.g. Ketchup bottle - A sharp blow to the
bottle is usually required to produce an
initial flow.
† A liquid that becomes less viscous and more
fluid under repeated applications of pressure
is referred to as thixotropic.
• Eg. Dental prophylaxis pastes, plaster of
Paris, resin cements, some impression
materials.

65. J. Prosthet. Dent. October, 1977. Vol
38, No.4

66. † Stress - Force induced by or resisting an
external force.
† Stress is calculated as force per unit area.
† Stress is equal and opposite in direction to the
load or external force.
† TYPES OF STRESS
• Tensile
• Compressive
• Shear

67. † Strain - Can be defined as change in length
per unit length of the body when subjected
to stress.
† Strain can either be elastic or plastic.
† Elastic strain is strain that totally disappears
once the external load that caused it is
removed.
† Plastic strain is strain that permanently
remains once the external load that caused
it is removed.

68. Stress Relaxation:
† After a substance has been permanently
deformed (plastic deformation), there are
trapped internal stresses.
† The displaced atoms are not in equilibrium
positions and are therefore unstable.
† Through a solid-state diffusion process
driven by thermal energy, the atoms can
slowly return to their equilibrium positions.

69. † This results in change in shape or
contour of solid and is called stress
relaxation which can lead to distortions in
the impression and subsequent lack of fit
of the material.
† Such is a problem with elastomeric
impression materials.

70. Creep and Flow:
† If a metal is held at a temperature near its
melting point and is subjected to a constant
applied stress, the resulting strain will increase
over time.
† Creep is defined as the time - dependent
plastic strain of a material under static load or
constant stress.
† Creep may also lead to an unacceptable fit of
FPD frameworks when a cast alloy with poor
creep resistance is veneered with porcelain at
high temp. - Sag

71. † Because of its low melting range, dental
amalgam can slowly creep from a restored
tooth site under periodic sustained stress,
such as those imposed by patients who clench
their teeth.
† Because creep produces continuing plastic
deformation, the process can be destructive to
a dental prosthesis.
† Higher the amount of
creep, greater is the
degree of marginal
deterioration in low
copper amalgams.

72. † The term ‘flow’ rather than creep has
generally been used in dentistry to
describe the rheology of amorphous
materials such as waxes.
† The flow of wax is a measure of its
potential to deform under a small static
load even that associated with its own
mass.
† A cylinder of prescribed
dimensions is subjected to a
given compressive stress for
a specified time and
temperature.† Creep or flow is measured as the % decrease
in length that occurs under these testing
conditions.

73. Svein Espevik (1975) Flow and creep of dental
amalgam, Acta Odontologica Scandinavica, 33:5,

74. † The amalgam samples were condensed by an
all-mechanical method under a compressive
stress of 14 MPa as described in IS0.
† The specimens were subjected to a
compressive stress of 36 MPa for 4 h at 37º C
after they had been stored 1, 2, 4 and 7 days
at 37º C for the creep measurements.
† For the flow measurements the specimens
were subjected to a compressive stress of 10.3
MPa (MN/m2) (IS0 R 1559) 3 h after
condensation and for 21 h.
† The reduction in length was continuously
measured with a displacement transducer

76. † An important goal of dentistry is to restore or
improve esthetics - colour and appearance of
natural dentition.
† Esthetic dentistry imposes severe demands on
artistic abilities of dentist and technician,
knowledge of underlying scientific principles of
color and other optical effects are essential.
† The perception of colour is the result of a
physiological response to a physical stimulus.

77. † Sensation is a subjective experience
whereas, the beam of light which is the
physical stimulus that produces the
sensation, is entirely objective.
† For an object to be visible, it must reflect
or transmit light incident on it from an
external source.

78. † Light is an electromagnetic radiation that can be
detected by the human eye.
† Eye is sensitive to wavelengths from 400nm –
700nm.
† This graph shows
relative visual response
of humans to
wavelength of light for a
normal observer and
one with protanopia.

79. Parameters of Colour
1. Hue :
• Describes the dominant colour of an
object.
E.g.: Red, yellow, green, blue or purple.
• This refers to the dominant wavelength
in the spectral distribution.

