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1. Dr. Raghuwar D Singh
Associate Professor
Prosthodontic Department
King George’s Medical University UP, Lucknow

2. Dental Materials:
 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

3. 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

4.  Strength Properties:
1. Proportional limit
2. Elastic limit
3. Yield strength
4. Diametral tensile strength
5. Flexural strength
6. Fatigue strength
7. Impact strength

5.  Other Mechanical properties:
1. Toughness
2. Fracture toughness
3. Brittleness
4. Ductility and Malleablility
5. Hardness

6. 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.

7.  Stress: Internal resistance to applied external force.

8. Types of stresses:

9. Types of stresses....
 Axial
Compressive Stress-
Tensile Stress-

10. ....Types of stresses
 Non Axial
 Shear – Tends to resist the sliding of
one portion of a body over another.
 Torsion
 Bending

11.  Flexural Stress: Bending forces

12. STRAIN
 Strain: change in length per unit original length when
stress is applied;
= Length / Original length
 Strain(ε)= Deformation/Original length

13.  Elastic Strain
 Plastic Strain

14. Mechanical Propertied based on
Elastic deformation
1. Stress- Strain diagram/ curve
2. Modulus of elasticity
3. Poisson’s ratio
4. Flexibility
5. Resilience

15. Stress-Strain curve
Strain
A
B
Stress
(Pa)
Toughness
C D

16. A
B
Stress
(Pa)
Strain
A
B
Stress
(Pa)
Strain

17. ELASTIC MODULUS
 Is a measure of elasticity
of the material: how stiff
the material is in the
elastic range.
 Elastic modulus=
Stress/Strain
 The slope of the curve
A
B
Stress
(Pa)
Strain
A
B
Stress
(Pa)
Strain

18. ...ELASTIC MODULUS

19. 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.

20. 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.

21. 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.”

22. Resilience:
The resistance of a
material to permanent
deformation.
Proportional limit
Elastic limit
A
Stress
(Pa)
Strain
A
Stress
(Pa)
Strain

23. STRENGTH PROPERTIES
1. Proportional limit
2. Elastic limit
3. Yield strength
4. Diametral tensile strength
5. Flexural strength
6. Fatigue strength
7. Impact strength

24. Strength properties:
 Strength is the stress that is necessary to cause fracture
or a specified amount of plastic deformation.

25. 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.

26. ELASTIC LIMIT
 The maximum stress that a material will withstand
without permanent deformation.

27. 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.

28.  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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