Shear bond strength of zirconia orthodontic brackets depending on surface pretreatment of bonding base

This study evaluated the shear bond strength (SBS) of zirconia orthodontic brackets under different surface pretreatment protocols to identify an optimal bonding strategy for clinical applications. Zirconia brackets (n = 94) were fabricated using 3 mol% yttria-stabilized zirconia powder and a ceramic injection molding technique. The bracket base was treated using one of the following: no treatment (Control), traditional alumina sandblasting (Group I), traditional alumina sandblasting with a 10-MDP-based primer (Group II), or silica-modified alumina sandblasting with a silane primer (Group III). Each group was divided into non-thermocycled and thermocycled subgroups. Brackets were bonded to the bovine enamel, and SBS was measured (10 brackets/subgroup). The failure mode was assessed using the Adhesive Remnant Index; and the debonded surfaces were analyzed by scanning electron microscopy and energy dispersive spectroscopy (2 specimens/condition). Within the limitations of this study, bracket base surface pretreatments significantly enhance the bonding strength of zirconia brackets. However, the combination of mechanical and chemical surface pretreatment results in excessive bond strength with a higher incidence of enamel damage upon debonding. Considering cost-effectiveness and procedural efficiency, the incorporation of traditional alumina sandblasting into the bracket base during manufacturing is recommended to ensure optimal bonding and safe debonding in clinical applications.