what is amalgam an alloy of?
silver, mercury and tin
how do we mix amalgam?
amalgamator - reduce exposure and encapsulated
how is amalgam set?
gamma rays
the reaction between mercury and silver tin?
silver mercury amalgam and tin mercury amalgam
what is bad about tin mercury amalgam
may leach contents and discolour
how do we get rid of tin mercury
higher copper amalgam
what’s the reaction between copper mercury amalgam, tin mercury and silver tin? What gamma does it produce?
copper mercury + tin mercury + silver tin
= copper tin + silver mercury
- silver mercury produces gamma 2
- unwanted
- reduced by adding copper
- responsible for corrosion and creep
PRO of amalgam (8)
long lasting
cheap
easy to use
wear resistance
compressive
chemical set
radioopaque
good contact points
CONS of amalgam (7)
aesthetic
doesn’t adhere to tooth
needs base underneath
needs polishing
poor tensile strength
thermal conductor
lichenoid-type reactions
What Compounds can be Created When Amalgamated, and what Gamma do they Produce?
silver tin = gamma 1
silver mercury = gamma 2
mercury tin = gamma 3
What are the 2 Forms of Amalgam Powder?
Spherical Form
- spray molten metal into fine mist, hardening as It softens
= softer and more flowable
Lathe Cut
- ingot of alloy and grind into powder
= less flowable, good for building large tooth structure
Why is 50% Mercury the Optimum?
- less is dry and crumbly
- but with more mercury = weaker restoration so pack the material to remove excess
Why can Zinc be Added?
- no benefit
- prevents silver from oxidising
- not needed if powder is manufactured in a vacuum
- can cause material to expand whilst setting as it absorbs moisture
Where is Amalgam Used? (6)
- larger cavities in posterior teeth
- teeth with heavy occlusal forces
- high caries rate patient
- posterior restorations extending subgingivally
- build up broken teeth prior to crown
- when aesthetics aren’t important
Which Features can Help a Tooth Retain Amalgam?
- dovetail design
- pits and grooves into the dentine
- undercut more than 70º
- no unsupported enamel
- wet RMGIC on the base of the cavity to chemically bond to amalgam
How is Mercury Harmful to the Environment?
converted by bacterial into methyl mercury
= highly poisonous
