Dental Impression is a negative replica of hard and soft tissues of the mouth that reproduces their shape and relationship. Materials used for these impressions are referred to as dental impression materials. They are utilized in Prosthodontics for teeth measurement and tissue placement, in Orthodontics for a treatment plan, restorative dentistry, maxillofacial prosthetics, and oral and maxillofacial surgery. There are some mandate properties that these materials must possess to be considered as an impression material. Good impression material should have a pleasing taste, odour, aesthetic colour, adequate time period for storage, dimensional stability, strength, and elastic properties. There should not be any toxic or irritating ingredients and should be economical and compatible with die and cast materials.
Impression materials are categorized on the basis of rigidity, viscosity, setting reaction, and elastomeric properties. Impression compound, alginate, zinc oxide-eugenol, plaster of Paris, Agar, etc are commonly used impression materials. Based on their properties they are either used for completely edentulous or partially edentulous patients. A reversible material named impression compound is used for the first impression for the complete dentures but it has poor flow characteristics. It is incapable of producing fine details, therefore, it is only used for extensions, border molding, etc. Impression Plaster or Plaster of Paris is one of the standard casting materials. It is very brittle. Alginate, irreversible impression material is used for impression making of partially edentulous patients. Prosthesis and casts for dental treatments are designed and created with it. The setting time and dimensional stability, both are less for Alginate. A secondary or final impression in complete denture patients is prepared from Zinc Oxide Eugenol. It is easily removable from the casting material when heated. Its rigidity is its main disadvantage.
