title: Biomimetically- and hydrothermally-grown HAp nanoparticles as reinforcing fillers for dental adhesives.
abstract: OBJECTIVE
  Differently prepared hydroxyapatite (HAp) nanoparticles were incorporated into the adhesive solution of a commercial adhesive system in order to evaluate the effect on microtensile bond strength to dentin.
  
  
  METHODS
  HAp nanoparticles (20 to 70 nm) were prepared by different processes (biomimetic and hydrothermal) and incorporated into the adhesive of the Adper Scotchbond Multi-Purpose (SBMP) system at various concentrations. Control (unfilled) and experimental groups (filled) were applied onto flat mid-coronal human dentin. Composite crowns were built up and cut into beams with a cross-sectional area of 0.65 ± 0.05 mm2. Specimens were fractured in tension and examined with a scanning electron microscope (SEM) for fractographic analysis. Microtensile bond strength (µTBS) data were analyzed using a two-way ANOVA and modified LSD test at a = 0.05. Analysis of the nanofiller distribution and ultramorphological characterization of the interface was performed by transmission electron microscopy (TEM).
  
  
  RESULTS
  HAp nanoparticle incorporation into the adhesive of SBMP significantly influenced µTBS to dentin depending on the fillers and the concentration used. A significant increase of the mechanical strength was obtained for the adhesives containing 1% (wt/vol) biomimetic and 5% hydrothermal silanized HAp particles, while the other particle fractions did not influence µTBS significantly. 10% (wt/vol) HAp particles significantly lowered the µTBS irrespective of the particle type used. TEM micrographs revealed nanoparticle dispersion through the adhesive layer but no deposition on or penetration into the hybrid layer.
  
  
  CONCLUSIONS
  HAp nanoparticle incorporation into SBMP increased bond strength to dentin by cohesively reinforcing the interface adhesive layer. At a concentration of 10% (wt/vol), nanofiller incorporation had a negative effect on bond strength.
authors.forename: Andrea
authors.initials: A
authors.lastname: Wagner
authors.forename: Renan
authors.initials: R
authors.lastname: Belli
authors.forename: Christian
authors.initials: C
authors.lastname: Stötzel
authors.forename: Andrea
authors.initials: A
authors.lastname: Hilpert
authors.forename: Frank A
authors.initials: FA
authors.lastname: Müller
authors.forename: Ulrich
authors.initials: U
authors.lastname: Lohbauer
mesh_terms: D000268:Adhesiveness; D040761:Biomimetic Materials / Q000737:chemistry*; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003460:Crystallization; D001840:Dental Bonding; D003738:Dental Cements / Q000737:chemistry*; D003804:Dentin / Q000648:ultrastructure; D017886:Durapatite / Q000737:chemistry*; D006801:Humans; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D019279:Resin Cements / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D014867:Water / Q000737:chemistry
chemical_list: D003738:Dental Cements; D008689:Methacrylates; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose; D012821:Silanes; D014867:Water; D017438:Bisphenol A-Glycidyl Methacrylate; C005044:hydroxyethyl methacrylate; D017886:Durapatite