The document discusses the mechanical and physical properties of dental materials that are important for prosthodontics. It describes key mechanical properties like stress, strain, strength, elasticity and hardness. It also outlines important physical properties such as color, viscosity, thermal expansion and corrosion resistance. Understanding the properties of dental materials helps in selecting appropriate materials that can withstand the challenges of the oral environment.

1. उ धरेदा मना मानं ना मानमवसादयेत् ।
आ मैव या मनो ब धुरा मैव रपुरा मनः ॥
- भगवान ी कृ ण

2. Mechanical and Physical
properties of dental materials
GUIDED BY PREPARED BY
DR.SAREEN DUSEJA DR.KISHAN CHAUHAN (1ST YEAR MDS)

3. Content
 Introduction
 Mechanical properties
 Physical properties
 Summary
 References
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4. Introduction
 In Prosthodontics, our principal goal is to improve and/or maintain the quality
of life of the dental patient which mostly requires the replacement of existing or
missing dentition.
 So the selection of good prosthetic material becomes very important to us.
 In the oral environment, restorative materials are exposed to various chemical,
thermal and mechanical challenges.
 We should learn properties of dental materials to understand behaviour of
particular material and how it can withstand the adverse conditions of the oral
environment.
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5. Mechanical properties
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6. Mechanical properties
 Physical science dealing with forces that acts on bodies and the resultant
motion, deformation or stresses that those bodies experience.
 Stress and Strain
 Strength properties
 Elastic properties
 Other important properties
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7. Stress
 internal reaction of material opposite to the applied external force, which is
equal in magnitude but opposite in direction to that external force.
 Stress = Force/Area, SI unit = Pascal ( Pa )
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Stress
Tensile Compressive Shear Flexural

8. Stress
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Tensile stress
Tends to stretch or
elongate a body
Compressive stress
Tends to shorten a
body
Shear stress
Sliding or twisting of
one portion of body
over another
Flexural stress
Bending forces
( compressive +
tensile )

9. Strain
 Change in length per unit length, Strain = ∆L/L
∆L
 Two types,
Elastic strain and Plastic strain
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L

10. Stress-Strain curve
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PL
YS
UTS/CS
Stress
Strain

11. Proportional limit
 Hooke’s law
elas c stress ∞ elas c strain
 material springs back after removal of force
 the point above which curve deviates from a straight line
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12. Yield Strength
 a specific amount of plastic strain
 parallel line crossing curve
 offset
 material begins to function in a plastic manner
 Ultimate Tensile/Compressive Strength is defined as the maximum stress that
a material can withstand before failure in tension/compression.
 Necking
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13.  Elastic limit
is greatest stress to which the material can be subjected such that it returns to its
original dimensions when the force is released.
 Permanent/Plastic deformation
occurs when material is deformed by stress at a point above the proportional
limit before fracture,
removal of the applied force will reduce the stress to zero but the plastic strain
remains and the object does not return to its original dimension when the force
is removed,
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14. Cold working
 repeated plastic deformation
 beyond their proportional limits
 lead to embrittlement ( reduced plasticity )
 to deform metal in small increments
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15. Young’s modulus
 relative stiffness or rigidity
 stress below the proportional limit
divided by its corresponding strain
 constant of proportionality
 slope of straight line ( elastic range )
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16.  Flexibility the flexural strain that occur when the material is stressed to its
proportional limit
 Poisson’s ratio within elastic limit, ratio of lateral to axial strain
 most rigid materials exhibit a Poisson's ratio of about 0.3
 most ductile materials such as soft gold alloys, show a high degree of reduction
in cross sectional area and higher Poisson's ratio
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17. Resilience
 amount of energy absorbed within a unit volume of a structure when it is
stressed to its proportional limit
 stress is not greater than proportional limit, elastic energy is absorbed
 so restorative material should exhibit a moderately high elastic modulus and
relatively low resilience
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18. Toughness
 ability of a material to absorb elastic energy and to deform plastically before
fracturing
 total area under a plot of tensile stress vs tensile strain
 defined as the amount of elastic
and plastic deformation energy
required to fracture a material
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19. Brittleness
 relative inability of a material to sustain plastic deformation before fracture
e.g. amalgams, ceramics, composits
 they sustain little/no plastic strain, fracture at or near the proportional limit
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20. Ductility
 ability of a material to sustain a large permanent deformation under a tensile
load before it fractures
 forming into wire
 decreases as the temperature is raised
 Au>Ag>Pt>Ni>Cu
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21. Malleability
 ability of the material to withstand rupture under compression
 hammering or rolling into a sheet
 increases with rise in temperature
 Au>Ag>Al>Cu
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22. Hardness
 in metallurgy resistance to indentation and in minerology resistance to
scratching
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Macro
hardness
Brinell
Rockwell
Micro
hardness
Vickers
Knoop other
Shore
Barcol

