Rheology of urethane dimethacrylate and diluent formulations

Objective: The purpose of this study was to measure the viscosity of resin formulations and investigate the relationship between diluent percentage and temperature. Methods: Resin formulations were prepared using UDMA and either TEGDMA or HEMA, or HPMA, as diluents at different percentages. Viscosities were obtained with a Bohlin Rheometer at 23°C for all formulations, and at 37 and 60°C for selected formulations. Results: The viscosity of the formulations exhibited Newtonian behaviour and decreased as the percentage of the diluent monomer increased, especially up to 40% of diluent. Linear regressions relating log(viscosity) and mass percent diluent, were obtained in the range 20-80% diluent. Viscosity also decreased as the temperature increased. Activation energies were calculated from Arrhenius plots, and ranged from 16.2-23.4 kJ mol-1. Significance: The viscosity of the resins controls the flow properties and thus has a significant effect on the deployment of the respective monomers. © 1999 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.