Clinical Aspects Of Glass Ionomer Cements Flashcards
(33 cards)
History of GIC
Glass silica cement was used before modern GIC
What is it and what was the disadvantages?
A glass powder mixed with phosphoric acid to produce a hard material
- doesn’t look good aesthetically
- poor wear resistance
What developments were made to glass silica cement?
- Instead of silicates, glass powder was used
- Instead of phosphoric acid, Poly-carboxylic acid was used
- Produced a tooth coloured filling
- Sets harder than silicate
- Increased wear resistance
- Released fluoride
- Chemically bonded to enamel and dentine
Chemical components of GIC?
Glass powder - Ion leachable glass (has chemical elements that can dissolve out)
+
Long poly acid chains
Inside a solution of water
How does GIC act when its first mixed and what is its clinical properties?
When GIC is first mixed it becomes a paste that’s quite easy to place in the cavity
- not too flowable
- sticky but manageable
GIC setting reaction
- Dissolution
- Gelation / hardening
- Maturation (increased hardening and improvement of properties of the material)
What happens during the first stage of dissolution?
During dissolution we add water to the acid (comes as a freeze dried powder)
Poly acid chain + H2O —> liberated hydrogen ions
Poly acid - long polymer chain with lots of carboxylic acid groups on it
When you add water to the poly chain, the hydrogen ions become liberated and can go off into the solution leaving negatively charged carboxyl groups behind on the poly acid chains
Describe the ions that are present
The glass particles are mainly silica but also contain other elements - calcium, aluminium and fluoride
Calcium-Alumino-Fluoro-Silicate glass
There are also others which make the material radiopaque and tooth coloured etc
What is the purpose of the liberated hydrogen ions?
When the hydrogen ions that have been liberated from the poly acid come in contact with the glass, they erode away at it. - Releasing the ions out into the solution
What happens to the ions now that they’re free in solution?
- They come into contact with poly acid chains which are negatively charged. Calcium and aluminium are positively charged, so attracted.
- As calcium has 2 negative charges, and aluminium has 3, they’re able to be attracted to 2 chains at the same time = cross linking effect occurring
- Whenever a calcium ion comes into contact with 1 chain, it grabs hold of another chain and locks the 2 together
- This happens repeatedly causing more and more of the poly acid chain to become locked together
- As this occurs, the fluoride that was bound to the calcium or aluminium is then released off into solution.
What happens during maturation?
Over time, more and more calcium and aluminium ions cross link acid chains.
Therefore overtime the material becomes more harder and stronger, but it takes time for all of the ions to bond and cross link.
Until they are cross linked however, they may be lost from the material into the saliva if the restoration gets wet - leaving it weak and the cross links cant be formed if the remaining ions are lost.
How do we combat the ions becoming lost?
After we first place a glass ionomer, and after it has initially hardened, in the gelation stage we apply a varnish which is a water proof coating over the top of the glass ionomer - This prevents the ions from being lost and allows the maturation stage to occur.
Benefits of glass ionomer
- Easy to use (doesn’t need bond, tolerates moisture) - more hydrophilic than composite as it contains water
- Chemically bonds to enamel and dentine (unlike composite which forms a micro mechanical bond)
- Releases fluoride
describe the adhesion to enamel and dentine
- Chemical bond
- Some of the hydrogen ions which we’ve seen before have attacked the glass to release ions, can also attack the tooth surface if they come into contact with it.
- This causes a release of calcium and phosphate from the apatite within the mineral component of the tooth
- Some of the phosphate diffuses off into the glass ionomer and some of the calcium and aluminium ions as well as fluoride from the glass ionomer diffuse into the tooth
How can we improve the chemical adhesion to the tooth?
Dentine conditioner
We need to remove the smear layer and clean the tooth surface first using 10% Poly-acrylic acid (dentine conditioner)
Apply for 20 seconds, then rinse and dry
Evidence of benefits of conditioner prior to glass ionomer?
If its not conditioned, the % of gap free margins (where the glass ionomer has stayed in good contact with the tooth surface is much lower after 100,000 chewing cycles than when conditioner is used.
The glass ionomer stays well bound to the tooth surface if dentine conditioner is used.
Is fluoride release consistent?
High fluoride release after the glass ionomer is first placed
Gradually fluoride is lost from the material and very little fluoride is left behind to disperse out.
Is there a benefit to fluoride release from GIC?
Some say the amount of fluoride release from glass ionomer may not be clinically effective - studies have shown 50% of GIC restorations are removed and replaced due to secondary caries. - Therefore showing the fluoride is not having a beneficial effect. However we are unsure as to why GIC was used in these teeth in the first place eg, may be used where composite wasn’t suitable or the teeth may have had residual caries before the GIC was placed.
Studies that show there is a positive effect from the fluoride
- Greater caries inhibition around the GIC restorations compared to amalgam
- Significantly greater caries prevention effect than composite
- Significantly fewer demineralised restoration margins in class II restorations in deciduous teeth
What is fluoride recharging with GIC?
GIC can absorb fluoride from toothpaste etc and slowly release it over time
Disadvantages of glass ionomer
- weak compared to other materials
- poor aesthetic compared to composite (tooth colour and translucency poor + they change colour over time)
- Poorer survival time compared to other materials (amalgam outlives GIC)
Over the years improvements were attempted to make GIC better what were they?
- 1985 Addition of amalgam powder (poor aesthetics + no benefit) More resistant to acid, lower flexural strength, more prone to abrasion
- 1989 Addition of HEMA to GIC
- 1990s Increased filler content
What is HEMA
Monomer that’s in the bonding agent
Can polymerise in the presence of blue light
Can be added as a liquid or chemically to replace some of the carboxylic acid groups on the poly aromatic chain
RMGIC
Resin modified GIC what is it?
- Better aesthetic
- Command set with blue light (don’t have to wait for maturation or gelation)
- Ability to set straight away - More resistant to losing ions during maturation
- Stronger
How does RMGIC work and what are the disadvantages?
When the glass ionomer is going through its gelation stage, we light cure it to set the components into place
Although this improves the properties of the glass ionomer, it means that it no longer forms chemical bonds with the tooth surface because the hydrogen ions are locked down and it cannot release fluoride as these are locked down.
- RMGIC stops acting like a GIC once cured
- Lower fluoride release + cannot be recharged
- Polymerisation shrinkage
Another development was Increased filler particles
describe how this works as well as the advantages and limitations
- Addition of smaller glass particles = occupy more space within the glass ionomer
- Eg, Fuji 9
- Suitable for fairly long term temporary restorations in posterior teeth
- Not a replacement for amalgam or composite
