Polymerization shrinkage of light-cured conventional and bulk-fill composites - the effect of cavity depth and post-curing
Abstract
Volumetric shrinkage (VS) of conventional, bulk-fill, and core build-up resin-based composites (RBCs) of various thickness (1-5mm) was measured using the modified bonded-disk method with confocal laser scanning microscopy. Additionally, the bottom-to-top ratio of Vickers hardness (%VH) was measured.
Conventional RBCs exhibited significantly higher VS than bulk-fill and core build-up RBCs (p<0.05). As specimen thickness increased, VS relative to volume (%VS) and difference in VS at each depth (VSdepth) decreased.
For conventional RBCs, there was a significant drop in VSdepth between 1mm and 2mm (p<0.05), and another drop was observed between 3mm and 4mm (p<0.05) where %VH decreased below 90%. For bulk-fill and core build-up RBCs, VSdepth decreased significantly between 2mm and 3mm (p<0.05), but %VH exceeded 90% even in 5mm deep cavities.
These results indicated that post-curing contributed to lower shrinkage in deeper layers, and that conventional RBCs were not adequately polymerized at the depth of over 3mm.