If concerned about mineral content of local water supplies, distilled or demineralized water can be substituted . (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. It reproduces detail with excellent results but its dimensional stability is only fair . Viscosity is altered by changing the amount of silica filler, which produces either a putty or less viscous wash material. It has a low wetting angle so it easily captures full arch impressions. They do not distort from water absorption, but because they are alcohol based, they distort easily when exposed to alcohol-based disinfectants, such as Lysol . Materials used without adequate knowledge of their characteristics can impair a successful outcome. When using polyvinyl siloxanes, moisture control is critical to ensure success for predictable clinical impression making. Also present are fillers, plasticizers, and triglycerides. When water is added, calcium ions from the calcium sulfate dehydrate react preferentially with phosphate ions from the sodium phosphate and pyrophosphate to form insoluble calcium phosphate. Loss of detail at impression margins is caused by moisture presence . Explain the most advantageous clinical feature that polyether impression materials possess. After reviewing the types and characteristics of the most common impression materials, it becomes apparent that hydrocolloids have a high hydrophilic nature that allows this material to capture accurate impressions in the presence of some saliva or blood . Polysulfide impression materials have a high resistance to tearing but stretch and do not recover completely elastically . 4. It is insoluble in water and its formation causes the material to gel . Three 0.1 gram samples were aseptically obtained from each packet. Disadvantages Non-aqueous elastomeric impression materials Polysulfides and polyethers are more hydrophilic. It sets by oxidation of the −SH groups, which results in chain lengthening and cross-linking and gives it elastomeric properties . 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 setting reaction of hydrocolloids is not affected by latex proteins from gloves. Accurate impressions depend on identifying the applications that do or do not fit each material’s characteristics. The viscoelastic properties are influenced by the molecular weight of the polymer powders and the power/liquid ratio . The addition silicones have the smallest change, approximately −0.15%, followed by the polyethers, approximately −0.2%. Depending on the manufacturer, many of the materials are available in cartridges for automixing and tubes or containers for hand spatulation. It is recommended that a disinfectant spray be used while the impression is placed in a plastic bag for 10 minutes, at which time the impression is rinsed with water immediately and the cast poured . – Custom trays are recommended for optimum results. Impression materials can be classified as readily wettable by gypsum (hydrophilic) or resistant to wetting (hydrophobic) ... hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > … Clinical studies have shown that the viscosity of the impression material is the most important factor in producing impressions and dies with minimal bubbles and maximum detail . Various viscosities and flow characteristics are also made available per individual manufacturer formulations. Because many dentists send their impressions to a laboratory to be poured, this characteristic should be considered when choosing an impression material . Materials such as hydrocolloids, polyethers, and methacrylates may require specific disinfection protocols to prevent distortion of the material after setting . Often, the choice of impression materials depends on the subjective choice of the operator based on personal preferences and past experience with particular materials. There are 4 groups of elastomers; polysulfide, condensation silicone, addition silicone and polyether; each differ in their setting mechanism and their physical and chemical properties. The accuracy of these final restorations depends greatly on the impression materials and techniques. 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. They are all polyethyl or polymethyl methacrylate materials combined with an alcohol-based plasticizer . The drawback of polysulfide addition is that the amount of sulfur in the system is increased, and this disturbs the sodium–sulfur balance in the mill, thereby generating higher emissions to the atmosphere. Impression materials are used to record intraoral structures for the fabrication of definitive restorations. 2017/2018. Impression Materials - Lecture note 1. The basic ingredient of a polysulfide impression material is a polyfunctional mercaptan of the average formula HS-(R-S-S)23-R-SH, where R is C2H4-OCH2-O-C2H4. The way to avoid latex contamination is to wear polyethylene gloves over the latex gloves or not wear latex gloves during the impression procedures. Within a few days, tissue conditioners become stiffer as a result of the loss of alcohol. – Hydrocolloid impression materials are quite hydrophilic, but the same cannot be said for all impression materials. It has been reported that vapor given off by polysulfide impression material may cause contamination. Because hydrocolloids are hydrophilic, they swell if immersed in water or disinfectant . Limitations of the polyvinyl siloxanes involve their hydrophobic nature . Most impression materials require a 1:1 ratio of base to catalyst. Diagnostic casts are used to aid in treatment planning. Note that addition silicones release hydrogen on setting and many require a 30-minute to 1-hour de-gassing period before pouring a master cast or the cast develops surface porosity. If cooled, the material sets slower. These materials have low tear strength and usually tear on removal if not careful . There is a greater tendency to trap air bubbles when pouring stone because of its moderately high contact angle, so greater care is required when pouring stone . 