WORKING TIMES OF ELASTOMERIC IMPRESSION MATERIALS DETERMINED BY DIMENSIONAL ACCURACY

The working times of five poly(vinyl siloxane) impression materials we re estimated by evaluating the dimensional accuracy of stone dies of i mpressions of a standard model made at successive time intervals. The stainless steel standard model was represented by two abutments having known distances between landmarks in three dimensions. Three dimensio ns in the x-, y-, and z-axes of the stone dies were measured with a tr aveling microscope. A time interval was rejected as being within the w orking lime if the percentage change of the resultant dies, in any dim ension, was statistically different from those measured from stone die s from previous time intervals. The absolute dimensions of those dies from the rejected time interval also must have exceeded all those from previous time intervals. Results showed that the working times estima ted with this method generally were about 30 seconds longer than those recommended by the manufacturers.