Dr. Brajendrasingh Tomar gave a lecture on the properties of dental materials. He discussed that dental materials aim to improve patients' quality of life by preventing disease, relieving pain, and enhancing appearance. Ideal dental materials would be biocompatible, bond permanently to teeth, match the appearance of natural tissues, exhibit similar properties to natural tissues, and promote tissue repair. Dental materials can be classified as preventive, restorative, or auxiliary. Physical properties are based on mechanics and include viscosity, shear stress, and hardness. Mechanical properties deal with forces and energies, and include stress, strain, strength, modulus of elasticity, resilience, and toughness. Common tests evaluate properties like

1. PROPERTIES OF DENTAL
MATERIALS
LECTURE BY:
Dr. BRAJENDRASINGHTOMAR
MDS
ASSOCIATEPROFESSOR
PROSTHODONTICS&IMPLANTOLOGY

2. WHAT ARE DENTAL MATERIALS?
 The overriding goal of dentistry is to maintain or
improve the quality of life of the dental patient. This goal
can be accomplished by preventing disease, relieving
pain, improving masticatory efficiency, enhancing
speech, and improving appearance.
 Because many of these objectives require the
replacement or alteration of tooth structure, the main
challenges for centuries have been the development and
selection of biocompatible, long lasting, direct-filling
tooth restoratives and indirectly processed prosthetic
material that can withstand the adverse condition of the
oral environment.

3. Ideal properties of a dental
material would be
 Be biocompatible
 Bond permanently to the tooth structure or bone
 Match the natural appearance of tooth structure and
other visible tissues.
 Exhibit properties similar to those of tooth enamel,
dentin, and other tissues, and
 Be capable of initiating tissue repair of regeneration of
missing or damaged tissues.

4. Classification of dental material
 May be classified as
o Preventive material
o Restorative material or
o Auxiliary materials

5. Physical properties
of
dental material

6. What are physical properties
 Physical properties based on the laws of mechanics,
acoustics, optics, thermodynamics, electricity,
magnetism, radiation, atomic structure, or nuclear
phenomena.

7. Viscosity
 Visosity is the resistancen of a liquid to flow.
 Most liquids, when placed in motion, resist imposed
forces that cause them to move. This resistance to fluid
(viscosity) is controlled by internal frictional forces
within the liquid. Thus viscosity is a measure of the
consistency of a fluid and its inability to flow. A highly
viscous fluid flows slowly.

8. Shear stress and shear strain
rate
 A liquid is placed between two metal plates, the lower
plate is fixed, and upper plate is being moved to the
right. The stress required to move the plate is called
shear stress ( = F/A or Force applied/ area of plate). The
changes produced is called shear strain rate ( = V/d or
Velocity of plate/distance covered).

9. Shear stress versus shear strain
rate curve
 To explain this viscous nature of some materials, a shear
stress versus shear strain rate curve can be plotted.
The rheologic behaviors of four types of fluids are shown
in figure.

10. 1. Newtonian: it is an ideal fluid demonstrates of shear
stress that is proportional to shear rate and then the plot
is a straight line. newtonian fluid has a constant
viscosity and exhibits a constant slope of shear stress
plotted against shear strain rate.
2. Pseudoplastic: if a material viscosity decreases with
increase in share rate it is said to exhibit pseudoplastic
behavior,

11. Mechanical properties
of
dental material

12. What are Mechanical properties
 Mechanical properties are defined by the laws of
mechanics, that is, the physical science that deals with
energy and forces and their effects on bodies.

13. Stress
 Whenever force acts on a body tending to produce
deformation, a resistance that is developed to the
external force application.
 force per unit area; a force exerted on one body that
presses on, pulls on, pushes against, or tends to invest
or compress another body; the deformation caused in a
body by such a force; an internal force that resists an
externally applied load or force.
 Stree is equal and opposite in direction to the
force(external) applied. This external force is also known
as load
Types of stress
1. Tensile stress 3. Shear stress
2. Compressive stress

14. Tensile stress
 Results in a body when it is subjected to
two sets of forces that are directed away
from each other in the same straight line.
The load tends to strech or elongate a
body

15. compressive stress
 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.

