title: Polymerization shrinkage kinetics and shrinkage-stress in dental resin-composites.
abstract: To investigate a set of resin-composites and the effect of their composition on polymerization shrinkage strain and strain kinetics, shrinkage stress and the apparent elastic modulus.
  
  
  
  Eighteen commercially available resin-composites were investigated. Three specimens (n=3) were made per material and light-cured with an LED unit (1200mW/cm(2)) for 20s. The bonded-disk method was used to measure the shrinkage strain and Bioman shrinkage stress instrument was used to measure shrinkage stress. The shrinkage strain kinetics at 23°C was monitored for 60min. Maximum strain and stress was evaluated at 60min. The shrinkage strain rate was calculated using numerical differentiation.
  
  
  
  The shrinkage strain values ranged from 1.83 (0.09) % for Tetric Evoceram (TEC) to 4.68 (0.04) % for Beautifil flow plus (BFP). The shrinkage strain rate ranged from 0.11 (0.01%s(-1)) for Gaenial posterior (GA-P) to 0.59 (0.07) %s(-1) for BFP. Shrinkage stress values ranged from 3.94 (0.40)MPa for TET to 10.45 (0.41)MPa for BFP. The apparent elastic modulus ranged from 153.56 (18.7)MPa for Ever X posterior (EVX) to 277.34 (25.5) MPa for Grandio SO heavy flow (GSO).
  
  
  
  The nature of the monomer system determines the amount of the bulk contraction that occurs during polymerization and the resultant stress. Higher values of shrinkage strain and stress were demonstrated by the investigated flowable materials. The bulk-fill materials showed comparable result when compared to the traditional resin-composites.
authors.affiliation: Biomaterials Science Research Group, School of Dentistry, University of Manchester, United Kingdom; College of Dentistry, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Hanan
authors.initials: H
authors.lastname: Al Sunbul
authors.affiliation: Biomaterials Science Research Group, School of Dentistry, University of Manchester, United Kingdom. Electronic address: nick.silikas@manchester.ac.uk.
authors.forename: Nick
authors.initials: N
authors.lastname: Silikas
authors.affiliation: Biomaterials Science Research Group, School of Dentistry, University of Manchester, United Kingdom; Photon Science Institute, University of Manchester, United Kingdom.
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D003188:Composite Resins; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D007700:Kinetics; D008422:Materials Testing; D058105:Polymerization
chemical_list: D003188:Composite Resins
keywords: Bulk-fill; Modulus of elasticity; Resin-composite; Shrinkage-strain; Shrinkage-stress; Strain rate