We investigate the competition of the various organic components of two representative adhesive systems for reactive defect sites at model surfaces of both SiO2 and Al2O3. The reaction energies of resin monomers, curing agents, and in some cases also of additional adhesion promoters with the defects are calculated. We applied a density-functional based tight-binding method including a self-consistent correction of the Mulliken charges, which has already proven to be a useful tool for computational materials science, delivering reliable structural and energetic information.