Glass Ionomers Flashcards
Name the different types of GIC’s (2)
- Conventional GI
- Resin Modified GI
- Self cure
- Light cured
State the uses of GIC’s (4)
- Restorative
- filling material e.g. RIVA, vitremer - Core build up
- Prior to restoration with crown e.g. vitremer crown core - Lining
- Underneath permanent fillings
e. g. Vitrebond - Luting
- Cementing indirect restorations
What are the components of a GIC? (2)
- Acid
- Liquid - Base
- Glass powder
What makes up the acid component of a GIC? (2)
- Polyacrylic acid
(Ionic monomers) - Tartaric acid
(added to control setting characteristics of the material)
What makes up the base component of a GIC?
- Silica
- Alumina
- CaF
- AlF
- Aluminium Phosphate
- NaF
Advantage of adding more silicone to a GICl?
More translucent
Define the term radiopaque
White area seen in an X-ray
Advantage of adding Strontium and Lithium salts to a GIC?
Can increase radiopacity (but play no part in chemistry reaction)
What affects the translucency of a GIC?
Ratio of alumina/silica
More silica = more translucent
Compare:
Anhydrous materials
Encapsulated materials
Anhydrous materials:
- The acid is freeze dried and added to the powder
- Liquid is distilled water (easier handling of material, particularly mixing)
Encapsulated materials:
- Consistent powder/liquid ratio
- Easier to use
- More consistent properties of mixed material
What are some of the variations that can exist in GIC composition? (2)
- Powder particle size can vary
<20um required for luting cement to give a low film thickness - Molecular weight of acid changes
- The higher the weight the better the mechanical properties of the set material
Advantage of small particle size?
> Smaller the particle size, the quicker the setting reaction and the more opaque the set cement
What are the 3 phases of the setting reaction?
- Dissolution
- Gelation
- Hardening
What happens during dissolution? (4)
- Acid into solution
- H+ ions attack the glass surface
- Ca, Al, Na and F ions are released
- Leaves silica gel around unreacted glass
What happens during gelation? (3)
- Initial set of material caused by formation of calcium polyacrylate, can take several mins
- Material will appear hard in mouth
What is the initial set of material due to?
- Ca ion cross linking with the polyacid by chelation with the carboxyl groups
- Ca ions = bivalent so can react with 2 molecules joining them
Why is crosslinking of Ca ions not ideal
The Ca can chelate with 2 carboxyl groups on the same molecule
What happens during the setting reaction? (4)
- Trivalent Al ions ensure good cross linking with an increase in strength
- Al polyacrylate formation takes a long time, doesn’t start for at least 30mins and can take a week/longer to be complete
- Al reaction ensures a higher degree of cross linking
- This improves mechanical properties of material
How does contamination affect the setting reaction?
- Al ions diffuse out material
- Excessive drying means water will be lost
- Saliva contamination causes absorption of water
- Leading to a weak material which will be rough, break up and have poorer aesthetics
How is conventional GIC protected during placement?
- Varnishes
- Resins
- Dentine/enamel bonding agents
- Unfilled Bis-GMS resins - Greases/gels
- Vaseline in paeds