This document discusses various aspects of casting alloys used in dentistry. It defines key terminology related to alloy composition and properties. Common metallic elements used in dental alloys are categorized as noble metals or base metals. Desirable properties for dental casting alloys include biocompatibility, corrosion resistance, and strength requirements. Alloys are classified based on their total noble metal content. Common heat treatments for dental alloys like homogenization, softening, and hardening are explained. Common alloys used for all-metal and metal-ceramic restorations are highlighted.

1. CASTING ALLOYS
Dr Sakshi
II Yr PG
Dptmnt of Prosthodontics
1

2. Introduction
• Alloy-combination of two or more metals
• Applications-all metal restorations,RPD,PFM
2

3. Terminology
• Eutectic alloys- the component metals have
melting temperatures close to each other
• Peritectic alloys- the melting temperatures of
the component vary in range
• Solidus temperature- first solid particle
liquifies
• Liquidus temperature- last solid particle
liquifies
3

4. 4
Metallic Elements Used In Dental Alloys
Noble Metals
• Gold
• Platinum
• Palladium
• Iridium, Ruthenium
and Rhodium
• Osmium
Base Metals
• Silver
• Copper
• Zinc
• Indium
• Tin
• Gallium
• Nickel

5. Desirable properties of Dental Casting
Alloys
• Biocompatibility
• Corrosion resistance
• Tarnish resistance
• Allergenic components in casting alloys
• Esthetics
• Thermal properties
• Melting range
• Compensation for solidification
5

6. Desirable properties contd…
• Strength requirements
• Fabrication of cast prostheses and frameworks
• Castability
• Finishing of cast metal
• Porcelain bonding
• Economic considerations
• Laboratory costs
6

7. Classification of dental casting alloys
• Alloy classification of the American Dental Association 1984
ALLOY TYPE TOTAL NOBLE METAL CONTENT
High noble(HN) Must contain > 40 wt% Au and >60 wt%
of noble metal elements(Au, Pt, Pd, Rh,
Ru, Ir,Os)
Noble (N) Must contain >25wt% of noble metal
elements(Au, Pt, Pd, Rh, Ru, Ir,Os)
Predominantly Base
Metal(PB)
Contain <25 wt% of noble metal elements
7

8. • May also be classified according to their
composition , their dental use or the relative
level of stress that the metal prosthesis will
sustain
• ISO/DIS 1562 Standard for casting gold alloys
lists 4 classes of gold alloys for all-metal
prostheses or resin-veneered prostheses:
• Type 1: Low strength-for castings subjected to
very slight stress(e.g. inlays), min Yield
strength-80 Mpa, min % elongation 18%
8

9. • Type 2: Medium strength-for castings subjected to
moderate stress(e.g. inlays,onlays and full crowns), min
yield strength- 180 Mpa, min %age elongation- 10%
• Type 3: High strength- for castings subjected to high
stress(e.g onlays, thin copings, pontics, crowns and
saddles) min yield strength- 270 Mpa
• Type 4: Extra-high strength- for castings subjected to
very high stress(e.g. saddles, bars, clasps, thimbles,
certain single units and partial denture frameworks)
min yield strength -360 Mpa, min %age elongation- 3%
9

10. 10

11. 11
RPD
Metal-Ceramic / All-Metal
Restorations
All-Metal
Restorations
Restoration
TypeAlloy Type
Pure Ti
Ti-Al-V
Ni-Cr-Mo-Be
Ni-Cr-Mo
Co-Cr-Mo
Co-Cr-W
Pure Ti
Ti-Al-V
Ni-Cr-Mo-Be
Ni-Cr-Mo
Co-Cr-Mo
Co-Cr-W
Base Metal
< 25 wt% of the
noble metal
elements
Ag-Pd-Au-Cu
Ag-Pd
PA (no Ag)
PAA
PA
PCG
PGA
Ag-Pd-Au-Cu
Ag-Pd
Noble
> 25 wt% of the
noble metal
elements
Au-Ag-Cu-PdAPA (5-12 wt% Ag)
APA (>12 wt% Ag)
AP (no Ag)
Au-Ag-Cu-PdHigh Noble
> 40 wt% Au,
> 60% of noble
metal elements

