IMPRESSION

Definition: It is the negative replica of the structures of the oral cavity be it hard(tooth) or soft(gingiva, mucous membrane) structures, which are used to fabricate the cast or model of the patient, and for making crowns, dentures, and other prosthesis.

CLASSIFICATION OF IMPRESSION MATERIALS.

I) Based on mode of setting & elasticity

a) Rigid

i) Reversible (thermoplastic)

E.g. impression compound

ii) Irreversible (thermosest)

E.g. Zoe impression paste

Impression plaster.

b) Elastic

i) Hydrocolloid

a) reversible

E.g. Agar

b) Irreversible

E.g. Alginate

ii) Elastomeric impression materials

E.g. Polysulfides

Polyether

Addition silicones

Condensation silicones

II) Based on type of impression & area of use

A) Dentulous

i) Primary

E.g. alginate

ii) Secondary:

E.g. Elastomers

Agar

B) Edentulous

i) Primary

E.g. Impression compound

Impression plaster

Alginate

ii) Secondary

e.g. ZOE impression paste

Elastomers for CD

III) Based on their use in dentistry

A) Edentulous

For complete denture prosthesis

e.g. Impression compound

zoe impression paste

alginate

Elastomers

B) Dentulous

i) FPD

ii) RPD

E.g. Agar

Alginate

Elastomers

IV) Based on the amount of pressure applied

i) Mucocompressive

e.g. Impression compound

ii) Mucostatic

e.g. Impression plaster

V) Based on the manipulation

A) Hand mixing

i) Kneading

e.g. Impression compound – wet kneading

putty consistency Elastomers

ii) Circular motion (with glass slab & spatula)

eg. Zoe impression paste

polysulfide

iii) Vigorous mixing

e.g. Alginate (figure of 8 motions)

B) Mechanical mixing

VI) Based on the tray used for impression

A) Stock tray

i) Types of tray

a) rim locked perforated

e.g. Alginate Elastomers

b) water cooled

e.g. Agar

c) Plastic

e.g Orthodontic Tray

ii) Based on type of Perforation

a) Perforated

e.g  Alginate

Elastomers

b) Non Perforated

e.g Impression Compound

B) Special Tray

i) base plate wax

e.g. Zoe impression paste

medium body

ii) resin

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