Properties of Zinc-Oxide Eugenol

CHEMISTRY

Constituents of a typical zinc oxide eugenol paste are:

BASE PASTE

REACTOR PASTE

Some pastes contain a substitute for eugenol e.g. a carboxylic acid.
The 2 pastes come in contrasting colours and are dispensed in a 1:1 ratio. They are mixed to give a paste of even colour. The setting reaction is shown below:

ZINC OXIDE (excess)   ZINC OXIDE (UNREACTED)
+ ® +
EUGENOL   EUGENOL

The set material contains both some unreacted zinc oxide and eugenol.
Any movement of the tray as the paste is hardening will lead to a deformed, inaccurate impression.
Setting time depends on:

1. Accelerator additives (e.g. zinc acetate, acetic acid)
2. Exposure to moisture on mixing or the addition of water will accelerate the reaction
3. Increasing temperature causes a faster setting reaction

Setting time is normally 4-5 minutes.

PROPERTIES

ADVANTAGES

1. Dimensional stability
2. Good surface detail
3. Can be added to
4. Mucostatic or mucocodisplacive

DISADVANTAGES

1. Cannot be used in very deep undercuts
2. Only sets quickly in thin section
3. Eugenol allergy in some patients