A comparison of elastic impression materials.

T ests for accuracy and other characteristics of elastic impression materials generally fall into one or more categories. These are: (1) Linear tests which measure the material itself (usually unidimensional) .le5 (2) Tests which depend upon the formation and measurement of gypsum dies made from the impression materials. In these tests, the dies are measured, not the impression material itself. The configurations of the test dies vary.6-g (3) Methods which employ the use of master dies and castings. Accuracy of the impression material in question is judged by trial of the master castings on the stone die replicas.*“-13 This is a report of an investigation of 14 elastic materials representative of those frequently used in dentistry for impression making. The purposes of the study were: ( 1) to develop and use a laboratory test method suitable for measuring the accuracy of impression materials; (2) to test the conformity of the impression materials to ADA Specification No. 19 (consistency and mixing and working times) ; (3) to compare, by indirect means, the accuracy of the impression materials 30 minutes after setting; (4) to demonstrate the dimensional changes that occurred in the impressions during the serial pouring of four sets of dies over a 24 hour period; and (5) to compare the accuracy of stone dies prepared promptly with the accuracy of those obtained after a 24 hour delay.