1. Mechanical Properties of
Dental Materials
-- Part 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
Stress
Strain
Mechanical Properties based on elastic deformation:
Stress- Strain diagram/ curve
Modulus of elasticity
Poisson’s ratio
Flexibility
Resilience

4. Strength Properties:
Proportional limit
Elastic limit
Yield strength
Diametral tensile strength
Flexural strength
Fatigue strength
Impact strength

5. Other Mechanical properties:
Toughness
Fracture toughness
Brittleness
Ductility and Malleablility
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
Stress- Strain diagram/ curve
Modulus of elasticity
Poisson’s ratio
Flexibility
Resilience

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

16. A B
Stress (Pa)
Strain
Resilience

17. ELASTIC MODULUS A B
Stress (Pa)
Strain
Resilience
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

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

23. STRENGTH PROPERTIES Proportional limit Elastic limit Yield strength
Diametral tensile strength
Flexural strength
Fatigue strength
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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