Dental Amalgam Flashcards
Why use Amalgam?
Inexpensive, easy to use, proven track record (over 100 years), familiarity, resin-free (less allergies than composite.
How does copper tie up tin in amalgam?
by reducing gamma-2 formation
How does copper effect creep?
reduces creep, reduces marginal deterioration
What does Zinc (Zn) do in manufacturing of amalgam?
decreases oxidation of other elements (sacrificial anode)
A silver-matrix containing filler particles of silver-tin
Filler (bricks)
Matrix=
Sn8Hg called gamma 2 (voids)
How is copper added?
Into the gamma sphere (Ag3Sn) with epsilon coating (Cu3Sn)
Most high-copper amalgams undergo a ____ ______
Net - contraction
What happens when contraction leaves a marginal gap?
Initial Leakage (post-operative sensitivity), reduced with corrosion over time
What type of alloy gives more contraction?
Type of alloy: spherical alloys have more contraction (less mercury)
Condensation Technique: greater condensation = higher contraction
Titration time: overtrituration causes higher contraction
What type of alloy strengthens faster?
spherical alloys (requires less mercury)
What does corrosion do to strength of restoration?
reduces strength
How long does it take for corrosion start in low copper amalgams?
6 months (sno2, SnCl, gamma-2 phase)
How long does it take for high copper amalgams to start corrosion?
6-24 months (SnO2, SnCl, CuCl, eta-phase Cu6Sn5)
What does creep correlate with?
marginal breakdown
Prevention of gamma-2 phase in creep requires what percent of copper?
> 12%
