Amalgam Flashcards
what are the two types of composite?
pre 1986 - conventional
post 1986 - high copper
what % copper in a low copper alloy? high copper alloy?
low - 5%
high - 30%
morphology of alloys?
lathe cut
spherical
what happens in the amalgam setting reaction?
Ag3Sn undergoes setting reaction
Cu gives strengthening effect on amalgam
Zinc acts as scavenger
trituration - ISO limit?
limit to +/- 0.19% expansion/contraction
what happens with poor moisture control and a zinc alloy?
zinc plus water gives zinc oxide and hydrogen
how much time between placement to function?
15-20 mins
after how long does it set to its final strength?
24 hours
Compressive strength is more than what?
the tensile strength
amalgam weak in thin sections
Hg gives strength of?
44-48%
when does creep occur?
when plastic deformation is under strength
what is creep?
clinically - amalgam flows manifesting as protrusions at restoration margins
what happens to amalgam as a result of creep?
fractures off producing ditching
what causes creep?
the gamma 2 phase is largely responsible
corrosion of the alloy
what happens during corrosion of the alloy?
releases Hg in marginal crevice
= localised expansion of amalgam
what is corrosion?
electrochemical interactions of different alloy phases with saliva as the electroylte
what is the gamma 2 phase?
gamma 2 phase is tin mercury phase = mercury free and ingested
what do corrosion products provide?
marginal seal
what phase undergoes the most corrosion?
high copper phase = CuSn phase
thermal properties of amalgam?
high thermal diffusivity
3 fold coefficient of thermal expansion of dentine = heat in mouth is transient
biological properties of amalgam?
mercury known to be toxic to CNS. High content of hg in the urine/blood of those with amalgam restorations than those without.
links of amalgam with what conditions?
multiple sclerosis
behavioral problems
psychiatric disturbances
how can mercury pollute the clinical environment?
water of dental unit
release of hg during trituration
range of mercury:alloy ratio?
5:8 to 10:8 alloy:mercury
how are drier mixes achieved?
achieved by mechanical mixing
how to remove excess mercury?
packing and condensation
dispensation of amalgam?
weight - most accurate - rarely used volume dispensers alloy tablets proportioning/mixing devices now is encapsulated
smaller particle size gives?
higher 1 and 24 hour strengths
extremely small particles?
too rapid to set
