![]() Three layer of relief agent were placed on each master die in order to have appropriate metal casting. The three master dies were trimmed and finishing line was marked by a red pencil. 1-h later, the stone casts were separated from the impressions and stored 24 h for final setting. Three master removable dies were provided by using metal pins. 20 ml of water were mixed with 100 g of Stone Type IV (Vel-mix Kerr, Romulus, MI, USA,) and vibrated for 30 s for bubble evacuation. The manipulations were based on manufacturers’ instruction. Three master dies were made by these impression materials: (A) Panasil Contact Plus (Kettenbach, Eschenburg, Germany), (B) Impergum (3M ESPE, Saint Paul, Minnesota, USA), and (C) Speedex Coltene (Asia Chemi Teb Co Tabriz, Iran, under the license of Coltene-Switzerland). Furthermore, the Impergum impressions were made by using one-step impression technique. Two step impression technique was administered for Panasil and Speedex. Then three special trays were prepared with three occlusal stops 24 h before making impressions. For making special trays, two layers of wax were placed on the model to enhance the space for impression materials. Some grooves were prepared on mesial, distal, lingual, and buccal surfaces of the model beneath the margins for making measuring guidelines. The finish line was circumferential 1 mm rounded shoulder with a 90° cavosurface angle. In this observational-analytical study, an acrylic model of upper premolar tooth was prepared based on conventional shoulder type marginal preparation, supragingivally. Hence, the aim of this study was to evaluate the accuracy of three types of impression materials (PE: Impergum, CS: Speedex, and AS: Panasil) with focusing on providing duplicated dies. 18 However, the ability of impression materials to make duplicate dies with successive accuracy has not been investigated widely. 10, 16, 17 It seems that the best approach to make a duplicate cast is to make a second impression. If an impression material characterizes printing an accurate and precise details of the surface, all provided duplicated dies could have well marginal adaptation with the master die. In some circumstances, such as fracture or crack in margins of a die, clinicians are obligated to provide repetitive impressions and duplicated dies to improve marginal adaptation. Some other studies about these impression materials have been done recently 13- 15, but debates about the accuracy of these impressions still remain. ![]() They stated that dimensional accuracy of new PE was comparable to conventional PE impression material after short-term storage. surveyed the dimensional accuracy of stone dies provided from standardized impressions with polyvinylsiloxanes (PVS), new PE (P2), and conventional PE (Impergum) impression materials. They found greater accuracy and stability with AS materials. They used three types of alginates, five commercial silicones, and two experimental silicones impression materials. ![]() evaluated the effective factors on impressions accuracy during different storage times and proportion of inorganic fillers. ![]() Their results showed low dimensional changes during pouring and repetition for all of the impression materials. conducted a study to evaluate four types of impression materials (CS, AS, PS, and PE), based on different model location, repetition, and time of pouring. They can maintain their accuracy even 1-week or later, however, they are technique sensitive for instance PE should be stored in <50% humidity. PE and silicones are accurate with high stability. ![]() Several elastic impression material silicones are available for dental use: Synthetic elastomeric materials (polysulfide, additional silicone and condensational silicone, and polyether ) and hydrocolloids. There are several factors which can affect the accuracy of definitive impression like: Quality of preparation (undercuts and tapering), impression technique, soft tissue management, and quality of wax pattern and casting. Marginal adaptation of a cast restoration can influence its durability due to: Lower accumulation of plaques in margins, enhancing structural properties (stability, resistance, low thickness of cement, and etc.), and higher esthetics. Furthermore, temporary restorations are essential for preservation of the tooth structure in the meantime of preparing cast models. Achieving optimum function and esthetic of restorations is very important, especially in replacing a missing tooth. ![]()
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