Gel strength and rate of gelation of soft polymers

A rheometer was used to characterize the gelation rate of six commercial short- to medium-term (chairside intra-oral gelation) denture soft-lining materials. Shear puncture force was measured from one to 60 days for six short- to medium-term materials as well as for three heat-cured (polymerizable) materials. The observed increase in puncture force with age of the specimen was considered to be a function of increased polymer chain entanglement and/or loss of plasticizer. Reduction in puncture force with age occurred for some materials as a result of hydration of the polymer gel. Rheometer setting time (gelation rate) and puncture force values for the intra-oral gelation materials were influenced by the quantity of ethyl alcohol present in the mixing liquid. In general, the higher the level of ethyl alcohol, the shorter the gelation time and the stronger the gel. The characterization of the properties may help develop improved prosthodontic treatment procedures, and allow better management of soft-tissue recovery following trauma.