title: Influence of increment thickness on microhardness and dentin bond strength of bulk fill resin composites.
abstract: OBJECTIVE
  To investigate the influence of increment thickness on Vickers microhardness (HV) and shear bond strength (SBS) to dentin of a conventional and four bulk fill resin composites.
  
  
  METHODS
  HV and SBS were determined on specimens of the conventional resin composite Filtek Supreme XTE (XTE) and the bulk fill resin composites SDR (SDR), Filtek Bulk Fill (FBF), x-tra fil (XFIL), and Tetric EvoCeram Bulk Fill (TEBF) after 24h storage. HV was measured either as profiles at depths up to 6mm or at the bottom of 2mm/4mm/6mm thick resin composite specimens. SBS of 2mm/4mm/6mm thick resin composite increments was measured to dentin surfaces of extracted human molars treated with the adhesive system OptiBond FL, and the failure mode was stereomicroscopically determined at 40× magnification. HV profiles and failure modes were descriptively analysed whereas HV at the bottom of resin composite specimens and SBS were statistically analysed with nonparametric ANOVA followed by Wilcoxon rank sum tests (α=0.05).
  
  
  RESULTS
  HV profiles (medians at 2mm/4mm/6mm): XTE 105.6/88.8/38.3, SDR 34.0/35.5/36.9, FBF 36.4/38.7/37.1, XFIL 103.4/103.9/101.9, TEBF 63.5/59.7/51.9. HV at the bottom of resin composite specimens (medians at 2mm/4mm/6mm): XTE (p<0.0001) 105.5>85.5>31.1, SDR (p=0.10) 25.8=21.9=26.0, FBF (p=0.16) 26.6=25.3=28.9, XFIL (p=0.18) 110.5=107.2=101.9, TEBF (p<0.0001) 63.0>54.9>48.2. SBS (MPa, medians at 2mm/4mm/6mm): XTE (p<0.0001) 23.9>18.9=16.7, SDR (p=0.26) 24.6=22.7=23.4, FBF (p=0.11) 21.4=20.3=22.0, x-tra fil (p=0.55) 27.0=24.0=23.6, TEBF (p=0.11) 21.0=20.7=19.0. The predominant SBS failure mode was cohesive failure in dentin.
  
  
  CONCLUSIONS
  At increasing increment thickness, HV and SBS decreased for the conventional resin composite but generally remained constant for the bulk fill resin composites.
authors.affiliation: Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Electronic address: simon.flury@zmk.unibe.ch.
authors.forename: Simon
authors.initials: S
authors.lastname: Flury
authors.affiliation: Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland.
authors.forename: Anne
authors.initials: A
authors.lastname: Peutzfeldt
authors.affiliation: Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland.
authors.forename: Adrian
authors.initials: A
authors.lastname: Lussi
mesh_terms: D003188:Composite Resins; D003804:Dentin; D006245:Hardness Tests; D033081:Shear Strength
chemical_list: D003188:Composite Resins
keywords: Dentin bonding; Depth of cure; Light-curing; Posterior restorative; Surface hardness