Introduction
An impression carries clinical information to the laboratory: the shape, volume and relationships of the tissues. A model poured from it must be an exact copy of the prosthetic field. Impression materials therefore have to meet a long list of requirements.
General requirements
- Harmless to patient and dental team, with a pleasant taste, smell and color.
- Different colors in two-part materials, so that mixing can be checked by eye.
- Long enough working time to form the impression while the material is plastic.
- Adhesion to the tray, but not to the teeth or mouth.
- Compatible with model materials, not disturbing their setting and separating easily.
- Able to be disinfected: in 1% sodium hypochlorite for 10 minutes, or 2% glutaraldehyde for 30 minutes.
- Strong enough not to tear on removal, in transport or during pouring.
- Accurate, reproducing details down to 20 µm.
- Volume changes that can be compensated: gypsum expands by 0.1 to 0.3%, so shrinkage within this range is compensable.
- Minimal residual deformation in elastic materials.