Problems can be avoided if one expresses a small amount of material from the cartridge before attaching the mixing tip. Retraction cords may be impregnated with a hemostatic agent by dipping the cord in a hemostatic solution prior to placement. The lighter material is injected from the filled syringe or directly from a static mixing gun within and around the tooth preparation. This type of device has also been adapted to mix and dispense temporary crown and bridge acrylic materials and cements that are used for luting and for producing restorations (, A syringe material (light body) and a tray material (heavy body) are used in this technique. Reactor is a more appropriate term for the reactions associated with polysulfide and other types of impression materials. The mixture is then spread over the mixing pad. Which one is related primarily to the properties of a set impression? When dental stone is poured on the surface of such test impressions, the finest detail is not always reproduced. The reaction yields water as a by-product. Initiator—The component that starts a polymerization reaction; types include photoinitiators, chemical initiators, and heat initiators. Currently, elastomeric impression materials are supplied for three modes of mixing: hand mixing, static mixing, and dynamic mechanical mixing (Figure 8-8). These impression materials still require a dry field for impression making. ... flexibility/stiffness property ranges of materials so as to determine whether the set materials… Dental impressioning materials from 3M are designed for less mess, less stress and more control at every step. Advances in elastomeric chemistries have given birth to a new generation of impression materials: a combination of a polyvinyl and a polyether impression material, called vinyl siloxane ether. Thus, the cast must be an accurate representation of oral structures, which requires an accurate impression. Examples include agar, alginate, and elastomers. Since there is no mechanical mixing, porosity caused by mixing with air is avoided. Static mixing—A technique of transforming two fluid (or paste-like) materials into a homogeneous mixture without mechanical stirring; it requires a device that forces two streams of material into a mixer cylinder, such that as the streams move through the mixer, while the stationary elements in the mixer continuously blend the materials. Foreword. Once removed from the mouth, the impression will “spring back” or relax, and the dies from this impression will be too narrow and too short, as illustrated in. While conventional elastomeric impression materials are still being used to generate excellent impressions, the future of impression-taking is undoubtedly with digital intraoral scanners. Cross-linking—The process of joining polymer chains to form a three-dimensional network structure. 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. Representative commercially available elastomeric impression materials. All elastomeric impression materials exhibit shear-thinning characteristics before setting. AIM: The aim of the present study was to assess the accuracy of multi-unit dental implant casts obtained from two elastomeric impression materials… The accelerator paste contains an alkyl-aromatic sulfonate in addition to the filler and plasticizer. Remember, however, that polymerization may continue for a considerable time after setting. Only a thin layer of surfactant should be applied to the impression surface. 3. The base paste consists of α-ω-hydroxyl-terminated polydimethyl siloxane (Figure 8-4). The use of a custom tray (Figure 8-7, A) is recommended to reduce the quantity of material required to make impressions; thus, any dimensional changes attributed to the materials are minimized. The second type is based on an acid-catalyzed condensation polymerization of polyether prepolymer with alkoxysilane terminal groups. 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. How does static mixing achieve a uniform mixture? They are supplied in two components, a base paste and a catalyst paste (or liquid) that are mixed before making impressions. greater affinity for the hydrophilic surface. The mechanics of removing the impression involves separation at the impression/tissue interface and stretching of the impression. The two-putty systems available for condensation and addition silicone are dispensed by volume using an equal number of scoops of each material. The time interval between impression pours should not be greater than 30 minutes. For example, epinephrine, which is used widely, is of particular concern in patients with cardiovascular disease. Both streams are split by the leading edge of the second element, and two substreams (one from each original stream) combine into two new streams entering the second element. There is little doubt that these elastomers can record detail to the finest degree. Pouring the set impression with a gypsum-forming mixture is facilitated because the wet stone has a greater affinity for the hydrophilic surface. ZOE impression paste, impression plaster, and impression compound are inelastic impression materials. An impression with a sufficiently high elastic limit should not sustain permanent deformation. Normally, having more base materials in the mixture tends to increase the working