Effect of impression technique and multiple pours on accuracy of stone models

The number of accurate repour models obtainable from a single impression is of clinical importance. This study was designed to compare the accuracy of initial and repour models obtained from an impression recorded in a hydrophilic addition curing silicone and to determine whether or not this accuracy is affected by the impression technique employed and whether any interaction between impression techniques and levels of pour existed. The laminated and putty wash plus spacer techniques were employed. Six impressions were recorded of a brass master model with each technique. Improved stone models were poured after 2 hours and then repoured in the same impression at 3, 4, 5 and 6 hours. Thus, 30 models were poured with each impression technique. Using a reflex microscope, measurements between two fixed points on the brass model were taken and compared with similar measurements obtained from the stone models. The analysis of variance indicates that no significant difference exists between impression techniques (p greater than 0.05) and between the first pour and first repour model (p greater than 0.05). With the material tested, this study indicates that the laminated and putty wash plus spacer techniques both give accurate impressions and that only two accurate models can be poured.