|Posted on April 13, 2019 at 8:55 AM|
Silver Amalgam restoration
Carving Silver amalgam Restoration is a challenge in clinical Practice and it becomes a nightmare during the undergraduate learning period. Establishing proper contacts and contours in the restoration is important for the longevity of the resoration .
An amalgam is an alloy of mercury and other metal(s). Dental Alloy is a powdered alloy of silver, tin, and other metals, which can be mixed (triturated) with mercury to form dental amalgam.
Old fashioned low copper Dental Amalgam Alloy
70% Silver gives strength and corrosion resistance.
25% Tin slows the setting time when the alloy is amalgamated, allowing the material to be placed and carved.
4% Copper increases the strength
1% Zinc (if present) improves the wettability of the alloy particles with the mercury.
Percentages are approximate
When Dental Alloy reacts with mercury, some of the alloy remains unchanged (especially at the centre of the powder particles). The part that reacts forms a matrix in which the un-reacted particles are suspended.
The unreacted phase is called the gamma phase. The matrix consists of a mixture of gamma-1 and gamma-2 phases.
Gamma phase : Ag3Sn - Silver/Tin, very strong & corrosion resistant.
Gamma-1 phase : Ag2Hg3 - Silver/Mercury, quite strong & corrosion resistant.
Gamma-2 phase : Sn7Hg - Tin/Mercury, weak & easily corroded, results in marginal breakdown of filling.