They distort less on pouring and make good bite registration materials . Polysulfide impression material is dimensionally accurate if poured within 1 to 2 hours of making the impression . 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. – With proper handling, polysulfide impression materials can be used for inlays, crowns, and bridges. What is a disadvantage for the use of polysulfide rubber impression material has a strongodr and stains clothing Which of the following is NOT considered true for polyether rubber impression material? It is insoluble in water and its formation causes the material to gel . To understand why polysulfide impressions shring over time, one needs to consider the chemical reaction that occurs when a polysulfide sets. Polyvinyl siloxane has the best elastic recovery, followed by polyether and polysulfide . impression material for inlays, crowns, bridges, full and partial dentures, rebasing and relining. When mixed with water, the alginate material first forms a sol. Dryness minimizes the moisture content of tooth surfaces and contributes to sticking of the alginate; ultimately, it leads to inaccurate cast pours. Making a cast in gypsum materials from an impression of dental anatomy aids dentists in designing and constructing removable and fixed prostheses. with sulfur or dithiocarbamate compounds before setting: What commonly used clinical items often cause contamination, sulfur and dithiocarbamate compounds are used in the vulcanization of latex rubber gloves, thorough washing of gloves with detergent, water, and agitation before handling or manipulating either the impression material or the tissues of which the impression is being made, Advantages of addition reaction silicone impression materials, excellent accuracy and dimensional stability, Disadvantages of addition reaction silicone impression materials, Improving detail registration and detail transfer involves, many of the same characteristics as polyxsiloxanes, low molecular weight polyether oligomer with terminal ehtylene imine reactive ring groups will react with aromatic sulfonic ester by dual ring opening with the resultant polymer being cross-linked, Contact of skin or mucous membranes with unmixed ester (polyether) may cause, this impression material may be available in one viscosity with a thinner, Advantages of polyether impression materials, Disadvantages of polyether impression materials, extremely stiff (difficult to remove from undercuts), Requirements of ideal impression materials with respective range of properties currently available impression materials, Properties before setting in ideal impression materials, Properties during setting in ideal impression materials, Properties after setting in ideal impression materials, What may cause dimensional change in an impression material after setting, What affects compatibility with die and cast materials, rigid custom try for minimal thickness of impression material, they do not recover from permanent deformation as well as some other impression materials, models should be poured as quickly as possible, Advantages of polysulfide impression materials, among the least expensive of the elastomers, Disadvantages of polysulfide impression materials, can stain clothing, skin, and other surfaces, Issues regarding patient satisfaction in polysulfide impression materials. has great flexibility, which may result in prblems when it is removed from mouth It has a terribly bitter taste and is relatively inexpensive. Polyethers involve the reaction of the polyether-containing imine ringed side chains with a reactant that opens the rings and causes chain lengthening and cross-linking to form a polyether rubber . What do you want from an impression material? In addition to these criteria, the following criteria should be considered: how well a material is tolerated by patients, obtaining the best results for the least amount of expense, and occurrence of minimal changes when in contact with disinfection chemicals. They show a weight loss of 4.9% to 9.3% after 24 hours as a result of the loss of alcohol. They adhere to themselves and are excellent for border molding and correctable impression technique. This is probably true with respect to any impression material when comparing hand spatulation to automixing. On removal of the impression, the alginate tears. Pour within 1 hour Silicone impression material The silicone impression materials are classified according to the type of chemical reaction by which they set. Materials used without adequate knowledge of their characteristics can impair a successful outcome. This material adheres to itself and can be used to border mold or make correctable impression techniques. Improved polyether formulations such as the “soft” polyethers are easier to remove, maintain proper rigidity for a wide range of applications, and capture fine detail even in moist conditions . Introduction to Dental Science 2 (DS1002:03) Academic year. The material is moderately rigid and can be more easily removed than polyether materials. Polyether has properties such that it can flow into critical areas with low pressure exerted, which results in accurate impressions and makes for fewer adjustments and remakes for the practice of dentistry. These materials should have low shrinkage upon polymerizing and remain stable, which allows them to be poured days after making the impression. Because they have an extended flow period, they serve well as functional impression materials. Flexible impressions are easier to remove from the mouth when set. Either placing a small amount of silicone lubricant over the teeth in a prophylactic paste or rehydrating through a rinse is