Investigation of the mechanical performance of young glass-ionomer cement using dynamic mechanical analysis

Glass-ionomer (or more correctly, glass polyalkenoate) cements have wide applications in dentistry. This paper reports an investigation using dynamic mechanical analysis (DMA) on the setting of typical conventional glass-ionomer cements of varying age. Rectangular section cement samples were stored for four weeks in distilled water at 37 degrees C before being tested. The experimental procedure involved the clamping of the sample in tensile mode and heating through a 37-95 degrees C temperature range in water. A general behavioral trend was followed where all the samples showed increased flexibility with rise in temperature until a "threshold" temperature was reached, whereupon sudden tensile stiffening was observed. The temperature at which the stiffening took place was dependent on the age of the cement, and was interpreted in terms of the secondary cement forming reactions of silica and phosphate. The younger samples stiffened at significantly lower temperatures than the older ones. The activated nature of glass-ionomer setting chemistry meant that younger cements could be prematurely aged through heating. Differential scanning calorimetry was used to study the effect of heating on the distribution of loosely bound water in the cements that had, and had not been exposed to a DMA cycle. Most notably, it was seen that the DMA process did not affect the water in the matrix. This leant further credence to the hypothesis that the stiffening observed during the DMA heating process was caused by accelerated network formation.