[The viscosity of Thiokol impression material during gelation (author's transl)]

Viscosity behavior of the impression materials is important property which determines the pressure and its distribution to be exerted on oral soft tissues in relation to the tray design and impression technique. The impression material, however, react to gel so fast to measure the viscosity during the reaction that it is still not completely elucidated. It would be able to seize the viscosity behavior of Thiokol impression material during the gelation unequivocally by retarding the oxidative condensation reaction using weak oxidative, lead monoxide. Based on the equal reactivity of SH groups of Thiokol liquid polymer there is no difference in statistic molecular weight distribution at any degree of the reaction between with lead monoxide and with the other oxidatives now in practical use. The viscosity measurement of the mixture of Thiokol LP-2, lead monoxide, and di-butyl phthalate was performed at the rates of shear ranged from 10(1.5) to 10(3.9) sec-1 at 20 degrees C. The viscosity of the mixture progressively increases after spatulation of the materials but yield value does not appear for the time being before setting, that is, the infinite network forming via the pendant SH groups could not take place until the most of SH groups were consumed, attributed to low concentration of poly-functional prepolymer in the liquid polymer. At early stages of the reaciton the viscosity behavior is approximately Newtonian at lower rates of shear and pseudplastic at higher rates of shear. As the reaction proceeds it becomes pseudplastic even at lower rates of shear.