The document discusses various physical properties of dental materials that are important for clinicians to understand. It describes properties like abrasion and abrasion resistance, viscosity, structural and stress relaxation, and creep and flow. Hardness tests are also covered, including macrohardness tests like Brinell and Rockwell, and microhardness tests like Knoop and Vickers. Understanding these physical properties helps clinicians select appropriate materials and improves the success of dental treatments.

1. PHYSICAL
PROPERTIES OF
DENTAL MATERIAL
PRESENTED BY- Dr. Shailja katiyar
Dept of prosthodontics
Shailja katiyar

2. CONTENTS
Introduction
What are physical properties
Physical properties includes:
• Abrasion and abrasion resistance
• Viscosity
• Structural and stress relaxation
• Creep and flow
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3. • Colour and colour perception
• Thermophysical properties
• Tarnish and corrosion
Conclusion
References
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4. INTRODUCTION
• The main goal in dentistry is to maintain or improve the quality
of life through replacement or alteration of tooth structure.
• Physical properties deals with the structure and nature of
matter.
• Dental material are specially fabricated material designed for
use in dentistry.
• Successful treatment by clinician relies upon good knowledge
of physical properties.
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5. What are physical properties
• Physical properties are based on the law of mechanics,
acoustics, optics, thermodynamics electricity,
magnetism, radiation ,atomic structure nuclear
phenomena.
• Physical properties are the measure of material .these
properties in dental research because they provide the
information needed to access the characteristics and
improvement in material under development
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6. Physical properties include:
Abrasion and Abrasion Resistance-
Abrasion is the process of scraping or wearing. (Phillips Science of
Dental Materials, 11th edition).
Abrasion resistance: It is the ability of material and structures
to withstand abrasion. It is a method of wearing down or rubbing
away by means of friction.

7. Clinical significance:
• Excessive wear of natural teeth that opposes a denture
porcelain teeth will occur.
• The bite of the patient cannot be altered but the wear
can be limited by:
1.Adjusting the occlusion
2. Polishing the abraded area

8. • Hardness:
• Property of being difficult to indent, cut or scratch.
(Phillips Science of Dental Materials, 11th edition) .
• Simply resistance to plastic deformation or permanent
deformation of material.
• Used within a given classification as an index of the
ability of a material to resist abrasion or wear

9. Abrasion and abrasion resistance
continued:
• The surface hardness tests commonly used in
dentistry are :
MACROHARDNESS TEST-1. Brinell hardness test
2. Rockwell hardness test
MICROHARDNESS TEST- 3. Knoop hardness test
4. Vickers hardness test
OTHERS- 5. Barcol hardness test
6. Shore hardness test

10. 1.Brinell hardness test:
• Oldest method used to test metals and alloys.
Eg- aluminum and copper alloys(lower forces)
cast iron and steel ( higher forces)
• Small steel or tungsten carbide ball, typically 10mm in
diameter,subjected to a weight of 123 N and it remain
contact to specimen for 30 sec.
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11. • Smaller the area of indentation , harder the material and larger the
BHN value.
Ratio of the load applied to the area of the indentation produced..

12. 2.Rockwell hardness test:
• Rockwell is a rapid testing method in which an instrument
applies a load to a material.This method is commonly used to
measure the hardness of materials. Material used- lead, zinc,
copper alloys, titanium, iron.
• A ball or metal cone indenter is normally used and the depth of
the indentation is measured with a sensitive dial micrometer.
• The indenter balls or cones are of different diameters and load
applications(60 to 150kg)
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13. • The advantages of Rockwell system is that hardness is
read directly and it is good for testing viscoelastic
materials.
• The disadvantages are that a preload is needed, greater
time required and the indentation may disappear
immediately on removal of the load.

15. 3.Knoop hardness test:
• The Knoop hardness test at a glance: A
microhardness test used for brittle materials
ceramic.
• Diamond is used as indenter having extended
pyramidal shape with the length to width ratio
being 7:1 and respective face angles are 172
degrees for the long edge and 130 degree for short
edge
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16. • Advantages of this method is that materials with a great range of
hardness can be tested by varying the test load.
• Disadvantages is that it needs very high polished and flat surface

