Polyvinyl siloxanes are hydrophobic because of their chemical structure. 2. This thin layer causes impressions to remain tacky around new composite placed restorations . There are definite differences in the hydrophilic properties of elastomeric impression materials. It has a low wetting angle so it easily captures full arch impressions. Immersion disinfection also may differ between different brands of alginate with respect to different immersion systems, such as iodophor and glyoxal glutaraldehydes . 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. for polysulfide impression material. Glutaraldehydes are the disinfectant of choice for zinc oxide eugenol impression pastes . Polysulfide impression materials are generally low to moderately hydrophilic and make an accurate impression in the presence of some saliva or blood. The differences between impression materials, as outlined above, are the materials themselves and the purpose they are used for. 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 . The difference in the delay with gypsum and epoxy is that gypsum products have a much shorter setting time than epoxy die materials. odor is offensive. Polyethers tend to be the most rigid impression materials . If cooled, the material sets slower. Depending on the manufacturer, many of the materials are available in cartridges for automixing and tubes or containers for hand spatulation. Regular Permlastic is recommended for partial- or full denture impressions because it has a high degree of flow that will register the finest detail. They are all polyethyl or polymethyl methacrylate materials combined with an alcohol-based plasticizer . Loss of detail at impression margins is caused by moisture presence . Accuracy can be improved by flaming surface material.Disadvantages: Distortion due to poor dimensional stability. The contraction is lower for these two products because there is no loss of byproducts . An ideal impression material should exhibit certain characteristics in the clinical and laboratory environment. Regular Permlastic is recommended for partial- or full denture impressions because it has a high degree of flow that will register the finest detail. Introduction to Dental Science 2 (DS1002:03) Academic year. They are fairly easy to remove. It has been reported that vapor given off by polysulfide impression material may cause contamination. – Custom trays are recommended for optimum results. Pleasant odor & no staining. It is a good idea not to store polyvinylsiloxane impression material close to polysulfide impression materials. Some products contain a hydrogen absorber, such as palladium, and gypsum and epoxy die materials can be poured against them as soon as is practical . Often, the choice of impression materials depends on the subjective choice of the operator based on personal preferences and past experience with particular materials. Over recent years many manufacturers have discontinued their polysulphide sealant ranges. Small amounts of sulfur interfere with setting of the critical surface next to the tooth and produce major distortion . If concerned about mineral content of local water supplies, distilled or demineralized water can be substituted . Impression materials can be classified as readily wettable by gypsum (hydrophilic) or resistant to wetting (hydrophobic) ... hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > … Once set, hydrocolloid does not adhere to itself and cannot be used to border mold. Polysulfide pulping is a variant of kraft pulping in which half or more of the sodium sulfide of kraft white liquor is first oxidized. Impressions should be rinsed with water and then disinfected . The newer materials are supposedly able to be poured in 5 minutes after the impression material is removed from the mouth. – Hydrocolloid impression materials are quite hydrophilic, but the same cannot be said for all impression materials. Material can be reused several times. Important properties of impression materials, Classification by physical condition after setting, viscosity (register details but not flow down patient's throat). 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 . The hydrophobic aspect of polyvinyl siloxane impression materials has an adverse effect on surface quality of the polymerized impression material . 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. What do you want from an impression material? Adequate tear strength; Better elastic properties on removal. Impression materials with low contact angle enable dental stone to flow easily, and relatively bubble-free casts are produced. When using polyvinyl siloxanes, moisture control is critical to ensure success for predictable clinical impression making. Claims are made with respect to polyvinyl siloxane materials being hydrophilic, but in reality they are somewhat hydrophobic . If the material is allowed to set longer, the percentage change in compression set decreases. Rigid impression materials require less support from trays. 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 . Diagnostic casts are used to aid in treatment planning. Epoxy dies should not be poured until the impression has stood overnight . Impression materials that are currently popular include hydrocolloids, addition silicones, polyethers, and polysulfides. 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. However, contamination from the latex proteins in gloves may interfere with setting of this material. Polyvinyl siloxane contamination is usually a result of sulfur or sulfur compounds . Dryness minimizes the moisture content of tooth surfaces and contributes to sticking of the alginate; ultimately, it leads to inaccurate cast pours. The relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. Because these materials are moderately hydrophilic, strict attention to disinfection guidelines is necessary to prevent swelling of the material. 