Reinforced Zinc Oxide Eugenol (ZOE) Material

Reinforced Zinc Oxide Eugenol (ZOE) Material

Manipulation of ZOE:

• Requirements:
  • Oil-impervious paper or glass slab.
  • Flexible stainless steel spat
• Mixing time —1 minute:
• Procedure: Two ropes of paste of the same length and width, one from each tube are squeezed onto the mixing slab in order to ensure the correct proportioning. Mixing is done with a flexible stainless steel spatula using circular motion until a streak-free mix is obtained. Setting Reaction The setting reaction is a typical acid-base reaction to form a chelate.

When the two pastes are mixed a acid-base reaction takes place which is known as “chelation” and the product is called “Zinc Eugenolate”.

ZnO    +  H₂ O  →  Zn (OH)₂

Zn (OH)₂   +    2HE           →      ZnE₂  +  2H₂
Base             Acid (eugenol)        Salt (Zinc eugenolate)

The chelate (zinc eugenol) forms a matrix surrounding a core of zinc oxide particles. The chelate is thought to form as an amorphous gel that tends to crystallize giving strength to the set mass.

Advantages of ZOE Impression Paste:

• It has enough working time to complete border molding.
• It registers accurate surface details.
• It is dimensionally stable.
• It can be checked in the mouth repeatedly without deforming.
• It does not require any separating media since it does not stick to the cast material.
• The minor defect can be corrected locally without discarding a good impression.

Disadvantages of ZOE Impression Paste:

• It requires a special tray for impression-making.
• It is sticky in nature and adheres to tissue.
• Eugenol can cause a burning sensation and tissue irritation.
• It cannot be used for making impressions of teeth and undercut areas, as it is inelastic in nature.