Noble Gold Alloys For Crowns And Bridges

Noble just means: A metal or alloy, such as gold, that is highly resistant to oxidation and corrosion.

I recommend a 75% gold or higher.

High-Noble Alloys

By definition, these alloys must have a noble metal content of at least 60 wt%, of which at least 40 wt% is gold. They usually contain a small amount of tin, indium, and/or iron which provides for oxide layer formation. This increases the alloy’s bond strength to porcelain by a factor of three. The disadvantages of these alloys include their lower rigidity and poor sag resistance during porcelain firing. There are three subclasses of high-noble alloys:

1. Gold-platinum

2. Gold-palladium

3. Gold-copper-silver-palladium

Gold-platinum alloys:

Initially developed as an alternative to palladium alloys, these can be used for full-cast as well as metal-ceramic restorations. Because they are subject to sag, they should be limited to short-span fixed partial dentures. They often contain silver or zinc as a hardener.

A typical composition is:

1. Gold 85%

2. Platinum 12%

3. Zinc 1%

4. Silver (in some brands)

Gold-palladium Alloys

Like gold-platinum alloys, these can be used for full-cast or metal-ceramic restorations. They usually contain indium, tin, or gallium to promote oxide layer formation for better bonding to porcelain.

A typical composition is:

1. Gold 52%

2. Palladium 38%

3. Indium 8.5%

4. Silver (in some brands)

Gold-copper-silver-palladium Alloys

These are used only for full-cast restorations because (1) their melting temperatures are too low for metal-ceramic use, and (2) they contain silver and copper which can green the porcelain and cause the metal casting to sag during porcelain firing.

A typical composition is:

1. Gold 72%

2. Copper 10%

3. Silver 14%

4. Palladium 3%

Noble Alloys

By definition, these alloys must contain at least 25 wt% noble metal. Because the noble alloys can contain a number of different metals, they are a rather diverse group. As a general rule, however, they have relatively high strength, hardness, and ductility. They may be yellow or white in color. When white, it is due to their palladium content. Palladium also gives them their relatively high solidus temperatures. The one exception are the gold-copper-silver-palladium alloys which are only used for full-cast restorations. The degree to which the noble alloys corrode varies because of their diverse compositions.

There are three subclasses of noble alloys:

1. Gold-copper-silver-palladium

2. Palladium-copper-gallium

3. Palladium-silver and Silver-palladium

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