Purpose: This study evaluated the dimensional accuracy of various impression materials for monophase elastic impression making. To isolate this parameter, a direct measurement of the impressions was made without taking the model material into consideration. Materials and Methods: A total of eight materials were tested; six impression materials
were addition-curing silicones, and two were polyether impression materials. All materials were processed according to the manufacturers’ instructions. A specially developed precision mold made of stainless steel served as a basis for measuring the elastomeric impression materials. Using a stereomicroscope at a temperature of 23.0 ± 1.0°C and with a precision linear adjustment and lathe, sights were set on the marking points of customized posts. The measurement was performed after the earliest time possible for fabricating the model according to the manufacturer (time 1) and after 90 minutes (time 2). In a one-way analysis of variance, multiple average comparisons of dimensional accuracy
were made (P ≤ .05) between the impression materials under investigation. Results: Under the conditions of this study, the impression materials tested demonstrated a very high dimensional accuracy. The arithmetic means of the dimensional changes ranged from –11 to 19 µm for both measuring times. Conclusion: Since as a rule, no significant dimensional changes occurred for the different impression materials between time 1 and time 2, this
time interval for fabricating a model can be recommended. Int J Prosthodont 2002;15:168–174.