23. 
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Brinell Steel ball Diameter of
indentation
Metals
Rockwell
Conical
diamond
pointer
Depth of
penetration
Widely used due
to convenience
Vickers Square based
pyramid
Diagonal
length
Brittle materials,
small specimens
Knoop Rhombohedral
pyramid
Length of
largest
diagonal
Both hard and
soft materials

24. 22:47 DR.KISHAN CHAUHAN 24

25. Shore and Barcol test
 less sophisticated
 rubber and plastic types dental materials
 resistance to indentation
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26. Physical properties
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27. Physical properties
 Based on structure and basic nature of materials, it includes atomic structure,
nuclear phenomena, optics, electronics and also thermodynamics.
 Rheology
 Color and optical effects
 Thermal properties
 Electrochemical properties
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28. Viscosity
 Rheology is study of flow characteristics of materials and its deformation
 Viscosity is resistance of a liquid to flow
 measured in poise ( Mpa/sec )
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29.  to explain viscous nature of some materials , shear stress v/s shear strain rate
curve can be plotted
Newtonian fluid
 an ideal fluid
 shear stress proportional to strain rate
 straight line of curve
 constant velocity under pressure
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30. Pseudoplastic fluid
 viscosity decreases with increasing strain rate, until it reaches a
nearly constant value e.g. ketchup, blood, nail-polish
Dilatant fluid
 viscosity increase with increasing stress
 material become more rigid under stress e.g. acrylic denture base
material
Plastic fluid
 material behaves rigid until a minimum of stress is applied ,then it
starts behaving like Newtonian fluid, e.g. clay, composite material
30

31. Creep
 time dependent plastic strain of material under static or constant
stress
 metals creep when temperature approaches hundreds of degrees
of its melting range, e.g. cast restorations
Flow
 measure of potential to deform under a small static load, even
associated with its own mass, e.g. is dental waxes
31

32. Color
 sensation induced from light of varying wavelengths reaching eye
 cone cells of retina
 approximately 400nm (violet) to 700nm (dark red)
32

33. 3 dimension of color
Munsell System ( Qualitative )
 Hue, particular variety
 Value, relative lightness
or darkness
 Chroma, degree of saturation
33

34. CIE LAB color system ( Quantitative )
 Commission Internationale del’Eclairage (CIE)
 L* represents the value of an object
 a* is the measurement along the red-green axis
 b* is the measurement along the yellow-blue axis
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35. Metamerism
 objects that appear to be color-matched under one type of light may appear
different under another type
35

36. Fluorescence
 absorption of light by a material and the spontaneous emission of light in a
longer wavelength,
 primarily occurs in the dentin, higher amount of organic material
 UV light is absorbed and fluoresced back in blue section
36

37. Dental Shade guides
 VITA Classical introduced in 1956 still is widely used for shade matching in
dentistry, It has 16 shade samples ( A1 to D4 )
37