17. 4.Vickers hardness test:
• Also known as 136 degree pyramid
test.
• The method is similar to BHN except that a 136 degree
diamond pyramid shaped indenter is forced into the
material with a definite load application.
• The indenter produces a square indentation, the diagnosis
of which are measured.
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18. •It is suitable for brittle materials so it is used for
the measurement of hardness of tooth structures
and also of dental casting gold alloys.
•A significant advantage of this test is that it can be
used for testing very small specimens.
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20. 5.Barcol hardness Test:
• Used to study the depth of cure of a resin composites.
• Has a spring loaded needle with a diameter of 1mm that is
pressed against the surface.
• If no penetration occur, reading reads 0.Reading decreases as
indentation increases .
• Depth of cure of a resin composite is tested by preparing
specimens varying in thickness 0.5 to 6.0mm.
• Then the top surface of the specimen is activated by a light
curing unit.
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22. 6.Shore hardness test:
• This method is used to determine the hardness of rubber
because the indentation disappear after removal of load.
• An instrument called Shore Durometer is used in the rubber
industry to determine the relative hardness of elastomers.
• The indenter is attached by a lever to a scale that is graduated
from 0 to 100.
• If the indentor completely penetrates the specimen , a reading
of 0 is obtained, and if no penetration occurs , a reading of 100
units results.
• The test has been used to evaluate soft denture liner , mouth
protectors and maxillofacial elastomers.
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23. • Knoop and Vickers test are called microhardness test.
• The Brinell and Rockwell are macrohardness test.
• Knoop and Vickers tests used loads less than 9.8N.The
indentations are small and are limited to a depth of less than 19mm.
• They are capable of measuring hardness in small regions of thin
objects.
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24. HARDNESS
TEST
SHAPE AND
DIMENSION OF THE
INDENTER
MATERIAL SUITED
FOR
TESTING
ADVANTAGES DISADVANTAGES
Brinell
Hardness
test
10mm diameter
Hardened steel or
carbide ball
Metals and metallic
materials in dentistry
This test is useful or best suited
for testing ductile materials
Hardness of cold
worked and annealed
materials is difficult to
measure. Not suitable
for brittle materials
Rockwell
Hardness
test
Diamond cones or
spherical balls with
diameters ranging
from1/16 to ½ inches
Metallic materials in
dentistry.
Direct reading of the depth of
indentation. Rapid testing time
Not suitable for brittle
materials.
Knoop
Hardness
test
Pyramid shaped
diamond indenter with
a rhomboidal base
Used for measuring
hardness of elastic
ductile, and brittle
materials
Used for very brittle materials
or thin sheets, where only a
small indentation may be made
for testing.
The need to optically
measures the indent
size, so the materials
require a highly
polished surface.
Vickers
Hardness
test
136°pyramid shaped
diamond indenting
tools with a square
Best suited for brittle
materials
It is very useful for measuring
the hardness of small areas and
hard materials
The need to optically
measure the indent
size, so the material
requires a highly
polished surface.

25. Structural and Stress Relaxation:
Stress is defined as the internal resistance set up by a
body when it is deformed.
Stress: force/area
• It is measured in N/m2 and this unit is specifically
called Pascal (Pa).
• Three Basic Types of Stresses
Based on the nature of the deforming force applied on
the body are tensile, compressive or shearing.

27. Structural and Stress Relaxation
Contd…
• Strain can be defined as change in length per unit
length of the body when subjected to stress.
• Has no definite unit. Strain may be elastic /reverts back
to original form or plastic/ permanent deformation.

28. Structural and Stress Relaxation Contd…

29.  Viscosity:
• Resistance of a liquid to flow .
• Thus viscosity is a measure of the consistency of a fluid and its resistance
to flow.
• Study of flow characteristics of materials and deformation is rheology. The
term rheology was coined by Eugene C. Bingham.
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30. Clinical implication of Viscosity in
dentistry:
• It is important to have a low viscosity molten metal during
casting in order to completely fill the mold.
• Impression material should have a sufficient degree of
fluidity to get the details and also the fairly complex areas
of tooth structure.
• Changes of viscosity of impression materials with time is
important.
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31. • Dental material have different viscosities depending on
the preparation for their intended clinical application.
More viscous nature of zinc polycarboxylate cement as
compared with zinc phosphate cement when these
material have been properly mixed as luting cements
can be observed during mixing. E.g. ZnPo4
viscosity>GIC when mixed in luting consistency

32. • To explain viscous nature of some materials shear
stress v/s shear strain rate curve can be plotted.

