This procedure results in what is essentially an intraoral custom-made tray formed by the putty. Syneresis—The expression of fluid onto the surface of gel structures. In this chapter, they are called elastomeric impression materials. The purpose of this article is to review and understand currently used elastomeric impression materials in the fabrication of complete dentures. When the material is used correctly, either custom or stock trays yield clinically acceptable impressions. What are the steps needed to produce casts and dies for prosthetic procedures? mixing tip will have a 2048- or 4096-striation structure, which can be treated as a uniformly mixed stream of material. Space for the light-body “wash” material is provided either by cutting away some of the “tray” putty or by using a thin polyethylene sheet as a spacer between the putty and the prepared teeth during preliminary impression making. Pouring of a stone cast in a polyether or polysulfide impression does not require the aid of a surfactant. Copyright © 1981 Published by Mosby, Inc. https://doi.org/10.1016/0022-3913(81)90018-4. The thick putty material is placed in a stock tray and a preliminary impression is made. There are two types of polyether impression materials. One should be aware that this is not economical, as a portion of the paste is not used. However, this hydrophobicity makes pouring with gypsum products challenging, as it increases the potential of forming voids in gypsum dies and casts. This material can be probed with a blunt instrument from time to time; when it is firm and returns completely to its original contour, the impression is sufficiently elastic to be removed. The material sets by cross-linking between terminal groups of the silicone polymers and the alkyl silicate to form a three-dimensional network (Figure 8-4). A mixture of the thin-consistency wash material is placed into the putty impression and on the preparation; then the tray is reseated in the mouth to make the final impression. These materials are somewhat difficult to mix because of the difference in the viscosity of the two components. Thus, mixing between substreams occurs before the next flow division that further increases the uniformity of the mixture. This phenomenon is called shear thinning (. Viscosity (×104 cp) of Single-Phase Vinyl Polysiloxanes at 37 °C. Prior to making an impression, a uniform thickness of tray adhesive is applied on the tray surface, extending over its edge, and it is allowed to dry (through evaporation of solvent). ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. Meanwhile, the material in the tray retains its medium viscosity, and, when seated, it can force the syringe material to flow past critical areas of the tooth preparation. The base paste consists of α-ω-hydroxyl-terminated polydimethyl siloxane (Figure 8-4). If one of the components is in liquid form, such as the catalyst for condensation silicones, a length of the base is dispensed from the tube onto a graduated mixing pad and drops of the liquid catalyst corresponding to the length of the base are added. One method for determining the time of removal is to inject some of the syringe material onto a space that is not in the field of operation before inserting the impression tray. In addition, there are fewer possibilities for contamination of the material. Addition silicone impression material is generally used as a “final impression material” for the fabrication of crowns and bridges. Usually, the two groups of materials are mixed simultaneously, each by a different person. When dental stone is poured on the surface of such test impressions, the finest detail is not always reproduced. A custom tray allows a uniform distribution of impression material between the tray and the object, which also improves accuracy. Cross-linking and setting are promoted by an initiator and an aromatic sulfonate ester (Figure 8-6, top), where R is an alkyl group. This surfactant migrates toward the surface of the impression material and has its hydrophilic segment oriented toward the surface—a phenomenon that makes the surface more wettable by water. The mass is then scraped up with the spatula blade and spread uniformly back and forth on the mixing pad. Irreversible implies that chemical reactions have occurred and that the material cannot revert to a previous state in the dental office. The impression material is inserted into the patient's mouth in a viscous state and transforms into viscoelastic state, upon withdrawal, influencing the residual deformation. Elastomeric Impression Materials 2. Dental impression making is the process of creating a negative form of the teeth and oral tissues, into which gypsum or other die materials can be processed to create working analogues. The base paste contains the polyether polymer, colloidal silica as filler, and a plasticizer such as glycol ether or phthalate. Dentistry — Elastomeric impression and bite registration materials. Pigments are added to give each material a distinct color. A nonionic surfactant can be added to the paste in the manufacturing process to render a degree of hydrophilicity to the surface of the material. The success of this technique depends on the pseudoplastic (shear thinning) properties of the materials. The phenomenon of viscoelastic behavior is discussed in subsequent sections. Areas and from the impression material mixing have 11 or 12 elements effect because of excessive pressure, some the. 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