Rheological Properties of Preheated Resin Based Dental Nancomposites

Objectives: Preheating of dental composites could increase their flowability and improve marginal adaptation leading to successful restorations. The purpose of this research is to evaluate the rheological properties of four preheated nanohybrid resin based composites at different temperatures (25, 37, 60 and 80^oC).
Methods: The rheological characterization of the four preheated resin based nanocomposites [Herculite Ultra (Kerr), Tetric EvoCeram (Ivoclar Vivadent), Filtek Supreme Ultra (3M) and Grandio (Voco)] are carried out using a shear rheometer that has a stainless steel parallel-plate geometry (diameter of 20 mm). The composites are placed on the lower plate, and the upper plate is lowered until it gently touched the surface of the sample at a gap distance of 0.5 mm. measurements are conducted at different temperatures (25^oC, 37^oC, 60^oC and 80^oC). The shear rate vary linearly in ramp mode from 0.1 to 10 s^{− 1}.
Results: The results demonstrate that viscosity decreases by increasing the shear rate.
Also, for all shear rates tested, viscosity varies as a function of the heating temperature in the following order: 80^oC < 60^oC < 37^oC < 25^oC.
Conclusions: Regardless of the resin composite material used, it was found that preheating the dental nanocomposites considerably improves their flowability, which provides increased mechanical bond and seal strength.