Improving Orthodontic Bracket Adhesion to Monolithic Zirconia: Pretreatment Protocols Across Different Zirconia Types.

PURPOSE: The increasing use of monolithic translucent zirconia for fixed dental restora-tions in orthodontic patients has created new challenges for reliable bracket bonding. This in vitro study evaluated the influence of different surface pretreatment protocols on the shear bond strength (SBS) of metal brackets bonded to 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 5-mol% yttria-stabilized partially stabilized zirconia (5Y-PSZ) ceramics using an adhesive resin cement. METHODS AND MATERIALS: Ninety-six specimens were prepared (n = 48 per zirconia type), each providing two bonding interfaces (n = 192). Three surface pretreatment protocols were tested: pumice slurry (PS), silicon carbide burr roughening (SiB), and alumina air-particle abrasion (AP). Metal brackets were bonded using an MDP-containing self-adhesive resin cement and a custom 3D-printed bonding device, applying a standardized load of 7.4 N. Half of the specimens were tested for SBS after 3 days of water storage at 37°C; the remaining half after artificial aging (37,500 thermocycles between 5°C and 55°C) for 150 days. SBS was measured using a universal testing machine. Data were analyzed using non-parametric tests (Kruskal-Wallis; Mann-Whitney U with Bonferroni-Holm correction; α = 0.05). RESULTS: Artificial aging significantly affected SBS, whereas zirconia type had no significant influence. After 3 days, no significant differences were observed among surface pretreatment methods. Following artificial aging, AP and SiB pretreatments achieved significantly higher SBS values than PS for both zirconia types. AP yielded the highest bond strengths overall (up to 51.3 MPa for 5Y-PSZ after 150 days). Spontaneous debonding occurred only in the PS groups. CONCLUSION: Although AP pretreatment achieved the highest bond strength values, its clinical application is limited by the risk of surface damage and uncontrollable intraoral pressures. SiB pretreatment provided clinically sufficient bond strength while preserving zirconia surfaces, representing a safer and more practical alternative. Pumice slurry alone was inadequate for reliable bonding. Thus, SiB can be recommended as a minimally invasive and effective clinical protocol for orthodontic bonding to zirconia restorations.