Objective: To evaluate the effect of different surface treatments and bonding modalities on the shear bond strength (SBS) between metallic orthodontic brackets and zirconia crowns.
Materials and methods: Sixty zirconia specimens were computer-aided design/computer-aided manufacturing milled, sintered, glazed, and embedded in acrylic resin. The specimens were divided into three groups according to the surface treatment applied: C: no surface treatment (control), S: sandblasted with 50 μm Al2O3, and D: Sof-Lex disc roughening. Each group was further subdivided into two subgroups according to the resin cement used: P: Clearfil Ceramic Primer + Panavia F2.0 (Kuraray) and R: RelyX U200 (3M/ESPE). Metallic orthodontic brackets were bonded to the labial surface of the specimens. All specimens underwent thermocycling. SBS test was applied using a universal test machine at a cross head speed of 1 mm/min. Data were analyzed using Mann-Whitney test (α = 0.05).
Results: Subgroup SP showed the highest SBS (20.8 ± 4.8 MPa), followed by subgroups SR (16.7 ± 4.6 MPa), DP (12.3 ± 2.8 MPa), and DR (11.6 ± 3 MPa). However, all specimens in the control group underwent debonding during thermocycling. The different surface treatment groups showed highly significant differences (P < 0.05), whereas the resin cement subgroups showed no significant differences (P > 0.05).
Conclusion: SBS between glazed zirconia crowns and metallic brackets strongly depended on the surface treatment applied. Sandblasting achieved the highest SBS. Roughening with Sof-Lex disc proved to be a reliable surface treatment modality for glazed zirconia. Bonding to untreated glazed zirconia surfaces led to bond failure. Both resin cements yielded strong SBS results.
Keywords: Orthodontic bracket; resin cement; shear bond strength; surface treatment; zirconia.