title: Impedance changes during setting of amorphous calcium phosphate composites.
abstract: To investigate the electrical properties of experimental light-curable composite materials based on amorphous calcium phosphate (ACP) with the admixture of silanized barium glass and silica fillers.
  
  
  
  Short-term setting was investigated by impedance measurements at a frequency of 1kHz, while for the long-term setting the impedance spectra were measured consecutively over a frequency range of 0.05Hz to 1MHz for 24h. The analysis of electrical resistivity changes during curing allowed the extraction of relevant kinetic parameters. The impedance results were correlated to the degree of conversion assessed by Raman spectroscopy, water content determined by gravimetry, light transmittance measured by CCD spectrometer and microstructural features observed by scanning electron microscopy.
  
  
  
  ACP-based composites have shown higher immediate degree of conversion and less post-cure polymerization than the control composites, but lower polymerization rate. The polymerization rate assessed by impedance measurements correlated well with the light transmittance. The differences in the electrical conductivity values observed among the materials were correlated to the amount of water introduced into composites by the ACP filler. High correlation was found between the degree of conversion and electrical resistivity. Equivalent circuit modeling revealed two electrical contributions for the ACP-based composites and a single contribution for the control composites.
  
  
  
  The impedance spectroscopy has proven a valuable method for gaining insight into various features of ACP-based composites. Better understanding of the properties of ACP-based composites should further the development of these promising bioactive materials.
authors.affiliation: Private Dental Practice, Dankovecka 9, 10040 Zagreb, Croatia. Electronic address: mpar@inet.hr.
authors.forename: Matej
authors.initials: M
authors.lastname: Par
authors.affiliation: Glass Laboratory, Ruđer Bošković Institute, Zagreb, Croatia. Electronic address: ana.santic@irb.hr.
authors.forename: Ana
authors.initials: A
authors.lastname: Šantić
authors.affiliation: Department of Physics and Biophysics, School of Medicine, University of Zagreb, Salata 3b, Zagreb, Croatia. Electronic address: ozren@mef.hr.
authors.forename: Ozren
authors.initials: O
authors.lastname: Gamulin
authors.affiliation: Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Gunduliceva 5, Zagreb, Croatia. Electronic address: marovic@sfzg.hr.
authors.forename: Danijela
authors.initials: D
authors.lastname: Marovic
authors.affiliation: Glass Laboratory, Ruđer Bošković Institute, Zagreb, Croatia. Electronic address: mogus@irb.hr.
authors.forename: Andrea
authors.initials: A
authors.lastname: Moguš-Milanković
authors.affiliation: Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Gunduliceva 5, Zagreb, Croatia. Electronic address: tarle@sfzg.hr.
authors.forename: Zrinka
authors.initials: Z
authors.lastname: Tarle
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry*; D003188:Composite Resins; D017097:Electric Impedance; D058105:Polymerization
chemical_list: D002130:Calcium Phosphates; D003188:Composite Resins; C519480:amorphous calcium phosphate
keywords: Electrical conductivity; Equivalent circuit modeling; Impedance spectrum; Ion-releasing composites; Polymerization kinetics; Raman spectroscopy