Rigidity of elastomeric impression materials

Summary The rigidity of an impression material should be less than a certain value in order that excessive forces are not required when taking impressions of undercut areas. Conversely, the impression should be sufficiently rigid to withstand the weight of stone whilst pouring the cast without distortion. This paper describes a method of determining elastic modulus values at times as early as the setting time of the material. Results indicate that the elastic modulus values increase from the setting time to 30 min after the start of mix. Values are presented for a representative range of elastomeric impression materials.