PALS probing of photopolymerization shrinkage in densely packed acrylate-type dental restorative composites.

Background: Using positron annihilation lifetime spectroscopy (PALS), microstructural changes in commercial dental restorative composites under light-curing polymerization were identified as a modification in mixed positron/Ps trapping, where the decay of positronium (Ps; the bound state of positrons and electrons) is caused by free-volume holes mainly in the polymer matrix, and positron trapping is defined by interfacial free-volume holes in a mixed filler-polymer environment. In loosely packed composites with a filler content of <70-75%, this process was related to the conversion of Ps-to-positron trapping.

Objectives: To disclose such peculiarities in densely packed composites using the example of he commercially available acrylate-based composite ESTA-3® (ESTA Ltd.