Dental casting alloys Casting is the most commonly used method for the fabrication of metal structures (inlays, crowns, partial denture frames, etc) outside the mouth. A pattern of the structure is first made in wax. This is then surrounded by an investment material. After the investment hardens, the wax is removed (burnt out) leaving a space or mould. Molten alloy is forced into this mould. The resulting structure is an accurate duplication of the original wax pattern. Terminology Several terms are used frequently when describing the elements or compositions or casting alloys. Precious metals Precious metals (or elements) refer to those that are of high economic value (i.e., are most expensive), such as gold, platinum, palladium, silver, (rhodium), (iridium), (ruthenium), and (osmium).
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Dental casting alloys2 Noble Metal These have been used for inlays, crowns, and bridges because of their resistance to corrosion in the mouth. Noble metal is resistant to tarnish and
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Dental casting alloys
Casting is the most commonly used method for the fabrication of metal
structures (inlays, crowns, partial denture frames, etc) outside the mouth.
A pattern of the structure is first made in wax. This is then surrounded by
an investment material. After the investment hardens, the wax is removed
(burnt out) leaving a space or mould. Molten alloy is forced into this
mould. The resulting structure is an accurate duplication of the original
wax pattern.
Terminology
Several terms are used frequently when describing the elements or
compositions or casting alloys.
Precious metals
Precious metals (or elements) refer to those that are of high economic
value (i.e., are most expensive), such as gold, platinum, palladium, silver,
(rhodium), (iridium), (ruthenium), and (osmium).
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Noble Metal
These have been used for inlays, crowns, and bridges because of their
resistance to corrosion in the mouth.
Noble metal is resistant to tarnish and corrosion even under extreme
conditions such as gold, palladium, platinum, rhodium, ruthenium,
iridium, and osmium.
All of these except silver are also noble metals. Nobility has the same
meaning as corrosion and electrochemical corrosion resistance. Since
silver is prone to tarnish, it is not included under this definition.
Silver is not a noble metal, because of its tendency to corrode in the
mouth.
Base-Metals
These are not noble metals; these metals include titanium, nickel, copper,
chromium, cobalt, iron, silver, zinc, and many others .
They are requiring in alloys for the strength and wear properties
necessary for dental restorations.
They are important components of dental casting alloys because of their
influence on physical properties, control of the amount and type of
oxidation, and their strengthening effect.
Such metals are reactive with their environment, and are referred to as
“base metals”. Some of the base metals can be used to protect an alloy
from corrosion by a property known as passivation.
Alloy
An alloy is defined as 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.
Metals are materials composed of metallic elements that possess the
characteristics of high thermal and electrical conductivity, ductility,
opacity, andluster. They also have relatively high strengths and generally
melt at high temperatures.
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General requirements of casting alloys
All cast metals in dentistry have some basic common requirements
These will be reviewed in categories of physical, chemical, mechanical,
and biological properties.
1- Physical Properties include:
b. Moderately high density (castability)
The density of an alloy is the amount of mass in grams that take up a