title: Effect of resin-composite filler particle size and shape on shrinkage-stress.
abstract: OBJECTIVE
  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 40s 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: School of Dentistry, University of Manchester, UK. julian.satterthwaite@manchester.ac.uk
authors.forename: Julian D
authors.initials: JD
authors.lastname: Satterthwaite
authors.forename: Amit
authors.initials: A
authors.lastname: Maisuria
authors.forename: Karin
authors.initials: K
authors.lastname: Vogel
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000379:methods*; D006244:Hardness / Q000528:radiation effects; D008422:Materials Testing; D010316:Particle Size; D058105:Polymerization / Q000528:radiation effects
chemical_list: D003188:Composite Resins; D003764:Dental Materials