Physical Property Evaluation of Elastomeric Impression Materials by Equotip Hardness Tester

Abstract

When taking a dental impression, it is necessary to decide the optimal time for removing the impression material. The removing time is important not only for accurate taking of the impression without any deformity, but also for minimizing the duration of the procedure. Until now, the decision about removing the impression material has been made on the basis of either the time recommended by the maker of the impression material, or material hardness determined by palpation by the operator. However, decisions made in such a way do not give optimal results, and therefore improved measurement methods and decision criteria are needed. In the present study, we evaluated the potential applicability of the Equotip hardness tester (Proceq, Switzerland), which is not only commonly used for measuring metallic and rock materials in industry, but also suitable for non-destructive and directiondefined measurement of small materials, by using the Equo effect. For this purpose, we prepared four commonly clinically used materials of three different types, and determined the correlation between their hardness that was measured after 60 minutes by the Equotip hardness tester and expressed as a L-value, and Young's modulus that was measured under the same experimental conditions. In addition, the hardness of impression materials was measured in real time by the tester, and the values compared with those measured by the recently used rheometer. The results obtained were as follows. 1) There was a significant correlation between Young's modulus and L-values, measured in the injection as well as putty type of dental elastomeric impression materials. 2) Correlation curves between the values measured by the rheometer and L-values could be obtained. 3) The load of the spring used in the rheometer markedly affected the final measured values. In contrast, the effect of the load of Equotip hardness tester on the final measured values was minimal. 4) It was concluded that the Equotip hardness tester is useful for the real time measurement of elastomeric properties of dental elastomeric impression materials. In addition, the measurement of L-values should be helpful for determining the optimal time for removing different dental elastomeric impression materials.