Effects of N-methacryloyl-omega-amino acid primer pretreatment on the bond strength of the resin to acid-etched dentin.
To ascertain the adhesion mechanism of resins to etched dentin treated with hydrophilic primers such as N-methacryloyl-omega-amino acids (NM omega A), the effect of the application of NM omega A primers on the bond strength of the resin and also the characteristics of the "hybrid layer" were investigated. Here, the concept of "hybrid layer" has been proposed previously by Nakabayashi et al. When the demineralized dentin was treated with the NM omega A solution, the bond strength increased remarkably, thus indicating the formation of a hybrid layer. It can be construed that NM omega A primers allowed for diffusion of the bonding agent to the dentinal collageous layer that was exposed by acid etching, and thereby the creation of a hybrid layer. To obtain an understanding of how NM omega A primers improved bond strength at the interface between the resin and dentinal collagen, the 13C-NMR spectra of NM alpha A were observed in the absence and presence of demineralized dentin. The 13C peak intensities of all of the carbons of the NM alpha A species were dramatically reduced in the presence of the dentin. Specifically, the reduction of the carbon peak intensity of carboxylic acid in the NM alpha A species was reduced by 30%. This indicated that the unionized carboxylic acid in the NM alpha A primer interacted with the dentinal collagen. Thus, the composite resin can be considered to adhere to the dentinal collagen through the unionized NM alpha A that interacts with the dentinal collagen.