title: Curing behaviour of high-viscosity bulk-fill composites.
abstract: OBJECTIVE
  This study aimed to assess the effect of curing conditions--exposure time, mode, energy density, and exposure distance--on the mechanical properties of high-viscosity bulk-fill resin-based composites (RBCs) measured at simulated clinical relevant filling depths.
  
  
  METHODS
  Three high-viscosity bulk-fill RBCs were investigated by assessing the variation in micromechanical properties in 200μm steps (Vickers hardness [HV] and indentation modulus [E]) within simulated 6-mm deep fillings (n=5) polymerized under 16 different curing conditions. The exposure duration was 5, 20, and 40s in the standard power mode; 3, 4, and 8s in the high power mode; and 3 and 6s in the plasma mode; the exposure distance was 0 and 7mm. Energy density ranged from 2.63 to 47.03J/cm(2). Measurements were performed after 24h of storage in distilled water at 37°C. The depth of cure (DOC) was calculated as the 80% hardness drop-off.
  
  
  RESULTS
  The results were compared using one- and multiple-way ANOVAs and Tukey's HSD post hoc test (α=0.05). The effect of the parameter material was significant and strong on all measured properties (p<0.05, partial eta-squared ηP(2)=0.492 for E, 0.562 for HV, and 0.087 for DOC). Energy density exerted the strongest influence on the measured properties in all materials, whereas the influence of the exposure distance was strong on DOC, low on E and not significant on HV. The high-viscosity bulk-fill RBCs respond heterogeneously to variations in curing conditions.
  
  
  CONCLUSIONS
  A lower energy density limit was identified, allowing for a 4mm material bulk placement (5.88J/cm(2) for EvoCeram Bulk Fill, 7.0J/cm(2) for x-tra fil, and 23.51J/cm(2) for SonicFill). This limit increased to 47.03J/cm(2) for a 5mm bulk placement, as claimed for SonicFill. To maintain mechanical properties in depth, however, an energy density of at least 23.51J/cm(2) is recommended for EvoCeram Bulk Fill and x-tra fil and 47.03J/cm(2) for SonicFill, respectively. This energy density should be achieved at moderate irradiance and increased curing time.
  
  
  CONCLUSIONS
  An exposure time of 20s at moderate irradiance is recommended for all materials for a 4 mm bulk placement.
authors.affiliation: Department of Operative/Restorative Dentistry, Periodontology and Pedodontics, Ludwig-Maximilians-University of Munich, Goethestr. 70, 80336 Munich, Germany. Electronic address: nilie@dent.med.uni-muenchen.de.
authors.forename: Nicoleta
authors.initials: N
authors.lastname: Ilie
authors.affiliation: Department of Operative/Restorative Dentistry, Periodontology and Pedodontics, Ludwig-Maximilians-University of Munich, Goethestr. 70, 80336 Munich, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Stark
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000379:methods; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D058626:Plasma Gases / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D058626:Plasma Gases; D011109:Polymethacrylic Acids; C501891:Tetric EvoCeram; C529733:X-tra fil composite resin; D014867:Water; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; C074277:ethoxylated bis-phenol A dimethacrylate; D017438:Bisphenol A-Glycidyl Methacrylate
keywords: Bulk-fill resin-based composites; Energy density; Hardness; Irradiance; Modulus of elasticity