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Glass Ionomer Cement (GIC) - Composition, Properties, Composition and Modifications

- Glass Ionomer Cement is also known as Polyalkenoate cement / Man-made dentin / Dentin Substitute / Aluminosilicate Polyacrylic cement (ASPA)
COMPOSITION :
Powder / Liquid Contents
Powder / Ion Leachable Glass
  • Silica           -          35 - 50 %
  • Alumina      -           20 - 30 %
  • NaF             -           3 - 6 %
  • AlF3            -           1.5 - 2.5 %
  • Aluminium Phosphate  -    4 - 12 %
  • Traces of Barium, Strontium for radioopacity
Liquid
  • Polyacrylic acid        -        45 %
  • Itaconic acid + Maleic Acid + Tricarballylic acid    - 5 % (Decreases Viscosity)
  • Tartaric acid (Increases working time)
  • Water   - 50 %
CLASSIFICATION:
Type I GIC - Luting cement
Type II GIC - Restorative Cement
Type III GIC - Liner
Type IV GIC - Fissure Sealant
Type V GIC - Orthodontic Cement
Type VI GIC - Core Build Up Cement
Type VIII and Type IX - Posterior packable GIC for atraumatic restorations
Among the first three types, the highest cumulative release of fluoride after 30 days is from glass ionomer liner.
- GIC was introduced as a potential replacement for silicate cement. It has been evolved as a hybrid from the silicate and polycarboxylate cement.
Light Polymerization:
The powder contains initiators for light curing and liquid component is modified with hydroxyethyl methacrylate (HEMA).
The polymerization starts when exposed to light and subsequently followed by acid base reactions. This is called dual cure GIC.
PROPERTIES:
GIC has low fracture toughness and wear resistance.
It is very sensitive to moisture, especially during initial setting reaction. During this period, absorption of water leads to weak cement and over drying will lead to cracks in the cement. Therefore, the surface of cement should be protected by coating with varnish or cocoa butter during setting. 
It bonds chemically to the tooth structure.
- The bond of enamel is always higher than that of dentin.
- It is relatively biocompatible, the pulpal reaction is greater than ZOE but less than Zinc Phosphate Cement.
- Due to continuous fluoride release, it has some anticariogenic property.
 
- Powder: Liquid ratio is 3:1 by weight. Mixing should be done by agate or plastic spatula.
- 10 % polyacrylic acid should be used for conditioning the cavity surface before insertion of the cement.
- Final finishing is done 24 hours after the insertion.
MODIFICATIONS OF GIC:
a) Miracle Mix or Silver Cement
Silver-Tin alloy powder is added to GIC Powder. None of the properties were improved and it gave a gray or blackish color to the cement. It is also called as silver alloy mix.
b) Glass Cermet or Cermet
Glass and metal ( Silver-tin-titanium) powders were sintered at high temperature and made to react with liquid. It improved the fracture toughness and wear resistance and at the same time maintained the esthetics.
c) Resin modified GIC
BisGMA, TEGDMA, are added to powder and HEMA to the liquid. With exposure of light polymerization is initiated along the methacrylate groups. After that the liquid reacts with the glass particles through acid base reaction. It improved the wear resistance and decreased the sensitivity to
water attack. 
d) Compomer (Polyacid modified composite resins)
It is a combination of composite and GIC. Glass particles are partially silanated (for bonding with the matrix) and are added as fillers in the composite resin. There is no water in the reaction. The properties were inferior to composites but superior to resin modified GIC.
e) Bilayered or Sandwich restoration
In this technique, GIC is used as a liner under composite restorations. It increases the retention form as GIC bonds both the tooth and composite and the fluoride content reduces secondary caries.
f) Tunneling restorations
Joining the occlusal lesion with the proximal lesion by means of a prepared tunnel under the involved marginal ridge. The marginal ridge remains intact. GIC is used as the restorative material in this technique.
g) Atraumatic restoration (ART)
Involves removal of affected tooth structure with hand instruments, followed up by restoring with GIC material (GC Fuji VIII).
h) High viscosity GIC
Used for atraumatic restorative treatment. They contain small particle sizes and a high P/L ratio, yielding greater compressive strength and excellent packability. Also used for core buildups, primary tooth fillings and intermediate restoration.
i) Calcium aluminate GIC
It is a hybrid product of calcium aluminate and  GIC. The GIC components are responsible for early properties (i.e. setting time, viscosity, and strength). The calcium aluminate contributes to basic pH, biocompatibility and reduction in microleakage. Also called as hydraulic cement.

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