Mold inversion and abrasion resistance of a type IV stone

The objective of this study was to determine whether placing the impression and diestone so the impression is on the top during setting affects the resulting die's abrasion resistance. Impressions of a brass bar with a milled 90 degrees edge were obtained by use of a polysulfide impression material in a rigid brass tray. A Type IV diestone was vacuum-mixed and vibrated into the impression. Eight procedures were compared: (1) no inversion; (2) inversion at initial set; (3,4) inversion one or two min before initial set; and (5,6,7,8) inversion 1.5, 3, 5, or 12 min after initial set. Each specimen was abraded 24 hours after mixing. Specimens inverted at 1.5 and 3 min after initial set were significantly more abrasion-resistant than were all other treatments.