zinc oxide eugenol impression
This material is used for recording edentulous ridges in a close fitting special tray or the patients existing dentures. The material is mixed in a 1:1 paste ratio and used in thin sections only (2-3mm) as a wash impression.
Vaseline is used as a separating agent on those areas requiring protection (soft tissues, skin etc). Firm pressure is used during impression taking.
Composition BASE PASTE REACTOR PASTE:
Constituents of a typical zinc oxide eugenol paste are:
- BASE PASTE
- Zinc oxide
- Inert oils (plasticiser)
- Gum rosin (increases setting time and improves cohesion)
- REACTOR PASTE
- Eugenol
- Zinc acetate/Mg Cl (accelerator)
- Fillers (talc or kaolin)
Some pastes contain a substitute for eugenol e.g. a carboxylic acid./chlorothymol NON EUGENOL TYPE 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.
Setting time
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
- Types: S.T
- Type I: hard minutes
- Type II: soft minutes
- Accelerators: water, magnesium chloride, zinc acetate or alcohol.
- Retarders: inert oils such as olive oils, mineral oil.
Factors affecting the setting time
Setting time depends on:
- Accelerator additives (e.g. zinc acetate, acetic acid)
- Retarders (inert oils such as olive oils, mineral oil.
- Exposure to moisture on mixing or the addition of water will accelerate the reaction
- Increasing temperature causes a faster setting reaction
- Cooling the glass slab and mixing spatula will increase ST Setting time is normally 4-5 minutes.
Advantages & Disadvantages
- Dimensional stability
- Good surface detail
- Can be added to
- Cannot be used in very deep undercuts
- Only sets quickly in thin section
- Eugenol allergy in some patients