Many Dental Appliances Are Constructed Outside the Patient - Free download as Word Doc (.doc / .docx), PDF File (.pdf), Text File (.txt) or read online for free. 16.1 Classification of impression materials by viscosity at a constant shear rate and temperature (23°C). 16.2 Impression materials. An inlay will incorporate the pits and fissures of a tooth, mainly encompassing the chewing surface between the cusps. E. Classification of Impression Materials 1. The key comparison between them is the amount and part of the tooth that they cover. i) Hydrocolloid. Dental Impression Materials / classification Elasticity Elastomers / … For such products, a dry field of operation is essential. Can wear Dentures overnight invites Denture Stomatitis? This can result in blow holes and loss of fine detail. When standing teeth are to be recorded, or when the patient has deep soft-tissue under-cuts, the set impression material must be flexible enough to be withdrawn past the undercuts and elastic enough to give recovery and an accurate impression. For instance, elderly with resorbed ridges, it is difficult to get retention in dentures. It is of great importance, therefore, that inaccuracies are minimized at this stage, otherwise they will be carried through and possibly compounded later on. Fig. Dental Implantation, Endosseous/methods; Dental Implants; Dental Impression Materials/classification* Dental Impression Technique* Dental Prosthesis, Implant-Supported An impression is imprint of the mouth. (3) Manipulative variables such as ease of handling, setting characteristics, etc. Impression materials The materials which are used to take impression of natural teeth and their supporting tissue they are called as Impression materials. impression plasters). (4) Additional factors such as cost, taste, colour etc. Temporary. – As mentioned earlier, those that replace lost tooth structure and restore the function of the teeth mus t be strong and hard. The thickest parts of the impression are compressed against the tray when they pass the widest part of the tooth crown. b) Elastic. Requirements for impression material: Accurate & persise - mainly depend on viscosity of the mixed and the ability of the impression material to adapt closely to both the soft and the hard tissues. A dental impression is an imprint of teeth and/or soft tissues, formed with specific types of impression materials that is used in different area of dentistry including Prosthodontics.. A correctly made dental impression will capture a part or all of a person's dentition and surrounding structures of oral cavity. The effects of thermal changes are minimized if the values of coefficient of thermal expansion of the impression material and tray material are small. Agar; b) Irreversible. Classification of impression materials is the most frequently asked question for exams. 16.3, the oversized die will result in a ‘loose-fitting’ crown. 16.3 Diagram illustrating the effect of setting contraction. Figure 16.6 gives a series of diagrams to illustrate what happens when an impression of an undercut tooth is recorded with (a) an elastic material, (b) a plastic material, and (c) a viscoelastic material. Impression materials is a group of auxiliary dental materials that is used in prosthodontics in the dentist’s everyday practice. SENN is supplied as a 2-paste automixing system and contains a polymer with polyether and siloxane (e.g., addition silicone) groups that will combine elements and benefits of both impression materials. Impression materials that are used today can be classified according to their composition, mechanism of setting, mechanical properties, and applications. They could be described as possessing rubbery characteristics. Impression is a negative replica of a mouth, same as film for a picture. a) reversible. E.g. Figure 16.2 lists the major groups of impression materials using the classification referred to above. (b) During removal – the impression material is subjected to both compressive and tensile stresses. This may effect the fine detail which can be recorded in impressions of hard tissues and may influence the degree of tissue compression or displacement achieved with soft-tissue impressions. The behaviour of viscoelastic materials is described on p. 15–16, where the influence of time as an important parameter is discusse/>. 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 16 Impression Materials: Classification and Requirements, 30 Polycarboxylates, Glass Ionomers and Resin-modified Glass Ionomers for Luting and Lining. wisdom tooth pain?. As per the name it imparts compression forces on mucosa.Hence, it is also known as Definite pressure impression.Since,it is applying compression forus to oral tissues,this technique ,has good retention While chewing.Material of Choice for Mucocompressive impressiontechnique includes Impression compound,Soft liners. Another complicating factor is the spacing of the impression tray. Materials which expand during setting result in undersized dies or casts. For the simple crown preparation, illustrated in Fig. According to philips scienceof dental materials impression materials are classified on thebasis of setting and elasticity.Mode of setting rigid ElasticSet by chemicalreaction (irreversible)Impression plaster,zinc oxide eugenol.Alginate,polysulfide,polyether, silicone,Set by temperaturechange (reversible)Compound, waxes Agar hydrocolloid. If a material is rigid after setting it may not be possible to remove it from undercut areas. The effect on the accuracy of fit of the resultant restoration depends on the type of restoration and the complexity of shape involved. Fig. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Start studying Chapter 46 Test Review. Zoe impression paste, Impression plaster. They reproduce an imprint faithfully, providing details of a high definition despite the presence of undercuts. Since no pressure is applied, Tissue health is preserved.Hence, it is also known as Minimal pressure technique. a) Rigid. Many dental appliances are constructed outside the patient’s mouth on models of the hard and/or soft tissues. Impression technique A method and manner used in making a negative likeness. The tray is required because the materials are initially quite fluid and require support. CRAIG Department of Biomaterials, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109 Adv Dent Res 2(l):51-64, August, 1988 ABSTRACT Major advances in impression materials and their application have occurred during the … Based on material use A. Inelastic or rigid. 4 Classification of agar hydrocolloid impression materials. A relatively fluid impression material confined in a close-fitting impression tray will compress the soft tissues to a greater extent than the same material used in a loosely-fitting tray. Receiving a qualitative impression is one of the main goals which the doctor faces at the prosthodontics treatment of patients with various diseases of a dento- Based on setting of materials … There are often significant variations between different brands of the same type of material and these variations can spread across the divisions between different levels of viscosity. These materials must have adequate elastic properties and adequate tear resistance, coupled with a rigidity which is low enough to enable the impression to be removed. Three Impression Material Classifications: A Comparison. To learn more about dentistry click on the link here, Impression Materials Classification with diagrams, Not eating can lose teeth? Classification of materials according to viscosity is not, therefore as simple as it may seem. The way in which the material interacts with saliva is another factor affecting fine-detail reproduction. (b) The impression material contracts towards the tray (providing it is bonded) and increases the impression space. Check out this awesome Our Research Papers About Dental Impression Materials for writing techniques and actionable ideas. Thus, certain materials which appear fairly viscous whilst under low stress conditions may become more fluid during the recording of the impression, when the material is placed under higher stress. Once positioned in the patient’s mouth, the materials undergo ‘setting’ by either a chemical or physical process. 1. Chemical Reaction or Physical Change – Impression mat erials set either by a chemical reaction or b y a physical change. 16.5b) as well as the viscoelastic properties of the material itself. Impressions are the Key for a good prosthesis. Fig. The impression recorded with the elastic material accurately records the true shape of the tooth with the correct degree of undercut. A more widely used classification of materials involves consideration of the properties of the set material. Figure 16.5 shows diagramatically the way in which a set material is placed under stress during the withdrawal of the impression. The newest class of impression material is the vinyl-polyether hybrids that include SENN (GC America, Alsip, IL; soon to be introduced in the U.S.). – Some restorative materials simulate the appearance of the tissues that are being replaced. Individual with deep undercuts, the material of choice for recording impression is alginate with perforated stock trays. The properties which are most important are rigidity and elasticity, since they determine whether an impression material can be used to record undercuts. The hydrophilic nature of the material allows it to be used in the. watch our you tube video on dental pathshala to understand the classification of impression materials. Let's understand the properties, behavior, uses, and manipulation of the various materials used in dentistry.. all simplified, just for you! Hence, we have silicone materials, alginates, etc. It may be less confusing if the terms rubbery and non-rubbery were used instead of elastic and non-elastic. Why wisdom tooth is called wisdom tooth? CLASSIFICATION OF IMPRESSION MATERIALS. It is difficult to calculate the precise value of the thermal contraction or to predict accurately the direction in which it operates since the contraction of the tray and that of the material act in opposite directions, providing the impression material remains attached to the tray. Classification of impression materials. Classification by Use – Materials used to replace lost oral tissues are called r estorative materials. Classification of impression materials: According to the elasticity of the materials. Hence impression materials are classified as being elastic or non-elastic. – The chemical reaction invo lves chain lengthening, cross-linking, or both. Establishment of the classification of and specification of the requirements for impression materials in powder form containing an alginate as the gel-forming ingredient. However, the latter terms have been used for many years and are therefore likely to be familiar to dentists. (c) This results in an oversized die. The degree of distortion depends on the severity of the undercut, the thickness of the impression material and the time for which the impression is maintained in a compressed state (Fig. A ____ is a reproduction of someone's bite with the use of wax or