Dental Amalgam Flashcards
What is dental amalgam?
an allow mixed with mercury
What is dental amalgam commonly used for?
posterior restorations
What is the alloy in dental amalgam made from?
silver
tin
copper solid particles
why is zinc added to dental amalgam ?
as a deoxidiser to make it less brittle
what is the composition of dental amalgam controlled by?
ISO standard
What is the setting reaction for dental amalgam?
set by reacting with mercury which results in phases
What are the dimensional changed during setting dental amalgam?
30 minutes - small shrinkage
30-60 minutes - expansion
What causes amalgam to shrink during setting?
mercury diffusing into the alloy
What causes dental amalgam to expand during setting?
crystallisation
What is the overall setting effect of dental amalgam?
net expansion/ contraction
What is the ISO limit on dental amalgam setting ?
+ or - 0.1% expansion/ contraction
At what time would you reach a functional compressive strength when setting dental amalgam?
15-20 minutes
At what time would you reach a final strength when setting dental amalgam?
24 hours
What minimum depth should be packed with dental amalgam?
2mm
How do you fill with dental amalgam?
in thin sections, overpack, then carve back the mercury layer
What happens in the particle is too small in dental amalgam?
too rapid a set so the mercury layer cannot be removed by manipulation
What is plastic deformation (creep) caused by?
chewing/ grinding causes amalgam to flow and protrude from the cavity margin, forming edges
What happens in low copper amalgam in the presence of saliva?
y2 phase breaks down and releases corrosion products and mercury
What are advantages of corrosion products?
corrosion products can form a marginal seal
Why cant pregnant woman have dental amalgam restorations?
mercury is toxic to the CNS
What is the composition of conventional amalgam?
silver 65%
tin 29%
copper 8%
other trace metals
What is the composition of high copper amalgam?
silver 40%
tin 32%
copper 30%
other trace metals
What are the advantages of high copper dental amalgam?
more strength
corrosion resistance
durability
resistance to tarnish
How is high copper amalgam cut?
spherical form by atomisation
How is conventional amalgam cut?
cut ingots into particles
