title: Chemical characterization and bioactivity of epoxy resin and Portland cement-based sealers with niobium and zirconium oxide radiopacifiers.
abstract: OBJECTIVE
  The purpose of this study was to characterize and to evaluate the bioactivity potential of experimental root canal sealers (ES) based on Portland cement, epoxy resin with nano- and micro-particles of niobium or zirconium oxide used as radiopacifiers in comparison to AH Plus and MTA Fillapex.
  
  
  METHODS
  Specimens of the sealers (10 mm in diameter×1 mm thick) were prepared and the radiopacity was evaluated according to ISO 6876 (2012) specifications. Characterization of the sealers was performed under the scanning electron microscope (SEM) immediately after setting and after immersion for 28 days in Hank's balanced salt solution (HBSS). In addition X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were also performed. The pH and calcium ion release were measured after 1, 7, 14, 21 and 28 days after completion of seating using a digital pH meter and an atomic absorption spectrophotometer, respectively.
  
  
  RESULTS
  The experimental sealers exhibited an average radiopacity of 2.5 mm thickness of aluminum, which was similar to MTA Fillapex (P>0.05) and inferior to AH Plus (P<0.05). AH Plus did not show bioactivity. Although the experimental sealers did not exhibit the formation of hydration product, they encouraged the deposition of crystalline spherical structures of calcium deficient phosphate. The highest pH and calcium release values were observed with the experimental sealers (P<0.01). ES-Nb-micro was the only sealer to present hexagonal shaped crystal deposition.
  
  
  CONCLUSIONS
  Novel root canal sealers based on a mixture of Portland cement, epoxy resin and radiopacifier exhibited a degree of bioactivity although no evidence of cement hydration was demonstrated on material characterization. The radiopacifier particle size had limited effect on the sealer microstructure and chemical properties.
authors.affiliation: Department of Restorative Dentistry, Araraquara Dental School, UNESP - Univ Estadual Paulista, Araraquara, SP, Brazil.
authors.forename: Raqueli
authors.initials: R
authors.lastname: Viapiana
authors.affiliation: Department of Restorative Dentistry, Araraquara Dental School, UNESP - Univ Estadual Paulista, Araraquara, SP, Brazil.
authors.forename: Juliane Maria
authors.initials: JM
authors.lastname: Guerreiro-Tanomaru
authors.affiliation: Department of Operative Dentistry, Dental Materials and Endodontics, Dental School of Bauru, University of São Paulo - USP, Bauru, SP, Brazil.
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Hungaro-Duarte
authors.affiliation: Department of Restorative Dentistry, Araraquara Dental School, UNESP - Univ Estadual Paulista, Araraquara, SP, Brazil.
authors.forename: Mário
authors.initials: M
authors.lastname: Tanomaru-Filho
authors.affiliation: Department of Restorative Dentistry, Faculty of Dental Surgery, University of Malta, Medical School, Mater Dei Hospital, Msida MSD 2090, Malta. Electronic address: josette.camilleri@um.edu.mt.
authors.forename: Josette
authors.initials: J
authors.lastname: Camilleri
mesh_terms: D002118:Calcium / Q000737:chemistry; D003287:Contrast Media; D004853:Epoxy Resins / Q000737:chemistry* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D009556:Niobium / Q000737:chemistry*; D010895:Pit and Fissure Sealants / Q000737:chemistry* / Q000494:pharmacology; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003287:Contrast Media; D004853:Epoxy Resins; D010895:Pit and Fissure Sealants; D009556:Niobium; D015040:Zirconium; C028541:zirconium oxide; D002118:Calcium
keywords: Characterization; Chemical properties; Dental materials; Mineral trioxide aggregate; Physical properties; Portland cement; Root canal sealers