Polyacrylic acid-metal adhesive bond joint characterization by x-ray photoelectron spectroscopy

The adhesive force to human tooth and metallic restoration of dental cements which contain polyacrylic acid (PAA) is found to be stronger than that of previous cements. Chemical interaction at the interface between metals and carboxylate groups of PAA were studied by x-ray photoelectron spectroscopic method combined with Ar+-ion beam etching technique to examine the mechanism of adhesion. A 2.5 wt% aqueous solution of PAA was painted on the surface of metal plates which are usual elements of dental alloy. Ar+-ion etching was used to scrape off in situ the PAA film coated on the metal plate gradually in the sample chamber of the ESCA equipment. After a few minutes of etching, ESCA spectra were observed. The profile of the spectra and binding energy of 4f5/2 and 4f7/2 levels of Au coated with PAA show little change by the Ar+-ion etching, and remain in the same state as those of uncoated Au. Similar behaviors were obtained in case of Pt. There are three chemical states on Sn plate coated with PAA. The lowest binding energy peak is assigned to pure Sn. The middle one is assigned to SnO2. The highest one corresponds to Sn combined with carboxylate groups of PAA. The chemical reaction corresponding to the highest binding energy peak seems to contribute to the strong adhesive force of these cements to Sn. These aspects of spectra corresponded to McLean's results which showed that these cements had weak adhesion to Au and Pt, but strong adhesive force to tinned Au and Pt.