Molecular insights into adhesive mechanisms of phosphate-based dental adhesives on zirconia surfaces: effects of zirconia crystal structure

This paper analyses the adhesion mechanisms of phosphate-based dental adhesives to zirconia materials based on density functional theory (DFT). Zirconia can be a mixture of three crystal structures: monoclinic, tetragonal and cubic. We investigated how these crystal surfaces influence adhesion. On all crystal surfaces, proton transfer occurs from the phosphate group in the adhesive to the zirconia surface. Among the surfaces, the monoclinic surface exhibits the highest adhesive strength. Interfacial interactions involving charge transfer are observed at all adhesive interfaces, which are particularly significant on the monoclinic surface. This is attributed to the low-coordination number of zirconium atoms specific to the monoclinic surface. Moreover, the strong Lewis basicity of these low-coordination zirconium atoms induces structural changes in the methacryloyl group, which acts as polymerization sites in the adhesive. These findings provide valuable insights for guiding the design of zirconia-based dental materials.