1H-NMR studies of the interaction of dental adhesive monomer, 4-META with calcium.

Our objective was to determine whether high-resolution proton-nuclear magnetic resonance (500 MHz) could be utilized for detection of ionic binding interaction of the 4-META resin system with calcium derived from hydroxyapatite. The stability of 4-META in aqueous medium was studied, findings indicated that 4-META was rapidly converted to 4-MET, a hydrate product of 4-META in 10% D2O/DMSO-d6. The 1H-NMR signals of the methacryloyloxyethoxy group of 4-MET remained intact following the addition of both monocalcium phosphate (MCP) and dicalcium phosphate dihydrate (brushite) solution, whereas those of its trimellitic portion were markedly shifted upfield depending on the phosphate concentration. The shielding effect followed by upfield shifts was due to the localization of electron density surrounding the carboxylate anions that were dissociated by the interaction with calcium counter cation. The shielding effect of 4-MET with brushite was larger than that with MCP. An ionic interaction of 4-MET derived from 4-META with calcium was demonstrated.