Dental Amalgam 1st Page (LEC)

Terminology of Amalgam Cements

silver paste
an alloy, one of the constituents of mercury

Components - Silver

increases strength
increase expansion
decreases setting time
decrease flow
corrosion

Components - Copper

increases strength and hardness
increases expansion
decreases setting time
decrease flow
tarnishes readily

Components - Tin

increase setting time
increases flow
decrease expansion
unites with Mercury (Hg)

Components - Zinc

reduces oxidation of the other metals in the alloy.
containing dental amalgams have a longer clinical life expectancy.
provides better clinical performance.

Other Constituents - Indium (In)

increases strength
decreases surface tension
reduces the amount of mercury
reduces creep and marginal breakdown

Other Constituents - Palladium (Pd)

reduced corrosion
greater luster

Other Constituents - Mercury (Hg)

activates reaction
only pure metal that is liquid at room temperature

Classification of Amalgam

Amalgam alloy particle geometry and size
Copper Content
Zinc Content

Alloy - Mercury Ratio

irregular particle pack poorly and require a large amount of Hg (50%-60%)
pre capsulated amalgam (spherical) has 42%- 45% mercury

Spherical Alloys

less mercury
easier to wet

Admixed Alloys

more mercury
difficult to wet

Reaction

silver - tin phase is called the gamma phase, composed of unreacted alloy particle

Gamma = Ag3Sn

unreacted alloy
strongest phase and corrodes the least
forms 30% of volume of the set amalgam

What happens when the mixing process of silver?

mixing process silver, tin and copper atoms are dissolved in the mercury where they start forming different precipitates.