Evaluation of microshear bond strength of orthodontic resin cement to monolithic zirconium oxide as a function of surface conditioning method

To evaluate the microshear bond strength (μSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) after different surface conditioning 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 Al₂O₃particles. 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).

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 Al₂O₃and CoJet increased the percentage of mixed failure type.

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.