80. 2. Value:
• Also called the gray scale.
• Relative lightness or darkness of a colour
or brightness of an object.
• Higher Value ~ Lighter shade
• Lower Value ~ Darker shade
• Value of natural teeth – 6
to 8

81. 3. Chroma:
• Represents strength/intensity of a
colour.
• Defined as degree of saturation of a
particular hue.
• Ex: (1) Red can vary from scarlet red
to pink.
(2) Colour of a
lemon is more
saturated yellow
than that of a
banana which is a
less saturated
yellow.

82. Munsell Colour System:
† It was introduced by Professor Albert
H. Munsell.
† Basic principles were first published
in 1905.
† It is based on rigorous measurements
of human subjects' visual
responses to color, putting it on a
firm experimental scientific basis.
† Because of this basis in human visual
perception, Munsell's system has
outlasted its contemporary color

83. The system consists of three independent
properties of color which can be
represented cylindrically in three dimensions as
an irregular solid color:• hue, measured by
degrees around
horizontal circles
• chroma, measured
radially outward from
the neutral (gray)
vertical axis
• value, measured
vertically on the core

84. † Hues are divide into 10
gradations:
• Yellow
• Yellow-red
• Red
• Red-purple
• Purple
• Purple-blue
• Blue
• Blue-green
• Green
• Green-yellow

85. Specifying a colour:
† A color is fully specified by listing the three
numbers for hue, value, and chroma in that
order.
† For instance, a purple
of medium lightness
and fairly saturated
would be:
5P 5/10, where
5P - color in the
middle of the purple
hue band,
5/ - medium value
10 - chroma

86. CIELAB colour system:
† The Commission Internationale de l’Eclairage
(CIE), an international color research group
published the CIELAB color system in 1976.
† It is characterized by uniform chromacities.
† Curves of spectral
reflectance versus
wavelength can be obtained
over the visible range (405-
407 nm) with a recording
spectrophotometer and
integrating sphere.

87. † Value (black to white) is
denoted as L*
(lightness),
† Chroma (a*b*) is
denoted as red (+a*),
green (-a*), yellow (+b*)
and blue (- b*)
† From the reflectance values and tabulated
color matching functions, the tristimulus
values (X,Y, Z) can be computed relative to
a particular light source.

88. † This aim of this study was to develop a
method to enhance the accuracy of a
tooth color matching machine.

90. Transparency:
† It is a property of a material, that allows
the passage of light in such a manner
that little distortion takes place so that
objects can be clearly seen through them
† E.g. glass, pure acrylic resin.

91. Translucency:
† Property of the material, which allows the
passage of some light and scatters or
reflects the rest . In such manner, the object
cannot be clearly seen through them.
† Translucency decreases with increasing the
scattering centers.† E.g. tooth enamel,
porcelain, composite
and pigmented acrylic
resin natural teeth.

92. Opacity:
† It is a property of the material that prevents
the passage of light. Opaque material
absorbs all of the light. Objects cannot be
seen through them.
† Eg. metal-ceramic restoration
† Black colour materials absorb all light colors.
† White colour materials reflect all light colors.
† Blue colour materials absorb all light colors
but reflect its color.

93. Metamerism:
† Phenomenon in which the color of an object
under one type of light appears to change
when illuminated by different light source.
† Because the spectral distribution of the light
reflected from or transmitted through an
object is dependent on the spectral content
of the incident light, the appearance of an
object is dependent on the nature of the
light in which the object is viewed.

94. † Clinical significance:
If possible, color matching should be done
under two or more different light sources,
one of which should be daylight, and the
laboratory shade matching procedures
should be performed under the same
lighting conditions.

95. Fluorescence:
† It is the absorption of light by a material and
the spontaneous emission of light in a longer
wavelength.
† In a natural tooth, it primarily occurs in the
dentin because of the higher amount of
organic material.
† UV light is absorbed and fluoresced back as
light primarily in the blue end of the
spectrum.
† Ceramic crowns or composite
restoration that lack a
fluorescing agent appear as
missing with when viewed
under a black light.