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

17. Strain
 If the stress produced is not sufficient to withstand the
external force load the body undergoes a change in
shape (deformation).
 Strain = change in length/original length
 It is a dimentionless quantity and may be elastic or
plastic or a combination of the two.

18. The S-S CURVE
 A plot of of the corresponding values of stress and
strain is referred to as s-s curve.

19. Proportional limit
 May be defined as the greatest stress that may be
produced in a material such that the stress is directly
proportional to strain.
Elastic limit
 Elastic limit is the maximum stress that a material can
withstand without undergoing permanent deformation.

20. Yield strength( proof strength)
 Yield strength is defined as the
stress at which a material exhibits
a specified limiting deviation from
proportionality of stress to strain”
or “it’s a defined as the stress at
which the material begins to
function in a plastic manner

21. Modulus of elasticity(MOE) or
Elastic modulus
 The term elastic modulus represents the relative
stiffness or rigidity of the material within the elastic
range.
 MOE = STRESS/STRAIN

22. FLEXIBILTY
 Maximum flexibility is defined as the strain, which occurs
when the material is stressed to its proportional limit.
 The relationship between the maximum flexibility,
proportional limit and MOE may be expressed
mathematically as follows:
MOE(E)= proportionl limit/ maximum flexibility

23. Resilience
 It can be defined as the amount of energy absorbed by a
structure when it is stressed to its proportional limit” or
it is the energy needed to deform the material to its
proportional limit.

24. Poisson’s ratio
 When a tensile force is applied to a cylinder or rod, the
object becomes longer and thinner. Conversely a
compressive force acts to make the cylinder or rod
shorter abd thicker.
 The strain in the direction of force is known as “
longitudinal strain.” and that perpendicular to it is known
as “lateral strain.”
 The ratio between the lateral strain and longitudinal
strain is called as “poission’s ratio”
 Poisson’s ration = lateral starin/longitudinal strain

25. Ductility & Malleability
 DUCTILITY Represents the ability of a material to sustain
a large permanent deformation under a tensile load
without rupture” or “it is the ability of a material to draw
into a wire under a force of tension.
 MALLEABILITY Represents the ability of a material to
sustain a large permanent deformation under a
compressive load without rupture” or “it is the ability of
a material to hammer into sheets under compression.

26. Elongation
 “The deformation that results from the application of a
tensile force is elogation.”
 The total percentage elongation includes both the elastic
elongation and plastic elongation

27. Toughness
 “ Toughness is the ability of the material to absorb
energy during plastic deformation up to fracture” or it is
the amount of energy required to stress the material to
the point of fracture.
 Unit Mega joule/m3

28. Brittleness
 “ it is defined as a tendency to fracture without
appreciable deformation is therefore oppsite of ductility”
 Brittle material is liable to frature at or near to its
proportional limit.
 Brittle material are good under compression but not
under tension.
 For examples: Gypsum products, dental cements, dental
amalgam. Dental ceramics

29. Strength
 “Strength is the capability of the material to withstand
stress without undergoing fracture.”
 Unit: MPa or PSI
1. Tensile strength
2. Compressive strength
3. Shear strength
4. Flexural strength
5. Impact strength
6. Fatigue strength
7. Tear strength
Types of strength

30. Tensile strength
 Tensile strength is determined by subjecting a rod, wire
or dumbell shaped specimen to a tensile loading (a
unilateral test) “tensile strength is defined as the
maximal stress the structure will withstand before
rupture”.

31. Diametral compresssion test
 Also called as “indirect tensile test” for
brittle material
 In this method a disk of the brittle
material is compressed diametrically in a
testing machine until fractures. The
compressive stress applied in the
specimen that introduces a tensile stress
in the material perpendicular to the
plane of the force application of the test
machine.

