Accuracy of three polyvinyl siloxane putty-wash impression techniques

Statement of problem. There is much discussion in the dental literature con cerning the effect of the impression technique on the accuracy of cast rest orations. Purpose. This study assessed the accuracy of 3 putty-wash impression techni ques using the same impression material (polyvinyl siloxane) in a laborator y model. Material and methods. The 3 putty-wash impression techniques used were (1) 1-step (putty and wash impression materials used simultaneously); (2) 2-ste p with 2-mm relief (putty first as a preliminary impression to create 2-mm wash space with prefabricated copings. In the second step, the wash stage w as carried out); and (3) 2-step technique with a polyethylene spacer (plast ic spacer used with the putty impression first and then the wash stage). Fo r each technique, 15 impressions were made of a stainless steel master mode l that contained 3 complete crown abutment preparations, which were used as the positive control. Accuracy was assessed by measuring 6 dimensions (int raabutment and interabutment) on stone dies poured from impressions of the master model. Results. One-way analysis of variance showed statistically significant diff erences among the 3 putty-wash impression techniques, for all intraabutment and interabutment measurements (P<.001). Overall discrepancies of the 2-st ep technique with 2-mm relief putty-wash impression technique were signific antly smaller than that in the 1-step and polyethylene putty-wash impressio n techniques. Conclusion. The polyvinyl siloxane 2-step, 2-mm, relief putty-wash impressi on technique was the most accurate for fabricating stone dies.