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Determining the complex modulus of alginate irreversible hydrocolloid dental material.

King S, See H, Thomas G, Swain M

Faculty of Dentistry, The University of Sydney, NSW 2006, Australia.

OBJECTIVES: The aim of the study is to investigate the visco-elastic response of an alginate irreversible hydrocolloid dental impression material during setting. METHODS: A novel squeeze film Micro-Fourier Rheometer (MFR, GBC Scientific Equipment, Australia) was used to determine the complex modulus of an alginate irreversible hydrocolloid dental impression material (Algident, ISO 1563 Class A Type 1, Dentalfarm Australia Pty. Ltd.) during setting after mixing. Data was collected every 30s for 10min in one study and every 10min for a total of 60min in another study. A high level of repeatability was observed. RESULTS: The results indicate that the MFR is capable of recording the complex shear modulus of alginate irreversible hydrocolloid for 60min from the start of mixing and to simultaneously report the changing visco-elastic parameters at all frequencies between 1Hz and 100Hz. The storage modulus shows a dramatic increase to 370% of its starting value after 6min and then reduces to 55% after 60min. The loss modulus increases to a maximum of 175% of its starting value after 10min and then reduces to 94% after 60min. SIGNIFICANCE: The MFR enables the changes in the complex modulus through the complete setting process to be followed. It is anticipated this approach may provide a better method to compare the visco-elastic properties of impression materials and assist with identification of optimum types for different clinical requirements. The high stiffness of the instrument and the use of band-limited pseudo-random noise as the input signal are the main advantages of this technique over conventional rheometers for determining the changes in alginate visco-elasticity.

Published 9 May 2008 in Dent Mater.
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