Rheological properties of endodontic sealers: the effect of time, temperature, and composition

This study was aimed to investigate the effect of different parameters such as shear rate, temperature, and time on the viscosity of four endodontic sealers. Furthermore, the effect of variations in powder to liquid ratio of two powder/liquid sealers upon their viscosity was evaluated. The tested sealers were AH Plus, Endofill, AH 26, and Epiphany self-etch (SE) sealer. As all of the tested sealers contain particles of resinous composites; shear thinning and some time-dependency of viscosity are expected. Therefore, steady shear viscosity and thixotropy behavior were assessed. The samples were examined at 25 and 37?°C with the shear rate ranged from 0.0001 to 100?s^?1. All sealers almost exhibited shear thinning behavior. At both temperatures of 25 and 37?°C, the viscosities of sealers were at the same order and ranked from the highest to the lowest as follows: Epiphany SE, AH Plus, AH 26, and Endofill. The samples with higher powder to liquid ratio of 3:1 exhibited higher viscosity compared to 2:1 ratio in both tested temperatures. With the exception of Epiphany SE and AH 26 (at shear rate less than 1?s^?1), viscosity of all sealers decreased with increasing temperature from 25 to 37?°C. All sealers exhibited time-dependent viscosity characteristics at the two examined temperatures.