33. NEWTONIAN FLUID: (CONSTANT FLUID)
• An ideal fluid
• Shear stress proportional to strain rate
• Straight line on curve
• Viscosity(n)=shear stress/ shear rate
• Constant velocity
Eg: water, zinc phosphate.
PSEUDOPLASTIC FLUID:
Viscosity decreases with increasing strain rate, until it reaches a
nearly constant value.
Eg :Monophase elastomeric impression materials.
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34. DILATANT FLUID:
• Viscosity increase with increasing stress.
• The material; become more rigid under stress(disadvantage)
Eg: Acrylic denture base, material, sand in water.
PLASTIC FLUID:
• Material behaves rigid until a minimum of stress is applied , then
it starts behaving like Newtonian fluid.
• Eg: clay suspension, composite material
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35. Creep and flow:
 Creep is defined as the time
dependent plastic strain of a
material under a static load or
constant stress.
•The term creep implies a relatively
small deformation produced by a
relatively large stress.

36. Creep and Flow contd…
• Creep is the property applied to solid materials/metals like
amalgam.
• Metal creep usually occurs as the temperature increases to
within a few hundred degrees of the melting range.
• Ceramic does not have creep because to high forces. of their
atomic structure, these material show cracks and fracture when
subjected.
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37. Dental amalgams contain from 42 to 52wt%Hg and begin melting at
temperature only slightly above mouth temperature. Because of its low
melting range, dental amalgam can slow creep from a restored tooth site
under periodic sustained stress

38. AMALGAM CREEP

39. Clinical significance:
• Creep may cause unacceptable deformation of a
dental restoration.
• It may also lead to unacceptable fit of a FPD,
when a cast alloy with porcelain at high
temperature.

40. FLOW:
• The property of the material to deform when subjected to stress
• The flow of wax is a measure of its potential to deform under a
small static load, even that associated with its own wax.
• Type 1 inlay wax show flow of 90% i.e. marked flow above
mouth temp. that is required to mould the wax for making wax
patterns. At room temp these waxes show flow of 1% that
permits removal of the wax pattern from the mouth.
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41. •Flow implies a greater deformation
produced more rapidly with
a smaller applied stress.
•The term flow is generally been
used in dentistry to describe
the rheology of amorphous
materials such as waxes.

42. Colour and colour perception:
• What is colour?
• Color is a sensation induced from light of varying wavelengths reaching
eye
• Cone cells of retina are responsible for spectral sensitivity.
• Sensation induced from light of varying wavelengths reaching eye.
Cone cells of retina are responsible for spectral sensitivity.
• Determined visually by measurement of hue, chroma and value.
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43. Color Perception:
• The phenomenon of vision can be explained by considering the
response of the human eye to light reflected from an object.
• Light from an object that is incident on the eye is focused in the retina
and is converted into nerve impulses, which are transmitted to the brain.
• Color perception is described by three objective by three objective
variables:
Hue
Value
Chroma

44. Hue:
It is defined as the particular variety of a colour, shade , variety or tint.
Eg: red, green , yellow etc.
Chroma:
The intensity of the colour , degree, of saturation of a particular hue.
Value:
It is defined as the relative lightness or darkness of a colour or the
brightness of an object.
Value of 0=black
Value of 10=white
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45. Hue:
• Hue is defined as the particular variety of a color, shade or tint. This
refers to dominant wavelength present in the special distribution.
Eg: RED, GREEN , YELLOW

46. Chroma:
• It is the degree of saturation of a particular hue.
e.g Red can vary from “scarlet” to “ light pink” where scarlet has high
saturation and pink has low saturation.
• Crown is not considered separately in dentistry, it is always associated with
hue and value of dental tissue, restoration and prosthesis.

47. Value:
• It is also known as grey scale. It is the vertical or z axis. Value
increases towards higher end (higher) and decreases towards lower
end ( darker Value
• Value of 0 = black
• Value of 10 = white

50. Colour Terminology:
• Opacity - The measure of impenetrability of visible light.
• Translucent-Diffused transmission of visible light.
• Transparent- Capable of transmitting light.