necessary to produce a new film over the teeth for accurate impressions. The hydrophobic aspect of polyvinyl siloxane impression materials has an adverse effect on surface quality of the polymerized impression material . Hydrocolloids would be considered the most hydrophilic. Clinically, if more working time is desired, polysulfide impression material should be used. Permlastic is a rubber base (polysulfide, condensation-cured, elastomeric) impression material available in three viscosities. In an alginate impression compound, calcium sulfate dehydrate, soluble alginate, and sodium phosphate are in the powder. Within a few days, tissue conditioners become stiffer as a result of the loss of alcohol. impression materials are summarized in Table 1. If the material is allowed to set longer, the percentage change in compression set decreases. When alginic acid (prepared from a marine plant) reacts with a calcium salt (calcium sulfate), it produces an insoluble elastic gel called calcium alginate. The surface tension of the liquid is changed, and increased wettability results . Impression materials with low contact angle enable dental stone to flow easily, and relatively bubble-free casts are produced. Various viscosities and flow characteristics are also made available per individual manufacturer formulations. The setting time is also relative short (4–5 minutes). Presence of moisture results in impressions with voids or pitted surfaces, and the detail reproduced is inferior. Alginate would be considered the most flexible of the impression materials, whereas polyethers would be considered the least flexible. Before they set, however, they are susceptible to contamination. The base consists of a polysulfide polymer (terminal/side chain −SH groups), titanium dioxide, zinc sulfate, copper carbonate, or silica. In recent years, dentists have turned toward using polyvinyl siloxanes and polyethers because of their improved physical and mechanical properties . Disadvantages: Adequate accuracy if poured immediately. unset impression material over wet oral structures, Why agar hydrocolloids have greater accuracy, due to their greater degree of recover after deformation around undercuts (elastic recovery/plastic deformation), combination of elastic and viscous (plastic or permanent) behaviors, seen in plastics and impression materials, Types of hydrophobic impression materials, How addition silicone can be made hydrophilic, Light body elastomers/impression materials, Regular or medium body elastomers/impression materials, Heavy body elastomers/impression materials, Registering oral structures: general considerations, Transferring detail to model: general considerations, can cause voids upon addition of stone slurry, "poly (vinyl) siloxane" or "vinyl polysiloxane", What initiates cross-linking in addition silicones, Contamination of addition silicone impression material. Explain why polyvinyl siloxane impression material is so popular. Another source of contamination is the oxygen-inhibited layer on the surface of resin materials that appears immediately after curing. University. 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 warmer they are, the faster they set. Polyvinyl siloxane materials are also thermally sensitive . Use of impression material within the formation of an indirect restoration. When the material has set, the impression is removed with a steady force. Impressions should be rinsed with water and then disinfected . Clinically, it should produce an accurate impression secondary to its adaptability to oral structures, have a consistency that is dimensionally stable to resist tearing but results in an atraumatic removal, set within a reasonable amount of time, demonstrate biocompatibility to include a hypoallergenic nature, and have a reasonable cost per use. If immersion disinfection (1% sodium hypochlorite or 2% potentiated glutaraldehyde) is performed (10–30 minutes), statistically significant dimensional changes are observed; these changes are on the order of 0.1%, and the quality of the surface is not impaired. silicate. Another source of contamination is the oxygen-inhibited layer on the surface of resin materials that appears immediately after curing. Solution Use very fluid, light body elastomeric impression materials ELASTOMERIC IMPRESSION MATERIALS a) Polysulfide, byproduct water. However, contamination from the latex proteins in gloves may interfere with setting of this material. Explain the most advantageous clinical feature that polyether impression materials possess. Polyethers tend to be the most rigid impression materials . Accurate impressions are necessary for construction of any dental prosthesis. These properties include improved dimensional accuracy, stability, wettability, excellent elastic recovery, flexibility, ease of handling, tear strength, ability to produce multiple casts from one impression, and superior ability to reproduce detail. Often, the choice of impression materials depends on the subjective choice of the operator based on personal preferences and past experience with particular materials. Polyvinyl siloxanes are hydrophobic because of their chemical structure. Calcium phosphate is formed because it has a lower solubility; thus the sodium phosphate is called a retarder and provides working time for the mixed alginate. The way to avoid latex contamination is to wear polyethylene gloves over the latex gloves or not wear latex gloves during the impression procedures. Impression Materials - Lecture note 1. It is a good idea not to store polyvinylsiloxane impression material close to polysulfide impression materials. Polyether Impression Materials. 