Correlation of resin viscosity and monomer conversion to filler particle size in dental composites

Objective. The viscosity of dental resin composites is important in their formulation and clinical use; it depends on the filler particle size and loading. We intend to study the viscosity and conversion of composites made of low dispersity spherical silica fillers. Methods. Experimental dental resin composites were formulated using low dispersity spherical silica particles of graded sizes (75, 150, 500, 350, 500, 1000 nm) at several loading levels with resins based on Bis-GMA and UDMA. Their rheological properties and double bond conversion were measured with a rheometer and differential scanning calorimeter, respectively. Results. The complex viscosity of the unpolymerized pastes can be fit to an extended Krieger-Dougherty equation that includes an adjustment factor to account for filler particle surface area. This relationship is also extended to estimate the degree of conversion, where the calculated or experimental viscosity is used to predict the resulting conversion. Significance. The enhanced understanding of the relationship of filler size, composite viscosity, and monomer conversion will allow improved accuracy in the prediction of the properties of dental resin composite formulations to obtain ideal viscosity for their clinical use and a high degree of conversion. (C) 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.