Transcript Physical Properties of Dental Materials Presented by Karma

BDS Ist Year Dental Material
Monday 10:00 to 11:00 AM
Dr Deeksha Arya
Assistant Professor
Department of
Prosthodontics
 Introduction
 Physical
properties of Dental Materials
 References
Physical properties of Dental Materials are
based on:

The laws of mechanics-Creep & flow ,
abrasion and abrasion resistance , viscosity
 Thermodynamics
e.g. Thermal conductivity ,
Thermal diffusivity and Coefficient of thermal
expansion
 Electricity
&Magnetism e.g tarnish and
corrosion
 Optics

–Metamerism ,Hue , chroma value
Radiation –Laser
Creepis defined as the time dependent plastic
strain of a material under a static load or
constant stress.
The magnitude of deformation depends on
 the materials
 the temperature
 the load
 the time of application of the load.
 Creep
may cause unacceptable deformation
of dental restorations .eg.-low-copper dental
amalgam.
 According to ADA SP. No 1 creep should be
below 3%.
Flow:
Ability of material to displace itself under
load.
Flow is dependent on:
 Temperature of the wax.
 Force applied.
 Length of time the force is applied.
 Flow increases as the melting point of the
wax is approached.
Abrasion is defined as the wearing away of a
substance or structure through a mechanical
process such as grinding, rubbing or
scraping.
 Hardness
has been used as an index of the
ability of the material to resist abrasion or
wear.
Viscosity -:
 Resistance of a liquid to flow.
 Dental material have different viscosities
depending on the preparation for their intended
clinical application.
 measured in units of MPa per second, or
centipoise (cP).
 most liquids decreases rapidly with increasing
temperature.

Pseudoplastic behavior

Plastic

Thixotropic –Dental prophylaxis paste,Plaster of
paris,Resin cements, impression material
Properties which are not related to force
applicationMass-related properties:
 Density
 Thermal properties:
 Thermal conductivity
 Thermal diffusivity
 Coefficient of thermal expansion and contraction
 Heat of fusion & latent heat of solidification
 Melting and freezing temperature
 Specific heat

 Less
specific properties:

Water sorption.
 Optical properties
 Color
It is the mass per unit volume of the material.
Units are gm/cm3 .
Clinical importance:
1- Retention of the upper denture.
2- Weight of complete or partial
denture.
3- During casting.
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.
Thermal diffusivity=Thermal conductivity
Density x specific heat
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.
Material
Density
(g cm-3 )
Specific
Thermal
heat
Conductivity
(Cal g-1 K-1) (W m-1 K-1)
Thermal
diffusivity
(cm2 s-1)
Water
1.00
1.00
0.44
0.0014
Dentin
2.14
0.30
0.57
0.00180.0026
Glass
ionomer
2.13
0.27
0.51-0.72
0.0022
Zinc
Phosphate
2.59
0.12
1.05
0.0030
Composite
1.6-2.4
0.20
1.09-1.37
Enamel
2.97
0.18
0.93
0.0047
Amalgam
11.6
0.005
22.6
0.96
Pure gold
19.3
0.03
297
1.18
0.00190.0073
 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.
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(α)
α=
L
L
original
final-
x (°C
L
original
final-
°C
original)
Material
α (ppm K-1 )
αmaterial
Aluminous porcelain
6.6
0.58
Dentin
8.3
0.75
8.5
0.77
Type II glass ionomer
11.0
0.96
Tooth enamel
11.4
1.00
Gold-palladium alloy
13.5
1.18
Gold(pure)
14.0
1.23
Palladium-silver alloy
14.8
1.30
Amalgam
25.0
2.19
Composite
14-50
1.2-4.4
Denture resin
81.0
7.11
Pit and fissure sealant
85.0
7.46
Inlay wax
400.0
35.1
Commercially pure
titanium
/
αtoothEnamel
Close matching of the coefficient of
thermal expansion (α) is important
between:
1-The tooth and the restorative materials
to prevent marginal leakage.
2-Opening and closing of gap results in
breakage of marginal seal between the
filling and the cavity wall, this breakage of
seal leads to:
Marginal leakage
 Discoloration
 Recurrent caries
 Hypersensitivity.

