Resin Modified Glass Ionomer Cements Flashcards
What is the aim of RMGIC’s?
To address the limitations of conventional glass ionomer cements by utilising the advantages of resin composite materials
What are the constituents of RMGIC’s?
- Conventional GIC + water soluble resin and modified poly(acrylic acids)
- Modified polyacrylic acids have pendant methacrylate groups grafted onto the polyacid chain
- HEMA resin
What is HEMA?
Hydroxyethylmethacrylate
- small highly reactive monomer molecule
- makes polymer polyHEMA
- Hydrophilic swelling when exposed to water —> absorbs 10% - 600% of its own dry weight of water
- HEMA monomer is cytotoxic - causes chemical dermatitis - need to be careful with unset material and soft tissues —> reduced cytotoxicity after polymerisation
What shouldn’t you do when applying HEMA based RMGIC?
- don’t place directly onto vital dental pulp tissue even in its polymerised form - release of free monomer into the surrounding dental hard/surround tissue may have toxicological effects on dental pulp & osteoblasts
- Need residual dentine thickness of at least 0.2-0.5mm
Why should you apply a sublining to the pulp before applying HEMA based RMGIC?
Protects the pulp due to HEMA’s cytotoxic traits & high exothermic setting reaction especially if the material is used in bulk
What are the powdered chemical constituents of RMGIC?
- Barium/Strontium/aluminosilicate glass = improved strength and radiopacity
- Vacuum-dried Polyacrylic acid = reacts with the glass to form the poly salt matrix
- Pigments = Allows for different shades
- Potassium persulphate Ascorbic acid = Redox catalyst system to provide the methacrylate cure
What are the liquid constituents of RMGIC?
- Polyacrylic acid = Reacts with the glass to form the poly salt matrix
- HEMA = water miscible resin
- Polyacrylic acid with pendent methacrylates (copolymer) = ability to undergo both acid-base and polymerisation reactions to help form interpenetrating network
- Tartaric acid = Sharpens the acid-base reaction set
- Water = permits reaction between the glass and Polyacid
- Photo-initiators = achieves light curing
How does the particle size effect application?
- Finer particles used in luting cements (luting agents function is to fill the void at restoration-tooth interface and mechanically lock the restoration in place)
- larger particles are for restorative work
- Progressive loss in translucency as particle size is reduced
What are the 2 types of setting reaction that take place within RMGIC?
- Acid-base - polyacrylic acid reacts with the glads to form the poly-salt matrix (as GIC) (provides early strength)
- Polymerisation of resin forms a scaffolding while the ionomer cement matrix is being formed
- essential that the resin is soluble in water as absence of water means no reaction will occur between the polyacid and glass
What’s the polymerisation component in RMGICs setting reaction?
- Light activated free-radical methacrylate reaction
- Layers must be 0.5mm or less to polymerise adequately
- Methacrylate will be uncured in the absence of light
- Dark-cure initiator system is sometimes incorporated to achieve adequate free-radical Methacrylate polymerisation where light cannot penetrate but there will be less cross-linking
- Dark-cure also reduces the Mechanical properties of the end material by 25-30%
What’s the setting reaction for Dual-Cured products?
- Acid-base reaction which commences at the start of mixing and continues for a substantial amount of time after all setting reactions have been completed (matrix is susceptible at this stage to extraneous water)
- Polyacrylic acid is mixed with aqueous solution of HEMA starting acid-base reaction - Light activation - occurs at the end of placement and is completed with 10 secs of light activation
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