I have never heard of nickel being mixed with gold in dental alloys. Can you post a link showing such. The usual alloys are:Platinum,Palladium,Silver,Copper.

Nickel apparently is sometimes used with gold jewelry to produce white gold.


Below are alloys used by Jensen:

http://www.jensenindustries.com/alloy/resources/element.htm

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[ Alloys ] [ Role of Elements ]


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.