title: Long Term Degree of Conversion of two Bulk-Fill Composites.
abstract: To investigate the long-term development of the post-cure degree of conversion (DC) for two flowable bulk-fill composites.
  
  
  
  Tetric EvoFlow Bulk Fill (TEFBF) and SDR were chosen due to their distinct compositional modifications that enable the decrease of translucency during polymerization and lower polymerization rate, respectively. DC was assessed using FT-Raman spectroscopy at the post-cure times of 0 h, 24 h, 7 d and 30 d. The post-cure behavior was analyzed by a mixed model ANOVA and partial eta-squared statistics.
  
  
  
  DC ranged from 61.3-81.1% for TEFBF and 58.9-81.6% for SDR. The initial (0 h) DC was significantly lower at a depth of 4 mm than at a depth of 1 mm (4.9% for SDR and 11.1% for TEFBF). Both materials presented a significant post-cure DC increase, up to 16.4% for TEFBF and 20.6% for SDR. The post-cure DC development was depth-dependent for TEFBF, but not for SDR. The post-cure DC increase was observed during 24 h for TEFBF and 7 d for SDR.
  
  
  
  Some of the bulk-fill composites may need longer times than the commonly accepted 24 h to reach the final conversion. This may be attributed to their compositional modifications that are mostly undisclosed by manufacturers. Our findings imply that investigations commonly performed 24 h post-cure may underestimate some of the bulk-fill composite properties, if these are affected by the slowly-developing DC. Reactive species may also be available for leaching out of the restoration during an extended time period, with possible implications on biocompatibility.
authors.affiliation: Private Dental Practice, Dankovecka 9, Zagreb, Croatia.
authors.forename: Matej
authors.initials: M
authors.lastname: Par
authors.affiliation: Private Dental Practice, Dankovecka 9, Zagreb, Croatia.
authors.forename: Matea
authors.initials: M
authors.lastname: Lapas-Barisic
authors.affiliation: Department of Physics and Biophysics, School of Medicine, University of Zagreb, Salata 3b, Zagreb, Croatia; Center of Excellence for Advanced Materials and Sensing Devices, Research Unit New Functional Materials, Bijenicka cesta 54, Zagreb, Croatia.
authors.forename: Ozren
authors.initials: O
authors.lastname: Gamulin
authors.affiliation: Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Gunduliceva 5, Zagreb, Croatia.
authors.forename: Vlatko
authors.initials: V
authors.lastname: Panduric
authors.affiliation: Private Dental Practice, Dankovecka 9, Zagreb, Croatia.
authors.forename: Nika
authors.initials: N
authors.lastname: Spanovic
authors.affiliation: Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Gunduliceva 5, Zagreb, Croatia.
authors.forename: Zrinka
authors.initials: Z
authors.lastname: Tarle
keywords: Composite Resins; Polymerization; Spectrum Analysis, Raman