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The present study has shown that there is no correlation between the free curing contraction of three selected addition-type silicone impression materials and the effective contraction determined as the accuracy of stone dies produced in dental impressions of these materials. Depending on specific rheologic properties, the free curing contraction of an impression material can be partly compensated for by flow. [ABSTRACT FROM AUTHOR]

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°C 15 min after mixing and maximum 0.03% contraction at 22°C during storage from 15 min to 24 h (Permagum®, President®, Reflect® and Reprosil®). 2: materials with more than 0.08% polymerization contraction at 22°C 15 min after mixing and significantly more than 0.03% contraction during storage at 22°C from 15 min to 24 h (Exaflex®, Xantogum®). [ABSTRACT FROM AUTHOR]