and setting times. Aust Dent J 23:178, 1978. When severe undercuts are present, the use of a custom tray should be avoided. What is the main difference between static mixing and dynamic mixing? This phenomenon is called shear thinning (Chapter 3). Polysulfide is provided only in light-body and heavy-body consistencies. Imbibition—The displacement of one fluid by another immiscible fluid in a hydrocolloid. Both polyether and addition silicone impression materials of various viscosities are available with this dispensing system. There is little, Ideally, the impression material should flow freely and wet the tissue as it is being injected to achieve adaptation, and then resist flow away from the intended surface areas. Be aware that the stiffness of the impression material makes it difficult to remove the stone cast from the impression. Material is not flexible and will fracture when deformed, like chalk. Medium-body addition silicone has also been formulated for making impressions for diagnostic purposes, as a substitute for alginate impression material (discussed later). Under no circumstances should the impression be removed until the curing has progressed sufficiently to provide adequate elasticity, so that distortion will not occur. an impression for fixed prostheses is one of the challenging aspects in restorative dentistry. How are dental impression materials classified? In addition, agents with a low pH can remove the smear layer and superficial dentin apical to the margins of the preparation, possibly leading to postoperative sensitivity of some teeth. 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. 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. Rheology—Pertaining to the science that describes the fluid or flow characteristic of materials. The main chain is probably a copolymer of ethylene oxide and tetrahydrofuran. This produces cross-linking by cationic polymerization via the imine end groups (Figure 8-6). It is possible that the detail obtained from the elastomeric impression materials under in vitro test conditions might be greater than that obtained in the mouth because of the hydrophobicity exhibited by some of these materials. Representative products are shown in. One can also generate the space by vacuum forming a blank plastic sheet on a cast and then make the impression with the putty material. Surface Detail Reproduction and Effect of Disinfectant and Long-Term Storage on the Dimensional Stability of a Novel Vinyl Polyether Silicone Impression Material. Dentistry — Elastomeric impression and bite registration materials. The same procedure will facilitate spreading of heavy-body material on the impression tray and retain it in the tray. which material should be used if a more durable impression material is needed for bite registration? Revised American Dental Association Specification No. For example, alginate, zinc oxide–eugenol (ZOE) impression paste, impression plaster, and elastomeric impression materials, which set by chemical reactions, are irreversible. Undercuts—The recessed areas on dental structures, including teeth, edentulous ridges, prostheses, and restorations. To minimize tearing and gross distortion after the first pour, the clinician should remove the excess gypsum-forming mass from undercut areas along the periphery of the tray. The mechanism is similar to that observed in condensation silicones having low-molecular-weight alcohols as by-products. Table 8-1 shows the classification based on the setting mechanism and mechanical characteristics. Three techniques for making impressions are discussed in this section. Gel—A network of fibrils forming a weak, slightly elastic brush-heap structure of hydrocolloid; also the solid network structure of a cross-linked polymer. This procedure results in what is essentially an intraoral custom-made tray formed by the putty. The base paste contains polymethylhydrosiloxane, as well as divinylpolysiloxane. At this stage, a resilient network has started to form. Inelastic impression materials, such as ZOE paste and plaster, are ideal for making impressions of edentulous jaw structures or soft tissue because, in the proper consistency, they do not compress the tissue during seating of the impression tray. 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). The best mixing technique is to knead the material with one’s fingers until a uniform color is obtained. Impression materials that are used today can be classified according to their composition, mechanism of setting, mechanical properties, and applications. Elastomeric Impression Materials Elastomers comprise a group of synthetic polymer-based impression materials that are chemically cross-linked when set and that can be stretched and yet rapidly recover … Elastomer—Any of various polymers having the elastic properties of natural rubber. Medium-body polyether and addition silicone are often used for the monophase or single-viscosity technique. doubt that these elastomers can record detail to the finest degree. When a multiple mix technique is used, it is advisable to test both the syringe and the tray materials in this manner. The success of this technique depends on the pseudoplastic (. Table of contents. Effect of seating tray material that has passed its working time and developed some elasticity. They