Glass Polyalkenoates Flashcards
what are GI’s derived from?
silicate cements
polycarboxylate cements
what are polycarboxylate cements?
zinc oxide with polycarboxylic acid
set cement = adhesive to tooth, poor appearance, poor mech properties
replace zinc oxide of polycarboxylate cements with what? Advantage?
replace zno with ion leachable glass
better appearance
less soluble
better mech. properites
Glass ionomer came about when?
1970’s
GI comes as?
powder to liquid
powder mixed with water
encapsulated
powder of GI?
sodium aluminasilicate glass plus 20% caF
liquid of GI?
aqueous solution of acrylic/iatonic acid copolymer
plus tartaric acid to control setting
GI setting reaction essentially?
an acid base reaction
unreacted what left?
glass cores
powder/water gi, powder?
sodium aluminasilicate glass + 20% caf
plus vacuum dried polyacid
powder reconstituted by mixing with?
either water or dilute aqueous solution of tartaric acid
proportioning of powder and liquid
scoop/dropper bottle
encapsulated
how to mix GI
spatula
mechanical by oscialltory/rotary
what does hand spatulation cause?
more air incorporation
increased porosity
porosity of viscous cements?
low porosity
porosity causes stress of material which causes?
cracks
properites of powder to water gi altered by?
p:l ratio
if encapsulated = consistent
cored structure description?
outer is rich in calcium
inner rich in aluminium
calcium 2+ allows?
al 3+
2 arms for cross linking the acid chain
3 arms
in the initial set reaction what is there more of?
calcium ion predominates over al
why is there more calcium in the initial set reaction?
calcium is at the outer surface so is the 1st thing the acid meets
calcium is more mobile in solution that Al
more likely that 2 chains will come along rather than 3
why is mixing difficult if GI stored in the fridge?
initiates acid crystallisation
how does GI bonded to the tooth?
by calcium ions
how does GI bond to collagen?
by H bonding - metallic ion bridging
how might bonding be boosted?
with a tooth cleanser
what does citric acid do?
removes the smear layer
gives no increased bond strength
what does polyacrylic acid do?
increases the bond strength
can only enhance the bond strength to what point?
to the limit of the tensile strength of the glass polyalkenoate cement
greater than tensile strength = failure of cement
thermal diffusivity of GI close to?
chemical set of GI is?
what can GI release and uptake?
dentine
exothermic
fluoride
GI has poor?
is it brittle?
what is GI susceptible to?
poor abrasion resistance
brittle
acid erosion = synergy of acid and mechanical wear
GI has a lack of?
what is its appearance like?
lack of radiopacity
good appearance
what are cermets?
Ag pellized mixture of glass and metal particles
are cermets able to release fluoride?
appearance is?
yes some
poor appearance
cermets have an increased?
compressive strength and fatigue limit
what is modified composite?
The filler is replaced with aluminosilicate glass - aims to encourage F release
how is modified composite set?
by light cured free radical polymerisation
reaction of modified composite?
no acid base reaction until later in process
resin contains acidic groups, once resin is set, water enhances and ionises then acid base takes place
what is a Giomer?
aluminasilicate glass is pre reacted with polyacid to give a prereacted glass polyalkenoate complex
2 types of reaction of a giomer?
1) surface reaction - reaction happens at surface. Gives better physical properties
2) Full : reaction of all particles at expense of properties. Sold because of F release. Hema added
how are giomers set?
both reactions are single paste VLC free radical polymerisation set
what form does RMGIC come in?
Powder to Liquid or encapsulated
what is the powder RMIGC?
ion leachable glass
what is the liquid for RMGIC? and what does it enable?
methacrylate resin = enables setting by polymerisation
what is the role of the polyacid in RMGIC?
reacts with glass by acid/base reaction
what is the role of HEMA in RMGIC?
enables resin/acid components to co exist in aqueous solution
what is the role of water in RMGIC?
essential for ionisation for acid/base reaction
what can also be present in some RMGIC?
chemical activators
on mixing RMGIC what happens?
if chem activators present what happens?
acid base starts
light activation = resin polymerisation
chem activators = further cure
what do the 3 setting reactions of GI allow?
work more quickly
incremental cure
the presence of the resin in RMGIC allows?
varnish not needed
when can you finish a RMGIC?
immediately
what is there significant amounts of with RMGIC?
shrinkage
RMGIC’s expand in what?
what can this benefit?
expand in water
can help seal
RMGIC’s are adhesive but are limited because?
what does this mean needs to be used?
- lack of free acid to form effective bond
- lack of sufficient ionic character to form bon
- lack of mobility of active spaces to form bond
= some need extra agents to bond
do RMGIC’s release fluoride?
yes varies material to material
major release conventional with high initial burst and capacity to reuptake
modified composite’s fluoride release is?
a lower sustained release
giomers and compomers have the same fluoride release because?
low pH allows greater release, at expense of material disintegration
advantages of composite?
strong
tough
radiopaque
quick set
disadvantages of composite?
no inhert adhesion
shrinkage
no f release
advantages of GI?
inhert adhesion
little shrinkage
F release
biocompatible
disadvantages of GI?
brittle not radiopaque wear prone slow set water sensitive
