RESUMEN
There is much controversy with regard to the effect of the impression technique on accuracy of cast restorations. The aim of this study was to evaluate the accuracy of 3 putty - wash impression techniques using polyvinyl siloxane material. Three putty-wash impression techniques were used for this experimental in vitro study. [1] two-step with 1mm relief [using prefabricated copings for wash space], [2] two-step technique with a polyethylene spacer and [3] one-step. For each-technique, 15 impressions were made of a maxillary edentulous model that contained 4 ITI analogue abutments [one with undercut]. The impressions were made by standard trays with same, space and poured with type IV dental stone. The stone die measurements were made on digital photographs by a computer software. The percentage of dimensional changes of intra abutment [diameter and height] and inter abutment were analyzed by ANOVA, Turkey HSD and t - student tests [a=0.05]. One way analysis of variance showed statistically significant differences among the 3 putty- wash impression techniques, for all measurements[P<0.05]. The dimensional changes of technique 1 were significantly less than another two techniques. There were significant differences between height and diameter of the dies with undercut in techniques 2 and 3 .The diameter of the die was increased in technique 1 and decreased in the other techniques. The height of the dies decreased and the intra abutment spaces increased in all impression techniques. The polyvinyl siloxane 2-step with 1 mm relief putty-wash impression technique was the most accurate for fabricating cast restoration