96. † The color of teeth encompasses only a
small portion of the total color space.
† The color ranges of human teeth have
been measured by different researchers at
different times and using different
methods and color notation systems.
† All of the studies indicate that human
teeth are in the yellow-red to yellow
portion of the spectrum, they are relatively
high in Value (light or bright), and they
have a relatively low Chroma
Colour of human
teeth:

97. † Shade guides are used in determining the
color of natural teeth so that artificial
substitute restorations will possess similar
color and esthetics.
† Clinical shade selection involves direct visual
comparison of the different color samples that
are present in a shade guide with the natural
teeth and determination of which one best
matches the teeth.

98. † The VITAPAN Classical shade guide
introduced in 1956 still is widely used for
shade matching in dentistry.
† It has16 shade samples.
† Grouped acc. to hue – A,B,C & D followed
by value 1 to 4.

99. † VITA SYSTEM 3D-MASTER introduced in 1998.
† It has 26 shades, divided into group 1to5.
† Tabs are marked using a number-letter-number
combination.
† First number i.e.
1-5 represent
Value.
† Letter L, M, R
represent Hue
from yellowish to
reddish.
† The second

103. Clinical suggestions for shade selection:
† Ensure the tooth condition is appropriate
(e.g. clean, hydrated) for matching.
† Tooth shades should be determined in
daylight or under standardized daylight
lamps and not under operation lamps.
† Since eyes usually tire after 5 -7 seconds,
it is recommended to make a selection
quickly.
† Avoid bright colors in the shade-taking
environment, i.e. no lipstick, tinted
eyeglasses, no bright-colored clothes.

104. † Consider the selection distance. A
selection made at one to three feet is
generally more useful than one made in
close proximity to the teeth.
† Evaluate the patient’s natural teeth to
determine their color characteristics by
looking at the cervical aspect of the teeth.
† Evaluate prospective shade guide
specimens one at a time by holding them
next to the tooth being matched.

105. Thermal Conductivity:
† Defined as the ability of a material to
transmit heat or cold.
† A low thermal conductivity is desired in
restorative materials used on the tooth
† High thermal conductivity is desirable
where the material covers soft tissue.

107. Thermal diffusivity is a measure of the
speed with which a temperature change
will spread through an object when one
surface is heated.
Clinical Importance:
• The value of thermal diffusivity of a
materials controls the time rate of
temperature change as heat passes
through a material.
• Cements which have low thermal
diffusivity are used for pulpal
protection.
Thermal diffusivity:

108. † In the oral environment, temperatures are
not constant during the ingestion of foods
and liquids. Under such conditions, thermal
diffusivity is important.
† For a patient drinking ice water, the low
specific heat of amalgam and its high
thermal conductivity favors a thermal shock
situation more than that is likely to occur
when only natural tooth structure is
exposed to the cold liquid.
† The low thermal conductivity of enamel and
dentin aids in reducing thermal shock and
pulpal pain when hot or cold foods are

109. † Metallic fillings in close proximity to the
dental pulp, causes thermal irritation of
the pulp through conductors of heat and
cold from food and drinks when not
properly insulated.
† For effective thermal protection the base
should have minimal thickness of 0.75
mm.

110. † Measurements of thermal diffusivity are
often made by embedding a thermocouple
in a specimen of material and plunging the
specimen into a hot or cold liquid.
† If the temperature recorded by the
thermocouple rapidly reaches that of the
liquid, this indicates a high value of
diffusivity.
† A slow response, on the other hand,
indicates a lower value of diffusivity

111. Journal of Endodontics
2018
The purpose of this study was to assess
temperature development in endodontic
sealers during different obturation
techniques in a closed system simulating
the surrounding biological structures at
body temperature

113. Coefficient Of Thermal Expansion:
† Refers to the amount of expansion and
contraction a material undergoes in
relation to temperature.
† Defined as the change in length per unit
length of the material for a 1°C change in
temperature is called the linear coefficient
of thermal expansion.

115. Close matching of the coefficient of thermal
expansion (α) is important between:
† The tooth and the restorative materials to
prevent marginal leakage.
† Opening and closing of gap results in
breakage of marginal seal between the
filling and the cavity wall, this breakage of
seal leads to:
 Discoloration
 Recurrent caries
 Hypersensitivity.
Clinical
Importance:

116. Heat of fusion:
It is the amount of heat in calories or
joules required to convert 1 gm of a
material from solid to liquid state at the
melting temperature.
Latent heat of solidification:
It is the amount of heat in calories or joules
liberated when 1 gm of a material is
converted from liquid to solid state.