51. Metamerism:
• A phenomena in which objects appear colour matched
under one type of light, and different under another
light source.
CLINICAL SIGNIFICANCE:
Colour matching should be done under natural light
source i.e. sun ( in the dental clinic, color matching could
be done using either white light or sunlight)

54. Fluorescence:
• Fluorescent material such as tooth enamel, absorbs near UV
radiation(300-400nm) and then re-emit radiant energy at a
lower frequency than it is absorbed.
• Tooth become the source of light and emits in wavelength 400-
500nm(blue-white region).
• Ceramic crown and ceramic agent that lack a fluorescent agent
appear as missing teeth when viewed in black light

56. Thermophysical Properties:
• Thermophysical properties can be defined as material
properties that vary with temperature without altering the
material’s chemical identity.
• When restorative materials are placed in deep cavities, heat
transmitted to vital dental pulp must be limited so as to prevent
thermal shock and trauma.
• While with denture bases its contact with mucosal surface is
desirable to convey sensation of heat and cold associated with
food and beverages. Such attributes are governed by properties
of thermal conductivity and thermal diffusivity.

57. 1.Thermal conductivity:
• Definition:- it is defined as the quantity of heat in calories per second
passing through a material 1 cm thick with a cross section of 1 cm
square having temperature difference of 1k (1 degree Celsius) and is
measure under steady state conditions in which temperature gradient
does not change.
• The international system(si) unit is watts per meter per Kelvin
[w× (m-1)×(K-1)].
• Materials that have high thermal conductivity are called conductors
whereas low thermal conductivity are called insulator .
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58. • Material that have a high thermal conductivity are called
conductors.
• Materials that have a low conductivity are called
insulators.
• The international system unit or measure for thermal
conductivity is watt per meter per second per degree
kelvin.
• The higher the thermal conductivity , the greater is the
ability of the substance to transmit thermal energy, and
vice versa.
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59. Clinical significance:
• Compared with resin-based composite that has a low
thermal conductivity, heat transferred more rapidly away
from the tooth when cold water contacts a ,metallic
restoration because of higher thermal conductivity.
• This increased conductivity of the metal compared with that
of the resin composite induces greater pulpal sensitivity,
which is experienced negligible, mild, moderate, or extreme
discomfort, as a depending upon patient previous trauma
and the pain response of the patient.
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60. 2.Thermal diffusivity:
• It is a measure of the rate at which a body with a
no uniform temp. reaches a state of thermal
equilibrium.
• The thermal conductivity of zinc oxide-eugenol is
slightly less than that of dentin, its thermal
diffusivity is more than twice that of dentin.
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61. Thermal Diffusivity contd…
• The low thermal conductivity of enamel and
dentin aids in reducing thermal shock and pulpal
pain when hot or cold foods are taken into the
mouth.

62. Relevance of thermal diffusivity:
• In the oral environment ,temperature are not constant during
the ingestion of foods and liquids. Under such conditions
thermal diffusivity is important.
• Typical values of thermal diffusivity in units of 10-4 CM2/ sec
are as follows:
• Pure gold-11,800
• Amalgam-960
• Composite-19-73
• Water-14
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63. 3.Coefficient of thermal expansion:
• . Definition:- It is defined as the change in length per unit of original
length of a material when its temperature is raised 1 degree Celsius.
α = δL÷ L × δ T
• L= original length
• Delta L= change in length
• Delta T= change in temperature
• The unit is mm/mk or ppm/k.
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64. • It dictates procedure for using wax pattern, casting
metal crown. Placing amalgam and composite
restoration and preparing metal ceramic crown and
bridges.
• The high thermal expansion co- efficient of inlay wax is
important as it is susceptible to temperatures changes
• e.g. an accurate wax pattern that fits a prepared tooth
contracts significantly when it is removed from tooth or
die in warmer areas and then stored in cooler area. This
dimensional change is transformed to a cast metal
restoration which is made from lost wax process.

65. Clinical significance :
• Close matching of the coefficient of thermal expansion 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 marginal leakage ,discolouration and hypersensitivity.
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66. • Glass inomer-22
• Dentin-18-26
• Enamel-47
• Zinc phosphate cement-30
• Thus a patient drinking ice water, low specific heat of amalgam
and its high thermal conductivity suggest that the higher
thermal diffusivity favours a thermal shock situation more than
is likely to occur when only natural tooth structure is exposed to
the cold liquid.
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67. Tarnish and corrosion:
TARNISH:
• Tarnish is a surface discoloration of the metal or even a slight
loss of the luster.
• This surface discoloration is due to either, the formation of hard
and soft deposits on the surface, or the formation of thin films
of oxides, sulphides or chlorides.
• Tarnish is often the first step of corrosion.
• Stain or discoloration arises from pigment-producing bacteria,
drugs containing chemicals such as iron or mercury and
absorbed food debris.
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68. CORROSION:
• CORROSION is the deterioration of a metal caused by reaction
with environment. It can cause severe and catastrophic
disintegration of metals. Tarnish is forerunner to corrosion
• Corrosion may occur due to moisture, atmosphere, acid or
alkaline solutions, & certain chemicals.
• Common e.g. rusting of iron, a complex chemical reaction in
which iron combines with oxygen in air & water to form
hydrated oxide of iron
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69. Corrosion cont..