32. Compressive strength
 Compressive strength or ‘crushing strength’ is
determined by subjecting cylindrical specimen to a
compressive load.
Shear strength
o The maximum stress that a material can withstand
before fracture in a share mode of loading
o The common method of testing the share strength of the
dental material is the “ punch method”

33. Impact strength
 Impact strength is the capibility of the mterial to
withstand fracture under an impact force” or “ energy
required to fracture a material under an impact force.”
 Impact strebgth can be tested by:
1. Charpy type impact tester.
2. Izod impact tester.

34. Fatigue strength
 A subject that has been subjected to a stress below the
proportional limit and subsequently relieved of this
stress should return to its original form without any
change in its properties or internal structure.When the
stress is repeated a great number of times, the strength
of materials may be drastically reduced and causes
ultimate failure. This is called Fatigue.

35. Hardness
 Hardness is defined as resistance to permanent scratching
or indentation or penetration.
 There are many surface hardness tests
1. Brinell hardness test:
brinell hardest test is one of the oldest tests employed for
determining the hardness of metals. In the brinell test, a
hardened steel ball is pressed under a specified load into the
polished surface of a material, the load is divided by the area
of the projected surface of the indentation, and the quotient is
reffered to as the brinell hardness number or BHN. Thus, for a
given load, the smaller the indentation, the larger is the
number, and the harder is the material.

36. 2. Rockwell hardness test
The rockwell hardness test is somewhat similar to the brinell
test in that a steel ball or a conical diamond point is used,
instead of measuring the diameter of the impression, the depth
of penetration is measured directly by a dial gauge on the
instrument. A number of indenting point with different sizes
are available for testing a variety of different material. The
rockwell hardness number (RHN) designated according to the
particular indenter and load employed.
3. Vickers hardness test
The vickers hardness test employs the same principal of
hardness testing that is used in brinell test. However, instead
of a steel ball, a square- based pyramid is used. Although the
impression is square instead of round, the method for
computation of the vickers hardness number (HV) is the same
as that for the BHN in that the load is divided by the projected
area of indentation. The lengths of the diagonals of the
indentation are measured and averaged. The vickers test is
employed in the ADA specification for dental casting gold
alloys.

37. 2. Rockwell hardness test
The rockwell hardness test is somewhat similar to the brinell
test in that a steel ball or a conical diamond point is used,
instead of measuring the diameter of the impression, the depth
of penetration is measured directly by a dial gauge on the
instrument. A number of indenting point with different sizes
are available for testing a variety of different material. The
rockwell hardness number (RHN) designated according to the
particular indenter and load employed.
3. Vickers hardness test
The vickers hardness test employs the same principal of
hardness testing that is used in brinell test. However, instead
of a steel ball, a square- based pyramid is used. Although the
impression is square instead of round, the method for
computation of the vickers hardness number (HV) is the same
as that for the BHN in that the load is divided by the projected
area of indentation. The lengths of the diagonals of the
indentation are measured and averaged. The vickers test is
employed in the ADA specification for dental casting gold
alloys.

38. 4.Knoop hardness test
The knoop hardness test employs a diamond-tipped tool
that is cut in the geometric configuration. The impression is
rhombic in outline, and the length of the largest diagonal is
measured. The projected area is divided into the load to
give the knoop hardness number (KHN).
o The knoop and vickers tests are classified as
microharness test in comparison with the brinell and
rockwell macrohardness test.

39. material hardness
Tooth enamel 270-380 KHN
Dentin 60-70 BHN
Porcelain(fused) 415 VHN
Yellow cast gold alloys
(hardened)
260 BHN
White gold ( as cast) 150 BHN
Amalgam 90 BHN
Co- Cr alloys 270-370 BHN
Composite restoration 25-35 BHN
Acrylic polymer( heat
cure)
18-22 BHN
Acrylic polymer ( self-
cure)
16-18 BHN
Stainless steel (cold
worked)
350 KHN
Stainless steel(soft) 180 KHN