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The effect of alginate impressions on the surface of cast gypsum. II. The role of sodium sulphate in incompatibility
Author(s) -
Jarvis R. G.,
Earnshaw R.
Publication year - 1981
Publication title -
australian dental journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.701
H-Index - 71
eISSN - 1834-7819
pISSN - 0045-0421
DOI - 10.1111/j.1834-7819.1981.tb03912.x
Subject(s) - gypsum , retarder , sodium , impression , sodium alginate , exudate , chemistry , salt (chemistry) , chemical engineering , materials science , metallurgy , composite material , organic chemistry , botany , biology , advertising , engineering , business
A bstract — It has been shown that the poor surfaces found on high strength cast gypsum which sets against alginate impressions are caused by the presence of sodium sulphate, a by‐product of the setting reaction of the alginate, in the exudate present at the interface between impression and setting cast. In many set alginate impression materials sodium sulphate is present in sufficient concentration to act as an effective retarder for the setting of the calcium sulphate hemihydrate mix, and this effect is greatest when, as in the case of high strength materials such as die stones, the water content of the mix is low. A considerable improvement in the surface of gypsum casts could be made by changing the composition of alginate impression materials to use a reactor other than a sulphate, a retarder other than a sodium salt, and an alginate other than sodium alginate. This would greatly reduce the concentration of both sodium and sulphate ions in the exudate, and could eliminate the effect of sodium sulphate as a retarder of the setting reaction.