38. 38
 VITA 3D-MASTER introduced in 1998, 26 shades divided into group 1 to 5
 First number i.e. 1-5 represent Value
 Letter L, M, R represent Hue from yellowish to reddish
 The second number designates Chroma

39. 39

40. Tips for shade taking
 tooth should be clean, hydrated
 daylight or standardized daylight lamps
 quickly
 avoid bright colors in the shade-taking environment
 selection distance, one to three feet
 cervical aspect
 specimens one at a time by holding them next to the tooth
40

41. Coefficient of thermal expansion
 change in length per unit of the original length per unit of a material when its
temperature is raised 10 K
 expressed in units of mm/m K or ppm/ K
 close matching of the coefficient of thermal expansion (α) is important
between the tooth and the restorative materials to prevent marginal leakage
ex., Enamel 11.4, Dentin 8.3
GIC 10.2-11.4, Porcelain 12.0, Amalgam 22.1-28.0, Composite 14-50
41

42. Tarnish
 is a surface discoloration of the metal or even a slight loss of the lustre,
 formation of hard and soft deposits on the surface,
 thin films of oxides, sulphides or chlorides,
 first step of corrosion,
42

43. Corrosion
 disintegration of a metal by reaction with its environment
 stain or discoloration arises from pigment producing bacteria, drugs, chemicals
and absorbed food debris
 although deposits are the main cause of the tarnish in the oral environment
 surface discoloration may also arise on a metal from the formation of thin films
such as oxides, sulfides, or chlorides
e.g. rusting of iron, a complex chemical reaction in which iron combines with
oxygen in air and water to form hydrated oxide of iron
43

44. 44
Corrosion
Chemical/dry
Electrochemical
/wet
Dissimilar metals
Heterogeneous
surface
Stress corrosion
Concentration
cell corrosion

45. Dry/Chemical corrosion
 direct combination of metallic and non-metallic elements
 electrolytes are absent, e.g. oxidation, halogenations, sulfurization
 less susceptible to occur in the mouth
 oxidation of metal surface during soldering and heat treatment procedures
45

46. Wet/Electrolytic corrosion
 corrosion occurs in presence of water or some other liquid electrolytes
 Galvanic cell corrosion
 Heterogeneous surface composition
 Stress corrosion
 Concentration cell corrosion
46

47. Galvanic cell corrosion
 difference in potential between dissimilar restoration in opposing or adjacent
tooth
 Galvanic shock, pain sensation caused by electric current generated by a
contact between two dissimilar metal forming a galvanic cell in oral environment
47

48. Heterogeneous surface composition
 different compositions of the metal surface, Ex.eutectic and peritectic alloys
 metallic grains with the less electrode potential are attacked and corrosion
results, Ex. amalgam restorations with polished and unpolished area
48

49. Stress corrosion
 combined effect of mechanical stress and corrosive environment
 usually in form of cracking
 ex. burnishing produces the localized stress in some part of structure
 if stressed metal is in contact in an electrolyte the stressed area will become
anode and will corrode
49

50. Concentration cell corrosion
 homogeneous metal or alloy can undergo electrolytic corrosion when there is a
difference in electrolyte concentration across the specimen
 ex. a metallic restoration which is partly covered by food debris will differ from
that of saliva, and this can contribute to the corrosion of the restoration
50

51. Protection against corrosion
 a thin, adherent, highly protective film : passive metals
 a thin surface oxide forms on chromium, is e.g. of a passivating metal, stainless
steel contain sufficient amounts of chromium to passivate the alloy
 avoid using dissimilar metals
 warned against using household bleaches for partial denture framework
 the surface of any dental restoration should be smooth, lustrous, polished,
provides easier cleaning and prevents accumulation of debris
51

52. References
• Phillips’ : Science of dental materials. 12th Ed.
• Craig’s restorative dental materials. 12th Ed.
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53. • Next will be Journal club presentation by Dr. Dipali Mungra.
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Thank you !!