They are virtually inert after set, and they can be trimmed and poured in any die material. Some vinyl gloves also may have the same effect because of the sulfur-containing stabilizer used in the manufacturing process . They have low rigidity and require rigid trays to support borders; otherwise they tend to distort. It sets by oxidation of the −SH groups, which results in chain lengthening and cross-linking and gives it elastomeric properties . Wettability of an impression material relates to the ability of the material to flow into small areas . Polyvinyl siloxane materials may require surfactants to lower the contact angle before pouring casts. If this material is overheated it may not recover to its normal setting time even after cooling, and it is recommended that this material be stored in a cool place and not in the sun (refrigerator or cool space). Distortion can be a problem if disinfection guidelines are not strictly adhered to. AU - Bae, Kwang Hak. They constitute the most widespread use of impression materials for fixed prosthetics . After the phosphate ions are depleted, the calcium ions react with the soluble alginate to form insoluble calcium alginate, which with water forms the irreversible calcium alginate gel. Polyethers are considered to have the highest tear strengths, whereas hydrocolloids have relatively low tear strengths . The accuracies varied among the 10 impression materials over three rounds. In recent years, dentists have turned toward using polyvinyl siloxanes and polyethers because of their improved physical and mechanical properties . Materials with a high wetting angle do not flow easily into small crevices and are poor candidates for use in fixed prosthodontics. The discrepancy of the alginate impression materials increased with storage time. The large loading of filler showed less discrepancy. There is also a greater tendency for alginate to stick to teeth if they are dry. These materials have low tear strength and usually tear on removal if not careful . If a comparison of the various categories of impression materials is made based on hydrophilic versus hydrophobic nature, wettability, the amount of detail reproduced, their dimensional stability, the rigidity of the material, the tear strength of the material, and the contact angle of the material, the selection of the right material is made easier. The relationship between static and mobile oral structures must be reproduced accurately … They contain functional groups that chemically attract and interact with water molecules via hydrogen bonding . Tissue conditioners are composed of a powder that contains poly (ethyl methacrylate) and a liquid that contains an aromatic ester-ethyl alcohol (up to 30%) mixture. The relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. The dimensional stability of an impression material reflects its ability to maintain the accuracy of the impression over time . If kept in a refrigerator, it is advisable to let the material come to room temperature before use, otherwise it takes a longer time than normal to set. It is recommended that a disinfectant spray be used while the impression is placed in a plastic bag for 10 minutes, at which time the impression is rinsed with water immediately and the cast poured . The setting times are relatively short (4–5 minutes), and the set is not altered or contaminated by latex gloves. Of all the materials, the addition type silicone materials, Aquasil and Exaflex, had relatively greater accuracy and stability. The hydrophilic nature of polyether impression material is manifested in carbonyl (C=O) and ether (C-O-C) groups, whereas polysulfide material has hydrophilic disulfide (-S-S-) and mercaptan (-S-H) groups . Most materials in this category do not adhere to themselves after they have set and would not be able to be used for border molding or correctable impression technique. It has been reported that vapor given off by polysulfide impression material may cause contamination. Materials with high contact angle require more careful pour technique and attention to produce accurate casts . Y1 - 2012 The accelerator (catalyst) has primarily lead dioxide with other substances, such as dibutyl or dioctyl phthalate, sulfur, and magnesium stearate and deodorants. Claims are made with respect to polyvinyl siloxane materials being hydrophilic, but in reality they are somewhat hydrophobic . The requirements of impression materials can be conveniently discussed under four main headings: (1) Factors which affect the accuracy of the impression. High ambient room temperature does not distort them, and they can be trimmed and poured with any die material for casts. When it does set, it does so immediately . Polysulfide impression materials are generally low to moderately hydrophilic and make an accurate impression in the presence of some saliva or blood. Flexible impressions are easier to remove from the mouth when set. Polyether and polysulfide impression materials also leave the mouth coated with a chemical film that inhibits polyvinyl siloxanes. The newer materials are supposedly able to be poured in 5 minutes after the impression material is removed from the mouth. Polyethers and some polyvinyl siloxanes fall into this category. Unfortunately, it does not adhere to itself, which makes it unavailable for border molding or correctable impression techniques. This material adheres to itself and can be used to border mold or make correctable impression techniques. In group B, a dual-cure acrylic resin was used, and for group C, plaster, which was also the impression material, was used. Practitioners should take this characteristic into consideration when selecting impression materials given the time available to the practitioner to pour casts during office hours. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. Factors affecting the accuracy of elastometric impression materials. They are fairly easy to remove. The relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. They would be detrimental in making full arch impressions of periodontally compromised or mobile teeth. Automixing cartridges tend to create fewer bubbles than hand spatulation. Methods. Factors that may cause sticking of the alginate include polishing of teeth, which removes a thin film overlying the teeth and actually prevents the hydrophilic nature of this material from wetting the teeth and reproducing detail . The second and third stone dies were made 1 and 24 h later, respectively. An ideal impression material should exhibit certain characteristics in the clinical and laboratory environment. This material comes in flavors and is not much of a problem from the standpoint of taste. 2. Results. It has a low wetting angle so it easily captures full arch impressions. It is recommended that one wait at least 30 minutes for the setting reaction to be completed before the gypsum casts and dies are poured . Vinyl polysiloxane silicones (also called addition silicones, polyvinyls, vinyls, and polyvinyl siloxane) are considered state-of-the-art for fixed partial denture impressions. The material is thicker when it is cold and more difficult to express and mix . Diluted sodium hypochlorite (bleach 5.25%, 1:10 dilution, 10 minutes at 20°C) provides American Dental Association–accepted disinfection but not sterilization for all materials, except zinc-oxide eugenol paste. 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