1. Zinc Oxide Eugenol
Impression material

2. Zinc Oxide Eugenol
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.

5. 1) Zinc Oxide Eugenol impression material
2) An impression taken in Zinc oxide eugenol

6. 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.

7. zinc eugenolate (chelate) (salt)
Setting reaction
Acid – base reaction.
Chelation reaction
Zinc oxide + water  zinc hydroxide
Zinc hydroxide + 2 eugenol Base Acid
zinc eugenolate (chelate) (salt)

8. Chelation:
Is the attachment of a molecule or ion to metal atom at more than one point.
The term is derived from the Greek word meaning “crab’s claw” indicating two pronged attachment.
A central zinc atom is held by two eugenol “claws”.

9. 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.

10. Factors affecting the setting time
Setting time depends on:
1. Accelerator additives (e.g. zinc acetate, acetic acid)
2.Retarders (inert oils such as olive oils, mineral oil.
3. Exposure to moisture on mixing or the addition of water will accelerate the reaction 4. Increasing temperature causes a faster setting reaction
5. Cooling the glass slab and mixing spatula will increase ST
Setting time is normally 4-5 minutes.

12. Manipulation.

14. properties Non toxic Adherence to tissues
Good surface detail in thin section
Good dimensional stability (little or no dimensional change on setting, 0.1% dimensional change during setting)
Can be added to with fresh zinc oxide eugenol
Stable on storage and good shelf life

15. Advantages & Disadvantages
1. Dimensional stability
2. Good surface detail
3. Can be added to
1. Cannot be used in very deep undercuts
2. Only sets quickly in thin section 3. Eugenol allergy in some patients

16. Plaster of Paris (Non Elastic)
Uses:
Secondary impression or final wash in a special tray.
Composition of powder:
Calcium sulphate hemihydrate.
Potassium sulphate or nitrate:
Accelerator
Flavouring agent.
Colouring agents.

17. Properties. Manipulation: Water / powder ratio.
55 to 60ml water to 100gm of powder.
Separating medium alcoholic solution of varnish. Or soap suspensions.
Properties.
Storage problems: kept in sealed containers.

18. Reaction:
Chemical reaction: crystalization
CaSO4 ½ H2O + H2O  CaSO4.2H2O + heat
Dimensional changes:
Setting expansion can be reduced to % by presence of K2SO4.
Soluble impression plaster:
Contains starch to facilitate the separation of impression from model by softening when immersed in hot H2O.