The Effect of Different Double- Step Impression Techniques on Accuracy of Stone Dies

Purpose: To investigate accuracy of dies obtained from different double-step putty-wash impression techniques. Materials and method: A master model was constructed having Co-Cr abutments (Remanium Star, Dentaurum, Germany) in a custom made acrylic dentoform (VertexDental B.V., The Netherlands) representing condition of missing maxillary left first molar. Impressions (Express, 3M ESPE, USA) were taken to the model with putty-wash technique following 5 different protocols: Group 1: Aluminum foil (Sanita, Beirut, Lebanon) was used as a spacer between the dentoform and the putty impression; Group 2: Escape grooves were carved in the putty impression before taking the wash impression using Putty cut (Zhermack, Badia Polesine, Italy); Group 3: No modification was done to the putty impression before taking the wash impression. Group 4: The tray was moved in ant-posterior rocking motion during setting of the putty impression. Group 5: The putty impression was taken with the temporary crowns (Prevision CB, Heraeus Kulzer GmbH, Germany) on the abutments simulating the condition of unprepared abutments. All impressions were poured using type IV stone material (Elite rock, Zhermack , Badia Polesine, Italy). Dies were then examined under a stereomicroscope (Leica M205 A, Leica microsystems, Switzerland) for accuracy using linear measurements between standardized points at the abutments compared to that on the master model. Data were collected and statistically analyzed. Results: Regarding inter-abutment distance, there was a statistically significant difference (p>0.05) between all groups. There was statistically no significant difference (p>0.05) between group 1 and group 4. There was statistically no significan difference (p>0.05) between group 2, 3 and group 5. Moreover, molar and premolar heights showed statistically significant (p<0.05) difference with all groups. Conclusions: The impression technique affects the accuracy of the stone die. Anteroposterior rocking movement technique showed the best accurate results, followed by foil technique. Further clinical studies are imperative for confirmation of the laboratorial findings.