M Suzuki’s research while affiliated with Showa University and other places

In order to clarify the role of a primer on the adhesion between dental precious metals and resin, surface-enhanced Raman scattering (SERS) technique has been applied to the structural analysis of the adhesive monomer, 6-(N-(4-vinylbenzyl)propylamino)-1,3,5-triazine-2, 4-dithione (VBATDT) adsorbed on colloidal Au surfaces. VBATDT is one of the major components of commercial primers. A mixture of a methanol solution of VBATDT and aqueous Au colloid was illuminated by the 647.1 nm line from a Kr ion laser to obtain the SERS. The most intense peak at 458 cm-1 due to C = S stretching in the Raman spectrum of solid VBATDT disappears completely in the SERS, while all the other peaks due to vinylbenzyl group vibrations remain unchanged. It suggests that some structural change occurs in VBATDT upon adsorption on Au which involves the C = S bonds and that the molecule undergoes thione-thiol-type tautomerization in the adsorption process. The SERS spectrum of a commercial primer containing VBATDT exhibits a similar spectral pattern. The present results lead us to conclude that some specific interactions exist between the sulfur atoms of VBATDT and Au surface to form chemical bond likes, which are effective to improve the bond strength between dental precious metals and resin. The ambivalent properties of the primer, chemical stability in storage and chemical affinity to Au, are also explained by the thione-thiol-type tautomerization of VBATDT on the basis of the spectroscopic evidence.

10-Methacryloyloxydecyl dihydrogen phosphate (M10P) for use in dentistry has recently been noted as an adhesive monomer contained in a metal primer. Although the treatment of a metal surface with primer before the application of resin is recognized to improve the adhesion between metal and resin, the role of M10P in the adhesion process has not been clarified. In this study, infrared reflection absorption (IRA) spectroscopy was employed to study the adsorption structures of M10P as well as 2-methacryloyloxyethyl dihydrogen phosphate (M2P) on evaporated silver substrates. The IRA spectra of the self-assembled films of those phosphates verified the adsorption of M10P or M2P on silver substrates from the methyl methacrylate solutions (5 x 10(-5) mol/L). The saturation coverages of M10P and M2P were completed after about 50 and 25 min, respectively. Two characteristic bands around 980 and 1080 cm-1 due to the PO(2-)3 stretching vibrations were observed. These results indicate that the phosphate groups of both monomers are adsorbed to silver surfaces in the dissociated form, -PO(2-)3, and form hydrophobic monolayers. The monolayer of M10P was found to be more durable against thermocycling in water than that of M2P by IRA measurements. The roles of M10P in the metal primer are presumably to form such a monolayer with appreciable durability and to promote polymerization with resin monomers.