Dental Adhesive Cement

Dental Cement

Write a short note on adhesive cement.
Answer:

• Generally, there are two adhesive types of cement in dentistry that undergo strong bond formation with enamel.
• The adhesive cement is glass ionomer cement and zinc polycarboxylate cement.

Glass Ionomer Cement:

Glass ionomer cement chemically bonds to enamel and dentin, though the precise mechanism of bonding is unclear,

There are two probable theories of adhesion:

• 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.
• 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 the removal of the smear layer without removing the 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, the 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.

Zinc Polycarboxylate Cement:

This cement bonds chemically with tooth structure. The Carboxyl group in the polymer molecule gets chelate with calcium in the tooth structure and makes a bond. Bond strength to enamel is from 3.4 to 13 MPa and for dentin it is 2.1 MP

Factors Affecting Adhesiveness of the Cement:

• Clean and dry tooth surface enhances bonding.
• If the inside surface of the metal crown is not clean, cement does not bond with the metal. For doing so the internal surface of the metal should be abraded.
• Adhesion is better to smooth surfaces.