DISPLACEMENT RHEOMETER - A METHOD OF MEASURING WORKING TIME AND SETTING TIME OF ELASTIC IMPRESSION MATERIALS

A new method of measuring both working time and setting time of elasto meric impression materials has been developed. A Displacement Rheomete r was used to monitor the development of elasticity in setting elastom ers. The results obtained with the Displacement Rheometer were compare d to the results of the ISO test as well as those of the Controlled St ress Rheometer. Working time using the ISO method was calculated accor ding to the standard method described in the specification, while for both the Controlled Stress Rheometer and the Displacement Rheometer wo rking times were the times when initial elastic recovery was observed at 23-degrees-C. With the Displacement Rheometer the setting time is t he time when the mixed material reaches optimal elastic recovery at 37 -degrees-C. Statistical analysis with ANOVA showed that for five of th e test materials there were no differences between the three methods. For three of the materials the working time determined by the ISO meth od was significantly longer than that determined by the other two meth ods. The advantages and disadvantages of each method are discussed and the Displacement Rheometer is recommended as a supplement to the stan dard specification method.