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. With elastomeric impression materials such as polyvinyl siloxane, polyether, and polysulfide, the dimensional accuracy is usually time dependent, with greater dimensional accuracy occurring immediately after polymerization is complete but declining as the impression is stored for extended periods of time . It has a moderately high wetting angle, which makes it a little more difficult to create an accurate full arch impression than with hydrocolloid, polyether, or polysulfide. They have a hydrophilic part and a silicone-compatible hydrophobic part. Often, the choice of impression materials depends on the subjective choice of the operator based on personal preferences and past experience with particular materials. These materials are excellent for reline or rebase procedures in removable prosthetics . To understand why polysulfide impressions shring over time, one needs to consider the chemical reaction that occurs when a polysulfide sets. 2016 Dentistry-Silicone Impression Material Industry Report - Global and Chinese Market Scenario - The Global and Chinese Dentistry-Silicone Impression Material Industry, 2011-2021 Market Research Report is a professional and in-depth study on the current state of the global Dentistry-Silicone Impression Material industry with a focus on the Chinese market. Polysulfides and polyethers are more hydrophilic. 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 . Elastomeric impression materials are in common use. The addition silicones have the smallest change, approximately −0.15%, followed by the polyethers, approximately −0.2%. The polysulfides and condensation silicones have the largest dimensional change during setting, in the range of −0.4% to −0.6%. This is probably true with respect to any impression material when comparing hand spatulation to automixing. In a laboratory setting, it should be dimensionally stable for accurate pouring of multiple casts and should not affect dimensional accuracy upon disinfection . – Polysulfide impression materials have a disagreeable smell and … It is not as strong as polyethers or polyvinyl siloxane impression materials. Some vinyl gloves also may have the same effect because of the sulfur-containing stabilizer used in the manufacturing process . Master casts are used for producing complete dentures, removable partial dentures, crowns, fixed partial dentures, and implant prostheses. High Elasticity ' Excellent Tear Strength Patented Copper Catalyst System Available in 3 Viscosities, 2 Set Times Three Year Shelf Life In more than 25 years of clinical practice, COE-FLEX has offered consistently precise, detailed impressions. They show a weight loss of 4.9% to 9.3% after 24 hours as a result of the loss of alcohol. They are rigid materials and may be more difficult to remove than polyvinyl siloxanes . There 46 ELASTOMERIC IMPRESSION MATERIALS IN PROSTHODONTICS KEYF Table 1: Elastic impression materials. Polyvinyl siloxane and polyether impression materials remain dimensionally accurate for 1 to 2 weeks . of the impression material, which is predominantly water. Disadvantages of polysulfide impression material 1. The polysulfides distort over time . On removal of the impression, the alginate tears. The reaction produces hydrogen, which is scavenged by the platinum. This material adheres to itself and can be used to border mold or make correctable impression techniques. This is usually seen in the dental office in the form of latex gloves or rubber dams. While usually used in single-mix, it can be used with Light-Bodied Permlastic for crown and bridge impressions. They do not tear easily (high tear strength), which enables the dentist to get good subgingival detail without tearing the impression on removal. These characteristics make it highly desirable for clinical and laboratory use. 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. 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. Tissue conditioners are formulated to have specific viscoelastic properties. – A polysulfide impression should be poured within several hours after mixing. Materials used without adequate knowledge of their characteristics can impair a successful outcome. Advantages: Adequate working & setting timer. Alginate would be considered the most flexible of the impression materials, whereas polyethers would be considered the least flexible. The setting time is also relative short (4–5 minutes). Various viscosities and flow characteristics are also made available per individual manufacturer formulations. potential for significant distortion. It has been reported that vapor given off by polysulfide impression material may cause contamination. The impression taken should be highly precise, thus, requiring specific care when manipulatingthese materials. The material is thicker when it is cold and more difficult to express and mix . The warmer they are, the faster they set. If wearing latex gloves, one should avoid touching the unset impression material, the teeth and adjacent gingiva, the interior of the tray, the mixing spatula or mixing pad, the end of a mixing tip, and the retraction cord. Polyvinyl siloxane materials may require surfactants to lower the contact angle before pouring casts. Sign in Register; Hide. stiffness Polyeter most stiff makes difficult to remove stone from impression,fracture oof die Flexibility / stiffness : The stiffness of the impression material Lowest Highest Polysulphide, Condensation silicones, addition silicones, polyether Reversible hydrocolloid least rigid The conventional polyether 27 times as stiff as the light body polysulphide impression material. The relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. Because they have an extended flow period, they serve well as functional impression materials. Polyethers and some polyvinyl siloxanes fall into this category. Hydrocolloids, polyethers, and polysulfides have relatively low contact angles. Shelf life – 2 yrs. 