dental amalgam Flashcards
What is the product of amalgamation?
alloy and mercury react to form silvery hard grey mass
why is the used of amalgam declining?
development of viable alternatives
concerns re. safety- mercury
what composition of amalgam was before 1896?
conventional amalgam
What composition post 1896?
high copper amalgam
What metals make up amalgam alloy?
Ag, Sn,Cu,Zn, Hg
What types of variations re. alloy morphology?
lathe cut
spherical
what element has strengthening effect on amalgam?
Cu
What element acts as scavenger in alloy production?
Zn
The setting reaction happens mostly on what element?
Ag3Sn
What dimensional changes occur in the first 30 minutes?
small shrinkage
Hg diffuses into alloy
What dimensional changes occur 30-60 minutes?
expansion- due to crystalisation
What is the overall effect of the amalgam setting reaction?
net expansion/contraction
What is the ISO limit of expansion and contraction?
0.1%
How long after placement is the restoration functional?
15-20 minutes
what long till restoration reaches final strength?q
24 hours
When is strength optimum?
When Hg is 44-48%
What helps to achieve optimum strength?
correct manipulation of material
removing mercury rich layer
What is creep?
plastic deformation under load
protrusions at restoration margins
What stage is largely responsible for creep?
gamma 2
what exacerbates creep?
corrosion of alloy
release of Hg in marginal crevice
What is corrosion?
electrochemical interaction of different alloy phases with saliva as electrolyte
What do products of corrosion do?
provide marginal seal
When is corrosion highest?
in high copper phase
gamma 2
What has mercury content of amalgam been linked to?
MS
Behavioural problems
Psychiatric disturbances
What aspects are of concern re. environmental pollution?
water of dental unit
release of Hg during trituration
crematoria
What techniques remove excess mercury?
packing and condensing
What does smaller particle of alloy achieve?
higher 1 and 24 hour strengths
What are the down sides to too small particles?
too rapid set
not enough working time to remove excess Hg