117. Clinical Importance:
In actual use of pure metal or casting
alloy must have low specific heat and low
heat of fusion, so it does not require
prolonged heating to come to a molten
state which may cause oxidation of the
metal , under conventional procedure.

119. Clinical Importance:
† For the fabrication of indirect metallic
restorations (casting), the melting
temperature of metals and alloys is
important in determining the melting
temperature used for casting
† During casting metal must be heated 100°C
above its melting temperature.
Melting and freezing
temperatures:

120. † The materials that are to be manipulated
directly in the mouth
Eg - waxes , impression compound etc.
should have a softening or melting point
slightly above the body temperature and
must harden to a desired degree of rigidity
at body temperature.
† An ideal solder for use on a particular alloy
will have a melting temperature 30-100ºC
< alloy.

121. † Specific heat is the
quantity of heat needed
to raise the temperature
of one gram of the
substance 1°C.
† Metals have low specific
heat, while non metals
have high specific heat
Specific heat:

122. Clinical Importance :
† It is very important because it shows how
much and how long a metal is to be
heated to bring it to the melting point.
† Because of the low specific heat of dental
gold alloys, prolonged heating is
unnecessary, during casting.

123. The aim of the study was to study the
thermal properties of cavity liners that
included calcium phosphate as inorganic
filler, in contrast to the conventional pulp
capping agents.

124. CONCLUSION:
1. For liner, its density ranged from 1.49 to
1.80 gcm-3; the thermal diffusivity was
0.12-0.15×10-2 cm2s-1; the specific heat
capacity was 1.01-1.27 Jg-1K-1; and the
thermal conductivity was 0.23-0.28 Wm-1K-
1. For the pulp capping agent, its density
ranged from 1.83 to 1.84gcm-3; the thermal
diffusivity was 0.18-0.19×10-2cm2s-1; the
specific heat capacity was 1.28-1.47Jg-1K-1
2. The thermal conductivity of liner was lower
than those of human dentin, pulp capping
agent, cast alloy, and composite resin for
restoration - suggesting that liner has a
good thermal insulation effect.

125. Water Sorption:
It represents the amount of water adsorbed
on the surface and absorbed into the body of
the material.
Clinical Importance:
† Acrylic resin denture base materials have
the tendency for water sorption.
† Hydrocolloid impression materials will
imbibe water if immersed in it leading to
dimensional changes.

126. Objective of the study was to investigate the
variation in water sorption and solubility
across a range of different core build-up
materials

128. † A proper knowledge of physical properties of
dental materials helps us in making correct
choice for various clinical restorations.
† This in turn increases the durability and life
span of the restoration.
† This will also enable us to select a material
that will have properties close to that of
natural tooth surface.

129. † Technique based system provide dentist
with distinct advantage in creating highly
esthetic natural looking restoration.
† With better understanding of properties
it is easier to select materials from a wide
range that is introduced in the market.

130. • Phillps’ Science of Dental Materials, 12th
edition, Anusavice, Shen, Rawls.
• Craig’s Restorative Dental Materials, 14th
edition, Ronald Sakaguchi, Jack Ferracane, John
Powers.
• Materials in Dentistry, Ferracane
• Tooth Colored Restoratives, Albers
• Dental Materials and Their Selection, 3rd
edition, William J. O’Brien.
• Journal of Biomedical Materials Research, Vol.
27, 747-755 (1993) 0 1993 John Wiley & Sons,
Inc.

131. • J. Prosthet. Dent. October, 1977. Vol 38, No.4
• Svein Espevik (1975) Flow and creep of dental
amalgam, Acta Odontologica Scandinavica,
33:5, 239-242.
• Kaohsiung Journal of Medical Sciences (2012),
48; 490-494.
• Thermal properties of dental materials –
Cavity Liners and Pulp Capping Agents. Dental
Materials Journal Vol. 23, 399-405, 2004
• Water Solubility and Sorption of core build-up
materials. Dental Materials, Volume 30, Issue
12, December 2014, Pages e324-e329