polysulfide impression material disadvantages
The accelerator (catalyst) has primarily lead dioxide with other substances, such as dibutyl or dioctyl phthalate, sulfur, and magnesium stearate and deodorants. They have low rigidity and require rigid trays to support borders; otherwise they tend to distort. While usually used in single-mix, it can be used with Light-Bodied Permlastic for crown and bridge impressions. Compatible with die and cast materials 10.Good keeping qualities Classification of Impression Materials Impression Material Elastic Non-Elastic Hydrocolloid Elastomers Impression Compound Reversible Zinc oxide Impression Plaster Hydrocolloid (Agar) Irreversible Hydrocolloid (Alginate) Polysulfide Silicon Polyether Accessories such as intraoral tips, mixing tips, and various types of tray systems are also important when weighing the advantages and disadvantages of the delivery systems of impression materials. When it does set, it does so immediately . 3. Small amounts of sulfur interfere with setting of the critical surface next to the tooth and produce major distortion . Tissue conditioners are composed of a powder that contains poly (ethyl methacrylate) and a liquid that contains an aromatic ester-ethyl alcohol (up to 30%) mixture. Glutaraldehydes are the disinfectant of choice for zinc oxide eugenol impression pastes . 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. impression materials what is an impression material and what does it do? Disadvantages: must be poured with dental stone immediately. Materials with a high wetting angle do not flow easily into small crevices and are poor candidates for use in fixed prosthodontics. Many impression materials are suitable for use in dentistry. 2. 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. (b) Disadvantages – The disadvantage of the material being predominantly water is that water evaporates from the surface of the impression if it is left exposed to air. The automixing products require no mixing pads or spatulation, and training in their use is less time consuming. They are a superior material to hydrocolloids and somewhat better than polyvinyl siloxanes . Diagnostic casts are used to aid in treatment planning. This is probably true with respect to any impression material when comparing hand spatulation to automixing. The base consists of a polysulfide polymer (terminal/side chain −SH groups), titanium dioxide, zinc sulfate, copper carbonate, or silica. 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. Because of their low wetting angle, they easily capture full arch impressions. 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. Also present are fillers, plasticizers, and triglycerides. Disadvantages: Adequate accuracy if poured immediately. Polyethers and some polyvinyl siloxanes fall into this category. 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. They contain hydrophobic aliphatic hydrocarbon groups around the siloxane bond . 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 . Loss of detail at impression margins is caused by moisture presence . Practitioners should take this characteristic into consideration when selecting impression materials given the time available to the practitioner to pour casts during office hours. Because of their hydrophilic nature, using polyether and polysulfide impression materials is more compatible with the inherent moisture present in mucosal tissues . 18. The relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. These materials are excellent for reline or rebase procedures in removable prosthetics . Because hydrocolloids are hydrophilic, they swell if immersed in water or disinfectant . It is a good idea not to store polyvinylsiloxane impression material close to polysulfide impression materials. Finally, if repetitive impressions are made, the film over the teeth is lost and prevents satisfactory impression. It has been reported that vapor given off by polysulfide impression material may cause contamination. poly dimethyl siloxane, other silicone, Ethyl. Alginate would be considered the most flexible of the impression materials, whereas polyethers would be considered the least flexible. – Hydrocolloid impression materials are quite hydrophilic, but the same cannot be said for all impression materials. The differences between impression materials, as outlined above, are the materials themselves and the purpose they are used for. 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. Presence of moisture results in impressions with voids or pitted surfaces, and the detail reproduced is inferior. It has been reported that vapor given off by polysulfide impression material may cause contamination. The material is thicker when it is cold and more difficult to express and mix . Disadv Are inelastic, cannot be removed past undercuts without fracturing or distorting. The more common types of impressions are used for fabricating diagnostic and master casts. Regular Permlastic is recommended for partial- or full denture impressions because it has a high degree of flow that will register the finest detail. – With proper handling, polysulfide impression materials can be used for inlays, crowns, and bridges. As with all materials, there are learning curves with respect to working with these different tissue conditioners and other types of impression materials. They contain functional groups that chemically attract and interact with water molecules via hydrogen bonding . If this material is overheated it may not recover to its normal setting time even after cooling, and it is recommended that this material be stored in a cool place and not in the sun (refrigerator or cool space). 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. 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