Glass Ionomer Flashcards
What are the uses of GI? and what are examples of each use?
Restorative - filling materials (riva, vitremer)
Core build up - prior to restoration with crown (vitremer crown core)
Lining - underneath permanent fillings (vitrebond, ionoseal)
Luting - cementing indirect restorations (fuji luting, vitremer luting cement, aquachem)
What are the liquid acid components of GI and what is their role?
Polyacrylic acid (ionic monomers) - usually copolymers of acrylic and itaconic acid or acrylic and maleic acid
Tartaric acid - added to control the setting times
What are the biggest glass base powder components of GI?
Silica, SiO2 (Silicone dioxide) 30% - 40%
Alumina, Al2O3 (Aluminium dioxide) 15% - 30%
Calcium Fluoride, CaF2 15% - 35%
What does adding strontium and lithium salts do?
can increase the radiopacity but these play no part in the reaction chemistry.
What does the ratio of alumina/ silica do?
The ratio of alumina/silica alters the translucency.
More silica more translucent.
What are the two variations of the acid being mixed with the base?
anhydrous materials (no water)
The acid is freeze dried and added to the powder
The liquid is distilled water
This makes for easier handling of the material, particularly mixing
encapsulated materials
Consistent powder/liquid ratio
Easier to use
Should be more consistent properties of the mixed material
What does the powder particle size dictate?
what size gives a luting cement a low film thickness?
The smaller the particle size the quicker the setting reaction and the more opaque the set cement.
<20 micrometres
What are the 3 phases of the setting reaction?
Dissolution
Gelation
Hardening
What occurs during dissolution phase?
Acid (H+ ions) attacks the glass powder, releasing metal ions (Ca, Al, Na & F). Leaves silica gel around unreacted glass
What occurs during the gelation phase?
how long does it take?
initial set due to calcium ion crosslinking with polyacrylic acid forming calcium polyacrylate
several minutes
What occurs during hardening phase?
how long does this take?
Continued crosslinking with aluminum ions for increased strength over time forming aluminium polyacrylate
increased strength
process does not start until 30 minutes and takes a week
What is important following gleation and why?
It is important that GIC is protected from moisture and dessication following gelation.
This is when it is ‘set hard’ in the mouth but before maturation has begun
What can contamination cause?
Aluminium ions diffuse out of the material
Excessive drying means water will be lost
Saliva contamination causes absorption of water
All lead to a weak material which will be rough, break up and have poorer aesthetics
What materals offer better protection after placement?
varnish (acetate)
resins (DBA, unfilled Bis-GMA)
Why is petroleum gel not as effective?
removed by action of lips and tongue
What was used in newer formulations to improve their ease of use?
Tartaric acid, this greatly improved their ease of use
Working time is largely unchanged but setting time is shortened
What are the properties of adhesion of GIC?
What is bond strength to enamel?
Can bond to enamel and dentine without the need for
use of an intermediate material
Bond strength not high compared with composite, about 5MPa
Good sealing ability with little leakage around margins
What is chemical bonding mechanism of GIC?
Chelation between carboxyl groups in the cement and Ca on the tooth surface.
Re-precipitation of complex mixture of calcium phosphate (from apatite) and calcium salts from the polyacid onto and into the tooth surface
Hydrogen bonding or metallic ion bridging to collagen
What does a good bond require?
What conditioner is best?
Clean surface
Conditioned surface
Conditioned, not etched.
Little or no tissue is removed.
Best conditioner appears to be polyacrylic acid
Purpose is to produce clean smooth surface
What does higher silica content improve?
higher translucency = better aesthetics
What are the mechanical properties of GIC compared to composite?
Lower compressive strength than composite. Less than
half. 80 – 110MPA
Poorer wear resistance than composite, subject to abrasion
Lower hardness than composite
Higher solubility than composite (dissolution of unprotected material during gelation phase, and long term erosion by acids)
Good thermal properties expansion similar to dentine
No contraction on setting
Once set less susceptible to staining and colour
change than composites
Fluoride release (recharge)
Brittle
Low aesthetics
How is fluroide released for GIC?
Initial fluoride release but this diminishes very quickly, over the first week.
then
recharges from environment
What were cermets developed for and why were they not useful?
Developed to overcome Glass Ionomer brittleness
Silver was added to the glass (equal volumes) to
increase toughness and wear resistance.
No evidence that this was the case, only ended up making a silver coloured GIC. Looks like dull amalgam
What are the power and liquid components of RMGIC?
Powder: Fluoro-alumino-silicate glass, barium glass, polyacrylic acid, initiators
Liquid: HEMA (resin), polyacrylic acid with methacrylate groups, water, initiators
Why does a redox reaction happen in some RMGIC after the conventional acid-base reaction?
What is it called?
- Free Radicals and Polymerization: The redox reaction generates free radicals. These free radicals act similarly to those produced during light-cure activation. They attack the methacrylate molecules (present in the resin component) and initiate the polymerization process, which hardens the material.
backup mechanism to ensure cure of full thickness of material
The REDOX reaction continues for about 5 minutes after initial mixing
What varies between manufacturers?
about conditioning of the tooth surface prior to cement placement.
What are the advantages of RMGIC?
Better physical properties
Lower solubility
Fluoride release
Better translucency and aesthetics
Better handling
Good bond to enamel and dentine
Set in cure
What are the disadvantages of RMGIC?
Polymerisation Contraction
Exothermic setting reaction
Swelling due to uptake of water (HEMA is extremely) hydrophilic
HEMA is toxic to the pulp it must be polymerised completely
Benzoyl iodides and bromides can be released which are cytotoxic
How is RMGIC compared to GIC?
Better aesthetics
Easier to use
Stronger
How is RMGIC compared to composite resin?
Easier to use
Fluoride release
What are the uses of RMGIC?
Dressing
Fissure sealant
Endodontic access cavity temporary filling
Luting
Orthodontic cement
Restoration of deciduous teeth
Restoration of permanent teeth
Base or Lining
What is the most likely reason for placing a resin modified glass ionomer lining under an amalgam restoration?
Thermal protection of the pulp
