Dr P. S. Prabu MDS Malabar Dental College & Research Centre

2. PHYSICALAND
MECHANICAL PROPERTIES
OF DENTAL MATERIALS
Dr P. S. Prabu MDS
Malabar Dental College &
Research Centre

3. Introduction
Rheological properties
Properties of materials in relation to light transmission and
absorption
Color – Three dimension of color
Measurement of color
Metamerism
Fluorescence
Thermo physical properties
Galvanism
Force
Stress
Flexural stress
Strain
Contents

4. Proportional limit
Elastic limit
Yield strength
Resilience
Elongation
Elastic modulus
Flexibility
Fatigue
Toughness
Brittleness
Ductility
Malleability
Strength
Tensile, Compressive, Shear
Hardness – Hardness tests
Summary
Contents

5. Introduction
Dental materials are developed by the producer
and selected by the dentist on the basis of
characteristic physical, chemical, mechanical,
and biological properties.

6. PHYSICAL PROPERTIES
Physical properties are based on laws of mechanics,
acoustics, thermodynamics, optics, magnetism,
radiation, atomic structure, or nuclear phenomena.
MECHANICAL PROPERTIES
Mechanical properties are defined by the laws mechanics
(ie) the physical science that deals with energy and forces
and their effects on bodies.

7. RHEOLOGICAL PROPERTIES
Rheology Is The Study Of Flow Of Material
For Liquid Flow Is Measured By Viscosity
For Solid Flow Is Measured by Creep And Flow
Viscoelasticity
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8. VISCOSITY
Viscosity Is The Resistance Of The Fluid To Flow
When a substance flows under the influence of external forces
(Gravity) the molecules or atom come into contact. Thus the bond
must be broken and remade and give rise to resistance to flow known
as viscosity.

9. Low Viscosity :Liquid such as water. The force
binding the molecules together are weak and easily
overcome
High Viscosity: Fluid with stronger intermolecular
attraction with large molecules
Viscosity Of Most Liquid Decreases
Rapidly With Increases In Temperatue
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10. Material Temperature ⁰c Viscosity cp
Agar 45 281,000
Alginate 37 252,000
Impression
Plaster 37 23.800
Polysulfide, 37 57,200
light
Polysulfide, 36 1,360,000
heavy
Silicone, 37 95,000
syringe
Silicone, 36 420,000
regular
Zinc oxide eugenol 31 99,600
Viscosity of dental impression materials

11. THIXOTROPIC
A liquid of this type becomes less viscous and more fluid under
repeated application of pressure.
Eg:
Zinc Oxide Eugenol Shows Reduced
Viscosity After Vigorous Mixing
Clinical significance
The rheological properties of a material are important ,as these
have a major influence on the handling characteristics of the
material

12. VISCOELASTICITY
Materials that have mechanical properties independent of strain are
termed elastic.
Materials that have mechanical properties dependent on strain are
termed viscoelastic. (ie) these materials have characteristics of an
elastic solid and a (viscous) fluid.
Material such as agar, alginate, elastomeric
impression materials and waxes are
viscoelastic
Clinical significance
Some materials have properties
between that of a solid and a
liquid,which makes them susceptible
to distortion.

13. • To explain viscous nature of some materials, shear stress v/s
shear strain rate curve can be plotted.
13

14. 14
NEWTONIAN FLUID:
- an ideal fluid,Shear stress proportional to strain rate,
-Viscosity(η)= shear stress(τ)/strain rate (ε)
-Constant velocity.eg. Water and newly mixed zinc phosphate cement
PSEUDOPLASTIC FLUID:
-viscosity decreases with increasing strain rate, until it reaches a nearly
constant value.
e.g. elastomeric Impression materials,poly carboxylate cements,
DILATANT FLUID
Viscosity increase with increasing stress.
The material become more rigid under stress(disadvantage)
e.g.-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.
e.g.- clay suspension, composite material

15. CREEP AND FLOW
Creep is defined as the slow change in dimensions of an object
as a result of prolonged exposure to high temperature or stress.GPT9
Static Creep: Time dependent deformation produced complete set of
solid subject to constant stress. Dental amalagam.
Dynamic Creep: produced when applied stress is fluctuating.
Flow is similar to creep generally used in dentistry to
describe the rheology of amorphous material such as waxes.

