alloy presentation

3. TERMINOLOGY
Alloy : two or more elements, at least one of which is
metal, and all of which are mutually soluble in the
molten state.

4. Classification of alloys
According to Use :
1)Alloys for all metal restorations" (e.g. inlays, posts,
crowns & bridges)
2) Alloys for metal ceramics restorations

5. According to Yield Strength and percentage
Elongation (ADA Classification)
Type I Soft
Type II Medium
Type III Hard
Type IV Extra hard

6. According to Nobility (ADA 1984)
A. High noble metal alloys
Contains greater or equal 40 wt% Au and greater or
equal 60 wt% of noble metals
B. Noble metal alloys
Contains greater or equal 25 wt% of noble metals
C. Predominantly base metal
Contains less than 25 wt% of noble metals

7. General Requirements of Casting Alloys
All cast metals in dentistry have some basic common
requirements
1) Resistance to tarnish and corrosion in the mouth.
2) Sufficiently strong for the intended purpose.
3) Biocompatible (non-toxic and non-allergic).
4)Easy to melt, cast, cut and grind (easy to fabricate).
5)Flow well and duplicate fine details during casting.
6) Minimal shrinkage on cooling after casting.
7) Easy to solder.
…

8. ALLOYS FOR ALL METAL
RESTORATIONS
. The early alloys were mostly gold alloys.. Currently, the use
of these alloys are slowly declining because of the:
1)Increased esthetic awareness has reduced the trend for
metal display.
2)Increasing popularity of all ceramic and metal ceramic
restorations.
3)Reducing popularity of resin and composite as veneering
material.

9. Classification
.
Type I Soft
Small inlays, class III and class V cavities which are not subjected to
great stress. They are easily burnished. These being highly malleable
and ductile have self-sealing margins like gold foil filling.
Type II Medium
Inlays subject to moderate stress,. They are less resistance to tarnish and
corrosion than type I.
Type III Hard
onlays, crown and bridges, situations where there may be great stresses
involved..
Type IV Extra Hard onlays subjected to very high stresses, partial
denture frameworks and long span bridges. These are less resistant to
tarnish and corrosion than type I,II and III alloys.

10. GOLD CONTENT
Traditionally, gold content of dental casting alloys was called:
1)Karat
2)Fineness.
Karat
It refers to the parts of pure gold present in 24 parts of alloy, e.g.
- 24 karat gold is pure gold.
- 22 karat gold is 22 parts pure gold and 2 parts of other metal.
" Fineness
Fineness of a gold alloy is the parts per thousand of pure gold. Pure gold
is 1000 fine.

11. PROPERTIES OF GOLD ALLOYS
Color :
modern gold alloys can vary from gold to white. It
depends on the amount of whitening elements (silver,
etc.) present in the alloy.

12. Melting Range :
Ranges between 920 to 960°C.
It indicates the type of investment required and the type
of heating source needed to melt the alloy.
Density :
, lower density more number of cast restorations per
unit weight,
. Gold alloys are lighter than pure gold
. Higher density alloys cast better than lower density
alloys.

13. Hardness :
The hardness indicates the ease with which these alloys
can be, ground or polished.
Gold alloys are generally more user friendly than the
base metal alloys which are extremely hard.
Modulus of Elasticity
Tarnish and Corrosion Resistance
. Noble metals are less reactive.
Elongation
indicates the ductility of the alloy.. Type I alloys are
easily burnished. Alloys with low elongation are very
brittle
Biocompatibility Gold alloys are relatively
biocompatible

14. Casting Shrinkage
All alloys shrink when they change from liquid to solid. The
casting shrinkage in gold alloys is less when compared
to base metal alloys.
.
Shrinkage affects the fit of the restoration. Therefore, it
must be controlled and compensated for in the casting
technique.

15. GoldGold(Au)(Au) →→
CopperCopper(Cu)(Cu) →→
SilverSilver(Ag)(Ag) →→
Corrosion resistanceCorrosion resistance
HardnessHardness
Counteract orange color of copperCounteract orange color of copper
Effects of Alloys ComponentsEffects of Alloys Components

16. PalladiumPalladium)) →→
PlatinumPlatinum(Pt)(Pt) →→
))66((ZincZinc→→
Increase strength and hardnessIncrease strength and hardness
Increase strengthIncrease strength
Prevent oxidation during meltingPrevent oxidation during melting
(O(O22 gettergetter((

17. The Minor Additions
Indium, Tin and Iron :
They help to increase the ceramic alloys bond
Calcium :
It is added to decreased CTE

18. METAL CERAMIC ALLOYS
Metal ceramic alloys are those alloys that are
compatible with porcelain and capable of bonding to
it.

