A Scanning Electron Microscopic Investigation of Bonding of Methacryloyloxyalkyl Hydrogen Maleate to Etched Dentin

Three types of methacryloyloxyalkyl hydrogen maleates-2-(methacryloyloxy)ethyl hydrogen maleate (2MEM), 1-(methacryloyloxymethyl)ethyl hydrogen maleate (MMEM), and 1-(methacryloyloxymethyl)propyl hydrogen maleate (MMPM)-were prepared for use as bonding agents. The relationships between the thickness of an acid-proof dentin layer and the bond strength and chemical structure of the synthesized monomers were investigated. The bond strengths of 2MEM/composite system to dentin treated with either 37% phosphoric acid solution or 10% citric acid-3% ferric chloride solution (10-3 solution) were superior to those of the others. The acid-proof dentin layer for all bonding agents containing the synthesized monomers at the resin-dentin interface was clearly visible in a scanning electron microscope, regardless of the types of dentin etching agents used. After treatment of the dentin with the phosphoric acid solution, the layers of 2MEM, MMEM, and MMPM were 5-6 μm, 3-4 μm, and 2-3 μm thick, respectively. When the dentin was treated with the 10-3 solution, the layer for each bonding agent was approximately 1 μm thick.