Purpose: To evaluate the microshear bond strength (μSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) after different surface conditioning methods. Materials and Methods: Two types of MZ (BruxZir Solid Zirconia, n = 60; Prettau-Zirkon, n = 60) with two types of surface finish (glazed, n = 30 per group; polished, n = 30 per group) were tested after two surface conditioning methods: 1. air abrasion with 30-μm silica coated aluminum oxide (Al2O3) particles (CoJet), or 2. air abrasion with 50-μm Al2O3 particles. The non-conditioned group acted as the control. A universal primer (Monobond-Plus) and an orthodontic primer (Transbond-XT Primer) were applied to all specimen surfaces. Orthodontic resin composite (Transbond-XT) was bonded using a mold and photopolymerized. The bonded specimens were subjected to μSBS testing (0.5 mm/min). Data were analyzed statistically using three-way ANOVA and the Sidac adjustment post-hoc test (α = 0.05). Failure modes were analyzed using a stereomicroscope (30X). Results: Mean μSBS values (MPa) did not show a significant difference between the two brands of MZ (p > 0.05). In both glazed (44 ± 6.4) and polished (45.9 ± 4.8) groups, CoJet application showed the highest μSBS values (p 0.001). The control group (34.4 ± 6) presented significantly better results compared to that of Al2O3 (30 ± 3.8) (p 0.05) on glazed surfaces, but it was the opposite in the polished groups (control: 20.3 ± 4.7; Al2O3: 33.8 ± 4.7; p 0.001). Adhesive failure was the dominant type in all groups. Conditioning MZs with Al2O3 and CoJet increased the percentage of mixed failure type. Conclusion: Air abrasion with CoJet followed by the application of universal primer improved the μSBS of orthodontic resin to both the polished and glazed monolithic zirconium oxide materials tested. Schlagwörter: air abrasion, monolithic zirconium oxide, zirconia, microshear bond strength, orthodontic bonding, surface conditioning method