16. Properties of materials in relation to light
transmission and absorption
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 Eg: glass, pure acrylic
resin.

17. • Translucency having the appearance between complete opacity and
complete transparency; partially .GPT9.
• In such manner, the object cannot be clearly seen through them .
Eg: tooth enamel, porcelain, and pigmented acrylic resin.
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.

18. OPALESCENCE
• Opalescent materials,such as dental enamel,are able
to scatter shorter wavelength of light.

19. COLOR
•Light is a form of electromagnetic radiant energy that can be
detected by human eye
•Eye is sensitive to wave length for approximately 400nm(violet) to
700nm(red)
•The combined intensities of the wave length present in a beam of
light determines the property called color

20. Tuesday, 17 March 2020

21. THREE DIMENSION OF COLOR
• HUE
• VALUE
• CHROMA
Hue : Refers to as dominant color of an object Eg: Blue, Green, Red
Value: Color can be separated in to light (High value) and dark
(Lower Value)This Lightness or Darkness which can be measured
independently of color hue is Called VALUE .
Eg: Tooth of low value appears Gray is non-vital

22. •Chroma: the purity of a color, or its departure
from white or gray;
•the intensity of a distinctive hue; saturation of
a hue;
• chroma describes the strength or saturation
of the hue
•A particular color may be dull or vivid this difference in color
intensity is called CHROMA
Chroma represent the degree of saturation of particular hue (color)
• Higher the Chroma more intense and darker is the color

23. MEASUREMENT OF COLOR
Most commonly used method to measure color
is the MUNSELL SYSTEM

24. • Clinical significance
The colour of an object is a human perception which
is a function of a triplet composed of the light source
,the object and the observer.
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25. Vita Classic Shade Guide
Four categories representing hue
A, yellow-red
B, yellow
C, gray
D, red-yellow-gray
Chroma is selected from gradations
within 1, 2, 3, 4
Eg: A3 = hue of red-yellow,
Chroma of 3
Yellow-red Yellow gray Red-Yellow-Red

26. • VITAPAN 3D-MASTER
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30. METAMERISM
The appearance of an object depend on the nature of light by which
the object is viewed.
Object that appears to be color matched under one type of light may
appear very different under another light source. This phenomenon
is called METAMERISM.

31. FLUORESCENCE
Fluorescence is the emission of light by an object at wavelength
different from those of incident light.
Fluorescence makes a definite contribution to the brightness and
vital appearance of human tooth.

32. THERMAL CONDUCTIVITY
THERMO PHYSICAL PROPERTIES
Heat transfer through the solid substance commonly occurs
through by means of conduction
Thermal conductivity or coefficient of thermal conductivity is the
quantity of Heat in calories per second that passes through a
specimen 1cm thick having a Cross sectional area of 1cm2 . When
the temperature difference between surface perpendicular to the
heat flow of the specimen is 1⁰.
Conductors
Insulators.

33. Thermal Diffusivity
• It is a measure of the rate at which a body with
a no uniform temperature 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.

34. COEFFICIENT OF THERMAL EXPANSION
Coefficient of thermal expansion is defined as the fractional
change in length of a given material per degree change in
temperature.GPT9
Eg: Coefficient of thermal expansion of inlay wax is important
because it is susceptible to temperature change. An accurate wax
pattern that fits a prepared tooth contract significantly when it is
removed from tooth or die in warmer area and the stored in cooler
area.

35. • Material Coefficient
• Inlay waxes 350-450
• Silicone impression material 210
• Polysulfide impression material 140
• Acrylic resin 76.0
• Porcelain 12.0
Clinical significance
The thermal properties of a dental material can influence the
sensation of hot and cold food and can cause mechanical failure
due to differential expansion and contraction.

