Purpose: Six impression techniques were evaluated using tapered and square impression copings.
Materials and methods: The absolute distortion was measured using a cast metal impression tray with fiduciary reference points external to the impression material. Measurements of the x, y, z coordinates on the master cast and the impressions were directly made with a travelling digitizing microscope. The difference between the coordinates of each of six sites in the impression and the corresponding reference site were compared.
Results: There was no significant difference between the techniques for the square copings but that there was a significant loss of accuracy in the z-axis with the tapered copings.
Conclusions: No significant differences were noted.