Abstract
The curing contraction of addition-type silicone impression materials was measured by the mercury bath method.The results point to a classification of this group of materials into the following two types:1)Materials with maximum 0.08% polymerization contraction at 22℃ 15 min after the start of mixing and maximum 0.03% contraction at 22℃ during storage from 15 min to 24 hours(Permagum, President, Reflect and Reprosil).2)Materials with more than 0.08% polymerization contraction at 22℃ 15 min after the start of mixing and significantly more then 0.03% contraction during storage at 22℃ from 15 min to 24 hours(Exaflex and Xantogum).
