Transcript Mechanical Properties of Dental Materials

Dr. Raghuwar D Singh
Associate Professor
Prosthodontic Department
King George’s Medical University UP, Lucknow
Dental Materials:
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Properties of Dental Materials – Physical, Mechanical
Biocompatibility
Micro structure of metal alloys
Impression materials
Gypsum product
Dental Resins – Denture base and Restorative Resin
Dental Amalgam
Dental Cements
Direct filling Gold
Dental casting alloys
Finishing and polishing materials
Dental Ceramics
Mechanical Properties of DM
 Mechanical Properties:
1. Stress
2. Strain
 Mechanical Properties based on elastic deformation:
1. Stress- Strain diagram/ curve
2. Modulus of elasticity
3. Poisson’s ratio
4. Flexibility
5. Resilience
 Strength Properties:
1. Proportional limit
2. Elastic limit
3. Yield strength
4. Diametral tensile strength
5. Flexural strength
6. Fatigue strength
7. Impact strength
 Other Mechanical properties:
1. Toughness
2. Fracture toughness
3. Brittleness
4. Ductility and Malleablility
5. Hardness
STRESS
 Force per unit area; Stress= Force/Area
 It is normally defined in terms of mechanical stress, which
is the force divided by the perpendicular cross sectional
area over which the force is applied.
 Stress: Internal resistance to applied external force.
Types of stresses:
Types of stresses....
 Axial
Compressive Stress-
Tensile Stress-
....Types of stresses
 Non Axial
 Shear – Tends to resist the sliding of
one portion of a body over another.
 Torsion

Bending
 Flexural Stress: Bending forces
STRAIN
 Strain: change in length per unit original length when
stress is applied;
= Length / Original length
 Strain(ε)= Deformation/Original length
 Elastic Strain
 Plastic Strain
Mechanical Propertied based on
Elastic deformation
1. Stress- Strain diagram/ curve
2. Modulus of elasticity
3. Poisson’s ratio
4. Flexibility
5. Resilience
Stress-Strain curve
C
B
Stress (Pa)
A
Toughness
Strain
D
Stress (Pa)
B
A
Strain
ELASTIC MODULUS
 Is a measure of elasticity
B
of the material: how stiff
the material is in the
elastic range.
Stress/Strain
 The slope of the curve
Stress (Pa)
 Elastic modulus=
A
Strain
...ELASTIC MODULUS
POISSON’S RATIO
 Ratio of lateral to axial
strain within the elastic
range.
 For an ideal isotropic
material of constant
volume the ratio is 0.5.
 Most material have
values of 0.3.
FLEXIBILITY
 Ability of a material to return to its original form
indicates its elasticity, but the strain taking place at
elastic limit is known as flixibility.
 Flexibility is bending capacity.
 It can be defined as the strain that occurs when the
material is stretched to its proportional limit.
RESILIENCE
 Defined as the amount of energy absorbed within a unit
volume of a structure when it is stressed to its
proportional limit.
 The property if often described as “springback potential.”
Resilience:
The resistance of a
material to permanent
deformation.
Stress (Pa)
Proportional limit
A
Elastic limit
Strain
STRENGTH PROPERTIES
1. Proportional limit
2. Elastic limit
3. Yield strength
4. Diametral tensile strength
5. Flexural strength
6. Fatigue strength
7. Impact strength
Strength properties:
 Strength is the stress that is necessary to cause fracture
or a specified amount of plastic deformation.
PROPORTIONAL LIMIT
 It is defined as the greatest stress that a material will
sustain without a deviation from the linear proportionality
of stress to strain.
ELASTIC LIMIT
 The maximum stress that a material will withstand
without permanent deformation.
YIELD STRENGTH
 Defined as the stress at which a material exhibits a
specified limiting deviation from proportionality of stress
to strain.
 It is the amount of stress required to produce a
predetermined amount of permanent strain usually 0.1%
or 0.2% which is called the Percent Offset.
 For brittle materials such as composites and ceramic –
Yield strength can not be measure.
 YS indicates a degree of permanent deformation (usually
0.2%)
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