Effect of undercuts on the accuracy of reheated addition-reaction silicone impressions.

Addition-reaction silicone impressions were made at 37 degrees C in two cylindrical trays of a truncated cone-shaped chromium-steel die. One tray size was used to obtain impressions with 1 mm thickness, from tray to the gingival margin of the preparation, while the second tray permitted a thickness of 4mm. The die was undercut aplical to the gingival margin using rings as described before permitting a variation of undercut depth from 0.5 to 1.5 mm. Stone dies were made from impressions after (1) cooling to 22 degrees C for 10 min or (2) cooling to 22 degrees C for 10 min and reheating to 37 degrees C for 30 min. Results revealed that reheating the impressions to mouth temperature before pouring the dies improved their accuracy and that depth of undercut had a definite but small effect on the accuracy of dies.