Dental Amalgam Flashcards
what is amalgam?
mixture of any metal/alloy with mercury (Hg)
what is an amalgamation reaction?
the chemical reaction when mixing mercury with alloy
dental amalgam is a mixture of what?
dental alloy and mercury
advantages of dental amalgam? 3
high compressive strength
easy to manipulate
low cost
disadvantages of amalgam? 3
poor aesthetics
potential for thermal irritation
creep
what is creep?
deformation under a load over time
what are the two compositions of dental amalgam?
conventional
high copper
what are the major components of dental amalgam? 5
silver Ag
tin Sn
copper Cu
zinc Zn
mercury Hg
what is the differences between the setting reaction of conventional and high copper dental amalgam?
absence of gamma 2 phase in high copper (tin-mercury)
replaced with copper-tin phase
what effect does copper have on dental amalgam?
it has a strengthening effect
what is the purpose of zinc in the setting reaction of dental amalgam?
prevents oxidation of the alloy during melting
what does trituration mean?
mixing
what is happening for the 1st 30mins of the setting reaction to dental amalgam?
small shrinkage while Hg diffuses into the alloy
what is happening between 30 and 60 mins?
expansion due to crystallisation
what is important to control during the setting reaction of dental amalgam?
moisture control
what dimensional changes occur to the setting reaction of amalgam if moisture contaminates the zinc containing alloy?
delayed expansion due to liberation of Hydrogen
larger expansion
the strength of dental amalgam develops fast or slow
slowly
dental amalgam is relatively weak in the first ?-?mins
15-20
it can take up to how many hours for dental amalgam to become high strength?
24hrs
dental amalgam has a better transverse, compressive or tensile strength?
compressive
where is dental amalgam weak?
thin sections
what are 2 possible effects of excessive creep?
ditching
gingival overhangs
what is the most corrodible phase of dental amalgam setting reaction? what happens?
gamma 2 breaks down into Hg and tin that are free and ingested
in high copper tin and copper and free
what can inhibit the corrosion process of dental amalgam?
phosphate buffer solution so saliva may provide protection
dental amalgam has high thermal conductivity. what can protect the pulp from thermal irritation
an insulating lining material
placement and removal of dental amalgam is banned for what patients?
pregnant
how does the particle size of the alloy effect dental amalgam?
smaller means higher 1 & 24hr strengths
if extremely small too rapid set -> cant remove excess Hg -> inferior properties
how does alloy particle shape effect dental amalgam?
if lathe-cut (irregular) - requires more Hg to achieve plasticity
if spherical (regular) - needs less Hg than lathe-cut thus superior properties
