DMS- RMGI Flashcards
What can Glass Ionomer Cement or Resin modified Glass Ionomer be used for?
- Desciduous tooth restoration
- Permanent tooth restoration
- Luting
- Orthodontic cement
- base or lining
- temporary filling
- dressing
- fissure sealant.
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What is conventional Glass Ionomer cement made of?
- Powder (base)
e. g. silica - Liquid (acid)
e. g. tartaric acid
Compare anhydrous Glass ionomer cement to encapuslated Glass ionomer cement
Anhydrous glass ionomer cement powder = freeze dried acid and the base.
Liquid- distilled water.
Encapsulated glass ionomer cement has a consistent powder and water ratio.
Discuss the effect of particle size on Glass Ionomer cement.
The smaller the particle size, the more opaque the material is.
The larger the particle size, the better the asthetic.
Describe the stages of Glass ionomer cement setting.
Dissolution (Mixing of the acid and the base)
H+ attack the glass surface releasing ions ( Ca, Al, F and Na)
This leaves an unreacted glass core and silica gel round the outside.
Gelation (initial set of the material)
Calcium ions cross link with the polyacid producing calcium polyacrylate.
Hardening (aluminium crosslinking)
aluminium ions cross link with the polyacid to produce aluminium polyacrylate.
Why do we protect the Glass ionomer cement after the inital set?
We protect it from moisture to prevent contamination that would weaken the material.
How do we protect the glass ionomer cement after the initial set?
- Varnishes e.g. acetate
- Resins e.g. dentine/ enamel bonding agents
- Gels e.g vaseline
Why do we condition Glass ionomer cement?
To clean the surface.
We use polyacrylic acid.
Discuss the mechanical properties of Glass ionomer cement
- Poor tensile strength
- low compressive strength
- poor wear resistance
- low hardness
- more soluble
- Simular thermal expansion to dentine
- Does not contract on setting
- Less suceptible to staining.
Discuss the fluoride release of glass ionomer cement
- It releases lots of fluoride initially, but the amount of fluoride released significantly reduces after a week.
- Can act as a fluoride reservoir- taking in fluoride for the environment (e.g. from toothpaste) and releasing it when there is less fluoride in the environment.
What is tartaric acid used for in Glass ionomer cement?
To reduce the setting time of glass ionomer cement
What is Resin modified glass ionomer made of?
Powder :
- fluoro-alumino-silate glass
- barium glass
- vaccum dried polyacrylic
- pottasium persulphate
- ascorbic acid.
- pigments
Liquid:
- tartaric acid
- HEMA (water miscible resin)
- water
- photo-initators (for light curing)
- Polyacrylic acid to undergo (acid base & polymerisation reactions)
Describe the setting reaction of Resin modified glass ionomer
There is Dual curing or Tri curing.
Dual curing:
- GIC setting
- Resin reaction (where cross linking of methacrylate produces a resin matrix)
Tri curing:
- GIC setting
- Redox reaction- ensures the restoration fully sets.
- Resin reaction
Compare Resin modified glass ionomer to glass ionomer cement.
Advantages
Stronger
good bond to enamel and dentine
lower solubility
fluoride release
better aesthetics and translucency
better handling
Disadvantages
Polymerisation Contraction as it now contains a resin
Exothermic setting reaction.
HEMA is hydrophillic so will take up water
HEMA is toxic to the pulp if not properly set.
Releases cytotoxic benzyoyl idoides and bromides.
