The automatic mixing system of an addition silicone impression material yields mixes and set material that comply with ADA specification no. 19 when testing is started at 0.5 minute rather than the specified 1.5 minutes. This change is reasonable because there is zero mixing time rather than the usual 45-60 second needed for standard two-paste rubber impression materials. Uniform mixing of base and catalyst occurs with the automatic system, with a fourth to a fifth as many bubbles in the mix as for comparable mixes obtained by hand spatulation. The automatic feature of the system simplifies mixing and nearly eliminates the training of assistants in the mixing of rubber impression material. The automatic mixing system is economical as it wastes only a third as much material as a typical hand-dispensing and mixing system. The properties and accuracy of the system are excellent and typical of addition silicones, including excellent recovery from deformation, low dimensional change on setting, and low flow. A wash or two-phase impression technique may be used with equal clinical accuracy.