title: Monomer conversion and shrinkage force kinetics of low-viscosity bulk-fill resin composites.
abstract: OBJECTIVE
  To investigate the subsurface degree of conversion (DC) and shrinkage force formation of low-viscosity (flowable) bulk-fill composite materials.
  
  
  METHODS
  Three flowable bulk-fill resin composites [SureFil SDR flow (SDR; Dentsply DeTrey), Venus Bulk Fill (VB; Heraeus Kulzer) and x-tra base (XB; VOCO)] and one conventional flowable control composite material [EsthetX flow (EX; Dentsply DeTrey)] were tested. The materials were photoactivated for 20 s at an irradiance of 1170 mW/cm2 and the DC (n=5) was recorded at 0.1-, 1.5- and 4-mm depth using Fourier transform infrared spectroscopy. Shrinkage forces (n=5) of 1.5-mm-thick specimens were continuously recorded for 15 min using a custom-made stress analyzer. Data were statistically analyzed by ANOVA, Tukey's HSD and Bonferroni's post-hoc tests (α=0.05).
  
  
  RESULTS
  SDR generated the significantly lowest shrinkage forces (22.9±1.4 N), but also attained the significantly lowest DC at 1.5-mm depth (67.5±0.8%). The conventional flowable composite EX generated the significantly highest shrinkage forces (40.7±0.7 N) and reached a significantly higher DC (74.4±1.3%) compared to SDR and XB at 1.5-mm depth. The shrinkage force values of VB (29.4±1.1 N) and XB (28.3±0.6 N) were similar (p>0.05). All materials attained significantly higher DC at 4-mm depth than at the near-surface.
  
  
  CONCLUSIONS
  The tested low-viscosity bulk-fill materials show lower shrinkage force formation than a conventional flowable resin composite at high levels of degree of conversion up to 4-mm incremental thickness.
authors.affiliation: Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb , Zagreb , Croatia.
authors.forename: Danijela
authors.initials: D
authors.lastname: Marovic
authors.forename: Tobias T
authors.initials: TT
authors.lastname: Tauböck
authors.forename: Thomas
authors.initials: T
authors.lastname: Attin
authors.forename: Vlatko
authors.initials: V
authors.lastname: Panduric
authors.forename: Zrinka
authors.initials: Z
authors.lastname: Tarle
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D007700:Kinetics; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D058105:Polymerization; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D013499:Surface Properties; D014783:Viscosity
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C510276:Esthet-X Flow; D008689:Methacrylates; C553871:Surefil SDR Flow; C542517:Venus flow composite resin; C529733:X-tra fil composite resin; C111840:flowable hybrid composite
keywords: Bulk-fill materials; flowable resin composites; polymerization; shrinkage stress