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
what is the biocompatibility of GIC
how compatible with living tissue
▹ bioactive
▹ low irritant despite low pH
H+ movt constrained by polymeric anion
restricts diffusion down dentinal tubules
what are the 7 advs of using GICs
▹ chemical bond to tooth
▹ long term F- release + uptake
▹ no shrinkage, exotherm or free monomer
▹ self repair by uptake of Ca2+ + PO43- from saliva to tooth surface
▹ potential to remineralise
▹ thermal expansion coefficient similar to tooth
▹ aesthetics
what are the 2 disadvs of GIC
▹ weaker than composites + amalgam, even though strength ↑ with age
▹ poor wear resistance early on
what are the main uses of GICs
▹ restoring anterior teeth
▹ with composite in sandwich technique
▹ tunnel restorations
▹ luting (cementing) + repair materials for crown + bridges
▹ cavity lining under amalgam/composites
▹ repair erosion lesions + fissure sealants
how are viscosity GICs different to conventional GICs
▹ ↑ viscosity
▹designed for atraumatic restoratives
▹ ↑ compressive strength (similar to composites)
▹ finer particle size powder - accelerate initial setting
▹ ↑ molecular weight
▹ ↑ F- release
what is in the powder compositions of cerments
▹ metal (silver) fused to GIC powder then ground
▹ OR metal powder mixed with GIC powder
▹ 5% titanium dioxide added -> improves colour
what is the liquid composition of cermets
▹ 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
what are the properties of cermet
▹ more abrasion resistant + ↓ brittle than conventional GICs -> cermets have added metal
▹ ↓ F- release + bond strength
▹ radiopaque
▹ difficult to handle
when are cermets used
▹ aesthetics not priority (silver colour)
▹ cermet/composite laminate technique
▹ linings for amalgam restorations
▹ repair of restoratives
