Aplied physics / dental implant courses by Indian dental academy

APPLIED PHYSICS
(Basic Principles)
INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
www.indiandentalacademy.com

CONTENTS
INTRODUCTION
APPLIED SURFACE PHENOMENA
PHYSICAL PROPERTIES
OPTICAL PROPERTIES
CONCLUSION
REFERENCES

INTRODUCTION
All materials made up of atoms
These atoms held together by inter
atomic forces called cohesive forces.
Matter exists in three forms
Difference in form is due to difference
in energy stateswww.indiandentalacademy.com

Surface tension
Wetting
Adsorption
Colloids
Capillary action
Adhesion
Applied surface phenomena

SURFACE TENSION
Referred as surface energy
“Increase in energy per unit area of
surface”
Energy at surface of a solid or liquid is
greater than in its interior
Inside a lattice all atoms are equally
attracted to each other
Inter atomic distances are equal and
energy is minimal

Where as in outer surface,atoms are not
equally attracted in all directions,infact
no atoms from out side
Higher the bond strength of a
substances,greater the surface energy
Metallic bonds are stronger and have
higher surface energies than
Vanderwaals of liquids
UNITS:Dynescm
Summary:-greater the surface
energy,greater the capacity for
adhesion www.indiandentalacademy.com

WETTING
“The degree of spreading of a liquid
drop on a solid surface”
Degree of wetting is measured by
contact angle
“It is the angle formed by the adhesive
and the adherent at their surface”
Zero degree contact angle indicates
complete wetting
Values above 90 degree indicates poor
wetting www.indiandentalacademy.com

Good wetting promotes capillary
penetration and adhesion
Indicates strong attraction between
liquid and solid surface molecules
Important factor in denture retention
A more natural appearance is
achieved if dentures are wetted by a
thin film of saliva
Hydrophobic substance are those that
exhibit high contact angles with waterwww.indiandentalacademy.com

ADSORPTION
“ Process in which a liquid or gas
adheres firmly to surface by
attachment of molecules to surface of
solid or liquid”
Thus, reducing their surface free
energy
Process of adsorption or adhesion to
surface of a substance is important in
wetting process, in which substance is
coated or wetted with a foreign
substance such as liquidwww.indiandentalacademy.com

Degree to which saliva wet or adhere
to surface of a denture depends on
tendency for surface adsorption
High-energy surfaces such as metals
adsorb molecules more readily than
low energy surfaces such as waxes.
Where, oxides have intermediate
surface energies

•COLLOIDS
First described by Thomas Graham
(1861)
Derived from Greek Word
Kolla: Glue, Oid: Like
Substances with two or more phases
Study of small particles and related
surface effects in form of surface
electrical charge or surface adsorption.www.indiandentalacademy.com

CLASSIFICATION OF COLLOIDS
Dispersed Continuous Type
phase phase
Solid Liquid Sol
Solid Gas Aerosol
Liquid Liquid Emulsion
Liquid Gas Aerosol (Fog)
Gas Liquid Foam
Gas Gas Foam

CAPILLARY PENETRATION
Penetration of liquids into narrow
crevice is known as capillary action
Surface energy of a liquid creates
pressure that drives liquid into
crevices, narrow spaces, and thin
tubes

Penetration co-efficient
Rate of movement of liquid into a
capillary space is related to
- Surface tension (ϒ)
- Contact angle (θ)
- Viscosity (n)
i.e. Penetration co-efficient (PC)=ϒCos
2nwww.indiandentalacademy.com

Liquid with low viscosity, high
surface tension and low contact angle
(i.e. good wetting) penetrates more
faster
Important in adhesion or retention of
denture

ADHESION
Bonding of dissimilar materials by
attraction of atoms or molecule

Classification
1.Mechanical adhesion
a. Microscopic penetration
b. stresses
2.Chemical adhesion
a. Primary forces
i. Ionic bonds
ii.Covalent bonds
iii.Metallic bonds
b.Secondary forces
(VanderWaals forces)www.indiandentalacademy.com

