If kept in a refrigerator, it is advisable to let the material come to room temperature before use, otherwise it takes a longer time than normal to set. Polyether impression materials are moderately hydrophilic and capture accurate impressions in the presence of some saliva or blood. impression materials what is an impression material and what does it do? – With proper handling, polysulfide impression materials can be used for inlays, crowns, and bridges. The catalyst paste has a cross-linking agent (aliphatic cationic starter) and filler and plasticizers. Polyethers are considered to have the highest tear strengths, whereas hydrocolloids have relatively low tear strengths . The differences between impression materials, as outlined above, are the materials themselves and the purpose they are used for. It reproduces detail with excellent results but its dimensional stability is only fair . However, contamination from the latex proteins in gloves may interfere with setting of this material. Some of the older impression materials (eg, zinc oxide eugenol impression paste, impression plaster, and impression compound) are still used in certain applications but are limited in use because they cannot be removed past undercuts without distorting or fracturing the impression . Polyvinyl siloxane contamination is usually a result of sulfur or sulfur compounds . 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. messy & stains clothes. Less distortion on removal. It has moderate ability to reproduce detail and costs relatively little compared with other impression materials. They are suitable for complete and partial dentures because they reproduce detail moderately. Viscosity is altered by changing the amount of silica filler, which produces either a putty or less viscous wash material. Vinyl polysiloxane silicones (also called addition silicones, polyvinyls, vinyls, and polyvinyl siloxane) are considered state-of-the-art for fixed partial denture impressions. The newer materials are said to contain a proprietary component that eliminates hydrogen bubbles, but it is best to read the guidelines for pouring specific brands of polyvinyl siloxanes before pouring stone. 20. Materials used without adequate knowledge of their characteristics can impair a successful outcome. It is not a rigid material, and impressions are easier to remove than with polyethers and polyvinyl siloxanes. – However, they are not as accurate as other non aqueous elastomeric materials. Hydrocolloids, polyethers, and polysulfides have relatively low contact angles. Polyvinyl siloxane materials may require surfactants to lower the contact angle before pouring casts. Disadvantages of polysulfide impression materials can stain clothing, skin, and other surfaces objectionable odor (onion, skunk, natural gas scents result from reaction) Polyvinyl siloxane has the best elastic recovery, followed by polyether and polysulfide . What do you want from an impression material? These surfactants act through a diffusion transfer of surfactant molecules from the polyvinyl siloxane into the aqueous phase. 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. Also present are fillers, plasticizers, and triglycerides. Disadvantages of polysulfide impression material 1. They can be used with most disinfection protocols and may be cold sterilized without danger of distortion . Impressions made in hydrocolloid are easier to remove than other materials and require rigid trays to prevent distortion in impression making and pouring of dental casts. There may be less waste of material associated with automixing and providing a more bubble-free mix resulting in more accurate casts. It is relatively low cost and comes in flavors that are more patient friendly. Use of impression material within the formation of an indirect restoration. 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 . Accurate impressions depend on identifying the applications that do or do not fit each material’s characteristics. Often, the choice of impression materials depends on the subjective choice of the operator based on personal preferences and past experience with particular materials. They contain hydrophobic aliphatic hydrocarbon groups around the siloxane bond . Another source of contamination is the oxygen-inhibited layer on the surface of resin materials that appears immediately after curing. The plasticizer makes each material unique and offers a different period of flow after the set. This is usually seen in the dental office in the form of latex gloves or rubber dams. Accurate impressions depend on identifying the applications that do or do not fit each material’s characteristics. Claims are made with respect to polyvinyl siloxane materials being hydrophilic, but in reality they are somewhat hydrophobic . Disadvantages: must be poured with dental stone immediately. The snap-set behavior of the soft polyether materials allows the material to not start setting before the working time ends. Tissue conditioners are formulated to have specific viscoelastic properties. Tissue conditioners are soft elastomers. The relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. Unfortunately, it does not adhere to itself, which makes it unavailable for border molding or correctable impression techniques. Finally, if repetitive impressions are made, the film over the teeth is lost and prevents satisfactory impression. Moisture from saliva or blood can interfere with accurate impressions. Impression Materials - Lecture note 1. 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. 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. They do not tear easily (high tear strength), which enables the dentist to get good subgingival detail without tearing the impression on removal. ... the procedure the dimensional inaccuracy of the alginate hydrocolloid limits its us more compatible with gypsum model materials than alginates. The tear strength of an impression material relates to how resistant a particular material is to tearing after setting . 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 . Materials and Methods: Twelve sealed packets of three different routinely used alginate impression materials were used. 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. 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 . Disadvantages Non-aqueous elastomeric impression materials This is probably true with respect to any impression material when comparing hand spatulation to automixing. Because they have an extended flow period, they serve well as functional impression materials. University. In these instances, permanent deformation occurs relative to the type of elastomeric impression material used . Solution Use very fluid, light body elastomeric impression materials ELASTOMERIC IMPRESSION MATERIALS a) Polysulfide, byproduct water. Polyvinyl siloxanes are fairly stiff, and depending on the viscosity of the material, they flow readily to capture areas of detail . 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 . The more common types of impressions are used for fabricating diagnostic and master casts. Because hydrocolloids are hydrophilic, they swell if immersed in water or disinfectant . 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. This result has been reported even with the new “hydrophilic” polyvinyl siloxane impression materials. 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 . Three 0.1 gram samples were aseptically obtained from each packet. 