36. TARNISH
TARNISH is the surface discoloration on a metal , or as a slight
loss or alteration of the surface finish or luster.
CORROSION
Chemical or electrochemical process in which a solid, usually a
metal, is attacked by an environmental agent, resulting in partial or
complete dissolution.
TYPES OF CORROSION REACTION
Chemical corrosion--- a) Dry corrosion
b) Wet corrosion

37. •Accelerated corrosion of a metal as a result of
electrical contact with a more noble metal in
a corrosive electrolyte; the resulting current flow
can produce nerve stimulation, unpleasant tastes, and other
physiological reactions commonly associated with this term-GPT9
•This results from a difference in potential between dissimilar fillings
in opposing or adjacent teeth. These fillings, in conjunction with saliva
as electrolytes, make up an electric cell.
•When two opposing fillings contact each other, the cell is
short-circuited, and if the flow of current occurs through the pulp, the
patient experiences pain and the more anodic restoration may corrode.
GALVANISM

38. HETEROGENOUS SURFACE
COMPOSITION
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39. DISSIMILAR METALS
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40. Force is generated through one body pushing or
pulling on another
The unit of force is the Newton, N
•Occlusal forces
•The maximum biting force on tooth ranges from 200 to 3500 N.
•The average biting forces on permanent teeth were 665,
450, and 220 N on molars, bicuspids, and incisors, respectively
•Biting force measurements on patients with removable partial
dentures are in the range of 65 to 235 N
•Patients with complete dentures, the average force on the molars
And bicuspids was about 100 N, whereas the forces on the
Incisors averaged 40 N.
FORCE

41. Tuesday, 17 March 2020
CORROSION OF NICKEL-BASED
DENTAL CASTING ALLOYS
• By Christopher & Richard shelton from journal of oral
&Craniofacial biomaterial sciences. Vol.23 No.6 2007
This study showed the importance of the level of Cr in Ni-
based alloys.
• The presence of higher Cr (25wt%) in bulk alloy led to a
superior corrosion resistance compared with lower Cr
(12.6wt%).
• At ph 2.5 the stability is greatly reduced for the alloy that
contained a lower Ch level where crevice corrosion was
observed.

42. STRESS
•A force exerted on one body that presses on, pulls on, pushes
against, or tends to invest or compress another body; an internal
force that resists an externally applied load or force.GPT9
Clinical significance
•When a load is applied to a tooth, this load is transmitted through the
material ,giving rise to stresses and strains. If these stresses and
strains exceed the maximum value the material can withstand ,fracture
is the most likely outcome.
Stress =
Force/Area

43. TYPE OF STRESS
Tensile stress
Compressive stress
Shear Stress
TENSILE STRESS
•Two set of forces that are directed away from each other in the same
straight line
•Tensile stress is caused by load that tends to stretch or elongate a body
Eg: A sticky candy can be used to remove crowns by means of tensile
force

44. COMPRESSIVE STRESS
Two set of forces in the same straight line but directed towards each other.
If a body is placed under a load that tends to
compress or shorten it the internal resistance
to such a load is called compressive stress.
SHEAR STRESS
Two forces directed parallel to each other a stress that tends to
resist a twisting motion or a sliding of one portion of a body
over another is a shear or shearing stress.

45. FLEXURAL (Bending) STRESS
Flexural stress is caused by bending force.
Flexural stress that are produced in a three unit bridge or fixed partial
denture
In fig: A tensile stress develops on the tissue side of FPD and
compressive stress develop on the occlusal side by bending force
The area tension represent potential fracture initiation site.
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46. Tuesday, 17 March 2020
Effect of 180 week water storage of flexural
properties of E-Glass & Silica fibre acrylic
resin composite
• By Pekkat.K.Vallittu
• 1)Storing test specimen in water decreased
their transverse strength & flexural modulous
• 2)Major reduction of the flexural properties
occured at first 4weeks of H2O storage
• I.J.P 2000; 13; 334-337

47. STRAIN
Strain is change in length per unit length when stress is applied; the
change in length/original length; the deformation caused in a body by
an external force.GPT9
Strain may be elastic or plastic.
Elastic strain is reversible
Plastic strain represent permanent deformation.

