Glass Polyakenoates Flashcards
name the two types of dental material derived from cement are?
- silicate cement
2. polycarboxylate cement
how is polycarboxylate cement made?
- ZnO
and - polycarboxylic acid
= set cement
what are some of the properties of polycarboxylate cement?
- adhesive to tooth substance
- poor appearance
- high solubility
- poor mechanical properties
what is replaced to give you a glass polyalkenoate?
the ZnO is replaced with ion leachable glass
what are the 3 benefits of a glass polyalkenoate over polycarboxylate cement?
- better appearance
- less soluble
- better mechanical properties
what are the 3 ways of supplying a glass polyalkenoate?
- powder / liquid
- powder / water
- encapsulated
what is the setting reaction for glass polyalkeoate?
basically acid/base
what gives the glass polyalkenoate a better appearance?
unreacted glass cores = translucent properties give
what is in the powder for glass polyalkenoate?
sodium aluminosilicate glass with about 20% CaF
what is the benefit of having CaF in the powder for glass polyalkenoate?
fluoride leaching
what are the 2 component of the liquid for glass polyalkenoate?
- aqueous solution of acrylic / itaconic acid copolymer
- tartaric acid
what is the function of the tartaric acid?
to control setting characteristics
in addition to sodium aluminosilicate glass with CaF what is in the powder to make glass polyalkenoate with water?
vacuum dried polyacid
what kind of mixing is most likely to give porosities? and why?
- hand spatulation due to more air incorporation
are viscous cements more or less likely to get porosities?
less likely
with fluid cements does mixing by hand or machine give more porosities?
more if mechanical as increased froth
if carrying out an experiment on glass polyalkenoates then what type of supply would you use and why?
the encapsulated as more consistency with measurements
why would you not store GI in the fridge?
- makes mixing difficult as initiation of acid crystalisation
what can be placed on top of GI to prevent it from getting exposed to moisture?
- Varnish
- resin bonding agent or fissure sealant
when does setting of a glass polyalkenoate begin?
when the acid comes into contact with the glass particles
give two examples of a cored structure?
- aluminosilicate glass
2. metals
how does GI bond to enamel?
Ca2+ ions
how does GI bond to dentine?
bonds to collagen with H bonding and metallic ion bridging
what is the purpose of citric acid and what does it not do?
to remove smear layer
cannot increase bond strength
what can increase bond strength of GI?
- polyacrylic acid
give 8 properties of glass polalkenoate?
- thermal diffusivity close to dentine
- chemical set is exothermic (2-5%)
- fluoride release and uptake
- brittle
- poor abrasion resistance
- good appearance
- susceptible to acid erosion
- lack of radiopacity
what are cermets?
silver (Ag) pelletised mixture of GLASS and METAL particles
what are the properties of cermets?
- radiopacity
- poor apperance
- some F- release
- increased compressive stress
- increased fatigue limit
- some flexural strength and abrasion resistance
what does RMGIC?
resin modified glass ionomer cement
what is the difference between modified composite and conventional? what is the aim of this?
filler replaced with aluminosilicate glass - to encourage Fluoride release
what is the setting reaction for modified composite?
light cured free radical polymerisation
when does the acid base reaction occur during the setting of modified composite?
late on in the process
why does it occur later?
(resin modified = contains acidic groups)
resin set water enters materials and ionised the acid and then acid base reaction
