Zirconia Adhesion of Phosphoric Acid Ester Monomers Studied by NMR

Objectives: The functional phosphoric acid ester monomers containing primers have been widely used for dental adhesives. The objective of this study is to analyze the atomic level interaction between zirconia and phosphoric acid ester monomers under different pH (acid or neutral).
Methods: Solid-state ³¹P NMR spectroscopy was performed to investigate the binding interaction of two types of phosphoric acid ester monomers, glycerophosphate-dimethacrylate (GPDM) and 10-methacryloyloxydecyl dihydrogen phosphate (MDP) in different pH conditions with zirconia. Contact angles were measured on zirconia surfaces with and without phosphoric acid ester monomers application. In addition, tensile bond strength (TBS) tests were conducted to determine the effect of different phosphoric acid ester monomers containing primers under different pH conditions to zirconia.
Results: Solid-state ³¹P NMR spectroscopy showed that both interacted GPDM and MDP provided broaden peaks that were positioned different from unreacted each monomer, implying the chemical interaction of all monomers with zirconia at atomic level. Acid MDP might have possibility to form covalent bond with zirconia by additional esterification on zirconia surface. MDP primed zirconia showed the higher contact angle than GPDM primed. The highest TBS was found in the group of MDP reacted with zirconia in acid condition.
Conclusions: These findings indicated that phosphoric acid ester monomers can chemically bound to zirconia. This chemical interaction can contribute to the adhesion behavior of phosphoric acid ester monomers to zirconia.