Bio-material Lecture

1. PHYSICAL
PROPERTIES OF
DENTAL
BIOMATERIALS
Dalia Sherief
Dental Biomaterials lecturer
AinShams University

2. THESE PROPERTIES ARE NOT
RELATED TO FORCE
APPLICATION.
They are:
1- Mass-related properties:
Weight,Composition,Density
2- Thermal properties:
- Heat of fusion & latent heat of fusion
-Thermal conductivity
-Specific heat and heat capacity
-Thermal diffusivity
-Thermal expansion and contraction
3- Optical properties:
Color and light

3. 4-Other properties:
Water sorption
Solubility and disintegration
Setting time
Shelf life

4. MASS- RELATED PROPERTIES
1-Weight and mass
 Weight: is the force with which a body is
attracted to earth(gravitational force of
attraction)
-Weight(w)=mass(m) x gravitational
acceleration(g)
gms x 980cm/sec2
 Mass: the quantity of matter in a body
regardless of its volume or of any forces
acting on it.
Mass= w
g
The mass of a body can be considered to be
constant; its weight, however, is not
constant, since the force of gravity varies
from place to place.

5. ENSITYD-2
It is the mass per unit volume of the material.
Units are gm/cm3 or pound/in2
Clinical importance in
Dentistry:
1- Retention of the upper denture.
-Denture base materials of lower density values
will be lighter, thus their retention will be better
compared to materials with higher density
This is important in upper dentures as
gravitational forces act on them and lower their
retention

6. 2- During casting procedure
Casting of a metal with high density will require
simpler casting machines(air pressure),while
metals with low density require complicated
casting machines(centrifugal)

7. 3-Composition:
The composition of materials is
reported as either weight percent
(w%) or atomic percent(a%)
a-Weight percent
w% of component A =
weight of component A in the mixture x100
Total weight of mixture
Atomic percent-b
a %of component A =
Number of atoms of component A x 100
Total number of atoms in mixture

8. THERMAL PROPERTIES
1-Heat of fusion
Heat of fusion (L) is the amount of heat in calories
or joules required to convert l gm of a material
at the meltingfrom the solid to the liquid state
temperature.
It is calculated as follows:
Q
L = ----------
m
Where L: is the heat of fusion.
Q: is the total heat absorbed.
m: is the mass of the substance
melted

9.  It is necessary to apply this
additional heat to the mass to
cause liquefaction , as long as the
mass remains molten this heat of
fusion is stored in it.
 When the mass is frozen or
solidified the heat stored in the
liquid is liberated .It is called
“latent heat of fusion”

10.  In this curve, the portion
a to b represents the
cooling of the liquid
 b to c represents the freezing
time and temperature.the temp.
remains constant through out
this time because of the liberation
of the Latent heat of fusion during
solidification
 Cooling of the solid continues from c to d
L&S

11. 2- Thermal Conductivity
Heat transfer through solids occur by thermal
conductivity.
Coefficient of thermal conductivity (K):
It is the amount of heat in calories or joules
passing per second through a body 1cm thick,
1cm2 cross sectional area when the temperature
difference is 1°C

12. Clinical importance in
Dentistry:
1- A large metallic restoration (e.g: amalgam)
that is near to the pulp may cause patient
discomfort as a result of temperature changes
caused by hot and cold food and drinks , unless
a non-metallic substances (cements) are placed
as a base under the restoration for insulation

13. 2- The amount of thermal conductivity of
denture base materials cause different soft
tissue response.
 A metal base which is a good thermal
conductor causes rapid tissue response.
Acrylic denture base cause a more delayed
response
 Thus high thermal conduction is preferred for
denture basses to maintain good health of the
tissues by conducting heat to and from the
supporting tissues through the denture base
Metallic denture
base
Metallic
denture base
Acrylic denture
base

14. 3- Specific heat and heat capacity
 Specific heat: It is the quantity of heat
needed to raise the temperature of one gram
of the substance 1°C.
 Heat capacity: It is the quantity of heat
needed to raise the temperature of the body
1°C and is controlled by the mass of the body.
Importance in dentistry:
Specific heat of metals and alloys is important during the
melting and casting process because it determines the
total amount of heat needed to raise the temperature of
the mass to the melting point

15. 4- Thermal diffusivity ( ∆ ) :
It is the measure of transient heat-
flow and is defined as the thermal
conductivity (K ) divided by the
product of the specific heat (Cp)and
the density (P)
K
∆ =-------------------
Cp x p
It describes the rate at which a body with
non-uniform temperature reaches
equilibrium

16. Applications in dentistry:
1- The effectiveness of a base under a
metallic restoration in preventing heat
transfer is directly proportional to the
thickness of the liner and inversely
proportional to the thermal diffusivity.
n.b: A material with high thermal
conductivity, low specific heat and low
density have high thermal diffusivity

17. 5-Thermal expansion and contraction
The linear coefficient of thermal expansion (
α ) is the change in length per unit length
of a material for a 1 OC change in
temperature and it is calculated as follows
:
L original-L final=α
L original x (°C final- °C original)

18.  Thermal expansion can be linear or
volumetric

19.  Applications of thermal expansion in
dentistry
1-Close matching of the coefficient of thermal
expansion (α) is important between:
A-The tooth and the restorative materials to
prevent marginal percolation (pumping in and
out of fluids and bacteria at tooth/restoration
interface),this leads latter to the breakage of the
marginal seal.

