A dental impression may be described as an accurate representation of part or all of a person's dentition and other areas of the mouth. It forms a "negative" of a person's teeth and gums which can then be used to make a cast or model (physical) of the dentition. This may be used for the fabrication of dentures, crowns or other prostheses.
An impression is carried out by placing a viscous liquid material into the mouth usually in a customised tray. The material then sets to become an elastic solid, and when removed from the mouth retains the shape of the teeth.
Common materials used for dental impressions are sodium alginate, polyether and silicones - both condensation-cured silicones and addition-cured silicones (Polyvinyl siloxane). Historically plaster of paris, zincoxide/eugenol and agar have been used.