title: The effect of alginate impressions on the surface of cast gypsum. II. The role of sodium sulphate in incompatibility.
abstract: Of the materials tested only two alginates, Palginex (D), and Echo (C), show good surface reproduction when Vel-Mix (1), Ainsworth Greenstone (4), and Investo Greenstone (5) are cast against them. The above two alginates were shown to have a potassium and sulphate rich exudate. The reasonable surface produced by CA-37 (A) can be attributed to a proportional decrease in the ratio of potassium to sulphate present in the exudate, compared with Echo (C) and Palginex (D). S.S. White (B), Kromopan (E), and Tissutex (G) produce poor cast surfaces when high strength gypsum products are set against them. The exudates from these alginates were found to consist almost entirely of sodium sulphate. This study suggests that one way to improve the surface compatibility of alginates with gypsum products would be to modify the chemistry of the impression material so that a reactor other than calcium sulphate is used, to eliminate the appearance of sulphate ions in the exudate. Moreover, sources of sodium ions should also be eliminated. Therefore soluble alginates other than sodium alginate should be preferred, and a retarder other than one or other of the forms of sodium phosphate should be used. These changes would ensure that sulphate, particularly sodium sulphate, would not be produced as a by-product of the setting reaction. This in turn would eliminate the effects of incompatibility at present encountered to a greater or lesser extent with most combinations of alginate impression materials and gypsum cast materials.
mesh_terms: D000464:Alginates / Q000032:analysis; D002133:Calcium Sulfate; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003734:Dental Casting Investment; D003761:Dental Impression Technique; D011188:Potassium / Q000032:analysis; D012964:Sodium / Q000032:analysis; D013431:Sulfates / Q000032:analysis; D013499:Surface Properties
chemical_list: D000464:Alginates; D003734:Dental Casting Investment; D013431:Sulfates; C012036:sodium sulfate; D012964:Sodium; D011188:Potassium; D002133:Calcium Sulfate