Effect of silica coating on microtensile bond strength of zirconia

Objectives: This study aimed to evaluate the adhesive properties of a MDP-containing resin cement to a colored zirconia ceramic, using a new laboratory silica coating technique in different priming conditions. Methods: 18 zirconia ceramic discs (Cercon base colored) were divided into two groups: the control group with no pretreatment, the other group was pretreated to get silica coating, by first spreading a thin layer of flowable composite resin (FiltekTM supreme XT) on the zirconia surface, and then sintered at 1200°C for 10 min. 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 (RelyXTM CERAMIC PRIMER).Then resin-composite discs (FiltekTM Z250) were bonded to the treated surface using a dual-cured MDP-containing resin cement (Panavia F 2.0). The bilayered 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 24h water storage, silica coating followed by silanization showed a significantly (P<0.001) higher MTBS value 45.0 (10.9) MPa, while in other priming conditions silica coating did not improve MTBS. Water storage affects (P<0.05) MTBS in the control group (24.1-30.3MPa to 2.8-3.1MPa), but only partially in the silica coating group (20.0-45.1MPa to 17.4-25.9MPa). SEM analysis revealed a failure mode change after water storage, from mainly mixed fracture into adhesive type. Conclusion: Durable bonding to zirconia cannot be established without surface pretreatment. The combination of silica coating with silane coupling can improve the bonding of resin cement to zirconia.