GIC setting and polyacid modified composite Flashcards
What is GIC?
Describe the composition of different types of Glass Ionomer Cement.
• GIC is a water based cement that consists of a Fluro-aluminosilicate glass base and polyakenoic acid as the liquid. It is formed via an acid-base reaction
• Liquid: is a 40-55% aqueous solution of polyalkenoic acid, combined with water.
In addition, 5-15% Tartaric acid is added to control setting reaction, retains the working time and sharpens the setting time
Is GIC acidic?
Due to the presence of polyalkenoic acid in its liquid component, the low pH of an unreacted cement can affect living tissues
A fully set cement has no acidic effect.
List the three types of GIC setting reactions
- Self cure
- Light- intiated self cure
- Light- cure
Describe self-cure three steps involved in self curing
Stage 1: Dissolution
• Hydrogen ion from the polyacrylic acid attacks the glass surface
(acid attack glass base)
• Calcium/ Strontium, aluminium and fluoride are released
Stage 2: Precipitation
• Calcium/ Strontium and aluminium ions binds to polyanions
• The calcium chains form first, producing a clinically early set that is relatively fragile and highly soluble in water
• The aluminium chains form over the next 24 hours which are strong and insoluble, providing the major physical properties of the GIC
Stage 3: Hydration
• Cross-links continue to develop and are progressively hydrated making them more rigid
What is the role of water in setting of auto- cure systems?
With 24 hours of setting reaction (precipitation), some water should be uptaken. This is because during hydration stage water makes it less prone to desiccation, stronger and more rigid and more translucent.
However, after hardening, fresh cement is extremely prone to the cracking due to drying of loosely bound water.
Hence these cements must be protected by application of some sort of varnish or vaseline. (vaseline for Fuji VII only)
How does GIC adhere to tooth structure?
Chemical bonding process
• Carboxyl group from polyacid penetrates and bond with Ca2+ in enamel and dentine
Fusion bonding process
• Strontium and Fluoride from the unset ionomer bond with Calcium and Phosphate in enamel and dentine. They eventually precipitate to form “Inter-diffusion Zone” which is stronger and more acid resistant.
Explain the setting reaction of light- initiated self cure.
• A red dye (ferric oxide) is incorporated in the glass ionomer.
• After irradiation from the light, the acid-base reaction – already on it’s way- will take place more rapidly.
• The pink shade absorbs heat energy easily, which accelerates the setting
reaction to 40 sec, compared with 1 min 40 sec without light
• The material does not have resin
• Is highly bactericidal due to a high fluoride release
• Can be used as fissure protection, root surface protection or as a lining material
Explain the setting reaction of light cure.
Resin-Modified Glass Ionomers sets partly from:
- An acid- base reaction between polyacrylic acid and Fluoro -aluminosilicate glass
- Photo- initiated polymerisation of HEMA monomer by camphoroquinone
- Oxidation- reduction reaction polymerisation of HEMA monomer
HEMA which is present in the resin formula will set following light initiation and will provide protection to the autocure system from immediate water uptake
What are two new types of products available?
- Compomer
- Giomers
They are polyacid- modified composite resin
What is a compomer? What is a giomer?
A compomer is a composite resin that uses an ionomer glass.
A giomer is a hybrid material: glass ionomer and composite.
Describe the composition of compomers
There is a small quantity of dehydrated polyalkenoic acid that is incorporated with the filler particles. There is no water in the composition.
Do compomers from an ion-exchange layer? Why?
NO.
• The acid-base reaction doesn’t occur until for some time after placement so it is not possible for a compomer to bond to tooth structure through an ion exchange mechanism. Acid etching is required as adhesive system
• The restoration must therefore be preceded by an application of a resin bonding agent, therefore compomers set only by light activation
Should compomers be used on occlusal bearing surfaces? Why?
No, because it isn’t filled with much filler particles, thus wear resistance is low
What are giomers composed of?
They are resin-based with pre-reacted glass ionomer particles (PRG).
Particles are made of fluorosilicate glass that has been reacted with polyacrylic acid prior to being incorporated into the resin
What are properties of giomers?
Do they require etching for placement?
Claims to have properties of GIC: such as fluoride release, fluoride recharge
And
Composite: such as excellent aesthetics, easy polishability
YES
