Influence of two kinds of zirconia primers on the bonding effect of zirconia ceramics

To evaluate the effect of two commonly used zirconia primers on the bond strength and durability of zirconia ceramics.

Zirconia wafers with a diameter of 5 mm and a thickness of 2 mm were cut and prepared by CAD/CAM (51). After sintering, sandblasting, ultrasonic cleaning and drying, the zirconia wafers are divided into three groups according to the types of zirconia primer: group A, no primer group; group B, Z-Prime plus; and group C, Clearfil Ceramic Primer, with each set containing 17 samples. The surface morphology of zirconia was observed by scanning electron microscopy after applying the coating primer according to the operation specifications. Then, the microshear bonding specimens were made, and the bonding strength was tested after water storage for 3 days and 5000 × thermocycling.

The surface of zirconia ceramics was roughened by sandblasting. After Z-Prime plus coating, the primer did not completely cover the zirconia surface, which is island like. After coating with the Clearfil Ceramic Primer, the primer was completely covered on the surface of zirconia ceramics without exposure to zirconia. Energy spectrum analysis showed that the content of C, O, Si and P in the coating area was relatively high. After primer coating, the bonding strength between zirconia and resin cement was significantly higher than that of group A (20.6 ± 2.1)MPa, P < 0.05, while there was no significant difference in the immediate bonding strength between group B (33.2 ± 3.9)MPa and group C (30.7 ± 2.4)MPa (P > 0.05). After 5000 × thermocycling, the bonding strength of group A was(4.1 ± 2.5)MPa, that of group B was (23.1 ± 2.3)MPa and that of group C was (28.9 ± 2.6)MPa. There were statistically significant differences among groups A, B and C. The aging adhesive strength of groups A and B was significantly reduced compared with the immediate adhesive strength (P < 0.05). Group C had the highest bonding strength after aging (28.9 ± 2.6) MPa, with no significant difference before and after aging (P > 0.05). After 5000 × thermocycling aging, the percentage of bonding failure in the fracture mode of group A increased from 66% to 100% and that of group B increased from 16% to 53%. In group C, the percentage of bonding failure increased from 20% to 24%.

The zirconia primers on the surface of zirconia ceramics after sandblasting can enhance the bonding strength and durability of zirconia.