The success of this technique depends on the pseudoplastic (. This method was originally developed for condensation silicone to minimize the effect of associated dimensional changes. Effect of seating tray material that has passed its working time and developed some elasticity. Which material should be used if a more durable impression material … What are the three classifications of impressions used in dentistry? 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. For example, epinephrine, which is used widely, is of particular concern in patients with cardiovascular disease. 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 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. Nonetheless, the hydrogen gas evolved can result in pinpoint voids in the gypsum casts poured soon after removal of the impression from the mouth. In addition, as the materials make turns along the helix, the rotational circulation causes a radial mixing of the materials. 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 term elastic means that the material is flexible and can be deformed and still return to its original form when unstressed. Remember, however, that polymerization may continue for a considerable time after setting. Recipient of First Annual Stanley D. Tylman Award, sponsored by the American Academy of Crown and Bridge Prosthodontics. the impression to remain in the mouth. Sulfur contamination from natural latex gloves inhibits the setting of addition silicone. Which of the seven criteria that ensure accurate impression making are related to the time the impression material is in the mouth? With the mechanical devices described earlier, the materials now can be mixed as needed by one individual. zinc oxide-eugenol (ZOE) although technique may vary, when assisting a dentist in taking an elastomeric impression, mix the light-bodied material … In addition, there are fewer possibilities for contamination of the material. The extruder gun insert is either catalyst or base. In particular, hot and humid conditions will accelerate the setting of polysulfide impression material. Which one is related primarily to the properties of a set impression? The reaction starts at the beginning of mixing and reaches its maximum rate soon after spatulation is complete (Figure 8-3). Impression materials were submitted to the following treatments: immersion in 5.25% sodium hypochlorite solution for 10 minutes, immersion in 2% glutaraldehyde solution for 30 … surface on the tray will increase adhesion. Altering the base/catalyst ratio will change the curing rate of these impression materials. The putty can be used as the tray material in conjunction with a low-viscosity silicone, that is referred to as the putty-wash technique. 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. Under no circumstances should the impression be removed until the curing has progressed sufficiently to provide adequate elasticity, so that distortion will not occur. Imbibition—The displacement of one fluid by another immiscible fluid in a hydrocolloid. Various types of casts and models can be made from gypsum products using an impression mold or negative likeness of a dental structure (Figure 8-1). Static mixing provides greater uniformity in proportioning and mixing, yields fewer voids in the mix, and reduces the mixing time. The lighter material is injected from the filled syringe or directly from a static mixing gun within and around the tooth preparation. The base paste, is a polysulfide polymer that contains a multifunctional mercaptan (-SH) called a polysulfide polymer, a suitable filler (such as lithopone or titanium dioxide) to provide the required strength, a plasticizer (such as dibutyl phthalate) to confer the appropriate viscosity to the paste, and a small quantity of sulfur, approximately 0.5%, as an, 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, The reaction starts at the beginning of mixing and reaches its maximum rate soon after spatulation is complete (, Polymerization of polysulfide impression material. Elastomeric materials include polysulfide, polyether, condensation-cured silicone, … After being removed from the mouth, the pressure in the impression is released and the putty recovers its “elastic deformation.” The distortion produced by the stiff, compressible putty results in a short, narrow die (Figure 8-10). Representative products are shown in. A custom tray allows a uniform distribution of impression material between the tray and the object, which also improves accuracy. The goal of impression making is to produce an accurate impression that can yield a cast or die that reproduces the surface details and precise shape of the original tissue as closely as possible. At this stage, a resilient network has started to form. The article focuses on polyether (PE), polysulphide, … The catalyst (or accelerator) paste contains lead dioxide, filler, and plasticizer as in the base paste, and oleic or stearic acid as a retarder to control the rate of the setting reaction. 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