An FT Raman spectroscopic investigation of dentin and collagen surfaces modified by 2-hydroxyethylmethacrylate

Although 2-hydroxyethylmethacrylate (HEMA) is commonly used for adhesive bonding to dentin, its role in promoting adhesion is not completely understood. Here, we use FT-Raman spectroscopy to elucidate further the nature of the interaction of HEMA with dentin. Ground dentin was exposed to 2.5% (w/w) nitric acid, washed, dried in air, and treated with HEMA. The samples were then sequentially washed with distilled water, with ET-Raman spectra being obtained after different wash times. Hydroxyapatite and bovine type I collagen were similarly treated with HEMA except for the acid exposure. The FT-Raman spectra of these samples were also recorded. The spectra of HEMA-treated, water-washed dentin and collagen revealed the following changes: (1) The band intensities of HEMA absorbed on dentin and collagen decreased with increasing wash times; (2) the nu(C=O) and nu(CCO) modes of HEMA at 1718 and 607 cm(-1), respectively, either disappeared or decreased after extensive washing; (3) the nu(C=C) (1640 cm(-1)) and delta(=CH2) (1403 cm(-1)) bands exhibited minor variations in band position and relative intensity. These results demonstrate that HEMA interacts with dentin both physically and chemically. The chemical interaction can be interpreted by either hydrogen bonding or the formation of a new bond to the ester group of HEMA.