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

Objectives: The aim of this study was to investigate the effect of variations in filler particle size and shape on the polymerization shrinkage-stress kinetics of resin-composites. Methods: 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. A Bioman instrument (cantilever beam method) was employed to determine the shrinkage-stress kinetics following 40 s irradiation (600 mW/cm 2) at 23 °C (n = 3). All data were captured for 60 min and the final shrinkage-stress calculated. Results: Shrinkage-stress varied between 3.86 MPa (SD 0.14) for S3 (spherical filler particles of 500 nm) and 8.44 MPa (SD 0.41) for I1 (irregular filler particles of 450 nm). The shrinkage-stress values were generally lower for those composites with spherical filler particles than those with irregular filler particles. The differences in shrinkage-stress with filler particle size and shape were statistically significant (p <0.001). Significance: Composites with spherical filler particles exhibit lower shrinkage-stress values compared to those with irregular filler particles. Shrinkage-stress and shrinkage-stress rate vary in a complex manner with variations in the size of the dispersed phase particles: a hypothesized explanation for the effect of filler particle size and shape is presented. © 2012 Academy of Dental Materials.