title: A comparative evaluation of polymerization stress data obtained with four different mechanical testing systems.
abstract: OBJECTIVE
  The null hypothesis was that mechanical testing systems used to determine polymerization stress (σ(pol)) would rank a series of composites similarly.
  
  
  METHODS
  Two series of composites were tested in the following systems: universal testing machine (UTM) using glass rods as bonding substrate, UTM/acrylic rods, "low compliance device", and single cantilever device ("Bioman"). One series had five experimental composites containing BisGMA:TEGDMA in equimolar concentrations and 60, 65, 70, 75 or 80 wt% of filler. The other series had five commercial composites: Filtek Z250 (3M ESPE), Filtek A110 (3M ESPE), Tetric Ceram (Ivoclar), Heliomolar (Ivoclar) and Point 4 (Kerr). Specimen geometry, dimensions and curing conditions were similar in all systems. σ(pol) was monitored for 10 min. Volumetric shrinkage (VS) was measured in a mercury dilatometer and elastic modulus (E) was determined by three-point bending. Shrinkage rate was used as a measure of reaction kinetics. ANOVA/Tukey test was performed for each variable, separately for each series.
  
  
  RESULTS
  For the experimental composites, σ(pol) decreased with filler content in all systems, following the variation in VS. For commercial materials, σ(pol) did not vary in the UTM/acrylic system and showed very few similarities in rankings in the others tests system. Also, no clear relationships were observed between σ(pol) and VS or E.
  
  
  CONCLUSIONS
  The testing systems showed a good agreement for the experimental composites, but very few similarities for the commercial composites. Therefore, comparison of polymerization stress results from different devices must be done carefully.
authors.affiliation: Department of Dental Materials, School of Dentistry, University of São Paulo, São Paulo, Brazil.
authors.forename: Flávia
authors.initials: F
authors.lastname: Gonçalves
authors.forename: Leticia C
authors.initials: LC
authors.lastname: Boaro
authors.forename: Jack L
authors.initials: JL
authors.lastname: Ferracane
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Braga
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation / Q000379:methods*; D055119:Elastic Modulus; D008422:Materials Testing / Q000295:instrumentation*; D058105:Polymerization
chemical_list: D003188:Composite Resins