[Studies of the dental methacrylic resins. (V) Effects of molecular weight and temperature on the plasticity (author's transl)].

The plasticity, the douing time, and the working time, of the mixture of powder-liquid type methacrylic resin were measured under the various circumstances of the elapsed time and the certain temperature. Six polymethyl methacrylates, whose molecular weight was prepared by mean of gamma-ray irradiation, were used as the polymer of resin, again methyl methacrylate being used as the monomer of resin. The results obtained are as follows: (1) The plasticity is reduced with the increase of the molecular weight of the polymer. (2) The plasticity, generally, is reduced with the time elapsed, but its values appear at 10 min. and 5 min. elapsed at 16 degrees C and 23 degrees C respectively. (3) The plasticities of the mixtures of polymers with 6 X 10(4), 8 X 10(4), 20 X 10(4) and 34 X 10(4) molecular weights are increased with the increase of temperature. The plasticities of the mixtures of polymers with 60 X 10(4) and 74 X 10(4) molecular weights at 0 min. time elapsed, indicate their maximum value at 30 degrees C. At 5 min. time elapsed plasticities of all mixtures indicate their maximum value at 23 degrees C. Over 5 min. time elapsed, however, the plasticity is reduced with the increase of temperature. (4) The doughing time and the working time are reduced with the increase of molecular weight of the polymer and the temperature.