Plastic restorations - Resin modified glass ionomer cements Flashcards
What is a resin modified glass ionomer?
it is close to a glass ionomer but has some resin it
What are the 2 hybrid materials?
compomer and resin modified glass ionomer
What are the advantages of resin based composites?
command set by visible light
better wear resistance
lower solubility
early compressive and flexural strength
good polishability
ability to retain its polish
What are the disadvantages of glass ionomer cements?
lower early strength
susceptibility to erosion
slower setting phase
risk detection
is resin hydrophobic or hydrophilic?
hydrophobic effectively
What are the constituents of RMGICS? (BASIC)
Are conventional glass ionomer cements and water-soluble resin and modified poly(acrylic acids)
What are olyacrylic acids?
they have pendant methacrylate groups or methacryloxy groups grafted onto the polyacid chain (copolymers)
= copolymers
What is the resin group?
usually HEMA
What is the glass ionomer part?
polyacid
tartaric acid
water
ion leachable glass
What is the resin part?
water soluble (miscible) monomer
What us HEMA?
SMALL HIGHLY REACTOVE MONOMER MOLECULE
Is glass ionomer hydrophobic or hydrophilic?
hydrophilic
What connects the hydrophobic resin composite and hydrophilic GI?
HEMA
What is the problem with HEMA?
it is a powerful dermatological sensitizer causing chemical dermatitis
What form is HEMA a hazard?
in the unset form, after polymerisation it is fine
What will happen f the level of HEMA polymerisation is low?
then unconverted monomer can leach out as polyHEMA which absorbs water very quickly
What is the effect of freed HEMA monomer?
move into surrounding dental hard and surrounding tissues
may potentially have toxological effects on the dental pulp and osteoblasts if polymer degrades
How does RMGIC decrease microleakage?
it seals the dentinal tubules opened during cavity preparation and decreases the risk of microleakage
decrease microcontamination
What are the constituents of RMGIC? (powder)
Barium, strontium or aluminosilicate glass
vacuum-dried polyacrylic acid
potassium persulphate
ascorbic acid
pigments
Why use barium, strontium or aluminosilicate glass? (powder)
improved strength
imparts radiopacity
What reaction makes the poly salt matrix? (powder)
vacuum-dried polyacrylic acid and glass
What provides the chemical cure (powder)
potassium persulphate
ascorbic acid
What are the chemical constituents? (liquid)
What does polyacrylic acid react with (liquid)?
reacts with the glass to form the poly salt matrix
What does the copolymer do (liquid)?
ability to undergo both acid-base and polymerisation reactions
helps form interpenetrating network (the set)
What is the polymerisation reaction due to?
resin
What is the acid-base reaction due to?
Glass ionomer
What sharpens the acid-base reaction set? (liquid)
tartaric acid
What is the role of water in RMGIC? (LIQUID)
permits reaction between the polyacid and the glass
What happens to translucency as particle size is reduced?
as particle size is reduced there is a progressive loss in translucency (gets more opaque)
What reaction does the water-miscible monomer permit?
polymerisation reaction
What else happens during the polymerised resin phase?
it forms a scaffolding while the ionomer cement matrix is being formed
What happens as the resin content is increased?
the acid-base reaction is slowed
as the resin matrix decreases the motility of the other ions to form the chemical reaction
When is the effect of the resin addition primarily seen?
during the initial stages of the set when the glass ionomer cement is weakest
Why does the resin need to be soluble in water?
as the cement remains water based
What happens if there is an absence of water?
there is no reaction between the polyacid and the glass
Why is there a limit in the number of resin systems used in the material?
due to its hydrophobicity
What 2 types of setting reaction stake place in the material?
acid-base
polymerisation
