amalgam Flashcards
what is amalgam?
an alloy of mercury and silver + tin
added copper and zinc too
pros and cons of using mercury?
mercury is a liquid at room temperature making it very workable
a con is that it is hard to dispose of due to its toxic nature in large amounts
how may you classify amalgam?
number of metals (bi, tri, quarternary)
uni or admixed (shapes)
- fine or coarse
- spheroidal or lathe cut
zinc content
copper content
how are different amalgam shapes cut?
lathe cut is where rough shapes are cut directly from the amalgam
spheroidal is where amalgam is passed into an inert gas which forms it into a spherical ball
use of silver in amalgam? p/c
silver adds strength to the amalgam mixture
it also helps to prevent contraction shrinkage
helps with setting
use of tin in amalgam? p/c
when combined with silver, it helps with setting via corrosion and creep
corrosion also a con - also contributes to shrinkage
also is weak
use of copper in amalgam? p/c
helps prevent a large amount of gamma2 phase being present.
helps to counter the corrosiveness of tin
what are the three gamma phases?
a mix of three different phases of the amalgam left after mixing.
Y/Gamma phase = mercury + silver-tin
- silver tin reacts with liquid mercury to form amalgam. This holds gamma1 and 2 together
Y1/Gamma 1 phase = mercury + silver alone
- extremely strong
Y2 = mercury + tin alone
- very weak
- however contributes to setting reaction and corrosion to seal margins
use of zinc in amalgam? P/C?
deoxidiser, scavenger for oxygen to strengthen the amalgam
delays expansion
give some good properties of amalgam?
corrosion can help to seal restoration margins
high abrasion resistance - good for posterior teeth
ok compressive strength
good handling properties and relatively fast mixing and setting time
give some negative properties of amalgam
poor biocompatibility
- toxic mercury hard to dispose of
no chemical bond to tooth surfaces
creep and viscoelasticity
poor aesthetics
high thermal conductivity and diffusivity (may need a liner)