2017/2018. Accurate impressions depend on identifying the applications that do or do not fit each material’s characteristics. A set impression must be sufficiently elastic so that it will return to its original dimensions without significant distortion upon removal from the mouth . Impression materials with the ability to produce detail in the range of 100 to 150 μm work well and are acceptable in the areas of removable prosthodontics . It has poor dimensional stability (imbibition or dessication is a problem), must be poured within 10 to 12 minutes of impression making or distortion becomes a major issue, and is good for only one pour per impression . It sets by oxidation of the −SH groups, which results in chain lengthening and cross-linking and gives it elastomeric properties . The hydrophobic nature of an impression material relates to its inability to work in a wet environment and still provide accuracy in an impression. impression materials what is an impression material and what does it do? Each of the materials has advantages and disadvantages, but they are each used for a different purpose and are effective and commonly used products in dentistry today. For the most part they have a neutral taste. In a laboratory setting, it should be dimensionally stable for accurate pouring of multiple casts and should not affect dimensional accuracy upon disinfection . 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 . It may allow for more than one pour if it is not too thin in areas. Polyethers consist of a base paste that is composed of a long-chain polyether copolymer with alternating oxygen atoms and methylene groups (O-[CH 2 ] n ) and reactive terminal groups. The viscosity is altered by adding different amounts of titanium dioxide powder to the base. When using automix cartridges, it is recommended to extrude 0.25 inches of material and discard before placing the mixing tip to remove any contaminated material or material that has been exposed for long periods of time to the environment. Impressions that wet the teeth well displace moisture and result in fewer voids. 2. The shrinkage is the result of the evaporation of volatile byproducts and the rearrangement of the bonds with polymerization. Sometimes it is best to make another appointment for new accurate impressions within 24 hours or such a time so that this film layer will re-wet the tooth surfaces . The viscoelastic properties are influenced by the molecular weight of the polymer powders and the power/liquid ratio . Sulfur compounds can poison the platinum-containing catalyst in addition silicone impression materials and result in retarded or no polymerization in the contaminated area of the impression . The hydrophilic versus hydrophobic nature of materials is discussed as it relates to flow characteristics, which result in more bubble-free impressions. It has dimensional instability which is due to the mode of polymerization of polysulfide which is of condensation type which gives off water as a by-product, whose evaporation from the set material causes dimensional contraction. Because these materials are moderately hydrophilic, strict attention to disinfection guidelines is necessary to prevent swelling of the material. The ability of an impression material to reproduce minute detail in the area of 20 to 70 μm is necessary in the area of fixed partial dentures . It generally captures a subgingival margin upon impression without tearing on removal, which is much better than hydrocolloids or polyvinyls. Spray with disinfectant for 10 minutes and rinse and dry immediately before pouring casts . They are a superior material to hydrocolloids and somewhat better than polyvinyl siloxanes . Polyvinyl siloxanes are fairly stiff, and depending on the viscosity of the material, they flow readily to capture areas of detail . Accuracy can be improved by flaming surface material.Disadvantages: Distortion due to poor dimensional stability. Hydrophobic; Can be electroplated with silver & copper. Because the addition silicones require a small amount of catalyst (platinum compound) to initiate the setting reaction, anything that interferes with the catalyst (preventing cross-linking of the material) causes the surface of the impression to remain tacky . 4. High impression dimensional stability materials usually can be poured within 1 to 2 weeks after the impression is made and still produce an accurate cast . The hydrophilic nature of an impression material relates to its ability to work in a wet environment and still provide accuracy in impression making. List the uses of polysulfide impression material and discuss its advantages and disadvantages. Unfortunately, it does not adhere to itself, which makes it unavailable for border molding or correctable impression techniques. This result has been reported even with the new “hydrophilic” polyvinyl siloxane impression materials. Shelf life – 2 yrs. These materials have demonstrated good accuracy in clinical evaluations and are thixotropic, which provides good surface detail and makes them useful as a border molding material. Distortion can be a problem if disinfection guidelines are not strictly adhered to. 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Affected when the material to hydrocolloids and somewhat better than hydrocolloid but not as good as polyether and! Flexible impressions are made with respect to different immersion systems, such as iodophor and glyoxal glutaraldehydes moisture of! Lower for these two products because there is no loss of alcohol poured. High degree of flow after the set is not as strong as polyethers or polyvinyl siloxane impression materials discussed.
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