| Au |
Gold
Soft, malleable yellow-colored metal.
While considered by many to be an ideal
dental material, in its unalloyed state
gold lacks sufficient strength and stiffness
for any dental application aside from
heavily cold worked, small direct foil
inlays.
Gold rich alloys have been used in
dentistry for centuries. Gold is noble
(inert) in the mouth, extremely malleable
for uncompromising marginal adaptation,
and similar to natural dentition in
terms of thermal expansion. Gold's kindness
to opposing dentition is unparalleled.
The longest lasting dental restorations
available at any price are properly
executed gold castings and foil inlays.
Gold adds to the color, tarnish and
corrosion resistance, and malleability
of an alloy. By itself, its thermal
expansion is too high to be used with
most commercial porcelains. It is therefore
useful to raise the thermal expansion
of palladium. Gold also increases the
density of an alloy.
|
| Pd |
Palladium
White (silver-colored) metal of the
platinum group. It is highly noble in
the mouth. Palladium has a higher intrinsic
strength and hardness than gold, a much
higher melting point, and a higher modulus
of elasticity. The thermal expansion
of palladium is too low to be used with
most commercial porcelains; it is therefore
used to lower the expansion of gold-based
PFM alloys.
Palladium will whiten gold dramatically.
Palladium raises the melting range of
gold alloy, raises the modulus, and
improves strength and hardness. Palladium
lowers the density of gold alloy.
Small amounts of palladium dramatically
improve the tarnish and corrosion resistance
of gold-silver-copper crown and bridge
alloys. It is an essential component
for preventing tarnish and corrosion
in Au-Ag-Cu alloys with gold content
below 68% by weight.
Gold and palladium are present in so
many PFM alloys because they compliment
each other's limitations, and they are
completely soluble in one another, both
as liquids and as solids.
|
| Pt |
Platinum
Platinum is used primarily in yellow
PFM alloys to raise the melting range,
increase the hardness, strength, and
modulus, and lower the thermal expansion
of gold. It is less effective than palladium
in these regards, but platinum is able
to affect these properties with less
of the detrimental impact on alloy color
that palladium has.
Platinum has a high density, which
contributes to the fact that the gold
and platinum-rich yellow ceramic alloys
have the highest densities of all dental
alloys.
|
| Ag |
Silver
Silver is used in Au-Ag-Cu crown and
bridge alloys to balance the reddening
effect of copper. Silver-rich Au-Ag-Cu
alloys tend to have a "greenish"
color. Together with copper, it is used
to control the strength and hardness
of crown and bridge alloys.
In PFM alloys, it is used primarily
to raise the thermal expansion of palladium.
Silver lowers the melting range of
both palladium and gold. It is claimed
to add fluidity to casting alloys and
solders. Silver can cause discoloration
of some dental porcelains, a phenomenon
known as "greening." However,
because of the very positive effects
silver has on the thermal expansion
(and cost!) of an alloy, most modern
porcelains are designed to resist this
discoloration.
|
| Cu |
Copper
Copper is a strengthener and color enhancer
in Au-Ag-Cu crown and bridge alloys.
Copper-rich Au-Ag-Cu alloys tend to
have a "reddish" color.
In PFM alloys, it is used primarily
in palladium based alloys to increase
thermal expansion. Copper is responsible
for the very dark oxide layer characteristic
of Pd-Cu-Ga alloys.
Copper is seldom used in higher gold
PFM alloys, because like silver, copper
can cause porcelain to discolor. Porcelain
discoloration does not occur if the
alloy matrix is predominantly palladium,
however, and the only occasions where
one periodically sees copper discoloration
is when porcelain is applied to some
formulations of silver free pre-solders.
|
| Zn |
Zinc
Zinc is used in crown and bridge alloys
primarily as an oxygen scavenger. Simply
put, zinc readily combines with oxygen
that may have dissolved in alloy when
it was in a molten state. This prevents
the oxygen from forming gas porosity
in the casting.
In PFM alloys, zinc may be used as
a strengthener or hardener, or to raise
the thermal expansion. Its primary effect
is a pronounced lowering of the melting
range.
|
| In |
Indium
Indium is used in crown and bridge alloys
to improve fluidity, or castability,
of Au-Ag-Cu alloys. In PFM alloys, it
strengthens and hardens both gold and
palladium, and raises the thermal expansion
of both. Indium lowers the melting range
of both gold and palladium, and contributes
to the formation of the bonding oxide.
|
| Sn |
Tin
Tin is used as a strengthener and hardener
in both gold and palladium PFM alloys.
Tin lowers the melting range of both gold
and palladium and raises the thermal expansion.
Tin contributes to bonding oxide formation.
|
| Ga |
Gallium
Gallium is used almost exclusively in
palladium based PFM alloys. Gallium can
be a potent strengthener, and it lowers
the melting range of palladium.
|
| Fe |
Iron
Iron is used almost exclusively as a strengthener
in Au-Pt based PFM alloys. Iron also appears
to contribute to a bonding oxide.
|
| Co |
Cobalt
Cobalt is occasionally used as a substitute
for copper in Palladium based PFM alloys.
Jensen uses cobalt in our LX Pre-solder
to help adjust the solder melting range
without the dramatic increase in thermal
expansion that would occur if silver were
used.
|
| Ru |
Ruthenium
Ruthenium is used primarily as a grain
refiner.
|
| Ir |
Iridium
Iridium is used primarily as a grain refiner.
|
| Re |
Rhenium
Rhenium is used primarily as a grain refiner.
|