48. PROPORTIONAL LIMIT
.
P
The proportional limit is defined that unit of stresses beyond which
deformation is no longer proportional to the applied load.-GPT9

49. ELASTIC LIMIT
•The greatest stress to which a material may be subjected and still
be capable of returning to its original dimensions when such
forces are released.GPT9
•Below the proportional limit point ‘p’ a material is elastic in
nature.
(ie) if the load is removed the material will return to its original
shape.
P

50. YIELD STRENGTH
•The strength at which a small amount of permanent (plastic)
strain occurs, usually 0.1% or 0.2%,and most frequently
measured in MPa or psi .GPT9
•The prosthesis becomes permanently
deformed if stress is equal to or greater
than the yield strength.
Clinical significance
•If at any point in a metal restoration
such as a three unit bridge the tensile
stress exceeds the yield stress , the
restoration will deform permanently.

51. RESILIENCE
•The term resilience is associated with “springiness”the
ability of the material to resist permanent deformation.
•RESILIENCE is defined as the amount of energy absorbed
by a structure when it is stressed not to exceed its
proportional limit.

52. •The deformation that results from the application of a tensile
force is elongation. GPT9
•Elongation is extremely important because it gives an indication of
the work ability of an alloy.
ELONGATION
Alloy % Elongation
Gold (type 111) 34.0
40% Au-Ag-CU 02.2
Nickel-chromium 01.1
Alloy % Elongation
Gold (type TV) 6.5
Nickel-chromium 2.4
Cobalt-chromium 1.5
Iron-chromium 9.0
Cobalt-nickel-chromium 8-10
Crown and bridge
Partial denture

53. ELASTIC MODULUS
The coefficient found by dividing the unit stress, at any point up to
the proportional limit, by its corresponding unit of elongation
(tension) or strain.GPT9
It represent the relative stiffness and rigidity of materials within
the elastic range.Young's modulus is the ratio of stress to strain
Material Elastic Modulus GPa*
Cobalt-chromium partial 218.0
denture alloy
Acrylic denture resin 2.65
Silicone rubber 0.002
(maxillofacial)

54. FLEXIBILITY
The flexibility is defined as the strain that occurs when the
material is stressed to its proportional limit and modulus of
elasticity
Flexibility = Proportional limit/ modulus of elasticity

55. TEAR STRENGTH
•Tear strength is a measure of the resistance of a material to
tearing forces.
•Tear strength depends on the rate of loading.
•More rapid loading rates result in higher values of tear strength.
•Clinically, the rapid removal of an alginate impression is
recommended to maximize the tear strength and also to minimize
permanent deformation.
Material Tear strength kN/m
Agar duplicating material 0.22
Denture liners 2.6-45
Impression materials
Agar 0.99
Alginate 0.47
Polysulfide 4.0
Tear strength of Dental materials

56. FATIGUE
• To break or fracture a material caused by repeated cyclic or applied
loads below the yield limit.GPT9
Application: Restorations in the mouth are often subjected to
cyclic forces of mastication. Metal clasp of removable partial
denture, complete denture made of various resins.
Clinical significance
•Whereas a material may be strong enough to withstand the loads
placed on it when initially put into use, this does not mean it will
always be able to withstand those loads

57. TOUGHNESS
The ability of a material to withstand stresses and strains without
breaking; resistance to fracture-GPT9.
The area under the elastic and plastic portions of a stress strain
curve

58. BRITTLENESS
Brittleness is the relative inability of a material to sustain
plastic deformation before fracture of a material occurs.
Eg: Ceramics are brittle at oral temperatures they sustained little
or no plastic strain before they fracture (ie) A brittle material
fractures at or near its proportional limits

59. DUCTILITY
It represents a ability of a material to sustain a large permanent
deformation under a tensile load without rupture.GPT9
A metal that can be drawn readily in to a wire is said to be ductile.
Ductility depend on tensile strength. ductility decreases as the
temperature is raised

