31P-NMR study of P-based dental adhesives and electron probe microanalysis of simulated interfaces with dentin

The structure and function of P in P-based dental adhesives have not been defined properly. The purpose of this study was to evaluate these parameters in some currently available materials. Five dental adhesives were selected: Bondlite, Clearfil New Bond, J&J Dental Adhesive, Prisma Universal Bond, and Scotchbond. High-resolution 31P-NMR spectroscopy was used to identify the phases of the incorporated P and the kinetics of monomer-bonded P in an aqueous environment. Areas of 5 mm diameter located on polished sound dentin were subjected to the corresponding adhesive treatments and covered with translucent molds of the same diameter, which were filled up to 1 mm length with a visible-light-cured hybrid composite. Following 60 sec of light exposure from lateral directions, the specimens were embedded in fast-setting resin, cross-sectioned, and analyzed in an electron probe microanalyzer. The elemental profiles of Ca, P, and Cl were determined from area and line scans. Great differences in the 31P resonance shifts were obtained from the tested adhesives, indicating the presence of monomer-bonded and free P. A rapid hydrolysis of the resin-bonded P in the presence of water was identified. The x-ray images revealed dentin demineralization, with distinct differences in the P distribution pattern and the P/Cl ratio.