12. RPD
Metal-Ceramic and All-Metal
Restorations
All-Metal
Restorations
Restoration
TypeAlloy Type
Pure Ti
Ti-Al-V
Ni-Cr-Mo-Be
Ni-Cr-Mo
Co-Cr-Mo
Co-Cr-W
Pure Ti
Ti-Al-V
Ni-Cr-Mo-Be
Ni-Cr-Mo
Co-Cr-Mo
Co-Cr-W
Base Metal
< 25 wt% of the
noble metal
elements
Ag-Pd-Au-Cu
Ag-Pd
Pd-Au (no Ag)
Pd-Au-Ag
Pd-Ag
Pd-Cu
Pd-Co
Pd-Ga-Ag
Ag-Pd-Au-Cu
Ag-Pd
Noble
> 25 wt% of the
noble metal
elements
Au-Ag-Cu-PdAu-Pt-Pd
Au-Pd-Ag) (5-12 wt% Ag)
Au-Pd-Ag (>12 wt% Ag)
Au-Pd (no Ag)
Au-Ag-Cu-PdHigh Noble
> 40 wt% Au and >
60% of the noble
metal elements
12

13. Reasons that alloys for all-metal restorations cannot be
used for metal-ceramic restorations
• The alloy may not form thin, stable oxide
layers to promote atomic bonding to porcelain
• Their melting range may be too low to resist
sag deformation or melting at porcelain firing
temperatures
• Their thermal contraction coefficients may not
be close enough to those of commercial
porcelains
13

14. Noble metals
• Used traditionally for inlays, crown and bridge
and metal-ceramic alloys because of their
tarnish and corrosion resistant property.
14

15. Predominantly Base Metal alloys
• Based on more than 75 wt% of base metal
elements or less than 25 wt% of noble metals
• Invaluable components of dental casting alloys
because of their –low cost
- influence on weight
- strength
- stiffness
- oxide formation
15

16. • More reactive with environment
• Cobalt and Nickel-based alloys derive their
corrosion resistance from the passivating
effect of chromium
• Also referred as non-precious or non-noble
alloys
16

17. Identification of alloys by principal
elements
• Classified based on the principal or most
abundant element(e.g a Palladium-based
alloy)
• Or named on the basis of the two or three
most important elements(e.g Ni-Cr or Ni-Cr-Be
alloys)
• Casting alloys can be based on Au,
Pd,Ag,Ni,Co,Cu or Ti as the principal element
17

18. 18

19. 19
CORING (Inhomogenous / Heterogenous
Alloy)
• When a solid-solution alloy is
cooled rapidly, as during
casting,the composition of a
rapidly cooled dendrite or
grain is not uniform.

20. 20
CORING (Inhomogenous Alloy)
• For example, the first embryo or
nucleus that forms at any higher
temperature is rich in Palladium, but
as the temperature decreases, the
palladium content decreases with an
increase in the silver content as each
succeeding layer solidifies. The
palladium content of the liquid
phase decreases, but its silver
content increases as the
solidification temperature is
approached.

21. 21
CORING ( Inhomogenous Alloy )
• With slow cooling, diffusion &
random distribution of atoms results,
with no coring.
• Rapid cooling quickly denies the alloy
the energy & mobility required for
diffusion of atoms to occur & the
cored structure is locked in at low
temperatures.

22. 22
CORING (Composition differences)
• Reducing the cooling rate
• Eliminates coring
• Produce an alloy with large
grain size
• Inferior mechanical
properties

23. 23
CORING ( Composition differences)
• At the solidification
temperature T the
composition of the outermost
layer of the dendrite is 65%
Palladium & 35% Silver. The
last liquid to solidify is rich in
Silver & solidifies between
the dendrites.

24. 24
CORING (Composition differences)
• Therefore, a cored structure
results, with the core
consisting of the dendrites
composed of compositions
with higher solidus
temperatures & the matrix
containing compositions
with a lower solidus.

25. 25
CORING (Heterogenous Structure)
• The potential of coring is
greater when there is a
wide separation of
solidus & liquidus lines.
• Example: Peritectic
alloys.

