1st chapter of dental materials ......useful for all the dental students.... Courtesy:My close friends nidhi & rahul..........

1. BY
NIDHI BARAI.
RAHUL BARIA.

2. Mechanical properties are defined by law of
mechanics that is the physical science dealing
with forces that acts on bodies and the
resultant motion ,deformation, or stress that
those bodies experience…

3. Brittleness Hardness Strength Ductility Malleability
compressive
tensile
shear
yield
flexural

4. When a force acts on body, tending to produce
deformation, a resistance is developed within
the body to this external force.The internal
resistance of the body to the external force is
called stress…
Stress=force/area

5. Results in a body when it subjected to two sets
of forces that are directed away from each
other in the straight line.The load tends to
stretch or elongate a body…

6. Results when the body is subjected to two sets
of forces in the same straight line but directed
towards each other.The load tends to or
shortens a body…

7. Shear stress is a result of two forces directed
parallel to each other. A stress that tends to
resist a twisting motion, or a sliding of one
portion of a body over another is a shear or
shearing stress…

9. Strain is expressed as change in length per unit
length of the body when a stress is applied …
Strain = deformation or change in length
/original length…

10. Elastic strain
Due to stress, if the body undergoes reversible
change in shape it is called elastic strain.
Plastic strain
Due to stress, if the body undergoes irreversible
change in shape it is called plastic strain.

11. The greatest stress that may be produced in a
material such that the stress is directly
proportional to strain…

12. Whenever forces is applied over a body ,
complex or multiple stresses are produced.
These may be a combination of tensile, shear
or compressive stresses.These multiple
stresses are called complex stresses…

13. If we take a cylinder and subject it to tensile
stress or compressive stress, there is
simultaneous axial and lateral strain.Within
the elastic range the ratio of the lateral to the
axial strain is called Poisson's ratio…

14. Elastic limit is the maximum stress that a
material will withstand without permanent
deformation.

15. The stress at which a material exhibits a
specified limiting deviation from
proportionality of stress to strain…

16. It represents the relative stiffness or rigidity of
the material within the elastic range.
Young’s modulus is the ratio of stress to strain.
Since stress is proportional to strain, the stress
to strain ratio would be constant.

17. It is defined as the strain that occurs when the
material is stressed to its proportional limit.
Maximum flexibility[EM]=proportional limit/
modulus of elasticity.

18. It is the energy required to fracture a material
under an impact force.
A charpy type impact tester is used.
Another instruments called izod impact tester
can also be used…

19. Once the elastic limit of the material is crossed
by a specific amount of stress, the further
increase in strain is called permanent
deformation…
i.e the resulting change in dimension is
permanent …

20. A structure subjected to repeated or cyclic
stresses below its proportional limit can
produce abrupt failure of the structure.This
type of failure is called fatigue…

21. It is defined as the energy required to fracture a
material. It is the property of the material
which describes how difficult the material
would be to break…

22. Relative inability of material to deform
plastically before it fractures…

23. It is the ability of material to withstand
permanent deformation under a tensile load
without rupture…
A metal that can be drawn into wire is said to
be ductile.

24. It is the ability of the material to withstand
rupture under compression ,as in hammering or
rolling into a sheet…
Most malleable metal is gold ,then silver ,
platinum and copper…

25. It is defined as the ability of a material to resist
scratching….

26. Brinell
Rockwell
Vickers
Knoop.

27. A diamond indenting tool is used. knoop
hardness values for both exceedingly hard
and soft materials can be obtained from this
test.
It is a type of microhardness test…

28. Enamel=300 KHN
dentin=65 KHN
Amalgam=90 KHN
Composite=55 KHN

29. Tendency of the liquid to flow…

30. It is the deformation under static load before
the material has completely hardened…

31. It is time dependent slow deformation in a
completely set material like solid metal due to
stress. It is a kind of slow flow….

32. It takes place under constant load….

33. It states the direct proportionality between the
two quantities is always a straight line of
graph…

34. It is the strength which resist bending , which
involves complex stress and strains as seen in
objects supported only at the ends…

35. It is the point at which the materials break…

36. It is the strength which resist repeated stresses
falling on it over and over again…
E.g. RPDS

37. It is a science that deals with flow of material…

38. Natural tooth enamel-400MPA
Natural tooth dentin-296MPA
Dental amalgam-310MPA
Dental porcelain-172MPA
Silicate cement-158MPA
Zinc phosphate cement-103MPA
Acrylic resin-96MPA…