Glass Ionomer Cements Flashcards
Why is the SiO2 to Al2O3 ratio important in the GIC powder composition?
The ratio governs reactivity
Which components in the GIC powder composition are important for radiopacity? (3)
- Sr2+
- Ba2+
- La3+ (lanthanum)
Which components in the GIC powder composition boost fluoride release? (3)
- Na3AlF6
- AlF3
- NaF
Which components in the GIC powder composition provides phosphate release? (2)
- P2O5 (Phosphorus pentoxide)
- AlPO4 (Aluminium phosphate)
At what temperature is the ion leachable glass melted at?
1150 – 1450°C
Describe the process of acquiring the cement version of the ion leachable glass (4)
- Melted at high temperature
- Rapid cool
- Grind into a powder
- Acid wash to control reactivity
What is the liquid composition of GIC?
- 50% Polyacryclic acid (PAA)
- 10% Tartaric acid
- 40% Water
What are the 3 stages of the GIC setting reaction?
- Dissolution phase
- Gelation phase
- Final Maturation
What occurs during the dissolution phase of the GIC setting reaction?
H+ ions from the PAA attack the glass liberating Ca2+ and Al3+
What other ions are released/formed during the dissolution phase of the GIC setting reaction? (3)
- Na+ released
- F- released
- Released silicon forms Si(OH)4
What happens to the liberated Ca2+ and Al3+ during the dissolution stage of GIC setting?
Ca2+ and Al3+ will be in the form of complexes with F- or tartaric acid
What is the benefit of tartaric acid in GIC?
They “hold” the cement forming ions (increasing working time) until the acid is partially neutralised
How does the GIC set in phase 2 occur?
- Polymer chain entanglement
- Cross-linking of the chains by: Ca2+ & Al3+
What do Ca2+ & Al3+ form in the gelation stage of GIC setting? (2)
- Hydrated Calcium
- Aluminium polyacrylates
How long can the final maturation stage of GIC setting take?
Can take 24 hours
What occurs during the final maturation stage of GIC setting?
- Ratio of bound to unbound water increases
- Strength increases
What occurs during early water exposure to GIC?
- Result in dissolution of reactive components
- Poor cement properties
What occurs during dehydration to GIC?
- Loss of water critical for the continuation of the setting reaction
- Poor cement properties
Explain the fluoride release from GIC
- Initial high level release from exposed glass particles
- Long term lower level release from deeper areas of the matrix
What can GIC release for caries inhibition? (3)
- F-
- Sr2+
- Ca2+
Comment on the biocompatibility of GIC
- Bioactive
- Low irritant despite low pH
What are some advantages of GIC? (7)
- Chemical bond to tooth
- Long-term fluoride release and uptake
- No shrinkage
- Self healing and can be repaired
- Potential to re-mineralize
- Thermal expansion coefficient similar to tooth
- Aesthetics
What are some disadvantages of GIC? (2)
What affect does age have on these?
- Weaker than composites and amalgam but strength increases with age
- Poor wear resistance at the early stage, improves with age
What are some uses of GIC? (6)
- Restorations for anterior teeth
- Tunnel restorations
- Luting
- Cavity lining
- Repair of erosion lesions
- Fissure sealant
What are the 2 powder compositions methods of cermets? (2)
- Metal (usually silver) fused to GIC powder then ground
- Metal powder mixed with GIC powder (Admix)
What are the delivery systems of cermets? (2)
- Hand mixed
- Encapsulated
List 2 advantages and 2 disadvantages of cermets (4)
- More abrasion resistant and less brittle than conventional GICs
- They are radiopaque
- Difficult to handle
- Fluoride release and bond strength are reduced compared to GICs
What are some of the uses for cermets?
- Cermet/composite laminate technique
- Linings for amalgam restorations
- Repair of restoratives
What is the liquid composition for Resin Modified Glass Ionomer Cements (RMGIC)? (5)
- PAA
- Tartaric acid
- Hydroxyethyl Methacrylate (HEMA)
- Bis-GMA
- Photo-initiator system
What is the powder composition for RMGIC? (2)
- Ion-leachable glass
- Photosensitiser
Comment on the dual setting of RMGIC
- Acid-base reaction of the glass ionomer cement
- Photo-initiated polymerisation of the monomer
What are some advantages of RMGIC? (7)
- Less soluble
- Less brittle
- Can be polished immediately
- Fluoride release is similar/higher than GIC
- Adheres to tooth
- High strength
- Longer working time with a rapid set
What are some disadvantages of RMGIC? (6)
- Addition of HEMA slows the acid base reaction
- Depth of cure is less than composite because less light transmission due to glass
- Polymerisation exotherm is higher than composites
- Polymeristaion shrinkage
- Swell in water
- Stain
What are the uses for RMGIC? (5)
- Cavity lining
- In the GIC-composite laminate technique
- As an anterior restorative
- Restorative for deciduous teeth
- Luting cement
What is the powder composition of Polyacid Modified Composites (PAMC)? (4)
- BisGMA (plus light cure)
- Ion-leachable fluoroaluminosilicate glass
- Acidic monomer
- Hydrophilic monomers
How is PAMC set?
The principle setting reaction is by photo initiation of the methacrylate groups
How is fluoride released by PAMC?
After curing, water uptake in the mouth allows the acid/base reaction to occur
Results in fluoride release over an extended period
but at a lower level compared to conventional GIC and RMGIC
What releases more fluoride PAMC or (RM)GIC?
PAMC releases fluoride at a lower level compared to conventional GIC and RMGIC
Comment on the handling properties of PAMC
Good handling properties
What are some of the uses of PAMC? (4)
- Proximal and abrasion cavities
- Permanent restorations in primary teeth
- Long-term temporary in permanent teeth
- More recently as a luting cement
What type of bonding agent is required with PAMC?
Require dentine bonding agent
Compare PAMC to Composites (2)
Shrinkage?
Mechanical properties?
- Shrinkage similar to composites
- Inferior mechanical properties compared to composites
How is PAMC placed in a restoration?
Require incremental placement