19. Several types of alloys are used. All have coefficient
of thermal expansion (CTE) values which match
that of porcelain..
lithium carbonate to porcelain

20. EVOLUTION OF METAL-CERAMIC ALLOYS
In early days before porcelain-metal bonding was clearly
understood, porcelain had to be retained by
mechanical means with the help of undercuts.
Later, it was discovered that adding 1% of base metals
like iron, tin, indium, etc. induced chemical bonding
by the formation of an oxide layer.

21. REQUIREMENTS OF ALLOYS FOR
PORCELAIN BONDING
In addition to the general requirements of alloys
mentioned earlier, metal ceramic alloys have some
special requirements in order to be compatible with
porcelain veneering.
1)It's melting temperature should be higher than the
porcelain firing temperature.
2)It should be able to resist creep or sag at these
temperatures.
3) It should not stain or discolor porcelain.

22. TYPES (CLASSIFICATION) OF METAL
CERAMIC ALLOYS
Alloys for metal ceramics restorations may be
categorized as:
1)High noble (commonly referred to as gold alloys)
a) Gold-palladium-platinum alloys
b) Gold-palladium-silver alloys
c) Gold-palladium alloys

23. 2)Noble (commonly referred to as palladium alloys)
Palladium-silver alloys
Palladium-gallium-silver alloys
Palladium-gold alloys
Palladium-gold-silver alloys
Palladium-copper alloys
Palladium-cobalt alloys
3)Base metal
Nickel-chromium alloys
Nickel-chromium-beryllium alloys
Cobalt-chromium alloys
Pure titanium
Titanium-aluminum-vanadium

24. THE HIGH NOBLE (GOLD BASED)
METAL-CERAMIC ALLOYS
As mentioned earlier, the high noble alloys contain
more than 40 wt.% gold and are therefore also
referred to as gold alloys or gold based alloys

25. Common Features of High Noble (Gold
Based) Alloys
Cost.
Color the color can range from white to gold
depending on the gold content.
Melting range Porcelain is fired at a temperature
of900 to 960°C. Thus obviously these alloys must
have melting temperatures much higher than the
temperatures at which porcelain is fired.
Density (depending on the gold content).
Because of the high gold and noble metal content,
these alloys have a high density.

26. Castability the high density of these alloys make
them easy to cast
Biocompatibility high noble alloys have had a
good and safe track record. They are not
known to cause any problems in the mouth.
Soldering Gold based alloys are quite easy to
solder
Tarnish and corrosion Because of their high
noble metal content, these alloys are extremely
stable in the oral environment

27. TYPES
The following three will be briefly described.
Gold-palladium-platinum alloys
Gold-palladium-silver alloys
Gold-palladium alloys

28. Gold-Palladium-Platinum Alloys
Composition
Gold ( 80 to 88 wt%)
Palladium (5 to 11 wt%)
Platinum (6 to 8 wt%)
Silver (0 to 4.9 wt%)
Base metals ( balance around 1%)

29. Gold-Palladium-Silver Alloys
Composition
Gold (39 to 77 wt%)
Palladium (10 to 44 wt%)
Silver (9 to 22 wt%)
Base metal (balance around 1%)
The silver has a tendency to discolor some
porcelains.

30. Gold-Palladium Alloys
Composition
Gold ( 44 to 55 wt%)
Palladium (35 to 45 wt%0
Base metals ( balance around 1%)
The absence of silver eliminates the discoloration
problem.

31. THE NOBLE (PALLADIUM BASED)
METAL-CERAMIC ALLOYS
. Currently, the noble metal-ceramic alloys are mostly
palladium based.
.
. Their properties were between that of the high noble
alloys and the base metal alloys.

