![]() 6 Another study reported the effect of contact time between alginate impression material and dental stone after 9 hours of contact time. Some have recommended separating the cast from the mold before dehydration of the alginate 18 others reported the effect of contact time between alginate impression and orthodontic plaster on cast properties after 12 hours of contact time. 6,17įew studies have discussed the effect of contact time. 14 The recommendation is to immediately pour the alginate impression with dental stone to avoid dimensional changes however, pouring can be delayed up to 60 minutes if the impression is kept in 100% humidity. ![]() 25, detail reproduction is satisfactory when a copy line of 50 µm in diameter is reproduced continuously across the stone. The requirements of ideal gypsum casts and dies include accurate reproduction of details, dimensional stability over time, enough hardness strength to withstand the fabrication process, and being resistant to inadvertent abrasions that may occur during fabrication. That reaction process is an exothermic chemical reaction. 11,14 Type III dental stone sets when mixing the powder particles with water. One of them is type III dental stone, which is used as cast and/or die material to construct prostheses and has high strength and slight setting expansion. 25, there are five types of gypsum products for dental uses. The gypsum used for dental applications is nearly pure calcium sulfate hemihydrates, produced by calcination of calcium sulfate dihydrate. 12 Chemically, dental stone is a mineral composed of calcium sulfate dihydrate. 11ĭental stone is extensively used in dental laboratories because of its low cost and easily modified properties. ![]() In addition, alginate produces insoluble alginate and sodium sulfate during the gelation process. 3,9,10 Alginate impressions contain water, which inhibits the setting of the gypsum material at the surface. 9Īlginate consists of a powder containing calcium or potassium sulfate and filler as primary components. 18 for alginate impression material regulates its use and accepts an error of 0.75 mm in the alginate impression as a maximum dimensional change. ![]() 8 The American Dental Association (ADA) Specification No. 1,4-7 Some clinicians still use alginate for definitive impressions. Despite its advantages over other materials, it has some problems with dimensional stability and water loss, which can affect the ability of alginate to reproduce details. 1,3,4Īmong the different types of impression materials, the most popular is alginate impression material (irreversible hydrocolloid). The impression is then poured using dental stone or other suitable materials to obtain a positive replica (ie, cast models and dies). 1-5 An impression is made to accurately record oral tissues and their spatial relationship. In conclusion, contact between alginate impression material and type III dental stone up to 6 hours did not affect the dimensional stability and richness of the surface hardness, though, was significantly affected.Ĭast models and dies are used daily in dental practice for many purposes, such as diagnosis, treatment planning, patient education, communication between clinicians and technicians, fabrication of custom trays, dental restorations, and orthodontic appliances. However, hardness was greater after 1 hour of contact time ( P =. Surface details did not deteriorate when contact time was increased, as all of the samples could reproduce all details after the 1-hour and 6-hour interval periods. The dimensional stability of the cast models was not affected when contact time was increased from 1 hour to 6 hours ( P =. An indentation on the cast was made and the depth of the indentation was then measured with a digital caliper to measure hardness. The samples were evaluated under light microscope for surface details and measured by digital caliper for dimensional stability. Thirty-seven cast models were separated from the impression after 1 hour (control group) and 30 cast models were separated after 6 hours (study group). ![]() Sixty-seven cast models were obtained from a stainless steel cylinder by using irreversible hydrocolloid impression material and type III dental stone. In this study, the authors tested the effect of contact time between an alginate impression and type III dental stone on cast model properties. Excessive contact of the alginate impression with the cast model over time may affect the model’s properties. The material is not dimensionally stable, however thus, it is necessary to pour the impression immediately after the molding is accomplished, or within 60 minutes if the impression is kept in 100% humidity. Alginate impression (irreversible hydrocolloid) material is commonly used in dental practice because it is easy to mix, low in cost, and well tolerated by patients. ![]()
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