1. Mechanical Properties

2. a: stiff, rigid b: flexible
Modulus of elasticity “Young’s Modulus” (E):
The constant of proportionality between stress and strain.
It represents the slope of the elastic portion of the stress-strain curve.
It measures the stiffness or rigidity
E = = = kg/cm2 MPa
stress
kg/cm2
Stress
Strain a b
strain
cm/cm
a: stiff, rigid
b: flexible

3. Clinical significance:
Denture base should be constructed of a rigid material:
To allow load distribution on the whole area.
To be used in thinner sections without the risk of bending.
To avoid bone resorption

4. Ductility and malleability:
Ductility is the ability of the material to withstand plastic deformation under tensile stress without fracture.
i.e. the ability of the material to be drawn into wires without fracture.
Malleability is the ability of the material to withstand plastic deformation under compressive stress without fracture.
i.e. the ability of the material to be hammered into thin sheets without fracture.
Stress
Strain

5. Brittleness:
When the material shows no or very little plastic deformation on application of load brittle.
Stress
Strain
Stress
Strain

6. Ductile materials Brittle materials
Fracture occurs far away from the P.L
Fracture occurs at or near the P.L
Necking takes place before fracture
Crack propagation take place till fracture
Examples: gold, nickel chromium alloys
Burnish-ability of casting margins
Examples: amalgam, porcelain, composite
Stress
Strain
Stress
Strain

7. Resilience:
It is the energy required to deform the material to the P.L. It is represented by the area under the elastic portion.

8. R= ½ stress x strain N.m/m3, joule/m3b
Strain
R= ½ stress x strain N.m/m3, joule/m3

9. Clinical significance:
Orthodontic wires capable of storing energy, and released over period of time
Acrylic resin teeth are more resilient than porcelain teeth
So transmit less forces to underlying bone

10. Toughness:
It is the energy required to stress the material to the point of fracture. It is represented by the area under the elastic and plastic portion.

11. Stress a b
Strain
N.m/m3, joule/m3

12. Clinical significance:
It is very important with brittle materials
Dicor is brittle but after incorporation of mica crystal during ceraming, toughness is increased

13. Stress Strain Stress Stress Strain Stress Strain Stress Strain Stress

14. Fracture toughness:
The ability of material to resist fracture through its resistance to crack propagation. Or the amount of energy required for fracture.
F.T. is related to crack propagation not crack initiation, surface condition is of little importance

15. Fracture toughness: Clinical significance:
Glass fillers in dental composite.
Addition of zirconia particles in porcelain.