Synonyms: Crown and bridge cement, Zinc oxyphosphate

APPLICATIONS:

Luting of restoration and orthodontic bands & brackets

Thermal insulation

Root canal restoration

High strength bases

Temporary restoration

CLASSIFICATION:

SETTING OF THE CEMENT:

Phosphoric acid in the liquid dissolves zinc oxide and reacts with aluminium phosphate to form aluminium phosphate gel on the remaining undissolved zinc oxide particles.

SETTING TIME: 2.5 to 8 minutes

MANIPULATION:

It is an exothermic process.

Zinc oxide cement is dispensed on the glass slab and divided into 6 increments(1/16, 1/16, 1/8, 1/4, 1/4, 1/4). It is followed by dispensing of the liquid.

Mixing of the cement should be initiated by the smallest increment with a thin spatula. There should be brisk spatulation with large, wide circular motions to dissipate the heat.

When the spatula is drawn away from the mixture, a strand of 12-19 mm should be produced. Such cement is suitable for cementation.

MIXING TIME:

For each increment: 15-20 sec

Total mixing time: 1.5-2 min

PROPERTIES:

MECHANICAL PROPERTIES: Compressive strength = 104 MPa, Tensile strength = 5.5 MPa, Elastic modulus = 13 GPa

SOLUBILITY: Less soluble in water (0.06%). Soluble in lactic, acetic and citric acids (in-vivo)

ADHESION TO TOOTH: Mechanical bonding ( In case of application of a cavity liner before applying zinc phosphate, it does not bond well due to less retention as it will create smoother surface with less interlocking)

BIOLOGICAL PROPERTIES: Phosphoric acid is acidic and cytotoxic. Younger patients are more susceptible to it because of more open dentinal tubules. Older patients with sclerotic dentin have a tortuous path for the entry of acid.