Properties of Impression Compound

CHEMISTRY

Made up of 3 constituents

1. Resins (e.g. wax)
2. Filler (e.g. talc or soapstone)
3. Lubricants (stearic acid or stearin)

It is a thermoplastic compound i.e. it softens when heated and hardens when cooled. This process does not involve a chemical reaction.

Impression compound is available in 2 forms:

1. Stick form - used for modifying impression trays. Softening temperature is 700C
2. Sheet form - used to take impressions of the mouth. Softening temp is 55-600C.

PROPERTIES

ADVANTAGES

1. Non irritant and non toxic
2. Reusable (but with re-use the constituents are leached out)
3. Can be reheated and readapted
4. Can support other materials for wash impressions
5. Mucocompressive

DISADVANTAGES

1. Poor dimensional stability
2. Poor surface detail
3. Expansion coefficient
4. Will distort if removed from undercuts