Diffusion bonding results when one
phase penetrates by diffusion into
surface of a second phase and forms a
hybrid layer.
Composite of two materials
Several factors affect the strength of an
adhesive bond
1. Cleanliness
2. Penetration of surface
3. Chemical reaction
4. Shrinkage of stresses
5. Thermal stresses
6. Corrosive environmentwww.indiandentalacademy.com

Forces involved in denture retention
1. Capillary force
2. Wetting of denture base by saliva
3. Thickness of saliva film
4. Surface tension of saliva
5. Viscosity of saliva
6. Atmospheric pressure

PHYSICAL PROPERTIES
Considered as the ways that
materials respond to changes in their
environments
Based on laws of mechanics,
acoustics, optics, thermodynamics,
electricity, magnetism, atomic
structure, or nuclear phenomenawww.indiandentalacademy.com

Classified as
I. Mechanical properties
II. Thermal properties
III. Electrical and
Electrochemical properties

Mechanical properties
Important in understanding and
predicting a material’s behavior under
load
STREES
Internal reaction to external force
When a force acts on body, tending to
produce deformation, a resistance is
developed to this external force
application

In a structure, designed as force per
unit area
Stress = force/area
Inversely proportional to cross
sectional area and directly
proportional to the load

Clinically, it is internal resistance of
the body in terms of force per unit
area and is equal and opposite in
direction of this external force
applied.
UNITS :Megapascals. (MPa)

TYPES OF STRESSES
Depending on type of force, divided
into
1.Tension: when body is subjected to
two sets of forces that are directed
away from each other in same
straight line

2.Compression: Occurs when body is
subjected to two sets of forces in
same straight line and directed to
each other.
3.Shear: Result of two forces
directed parallel to each other

STRAINSTRAIN
Expressed as change in length per
unit length of body when a stress is
applied.
Dimensionless quantity, expressed as
Strain = deformation / original length
Hence, each type of stress is capable
of producing corresponding
deformation in a bodywww.indiandentalacademy.com

Regardless of composition or nature of
material, magnitude and type of stress
applied to material, deformation and
strain result with each other
COMPLEX STRESSES:
Combination of tensile, shear or
compressive stress
Hence, whenever, force is applied over a
body, complex or multiple stresses are
produced. www.indiandentalacademy.com

PROPORTIONAL LIMIT
“The greatest stress that may be
produced in a material such that the
stress is directly proportional to
strain”
Below proportional limit, no
permanent deformation occurs

When stress is removed,
structure will return to its
original dimensions.
Region of stress-strain curve
below proportional limit is called
elastic region.

Application of a stress greater than
proportional limit results in a
permanent irreversible strain
This region of stress strain curve
beyond proportional limit is called the
plastic region.

ELASTIC LIMIT
“The maximum stress that a material
will withstand without permanent
deformation”
Both proportional limit and elastic
limits are often interchangeable in
referring to stress involved.

Thus, differ in fundamental concept
that, one describes elastic behavior
of material whereas other deals with
proportionalities of strain to stress
in a structure.

YIELD STRENGTH
“The stress at which a materials
exhibits a limiting deviation from
proportionalities of stress to strain”
It is a stress at which material begins to
functions in a plastic manner.

At this stress a limited permanent
strain occurs
It is always greater than elastic or
proportional limit

MODULUS OF ELASTICITY
“The ratio of stresses to strain up to
or less than proportional limit”
The measures of elasticity of a
material is described by this term
Also referred to as elastic modulus or
Young’s modulus

Represents stiffness of a material
within elastic range
Determined from a stress strain
curve by calculating ratio of stress to
strain
Elastic Modulus = Stress/Strain
It has same units as stress and is
usually reported in MPa or Gpa.www.indiandentalacademy.com

