PubMed · 4574329
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F Bollmann, H Meiners. 1973-05-10. [Bandless impression technic with elastomers].. https://pubmed.ncbi.nlm.nih.gov/4574329/
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Dental impression materials for prosthodontic treatment must be easy to use, precisely replicate of oral tissue, be dimensionally stable, and be compatible with gypsum materials. The dimensional accuracy of all materials is affected by thermal changes; impression materials shrink during cooling from mouth temperature (37 degrees C) to room temperature (23 degrees C). Five kinds of light body addition-reaction silicone impression materials [Contrast (CT), Voco Co., Germany; Examix (EM), GC Co., Japan; Extrude (EX), Kerr Co., USA; Imprint II (IM), 3M Co., USA; Perfect (PF), Handae Chemical, Korea] were tested by making cylindrical specimens (6 mm diameter and 12 mm height). The thermal expansion of the impression materials was measured with a thermomechanical analyzer (TMA 2940, TA Instruments, USA) between 23-37 degrees C. Data were analyzed via the Mann-Whitney Usage Test. To simulate actual dental impressions, tooth and tray shapes were modeled to measure the linear shrinkage of impression materials at anterior and posterior locations. The thermal expansion of impression materials tested decreased as follows: CT >or= PF >or= EM >or= EX >or= IM (p < 0.05). The anterior region changed more than the posterior region for the same impression materials. The dimensional changes averaged more than 40 microm in the anterior region, but less than 40 microm in the posterior region for all materials. Thermal expansion coefficients of some impression materials were significantly different from each other (p < 0.05), and the anterior region had more dimensional change than the posterior region for the same impression materials.
STATEMENT OF PROBLEM: Dual-arch trays are often used to make simultaneous impressions of a prepared tooth and the opposing teeth. Many dentists are concerned with the accuracy of the casts generated from this type of impression. PURPOSE: The purpose of this investigation was to compare the accuracy of stone casts of a prepared tooth generated using 2 types of dual-arch impression tray/impression material combinations. MATERIAL AND METHODS: The maxillary left first molar on a dentoform mounted on an articulator was prepared for a full-coverage gold crown. Ten impressions were made with either a plastic (P) or metal (M) tray and a polyether (PE) or vinyl polysiloxane (VPS) impression material. Each impression was cast in improved dental stone, and the buccolingual dimension of the die was measured at the midpoint of the buccal and lingual gingival margins. The prepared tooth (T) served as the control. The data were analyzed using a 2-factor analysis of variance (ANOVA) alpha=.05. RESULTS: The P/VPS combination (10.673 mm) produced the largest die, followed by P/PE (10.602), T (10.508), M/PE (10.484), and M/VPS (10.472). The 2-factor ANOVA showed a significant difference between the tray types but not between the impression materials. CONCLUSION: The metal trays produced dies smaller than the tooth, and the plastic trays produced dies that were larger.
PURPOSE: This in vitro study compared 5 different dowel space impression techniques using polyvinyl siloxane impression material to determine which method produced fewer voids in the dowel space impression. MATERIALS AND METHODS: Five techniques were used to make impressions of a prepared dowel space in a simulated endodontically treated tooth. Technique I used a 25-gauge anesthetic needle to act as a vent at the apex of the preparation to reduce voids produced during the expression of light body impression material. The anesthetic needle was removed after the impression material was injected, and an impression post was then inserted to the depth of the preparation. Twenty impressions made using this technique were compared with other techniques that used the vent without a post, no vent with a post, no vent without a post, and a lentulo spiral with a post (Techniques II through V, respectively). The percentage of impressions with voids from each group was compared to determine which technique consistently produced a void-free impression of the complete preparation length. If voids were observed in the impression, the specimen was considered inadequate. RESULTS: The percents of void-free impressions using Techniques I through V were 100%, 70%, 40%, 60%, and 20%, respectively. CONCLUSIONS: Using a 25-gauge needle as a vent while expressing impression material into the dowel space followed by placing the impression post consistently produced void-free dowel space impressions.