Resin Modified Glass Ionomer Cements Flashcards Preview

Semester II - Dental Materials > Resin Modified Glass Ionomer Cements > Flashcards

Flashcards in Resin Modified Glass Ionomer Cements Deck (16)
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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?


- 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?

1. Acid-base - polyacrylic acid reacts with the glads to form the poly-salt matrix (as GIC) (provides early strength)

2. 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?

1. 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

2. Light activation - occurs at the end of placement and is completed with 10 secs of light activation