Glass polyalkenoates Flashcards
what is glass polyalkenoate formerly called?
glass ionomers
glass polyalkenoates generally contain what?
powder: sodium aluminosilicate glass and CaF
polyacid
glass polyalkenoates have a composite structure explain
silaceous hydrogel with unreacted glass cores floating about
what kind of reaction is the setting reaction of glass polyalkenoates?
acid base -> salt
what are the 2 phases in the setting reaction of glass polyalkenoates?
initial set - first few minutes
final set - about 24hrs after completion
what is the structure of a glass particle in glass polyalkenoate
at the initail set of glass polyalkenoates what ion predominates? why?
Ca+ ion
as more accessible on the outer surface of the glass particle
and
Ca+ is more mobile than Al3+
Ca+ only cross-links with 2 chains but Al3+ cross links with 3 chains
what ion perdominates in the final set of glass polyalkenoates?
Al3+
glass polyalkenoates are not fully set until after 24hrs. they are moisture sensitive until final set, what do dentists thus do?
apply a varnish or unfilled resin
positives of glass polyalkenoates
adheres to tooth substance
tooth coloured and translucent
fluoride uptake and release
negatives of glass polyalkenoates
brittle and relatively poor abrasion resistance
susceptible to acid erosion
what are the uses of glass polyalkenoates?
restorative
luting (e.g cementing in crowns)
lining/base
how does glass polyalkenoate bond to tooth substance?
bonds with Ca+ ions
bonds with collagen through H bonds and metallic ion bridging
how can the bond strength of glass polyalkenoates be increased by prepping the tooth?
apply citric acid -> removes the smear layer
apply polyacrylic acid -> slightly etch tooth surface
what are cermets composed of?
mixture of glass and metal particles
introduction of silver
positives of cermets
radiopacity
some fluoride release
increased compressive strength
increased fatigue limit
negatives of cermets
poor appearance
what does modified composite consist of?
filler in composite replaced with aluminosilicate glass to encourage fluoride release
what is the setting reaction type for modified composite?
light cured free radical polymerisation
what do giomers consist of?
same as modified composite but aluminosilicate glass is prereacted with polyacid to form prereacted polyalkenoate complex
what are the two types of giomers?
surface reaction
full reaction
what type of setting reaction is giomers?
VLC free radical polymerisation
in RMGIC what is the purpose of methacrylate resin?
enables setting by polymerisation
in RMGIC what is the purpose of polyacid?
reacts with glass by acid base reaction
in RMGIC what is the purpose of HEMA
enables resin and acid components to coexist in aqueous solution
in RMGIC what is the purpose of water?
essential for ionisation of acid/base reaction
what happens to RMGIC in the presence of water?
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