title: Intrinsic 'soft-start' polymerisation shrinkage-kinetics in an acrylate-based resin-composite.
abstract: OBJECTIVE
  A resin-composite based on multi-acrylate monomers was to be evaluated for any differences in the setting shrinkage-strain kinetics relative to more conventional formulations based on di-methacrylate monomers.
  
  
  METHODS
  Four resin-composites were examined for shrinkage-strain over time periods up to 60 min, from initial irradiation, using a 'bonded disk' measurement device. One material was evaluated with a standard and also a two-level (low to high) blue light irradiation regime. The test material (Solitaire), and the other two controls were studied under fixed-(normal) level irradiation by blue light. Measurements were made at 23 and 37 degrees C.
  
  
  RESULTS
  The low-high light irradiation applied to one di-methacrylate composite led to a highly significant (p < 0.001) reduction in shrinkage-strain to a minimal level for the initial 0.2 min. The fixed-level irradiation with the acrylate-composite also led to a formally identical, but intrinsic 'soft-start' shrinkage-delay regime; significant at p < 0.001. Di-methacrylate composites under the same fixed-level light regime did not exhibit shrinkage delay. Both di-methacrylate and multi-acrylate composites exhibited increases in the range 18-29% in final equilibrium shrinkage-strain by increase of specimen temperature.
  
  
  CONCLUSIONS
  Reductions in the rate of initial shrinkage of light-cured restoratives may have clinical benefits for restoration bond-integrity nearly as important as reductions in the final equilibrium shrinkage-strain. This may be achieved either by special light irradiation regimes (low to high, or ramped) or in favourable cases by novel monomer-composite formulations and setting chemistry (e.g. Solitaire). The bonded disk shrinkage-strain measurement technique is suitable for the elucidation of such rapid kinetic and temperature-dependent events during photo-polymerisation setting processes.
authors.affiliation: Biomaterials Science Unit, University of Manchester Dental School, UK. david.watts@man.ac.uk
authors.forename: D C
authors.initials: DC
authors.lastname: Watts
authors.forename: A
authors.initials: A
authors.lastname: al Hindi
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D007700:Kinetics; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry*; D018709:Statistics, Nonparametric
chemical_list: D000180:Acrylic Resins; C084111:Charisma composite resin; D003188:Composite Resins; D011108:Polymers; D011109:Polymethacrylic Acids; C113049:Solitaire composite resin; C090969:Tetric