Setting stresses in composites for two different curing modes.

As a continuation of a study into the development of the polymerization shrinkage stress of chemically initiated composites (CC), the development of the polymerization shrinkage stress of light-initiated composites (LC) in relation to the configuration-factor was determined. During setting, the LC composites generated a higher polymerization shrinkage stress, developed higher cohesive strength to resist this stress and showed less flow than their CC analogues. Trying to find a comprehensive explanation for the differences in behavior of stress development in LC and CC composites, the effect of mixing-in of porosity was also investigated on LC composites. Mixing-in of porosity slowed down and decreased the shrinkage stress development. This was attributed to either oxygen inhibition due to admixed air or to an increase of free surface from the presence of pores within the bulk of the composite.