title: Physico-mechanical characteristics of commercially available bulk-fill composites.
abstract: OBJECTIVE
  Bulk-fill composites have emerged, arguably, as a new "class" of resin-based composites, which are claimed to enable restoration in thick layers, up to 4mm. The objective of this work was to compare, under optimal curing conditions, the physico-mechanical properties of most currently available bulk-fill composites to those of two conventional composite materials chosen as references, one highly filled and one flowable "nano-hybrid" composite.
  
  
  METHODS
  Tetric EvoCeram Bulk Fill (Ivoclar-Vivadent), Venus Bulk Fill (Heraeus-Kulzer), SDR (Dentsply), X-tra Fil (VOCO), X-tra Base (VOCO), Sonic Fill (Kerr), Filtek Bulk Fill (3M-Espe), Xenius (GC) were compared to the two reference materials. The materials were light-cured for 40s in a 2mm×2mm×25mm Teflon mould. Degree of conversion was measured by Raman spectroscopy, Elastic modulus and flexural strength were evaluated by three point bending, surface hardness using Vickers microindentation before and after 24h ethanol storage, and filler weight content by thermogravimetric analysis. The ratio of surface hardness before and after ethanol storage was considered as an evaluation of polymer softening. Data were analyzed by one-way ANOVA and post hoc Tukey's test (p=0.05).
  
  
  RESULTS
  The mechanical properties of the bulk-fill composites were mostly lower compared with the conventional high viscosity material, and, at best, comparable to the conventional flowable composite. Linear correlations of the mechanical properties investigated were poor with degree of conversion (0.09<R<0.41) and good with filler content (R>0.8). Softening in ethanol revealed differences in polymer network density between material types.
  
  
  CONCLUSIONS
  The reduction of time and improvement of convenience associated with bulk-fill materials is a clear advantage of this particular material class. However, a compromise with mechanical properties compared with more conventional commercially-available nano-hybrid materials was demonstrated by the present work.
  
  
  CONCLUSIONS
  Given the lower mechanical properties of most bulk-fill materials compared to a highly filled nano-hybrid composite, their use for restorations under high occlusal load is subject to caution. Further, the swelling behaviour of some of the bulk-fill materials may be a reason for concern, which highlights the critical requirement for a veneering material, not only to improve aesthetic quality of the translucent material, but to reduce the impact of degradation.
authors.affiliation: School of Dentistry and Stomatology, Université catholique de Louvain, Brussels, Belgium; Institute of Condensed Matter and Nanoscience, Bio- and Soft-Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium. Electronic address: julian.leprince@uclouvain.be.
authors.forename: Julian G
authors.initials: JG
authors.lastname: Leprince
authors.affiliation: Biomaterials Unit, University of Birmingham, College of Medical and Dental Sciences, School of Dentistry, St Chad's Queensway, Birmingham B4 6NN, UK.
authors.forename: William M
authors.initials: WM
authors.lastname: Palin
authors.affiliation: Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Julie
authors.initials: J
authors.lastname: Vanacker
authors.affiliation: Department of Restorative and Esthetic Dentistry, Lebanese University, Beirut, Lebanon.
authors.forename: Joseph
authors.initials: J
authors.lastname: Sabbagh
authors.affiliation: Institute of Condensed Matter and Nanoscience, Bio- and Soft-Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium.
authors.forename: Jacques
authors.initials: J
authors.lastname: Devaux
authors.affiliation: School of Dentistry and Stomatology, Université catholique de Louvain, Brussels, Belgium; Institute of Condensed Matter and Nanoscience, Bio- and Soft-Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium.
authors.forename: Gaetane
authors.initials: G
authors.lastname: Leloup
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D000431:Ethanol / Q000737:chemistry; D006244:Hardness; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000379:methods; D008422:Materials Testing; D055595:Mechanical Phenomena; D008689:Methacrylates / Q000737:chemistry; D053761:Nanocomposites / Q000737:chemistry; D018583:Pliability; D058105:Polymerization; D012997:Solvents / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013314:Stress, Mechanical; D013818:Thermogravimetry; D013997:Time Factors; D014783:Viscosity
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C509998:Grandio; D008689:Methacrylates; D012997:Solvents; C553871:Surefil SDR Flow; C501891:Tetric EvoCeram; C488393:Venus (composite resin); C529733:X-tra fil composite resin; D000431:Ethanol
keywords: Bulk-fill; Degree of conversion; Dental composite; Elastic modulus; Flexural strength; Microhardness; Polymer network density