Glass Ionomer Cements Flashcards
Give 8 applications of GIC.
- Restorations for class III lesions
- Luting
- Bonding/conditioning
- Protection underneath composites and amalgams
- Suited for minimally invasive procedures
- Deep carious lesions
- Fissure sealing
- Protection of root surfaces against caries
What is the composition of GIC (5 parts)?
- Polyalkenoic acid
- Glass powder: Calcium fluoroaluminosilicate glass.
- Tartaric acid
- Water
- Heavy metal salts for radiopacity
What does the base of GIC compose of and what is its role?
- Calcium fluoroaminosilicate.
- The calcium contact allows Al3+, Ca2+ and F- to all leach out and take part in the acid-base reaction.
- This is caused by calcium, which can also be replaced by stronium and sodium which can both do the same role.
What does the acid of GIC compose of?
Polyalkenoic acid: Water soluble poly acids
What is the role of tartaric acid in GIC?
It interacts with glass particles, breaking off the Al3+ ions which then take part in the acid-base reaction.
Give 3 positives tartaric acid has in GIC.
- Improves handling
- Extends working time
As the t. acid inhibits the dissociation of polymeric acid thereby delaying the onset of the intial setting.
- Sharpens set.
What are the 3 stages in the setting reaction of GIC?
Stage 1:
- Powder and liquid mixed together leading to the outer layers of the glass to be attacked by the H+ ions of the acid.
- The glass becomes depleted of Al3+, Ca2+, Na+ and F- as a result.
Stage 2:
- Calcium ions react with carboxyl groups in the polyalkenoic acid leading to salt precipitation (hardening).
- This is the initial setting stage where calcium ions crosslink.
Stage 3
- Hardening can take over a week.
- After 30 mins, alumunium ions react with the polyalkenoic acid and polyacrylates are formed.
- Ionic crosslinks such as this increase, leading to increases in compressive strength and dimeful tensile strength.
Why has encapsulation of GIC been phased in?
As the ratio of powder to liquid produced on hand-mixing is susceptible to operator induced variability.
Give 3 forms GIC is dispensed in.
- Powder and liquid phase (the acid)
- Powder + acid (freeze dried) + water
- In capsules: pre-dispensed amount of powder and liquid phase.
Give 2 other types of GIC cements.
- Glass carbomer: contains bioactive glass
- Equia forte: contains ultrafine reactive glass
Give 5 roles of aqueous systems in the GIC reaction.
- Provides ion transport
- Acid-base setting reaction- ions attack the base.
- Responsible for fluoride release.
- Bound into the set cement
- Affects ultimate stability
What can early water contamination do to the GIC setting reaction?
- Loss of polyacrylate chains
- Al3+ ions may diffuse out
- Absorption of water
- Loss of transluency
- Loss of physical properties
What can dehydration do to the GIC setting reaction?
- Cracking and fissuring of the cement.
- Softening of the surface
- Loss of matrix forming ion
How does adhesion between GIC and the tooth structure work?
The polyacid attacks the dentine and enamel and displaces calcium and phosphate ions.
Then the ions migrate to the cement to form an ion enriched layer which is stronly attached to the tooth structure (chemical bonding).
Also micromechanical attachment by removal of smear layer by dentine conditioner prior to GIC application.
Give 5 positives of GIC.
- Bulk placement is possible.
- Does not require bonding agents
- Fluoride release: GIC’s release fluoride and it is believed that this increases caries resistance.
- Once set has low solubility so does not interact with the environmental moisture.
- Acceptable aesthetics
Give 3 negatives of GIC.
- Poor aesthetics: appears as dense and opaque, due to phase separation of glass and mismatch of refractive index.
Can be overcome by chaning the Al, Ca and F content but this affects strength adversely.
- Low fracture toughness in comparison to composite.
- Susceptible to early water contamination in early stages of application
Can be combatted using copal varnish or composite over the GIC.
How do resin modified glass ionomers (RMGIC) set and how is this achieved?
- Same as GIC +
- 2 hydroxyethylmethacrylate (HEMA) an ampophillic molecule that can be photopolymerised.
Why does RMGIC set and is it rapid?
- Setting occurs primarily due to the acid base reaction.
- The rapid set is due to the polymerisation of 2-HEMA.
After polymerisation in RMGICs, what continues?
The acid base reaction continues after preliminary hardening.
Give 2 positives of RMGIC over GIC.
- Early stage dessication is reduced.
- Compressive, tensile and shear strength are higher.
Give a negative of RMGIC over GIC.
2-HEMA is cytotoxic, so unreacted HEMA can be cytotoxic to pulp tissues and osteoblasts.
Why may lining materials be used underneath GIC?
In case of pulpal exposure, or very thin intervening dentine layer as necrosis may occur and inhibit calcific repair.
What do giomers contain and give 3 properties of it.
Surface pre-reacted GIC filler particles within a resin matrix.
- Fluoride release
- Recharge of GICs
- Aesthetics.
Why is the adhesive nature of GIC a big advantage?
So there is less marginal leakage in comparison to composite.
