Dental Amalgam Flashcards
what is dental amalgam a product of
amalgamation
what is amalgamation
alloy + mercury react to form silvery hard grey mass
what makes amalgam unappealing
poor aesthetic
why is dental amalgam use declining
development of viable alternatives
safety and enviro pollution
what are the two compositions of amalagam
conventional
high copper
what is x ray refraction used for
to work out crystal structure a scatters rays to work out distance between etc
what is most common composition of amalagam used today
conventional superseded by high cooper
what si the compositor of conventional
65% Ag (min) 29% Sn (max) 6% Cu (max) 2% Zn (max) 3% Hg (max)
what si the composition of high copper composition
40% Ag (min) 32% Sn (max) 30% Cu (max) 2% Zn (max) 3% Hg (max)
how do variations of alloy morphology come about
lathe cut
spherical
what is a lathe
used to cut off bits of alloy into finer or coarse - changing how much in contact with mercury
what is better about the high copper comp to the conventional
reaction changes gamma 2 slim and replaced
better corrosion resist and less susceptible to creep
what is the effector of a greater amount of Ag(3)Sn
undergoes setting reaction
what effect does copper have on amalgam
strengthening effect
what does Zn act as in alloy production
scavenger which can complex with oxygen - leading to problems
what may be eliminated in an inert atmosphere
Zn
what is mixing termed as
trituration
what are the dimensional changes take pace
30 mins - sell shrink
30-60 mins - expansion
why at 30 mins is there a small shrinkage
Hg diffuses into alloy
why at 30-60 mins expansion
due to crystallation
what is the overall effect of size changes
net expansion/contraction
(+/-) 0.1%
what does it mean hangs is given off
poor moisture control and Zn containing alloy - gas given off = greater expansion
what is the tie of placement to function
15-20 mins
when is final strength of malaga reached
24 hours
what is compressive fore greater than
tensile and transverse
when is madam weak
in this sections
what is strength proportional of
Hg content
what is the optimum of Hg
44-48%
what si the creep prperty
plastic deformation under load
what does the creep property clinically flow as
manifesting as protrusions at restoration margins
what is ditching
fracture off of restoration margins
what is largely responsible fro creep
gamma 2 largely responsible
what does corrosion of allow exacerbates release
Hg in marginal crevice
localised expansion
what is corrosion of amalgam
electrochem reaction of diff alloy phases with saliva as electrolyte
- gamma 2 anode
what does gamma 2 do in corrosion of amalgam
breaks down to Sn and Hg
latter remains free and is ingested
what do corrosion products provide
marginal seal
in high copper phase what is undergoing most corrosion
Cu-Sn
what does the metal of amalgam mean about thermal property
high thermal diffusivity
what can Hg be toxic about
CNS
- signs and symptoms
why are some linked condones with amalgam
multiple sclerosis
psychiatric distrnbace
how to protect against enviro pollution go Hg
water of dental unit
release ofHg during titration
crematori
what are somemanipulatve variables
alloy:Hg (5.8:10.8)
how are drier mixes achieved
mechanical mixing
what removes excess Hg
packing nd condensation
what is dispensation
weight rarely used volume dispensers alloy tablets proportioning and mixing
what is important about particle size of alloy
smaller achieves higher 1 and 24 strengths
if too small too rapid set
