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Zinc Oxide Eugenol

Zinc Oxide Eugenol. Impression material. 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.

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Zinc Oxide Eugenol

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  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.

  3. Composition • 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./chlorothymolNON EUGENOL TYPEThe 2 pastes come in contrasting colours and are dispensed in a 1:1 ratio. They are mixed to give a paste of even colour.

  4. Setting reaction • Acid – base reaction. • Chelation reaction • Zinc oxide + water  zinc hydroxide • Zinc hydroxide + 2 eugenolBase Acid zinc eugenolate (chelate) (salt)

  5. 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”.

  6. 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 10 minutes • Type II: soft 15 minutes • Accelerators: water, magnesium chloride, zinc acetate or alcohol. • Retarders: inert oils such as olive oils, mineral oil.

  7. 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 reaction4. Increasing temperature causes a faster setting reaction 5. Cooling the glass slab and mixing spatula will increase ST • Setting time is normally 4-5minutes.

  8. Manipulation.

  9. 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

  10. Advantages & Disadvantages 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

  11. 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.

  12. 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.

  13. Reaction: Chemical reaction: crystalization CaSO4 ½ H2O + H2O  CaSO4.2H2O + heat Dimensional 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.

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