Effect of retarder on compression set of an addition silicone

Use of a retarder with a light-bodied addition silicone according to the manufacturer's recommendations increased the working time but resulted in poorly fitting crowns fabricated from these impressions. The compression set of the retarded mixes at the recommended time of removal was 3.2% compared with 0.08% for the nonretarded control. Increasing the time for removal by one minute resulted in a satisfactory compression set of 0.19%. It is recommended that if a retarder is used with an addition silicone, the correct time of removal should be determined by the compression set.