We have shown that Computed Microtomography (CMT) is able to map the internal distribution of the filler particles in ProTaperTM, LexiconTM, and GuttaCoreTM materials, and explain the differences in their tensile and ductility properties, prior to mechanical manipulation. Working of uncrosslinked ProTaperTM and LexiconTM samples resulted in a five-fold increase in ductility and the tensile elongation at break. CMT mapping of the internal structure showed that large, periodic, striations formed across the interior of the sample corresponding to the formation of regions with low filler particle density. In contrast to metals which harden upon working, this migration of particles away from the high stress regions resulted in stress softening, as predicted by the Mullins effect. The results indicate that CMT is an effective method for 3-D visualization of the internal particle distribution which permits the determination of structure-property relationships and facilitates the design of new materials.
Keywords: Computed microtomography; Mullins effect; Nanocomposite materials; Particle redistribution; Stress softening.