title: Contraction stress of low-shrinkage composite materials assessed with different testing systems.
abstract: OBJECTIVE
  The contraction stress of a silorane-based material and a new low-shrinkage nanohybrid composite were compared to three conventional dimethacrylate-based resin composites using two different measuring systems. It was hypothesized that the silorane-based material and the low-shrinkage nanohybrid composite would exhibit lower contraction stress than dimethacrylate-based composites irrespective of measuring system.
  
  
  METHODS
  The materials tested were Filtek Silorane LS (3M ESPE), Venus Diamond (Heraeus Kulzer), Tetric EvoCeram (Ivoclar Vivadent), Quixfil (Dentsply DeTrey), and Filtek Z250 (3M ESPE). Shrinkage stress was assessed using a stress-strain analyzer consisting of two opposing attachments, one connected to a load sensor and the other fixed to the device, or a system fixed to a universal testing machine with an extensometer as a feedback system. All specimens were light-cured with 20 J/cm(2); the contraction force (N) generated during polymerization was continuously recorded for 300 s. Contraction stress (MPa) was calculated at both 40 s and 300 s. Data were statistically analyzed by three-way ANOVA and Tukey's post hoc test (alpha=0.05).
  
  
  RESULTS
  Venus Diamond exhibited the lowest stress under both experimental conditions. Stress values scored as follows: Venus Diamond<Tetric EvoCeram<Filtek Silorane LS<Quixfil<Filtek Z250 (p<0.05). Stress values measured with the stress-strain analyzer were significantly lower than those measured with the universal testing machine with feedback.
  
  
  CONCLUSIONS
  The hypothesis was partially rejected because only Venus Diamond exhibited the lowest stress values among the tested materials. Contraction stress was higher for all composites when measured in a test system with a feedback. This study confirms that simply reducing the shrinkage does not ensure reduced stress development in composites.
authors.affiliation: Department of Biomedicine, Unit of Dental Sciences and Biomaterials, University of Trieste, Trieste, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Marchesi
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Breschi
authors.forename: Francesca
authors.initials: F
authors.lastname: Antoniolli
authors.forename: Roberto
authors.initials: R
authors.lastname: Di Lenarda
authors.forename: Jack
authors.initials: J
authors.lastname: Ferracane
authors.forename: Milena
authors.initials: M
authors.lastname: Cadenaro
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis / Q000379:methods*; D017220:Dentin-Bonding Agents; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing / Q000379:methods; D008689:Methacrylates; D053761:Nanocomposites; D062047:Silorane Resins; D012833:Siloxanes
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; D008689:Methacrylates; D062047:Silorane Resins; D012833:Siloxanes