Lecture 4 Flashcards
Gamma (unreacted)
is the strongest phase – gamma 2 is weakest phase.
In low copper, you have Ag3SN – gamma 2 is SnHg.
Gamma 2 has an
interconnected framework – it is a mesh. If you have corrosion at the surface, it will be within the restoration as well.
Has high creep (permanent deformation over constant cyclic loading). Creep causes flash, which starts to chip.
Copper replaces
Sn, reduces amount of gamma 2 tremendously
N’ – etta prime
Much stronger, prevents sliding of gamma 1, minimizes creep and marginal breakdown.
More mercury is
more expansion
Zn forms a
hydrogen gas when in contact with water
Sulfides and chlorides are what
discolor teeth by amalgams
Seal smear layer, use varnish
otherwise it will continue to release fluids
Varnish/resin
disintegrates after awhile, so etta prime corrosion fills it in.
Wedging
compensates for thickness of bands
Lathe cut (irregular shavings of Ag3-Sn)
low packing density: more spaces
higher condensation forces required
tight contact
higher surface area: more Hg & more expansion
Spherical (spheroidal Ag-Cu particles)
pack more efficiently & slide easily (less voids & higher strength)
difficult to achieve proximal contact
Large diameter condenser for proper condensation pressure
II- High copper amalgam:
) Cu6Sn5 (η′ phase ) stronger & more corrosion resistant than γ2 less
prone to pitting.
b) Formation of eta phase prevents sliding of γ1 thus minimizing creep & marginal breakdown.
Admixed
2 step reaction (1 particle type is 1 step)
> 0.01%
Zn containing if moisture contamination cause delayed expansion
