Influence of Bonding Protocols on Ceramic Brackets Applied to Zirconia

Objectives: The purpose of this study was to measure the shear bond strength of orthodontic ceramic brackets to glazed zirconia conditioned with different types of primer systems. Determinate which primer/etch protocol was more effective conditioning the zirconia glazed substrate before being bonded to the ceramic-bracket interface. And propose a more effective surface-treatment protocol alternative that has the minimally invasive factor orthodontics are looking for to preserve the zirconia integrity in terms of color, value and strength because grinding the Y-TZP surface with a diamond bur deteriorates all these terms.
Methods: Industrially manufactured Y-TZP ceramic blocks were CAD/CAM milled to an area of 10 x 10 mm² and a thickness of 5 mm (n=40). Randomly assigned into four groups following the next surface treatments: (ZPP) Zirconia Primer and Porcelain Primer; (ZUB) Universal Bonding; (ZCP) Ceramic Primer; and Orthodontic Primer with Ceramic Primer (ZOC). All the specimens were conditioned by 50 µm Al₂O₃ sandblasting and 4% hydrofluoric acid etching. A ceramic bracket was bonded to each surface with orthodontic resin cement, and all specimens underwent thermal cycling. The shear bond strength of the specimens was measured by a universal testing machine. And a scanning electron microscope were used to image the zirconia surfaces.
Results: Groups ZPP and ZOC showed significantly higher shear bond strength than the other groups. No statistically significant differences were found among groups ZUB and ZCP. In groups ZPP and ZOC, bonding failed at the interface between the resin cement and bracket base or showed complex adhesive and cohesive failure.
Conclusions: Porcelain primer and Zirconia Primer synergy is the most appropriate choice for bonding a ceramic bracket to the surface of a glazed zirconia with resin cement.