Effect of an experimental zirconia-silica coating technique on micro tensile bond strength of zirconia in different priming conditions

Objectives
This study aimed to evaluate the adhesive properties of a MDP-containing resin cement to a colored zirconia ceramic, using an experimental zirconia-silica coating technique with different priming conditions.

Methods
18 zirconia ceramic discs (Cercon base colored) were divided into two groups: the control group and the experimental zirconia-silica coating group. Specimens in each group were further divided into 3 subgroups (n = 3) according to the priming conditions: no primer, a MDP-containing primer (ED Primer II) or a silane coupling primer (RelyX™ Ceramic Primer). Then resin-composite discs (Filtek™ Z250) were bonded to the treated surface using a MDP-containing resin cement (Panavia F 2.0). The bi-layered specimens were cut into microbars and 20 microbars were randomly selected from each specimen, half of which were stored in 37 °C water bath for 24 h, and the other half were stored for 30 days. After water storage, the samples were exposed to a micro tensile bond strength test (MTBS). The results were analyzed by ANOVA, while the fracture surfaces were examined by SEM.

Results
After 24 h water storage, zirconia-silica coating followed by silanization showed a significantly (P < 0.001) higher MTBS value 45.0 (10.9) MPa. Water storage affected (P < 0.05) MTBS in the control group (24.1-30.3 MPa to 2.8-3.1 MPa), but only partially in the zirconia-silica coating group (20.0-45.1 MPa to 17.4-25.9 MPa). SEM analysis revealed a failure mode change after water storage.

Significance
The combination of zirconia-silica coating with silane coupling can improve the bonding of resin cement to this colored zirconia.