60. MALLEABILITY
The ability of a material to sustain considerable permanent
deformation without rupture under compression.
Ex: Hammering or rolling in to a sheet
Most malleable and ductile metals
Gold
Sliver
Platinum – Ductility
Copper - Malleability

61. Strength it is the maximal stress required to fracture a structure
The three type of strength are:-
-Tensile strength
-Compressive strength
-Shear strength
Tensile strength
Tensile strength is defined as the maximal
stress the structure will withstand before
rupture

62. DIAMETRAL COMPRESSION TEST
In this method, the compressive load is place by a flat plate against
the side of a short cylindrical specimen. The vertical compressive
force along the side of the disk produce as a tensile stress that is
perpendicular to the vertical plane that passes
through the center of the disk. Fracture
occur along the vertical plane. In this
situation the tensile stress is directly
proportional to the compressive load
applied.
(Brazilian test)

63. COMPRESSIVE STRENGTH
Compressive strength or crushing strength is determined by
subjecting a cylindrical specimen to a compressive load. The
strength value is obtained from the cross sectional area and force
applied. Though the load is compressive in nature the failure is
due to complex stresses

64. SHEAR STRENGTH
Shear strength is a maximum stress that a material can
withstand before failure in a shear mode of loading. It is
tested using the punch or push out method
Application: It is used to study the inter face between
the two materials Eg: Porcelain fused to metal
Punch tool

65. Shear bond strength of denture reline
polymers to denture base polymer;
• By Yutaka Takahashi & John Chai
• To characterize the shear bond strength
established between 4 denture base polymer 4
denture reline polymer
• Affected Bond Strength found to be relatively
low.
• I.J.P 2001-14-271
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66. HARDNESS
Hardness is resistance to indentation. Hardness of a material
is influenced by various factors such as strength,
proportional limit, ductility, malleability.
Hardness Test:-
-Brinell's Hardness Test
-Rockwell Hardness Test
-Vickers hardness Test
- Knoop Hardness Test

67. Brinell’s Hardness Test:-
Hardened steel ball is pressed in to a polished surface of a material under a
specified load the load is divided by the area of the surface of the indentation
and the value is referred to as Brinell's Hardness Number
BHN = Load /Area of indentation
Application:- Used for measuring hardness of metals Not suitable for
brittle materials
Brinells hardness tester

68. Rockwell Hardness Test:-
A steel ball or a conical diamond point is used, in this test the depth
is measured directly by a dial gauge on the instrument
Application:- Used for measuring hardness of metals
Rockwell hardness tester

69. Vickers hardness Test:-
It is similar to Brinell's test however instead of steel ball, a diamond in the
shape of square pyramid is used here impression is square. The load is divided
by the area of the indentation.
Application:- Suitable for brittle materials, measuring hardness of
tooth structure
Vickers hardness tester

70. Knoop Hardness Test:-
A diamond indenting tool is used. The impression is rhombic in shape.
Values of exceeding hard and soft materials can be obtained
by this test.

71. The Shore And The Barcol
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Barcol test
The shore test
A metal indenter that is spring loaded is used .The hardeness
number is based depth of penetration and is read directly from a
guage .
Application: Measure the hardness of rubber and plastics

72. SUMMARY
• The physical properties of oral restorations must adequately
withstand the stresses of mastication. Restorations and
appliances should be designed so resulting forces of
mastication are distributed as uniformly as possible. Lastly,
remember that dental material behavior depends on
interrelated physical, chemical, optical, mechanical, thermal,
electrical, and biological properties, and improvement of one
specific property often leads to a reduction in another
property.
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74. Reference
phillips science of dental materials –
Eleventh Edition
Mc cabe Applied Dental Materials Ninth
Edition
William O Brian Dental Materials Selection
fourth Edition
Craig Restorative Dental Materials– thirteen
Edition
Journal for oral&craniofacial biomaterial
sciences vol.23 no.2 feb. 2007
vol.23 no.6 june 2007
vol.23 no.3 march 2007