26. 26
CORING (Composition differences)
• DISADVANTAGE:
• Inferior mechanical properties
• Corrosion resistance of alloys is
reduced.
Heat treatment is sometimes used to eliminate
the cored structure.

27. 27
HEAT TREATMENT OF HIGH
NOBLE AND NOBLE METAL
ALLOYS:

28. 28
HOMOGENIZATION
• In coring, rapid cooling of the alloy results in
the so called cored structure. The atoms tend
to diffuse to reduce segregation.
• Under conditions of equilibrium, the alloy
composition should be 65% Palladium & 35%
Silver throughout, and atomic diffusion
during cooling controls such a situation.

29. 29
HEAT TREATMENT OF HIGH NOBLE AND NOBLE
METAL ALLOYS:
• HOMOGENIZATION:
The cast alloy is held at a temperature near its
solidus temp to achieve the maximum amount of
diffusion without melting (up to a period of 6 hours
in some instances)
This treatment allows atomic diffusion to occur
which eliminates as-cast compositional non-
uniformity.

30. 30
HEAT TREATMENT OF HIGH NOBLE AND NOBLE
METAL ALLOYS:
• This treatment results in:
1: Increase in tarnish and corrosion resistance.
2: increase in the ductility of the alloy.

31. 31
HOMOGENIZATION
• Faster the alloy is cooled from its
liquidus temperature, the more nearly
the cored compositions are approached.
• During slow cooling, there is greater
atomic diffusion & greater probability of
achieving equilibrium.

32. 32
HOMOGENIZATION
• If the alloy is cooled rapidly from its liquidus
temperature, the coring can be relieved by a heat
treating process.
• The alloy is held at a temperature near its solidus
temperature so that solid-state atomic diffusion
can occur.
• Little or no grain–growth occurs when a casting is
heat treated.

33. 33
HOMOGENIZATION
• This heat treating process
of cast alloy to eliminate
composition differences
caused by coring is called
as homogenization.

34. 34
Purpose of heat treatment
(1)Soften the metal prior to shaping;
(2)Relieve the effects of strain hardening that
occurs during cold forming;
(3)Achieve the final strength and hardness
required in the finished product as one of the
end manufacturing processes.

35. 35
SOFTENING HEAT TREATMENT / SOLUTION HEAT
TREATMENT:
• It involves heating the casting to a temperature
below the solidus (usually 700 degree Celsius),
holding for a short period of time (typically 10
min) so that the alloy returns to random
substitutional solid solution , and then quenching
to retain this atomic arrangement at room
temperature.
• Indicated prior to adjusting, burnishing and
polishing

36. 36
SOFTENING HEAT TREATMENT
• Heating casting to temperature 700°C
• Holding for 10 min
• Quenching
Heat -> Soaking -> Cooling

37. 37
SOFTENING HEAT TREATMENT / SOLUTION HEAT
TREATMENT:
• DECREASE IN:
A. Tensile strength,
B. Hardness and
C. Proportional limit
• INCREASE IN:
---Ductility.
This treatment is indicated for structures
that are to be ground, shaped or otherwise
cold worked, either in or out of the mouth.

38. SOFTENING HEAT TREATMENT
• Any minor adjustments, such as bending of
clasps, etc., are made at this stage whilst the
alloy is still in the softened state.
• If adjustments are made, a low temperature
stress relief anneal should be carried out.
38

39. 39
HARDENING HEAT TREATMENT
• The age hardening of the dental alloys can be
accomplished in several ways. One of the most
practical hardening treatments is by SOAKING
or AGEING the casting at a specific temperature
for a definite time, usually 15 to 30 minutes,
before it is water quenched.
• The ageing temperature depends on the alloy
composition but is generally between 200 and
450 degree Celsius.

40. 40
HARDENING HEAT TREATMENT/ AGE
HARDENING TREATMENT
• This treatment is
indicated for metallic
partial dentures,
bridges and other
similar structures.

