Chemical Adhesion of Polyalkenoate-based Adhesives to Hydroxyapatite

Purpose: To evaluate the chemical interaction between synthetic hydroxyapatite (HAp) and polyalkenoic acid copolymer- based (also known as Vitrebond copolymer [VCP]) adhesives. Materials and Methods: Six dentin adhesive formulations were used: 1) Adper Single Bond Plus (SB); 2) SB formulation without VCP (SBnoVCP); 3) Adper Easy Bond (EB); 4) EB formulation without VCP (EBnoVCP); 5) Scotchbond Universal adhesive (SBU); 6) SBU formulation without VCP (SBUnoVCP). Each adhesive was mixed with HAp, polymerized, and analyzed using FTIR and 13C/31P NMR spectroscopy. Results: The FTIR spectra of SB+HAp indicated that the carbonyl group changed absorption wavenumber compared to that of SBnoVCP+HAp. 13C NMR analysis showed that the presence of methacrylated phosphoric esters in the EB and SBU formulations led to similar carbonyl resonance with or without VCP. 31P NMR revealed a resonance shift at 0.5 ppm for SB+HAp, EB+HAp and SBU+HAp spectra. In comparison with EB+HAp and SBU+HAp, a slight fade-out of the same resonance shift for EBnoVCP+HAp and SBUnoVCP+HAp was observed without completely disappearing, respectively, meaning that VCP might induce a modification of phosphorus moieties in addition to the ionic interaction between phosphate ester groups and HAp. Conclusion: Our data suggests that a chemical interaction occurred between VCP-containing adhesives and synthetic HAp. Keywords: dentin-bonding agents, glass-ionomer cements, hydroxyapatites, spectroscopy, Fourier Transform Infrared