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Background: Amongst the rubber base impression materials, the polyvinyl siloxanes are superior in accuracy and dimensional stability. Several impression techniques have been recommended with these materials.

Aims and objectives: To evaluate and compare the time dependent dimensional accuracy of polyvinyl siloxane impressions made with two impression techniques.

Materials and methods: A stainless steel master die simulating a three unit fixed partial denture preparation was fabricated. Impressions were made with polyvinyl siloxane materials {Reprosil Putty, Aquasil Ultra Heavy, Aquasil Ultra LV (Dentsply International)}using two-step putty/light-body technique using stock tray and one-step simultaneous dual viscosity technique using custom tray. The impressions were repeatedly poured at 1 hour, 6 hours, 24 hours and 7 days. Interpreparation distance and occlusogingival dimension were measured in the recovered stone dies (Type IV, Kalrock) using a travelling microscope calibrated to an accuracy of 0.001 cm.

Results: Results of this study indicated that the casts made with the 2-step putty/light-body technique using a stock impression tray and the simultaneous/ dual viscosity technique using custom made tray were dimensionally accurate and the polyvinyl siloxane silicones are dimensionally stable impressions for one week period, even though preferable pouring time can be considered as 1 hour to 24 hours

Conclusion: Repeated pouring of the impressions at the four different time periods did not significantly affect the accuracy of the casts produced by any of the techniques. Proper manipulation of the impression material is probably more important in determining the accuracy of an impression than which technique is selected for making

the impressions.

Accuracy, Dimensional stability, Elastic recovery, Vinyl polysiloxane, Repeated pouring