41. 41
HARDENING HEAT TREATMENT
• Heating casting to temperature above
450 degree Celsius
• 15-30 minutes
• Slow cooling till temp drops 200
•
• Quenching

42. 42
HARDENING HEAT TREATMENT /AGE HARDENING:
• INCREASE IN:
• Tensile strength
• Hardness
• Proportional limit
• DECREASE IN:
---Ductility.
Indicated for metallic partial dentures, saddles,
FPDs

43. REPOLISHING
• Following hardening the casting is repolished
and, in the case of a denture, the teeth are
added in order to complete the job.
43

44. HEAT TREATMENTS
• Ideally, all hardening and softening heat
treatments should be carried out in a
pyrometrically controlled furnace.
• The castings should be supported by sand or
another refractory material in order to
prevent ‘sag’ at elevated temperatures.
44

45. Casting shrinkage
• Occurs in 3 stages:
1. Thermal contraction of the liquid metal
between the temperature to which it is
heated and the liquidus temperature
2. Contraction of the metal inherent in its
change from the liquid to the solid state
3. Thermal contraction of the solid metal occurs
on further cooling to room temperature
45

46. 1. Alloys for all-metal and resin-
veneered restorations
a) Silver-Palladium alloys
b) Nickel-Chromium and Cobalt- Chromium
alloys
c) Titanium and Titanium alloys
46

47. a)Silver-Palladium alloys
• White, predominantly silver in composition
• <25% Palladium-provides nobility and promotes
tarnish resistance
• May or may not contain copper and a small
amount of gold
• Casting temperatures in the range of yellow
gold alloys
• Limitation-tarnish and corrosion
47

48. b)Ni-Cr and Co-Cr alloys
• Rarely used for all-metal restorations
• Described under metal-ceramic prostheses
section
48

49. c)Titanium and titanium alloys
• Used for all-metal and metal-ceramic
prostheses,implants and removable partial
denture frameworks
• Most biocompatible metal used for dental
prostheses
• Known as Commercially pure Titanium(CPTi)
49

50. • Acc to American Society for Testing and
Materials(ASTM), 5 unalloyed grades of CP Ti
(Grades 1-4 and Grade 7),based on
concentration of oxygen(0.18wt% to 0.40wt%)
and iron (0.2wt% to 0.5wt%)
• Other impurities include nitrogen(0.03wt%to
0.05wt%), Carbon (0.1wt%)and
hydrogen(0.015wt%)
50

51. Grade 1 CPTi-
• purest and softest form
• moderately high tensile strength(240 Mpa)
• moderately high stiffness(MOE-117GPa)
• low density(4.51g/cm3)
• Low thermal expansion coefficient (9.4X10 -6
/0C)
51

52. • MOE comparable to that of enamel and noble alloys
but lower than other base metal alloys
• Very resistant to tarnish and corrosion
• Corrosion protection derived from a thin (10nm)
passivating oxide film that forms spontaneously
• Because oxidation rate of titanium increases
markedly above 900°C,it is desirable to use ultralow-
fusing porcelains(sintering temperature<850°C) for
titanium-ceramic prostheses
52

53. • High melting point(1668°C)
• Special casting machine with arc-melting
capability and an argon atmosphere is
typically used along with compatible casting
investment
• Because of the reaction with investment, a
very hard so-called alpha case having a
thickness of approximately 150 µm forms at
the surface of cast dental titanium alloys
53

54. • For cast CPTi, the HV increases from a bulk value
of nearly 200 approx 650 at a depth of 25 µm
below the surface and special tools are required
in the dental lab for finishing and adjusting CPTi
castings
• Because of the presence of Alpha case, special
surface modifications of cast titanium ,using
caustic NaOH-based solutions or silicone nitride
coatings employed to improve bond between
cast CPTi and dental porcelain
54

55. • Has highest melting temperature and is highly
resistant to sag deformation of metal
frameworks at porcelain sintering temperatures
• Low thermal expansion coefficient
• Low-expansion dental porcelains necessary for
bonding to titanium
55

56. • CPTi undergoes allotropic transformation from
a hexagonal close-packed crystal structure (α
phase) at 885°C to a body-centered crystal
structure (β phase)
• 4 possible types of Ti alloys can be produced
- α
- Near-α
- α-β
- β
56

57. • α alloy-form no β phase on cooling
• Near-α phase alloy-form limited β phase on
cooling
• α-β alloy contain α phase at room temperature
and may contain retained β phase and or
transformed β phase
• β alloy retain β phase on cooling and can
precipitate other phases as well
57