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 automixing products require no mixing pads or spatulation, and training in their use is less time consuming. The shrinkage is the result of the evaporation of volatile byproducts and the rearrangement of the bonds with polymerization. Inaccurate portions can be remade without having to remakethe entire impression. 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. Polyether and polysulfide impression materials also leave the mouth coated with a chemical film that inhibits polyvinyl siloxanes. Many impression materials are suitable for use in dentistry. If concerned about mineral content of local water supplies, distilled or demineralized water can be substituted . 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. Impression materials are used to record intraoral structures for the fabrication of definitive restorations. 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. Polysulfides and polyethers are more hydrophilic. It has a terribly bitter taste and is relatively inexpensive. Polysulfide impression materials are generally low to moderately hydrophilic and make an accurate impression in the presence of some saliva or blood. Because many dentists send their impressions to a laboratory to be poured, this characteristic should be considered when choosing an impression material . Master casts are used for producing complete dentures, removable partial dentures, crowns, fixed partial dentures, and implant prostheses. While usually used in single-mix, it can be used with Light-Bodied Permlastic for crown and bridge impressions. Bubbles in the impression can occur when you spatulate and entrap air into the mix. 2017/2018. impression materials are summarized in Table 1. – Custom trays are recommended for optimum results. Sitffer & harder than polysulfide material. The polysulfides distort over time . The warmer they are, the faster they set. Once set, hydrocolloid does not adhere to itself and cannot be used to border mold. The hydrophobic aspect of polyvinyl siloxane impression materials has an adverse effect on surface quality of the polymerized impression material . They work well for implant impressions, in which posts must be transferred accurately . 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? Plasticizers are moderately hydrophilic and make an accurate impression in the presence of some saliva or blood. Polyether impression material is an elastic-type material, as are the polysulfide and silicone materials. Once set, polyvinyls are fairly inert, and there have been no reports of any disinfectants that damage them. Their tear strength is better than hydrocolloid but not as good as polyether . For condensation silicone impression material 14. Limitations of the polyvinyl siloxanes involve their hydrophobic nature . Automixing cartridges tend to create fewer bubbles than hand spatulation. When using polyvinyl siloxanes, moisture control is critical to ensure success for predictable clinical impression making. Explain the most advantageous clinical feature that polyether impression materials possess. The properties and handling characteristics of various contemporary impression materials are discussed in this section. Impressions that wet the teeth well displace moisture and result in fewer voids. – Hydrocolloid impression materials are quite hydrophilic, but the same cannot be said for all impression materials. The difference in the delay with gypsum and epoxy is that gypsum products have a much shorter setting time than epoxy die materials. To understand why polysulfide impressions shring over time, one needs to consider the chemical reaction that occurs when a polysulfide sets. The viscosity is altered by adding different amounts of titanium dioxide powder to the base. When the material has set, the impression is removed with a steady force. Pleasant odor & no staining. 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. Practitioners should take this characteristic into consideration when selecting impression materials given the time available to the practitioner to pour casts during office hours. It is not accurate enough for fixed partial dentures but is used for partial framework impressions . If the material is allowed to set longer, the percentage change in compression set decreases. Because the material has a low wetting angle it makes a full arch impression easier than with polyvinyl siloxanes or polyethers. Polyvinyl siloxanes are hydrophobic because of their chemical structure. While usually used in single-mix, it can be used with Light-Bodied Permlastic for crown and bridge impressions. 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 . The dimensional stability of an impression material reflects its ability to maintain the accuracy of the impression over time . Because these materials are moderately hydrophilic, strict attention to disinfection guidelines is necessary to prevent swelling of the material. When alginic acid (prepared from a marine plant) reacts with a calcium salt (calcium sulfate), it produces an insoluble elastic gel called calcium alginate. Before they set, however, they are susceptible to contamination. Regular Permlastic is recommended for partial- or full denture impressions because it has a high degree of flow that will register the finest detail. Polysulfide Properties: accurate , high tear strength, unacceptable odor. 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. These materials should have low shrinkage upon polymerizing and remain stable, which allows them to be poured days after making the impression. The accelerator (catalyst) has primarily lead dioxide with other substances, such as dibutyl or dioctyl phthalate, sulfur, and magnesium stearate and deodorants. Because some polyvinyl siloxane materials exhibit a phenomenon known as hydrogen out-gassing, if you pour casts too soon the stone captures these bubbles and produces a cast with pitted areas . A set impression must be sufficiently elastic so that it will return to its original dimensions without significant distortion upon removal from the mouth . Polyvinyl siloxanes are generally hydrophobic. Most impression materials require a 1:1 ratio of base to catalyst. 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. Polysulfide impression materials are supplied as two paste systems. silicate. A potential problem when using irreversible hydrocolloid is the tendency for this material to stick to teeth, which occurs when alginate radicals in the impression material form chemical bonds with hydroxylapatite crystals of the enamel. It may allow for more than one pour if it is not too thin in areas. has great flexibility, which may result in prblems when it is removed from mouth The more common types of impressions are used for fabricating diagnostic and master casts. 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). A snap removal of force. The setting time is also relative short (4–5 minutes). They are all polyethyl or polymethyl methacrylate materials combined with an alcohol-based plasticizer . Permlastic is a polysulfide, condensation-cured, elastomeric impression material in three viscosities. Is considered to have the largest dimensional change during setting, in contrast to alginate, which has a degree. Period, they flow readily to capture areas of detail at impression margins is caused by moisture presence distortion. Siloxane materials may require specific disinfection protocols to prevent swelling of the bonds polymerization. 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