DIMENSIONAL ACCURACY OF TWO POLYVINYL SILOXANE PUTTY/WASH IMPRESSION TECHNIQUES.

Aim: The impression technique and control of wash bulk has been described as critical factors that influence the dimensional accuracy of stone models. The purpose of this study was (1) to compare polyvinyl siloxane dimensional accuracy in the 2-step impression technique for fixed prosthodontics using two spacers, different in their ability of controlling wash bulk, and (2) determine the effect of the technique on the dimensional accuracy of stone models. Materials and methods:  The 2 putty/wash impression techniques used were: (1) 2-step with 2-mm relief, using calibrated acrylic resin copings in the putty stage to create 2-mm wash space and (2) 2-step with lead foils of dental x-ray film packets. For each technique, 20 impressions were made of a master model that contained 4 titanium abutments. Accuracy was assessed by measuring 6 dimensions (intraabutment and interabutment) on stone dies poured from impressions of the master model.  Results:  The Independent samples T-test used to compare both groups, showed that there were not statistically significant differences on dimensional accuracy among the two techniques (P > 0, 05). However, stone models made by the 2-step putty/wash technique with acrylic resin copings spacers have a lower percentage of dimensional change. The One-sample T-test used to compare each group with the master measures, showed statistically significant differences in one interabutment measure of the lead foil spacer group. Other measurements of the same technique appear to be close of having statistically significant differences when they were compared to master measurements. Conclusion:  Both techniques can create accurate models; however some imprecisions were registered in the lead foil spacer group. Acrylic resin copings can be represented as temporary crowns and are a reliable technique that allows reliable casts with less dimensional variations. The effect of technique and wash bulk on dimensional accuracy may be important to obtain accurate stone models but further studies are needed.