Factors that influence the setting characteristics of encapsulated glass ionomer cements.

The slow rate of the setting reaction of glass ionomer cements (GICs) is one of the problems associated with their clinical use. The manufacturers of these materials suggest that increasing the mixing time will increase the rate of reaction and it was the purpose of this study to investigate the limits of this relationship. The method used to monitor the setting reaction with Differential Thermal Analysis (DTA). The results obtained using DTA were compared with those obtained using the ISO penetrometer method as defined in the ISO standard for water-based cements, ISO 9917:1991E. It was shown that increasing the mixing time of cements did not significantly reduce the setting time (P > 0.05). Under the conditions of the study it was only possible to measure a working time for the Chemfil II (and then only if it was mixed for less than 12 s). Storing the capsules at 4 degrees C did enable a working time to be measured using the DTA for all the materials, however these storage conditions also produced a significant increase in the setting time which would be undesirable to the clinician. The penetrometer method underestimated the duration of the setting reaction by up to 32% compared with the DTA method. However it was a quick and reproducible method of measuring setting time and as such may still be an appropriate method for use in the ISO standards.