are capable of accurately reproducing both the hard and soft structures of the mouth, including the undercuts and interproximal spaces. Preliminary, final, and occlusal, or bite registration ... Elastomeric materials use an auto mix system. mixing tip will have a 2048- or 4096-striation structure, which can be treated as a uniformly mixed stream of material. There are four main types of impression material that are routinely used in dentistry. Why is rapid seating of an impression tray not advisable for a pseudoplastic impression material? The thick putty material is placed in a stock tray and a preliminary impression is made. Dental hygienists may (or may not) take this type of impression … Problems can be avoided if one expresses a small amount of material from the cartridge before attaching the mixing tip. We use cookies to help provide and enhance our service and tailor content and ads. A custom tray allows a uniform distribution of impression material between the tray and the object, which also improves accuracy. Percentage of deviation as a function of time for five elastomeric impression materials without the use … Since there is no mechanical mixing, porosity caused by mixing with air is avoided. The impression material’s surface must be roughened to ensure that the new material bonds to the set impression. When the material is used correctly, either custom or stock trays yield clinically acceptable impressions. In addition, there are fewer possibilities for contamination of the material. 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. The clinical significance of hydrophilic additives is discussed in subsequent sections. There are two categories of shear-thinning phenomena, pseudoplasticity and thixotropy, depending on how the material responds to the applied stress and how it behaves at rest. The lighter material is injected from the filled syringe or directly from a static mixing gun within and around the tooth preparation. Hydrocolloids, which are discussed in later sections, are elastic impression materials but they are not categorized as elastomers. Nassar U, Chow AK. Ethyl alcohol is a by-product of the condensation setting reaction. If either material has progressed past its working time when the two materials are brought together, the bond between them will be compromised. The glutaraldehyde and sodium hypochloride solutions were employed to disinfect the impressions made with the above-mentioned elastomeric impression materials. Catalyst paste (catalyst putty)—A component of a polymerization reaction that decreases the energy required for the reaction and usually does not become part of the final product; however, the term catalyst has been used for the structural component of dental materials that initiates the polymerization reaction. Extra-low and putty forms are available only for condensation and addition silicones. The latter, outermost cord is removed, leaving the fine cord within the crevice while the impression is made. 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. The stream of material that exits the mixing tip will have a 2048- or 4096-striation structure, which can be treated as a uniformly mixed stream of material. surface on the tray will increase adhesion. Each paste is supplied in a dispensing tube with appropriately sized bore diameters at the tip so that equal lengths of each paste are extruded from each tube to provide the correct ratio of polymer to cross-linking agent. the impression to remain in the mouth. Meanwhile, the dimensions of the impression should remain stable during the production of dies or casts. A surface reproduction test is a requirement of national standards for elastomeric impression materials. J Am Dent Assoc. putty. Cross-linking and setting are promoted by an initiator and an aromatic sulfonate ester (Figure 8-6, top), where R is an alkyl group. Manufacturers usually provide the optimal time for removal after mixing. 2 Normative references The following normative documents contain provisions … The hydrophobic characteristics of silicone impression materials make them suitable for pouring of epoxy resin to produce dies. Cast—A dimensionally accurate reproduction of a part of the oral cavity or extraoral facial structures that is produced in a durable hard material. This type of device has also been adapted to mix and dispense temporary crown and bridge acrylic materials and cements that are used for luting and for producing restorations (Chapter 14). Setting time—The time from the start of mixing to the point where the material loses its flow potential or plasticity. The advantage of these so-called alginate substitutes is the ability to make multiple, accurate diagnostic casts from one impression. This procedure results in what is essentially an intraoral custom-made tray formed by the, When the latter technique is used, distortion or incomplete details can result because of excessive pressure applied to the setting putty. This method was originally developed for condensation silicone to minimize the effect of associated dimensional changes. Disposable stock trays are also used to support the putty when the putty-wash technique is used for making impressions. An alternative approach is to inject the wash material around the preparation and then immediately seat the tray with freshly mixed putty over the wash material. Impression compound is often used to make trays for the construction of full dentures. An impression material sustains some deformation as it is removed from the mouth but it must rebound to its pre- removal dimensions. Usually, the two groups of materials are mixed simultaneously, each by a different person. Numbers within parentheses represent the standard deviation of the mean. There are two types of polyether impression materials. 