Introduction to Glass ionomer cement (GIC) Flashcards
Describe the general composition of Glass Ionomer Cements.
- Water based cement
- It is formed from the acid-base reaction between a polyalkenoic acid and an ion-leachable calcium or strontium aluminosilicate glass base, which contains fluoride.
- This is fused, quenched and ground and sieved to obtain a particle size between 4-50µm
- Finer particles = luting cements and lining cements
- Coarser particles for restorative materials
Describe the composition of Conventional GIC
Glass:
- Base is made of an ion leachable calcium or strontium aluminosilicate glass base which contains fluoride.
- Glass is called “fluoroaluminosilicate” glass. It is made of silica, alumina, CaF, cryolite and aluminium phosphate. (95%)
- Polyacrylic acid powder 5%
Liquid:
- 40-55% aqueous solution of polyalkenoic acid
- 50% distilled water
Examples:
Fuji IX, Fuji IX Fast, Fuji IX Extra
Describe the composition of Resin Modified GIC
Glass:
Fluoroaluminosilicate
Liquid:
- 20-30% distilled water
- 20-30% polyacrylic acid
- 30-35% Hydroxyethylmethacrylate (HEMA)
- <10 %Urethane dimethacrylate (UDMA)
- <1%Camphoroquinone
Describe the GIC adhesion process
• The polyacid (the glossy surface of the GIC) penetrates the tooth structure, and forms a stable bond with the Ca found in dentine and enamel
• Ca and Phosphate from the enamel/dentine and strontium and fluoride from the GIC intermix and precipitate, forming an interphase known as the “interdiffusion zone”
* This zone is stronger and more acid resistant than tooth or GIC. It forms a strong, adhesive interface between tooth structures and GIC, while also acting as a bacteria proof fused seal
Explain the smear layer and thus the purpose of polyacrylic acids?
• The smear layer is the accumulation of tooth structure, plaque, bacteria, saliva and sometimes blood
• It is produced by cavity preparation with rotary instruments/ hand instruments
• It sticks to the surface of enamel and dentine, plugging the opening of the dentinal tubules which cannot be washed off by air-water spray
• It interferes with the bonding of adhesive dental cements
• Polyacrylic acid is a mild acid which opens up the dentine tubules, exposing clean surface with maximum mineral content still present for adhesion
* Polyacrylic acid is a part of glass ionomer system therefore any remaining residue will not interfere with setting reaction
List the properties of GIC (11)
- Biocompatibility
- Radiopacity
- Wear
- Ageing
- Fluoride release
- Fracture resistance
- Coefficient of thermal expansion
- Dimensional change
- Bonding
- Dissolution and disintegration
- Colour and translucency
Describe the bonding component of GIC property
• Bonds to enamel and dentine
• The higher the mineral content in the cavity prep, the greater the bond. In the order of strongest to he weakest bond: Enamel, sclerotic dentine, sound dentine, caries affected dentine
• 80% of bond strength achieved after 15 mins, continue to increase for several days
* RMGIC has higher shear bond strength due to the presence of HEMA which enhances adhesion of dentine and the cement
Describe the biocompatability component of GIC property
• Gingiva and oral mucosa are very tolerant to glass ionomer
• Freshly mixed GIC is acidic – pH 2 at 5 mins, pH 3 at 10 min
• GIC cannot be placed directly on exposed pulp tissue
* RMGIC is not as biocompatible compared to conventional GIC due to the presence of HEMA which can diffuse through dentine to pulp. It only releases the first 24 hours after placement
Describe the fluoride release component of GIC property
- Following placement, the initial fluoride release is quite high during the first week but declines rapidly and stabilises to a low but constant level over 2 – 3 months
- Glass ionomer has the potential to act as a fluoride reservoir
- Advantages: remineralisation of surrounding tooth structure, inhibition of plaque formation and possible reduction in the recurrence of caries.
Describe the dissolution and disintegration component of GIC property
• Freshly set cements – susceptible to water exchange across its immature outer surface
• Water is responsible for ion transport
• Provided GIC is kept moist, small shrinkage will occur. If it is too dry, GIC will lose water and the material will begin to manifest cracks
* If there is too much water, then ions (Al and Ca) will leach out, compromising the strength of the GIC
* Must protect with Vaseline/coca butter or varnish (unfilled resin, G-Coat) to prevent excessive water movement
Describe the dimensional change component of GIC property
• Glass Ionomers contract approximately 3% by volume on setting
• Resin-modified glass ionomers show a small initial shrinkage at the time of light activation
* Overtime, the set material will take up water and expand to some degree
Describe the fracture resistance component of GIC property
• Susceptible to fracturing: Lack rigidity compared with hybrid composite and amalgam
* Avoid occlusal bearing load and bending
Describe the coefficient of thermal expansion component of GIC property
- The linear coefficient of thermal expansion of tooth structure is 11.4 x 10 -6 /° C , while glass ionomer materials are 10-11 x 10 -6 /°C, so microleakage is minimal
Describe the colour and translucency component of GIC property
• Both autocure and resin-modified provide adequate colour matching and translucency.
• GIC takes at least 24 hours to fully mature and develop translucency
• Translucency increases as cement ages
* Resistance to stain if the surface has a good finish
Describe the radiopacity component of GIC property
• Can be achieved by incorporation of barium (Ba), strontium (Sr) or lanthanum (La)
* Most glass ionomers are more radiopaque than dentine and enamel
