The set impression materials can be rigid (inelastic) or elastic. No. Check out this awesome Our Research Papers About Dental Impression Materials for writing techniques and actionable ideas. The material sets by cross-linking between terminal groups of the silicone polymers and the alkyl silicate to form a three-dimensional network (Figure 8-4). If the impression does not stay, the compound is most likely set. The filled tray is then inserted in the mouth and seated over the syringe material, which has been extruded on hard and/or soft tissue. The terms catalyst and accelerator used here and with other impression materials are actually misnomers. Accelerator—A compound that speeds up the reaction; also refers to the catalyst in the reaction of impression materials. Please remember, overworking the compound may cause it to set too quickly, or even cause it to set during the kneading process. Soaking in warm water-bath [Sheets or cakes] Over a flame. Aust Dent J 23:178, 1978. Prolonged … In addition, there are fewer possibilities for contamination of the material. Condensation polymerization of α-ω-hydroxy-terminated poly (dimethyl siloxane) with tetraethyl orthosilicate in the presence of stannous octoate (catalyst). Sulfur contamination from natural latex gloves inhibits the setting of addition silicone. Micelle—An aggregate of surfactant molecules or ions in solution. In the context of impression materials, it is the uptake by agar or alginate when immersed in water. Removal of the impression at this stage will cause … The safest method is to make a new impression when bubbles or similar defects are detected in critical areas. [Sticks]  Dry kneading … TYPE I Low Fusing - Green stick compound- 54 C Medium Fusing – Impression compound - 8. A dental alginate impression gel and used chalks were selected and mixed in a ... Gypsum is a model CaO-containing compound. Impression Compound Manipulation: 1.As impression compound is of low thermal conductivity, [Type of bonding] adequate time should be given for uniform heating Flow during impression taking. After flowing through “n” elements, the number of layers in the stream of material increases to 2n. Extra-low and putty forms are available only for condensation and addition silicones. Pouring the set impression with a gypsum-forming mixture is facilitated because the wet stone has a, There are two types of polyether impression materials. Material is not flexible and will fracture when deformed, like chalk. A fine cord is placed at the base of the crevice to facilitate moisture control, with a larger cord placed on top of the first and near the coronal extent to displace the gingiva laterally. This type of device has also been adapted to mix and dispense temporary crown and bridge acrylic materials and cements that are used for luting and for producing restorations (Chapter 14). The compound is manipulated by index finger into the deep buccal sulcus area. Usually, the two groups of materials are mixed simultaneously, each by a different person. Mixing is done solely by kneading … The time interval between impression pours should not be greater than 30 minutes. This process is known as flow division. Change the gate locations. In this section, the properties relevant to impression making with elastomers are described. In using this device, thorough mixing of higher-viscosity materials can be achieved with little effort. For example, epinephrine, which is used widely, is of particular concern in patients with cardiovascular disease. Extrusion is treated in a separate chapter (Chapter 15). Non-Elastic Impression Material - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. How does static mixing achieve a uniform mixture? Setting time—The time from the start of mixing to the point where the material loses its flow potential or plasticity. All elastomeric impression materials exhibit shear-thinning characteristics before setting. Once the clay has warmed, knead it with your hands for about a minute, then roll out the clay into … The mixer elements are a series of alternating right- and left-turn 180° helixes positioned so that the leading edge of one element is perpendicular to the trailing edge of the next (Figure 8-9, B). Polysulfide is provided only in light-body and heavy-body consistencies. the impression to remain in the mouth. The same procedure will facilitate spreading of heavy-body material on the impression tray and retain it in the tray. This phenomenon is called shear thinning (. In addition to excessive pressure, some of the distortion in putty-wash impressions may be attributable to inadequate space for the wash material. Model—A positive full-scale replica of teeth, soft tissues, and restored structures used as a diagnostic aid for the construction of orthodontic and prosthetic appliances; a facsimile used for display purposes. The main chain is probably a copolymer of ethylene oxide and tetrahydrofuran. In contrast to the condensation silicone, the addition silicone is based on addition, Polymerization of addition silicone. Thus, the cast must be an accurate representation of oral structures, which requires an accurate impression. Kneading is performed. When dental stone is poured on the surface of such test impressions, the finest detail is not always reproduced. Table 8-3 lists working and setting times for the various kinds of elastomeric materials as measured by an oscillating rheometer. Impression compound is a thermoplastic material; it is presented as a sheet of material, which is warmed in hot water (> 55–60 °C) for one minute, and loaded on a tray prior to impression taking. Due to a high coefficient of thermal expansion, the dimensions of the impression are not … To not disturb the impression the aerosol can should be kept at a distance of 25 to 30 cm and moved in a zigzag pattern while going from one end of the impression to the other. One should be aware that this is not economical, as a portion of the paste is not used. Also, excessive wet kneading can incorporate water into the mix and change the flow properties of the compound. The mixing tip is made of helical mixer elements in a cylindrical housing (Figure 8-9). Kneading of the material ensures further uniform softening. The objective of placing a retraction cord is to displace the gingival tissue laterally away from the margin of the preparation. greater affinity for the hydrophilic surface. When heated in a water bath at about 65°C (149°F) it becomes plastic and can be moulded … In addition, disposable stock trays (Figure 8-7, B) work satisfactorily. Note that the use of less material in a custom tray reduces the compressibility of the impression, which can make removal of the impression tray more difficult. A slightly roughened surface on the tray will increase adhesion. To demonstrate the reality of … Temperature range : 55 – 60 ºC. One or two gingival retraction cords are placed under the margin around the tooth for at least 5 min before making impressions. To produce accurate replicas of intra- and extraoral tissues, the impression materials should be (1) sufficiently fluid to adapt to the oral tissues, (2) viscous enough to be contained in a tray, (3) able to transform (set) into a rubbery or rigid solid in the mouth in a reasonable time (less than 7 min), (4) resistant to distortion or tearing when removed from the mouth, (5) dimensionally stable long enough to allow one or more casts to be poured, (6) biocompatible, and (7) cost-effective in terms of time as well as the expense of the associated processing equipment. Impression compound – wet kneading, putty consistency Elastomers ii) Circular motion (with glass slab & spatula) Static mixing provides greater uniformity in proportioning and mixing, yields fewer voids in the mix, and reduces the mixing time. The mixing tips vary in their diameter, length (number of helical mixer elements), and the size of openings for a specific consistency. Due to poor thermal conductivity, the layer adjacent to the mouth tissues will remain soft. The silicone pastes … Zoe impression paste, Impression plaster. *Numbers within parentheses represent the standard deviation of the mean. Manufacturers may add a noble metal, such as palladium, as a scavenger for the released hydrogen gas. An alternative to the setting of polysulfide impression does not stay, the of... A 2048- or 4096-striation structure, which can be used for pouring models also refers to catalyst! Is probably a copolymer of ethylene oxide and tetrahydrofuran water into the mixing will! 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