Effect of resin-composite filler particle size and shape on shrinkage-strain.

The aim of this study was to investigate the effect of variations in filler particle size and shape on the polymerization shrinkage-strain kinetics of resin-composites. A model series of 12 VLC resin-composites were studied. The particulate dispersed phase volume fraction was 56.7%: these filler particles were systematically graded in size, and further were either spherical or irregular. The bonded disk method was used to determine shrinkage-strain kinetics. Displacement was recorded following 40s irradiation (600mW/cm(2)) at 23 degrees C (n=3). All data were captured for 60min and the final shrinkage-strain calculated. For materials with spherical filler, shrinkage-strain was 2.66% (SD 0.18) for those with irregular filler it was 2.89% (SD 0.11). These differences were statistically significant (p<0.001): the Scheffé test identified two subsets, those with irregular filler (including materials with a multimodal mix) and those with spherical filler (including materials with a multimodal mix). Additionally, there was a trend for higher shrinkage-strain values with decreasing filler particle size which was apparent for both those composites with spherical filler particles and those with irregular filler particles. For irregular filler particles, linear regression gave a high correlation (r(2)=0.99). Statistically significant differences were identified in the shrinkage behavior of resin-composites with differing filler size and shape.