clinical aspects of amalgam Flashcards
Components and chemistry ◦ Properties ◦ Relating properties to clinical use ◦ Compare with other materials ◦ Safety
what is amalgam
an alloy of mercury with another metal or other metals
what is dental amalgam
consists of silver mercury and tin with some other metals to modify the properties
what is the chemical equation of amalgam
Ag + Sn —> Ag3Sn
what is the shape of amalgam
lathe cut
spherical
what is amalgam currently stored in
in a capsule and the mercury and the amalgam alloy are separated by a membrane but is ruptured before being placed in the amalgamator
what are the three possible stages of the dissolved metals
Ag+Sn—->Ag3Sn known as the gamma phase
Ag+ Hg—-> Ag2Hg3 known as the gamma phase 1
Hg+ Sn —->Sn7Hg known as the gamma phase 2
what is gamma 2 responsible for
corrosion
creep
decrease in strength
what does the addition of copper
AgCu + Sn7Hg ( gamma 2) = Cu6Sn5 +Ag2Hg3 ( gamma 1)
reduces the gamma 2 phase
what is the typical modern amalgam powder composed of
silver
tin
copper
zinc
what is the powder:liquid ratio
Ideally final amalgam restoration should contain <50% mercury
how much mercury should be added to make the mixture movable
more than 50% to make it movable
what happens if there less than 50% mercury in the filling
it makes the amalgam very dry
what happens when the amalgam is packed
the mercury is drawn to the top and the excess is scraped away during carving
what do we use to pack the amalgam
the condenser
what layer lies on top of the restoration
the mercury rich layer which we can then scrap away
what are the properties of spherical amalgam
softer more flowable