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1. Mechanical Properties of
Dental Materials
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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2. Introduction
 According to the law of mechanics it is defined
as the physical science that deals with energy
and forces and their effects on bodies. Thus all
mechanical properties are measures of the
resistance of a material to deformation or
fracture under an applied force
 .It can be: 1)elastic or reversible deformation
2)plastic or irreversible deformation
3) a combination of both.
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3. Stress Stress is the force per unit area
Stress = force/area
1Pa = Newton / sq. meter
= mega Newton / sq. millimeter
= 1 MPa
Types of stresses
a) Compressive stress
b) Tensile stress
c) Shear stress
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4. Strain Change in length per unit length
of a body when it is subjected
to a stress
Strain = deformation / original
length
Types
a. Elastic strain- reversible
b. Plastic strain- irreversible
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5. Modulus of Elasticity
 It represents the STIFFNESS of the
material with in elastic range.
 It is the ratio of stress and strain or the
slope of linear region of curve.
Elastic modulus = stress / strain
(within elastic limit)
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6. Strength
It is the stress necessary to cause fracture or a
specified amount of plastic deformation
Types
a. Ultimate tensile strength
b. Shear strength
c. Compressive strength
d. Flexural strength
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7. Proportional limit
It is the greatest stress that a material will
sustain without a deviation from the
proportionality of stress to strain
Poisson’s ratio
It is the ratio of lateral to axial strain within
elastic range.
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8. Elastic limit
It is the maximum stress a material will
withstand without permanent deformation.
Yield strength
Stress at which a material begins to function
in a plastic manner
Flexibility
It is the strain that occurs when material is
stressed below proportional limit.e.g. inlay
restoration, orthodontic appliance.
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9. Resilience
It is the amount of energy absorbed by a
structure when it is stressed to its proportional
limit.
Or
it is the resistance of material to permanent
deformation.
Toughness
It is the amount of energy required to
fracture a material
or
It is the resistance of a material to fracture.
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10. Fatigue strength
It is the stress at which the material fails
under repeated loading.e.g. complete
denture, implants, metal clasps of CPD.
Endurance limit
It is the stress at which a material can be
loaded infinite number of times without
failing.
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11. Brittleness
It is inability of a material to undergo
plastic deformation before fracture. E.g.
amalgam, ceramics, composites.
Impact strength
It is the total energy absorbed before a fracture
when struck by a sudden blow. E.g. fused
glasses, cements, amalgam,some plastics
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12. Ductility
It is the ability of a material to sustain a
large permanent deformation under
tensile load before it fractures.
Malleability
It is the ability of a material to sustain
considerable permanent deformation
without rupture under compression.
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13. Hardness
It is a property that is used to predict the
wear resistance of a material and its
ability to abrade opposing dental
structures.
Macro hardness test
a. Brinell hardness test
b. Rockwell hardness test
Micro hardness test
a. Vickers hardness test
b. Knoop hardness test
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14. Conclusion
Mechanical properties are important in
understanding and predicting a materials
behavior under various conditions, therefore it
helps in the diagnosis of clinical failures
(whether they are caused by material
deficiencies, human errors or patient factors).
Thus it helps in understanding the design
modifications that will improve the fracture
resistance of restoration.
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15. Thank you
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