CSA Amalgam Flashcards
What is amalgam?
an alloy of mercury
What is mercury ?
liquid at room temperature and only freezes at -39
o form alloys at room temp.
• A toxin that build up and doesn’t break down in food chain
Is dental amalgam inert?
yes
What is the WHO max exposure levels for mercury ?
o 300mg per week
o And/or 25 mg/m3
What does capsule contain ?
o Metal alloy
o Liquid mercury Normally very pure
What does amalgam alloy contain?
o 69% Ag
o 19% Sn
o 11% Cu
o 1% Zn
What does Ag3Sn ratio place alloy in ?
gamma phase
What does mercury do to surface of alloy once mixed?
dissolves it forming new compounds not soluble and precipitate out liquid mercury forming gamma 1/2 phases
What is gamma 1 phase referred to?
the matrix, holds whole structure together
What is gamma 2 phase known for ?
being susceptible to corrosion, can lead to margin failure
What does amalgamator do?
“amalgam alloy” and mercury in capsule separated by membrane > ruptured when button ,
How do we get rid of gamma 2 phase (Sn7Hg)
• Additions of Cu3Sn mops up gamma 2 somore gamma 1 phase and some fine rod like crystals of Cu6Sn5
How is Cu3Sn added to ?
straight into alloy so alloy is 2 intermetallic compounds (Ag3Sn + Cu3Sn) OR added in fine powder
what is retention like with amalgam?
Retention is mechanical, cavities require an undercut
What can happen to silver over time?
tarnish into grey
What is required with amalgam if the cavity is large?
• Therapeutic liner or base material
What is good about amalgam?
good compressive strength
What forms on layer of surface of amalgam?
corrosion layer
What cut of alloys is good
o Spherical to allow amalgam to flow better during condensation + also small amounts of Hg needed to produce a workable material > decreases amount of gamma 1 phase
What can occur with amalgam ?
creep
How is creep formed with amalgam ?
plastic deformation of amalgam due to stresses placed >lead to restoration failure
