Chemical Adhesion of Polyalkenoate-based Adhesives to Hydroxyapatite

Objectives: To study the chemical interaction between hydroxyapatite (HAp) and a polyalkenoic acid copolymer (also known as Vitrebond copolymer, VCP)-based adhesives using FTIR spectroscopy and ¹³C/ ³¹P NMR spectroscopy in solid state.
Methods: Four dentin adhesives were used - Adper Single Bond Plus (SB, 3M ESPE), an etch-and-rinse VCP-based adhesive; experimental Adper Single Bond Plus without VCP (SBnoVCP, 3M ESPE); Adper Easy Bond, a self-etch VCP-based adhesive (EB, 3M ESPE); and experimental Adper Easy Bond without VCP (EBnoVCP, 3M ESPE).
FTIR spectra were recorded using the KBr-technique. Infrared spectra of KBr pellets were recorded under the 4000-400 cm^-1range, 4 cm^-1 resolution and 64 scans.
For the NMR analysis, both ¹³C and ³¹P spectra were recorded at room temperature with a spectrometer, using 4 mm rotors of zirconium with a spinning speed of 8 and 9 kHz, respectively.
Results: FTIR: For the SB+HAp spectra, CO-stretching carbonyl group changed the position in comparison to that of SBnoVCP+HAp. EB+HAp and EBnoVCP+HAp resulted in similar CO-stretching carbonyl group position.
¹³C NMR: The presence of methacrylated phosphoric esters in the EB formulation led to similar carbonyl resonance for both EB+HAp and EBnoVCP+HAp.
³¹P NMR: A resonance at 0.5 ppm was observed within the SB+HAp spectra. The presence of VCP resulted in acidic modification of the ³¹P environment.
Conclusions: Chemical interaction between VCP and HAp was observed for SB. For EB, however, chemical bonding between VCP and HAp was not confirmed.