[Measuring the accuracy of various elastomeric impression materials using a CNC coordinate measuring device (Part 1)]. 
This study compares the accuracy of 23 impression materials.  With each material seven impressions of a stainless steel master die were taken under standardized conditions.  Characteristical dimensions of the master die and of the stone dies as well were determined by means of a CNC coordinate measuring device.  Differences in prepared tooth heights ranged between -36 and +19 microns.  The occlusal distances between prepared teeth were 2 to 54 microns greater on the stone dies than on the master die.  Diameters differed by -89 to +52 microns.  The two phase impressions tended to result in stone dies of reduced size, whereas single phase and double mix impression techniques produced larger stone dies than the master die.