58. • Vanadium- one of the alloying elements
• Has bcc structure
• Isomorphous with β phase
• β phase stabilizer
• Causes transformation from β phase to α phase
to occur at lower temperatures on cooling
58

59. • Aluminium
• α phase stabilizer
• Causes transfromation of α phase to β phase to
occur at a higher temperature on heating
• Aluminium,tin and Zirconium –soluble in both
α and β phases.
59

60. • Ti-6Al-4V- most widely used alloy in dentistry
• α –β alloy
• Has greater strength than CPTi but not as
biocompatible
60

61. 2) High Noble and Noble alloys for
Metal-Ceramic prostheses
• Share at least 3 common features:
1. Have the potential to bond to dental
porcelain
2. Possess Coefficient of Thermal Contraction
compatible with those of dental porcelains
3. Solidus temperature sufficiently high to
permit the application of low-fusing
porcelains
61

62. 62
Ceramic-Metal Bond
• Typically, COTE of porcelain = 13.0 to 14.0 x 10-6/°C
and the metals = 13.5 to 14.5 x 10-6/°C .
• The difference of 0.5 x 10-6/°C causes the metal to
contract slightly more than does the ceramic during
cooling after firing the porcelain.
• This condition puts the ceramic under slight residual
compression, which makes it less sensitive to applied
tensile forces.

63. 63

64. Sag deformation
• These alloys must have a thermal expansion
/contraction coefficient that is comparable to or
slightly greater than that of the veneering
porcelain
• Must have sufficiently high melting range to
avoid sag deformation or melting during
sintering of porcelain veneers
64

65. Sag-deformation in a fixed partial denture framework
65

66. Sag deformation can be corrected in
any of the following ways:
1. The FPD can be sectioned and soldered to
obtain an acceptable fit on the prepared dies
2. Cast-joining of the bridge sections can be
performed . This includes
Placing undercut slots in the walls of the sectioned
pieces for mechanical retention, indexing the
units, waxing and spruing, investing and burning
out the wax or resin and casting new metal into
the sectioned area
66

67. 3. Remake of the cast structure with a sag-
resistant alloy
67

68. Gold-Palladium-Silver alloys(low silver
content)
• Contain 5% to 11.99% Ag
• Composition
– Au (45-52%); Pd (26-31%); Ag (5-12%); In, Sn (5-7%)
– (high noble)
• Excellent resistance to tarnish and corrosion
• No technique sensitivity associated with porcelain bonding
and thermal contraction
• Disadvantage- porcelain discoloration when silver vapour is
released and deposited on porcelain surface
68

69. • Advantages
– Higher melting range
– Better sag and creep resistance
– Higher yield strength and MOE
for long span FPDs
– Good castability
– Easily finished and polished
– Non-toxic and lower cost v.s. Au-
Pt-Pd alloys
69
Disadvantages
Ag may cause greening of
porcelain.
White color may show through
tissues as gray and may not be
as acceptable as gold collars.
High Pd content may increase
the risk of H2 gas absorption
during casting, and bonding of
porcelain may be affected by
oxidizing procedures

70. Gold-Palladium-Silver alloys(high Silver
content)
• Contains 12% Ag or more
• White colored
• Used because of their lower cost and
comparable physical properties
• Improved resistance to creep
deformation(sag)
• Difficult to burnish
• Porcelain discoloration
70

71. Gold-Palladium alloys
• Designed to overcome porcelain discoloration
effect
• Excellent castability,corrosion resistance and
adherence to porcelain
• E.g. Olympia, Lodestar, Argedent 65SF
71

72. • Composition
– Au (45-52%); Pd (38-45%); In (8.5%); Ga (1.5%)
– (high noble)
• Advantages
– same as for Au-Pd-Ag alloys with the addition of
potentially better porcelain color due to lack of Ag
• Disadvantages
– same as for Au-Pd-Ag alloys with the exception of
porcelain greening
72

73. Palladium-Gold Alloy
• Less popular because of price volatility
• No procelain discoloration
Palladium-Gold-Silver alloy
• Porcelain discoloration
• High range of thermal contraction coefficients
73