POISSON’S RATIO
During axial loading in tension or
compression there is a simultaneous
axial and lateral strain
Hence, within elastic range, ratio of
lateral to axial strain is called
Poisson’s ratio

In tensile loading, Poisson’s rate
indicates that reduction in cross
section is proportional to elongation
during elastic deformation
The reduction in cross section
continues until material is fractured

FLEXIBILITIES
“the strain that occurs when the
material is stressed to its proportional
limit”

Relation between maximal flexibility,
proportional limit and modulus of
elasticity may be expressed as
Modulus of
elasticity = Proportional limit (P)
Maximum flexibility (Em)

Though, some materials withstand
high stresses and show minimum
deformation, but in some instances
where large strain or deformation is
needed with a moderate or slight
stress.

RESILIENCE
Basically an express of energy
“The amount of energy absorbed
by a structure when it is stressed
not to exceed it proportional limit”

The resistance of a material is usually
measured in terms of its modulus of
resilience, that is the amount of
energy stored in a body when one unit
volume of a material is stressed to its
proportional limit.

Expressed as
Modulus of
elasticity (R)=Proportional limit (P2
)
Maximum flexibility (2E)

IMPACT
Used to describe reaction of a
stationery object to a collision with a
moving object
Depending upon resistance of impact,
energy is stored in body without
causing deformation or with
deformation www.indiandentalacademy.com

Impact strength
“The energy required to fracture
a material under a impact force”
Deformation
Once the elastic limit of material is
crossed by a specific amount of stress,
further increase in strain is
permanent deformation
i.e. The resulting change in dimension
is permanent or material has
undergone a permanent deformation.
Permanent

STRENGTH
It is maximal stress required to
fracture a structure
Basically three types of strength
Tensile strength
Compressive strength
Shear strengthwww.indiandentalacademy.com

It measures collective inter-atomic
forces and not individual atomic
attraction or repulsion
It is not necessarily equal to stress at
fracture
Flexure strength: Also referred as
transverse strength or modulus of
rupture.
It is collective measurement of all
stresses simultaneous applied.

FATIGUE
If a structure is subjected to repeated or
cyclic stress below its proportional limit can
produce abrupt failure of the structure
This type of failure is called fatigue
Its behavior is determined by subjecting a
material to a cyclic stress of a maximum
known value and determining the number of
cycles that are required to produce failure

STATIC FATIGUE
It is a phenomenon exhibited by some
ceramic materials
These materials support a high static
load for long period time and then fail
abruptly
This type of failure occurs only when
materials are stored in a wet
environment
This property is related to effect of on
highly stressed surface of material.www.indiandentalacademy.com

TOUGHNESS
“The energy required to fracture a
material”
It is a property of the material, which
describes how difficult material to
break.

BRITTLENESS
It is relative inability of a material to
sustain plastic deformation before
fracture of a material occurs.
Generally, it is considered as opposite
of toughness

DUCTILITY AND MALLEABILITY
Ductility
“The ability of a material to withstand
permanent deformation under a tensile
load without rupture”.
A metal may be drawn into a wire and
said to be ductile
It depends on tensile strength
Decreases with increase in temperaturewww.indiandentalacademy.com

Malleability
“The ability of a material to withstand
permanent deformation without rupture
under compression”
Increases with increase in temperature
Gold is the most ductile and malleable
metal followed by silver, platinum and
copper

Measurement of Ductility:
three common methods
1.Percent elongation after fracture
2.Reduction in area in the fractured
region ends
3.Cold bend test

HARDNESS
“It is the ability to withstand
permanent deformation in form of
indentation load”
Several types of surface hardness test

BRINELL HARDNESS NUMBER
(BHN)
Hardened steal ball is pressed into
polished surface of a material under a
specified load.
Load is divided by area of surface of
indentation and quotient is referred to as
Brinell hardness number or BHN.
BHN = Load / Area of indentation.www.indiandentalacademy.com

ROCKWELL HARDNESS NUMBER
(RHN)
Somewhat similar to the BHN test in that
a steel ball or a conical diamond point is
used.
However instead of measuring diameter
of impression, depth is measured directly
by a dial gauge on instrument.
The RHN test has a wider range of
application for material, since BHN test is
unsuitable for brittle materials.www.indiandentalacademy.com

VICKERS HARDNESS TEST (VHN)
Similar to BHN test
Instead of steel ball, a diamond is in
shape of a square pyramid
The method of analysis of VHN is same
as BHN
ie., the load is divided by the area of
indentation.

