impression materials --- impression waxes & zinc oxide eugenol pastes

what are impression waxes?

• non-elastic, which can be further classified as thermoplastic

what are impression waxes mostly used for?

corrective impression material

what are zinc oxide and eugenol impression pastes classified as?

• non-elastic, which can be further classified as rigid

what are zinc oxide and eugenol impression pastes?

• rigid impression material

• most useful in complete denture prosthodontics (edentulous patients)

setting reaction of zinc oxide and eugenol impression pastes

• zinc oxide + water → zinc hydroxide

  • then reaction occurs as a typical acid-base reaction (chelation)

• zinc hydroxide + eugenol → zinc eugenolate + water

instruments required for manipulation of zinc oxide and eugenol impression pastes

• paper mixing pad or a glass pad

• stiff-bladed cement spatula

• paste solvent

• vaseline

setting time of zinc oxide and eugenol impression pastes

• once the material is in place in the patients mouth, it should set fast

rigidity and strength of zinc oxide and eugenol impression pastes

unyielding when it is removed from the mouth and resists fracture

dimensional stability of zinc oxide and eugenol impression pastes

less than 0.1% shrinkage occurs during hardening (satisfactory dimensional stability)

zinc oxide and eugenol impression pastes reproduction of tissue details

it has excellent reproduction of tissue details

how is separation of the impression from the cast done in zinc oxide and eugenol impression pastes

• separation is done after gypsum setting is done by immersing in hot water (50 - 60 C) for 5-10 minutes

what are the advantages of zinc oxide and eugenol impression pastes?

1. adheres well to dry surface of impression tray

2. adequate working time

3. dimensionally stable

4. hard / strong enough

5. compatible with cast material (no separating medium is needed)

6. registers accurate details of the tissue

7. can be disinfected by immersion in 2% acidic glutaraldehyde solution (cidex) for 10 minutes

what are the disadvantages of zinc oxide and eugenol impression pastes?

• may cause burning sensation to oral tissues due to eugenol

• cannot be used in case of the presence of undercut

• difficult to clean

• temperature and humidity influence the setting time

applications of zinc oxide and eugenol impression pastes in dentistry:

1. corrective impressions of edentulous jaws (secondary impressions)

2. relining impressions for complete denture

3. bite-registration paste of ZO & E used for recording jaw relations

4. Modified zinc oxide & eugenol materials used as:

   • surgical dressings

   • temporary filling materials (temp. restorations)

   • root canal filling materials

   • cementation of temporary crowns & brides