Zinc Oxide Eugenol

Zinc Oxide Eugenol Impression materialZinc 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.

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1) Zinc Oxide Eugenol impression material2) An impression taken in Zinc oxide eugenolCompositionConstituents of a typical zinc oxide eugenol paste are:BASE PASTEZinc oxide Inert oils (plasticiser) Gum rosin (increases setting time and improves cohesion)REACTOR PASTEEugenol 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 reactionAcid base reaction. Chelation reactionZinc oxide + water zinc hydroxide Zinc hydroxide + 2 eugenol Base Acid

zinc eugenolate (chelate) (salt)7Chelation: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 crabs claw indicating two pronged attachment.A central zinc atom is held by two eugenol claws.

8Setting timeThe 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 timeTypes: S.TType I: hard 10 minutesType II: soft 15 minutesAccelerators: water, magnesium chloride, zinc acetate or alcohol.Retarders: inert oils such as olive oils, mineral oil.

Factors affecting the setting timeSetting 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 reaction4. Increasing temperature causes a faster setting reaction 5. Cooling the glass slab and mixing spatula will increase STSetting time is normally 4-5 minutes.

11Manipulation.

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13propertiesNon 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

Advantages & Disadvantages ADVANTAGESDISADVANTAGES

1. Dimensional stability2. Good surface detail3. Can be added to

1. Cannot be used in very deep undercuts2. Only sets quickly in thin section 3. Eugenol allergy in some patients

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.Plaster of Paris (Non Elastic)16Manipulation: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.17Reaction:Chemical reaction: crystalizationCaSO4 H2O + H2O CaSO4.2H2O + heatDimensional changes:Setting expansion can be reduced to + 0.06% by presence of K2SO4.Soluble impression plaster:Contains starch to facilitate the separation of impression from model by softening when immersed in hot H2O.18