Dynamic viscoelastic properties in torsion of four commercially available resins for crown and bridge.

In order to clarify the viscoelastic properties of four commercial resins for crown and bridge, the dynamic shear modulus (G'), Knoop hardness (KHN), filler content, quantity of unreacted substance and thermal expansion were measured. The results were as follows. The G' (37 degrees C) of each material ranged from 2.61-11.1 GPa, and gradually decreased with increasing temperature. KHN (23 degrees C) ranged from 29.4 to 120, and the most significant correlation (0.999) was found between G' and KHN. Of the relationship among G', filler content and unreacted substance, there was a highly significant correlation (0.980) between G' and filler content. The coefficient of linear-thermal expansion (alpha) also ranged from 17.9-65.0 x 10(-6)/degree C (25-60 degrees C), and the correlation (-0.961) between G' and alpha was meaningful. It can be presumed that the temperature dependence of G' is closely connected with the specific volume of each material, together with an increase in temperature.