2. Wettability of an impression material relates to the ability of the material to flow into small areas . They adhere to themselves and are excellent for border molding and correctable impression technique. They contain functional groups that chemically attract and interact with water molecules via hydrogen bonding . They are fairly easy to remove. VPS impression materials are better able to handle the stretching and compressive forces that impressions are subject to during this step, with evidence showing them to exhibit better elastic recovery than other elastomers, as well as less permanent deformation . This is probably true with respect to any impression material when comparing hand spatulation to automixing. List the uses of polysulfide impression material and discuss its advantages and disadvantages. Alginate would be considered the most flexible of the impression materials, whereas polyethers would be considered the least flexible. The preparation and adjacent soft tissues can be cleaned with 2% chlorhexidine to remove contaminants . It has an excellent ability to reproduce detail and is dimensionally stable, which allows multiple pours of accurate casts for several weeks after impressions are made if no tears are present in the material. – With proper handling, polysulfide impression materials can be used for inlays, crowns, and bridges. of the impression material, which is predominantly water. Polysulfide impression materials are supplied as two paste systems. They do not tear easily (high tear strength), which enables the dentist to get good subgingival detail without tearing the impression on removal. Where subgingival margins are concerned, this can be an important criterion. The hydrophobic nature of an impression material relates to its inability to work in a wet environment and still provide accuracy in an impression. Polyether Impression Materials. 19. ... the procedure the dimensional inaccuracy of the alginate hydrocolloid limits its us more compatible with gypsum model materials than alginates. Aquasil (Caulk/Dentsply) is slightly hydrophilic . These hydrophilic polyvinyl siloxanes have improved wettability , and they are only clinically acceptable under dry conditions . Polyether and polysulfide impression materials also leave the mouth coated with a chemical film that inhibits polyvinyl siloxanes. 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. The impression taken should be highly precise, thus, requiring specific care when manipulatingthese materials. (Such changes would be insignificant for clinical applications, such as study models and working casts.) 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 . Disadvantages: must be poured with dental stone immediately. Automixing cartridges tend to create fewer bubbles than hand spatulation. Finally, if repetitive impressions are made, the film over the teeth is lost and prevents satisfactory impression. Explain why polyvinyl siloxane impression material is so popular. Accurate impressions are necessary for construction of any dental prosthesis. There 46 ELASTOMERIC IMPRESSION MATERIALS IN PROSTHODONTICS KEYF Table 1: Elastic impression materials. This material does taste bitter, although it is currently flavored to offset the taste. Elastomeric impression materials are in common use. These characteristics make it highly desirable for clinical and laboratory use. Because their wetting angle is low, they capture a full arch impression easier than with polyvinyl siloxanes . Polyether impression materials are moderately hydrophilic and capture accurate impressions in the presence of some saliva or blood. 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. Many impression materials are suitable for use in dentistry. Hydrocolloids, polyethers, and polysulfides have relatively low contact angles. They show a weight loss of 4.9% to 9.3% after 24 hours as a result of the loss of alcohol. Adequate tear strength; Better elastic properties on removal. An ideal impression material should exhibit certain characteristics in the clinical and laboratory environment. The accelerator (catalyst) has primarily lead dioxide with other substances, such as dibutyl or dioctyl phthalate, sulfur, and magnesium stearate and deodorants. 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 . Disadvantages of polysulfide impression materials can stain clothing, skin, and other surfaces objectionable odor (onion, skunk, natural gas scents result from reaction) The more common types of impressions are used for fabricating diagnostic and master casts. impression materials what is an impression material and what does it do? 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 . 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. There is also a greater tendency for alginate to stick to teeth if they are dry. Disadv Are inelastic, cannot be removed past undercuts without fracturing or distorting. The newer materials are supposedly able to be poured in 5 minutes after the impression material is removed from the mouth. Once set, polyvinyls are fairly inert, and there have been no reports of any disinfectants that damage them. When alginic acid (prepared from a marine plant) reacts with a calcium salt (calcium sulfate), it produces an insoluble elastic gel called calcium alginate. All types of elastomeric impression materials undergo shrinkage caused by polymerization, and materials with reaction byproducts undergo additional contraction. Sitffer & harder than polysulfide material. 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? These materials should have low shrinkage upon polymerizing and remain stable, which allows them to be poured days after making the impression. Before they set, however, they are susceptible to contamination. 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 . The material is thicker when it is cold and more difficult to express and mix . 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 The setting times are relatively short (4–5 minutes), and the set is not altered or contaminated by latex gloves. Pour within 1 hour Silicone impression material The silicone impression materials are classified according to the type of chemical reaction by which they set. Introduction to Dental Science 2 (DS1002:03) Academic year. has great flexibility, which may result in prblems when it is removed from mouth 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 relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. Permlastic is a polysulfide, condensation-cured, elastomeric impression material in three viscosities. 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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