Some Properties of Elastomeric Impression Materials Used in Fixed Prosthodontics

Impression materials used in the various phases of denture construction may be classified as being rigid, thermoplastic, or elastic substances. Elastic impression materials are those that remain in an elastic or flexible state after they have been removed from the mouth. The elastic impression materials are most generally used for the making of impressions for removable partial dentures, immediate dentures, and crowns and fixed partial dentures when tooth and tissue undercuts and surface detail must be recorded with accuracy. Properties of clinical interest are (1) toxicity, (2) color of the base and accelerator, (3) time required for mixing, (4) working time, (5) consistency, (6) permanent deformation during removal, (7) dimensional stability, (8) flow after setting, (9) flexibility, (10) reproduction of detail, (11) compatibility with die and model materials and (12) deterioration during storage of the unmixed material. These properties are important in choosing a material.