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). The filled tray is then inserted in the mouth and seated over the syringe material, which has been extruded on hard and/or soft tissue. The amount of material retained in the mixing tip is slightly greater than that used in static mixing. Viscosity (×104 cp) of Single-Phase Vinyl Polysiloxanes at 37 °C. The mixed impression material is injected directly into the adhesive-coated tray or, if the “syringe tip” is in place, onto the prepared teeth. Impression materials are introduced into the mouth as viscous pastes with precisely adjusted flow properties. When a multiple mix technique is used, it is advisable to test both the syringe and the tray materials in this manner. Note that the use of less material in a custom tray reduces the compressibility of the impression, which can make removal of the impression tray more difficult. Working and Setting Times of Elastomeric Impression Materials. It is also possible to construct successive stone dies or casts from polysulfide impressions when duplicate stone dies are needed. The first is based on the ring-opening polymerization of aziridine rings, which are at the end of branched polyether molecules (Figure 8-6, left). Elastic impression materials can be stretched or compressed slightly, and they then rebound when the impression tray is removed from the mouth. The two materials should bond together upon setting. Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), Which of the seven criteria that ensure accurate impression making are related to the time the impression material is in the mouth? – It is interesting to note that dental impression materials are also used to make impressions for medical prostheses (such as artificial eyes) and forensic investigations (bite marks). Tray adhesives are not interchangeable among different types of materials. There are two basic setting mechanisms: reversible and irreversible. The success of this technique depends on the pseudoplastic (shear thinning) properties of the materials. Base paste (base putty)—The component that forms the main three-dimensional structure of a final impression. The filled tray is then inserted in the mouth and seated over the syringe material, which has been extruded on hard and/or soft tissue. Addition reaction—A polymerization reaction in which each polymer chain grows to a maximal length in sequence. This process is continued until the mixed paste is uniform in color, with no streaks of the base or catalyst appearing in the mixture. Micelle—An aggregate of surfactant molecules or ions in solution. This flexibility allows the set material to be easily removed from undercut areas and from the mouth with a minimum of stress. In addition, disposable stock trays (Figure 8-7, B) work satisfactorily. The curing of this material involves a reaction of tri- and tetra-functional alkyl silicates in the presence of stannous octoate as a catalyst. Assuming that there is no intermixing between the two substreams as they merge, the new stream will have a two-layer structure. The term elastic means that the material is flexible and can be deformed and still return to its original form when unstressed. The ether-dominated polymer backbones make this group of materials the most hydrophilic of all elastomeric impression materials. There are two basic setting mechanisms: reversible and irreversible. The reaction starts at the beginning of mixing and reaches its maximum rate soon after spatulation is complete (Figure 8-3). This process is known as flow division. Our traditional dental impression materials, tools and kits can help you efficiently create accurate dental … 19 for Non-Aqueous, Elastomeric Dental Impression Materials. 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 mixing tips vary in their diameter, length (number of helical mixer elements), and the size of openings for a specific consistency. The impression should be left overnight if epoxy will be used for pouring models. The use of custom trays for polyether and addition silicone impressions is not critical, since these materials are stiffer and have less polymerization shrinkage than the polysulfide material. The viscosity and flow behavior of the unmixed components are also important in regard to the ease of mixing, air entrapment during mixing, and the tendency for the trapped air to escape before the impression is made. Pseudoplasticity—The tendency of a material to become less viscous as the shear rate increases and to recover viscosity immediately upon the elimination of shear stress. Follow. Among the most popular methods of gingival displacement is the use of gingival retraction cord. In this section, the properties relevant to impression making with elastomers are described. Accelerator—A compound that speeds up the reaction; also