title: Flowability of composites is no guarantee for contraction stress reduction.
abstract: OBJECTIVE
  The purpose of this study was to measure the contraction stress development of three flowable resin-composite materials (Grandio Flow, VOCO GmbH, Cuxhaven, Germany; Tetric Flow, Ivoclar Vivadent, Schaan, Liechtenstein; Filtek Supreme XT Flowable Restorative, 3M ESPE, ST. Paul, MN, USA) and an universal micro-hybrid composite resin (Filtek Z250, 3M ESPE, St. Paul, MN, USA) during photopolymerization with a halogen curing light, using a novel stress-measuring gauge.
  
  
  METHODS
  Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40s. The contraction force (N) generated during polymerization was continuously recorded for 180s after photo-initiation. Contraction stress (MPa) was calculated at 20s, 40s, 60s, 120s and 180s. Data were statistically analyzed.
  
  
  RESULTS
  Filtek Supreme XT Flowable Restorative exhibited the highest stress values compared to other materials (p<0.05), while the lowest values were recorded with Tetric Flow (p<0.05). Tetric Flow was also the only flowable composite showing stress values lower than the conventional composite Filtek Z250 (p<0.05).
  
  
  CONCLUSIONS
  Flowable composites investigated with this experimental setup showed shrinkage stress comparable to conventional resin restorative materials, thus supporting the hypothesis that the use of flowable materials do not lead to marked stress reduction and the risk of debonding at the adhesive interface as a result of polymerization contraction is similar for both type of materials.
authors.affiliation: Department of Biomedicine, Unit of Dental Sciences and Biomaterials, University of Trieste, Via Stuparich, 1, I-34125 Trieste, Italy. m.cadenaro@fmc.units.it
authors.forename: Milena
authors.initials: M
authors.lastname: Cadenaro
authors.forename: Giulio
authors.initials: G
authors.lastname: Marchesi
authors.forename: Francesca
authors.initials: F
authors.lastname: Antoniolli
authors.forename: Carel
authors.initials: C
authors.lastname: Davidson
authors.forename: Elettra
authors.initials: E
authors.lastname: De Stefano Dorigo
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Breschi
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D055115:Light-Curing of Dental Adhesives; D044367:Phase Transition; D012212:Rheology; D014783:Viscosity
chemical_list: D003188:Composite Resins; C474035:Filtek Supreme; C509998:Grandio; C452226:tetric flow composite resin