70. Various causes of tarnish and
corrosion:
• Eggs & other food contain significant amount of sulphur,
various sulphides (hydrogen or ammonium sulphides) corrode
silver, copper, mercury & similar metals present in dental alloys.
• water, oxygen & chlorine ions present in saliva.
• various acidic solutions such as phosphoric , acetic, & lactic
acids at proper concentration & pH promote corrosion.
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72. Non aqueous (dry) or chemical
corrosion:
• In which there is a direct combination of metallic and non-
metallic elements .
• Electrolytes are absent
e.g. oxidation, halogenations, or sulfarization reaction. .
• This type of corrosion is less susceptible to occur in the mouth.
E.g.: oxidation of metal surface during soldering and heat
treatment procedures.
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73. Aqueous (wet) or electrolytic
corrosion:
• Corrosion occurs in presence of water or some other liquid
electrolyte.
• Only this type of corrosion occur in mouth.

74. Types of electrolytic corrosion:
• Galvanic cell corrosion.
• Stress corrosion.
• Concentration cell corrosion
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75. Galvanic cell Corrosion:
• Galvanism is results of difference in potential
between dissimilar restoration in opposing or
adjacent tooth.
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76. Galvanic Shock:
• A pain sensation caused by electric current
generated by a contact between two dissimilar
metal forming a galvanic cell in oral environment
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79. Clinical Significance of Galvanic
Currents:
• As long as metallic dental restoration materials are
employed there seems to be little possibility that the
galvanic currents can be eliminated.
• Galvanic Shock A pain sensation caused by electric
current generated by a contact between two dissimilar
metal forming a galvanic cell in oral environment.

80. Stress Corrosion:
• The imposition of stress increases to internal energy of
an alloy either through elastic displacement of atoms or
creation of micro strain fields associated with
dislocation. The tendency to undergo corrosion will be
increased called stress corossion .
• Example, a metal which has been stressed by
burnishing produces the localized stress in some part of
structure If stressed and under stressed metals are in
contact in an electrolyte the stressed area will become
anode and will corrode.
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82. Concentration cell corrosion/crevice
corrosion:
Electrochemical corrosion is called concentration cell corrosion, which
occurs whenever there is variation of electrolytes or in composition of given
electrolytes.
• Example:
1. Accumulation of food debris in interproximal areas between the teeth
particularly if oral hygiene is poor.
2.. Difference in oxygen concentration between parts of same restoration
with greatest attack at areas containing least oxygen. Oxygen deprived
becomes and as it is covered by food debris while surface around rim of a
scratch or pit becomes cathode.

84. Concentration cell corrosion/Crevice
corrosion cont…
3. Irregularities likes pits, scratches and reacts are an excellent
example. Thus to protect such pitting corrosion all metallic
restoration must be polished.
• It occurs at cervices and marginal gaps of crown and bridges.
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85. Protection against corrosion:
• 1. A highly effective protection utilizes certain metals that develop
thin, adherent highly protective film by reaction with environment
such metal is said to be passive.
• A thin surface oxide forms on chromium is a good examples
Example:
1. stainless Steel which contains sufficient amount of chromium added
to iron and its alloy to passviate alloy.
• 2. Titanium and its alloy are widely used because of its favorable
combination of physical chemical and biological properties as well as
their resistance to corrosion,
• 3. Noble metal resist corrosion.

86. Conclusion:
• A proper knowledge of physical properties of dental
material helps us in making correct choice for various
clinical restorations. This in turn increases the durability
and life span of the restoration.
• When tooth shade is selected using conventional means,
knowledge & skill of practitioner comes into play.
• Technique based system provide dentist with distinct
advantage in creating highly esthetics , natural looking
restoration
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87. References:
• Phillips science of dental material 10th & 11th edition
• Dental material –S. Mahalaxmi.
• Google for images