20. B- Porcelain and metal in ceramo-metallic/PFM
restorations (crowns and bridges) to provide
metal ceramic bonding ,a large difference in the
coef. of thermal expansion may lead to the
debonding ceramic facing from the surface of the
metallic restoration.

21. 2-Of particular importance in casting
investments is the coefficient of thermal
expansion of the three crystalline
polymorphic forms of silica.
Thermal expansion of investment occurs
during wax elimination to compensate the
shrinkage of metal during cooling to room
temperature.

22.  Crystobalite shows the greatest expansion at
the lowest temperature
 Quartz requires a higher temperature to
develop on equal amount of expansion as
crystobalite.
 Tridymite shows a lower thermal expansion.
 The amorphous type of silica (fused silica)
has the lowest thermal expansion

23. OPTICAL PROPERTIES
1-Light
Nature of light
Light is waves of electromagnetic
radiation.The visible electromagnetic
radiation is in the range from 400-700
nanometers.
Or
Stream of particles of electromagnetic energy
(photons)

24. Light and interfaces
When a light beam traveling in one medium
(air) meets a layer of another medium, the
results are:
A-Reflection:
A-Smooth surface: Reflections on a smooth
surface give a glossy appearance to the surface.
B-Rough surface: Reflected light rays from a
rough surface are scattered (i.e: in all directions).
The surface appears to have little gloss (i.e dull)

25. The restoration should have a
highly smooth and polished surface
to simulate the tooth structure.

26. B-Refraction
It is the change of the direction of a beam of light
on entering second medium.
Refraction results from the difference in
refractive indices (speed of light) of the two
media.
Therefore, for perfect matching the
refractive index of the restoration should
be equal to the refractive index of the
tooth.

27. C-Scattering
 Presence of scattering centers (eg.
opacifiers, air bubbles) in the second
medium cause light to emerge in all
directions. Opacity increases with
increasing scattering
 Opacifiers and air bubbles should be
minimal in restoration so it would appear
translucent not opaque

28. D-Transmission
It is the light transmitted through the
medium
 Diffuse(scattered) transmission gives a
translucent appearance.
 Non diffuse transmission gives
transparent appearance

29. OPACITY, TRANSLUCENCY
AND TRASPARENCY
 Opacity is a property of materials that
prevents the passage of light. An opaque
material either absorb or reflect some or
all of the incident light.
 Translucency is a property of substances
that permits the passage of light but
diffuses the light.
Objects cannot be seen clearly through
these materials.
Tooth enamel, dental porcelain,
composite resin and dental plastics are
translucent.

31. Transparent materials allow the passage of
light in such a with minimal diffusion.
Objects may be clearly seen through
them.
Opaque
Opaque, translucent and
transparent

32. 2-Color
 Parameters of color:
A-Hue: it is the dominant wave length.
 Light having short wavelengths (350 nm)
is violet in colour,
 Light having long wavelengths ( 700 nm )
is red.
 Between these two wavelengths are those
corresponding to blue, green yellow and
orange light.


34. •When white light falls on the
object, the object absorbs all
wavelengths and reflects only the
wavelength of its color.
This is how we see the color of an
object
•If the object absorbs all wave
lengths of light it will appear
black,,,if it reflects all wave lengths
it will appear white

35. Primary colors: Blue,green and red are primary
colors. Combining suitable proportions of lights of the
three primary colors results in white.
Secondary colors: Each secondary color results
from the combination of two primary colors e.g . green and
red gives yellow .
Complementary colors : Two colors are
complementary to each other when their combination
results in white
eg . yellow is the complementary color of blue .

36. B-Chroma or saturation: It is a
measurement of color intensity.
A beaker of water containing one drop of
colorant is lower in chroma than a beaker
of water containing ten drops of the same
colorant.
Parameters of color

37. C-Value: It represents the lightness or
darkness of a color.
A black standard is assigned a value of 0
A white standard is assigned 100.
A tooth of low value appears gray and
non–vital.

38. FACTORS AFFECTING COLOR
APPERANCE
A-Light Source
Color content: Different sources have
different color contents .
Example: Incandescent light has a color
content different from that of
fluorescent light. The change in color
matching of two objects under
different light sources is called:
METAMERISM .

39. B-Object:
Smooth surface, rough surface,
opaque,translucent,transparent
…etc
C-Observer:
1-Response: human eye is most
sensitive to the green region.
2-Color vision: Color blindness is
the inability to distinguish
certain colors.


40. 3-Optical illusion: The effect of the
background on color appearance
example: A color appears darker against a
light background and lighter against a
dark background.
4. Color Fatigue: Constant stimulus of one
color decreases the response to that color
.A. complementary color image persists
after removal of the stimulus.

41. OTHER PROPERTIES
1) Water sorption:
Water sorption of a material represents the
amount of water adsorbed on the surface
and absorbed into the body of the material
It is associated with dimensional change
and decrease in strength.
2)Solubility and disintegration:
Solubility and disintegration are measured
by storage of the material for 24 hrs or
longer in water or acids and measuring
the weight change.

42. 3) Setting time and working time:
Setting time: It is the time required for a
material to set or harden from a plastic or
fluid state.
Working time :time during which the
material can be manipulated (worked
with).
Working time is a part of the setting time

43. 4) Shelf life:
Shelf life is the change in quality of
materials during storage . The
temperature , humidity , time of storage ,
and type of the container are all
significant factors .