74. 74
Gold-Platinum-Palladium Alloys
(Au-Pt-Pd)
• Composition
– Au (84-86%); Pt (4-10%); Pd (5-7%); Ag (0-5%); Fe,
In, Sn (2-3%)
– (high noble)
• Advantages
– Excellent bonding to porcelain
– Reproduces fine margins and occlusal detail
– Easily finished and polished
– Corrosion resistant and non-toxic
– Adequate yield strength and MOE (most cases)

75. • Disadvantages
– low sag and creep resistance
– not strong enough for long span FPDs
– High cost
75

76. Palladium-Silver Alloys
(Pd-Ag)
• Composition
– Pd (53-88%); Ag (30-37%); In (4-7%); Sn (4-7%)
– (noble)
• Advantages
– High yield strength and MOE
– Better sag and creep resistance
– Non-toxic and low cost
• Disadvantages
– Castability < gold alloys
– High Ag porcelain greening, ↓bonding
– High Pd  ↑gas absorption and poor color
76

77. 77
High Palladium Alloys
• Composition
– Pd (74-88%); Cu (10-15%); Ga (9%); Au (0-2%); Co (4-5%);
In (0-5%)
– (noble)
• Advantages
– High yield strength and sag and creep resistance
– Non-toxic, low cost
– Castability = gold alloys (easy)
– Excellent porcelain color

78. 78
High Palladium Alloys
• Disadvantages
– Porcelain bond strength may be variable.
– High Pd content  ↑ H2 gas absoption, poor solderability
– Can’t be used with carbon investments or crucibles
• Carbon or Silicon contamination will cause brittle castings which
may crack or tear at grain boundaries under stress.

79. Palladium-Silver alloys
• First gold free noble alloy
• Occasionally called semi-precious alloys
• Composition-53-61% Pd
28-40% Ag
Tin and Indium added to
increase alloy hardness and to promote oxide
formation and adequate bonding to porcelain
79

80. • Silver discoloration effect most severe because
of high silver content
• Adherence to porcelain- acceptable
• Thermal compatibility good
80

81. Palladium-Copper-Gallium alloys
• Very popular in 1990s
• Dark brown or black oxide layer formed during
oxidation and subsequent porcelain firing cycles
• Mask this oxide layer with opaque procelain
Palladium-Gallium-Silver alloy
• Lighter-colored oxide layer than Pd-Cu alloys
• Thermally compatible with lower expansion
porcelains
• Lower hardness-can be adjusted in lab and chair
side
81

82. 82
Palladium in PFM Alloys
• Hardens the alloy
• Whitens the alloy
• Increases the alloy’s casting temp.
• Increases the alloy’s MOE
• Renders silver tarnish resistant
• Decreases the alloy’s density
• Decreases the alloy’s thermal coef. of exp.

83. • Copper (Cu) ***
– Principle hardener in gold alloys
– Conc. >12% of Au amount  alloy can be heat
treated
– Conc. >18%  decrease the melting temp of the
alloy
83

84. • Copper (Cu) ***
– When alloyed with Ag, Cu increases the alloy’s hardness
and decreases melting temp.
– Cu imparts a reddish color to the metal and contributes
most to the corrosion of gold alloys.
– Ag/Cu ratio is important to tarnish resistance (but not as
important as the Ag/Pd ratio).
– Cu is not found in PFM alloys due to its tendency to
discolor the porcelain.
84

85. Zinc (Zn)
– O2 scavenger
– 1-2% helps to
counteract the
absorption of O2 by
silver.
– Increases the
castability, decreases
porosities, and
increases the hardness
and brittleness of the
alloy
85
Indium (In), Tin (Sn),
Iron (Fe)
Hardens the alloy
(Provides oxides
for ceramic
bonding in PFM
alloys)

86. 86
• Iridium (Ir),
Ruthenium (Ru),
Rhenium (Rh)
– Grain refining
Gallium (Ga)
Added to high Pd
alloys or non-silver
Au/Pd metal ceramic
alloys to compensate
for a decrease in the
TCOE caused by the
elimination of the Ag.
(Also provides oxides
for ceramic bonding)

87. 87
Minor Elements in PFM Alloys
• In, Sn, Fe, Ga - provide metallic oxides for porcelain
bonding, and harden the alloy.
• Ga - increases the thermal coef. of exp. to
compensate for decreased or absence of Ag.