32. TYPES
Palladium-silver alloys
Palladium-copper –gallium alloys
Palladium- gallium

33. Common Features of Palladium Based
(Noble) Alloys
Cost their cost range between that of the gold
alloys and the base metal alloys.
Color they are white in color.
Density they are less denser than the gold alloys.
The density ranges from 10.5 to 11.5 gm/cm",
Castability these alloys have a lower density
than the gold alloys and so do not cast as well.
However, they are better than the base metal-
ceramic alloys in this regard.

34. .
Melting range a typical melting range is 1155 to
1304°C.
Porcelain bonding Like the gold alloys, base
metals like tin, indium, etc are added to assist
porcelain bonding.
Tarnish and corrosion Because of their high
noble metal content, these alloys are extremely
stable in the oral environment.
Biological considerations These alloys are very
safe and biocompatible

35. 1.PAllADIUM -SILVER AllOYS
Palladium is added to provide nobility and resistance
to tarnish.
They are white in color.
. They have a significantly lower density than gold alloy.
Their popularity has declined a little because of the
greening problem.( greenish-yellow discoloration)

36. 2.Palladium-Copper-Gallium Alloys
These are relatively new alloys..
Composition
Palladium (74 to 80 wt%)
Copper (5 to 10 wt%)
Gallium (4 to 9 wt%)
Gold (1 to 2 wt%)
Base metal (around 1 wt%)

37. Esthetics Copper does cause a slight discoloration
of the porcelain, but is not a major problem.
Black oxide layer. Care should be taken to mask this
completely with opaquer..
Castability These alloys are more technique
sensitive. Slight errors can lead to faulty castings.

38. 3.Palladium-Gallium Alloys
Composition
Palladium 75 wt%
Gallium 6 wt%
Gold 6 wt%
Base metal around 1 wt%
.

39. BASE METAL ALLOYS FOR METAL CERAMIC
RESTORATIONS
Developing countries have shown a preference
for base metal-ceramic alloys. This is because
the economic concerns
Nickel-chromium (nickel based) alloys
Cobalt-chromium (cobalt based) alloy

40. NICKEL-CHROMIUM ALLOYS
Basic elements:
Nickel 61 to 81 wt%
Chrome 11 to 27 wt%
Molybdenum 2 to 9 wt%

41. General Features and of Nickel Based
Alloys
Cost they are the cheapest of the casting alloys.
Color They are white in color.
Melting range a typical melting range is 1155 to
1304°C. The melting range of these alloys like the
gold ceramic alloys are high.
Density ranges from 7.8 to 8.4 gm/cm-'. They have
just half the density of the gold alloys making
them much lighter. One can get more castings per
gram compared to the gold alloys.

42. Castability they are extremely technique
sensitive. One reason may be their lower
density compared to the gold alloys.
Hardness and workability. They tend to be
much harder than the high noble metal
ceramic alloys.
. Yield strength ranges from 310 to 828 MPa.
These alloys are stronger than the gold and
palladium based alloys.
Porcelain bonding These alloys form an
adequate oxide layer which is essential for
successful porcelain bonding. However…
Sag resistance These materials are far more
stable at porcelain firing temperatures than the
gold based alloys. They have a higher sag
resistance.

43. COBALT CHROMIUM ALLOYS
Cobalt-chromium alloys have been available since the
1920's.
high strength.
. These alloys are also known as 'stellite' because of their
shiny, star-like appearance.
.

44. Composition
Cobalt 35 to 65%
Chromium 23 to 30 %
Nickel 0 to 20 %
Molybdenum 0 to 7 %
Iron 0 to 5 %
Carbon up to 0.4 %

45. APPLICATIONS
1)Denture base
2)Cast removable partial denture framework
3)Crowns and bridges
4)Bar connectors

46. Advantages of base metal
alloys
1) Lighter in weight.
2) Better mechanical properties
3) Less expensive than gold alloys.

47. Disadvantages
1) More technique sensitive.
2) Complexity in production of dental appliance.
3) High fusing temperatures.
4) Extremely hard, so required special equipment
for finishing.
5) The high hardness can cause excessive wear of
restorations and natural teeth contacting the
restorations.

48. TITANIUM AND ITS ALLOYS
1)excellent biocompatibility,
2)light weight,
3) good strength ability to passivate.

49. Uses in Dentistry
1)Metal ceramic restorations
2)Dental implants
3)Partial denture frames
4)Complete denture bases
5) Bar connectors
(In dentistry it is especially useful as an alternative alloy
to those who are allergic to nickel