DML3: Modifications of GICs Flashcards
What is the powder composition of cermets
- metal (usually silver) fused to GIC powder which is then ground
- OR metal powder mixed with GIC powder = admix
- titanium dioxide is added to improve colour (reduces silver colour)
What is the liquid composition of cermets
Same as GIC, can be hand mixed or encapsulated
What are the properties of cermets
- More abrasion resistant and less brittle than GIC
- Fluoride release and bond strength is reduced
- They are radiopaque
- They are difficult to handle so only the encapsulated form is typically used
What are cermets used for
- cermet/compositve laminate technique
- linings for amalgam restorations
- repair of restorations
What is the liquid comsposition of resin modified glass ionomer cements (RMGICs)
- PAA, tartaric acid
- Water compatible vinyl monomer = HEMA or PAA with pendant
- Photo-initiator system (for light cure), may contain Bis-GMA or UDMA
What is the powder composition of RMGIC
Ion leachable glass and photosensitised
Outline the setting reaction for RMGIC
It has dual setting which occurs simultaneously
- Acid-base reaction of the GIC
- Photo-initiated polymerisation of the monomer
What is the main difference in the set structure of RMGIC and GICs
RMGIC has an interpenetrating network of poly salt matrix entangled with poly(hydroxyethyl methacrylate)
What are the advantages for RMGIC (7)
- Less soluble
- Less brittle (due to addition of resin polymer)
- Can be polished immediately
- Fluoride release is similar/higher than conventional GIC
- Adhesion to tooth
- Better compressive strength
- Longer working time (>20s) and rapid command set
What are the disadvantages of RMGIC
- Addition of HEMA slows the acid base reaction because the components are further apart as they have been diluted
- Depth of cure is less due to reduced light transmission of the filler
- Polymerisation exotherm is higher than composites
- Undergo polymerisation shrinkage
- Swell in water after curing as PHEMA is a hydrogel that absorbs water
- Must be photo-cured quickly otherwise IPN not formed
- Unpolymerised HEMA will leach out so increased cytotoxicity
- Stains as water and liquid uptake occurs
- HEMA, Bis-GMA and PAA can separate in the bottle
What is tricure RMGIC and why is it used
This is where it undergoes
- Photo cure
- Room temperature cure
- Acid-base reaction
It is needed to eliminate the need for layering in deep cavities and it also reduces swelling of the restoration as it decreases the absorption by PHEMA
What are the uses of RMGIC
- Cavity lining
- GIC-composite laminate technique
- Anterior restoration
- Restorative for deciduous teeth
- Luting cement
What is the powder composition of poly acid modified composites (PAMC)
- Bis-GMA/UDMA + visible light curing system
- Ion leachable fluoroaluminosilicate glass filler + conventional fillers
- Acidic monomer = bifunctional with pendant carboxylic groups
- Hydrophilic monomers to aid water absorption and F- release
- Moisture and light sensitive during storage
What is the importance of the acidic monomer and hydrophilic monomer in poly acid modified composites (PAMC)
They bring COOH groups which increases water absorption which is needed for the acid-base reaction to occur
What is the purpose of the following within PAMCs
- UDMA
- Acid pendant resin
- Crosslinking resin
- Strointium flurosilicate glass
- Camphaquinone/amine
- Stabilisers
- Base resin which polymerises to form the matrix of the cement
- Acidic hydrophilic matrix providing COOH groups
- Harder and tougher matrix to give strength as this is compromised by the hydrophilic monomers
- Filler and source of F-, undergoes acid-base reaction
- Photoinitiator system
- Extends shelf life
What is the main advantage of PAMC
After curing, the water uptake in the mouth allows the acid base reaction to occur and this causes fluoride release over an extended period (but this is at a lower level compared to GIC and RMGIC)
What are the properties of PAMC
- good handling and adapt well to cavity walls
- require dentine bonding agent and incremental placement
- shrinkage is similar to composites
- level of water uptake is similar to composites but faster
- water uptake compensates for shrinkage
- inferior mechanical properties compared to composited due to hydrophilic acidic monomers
When is PAMC used
- low stress situations
- proximal and abrasion cavities
- permanent restorations in primary teeth
- long term temporary in permanent teeth
- luting cement
What are giomers
Composite resin plus pre-reacted glass ionomer particles as a filler
- these have the fluoride release and recharge of GIC
- and the superior properties of composite
- used as a restorative, luting cement and fissure sealant