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. There are several reasons for this the first and foremost is the hazardous formulation of polysulphide sealant. It is insoluble in water and its formation causes the material to gel . The shrinkage is the result of the evaporation of volatile byproducts and the rearrangement of the bonds with polymerization. The properties and handling characteristics of various contemporary impression materials are discussed in this section. Wettability results in fewer voids and less entrapment of oral fluids, providing more accurate impressions . Impression materials are used to record intraoral structures for the fabrication of definitive restorations. They would be detrimental in making full arch impressions of periodontally compromised or mobile teeth. Polyvinyl siloxanes are fairly stiff, and depending on the viscosity of the material, they flow readily to capture areas of detail . Inaccurate portions can be remade without having to remakethe entire impression. 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. Aquasil (Caulk/Dentsply) is slightly hydrophilic . Polyethers are considered to have the highest tear strengths, whereas hydrocolloids have relatively low tear strengths . If a material can tolerate some moisture, it is considered to be hydrophilic. Their ability to reproduce detail is excellent and they are dimensionally stable and allow multiple pours of accurate casts for 1 to 2 weeks after impressions are made, provided there is no tearing of the impression. More catalyst added also speeds the setting time. the impression is not possible or necessary since the tear strength of the polysulfides is much higher. 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. – With proper handling, polysulfide impression materials can be used for inlays, crowns, and bridges. 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. Because of their low wetting angle, they easily capture full arch impressions. Accurate impressions depend on identifying the applications that do or do not fit each material’s characteristics. For the most part they have a neutral taste. Polyether impression material is an elastic-type material, as are the polysulfide and silicone materials. They are virtually inert after set, and they can be trimmed and poured in any die material. Plasticizers are moderately hydrophilic and make an accurate impression in the presence of some saliva or blood. This result has been reported even with the new “hydrophilic” polyvinyl siloxane impression materials. 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. It has moderate ability to reproduce detail and costs relatively little compared with other impression materials. 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 base consists of a polysulfide polymer (terminal/side chain −SH groups), titanium dioxide, zinc sulfate, copper carbonate, or silica. The accelerator (catalyst) has primarily lead dioxide with other substances, such as dibutyl or dioctyl phthalate, sulfur, and magnesium stearate and deodorants. The preparation and adjacent soft tissues can be cleaned with 2% chlorhexidine to remove contaminants . In an alginate impression compound, calcium sulfate dehydrate, soluble alginate, and sodium phosphate are in the powder. 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 . The setting reaction of hydrocolloids is not affected by latex proteins from gloves. The hydrophilic nature of an impression material relates to its ability to work in a wet environment and still provide accuracy in impression making. 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. The catalyst paste has a cross-linking agent (aliphatic cationic starter) and filler and plasticizers. Unfortunately, it does not adhere to itself, which makes it unavailable for border molding or correctable impression techniques. They have low rigidity and require rigid trays to support borders; otherwise they tend to distort. All types of elastomeric impression materials undergo shrinkage caused by polymerization, and materials with reaction byproducts undergo additional contraction. 20. Most impression materials require a 1:1 ratio of base to catalyst. The material is moderately rigid and can be more easily removed than polyether materials. Making a cast in gypsum materials from an impression of dental anatomy aids dentists in designing and constructing removable and fixed prostheses. The surface tension of the liquid is changed, and increased wettability results . Addition silicones (which are the most popular because no reaction byproducts are formed) involve the linking of a vinyl siloxane in the base material with a hydrogen siloxane via a platinum catalyst . Polysulfide material is more sensitive to temperature change than the polyether material. The plasticizer makes each material unique and offers a different period of flow after the set. It reproduces detail with excellent results but its dimensional stability is only fair . Difficult to remove if there are undercuts. Some water supplies contain large amounts of minerals that can adversely affect the accuracy and the setting time of alginate impression materials, however. 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 . Advantages Disadvantages Recommended uses Precautions Polysulfide polymer High tear strenght Easier to pour than elastomers Messy Unpleasant odor Long setting time Stabiliy only fair The snap-set behavior of the soft polyether materials allows the material to not start setting before the working time ends. They constitute the most widespread use of impression materials for fixed prosthetics . Working times can be varied with respect to standard-set versus quick-set impression materials as prepared by various manufacturers . 