Clinical Aspects Of Glass Ionomer Cements

Question 1

History of GIC

Glass silica cement was used before modern GIC

What is it and what was the disadvantages?

Answer 1

A glass powder mixed with phosphoric acid to produce a hard material

• doesn’t look good aesthetically
• poor wear resistance

Question 2

What developments were made to glass silica cement?

Answer 2

• 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

Question 3

Chemical components of GIC?

Answer 3

Glass powder - Ion leachable glass (has chemical elements that can dissolve out)
+
Long poly acid chains

Inside a solution of water

Question 4

How does GIC act when its first mixed and what is its clinical properties?

Answer 4

When GIC is first mixed it becomes a paste that’s quite easy to place in the cavity

• not too flowable
• sticky but manageable

Question 5

GIC setting reaction

Answer 5

1. Dissolution
2. Gelation / hardening
3. Maturation (increased hardening and improvement of properties of the material)

Question 6

What happens during the first stage of dissolution?

Answer 6

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

Question 7

Describe the ions that are present

Answer 7

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

Question 8

What is the purpose of the liberated hydrogen ions?

Answer 8

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

Question 9

What happens to the ions now that they’re free in solution?

Answer 9

1. They come into contact with poly acid chains which are negatively charged. Calcium and aluminium are positively charged, so attracted.
2. 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
3. Whenever a calcium ion comes into contact with 1 chain, it grabs hold of another chain and locks the 2 together
4. This happens repeatedly causing more and more of the poly acid chain to become locked together
5. As this occurs, the fluoride that was bound to the calcium or aluminium is then released off into solution.

Question 10

What happens during maturation?

Answer 10

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.

Question 11

How do we combat the ions becoming lost?

Answer 11

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.

Question 12

Benefits of glass ionomer

Answer 12

• 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

Question 13

describe the adhesion to enamel and dentine

Answer 13

• 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

Question 14

How can we improve the chemical adhesion to the tooth?

Answer 14

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

Question 15

Evidence of benefits of conditioner prior to glass ionomer?

Answer 15

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.

Question 16

Is fluoride release consistent?

Answer 16

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.

Question 17

Is there a benefit to fluoride release from GIC?

Answer 17

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

Question 18

What is fluoride recharging with GIC?

Answer 18

GIC can absorb fluoride from toothpaste etc and slowly release it over time

Question 19

Disadvantages of glass ionomer

Answer 19

• 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)

Question 20

Over the years improvements were attempted to make GIC better what were they?

Answer 20

• 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

Question 21

What is HEMA

Answer 21

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

Question 22

RMGIC
Resin modified GIC what is it?

Answer 22

• 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

Question 23

How does RMGIC work and what are the disadvantages?

Answer 23

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.

1. RMGIC stops acting like a GIC once cured
2. Lower fluoride release + cannot be recharged
3. Polymerisation shrinkage

Question 24

Another development was Increased filler particles

describe how this works as well as the advantages and limitations

Answer 24

• 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

Question 25

Problems with current Glass ionomers?

Answer 25

• weak - (fracture easily, wear is high)
• complicated to use (conditioner + placement + varnish)
• waiting time - sticky at first, short workable time
• resin modified materials cease to act like GIC once light cured (doesn’t release fluoride or chemically bond to tooth)

Question 26

Newest development of glass ionomers - Zinc reinforcement

Advantages + disadvantages?

Answer 26

• calcium replaced by zinc (both positive ions with 2+)
• therefore chemical reactions are similar to calcium but has increase strength
• doesn’t require conditioner or varnish (can be placed directly into cavities)
• good for children - fast process and easy to place
• lasts several months - few years
• unsure about long term use as relatively new material
• Undergoes a maturation stage 7 days (further cross linking)
• 4-6 months = increase in physical properties
• Fluoride release + fluoride recharge
• Poor aesthetics (white but not tooth coloured)

Question 27

Indication of GIC?

Answer 27

• When cavities go sub-gingivally
  as moisture control is hard and GIC doesn’t require a dry cavity (composite would be hard to use as moisture control would be impossible and amalgam would require quite a destructive cavity prep to make it 2mm deep + have areas of undercut)
• For temporary restorations (Temporisation)
  Eg pt has lost restoration or cavity is deep / near pulp
  GIC simple to use in these situations - no need for condition or varnish afterwards - simply dry cavity and place GIC in.
  Easy to drill out without removing sound tooth tissue as its white in colour
  Difficult with composite as you cannot always differentiate composite to tooth tissue

Question 28

Stepwise excavation - how is GI used and beneficial?

Answer 28

• with deep cavities we may leave some of the caries behind and place GI directly into the cavity.
• the release of fluoride + ability of GI to seal the cavity chemically
• caries / bacteria that is left behind gets starved of food supply and dies off thus, preserving the life of the tooth

Question 29

GI as a fissure sealant

Answer 29

• Chemically bonds to tooth tissue so can be used as a fissure sealant
• Not as flowable but effective in areas where moisture control is difficult

Question 30

Main use of GI?

Answer 30

• Restoring cervical cavities
• Not good for areas of stress / biting surfaces
• Ideal for areas where there’s less stress
• Not as good as composite for aesthetics but can chemically bond and release fluoride
• Ideal for cavities near gingival margin

Question 31

Traditional GIC

Type?
Clinical usage?
indications?

Answer 31

Type
- Chemfill
- Fuji triage
- Fuji IX

Clinical usage
- Conditioner 10% Poly-acrylic acid
- Varnish as soon as finished to prevent loss of Al / Ca ions

Indications (poor aesthetics, so use in posterior teeth)
- sub-gingival restorations
- temporary restorations
- stepwise excavation

Question 32

Resin modified GIC

Type?
Clinical usage?
indications?

Answer 32

Type
- Fuji II

Clinical usage
- Conditioner 10% poly acrylic acid
- Light cure (already matured before pt leaves)
- No varnish

Indications (better aesthetics)
- Non load bearing restorations - (good for cervical restorations and anterior teeth)
- Use to bond amalgam into place where the retention isn’t good

Question 33

Zinc reinforced GIC

Type?
Clinical usage?
indications?

Answer 33

Type
- Chemfill rock

Clinical usage
- No conditioner
- No varnish

Indications
- Long term / temporary
- Good for caries management / pt with many various lesions
(Fluoride release will help stabilise pt caries)
- Fissure sealant
- Good for areas where moisture control is hard to achieve