Impression Materials - Lecture note 1. The more common types of impressions are used for fabricating diagnostic and master casts. 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 . The hydrophobic aspect of polyvinyl siloxane impression materials has an adverse effect on surface quality of the polymerized impression material . Tissue conditioners are soft elastomers. High ambient room temperature does not distort them, and they can be trimmed and poured with any die material for casts. Polyethers are considered to have the highest tear strengths, whereas hydrocolloids have relatively low tear strengths . Accurate impressions depend on identifying the applications that do or do not fit each material’s characteristics. 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 . Polyvinyl siloxane materials may require surfactants to lower the contact angle before pouring casts. They contain hydrophobic aliphatic hydrocarbon groups around the siloxane bond . This material comes in flavors and is not much of a problem from the standpoint of taste. Flexible impressions are easier to remove from the mouth when set. 18. impression material for inlays, crowns, bridges, full and partial dentures, rebasing and relining. dental impression is negative imprint of hard (teeth) and soft tissues in the mouth. 4. Permlastic is a rubber base (polysulfide, condensation-cured, elastomeric) impression material available in three viscosities. 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 . 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. (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. Wettability of an impression material relates to the ability of the material to flow into small areas . They work well for implant impressions, in which posts must be transferred accurately . impression materials what is an impression material and what does it do? This material does taste bitter, although it is currently flavored to offset the taste. 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. James Cook University. odor is offensive. Finally, if repetitive impressions are made, the film over the teeth is lost and prevents satisfactory impression. While usually used in single-mix, it can be used with Light-Bodied Permlastic for crown and bridge impressions. Because their wetting angle is low, they capture a full arch impression easier than with polyvinyl siloxanes . When the material has set, the impression is removed with a steady force. The hydrophilization of polyvinyl siloxanes is enhanced with the incorporation of nonionic surfactants. Making a cast in gypsum materials from an impression of dental anatomy aids dentists in designing and constructing removable and fixed prostheses. Over recent years many manufacturers have discontinued their polysulphide sealant ranges. Less distortion on removal. 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 . They have low rigidity and require rigid trays to support borders; otherwise they tend to distort. 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 . Wettability results in fewer voids and less entrapment of oral fluids, providing more accurate impressions . Materials with a low wetting angle flow extensively. The setting time is also relative short (4–5 minutes). List the uses of polysulfide impression material and discuss its advantages and disadvantages. It is not accurate enough for fixed partial dentures but is used for partial framework impressions . Advantages: Adequate working & setting timer. Disadvantages of polysulfide impression materials can stain clothing, skin, and other surfaces objectionable odor (onion, skunk, natural gas scents result from reaction) Materials with a high wetting angle do not flow easily into small crevices and are poor candidates for use in fixed prosthodontics. University. Introduction to Dental Science 2 (DS1002:03) Academic year. 9. Polyvinyl siloxane and polyether impression materials remain dimensionally accurate for 1 to 2 weeks . 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 . 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 . Unfortunately, it does not adhere to itself, which makes it unavailable for border molding or correctable impression techniques. Aquasil (Caulk/Dentsply) is slightly hydrophilic . 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 . The way to avoid latex contamination is to wear polyethylene gloves over the latex gloves or not wear latex gloves during the impression procedures. The relationship between static and mobile oral structures must be reproduced accurately for an optimum cast. impression materials are summarized in Table 1. silicate. Impression materials are used to record intraoral structures for the fabrication of definitive restorations. 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 . Rigid impression materials require less support from trays. Most materials in this category do not adhere to themselves after they have set and would not be able to be used for border molding or correctable impression technique. When alginic acid (prepared from a marine plant) reacts with a calcium salt (calcium sulfate), it produces an insoluble elastic gel called calcium alginate. 2017/2018. Working times can be varied with respect to standard-set versus quick-set impression materials as prepared by various manufacturers . 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. There is also a greater tendency for alginate to stick to teeth if they are dry. Disadvantages: Adequate accuracy if poured immediately. 