Investigations of silane-MDP interaction in universal adhesives: A ToF-SIMS analysis

The purposes of this study were to investigate whether the presence of silane in universal adhesives affects the functions of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and adhesion to zirconia.

Two silane-containing universal adhesives (Scotchbond Universal (SBU) and Clearfil Universal-Bond (CUB)) and two silane-free adhesives (All-Bond Universal (ABU) and SE-Bond primer (SE)) were individually applied on zirconia disks. Time-of-flight secondary-ion-mass-spectrometry (ToF-SIMS) examined the distributions of MDP- and silane-related ions, as well as evidence of zirconium phosphate (ZrP) compounds, on the surface and interfacial regions using a depth profiling mode. The hydrophilicity and resin wettability of the treated zirconia were examined using a contact angle test. For the shear bond strength (SBS) test, the zirconia disks were air-blasted, treated with the assigned adhesives, and bonded with pre-cured composite cylinders using a resin cement. These resin-zirconia assemblies received a bond test after 24-h storage.

Both SBU and CUB exhibited silane-related ions and ZrO₂(OH)^-, but fewer PO^- ions in the interfacial regions. CUB had more siloxane-related ions. SE-treated zirconia had abundant PO^- ions and particularly high PO₃^-- and ZrP- related ions in the interfacial regions. The silane-free adhesives exhibited a higher affinity to both water and adhesive liquids. SE showed significantly higher SBSs compared to ABU, while SBU and CUB were not statistically different.

The silane content may cause hydroxylation of zirconia and affect MDP adsorption. An acidic pH accelerated the condensation of silanol. The bond performance of the MDP-based adhesive could be influenced by the silane content and other components.