title: Bulk-fill resin composites: polymerization properties and extended light curing.
abstract: OBJECTIVE
  The aim was to evaluate the polymerization properties of bulk-fill resin composites using two different light-curing protocols, in terms of degree of conversion (%DC), Vickers hardness (HV), polymerization volume shrinkage (PVS) and polymerization shrinkage stress (PSS) and compare them to conventional condensable and flowable resin composites.
  
  
  METHODS
  Filtek BulkFill (FBF, 3MESPE, Germany), SDR (Dentsply, Germany), TetricEvoCeram BulkFill (TBF, Ivoclar-Vivadent, Liechtenstein), Venus BulkFill (VBF, Heraeus, Germany), X-traBase (XTB, Voco, Germany), FiltekZ250 (3MESPE) and Filtek Supreme XTE Flowable (FSF, 3MESPE) were investigated. Light-curing was performed for 30 s or according to manufacturers' instructions (1200 mW/cm2, Bluephase20i, Ivoclar-Vivadent). For %DC and HV, discs (n=5) of 2 or 4 mm in thickness were prepared and stored for 24h in distilled water at 37°C. %DC was determined by FTIR-ATR-spectroscopy. %DC and HV were measured at the top and bottom of the specimens. PVS was measured using Archimedes method (n=6). PSS measurements (n=10) were carried out using 5 mm diameter PMMA rods as bonding substrates with a specimen height of 1 mm in a universal testing machine. Data were analyzed using one- and two-way ANOVA (α=0.05).
  
  
  RESULTS
  Except Z250 in the manufacturers' light-curing mode, all materials showed no significant inferior %DC at 4 mm thickness. When light cured for 30 s Z250 had no significant differences in %DC at 2 or 4 mm when compared to top. FBF, TBF, FSF and Z250 displayed significant reduced HV at 4 mm in both curing modes. Z250 and TBF showed the lowest PVS and FSF the highest PSS in both curing modes.
  
  
  CONCLUSIONS
  All investigated bulk-fill composites obtained sufficient polymerization properties at 4 mm depth. Enhanced curing time improved the investigated polymerization properties of bulk-fills and Z250.
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, Friedrich-Alexander University of Erlangen-Nuernberg, Glueckstr. 11, D-91054 Erlangen, Germany. Electronic address: zorzin@dent.uni-erlangen.de.
authors.forename: José
authors.initials: J
authors.lastname: Zorzin
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, Friedrich-Alexander University of Erlangen-Nuernberg, Glueckstr. 11, D-91054 Erlangen, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Maier
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, Friedrich-Alexander University of Erlangen-Nuernberg, Glueckstr. 11, D-91054 Erlangen, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Harre
authors.affiliation: Department of Materials Science and Engineering, Institute of Glass and Ceramics, Friedrich-Alexander University of Erlangen-Nuernberg, Martensstr. 5, D-91058 Erlangen, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Fey
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, Friedrich-Alexander University of Erlangen-Nuernberg, Glueckstr. 11, D-91054 Erlangen, Germany.
authors.forename: Renan
authors.initials: R
authors.lastname: Belli
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, Friedrich-Alexander University of Erlangen-Nuernberg, Glueckstr. 11, D-91054 Erlangen, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Lohbauer
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, Friedrich-Alexander University of Erlangen-Nuernberg, Glueckstr. 11, D-91054 Erlangen, Germany.
authors.forename: Anselm
authors.initials: A
authors.lastname: Petschelt
authors.affiliation: Dental Clinic 1 - Operative Dentistry and Periodontology, Friedrich-Alexander University of Erlangen-Nuernberg, Glueckstr. 11, D-91054 Erlangen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Taschner
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D006244:Hardness; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D058105:Polymerization; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003188:Composite Resins
keywords: Bulk-fill; Degree of conversion; FTIR spectroscopy; Irradiance; Resin composites; Shrinkage stress; Vickers hardness; Volume shrinkage