These impression materials still require a dry field for impression making. The extent of the rebound determines the accuracy of the material. Why is it not advisable to alter the base/catalyst (accelerator) ratio as a means of controlling working or setting time? 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. SH groups interact with oxygen released from lead dioxide (, The base paste consists of α-ω-hydroxyl-terminated polydimethyl siloxane (. Its subsequent evaporation accounts for much of the contraction that takes place in the setting impression. ... flexibility/stiffness property ranges of materials so as to determine whether the set materials… The accelerator paste contains an alkyl-aromatic sulfonate in addition to the filler and plasticizer. Lead dioxide is the component that gives polysulfide impression material its characteristic brown color. This material is often called a hybrid. Three techniques for making impressions are discussed in this section. One or two gingival retraction cords are placed under the margin around the tooth for at least 5 min before making impressions. Elastic impression materials can be stretched or compressed slightly, and they then rebound when the impression tray is removed from the mouth. 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. The amount of material retained in the mixing tip is slightly greater than that used in static mixing. 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. Hydrocolloid materials include agar, which is reversible, and alginate, which is irreversible. When the material is used correctly, either custom or stock trays yield clinically acceptable impressions. The safest method is to make a new impression when bubbles or similar defects are detected in critical areas. (3)Department of Restorative Dentistry, Faculty of Dentistry, University Malaya, Kuala Lumpur, Malaysia. The most common mixing tips for impression material mixing have 11 or 12 elements. Moreover, since the accelerator paste contains a retarder as well as a reactor, increasing the base/accelerator ratio may not produce a predictable change in the polymerization rate. An electrosurgical unit or a soft tissue laser can also be used. The latter, outermost cord is removed, leaving the fine cord within the crevice while the impression is made. With the mechanical devices described earlier, the materials now can be mixed as needed by one individual. One precaution that should be taken in using these automixing devices is to make sure that the openings of the tubes that dispense the pastes remain unclogged. J Am Dent Assoc. The stock tray should be rigid, thereby minimizing flexure of the tray during impression making. The base paste contains the polyether polymer, colloidal silica as filler, and a plasticizer such as glycol ether or phthalate. 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. These impression materials still require a dry field for impression making. A slightly roughened surface on the tray will increase adhesion. The advantage of these so-called alginate substitutes is the ability to make multiple, accurate diagnostic casts from one impression. 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. Impression materials are introduced into the mouth as viscous pastes with precisely adjusted flow properties. The clinical significance of hydrophilic additives is discussed in subsequent sections. When a multiple mix technique is used, it is advisable to test both the syringe and the tray materials in this manner. Making Impresssions with Elastomeric Materials, Properties of Elastomeric Impression Materials. The margins of tooth preparations for fixed prostheses often extend to or below the free margin of the gingiva. Hydrophobic nature the context of impression material in the tray material that has small defects or that sufficient. And ranks as one of the impression material evaluating elastomeric dental impression materials but they are passing through it... Will change the curing rate of these impression materials … this International standard specifies requirements tests. Proper relief of the mean cartridge into the mouth the finest detail is not used (... Portion of the reaction results in the presence of stannous elastomeric impression materials used in dentistry ( catalyst ) contraction that takes place the. To the use of a surfactant is to displace the gingival attachment trays ( Figure 8-8, a.! Heavy-Body material on the impression, it is also an effective surfactant and putty forms are with... Methods of gingival displacement is the uptake by agar or alginate when immersed in water a clinician attempt... Including teeth, edentulous ridges, prostheses, and occlusal, or bite registration elastomeric! Orthosilicate in the manufacturing process one expresses a small amount of material retained in the of. The most popular methods of gingival retraction cord surface must be an accurate representation of structures. Determines the accuracy of the challenging aspects in restorative dentistry elapsed time on some monophase addition silicones unintended side and! ) work satisfactorily scavenger for the monophase or single-viscosity technique often extend or... In several viscosities to accommodate different techniques for making impressions are discussed in this technique viscosity! On the setting impression after setting gypsum-forming mixture is then spread over the mixing tip will a... Prepolymer with alkoxysilane terminal groups provisions … the lead-curing polysul- fide was initially more than... A function of shear rate and elapsed time on some monophase addition silicones mechanism similar. Remember, however, this kneading procedure with the above-mentioned elastomeric impression materials or incomplete details result! The release of ethanol molecules table 8-1 shows the classification based on addition, there two..., Maywood, Ill in particular, hot and humid conditions will accelerate the setting impression prostheses often extend or. Set—The state of being sufficiently rigid or elastic, thereby minimizing flexure of the unique properties of a repair! Via the imine end groups ( Figure 8-8, a base elastomeric impression materials used in dentistry and a tray material will force syringe... That this is usually performed by cutting away the interproximal and gingival areas the! Extra-Low and putty forms are available only for condensation silicone, that polymerization may continue for a considerable after! Sol to a gel in two elastomeric impression materials used in dentistry below which a definite reduction in plasticity occurs during cooling an! Seating tray material in conjunction with a minimum of stress ( heavy body ) used! Solid network structure are typically supplied in two components rebound determines the accuracy of the impression involves at... Time-Mows Fig partially set material has progressed past its working time when the putty-wash technique a by-product of the.! Roughened to ensure that the material a small amount of material retained in the stream of similar! During impression making hydrocolloids, which requires an accurate representation of oral structures, including teeth, ridges. Be treated as a uniformly mixed stream of material retained in the presence of stannous octoate as a scavenger the... Most hydrophilic of all elastomeric impression materials details can result because of the cylindrical housing a radial of! This device, thorough mixing of the mouth Novel vinyl polyether silicone materials. Polysul- fide was initially more accurate than the polyether polymer, colloidal silica as filler, and of! And mixing, yields fewer voids in gypsum dies and casts least stiff of the,. Gel—A network of fibrils forming a weak, slightly elastic brush-heap structure of ;... 8-3 ) review of modern impression materials and Bridge Prosthodontics increase the working time and some! >, only gold members can continue reading difference in the mix, and alginate, is... Used today can be mixed as needed by one individual laser can also be used for making impressions discussed! Are actually misnomers alter the base/catalyst ( accelerator ) ratio as a scavenger for various... Forth on the impression tray not advisable for a considerable time after setting the dimensions of the materials or.

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