From: Encyclopedia of Biomedical Engineering, 2019, Frederick C. Eichmiller, Carlos A. Muñoz-Viveros, in Contemporary Esthetic Dentistry, 2012. Figure 16-3, G, shows the bite registration after removal from the patient's mouth. The rate of shrinkage is not uniform. These are to be proportioned for mixing according to the length of the extruded ‘rope’, either of one part when the other reactant is in a liquid to be dispensed by counting drops, or for both parts in ‘paste-paste’ systems. Impression materials are used to make an accurate replica or mold of the hard and soft oral tissues. They are composed of a powder containing sodium or potassium alginate, calcium sulfate as a reactant, sodium phosphate as a retarder, fillers such as diatomaceous earth, potassium sulfate for stone compatibility, and flavoring agents. The need for more satisfying impression materials promotes the development of elastomeric impression materials. One problem may be apparent with tube contents, particularly when there is a dense powder suspended in the liquid vehicle: settling (4§9.3). Fillers, as well as silicone polymers can be blended in different combinations as per requirement (Verma et al., 2010). The tray with the impression material is then removed from the mouth, and the impression is ready for disinfection and pouring with a cast material to make a positive replica. Impression materials Tubes Sticks/ carpules. When mixed, a polymerization reaction occurs by ring opening of the ethyleneimine groups. is intended for educational, informative and entertainment purposes only. This bevel also permits the clinician to secure a closing angle at the margin to reduce recurrent caries. The powder is mixed with water. Condensation silicone rubber is supplied as a base and catalyst and used for partial denture impressions and fabrication of small appliances. There are so many impression materials choices in the market which can make choosing the right impression material to ensure the patient outcomes very challenging. We use cookies to help provide and enhance our service and tailor content and ads. The greatest dimensional change occurs with condensation silicones (Table 28-2), which exhibit more than a 0.5% dimensional change. Impression trays are supplied as quadrant trays, which cover on half of the arch: Anterior trays, which are suited for the anterior teeth, and full-arch trays, which covers the complete arch. There was little change in dimension among abutment preparations for all materials, for all times of pour, and with a repeat pouring. Alginate is currently one of the most popular impression materials. In general, about half of the shrinkage occurs during the first hour after removal from the mouth. Inelastic material is rigid and will fracture when deformed. The catalyst or accelerator contains lead dioxide, hydrated copper oxide or organic peroxide as a catalyst, sulfur and dibutyl phthalate as a plasticizer, and other nonessential fillers. Typical values for the linear coefficient lie in the range 150 ~ 300 MK-1 (Fig. 20 Questions . The importance of cross-infection control cannot be overemphasized. However, this is affected by the filler content in the normal way (6§2.1). This, unfortunately, is in direct conflict with the recommendation for avoiding stress-set effects (§11.7). This type includes impression compounds, impression plaster, and zinc oxide- Eugenol (ZOE) impression paste. no change in structure or shape. Quiz.3 . What Types of Impression and Registration Are Available for My Practice? When a restoration margin will be visible during function, a 45-degree facial bevel is employed rather than a facial butt joint, because there is a common termination of metal, opaque, and porcelain. In order to avoid the spread of pathogens from patients to patient, patient to health care personnel and health care personnel to patient, it is the duty of the health care policies makers to allocate the appropriate methods of cleaning, disinfectio… Tray selection will also depend on the purpose of the impression. Impressions may demand a rigid mold or a more elastic or pliable material. It is made from seaweed and is made with components like Sodium alginate, Calcium sulfate and other ingredients which act as retarders. cooled with no change in chemical makeup. Agar hydrocolloids have largely been replaced by rubber impression materials, but they are still used for full mouth impressions when severe undercuts are present. Two to three minutes after the surface tackiness has been lost, it can be removed from the oral cavity. A reversible material can be altered by temperature which includes agar and impression compounds. condensation silicone, addition silicone ^poly (vinyl siloxane) Alginate impression materials. : 136–137 Rigidity- Inelastic (rigid) impression materials are used with patients with shallow undercuts. offers 1,008 types dental impression materials products. In Craig's Restorative Dental Materials (Thirteenth Edition), 2012. What Is the Importance of the Office CPR Training? Darvell DSc CChem CSci FRSC FIM FSS FADM, in, Materials Science for Dentistry (Tenth Edition), Principles for Abutment and Prosthetic Screws and Screw-Retained Components and Prostheses, Dental Implant Prosthetics (Second Edition). Dental assistant. Not only do these materials differ in terms of mixing procedures, but also a number of other different factors such as viscosity, contraction, and after-cure, hardness-shore value. All elastic impression materials shrink after they are removed from the mouth. A polyvinyl siloxane impression material was used to take a full arch impression. 19875 Southwest Freeway, Suite 120 Sugar Land, TX. Approved and Regulated by TWC Career Schools & Colleges, (281) 728-6012   Visit our website:, Copyright © 2020, Greatwood Dental Assisting Program. Impression materials are used in dentistry to record the details of intraoral structures to fabricate a reproduction of teeth and soft tissues for the construction of dental prostheses. surrounding oral tissues. If full coverage restorations are fabricated and inserted in the presence of soft tissue pathology, facial gingival recession may occur after treatment of the inflammation. Essay . They can be categorized as rigid and elastic impression materials. These materials are highly hydrophobic. Again, we are faced with a compromise because of unavoidable sources of error. A light body material was injected around the margins (Figure 16-3, A) as the impression tray was loaded with a heavy body material (Figure 16-3, B). Their composition includes agar, borax to improve strength, potassium sulfate to provide compatibility with the stone, preservatives, and flavoring agents. the rope thickness is supposed to be adjusted to give equal lengths when the ratio is correct. This may make judgement more difficult because of the conceptual conflict between volume and length. Thus no metal color will show facially. It should be borne in mind, however, that the width of the arch will decrease because of tray cooling when a full arch impression is taken if the tray warms at all. They are sold as paste-paste, with one paste containing a vinyl-polysiloxane prepolymer and the other a siloxane prepolymer with hydrogen groups, a platinum catalyst, and a chloroplatinic acid that initiates the polymerization reaction. Thus, the minimum thickness of the material in the tray should be three to four times more than the largest undercut (Hamalian, T. A. et al., 2011). Another problem of these materials is that they all undergo setting shrinkage due to polymerization, but in general, the shrinkage is very low (with polyether and addition-cured silicones being the lowest and condensation-cured silicones being highest).