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. Often, the choice of impression materials depends on the subjective choice of the operator based on personal preferences and past experience with particular materials. Vinyl polysiloxane silicones (also called addition silicones, polyvinyls, vinyls, and polyvinyl siloxane) are considered state-of-the-art for fixed partial denture impressions. This is usually seen in the dental office in the form of latex gloves or rubber dams. 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 . 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. Explain why polyvinyl siloxane impression material is so popular. Difficult to record details because of high viscosity. Master casts are used for producing complete dentures, removable partial dentures, crowns, fixed partial dentures, and implant prostheses. It has a terribly bitter taste and is relatively inexpensive. Regular Permlastic is recommended for partial- or full denture impressions because it has a high degree of flow that will register the finest detail. Disadvantages Non-aqueous elastomeric impression materials 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 . They are rigid materials and may be more difficult to remove than polyvinyl siloxanes . The catalyst paste has a cross-linking agent (aliphatic cationic starter) and filler and plasticizers. Viscosity is altered by changing the amount of silica filler, which produces either a putty or less viscous wash material. Materials with high dimensional stability are the polyethers and polyvinyl siloxanes, in contrast to alginate, which has a low dimensional stability. Polyvinyl siloxanes are fairly stiff, and depending on the viscosity of the material, they flow readily to capture areas of detail . 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. This thin layer causes impressions to remain tacky around new composite placed restorations . Immersion disinfection also may differ between different brands of alginate with respect to different immersion systems, such as iodophor and glyoxal glutaraldehydes . – Hydrocolloid impression materials are quite hydrophilic, but the same cannot be said for all impression materials. Loss of detail at impression margins is caused by moisture presence . The material is thicker when it is cold and more difficult to express and mix . Polysulfide impression materials are supplied as two paste systems. Polyvinyl siloxanes are generally hydrophobic. – However, they are not as accurate as other non aqueous elastomeric materials. Disadv Are inelastic, cannot be removed past undercuts without fracturing or distorting. 5. Because of their hydrophilic nature, using polyether and polysulfide impression materials is more compatible with the inherent moisture present in mucosal tissues . Sign in Register; Hide. Moisture from saliva or blood can interfere with accurate impressions. Plasticizers are moderately hydrophilic and make an accurate impression in the presence of some saliva or blood. Often, the choice of impression materials depends on the subjective choice of the operator based on personal preferences and past experience with particular materials. Dryness minimizes the moisture content of tooth surfaces and contributes to sticking of the alginate; ultimately, it leads to inaccurate cast pours. 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? 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. As with all materials, there are learning curves with respect to working with these different tissue conditioners and other types of impression materials. This is probably true with respect to any impression material when comparing hand spatulation to automixing. Materials with high contact angle require more careful pour technique and attention to produce accurate casts . A set impression must be sufficiently elastic so that it will return to its original dimensions without significant distortion upon removal from the mouth . Materials and Methods: Twelve sealed packets of three different routinely used alginate impression materials were used. 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 . 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. They are fairly easy to remove. To understand why polysulfide impressions shring over time, one needs to consider the chemical reaction that occurs when a polysulfide sets. Diagnostic casts are used to aid in treatment planning. For condensation silicone impression material 14. Hydrocolloids, polyethers, and polysulfides have relatively low contact angles. These hydrophilic polyvinyl siloxanes have improved wettability , and they are only clinically acceptable under dry conditions . 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. The polysulfides distort over time . * Secondary impression for edentulous ridge. The difference in the delay with gypsum and epoxy is that gypsum products have a much shorter setting time than epoxy die materials. All types of elastomeric impression materials undergo shrinkage caused by polymerization, and materials with reaction byproducts undergo additional contraction. Polysulfide impression materials are generally low to moderately hydrophilic and make an accurate impression in the presence of some saliva or blood. has great flexibility, which may result in prblems when it is removed from mouth The warmer they are, the faster they set. If concerned about mineral content of local water supplies, distilled or demineralized water can be substituted . In a laboratory setting, it should be dimensionally stable for accurate pouring of multiple casts and should not affect dimensional accuracy upon disinfection . Aquasil is an exception because it does adhere to itself after setting. Polysulfide pulping is a variant of kraft pulping in which half or more of the sodium sulfide of kraft white liquor is first oxidized. Impression materials that are currently popular include hydrocolloids, addition silicones, polyethers, and polysulfides. While usually used in single-mix, it can be used with Light-Bodied Permlastic for crown and bridge impressions. There 46 ELASTOMERIC IMPRESSION MATERIALS IN PROSTHODONTICS KEYF Table 1: Elastic impression materials. It is relatively low cost and comes in flavors that are more patient friendly. – Polysulfide impression materials have a disagreeable smell and … 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 . It is not as strong as polyethers or polyvinyl siloxane impression materials. It is a good idea not to store polyvinylsiloxane impression material close to polysulfide impression materials. potential for significant distortion. 