The length of the diagonals of the
indentation (sides of the diamond) are
measured and averaged.
Vickers test is used for dental casting
gold's.
This test is used for brittle materials
but is not suitable for elastic
materials. www.indiandentalacademy.com

KNOOP HARDNESS TEST (KHN)
Diamond indenting tool is used.
Its value is independent of ductility of
material
Values for both exceedingly hard and soft
materials can be obtained from this test.

KNOOP and VICKERS tests are
classified as Micro hardness tests
BRINELL and ROKWELL test are
classified as Macro hardness tests.
Other tests like SHORE and
BARCOL,
These are sometimes employed for
measuring hardness of rubber and
plastics.

ABRASION RESISTANCE
Like hardness, abrasion is influenced by
a number of factors.
Hardness is used to indicate the ability
of a material to resist abrasion.
Useful for comparing materials in same
classification, eg. one brand of cement is
compared to another and their abrasion
resistance is quoted in comparison to one
another. www.indiandentalacademy.com

However, it may not be useful for
comparing materials of different
classes.
The only reliable test for abrasion is
via a test procedure

RELAXATION
Every element in nature makes an
attempt to remain in a stable form.
If an element is changed from its
equilibrium or stabilized form by either
physical or chemical means it tries to
come back to its original form.
After substances have been
permanently deformed, there are
trapped internal stresses which cause
displacement of the atoms.www.indiandentalacademy.com

This condition is unstable
Atoms wish to return to their normal
positions.
This results in a change in shape or
contour in the solid as atoms or
molecules rearrange themselves.
This change in shape due to release of
stresses is known as relaxation. The
material is said to warp or distort.www.indiandentalacademy.com

RHEOLOGY
The study of flow matter is the
subject of Rheology
Viscosity is the resistance offered
by the liquid when placed in motion.

THIXOTROPHIC CREEP
Time dependent plastic deformation,
which occurs when a metal is
subjected to a constant load near its
melting point is known as creep.
This may be static or dynamic in
nature.

STATIC CREEP
This is time dependent deformation
produced in a completely set solid
subjected to a constant stress.
DYNAMIC CREEP
Refers to the phenomenon when the
applied stress is fluctuating, such as
in fatigue type test.www.indiandentalacademy.com

FLOW
Although creep or flow may be
measured under any type of stress
Compression is usually employed for
testing of dental materials.

THERMAL PROPERTIES
Heat flow through a material
Metals tend to be good conductors of
heat
The rate at which heat flows through a
material is expressed as thermal
conductivity or thermal diffusivity.

Thermal conductivity(k)
It is a measure of speed at which
heat travels (in calories per second)
through a given thickness of material
(1 cm), when one side of material is
maintained at a constant temperature
that is 10degree C, higher than the
other side.
Expressed in units of cal cm/cm2 sec
0C.

Thermal diffusivity
Thermal conductivity gives an idea
of the relative rates at which heat flows
through various materials
But, fails to take into fact that various
materials require different amounts of
heat (Calories) to raise their
temperatures in an equal amount.

Thus, thermal conductivity alone will
not express, how rapidly interior
surface under a crown will heat up
when exterior surface is heated.
The thermal diffusivity (h) of a
material (expressed in units of
mm2
/sec) is dependent on its thermal
conductivity, heat capacity (Cp
), and
density (p):
H = k
(Cp
X p
) www.indiandentalacademy.com

Co-efficient of Thermal expansion
“Change in length per unit of the
original length of a material when its
temperature is raised 10degreeC”
The unit of α can be expressed also as
µm/ cm degree C.
A tooth restoration may expand or
contract more than tooth during a change
in temperaturewww.indiandentalacademy.com

OPTICAL PROPERTIES
Color
Perception of color of an object
is result of a physiological response
to a physical stimulus.
Sensation is a subjective experience.

