Author:

Abstract:

Adhesive biomaterials capable of chemically bonding to tooth tissue have been shown to contribute to bond durability (Inoue et al., JDR 2005), most likely because chemical interaction enhances the molecular-level contact at the interface. Objectives: While ionic bonding of carboxylic acid groups to Ca of hydroxyapatite (HAp) has been proven using high-resolution X-ray Photoelectron Spectroscopy (XPS) (Yoshida et al., JDR 2000, 2004), the actual chemical bonding of phosphoric-acid derivatives with HAp remained unresolved. Since HAp also contains phosphorus, it impedes clear detection of changes in the XPS phosphorus spectrum that would be indicative of chemical interaction. Methods: We therefore deposited monomolecular layers of 10-methacryloxydecyl dihydrogen phosphate (MDP) on HAp for XPS analysis of its ‘C-O-P' carbon. In the C1s spectrum, the C-O-P carbon of MDP however overlaps with its ether carbon (‘C-O-C'). We therefore also analyzed the interaction of mono-n-dodecyl phosphate (DDP) with HAp that also contains the C-O-P carbon, but not the ether carbon. In addition, the experimental XPS data were compared to theoretical data calculated using the Amsterdam Density Functional (ADF) method. Results: High-resolution XPS revealed a significant C1s chemical shift difference of about 0.4 to 0.5 eV for the C-O-P component for both MDP and DDP, suggesting chemical bond formation of their phosphate group to Ca of HAp. The theoretical calculations using the ADF method were in close agreement with the XPS observed spectra. Conclusion: Also MDP chemically interacts with HAp, as shown before (Yoshida et al., JDR 2004) in a very intense and prompt manner.