3. Epoxy dies should not be poured until the impression has stood overnight . – With proper handling, polysulfide impression materials can be used for inlays, crowns, and bridges. An ideal impression material should exhibit certain characteristics in the clinical and laboratory environment. Because the material has a low wetting angle it makes a full arch impression easier than with polyvinyl siloxanes or polyethers. These materials are excellent for reline or rebase procedures in removable prosthetics . These materials have low tear strength and usually tear on removal if not careful . The reaction produces hydrogen, which is scavenged by the platinum. Materials such as hydrocolloids, polyethers, and methacrylates may require specific disinfection protocols to prevent distortion of the material after setting . These materials should have low shrinkage upon polymerizing and remain stable, which allows them to be poured days after making the impression. Impressions should be rinsed with water and then disinfected . second pour is less accurate. 19. 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. Polyvinyl siloxane contamination is usually a result of sulfur or sulfur compounds . 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. Most impression materials require a 1:1 ratio of base to catalyst. It sets by oxidation of the −SH groups, which results in chain lengthening and cross-linking and gives it elastomeric properties . Presence of moisture results in impressions with voids or pitted surfaces, and the detail reproduced is inferior. 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 . This result has been reported even with the new “hydrophilic” polyvinyl siloxane impression materials. 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 surface tension of the liquid is changed, and increased wettability results . It has a low wetting angle so it easily captures full arch impressions. However, contamination from the latex proteins in gloves may interfere with setting of this material. It is a good idea not to store polyvinylsiloxane impression material close to polysulfide impression materials. These characteristics make it highly desirable for clinical and laboratory use. Materials used without adequate knowledge of their characteristics can impair a successful outcome. 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. More catalyst added also speeds the setting time. Because hydrocolloids are hydrophilic, they swell if immersed in water or disinfectant . Before they set, however, they are susceptible to contamination. Explain the most advantageous clinical feature that polyether impression materials possess. If a material can tolerate some moisture, it is considered to be hydrophilic. 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 of their low wetting angle, they easily capture full arch impressions. 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. 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. Inaccurate portions can be remade without having to remakethe entire impression. 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). Accurate impressions are necessary for construction of any dental prosthesis. The hydrophobic nature of an impression material relates to its inability to work in a wet environment and still provide accuracy in an impression. 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 are virtually inert after set, and they can be trimmed and poured in any die material. Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), on Impression Materials: A Comparative Review of Impression Materials Most Commonly Used in Restorative Dentistry, Recent Advances in Materials for All-Ceramic Restorations, Posterior Amalgam Restorations—Usage, Regulation, and Longevity, Adhesion to Tooth Structure Mediated by Contemporary Bonding Systems, Dental Cements for Definitive Luting: A Review and Practical Clinical Considerations, Base Metal Alloys Used for Dental Restorations and Implants. Polyethers tend to be the most rigid impression materials . Disadvantages: must be poured with dental stone immediately. It has been reported that vapor given off by polysulfide impression material may cause contamination. 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. 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. Compress soft tissue while making impression. They distort less on pouring and make good bite registration materials . When it does set, it does so immediately . What do you want from an impression material? Elastomeric impression materials are in common use. This material adheres to itself and can be used to border mold or make correctable impression techniques. 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. 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 .

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