According to Grassmann’s laws, eye
can distinguish differences in only
three parameters of colors.
These parameters are dominant
wavelength, Luminous reflectance,
and excitation purity.

THREE DIMENSIONS OF COLOR
Hue : Associated with color of an object
Value: It can be separated into light and
dark shades.
The lightness which can be measured
independently of color hue is called value.

Chroma: may be dull or more vivid.
Difference in color intensity or
strength is called chroma.
Represents degree of saturation of
a particular of HUE (color)
Higher the chroma the more intense
and mature is the color.
It cannot exist by itself but is always
associated with hue and value.

Measurement of color
Measured in reflected light by
instrumental or visual technique.
A popular system for the visual
determination of color is Munsell
Color System.
It is a co-ordinate system, which can
be viewed as a cylinder.www.indiandentalacademy.com

Lines are arranged sequentially
around perimeter of cylinder, while
chroma increase along a radius out
from axis.
The value co-ordinate varies along
length of cylinder from black at the
bottom to neutral gray at the center to
white at the top.
Clinically color matching is done by
use of shade guides.www.indiandentalacademy.com

Surface finish and thickness
When white light shines on a solid,
some of the light is directly reflected
from the surface, and it remain white
light.
This light mixes with light reflected
from body of material and dilutes
color.

As a result, an extremely rough
surface appears lighter than a
smooth surface of same material.
The thickness of a restoration can
affect its appearance.

PIGMENTATION
Esthetic effects are sometimes
produced in a restoration by the
incorporation of colored pigments in
non-metallic materials.
The mixing of pigments therefore
involves process of subtracting colors.
Usually inorganic pigments rather
than organic dyes are used because
pigments are more permanent and
durable in their color qualities.www.indiandentalacademy.com

METAMERISM
Objects that appear to be color matched
under one type of light but may appear
very different under another light
source.
Quality and intensity of light are factors
that must be controlled in matching
colors in dental restorations.
Colors should be matched in light
corresponding to that of use.www.indiandentalacademy.com

FLUORESCENCE
It is emission of luminous energy by
a material when a beam of light is
shone on it.
The wavelength of emitted light
usually is longer than that of the
exciting radiation.
Typically, blue or ultraviolet light
produces fluorescent light that is in
the visible range.www.indiandentalacademy.com

Opacity, Translucency, and Transparency
The color of an object is modified not
only by intensity and shade of pigment
or coloring agent but also by
translucency or opacity of object.
Opacity is a property of material that
prevents passage of light.
An opaque material may absorb some
of light and reflect remainder.www.indiandentalacademy.com

Translucency is a property of
substances that permits passage of
light but disperses light so that
objects cannot be seen through
material.
Some translucent materials used in
dentistry are porcelain, composite
resins, and dental plastics.

Transparent materials allow passage
of light in such a manner that little
distortion takes place and objects may
be clearly seen through them.
Transparent substances such as glass
may be colored if they absorb certain
wavelength and transmit others.

Conclusion
Three interrelated factors are
important in long term function of
dental materials
1. Material choice
2. Component geometry i.e To
minimize stress concentration
3. Component design i.e To distribute
stress as uniformly as possible
The dental material behavior is
dependent on inter-related various
properties

REFERENCES
1.Applied dental materials-8th
edition-
John.Mc cabe and Angus W.G.Walls
2.Clinical aspects of dental materials –
Marcia Gladwin
3.Restorative dental materials-Robert
G Craig
4.Science of dental materials –Phillips
5.Notes on dental materials-E.C.Combewww.indiandentalacademy.com

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