Linear dimensional changes in addition curing silicone impression materials

Five vinyl polysiloxane addition curing impression materials were evaluated on the basis of linear dimensional change occurring as a function of time between making an impression and pouring the die. The dies were measured and compared to a master model to determine the linear change in the impression material. One material produced an overall larger die, but the greatest increase in size deviated from the master model by only 0.1%. Permagum putty-wash material consistently produced undersized dies, with the greatest change being 0.3%. Three materials randomly produced smaller or larger dies, differing from the master model by only 0.08% for the smallest die to 0.07% for the largest. No consistent pattern of increase or decrease in die size occurred with time. Dies produced at 168 hours were as accurate as those produced at 10 minutes.