Rheological properties of resin composites according to variations in composition and temperature

To study the effect of compositional variables and temperature (25°C and 37°C) on the rheological properties of contemporary resin composites.

Fourteen commercial resin composites with different resin matrices of Bis-GMA and TEGDMA, different filler loading (41-65, v/v) and particle sizes (ranging 5nm to 20μm) were studied using a parallel plate rheometer. Shear sweep measurements were made to determine each composite's viscosity over the angular frequency range of ω=10(-4)-10(2)rad/s. Data were analyzed using one way ANOVA, Bonferroni post hoc and t-independent tests (p<0.05).

All composites exhibited viscosity reducing with shear rate (pseudoplasticity). Viscosity averages were calculated over the shear rate range. These viscosities increased as the percentage of filler loading (by volume) increased ranging between 0.05-349.33kPas at 25°C and 0.03-132.00kPas at 37°C. Filtek Supreme XTE exhibited the highest viscosity at both temperatures (p<0.05). Filtek Bulk Fill on the other hand, showed the lowest viscosity at both temperatures (p<0.05). Viscosity significantly decreased with the increase in the temperatures for all materials (p<0.05). The reduction ranged from 40.8% (for Venus Diamond Flow) to 92.2% (for Spectrum TPH3).

There was a considerable variation in the resin composite viscosities measured at 25°C as an average value for shear-rate sweep. The factor between the least and highest viscosities was about 7000. The formulation differences that led to such a great variation were primarily: (i) volume fraction of fillers and (ii) particle size, the latter influencing total particle surface area. Rheological properties such as viscosity are key parameters influencing perceived differences in handling behavior of resin composites.