elastromeric material. Dental impression.Materials. This … Punj et al. The composition of the materials is … The term elastic as applied to impression materials is fairly unequivocal since the materials which form this group all possess the ability to be stretched or compressed and give a reasonable degree of elastic recovery following strain. Sep-Oct 2000;48(5):510-2, 514, 516. The function of an impression material is to accurately record the dimensions of the … Fig. The fine detail recorded in an impression will only be transferred to the gypsum cast if there is adequate ‘wetting’ of the impression surface by the freshly mixed dental stone or plaster. Based on the degree of tissue Compression or the amount of pressure applied on the tissues. i) Reversible (thermoplastic) E.g. (b) Contraction results in an oversized impression space. A low contact angle is favourable as it indicates good wetting. Start studying Impression materials. Dentist must know the impression materials used for specific condition. Classification 1. Table 8-1 shows the classification based on the setting mechanism and mechanical characteristics. (a) If the impression material is bonded to the tray, contraction occurs towards the tray. Most dentists are able to associate a material from a particular chemical group with a particular set of characteristics or properties which render it suitable for some applications but not for others. It is very important for us to understand taking a good impression using a correct impression technique. – NUTRITION AND ORAL HEALTH. The figures show the different test apparatus, instruments and components. The accuracy of the model depends on the accuracy of the impression in which it was cast. The accuracy of ‘fit’ and the functional efficiency of the appliance depends upon how well the model replicates the natural oral tissues. Materials that very fluid are called mucostatic impression materials because they are less likely to compress soft tissues. Classification of impression materials (AVAILABLE) Rigid impression materials (AVAILABLE) Dental compound (AVAILABLE) To support my research on impression materials I asked two dentists their opinions on the different impression materials: Silicones are the most dimensionally stable of all the materials and will keep their shape even if left for long periods. This standard replaces ISO/R 1563/1970 of which it constitutes a technical revision. Fig. Additional retention is achieved by using perforated trays. Dental material 780. denture prostheses. For most materials, the dimensional change is a contraction and, providing the impression material is firmly attached to the impression tray, this produces an expansion of the impression ‘space’ and an oversized die, as illustrated in Fig. Impression materials are generally transferred to the patient’s mouth in an impression ‘tray’. Classification of Impression materials. Precision impression making materials of lightly flowing consistency with ideal flow characteristics, maximum wetting power, and elastic resilience. This technique was given by henry Page.A very good example of mucostatic technique can be Impression plaster. In addition to the requirements given above, there are two further requirements which apply specifically to materials used for recording undercuts. The ‘setting’ of impression materials, whether it involves a chemical reaction or simply a physical change of state, generally results in a dimensional change which, naturally, affects accuracy. impression waxes) and in other cases are very rigid but show little evidence of plastic deformation (e.g. Impression plaster; Zinc oxide eugenol; Compound wax; B. Elastic. Dental Materials PRIME. Which of the following is not considered a classification of impression materials? The thickness corresponds to specific spacing, and can be classed as spaced, where about 3mm of space is left between the tray and the mucosa for the impression material to occupy, or closely adapted, where less space is left for the impression material. It is important that the impression material remains attached to the impression tray during the recording of the impression. Before setting, the property most normally used to characterise materials is viscosity. – Impression materials set by che mical reactions to form elastic rubber materials are called thermoset. We develop hydrophilic impression making silicones for every indication (corrective and double mix technology, kneadable working impression making for functioning rim design, sandwich technology, monophase impression making). It should be remembered however, that viscosity often varies with the applied stress (p. 19). Any substance or combination of substances used to record an impression or negative reproduction those are called as impression materials. In cases where the impression is made from a hydrophobic material the hydrophilic slurry of calcium sulphate hemihydrate in water may not be able to approach closely enough to the surface of the impression (on a microscopic scale). Many criteria may be used to classify impression materials. The most widely used and understood method is to classify them according to chemical type. 16.4 Diagram illustrating the effects of thermal contraction. Major advances in impression materials and their application have occurred during the last decade, with greater emphasis being placed on rubber impression materials than on dental compound, zinc oxide-eugenol, and agar and alginate. Impression materials are also classified as reversible (compounds and hydrocolloids) or irreversible (silicones, polyethers, and alginates). When a substance behaves in this way, it is said to be pseudoplastic. After ‘setting’, the impression is removed from the patient’s mouth and the model cast using dental plaster or stone. This requires a low viscosity or a degree of pseudoplasticity. As the name signifies Muco static means no pressure is applied On the tissues while taking Impression. 