Zirconia surface modification by a novel zirconia bonding system and its adhesion mechanism

Bonding to zirconia has been of great interest over the last 10-15 years. The aim of this study was to develop a zirconia bonding system and clarify its adhesion mechanism.

A zirconia primer was prepared using tetra-n-propoxy zirconium (TPZr) and water. A silane primer was also prepared using γ-methacryloyloxypropyltrimethoxysilane (γ-MPS) and hydrochloric acid. After the zirconia primer was applied to the oxidized zirconia surface, the silane primer was applied to the ZrO₂-functionalized layer and the resin cement was applied to the silane-modified layer. Ceramic Primer II was used as a typical MDP-based ceramic primer. Shear bond strengths were measured using a universal testing machine. To clarify the enhancing mechanism of the zirconia bonding system, X-ray photoelectron spectroscopy (XPS) analyses were performed.

The zirconia bond strength was affected by the surface wettability of zirconia, and the compositions of TPZr and water utilized in the zirconia primer. When the zirconia primer, consisting of 10μL TPZr and 13μL water, was applied to the zirconia surface that had been oxidized by H₂O₂ above 10%, the maximum bond strength of 8.2MPa was obtained. The mechanism of the zirconia bonding system was established as follows: the hydrolyzed zirconium species formed a more reactive ZrO₂-functionalized layer on the oxidized zirconia surface, and the hydrolyzed γ-MPS species adsorbed on that layer introduces a chemical bonding to the resin.

The novel zirconia bonding system enhanced the bonding performance of the resin, and showed a greater bond strength than an MDP-based ceramic primer.