Heat of fusion is the amount of heat in
calories or joules required to convert l gm
of a material from the solid to the liquid
state at the melting temperature.
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 required prolonged
heating to come to a molten state which
may cause oxidation of the metal , under
conventional procedure.
Latent heat of solidification is the
amount of heat in calories or joules
liberated when 1 gm of a material is
converted from liquid to solid state.
Clinical Importance:
 For
the fabrication of indirect metallic
restorations (casting), the melting
temperature of metals and alloys is
important in determining the melting
machine used for casting
 During
casting metal must be heated 100°C
above its melting temperature.
 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 user on a particular
alloy will have a melting temperature 30
C-100 C less than that of the alloy.
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 .
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.
Water Sorption:
It represents the amount of water
adsorbed on the surface and absorbed
into the body of the material.
Clinical Importance:
1- Acrylic resin denture base materials have
the tendency for water sorption.
2- Hydrocolloid impression materials will
imbibe water if immersed in it leading to
dimensional changes.
Tarnish:
Surface discoloration on a metal or even a slight
loss or alteration of the surface finish or lusture.
Tarnish usually occurs due toFormation of hard and soft deposits on the
surface of the restorations .e.g.-calculus , mucin
and plaque.
Corrosion is not a surface discoloration but actual
deterioration of a metal by reaction with the
environment .
Corrosion may be classified as:
 Chemical
corrosion is a direct effect on
the metal surface by oxidation,
halogenations or sulfurization reaction.
 Acidity
and alkalinity may give rise to
corrosion by direct attack , particularly if
there is any defect in the constitution of
the alloy.
Electrolytic corrosionChemical corrosion leads to electrolytic
corrosion.
 Electrolytic corrosion may takes place in the
mouth with saliva acting as an electrolyte.
when the following condition are present in it:
 Different metals and alloys
 Heterogeneous composition of alloys
 Cold work metal
 Difference in oxygen tension

 Galvanic
corrosion
 Stress corrosion
 Concentration cell corrosion or Crevice
corrosion
Galvanic Corrosion:




Galvanic corrosion occurs when dissimilar metals lie in
direct physical contact with each other.
Eg- if a gold restoration comes in contact with an
amalgam restoration , the amalgam forms the anode and
starts corroding.
When two restoration touch causes sharp pain.
The best precaution is to avoid dissimilar metals in
contact.
The perception of the Color of an object is the
result of a physiological response to a physical
stimulus (light).
Light is an electromagnetic radiation that can be
detected by the human eye. It can be seen that the
visible electromagnetic radiation is in the range
from 400-700 nanometers.
Transparency
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.
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.
Opacity
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 color materials absorb all light colors.
• White color materials reflect all light colors.
• Blue color materials absorb all light colors
but reflect its color.
 Ideal
restorative material should match the
color of the tooth it restores.
 In maxillofacial prosthetics the color of the
gums ,external skin and eyes have to be
duplicated.
 Clinically in the operatory or dental lab ,
color selection is usually done by the use to
shade guides.
COLOR
Color parameters:
A- Hue:
It is the dominant wave length. It
represents the color of the material, i.e
yellow, green, red and blue.
B- Chroma:
It represents the strength of the color
or degree of saturation of the color
(color intensity).
C- Value:
It represents the lightness or darkness
of color (the amount of grayness).
A tooth of low value appears gray and
non–vital = DEAD,
Therefore, it is the most important
parameter. Because it is intimately
related to the aspect of vitality in
human teeth.
Shade guide is used for color matching.
So, it is important to match colors under
appropriate conditions.
1- Source:
Different sources have different color
content. i.e. Incandescent light has a
color content different from that of
fluorescent light.
2- Surrounding:
Colors of wall, lips or clothes of the
patient modify the type of light reaching
the object.
3- Object:
A- Translucency:
It controls lightness or darkness of color.
High translucency gives a lighter color
appearance (higher value) i.e more vital
tooth appearance
B- Surface texture (surface finish):
This determines the relative amount of light
reflected from the surface, smooth surface
appears brighter than rough surface.
C- Presence of scattering centers as inclusions
or voids:
This increase opacity and lower the value
(more dark)
D- Fluorescence:
 It makes the teeth bright and vital, as it
increases the brightness.
 Light
used in “discotheques” or even under
some fluorescent light under such
conditions artificial teeth or restorations
without any fluorescence completely black
out.
E- Thickness:
The thickness of a restoration can affect its
appearance. Increase in thickness, increase
opacity, and lower the value.
F- Metamerism:
It is the change of color matching of two
objects under different light sources.
4- Observer:
A- Color response:
Eye responds differently among individuals.
B- Color Vision:
Some individuals may have color blindness
and inability to distinguish certain colors.
C- Color Fatigue:
Constant stimulus of one color decreases
the response to that color.
Light Amplification by Stimulate Emission
of Radiation.
The principle of laser production is
simply that an element or compound
(medium) can be excited by high energy
to produce a special type of light called
laser
Characteristics of laser beam:
a- Monochromatic :

all photons have the same wave length.
b- Coherent :
 all waves are bin phase (have the same
speed ).
c- Collimated :
 all waves are parallel ( minimum divergence
)
Surgery for removal of soft tissues.
Removal of initial carious lesions.
Curing of composite resin.
 Philips’
Science Of Dental Material by
Kenneth J. Anusavice DMD PhD (Jun 17, 2003)
 Notes on Dental Materials (Dental Series) by
E. C. Combe (Nov 1992)