Bonding effectiveness of luting composites to zirconia ceramics

Bonding to dental zirconia ceramics has been shown to be challenging. Objectives: To evaluate the effect of mechanical surface conditioning and artificial aging on the micro-tensile bond strength (µTBS) of two dual-cure composite cements to zirconia ceramics. Methods: Fully sintered IPS e.max ZirCAD (Ivoclar-Vivadent) blocks were either (1) not pre-treated or (2) subjected to tribochemical silica coating (CoJet, 3M ESPE) for 2 sec (at a distance of about 10 mm). Next, the silane coupling agent Clearfil Ceramic Primer (Kuraray) was applied during 60 sec, followed by gentle air-drying, after which two zirconia blocks were bonded together using one of two dual-cure composite cements (Panavia F2.0 or Clearfil Esthetic Cement, Kuraray). The specimens were trimmed at the interface to a cylindrical hour-glass shape (diameter = about 1.2 mm). All specimens were stored for 7 days in distilled water at 37°C, after which they were randomly divided into 2 subgroups; half of the specimens were subjected to 10,000 thermocycles between 5 and 55°C during 10 days; the other half were further immersed in 37°C water for 10 days (n=15-20 per group). After storage, the µTBS was determined in MPa. Data were analyzed with Weibull, three-way ANOVA and Turkey's test (P<0.05). Fractographic analysis was performed using SEM. Results: Weibull analysis revealed the highest (scale-parameter of 54), most reliable (shape-parameter of 3.5) and least low (Blife significantly higher at 10% unreliability) values for the CoJet-Panavia F2.0 group, thereby scoring significantly higher than any other group. Without tribochemical silica coating, the lowest µTBS was measured for Panavia F2.0 (Tukey, p<0.05). When Clearfil Esthetic cement was used, neither tribochemical silica coating, nor thermocycling influenced the µTBS. Conclusion: Mechanical surface conditioning using tribochemical silica coating appeared needed for Panavia F2.0 to effectively bond to zirconia ceramics, while not for the more hydrophobic Clearfil Esthetic Cement.