88. Discoloration of Porcelain by silver
• Colloidal dispersion of silver atoms entering
body and incisal porcelain or glazed surface
from vapor transport or surface or surface
diffusion may cause color changes, including
green, yellow-green, yellow-orange, orange
and brown hues. Generally called greening
88

89. • Certain porcelains resistant to silver
discoloration
• 2 metal coating agents may be used to reduce
porcelain discoloration effects
• Pure gold film can be fired on a metal
substrate to reduce surface silver
concentration
89

90. • Ceramic conditioner can also be fired on the
metal surface as a barrier between the alloy
and porcelain
• Neither of these procedures recommended as
cause an extra layer may reduce the metal-
porcelain bond strength
90

91. Thermal compatibility and
incompatibility of metal-ceramic systems
• Ability of a metal and its veneering porcelain
to contract at similar rates
• Clinical success of porcelain-veneered
restorations also depends on acceptable
adherence ,framework or coping fit, esthetics
and the absence of high residual tensile stress
91

92. • Transient stress- instantaneous stress at given
temperature during the cooling cycle
• Residual stress- stress distribution which exists
at room temperature
92

93. Partial denture alloys
• Made from alloys based primarily on Nickel,
Cobalt or Titanium as the principal metal
component
• Nickel-malleable, ductile, silver-colored
transition element, melting point-1450°C
• Cobalt-silver-colored transition element,
melting point- 1500°C
• Chromium-added to prevent corrosion and
tarnish
93

94. Base metal alloys for cast metal and
metal-ceramic prostheses
• Reasons for the use of nickel-chromium alloys
in dentistry:
1. Nickel combined with chromium to form a
highly corrosion resistant alloy
2. Ni-Cr alloys-popular in 1980s as low cost
metals
3. Ni-Cr and Ni-Cr-Be alloys relatively
inexpensive
94

95. • 4. Nickel alloys have excellent mechanical
properties such as high elastic modulus
(stiffness), high hardness and a reasonably
high elongation(ductility)
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96. Biological hazards and precautions
• Beryllium dust and vapour –contact dermatitis
to severe chemical pneumatitis
• Coughing,chest pain, general weakness to
pulmonary dysfunction
• Nickel- contact dermatitis
96

97. Alternatives to cast-metal technology
1. Sintering of burnished foil
2. CAD-CAM processing
3. Copy milling
4. Electroforming
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98. 1. Sintering of burnished foil
• Most commonly used commercial foil system-
a) Captek P and Captek G-used to fabricate
crown copings and FPD abutments
b) Capcon and Capfill-used to connect copings
c) Captek Repair Paste and Capfill –add
materials to Captek structures
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99. • Captek copings contain 88.2 wt% Au, 9.0wt%
Pt, 2.8wt% Ag.
• Coping made with a thickness of 0.25mm for
anterior crowns and 0.35mm for posterior
crowns
• Advantage- very low metal thickness achieved
ensures minimal tooth reduction
or improved esthetics
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100. 2. CAD-CAM processing
• Developed in early 1980s to produce ceramic
inlays and crowns
• Optical scanning procedure eliminates the
need for an impression
• Homogenous ,high quality materials with
minimal porosity
• Could also be used to prepare prostheses from
CPTi or Ti-6Al-4V alloy
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101. 3. Copy milling
• Tracing the surface of a pattern that is then
replicated from a blank of ceramic ,composite
or metal that is ground,cut or milled by a
rotating wheel whose motion is controlled by
a link through the tracing device
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102. 4. Electroforming
• Master cast of prepared tooth prepared and
coated with a special die spacer to facilitate
separation of the duplicating material
• Dies duplicated with a gypsum product
• After applying a conductive silver layer to its
surface,die is connected to a plating head and
connected to a power source and then placed
in a plating solution
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103. • After a sufficiently thick layer of gold or other
metal is deposited, the gypsum is removed
and the coping is sandblasted
• The coping is then coated with a bonding
agent during the wash bake,and subsequent
ceramic layers are condensed and sintered in a
conventional way
103

104. Thank you
104