Glass Ionomer Cement As A Luting Cement

Glass Ionomer Cement As A Luting Cement

Describe its biological and chemical bonding properties. Add a note on its modifications. Mechanism of bonding with tooth structure.

Answer:

Biological Properties:

• Pulpal response to glass ionomer cement is mild.
• Type I GIC is more acidic than Type II GIC because of the lower powder-to-liquid ratio. Sensitive patients show painful responses to GIC luting cement.
• Deeper areas are protected by calcium hydroxide cement before giving GIC restoration.

Chemical Bonding Properties:

Glass ionomer cement chemically bonds to enamel and dentin, though the precise mechanism of bonding is unclear, there are two probable theories of adhesion:

1. The first theory suggests that polyacid molecules chelate with calcium on the tooth interface. This is supported by the formation of the interfacial calcium polyalkeonate salt.

2. According to another theory the acid present in the fresh mix when contacts the tooth structure acts as a self-etching agent leading to the dissolution of hydroxyapatite crystals which results in the release of calcium and phosphate ions. Hydrogen ions are rapidly buffered by the phosphate ions from hydroxyapatite crystals and pH begins to rise.

To maintain an electrolytic balance, phosphate ions take with them a calcium ion; these calcium ions are then taken up by the carboxylic groups adjacent to the tooth to form an ion-enriched layer composed of calcium-phosphatepolyalkeonate complexes which are firmly bound to both enamel and dentin.

• So, the polyacid chains are bound to a reprecipitated layer on the tooth surface. In conclusion, the adhesive mechanism of glass ionomer cement primarily involves the chelation of carboxyl groups of the polyacids with the calcium in the hydroxyapatite of the enamel and dentin.
• Because of the greater homogeneity and inorganic content of enamel, glass ionomer cement bonds better to enamel than to dentin. It is always preferred to condition the tooth surface before bonding for improving the bonding of GIC with tooth structure.
• Conditioning causes removal of the smear layer without removing smear layer plugs from the dentin tubule orifices or calcium ions. A commonly used conditioner for glass ionomer cement is polyacrylic acid (10 to 25%) applied for 10 to 15 seconds.
• After using conditioner, use of the dilute solution of ferric chloride on the tooth has been shown to improve the bonding by deposition of Fe3 + ions which further increases the ionic interaction between the cement and dentin. It chemically bonds to dentin/enamel.