Accuracy of Working Casts and Dies Using Polyvinyl Siloxane Impressions

Objective: This study aimed to evaluate the effect of spacer on the accuracy of working casts and dies produced from fast-setting polyvinyl siloxane impressions. Methods: Twenty Impressions of the mandibular arch of a modified Dentoform master model incorporating a stainless steel circular crown preparation were made, using a fast-set Polyvinyl siloxane (Affinis perfect impressions Coltene/Whaladent AG) using 2/step impression technique with and without a spacer. Gypsum working casts and dies were produced from the poured impressions. Measurements of the master model and working casts were carried out including anteroposterior (AP) and cross-arch (CA) dimensions. The stainless steel circular crown preparation incorporated within the master model was also measured in buccolingual (BL), mesiodistal (MD), and occlusogingival (OG) dimensions and compared to measurements from recovered gypsum dies. Linear measurements were made using a measuring stereomicroscope. Results: Double impression technique without spacer showed statistically significant higher mean percent relative change than double impression technique with spacer. With each technique, the means percent relative change in die measurements showed statistically significant higher mean values than cast measurements. There was no statistically significant difference between means percent relative change in the BL and MD dimensions which showed the statistically significant highest mean values. The means percent relative change in the OG dimension showed the statistically significant lowest mean value. Conclusions: Accuracy of fast-setting polyvinyl siloxane impression material was favorably affected with the use of spacer, as the space resulted from contraction of the putty material was not enough to produce accurate detail reproduction by the light material. The working dies; from the fast- setting polyvinyl siloxane impression material without spacer demonstrated an increase in (mesio-distal and bucco-lingual) dimensions, while for cast dimensions, there was no difference between the two techniques.