DML3 - GICs Flashcards
what are the main components in the GIC powder composition
▹ ion leachable/ionomer glass
▹ basic components (SiO2-Al2O3- CaF2/SrF2)
▹ other components = radiopacity, ↑ fluoride release, to provide with phosphate
why is the SiO2 to Al2O3 ratio important in the powder composition
governs reactivity
what happens in the ion leachable glass processing
▹ all components in powder composition melted at high temp
▹ rapid cool
▹ grind to powder
▹ acid wash powder - controls reactivity
what is in the liquid composition of GICs
▹ 50% Aq polyacrylic acid (PAA)
(OR copolymer of acrylic + itaconic acid, OR other COOHs)
▹ 10% Aq Tartaric acid
▹ both acids freeze dried + mixed with powder
▹ water added
why are carboxylic (alkenoic) acid monomers combined
combine monomers (cross link) to increase strength of acid
what are the 3 main steps of the GIC setting reaction
sets by acid-base reaction
- Dissolution stage
- Gelation
- Final maturation
what happens in the 1st stage of GIC setting reaction
Dissolution stage
▹ H+ ions from polyacid dissociate + attack the glass freeing the CATions (Ca2+ + Al3+)
▹ other ions released too (Na+, F-, silicon forms)
▹ 9Ca2+ + Al3+) - form complexes with tartaric acid + F-
what is the action of tartaric action in the setting process
▹ tartaric acid complexes are stable up to a certain pH
▹ they hold cement forming ions ( ↑ working time) until acid is partially neutralised
▹ the ions released (complexes not stable) -> sharp set ( real↑viscosity growth)
what happens in the 2nd stage of GIC setting reaction
Gelation + hardening stage
▹ set occurs by polymer chain entanglement + cross-linking (ionic bonds) of chains by: Ca2+ - initial set + Al3+ final set
▹ forms hydrated CA- + Al- polyacrylates
what happens in the 3rd stage of GIC setting reaction
final maturation
▹ ratio of bound:unbound water ↑
▹ ↑ strength, can take 24hrs
▹ thats why cement need to be protected immediately after placement
why is it important to maintain right water balance for GIC + why it needs protection straight after placement
▹ early water exposure -> dissolution of reactive components (cross link ions)
▹ dehydration -> critical water loss to continue setting reaction
cement = poor properties
how is adhesion/chemical bonding achieved for GIC cement
▹ tooth surface conditioned with PAA sol
▹ removes smear layer -> surface chemically active
▹ Chelation of Ca2+ = strong ionic bond between tooth + cement is strong ionic bond
▹ extra 2ndary bonding with amino grps
▹ continuous ion exchange between tooth + (polyaicd/GIC cement)
what is chelation of Ca2+ during the adhesion for GIC cement
Ca2+ from hydroxyapatite from tooth surface + COO- from PAA conditioner form strong ionic bond
how is fluoride released from GIC + why is it its main benefit
▹ initial ↑ release from exposed glass particles
▹ long term low F- release from deep matrix areas
▹ fluoride uptake by enamel + dentin
▹ inhibits demineralisation
how does GIC able to inhibit caries
▹ F- release + (Ca2+, Sr2+)
▹ involves continuing ion exchange cement/tooth/saliva
▹ (Ca2+, Sr2+) diffusion transfer to enamel/dentine
▹ possible remineralisation