16.3. This obviously has a negative effect on the ability to achieve an adequate impression, but more seriously may undermine the viability of the remaining teeth as they may be subjected to a considerable stress if an attempt is made to remove the impression. This new class of impression material combines properties from addition silicone and polyether impression materials. 16.4. I) Based on mode of setting & elasticity. Thus, materials which are initially very fluid are often classified as mucostatic impression materials because they are less likely to compress soft tissues, whilst materials which are initially more viscous are classified as mucocompressive. Some products are hydrophobic and may be repelled by moisture in a critical area of the impression. (a) The tray contracts and reduces the impression space. The impression stage is the first of many stages involved in the production of dentures, crowns, bridges, orthodontic appliances etc. For greatest accuracy, the dimensional change should be minimal. The requirements of impression materials can be conveniently discussed under four main headings: In order to record the fine detail of the hard or soft oral tissues, the impression material should be fluid on insertion into the patient’s mouth. Based on the degree of tissue Compression or the amount of pressure applied on the tissues. Elastic impression materials include reversible (agar-agar), irreversible (alginate) hydrocolloids and synthetic elastomers (polysulfides, polyethers, silicones). impression compound; ii) Irreversible (thermosest) E.g. However, silicones work best in a dry environment and may not be ideal if there is a lot of saliva. Figure 16.1 gives a simplified classification according to viscosity in which materials with the highest viscosity are shown at the left of the figure and those with the lowest viscosity are shown on the right. As the name signifies Muco static means no pressure is applied On the tissues while taking Impression. The term non-elastic however, is not a particularly good term with which to describe a group of products which in some cases are clearly plastic (e.g. This is illustrated in Fig. Thus, materials which are initially very fluid are often classified as mucostatic impression materials because they are less likely to compress soft tissues, whilst materials which are initially more viscous are classified as mucocompressive. Classification according to elastic properties and chemical type. The impression recorded with the viscoelastic material gives a distorted shape. On being withdrawn from the patient’s mouth, which is typically at a temperature of 32–37°C, into the dental surgery, at a temperature of around 23°C, the impression undergoes approximately 10°C cooling. We need to understand which impression material and technique are used in an individual. Regardless of the topic, subject or complexity, we can help you write any paper! Title: Impression materials (requirement and classification) 1 Impression materials (requirement and classification) Dr. Waseem Bahjat Mushtaha ; Specialized in prosthodontics; 2 Definition . E.g. Other methods of classification are sometimes used and these may be based upon consideration of the properties of the materials either before or after setting. Impression materials: basic properties Gen Dent. REVIEW OF DENTAL IMPRESSION MATERIALS R.G. Other materials are more compatible with moisture and saliva and no special precautions are necessary. Agar hydrocolloids have largely been replaced by rubber impression materials, but they are still used for full mouth impressions when severe undercuts are present. This factor is primarily responsible for governing the principal applications of the materials. As we say, first impression should be good,likewise a dental impression recorded should cover all minute details of the mouth. So, we use mostly admixed technique with resorbed ridges. Inlays and onlays are used in molars or premolars, when the tooth has experienced too much damage to support a basic filling, but not so much damage that a crown is necessary. Mucostatic Impression technique. The impression recorded with the plastic material has been grossly distorted during removal and has not recorded any undercut. This results in thermal contraction, the magnitude of which depends on the value of coefficient of thermal expansion of the impression material and impression tray to which it is attached. 16.5 Diagram illustrating how an impression material is placed under stress during removal from an undercut area. Impression techniques can be broadly classified into Muco static, Muco compressive, and selective pressure technique. But retention is not good for mucostatic impression technique. Impression techniques can be broadly classified into Muco static, Muco compressive, and selective pressure technique. As the impression is withdrawn it is likely that the material is also subjected to tensile stresses as the trapped material is stretched. 1 Non elastic : a. Partial detachment may cause gross distortions of the impression which may remain undetected and will almost certainly lead to ill-fitting appliances or restorations. 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