title: Analysis of strain gage method for measurement of post-gel shrinkage in resin composites.
abstract: OBJECTIVE
  The objective of this study was to refine a strain gage method for measuring polymerization contraction of resin composites and to isolate the net post-gel contraction by identifying factors contributing to the measured strains. The hypothesis to be tested was that carefully controlled strain gage measurements of composite polymerization could isolate post-gel contraction events.
  
  
  METHODS
  Composite was placed on a biaxial strain gage and light-cured. This method enabled real-time registration of the progress of shrinkage strain, corresponding to elastic modulus development. Strain from the two axes of the strain gage were averaged and plotted as a function of time. A representative curve was calculated from the mean of ten measurements. The following factors influencing the total contraction measurement were evaluated: thermal expansion of the gage, thermal expansion of the composite due to the exothermic reaction and exposure to the curing light, and adhesion of the composite to the gage. These parameters were measured so that the net deformation of the composite during polymerization could be calculated.
  
  
  RESULTS
  Parametric studies of pre-cured and photointiator-free materials confirmed the hypothesis that strain gages measure post-gel contraction. Thermal artifacts were measured and subtracted from the total strain output.
  
  
  CONCLUSIONS
  Strain gages are suitable for measuring the clinically significant phase of composite polymerization contraction.
authors.affiliation: Dept of Biomaterials and Biomechanics, Oregon Health Sciences University, Portland, Oregon, USA. sakaguch@ohsu.edu
authors.forename: R L
authors.initials: RL
authors.lastname: Sakaguchi
authors.forename: A
authors.initials: A
authors.lastname: Versluis
authors.forename: W H
authors.initials: WH
authors.lastname: Douglas
mesh_terms: D000268:Adhesiveness; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D004058:Diffusion; D004548:Elasticity; D005782:Gels; D006358:Hot Temperature; D006801:Humans; D008027:Light; D011108:Polymers / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D012822:Silicon Dioxide; D013314:Stress, Mechanical; D013499:Surface Properties; D013816:Thermodynamics; D013997:Time Factors; D014159:Transducers; D014783:Viscosity; D015040:Zirconium
chemical_list: D003188:Composite Resins; C092421:Conquest composite resin; D005782:Gels; D011108:Polymers; D019279:Resin Cements; C083568:Z100 composite resin; C078905:Bisfil; C065771:P50 composite resin; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D015040:Zirconium