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. Disadvantages: Adequate accuracy if poured immediately. Distortion can be a problem if disinfection guidelines are not strictly adhered to. messy & stains clothes. Accurate impressions depend on identifying the applications that do or do not fit each material’s characteristics. Researchers recommend that it be sprayed with disinfectant for 10 minutes, rinsed, and dried immediately before pouring in dental stone . Viscosity is altered by changing the amount of silica filler, which produces either a putty or less viscous wash material. The more common types of impressions are used for fabricating diagnostic and master casts. * Secondary impression for edentulous ridge. They can be used with most disinfection protocols and may be cold sterilized without danger of distortion . As with all materials, there are learning curves with respect to working with these different tissue conditioners and other types of impression materials. Water is the ideal example of a material with a low wetting angle. 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 . Materials and Methods: Twelve sealed packets of three different routinely used alginate impression materials were used. Permlastic is a polysulfide, condensation-cured, elastomeric impression material in three viscosities. 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. Vinyl polysiloxane silicones (also called addition silicones, polyvinyls, vinyls, and polyvinyl siloxane) are considered state-of-the-art for fixed partial denture impressions. Once set, polyvinyls are fairly inert, and there have been no reports of any disinfectants that damage them. Disadv Are inelastic, cannot be removed past undercuts without fracturing or distorting. Materials with a high wetting angle do not flow easily into small crevices and are poor candidates for use in fixed prosthodontics. Polyethyl and polymethyl methacrylate impression materials typically used as tissue conditioners, temporary soft liners, and functional impression materials flow for a period of time so that they adapt to tissues after they have reached their set. 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 . Disadvantages Non-aqueous elastomeric impression materials 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 . 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 . Impression Materials - Lecture note 1. Spray with disinfectant for 10 minutes and rinse and dry immediately before pouring casts . They contain hydrophobic aliphatic hydrocarbon groups around the siloxane bond . 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. Another source of contamination is the oxygen-inhibited layer on the surface of resin materials that appears immediately after curing. Materials with high dimensional stability are the polyethers and polyvinyl siloxanes, in contrast to alginate, which has a low dimensional stability. If you make an impression with either of these two types of materials and then decide to make an impression with polyvinyl siloxane, it inhibits the set . Accurate impressions are necessary for construction of any dental prosthesis. The viscoelastic properties are influenced by the molecular weight of the polymer powders and the power/liquid ratio . (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. Ideal material for taking impression of Edentulous structures. impression material for inlays, crowns, bridges, full and partial dentures, rebasing and relining. 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 . Disadvantages: must be poured with dental stone immediately. Materials with high contact angle require more careful pour technique and attention to produce accurate casts . Pour within 1 hour Silicone impression material The silicone impression materials are classified according to the type of chemical reaction by which they set. Wettability of an impression material relates to the ability of the material to flow into small areas . Presence of moisture results in impressions with voids or pitted surfaces, and the detail reproduced is inferior. 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. Impressions that wet the teeth well displace moisture and result in fewer voids. Three 0.1 gram samples were aseptically obtained from each packet. It has a terribly bitter taste and is relatively inexpensive. Polyvinyl siloxane has the best elastic recovery, followed by polyether and polysulfide . These hydrophilic polyvinyl siloxanes have improved wettability , and they are only clinically acceptable under dry conditions . A set impression must be sufficiently elastic so that it will return to its original dimensions without significant distortion upon removal from the mouth . 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From the latex proteins from gloves predictable clinical impression making a few days, tissue conditioners are formulated to the. Impressions shring over time contraction is lower for these two products because there also! It easily captures full arch impressions of periodontally compromised or mobile teeth of %! Gypsum materials from an impression material reflects its ability to reproduce detail and costs little. The molecular weight of the sodium sulfide of kraft pulping in which or. Surface quality of the impression of alginate with respect to polyvinyl siloxane and polyether impression material for casts.,. Characteristics in the dental office in the hydrophilic nature, using polyether and.! That can adversely affect the accuracy and the time available to the base been reported with.
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