It is a metal containing two or more elements, at least one of which is

metal, and all of which are mutually soluble in the molten state.

: They are materials resist corrosion in the mouth. (gold,

platinum, palladium, silver, rhodium, ruthenium, iridium, osmium).

: This term indicates the intrinsic value of the metal.

The eight noble metals are also precious metal, but all precious metals are

not noble.

: Pure gold is soft, ductile, yellow hue. The density is 19.3

gm/cm3, melting point is 1063°C, good chemical stability, not corrode

and not tarnish.

: Whitest metal, its density is 10.4 gm/cm3, melting point is

961°C.

: Its density is 12.02 gm/cm3, melting point is 1552°C.

: its density is 21.65 gm/cm3, melting point is 1769°C.

: These are not noble metals, (chromium, cobalt, nickel,

copper,…..etc).

They are important components of dental casting alloy because:

a- Their influence on physical properties.

b- Control of the amount and type of oxidation.

c- Their strengthening effect.

Type I: soft.

Type II: medium.

Type III: hard.

Type IV: extra-hard.

1- Binary (2 elements).

2- Ternary (3 elements).

3- Quaternary (4 elements).

1- Alloys for all metal; metal with resin veneer restorations.

2- Alloys for metal ceramic restorations.

3- Alloy for removable dentures.

1- It should not tarnish and corrode in the mouth.

2- It should strong.

3- Biocompatible (non-toxic, non-allergic).

4- It should be easy to fabricate (melt, cast, cut, and grind).

5- It should flow well, and duplicate fine details during casting.

6- It should have minimal shrinkage on cooling after casting.

7- It should easy to solder.

Alloys for all metal restorations

1- Gold alloys (composed of gold, copper, silver, platinum, palladium, and

other additives).

2- Silver-palladium alloys.

3- Nickel-chromium alloys.

4- Cobalt-chromium alloys.

Alloys for metal ceramic restorations

1- Gold-palladium-platinum alloys.

2- Palladium-silver alloys. Cheap

3- Nickel-chromium alloys.

Figure (5-1):

Cutaways of all-

ceramic crown

(left) and

porcelain fused to

metal crown

(right).

HOW DOES PORCELAIN BOND TO THE ALLOY?

Ceramic adheres to metal primarily by chemical bond. A covalent bond is

established by sharing 02 in the elements in the porcelain and the metal

alloy.

These elements include silicon dioxide (Si02 in the porcelain and

oxidizing elements such as silicon, indium, and iridium in the metal alloy.

Alloys for removable dentures

8- It should be light weight.

9- It should have high stiffness (to make the framework thin).

10- It should have good fatigue resistance.

11- It should not react to commercial denture cleanser.

12- Economical consideration.

Alloy used:

a- Cobalt (to give hardness, strength, rigidity).

b- Chromium (to ensure corrosion resistance by passivating effect).

c- Nickel (to decrease fusion temperature and increase ductility).

d- Molybdenum or tungsten (to increase hardness).

e- Iron and copper (to increase hardness).

f- Manganese and silicon (to prevent oxidation).

g- Boron (to increase hardness and deoxidizer).

h- Carbon (to strengthen the alloy).

a- Nickel.

b- Chromium.

c- Molybdenum.

d- Other minor additions like aluminum, iron, silicon, copper, manganese, tin.

The function of each ingredient is discussed previously