title: Raman spectroscopic assessment of degree of conversion of bulk-fill resin composites--changes at 24 hours post cure.
abstract: OBJECTIVE
  The aim of this study was to determine degree of conversion (DC) of solid and flowable bulk-fill composites immediately and after 24 hours and investigate the variations of DC at surface and depths up to 4 mm.
  
  
  METHODS
  Eight bulk-fill composites (Tetric EvoCeram Bulk Fill [shades IVA and IVB], Quixfil, X-tra fil, Venus Bulk Fill, X-tra Base, SDR, Filtek Bulk Fill) were investigated, and two conventional composites (GrandioSO, X-Flow) were used as controls. The samples (n = 5) were cured for 20 seconds with irradiance of 1090 mW/cm(2). Raman spectroscopic measurements were made immediately after curing on sample surfaces and after 24 hours of dark storage at surface and at incremental depths up to 4 mm. Mean DC values were compared using repeated measures analysis of variance (ANOVA) and t-test for dependent samples.
  
  
  RESULTS
  Surface DC values immediately after curing ranged from 59.1%-71.8%, while the 24-hour postcure values ranged from 71.3%-86.1%. A significant increase of DC was observed 24 hours post cure for all bulk-fill composites, which amounted from 11.3% to 16.9%. Decrease of DC through depths up to 4 mm varied widely among bulk-fill composites and ranged from 2.9% to 19.7%.
  
  
  CONCLUSIONS
  All bulk-fill composites presented a considerable 24-hour postcure DC increase and clinically acceptable DC at depths up to 4 mm. Conventional control composites were sufficiently cured only up to 2 mm, despite significant postcure polymerization.
authors.forename: M
authors.initials: M
authors.lastname: Par
authors.forename: O
authors.initials: O
authors.lastname: Gamulin
authors.forename: D
authors.initials: D
authors.lastname: Marovic
authors.forename: E
authors.initials: E
authors.lastname: Klaric
authors.forename: Z
authors.initials: Z
authors.lastname: Tarle
mesh_terms: D003188:Composite Resins / Q000627:therapeutic use*; D055117:Curing Lights, Dental; D006801:Humans; D008689:Methacrylates / Q000627:therapeutic use; D058105:Polymerization; D013059:Spectrum Analysis, Raman; D013997:Time Factors
chemical_list: D003188:Composite Resins; D008689:Methacrylates; C501891:Tetric EvoCeram; C488393:Venus (composite resin); C529733:X-tra fil composite resin