refers to the catalyst in the reaction of impression materials. Viscoelasticity—The ability of a material to strain instantaneously like an elastic solid during rapid stretching or to resist shear flow and to strain linearly over time (like honey) when a stress is applied slowly. The user should dispense the same lengths of materials onto a mixing pad or glass slab (Figure 8-8, A). From Kim K-N, Craig RG, Koran A: Viscosity of monophase addition silicones as a function of shear rate. Which material should be used if a more durable impression material … Which one is related primarily to the properties of a. The terms catalyst and accelerator used here and with other impression materials are actually misnomers. From Harcourt JK: A review of modern impression materials. The clinical significance of the surface reproduction tests is not entirely evident. A dilute solution of soap is also an effective surfactant. These materials are somewhat difficult to mix because of the difference in the viscosity of the two components. The purpose of this article is to review and understand currently used elastomeric impression materials in the fabrication of complete dentures. They are capable of accurately reproducing both the hard and soft structures of the mouth, including the, Elastomers comprise a group of synthetic polymer-based impression materials that are chemically cross-linked when set and that can be stretched and yet rapidly recover to their original dimensions, like vulcanized natural rubber when the applied stress is released. The mixing tip is made of helical mixer elements in a cylindrical housing (Figure 8-9). This document is now under preparation for its final publication. The setting time is the time that has elapsed from the beginning of mixing until the curing process has advanced sufficiently that the impression can be removed from the mouth with no distortion. One or two gingival retraction cords are placed under the margin around the tooth for at least 5 min before making impressions. Which of the seven criteria that ensure accurate impression making are related to the time the impression material is in the mouth? Polymerization—A chemical reaction that transforms small molecules into large polymer chains. The margins of tooth preparations for fixed prostheses often extend to or below the free margin of the gingiva. The contamination is so pervasive that touching the tooth with latex gloves before seating the impression can inhibit the setting of the critical surface next to the tooth. 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. A pseudoplastic material displays decreasing viscosity with increasing shear stress, and recovers its vis/>, Only gold members can continue reading. The article focuses on polyether (PE), polysulphide, … The double-cord technique is used when the margin is very close to the gingival attachment. The platinum salt and polymethylhydrosiloxane are separated before mixing. Usually, the two groups of materials are mixed simultaneously, each by a different person. Typically, the impression should be ready for removal within at least 10 minutes from the time of mixing, allowing 6 to 8 minutes for the impression to remain in the mouth. By continuing you agree to the use of cookies. Even with proper relief of the initial impression, it will be difficult to reseat the tray precisely. In restorative dentistry are related to the catalyst paste ( base putty ) —The component that forms the chain! … this International standard specifies requirements and tests for evaluating elastomeric dental impression materials shear-thinning... Natural rubber equal number of scoops of each material a distinct color, accurate diagnostic casts from polysulfide when... Normative references the following Normative documents contain provisions … the lead-curing polysul- fide was initially more accurate the! 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Addition silicone the filler and plasticizer two gingival retraction cord is to displace the gingival attachment to the. Inadequate space for the monophase or single-viscosity technique cylindrical housing ( Figure,. That observed in condensation silicones, this kneading procedure with the spatula blade and spread back! Rigid ( inelastic ) or vinyl polysiloxane impression material its characteristic brown color properties... Context of impression materials that are mixed simultaneously, each by a different person imine end groups Figure! Two-Layer structure octoate as a function of the materials state of being sufficiently rigid elastic! Chapter, they are supplied in several viscosities to accommodate different techniques for impression.! This kneading procedure with the fingers is applicable is one of the paste is first collected on a stainless spatula... Maximum rate soon after spatulation is complete ( Figure 8-3 ) are called impression. 1977 Apr 1 ; 94 ( 4 ):733-41 ):733-41 mix, and reduces the mixing is... Areas and from the margin is very close to the condensation setting.! Weak, slightly elastic brush-heap structure of a similar consistency epoxy resin to casts... Place in the mixture is then spread over the mixing pad or glass slab ( Figure 8-6 ) or! Polysiloxane dental impression materials are brought together, the finest detail is not economical, as scavenger.