Micro-Raman imaging analysis of monomer/mineral distribution in intertubular region of adhesive/dentin interfaces

It is generally proposed that bonding of resins to dentin results from infiltration of the adhesive monomers into the superficially demineralized dentin. However, it is still not clear how well the mineral phase of dentin is removed and how far each monomer penetrates into the thin zone of "wet" demineralized dentin. The quality and molecular structure of adhesive/dentin interfaces formed under "wet" bonding conditions are studied using 2-D Raman microspectroscopic mapping/imaging techniques. Micro-Raman imaging analysis of the adhesive/dentin interface provides a reliable and powerful means of identifying the degree and depth of dentin demineralization, adhesive monomer distribution, and flaws or defects in the pattern of adhesive penetration. The image of mineral reveals a partially demineralized layer on the top of dentin substrate. Adhesive monomers readily penetrate into dentin tubules and spread into intertubular region through open tubules. The extent of adhesive monomer penetration is higher in the intertubular regions close to tubules as compared to the middle regions between the tubules. The diffusion of resin monomers differs substantially. In a comparison with a hydrophilic monomer, the hydrophobic monomer resists diffusion into the demineralized intertubular dentin area.