EFFECT OF THREE SURFACE TREATMENTS ON SHEAR BOND STRENGTH OF METAL BRACKETS TO LAYERED ZIRCONIA

Background: Orthodontic bonding has evolved from Buonocore’s acid-etching technique, allowing direct bonding,
especially crucial in adult orthodontic treatment and aesthetic dental care. Ceramics, notably zirconium-based materials, are favoured for their aesthetics and mechanical properties. However, achieving strong adhesive bonds to composite or ceramic restorations while minimising bond failure remains challenging, with mechanical enamel etching risking restoration integrity. Combining chemical treatments with silane application is proposed to enhance adhesion while preserving ceramic integrity.
Methods: Fifty-two zirconia discs were randomly allocated to four groups: control, diamond burs, sandblasting, and
9.6% hydrofluoric acid (HFA). After surface treatment, discs were coated with a silane primer, cured, and bonded with pre-adjusted stainless steel brackets. A universal testing machine was employed to measure each specimen’s shear bond strength (SBS), while scanning electron microscopy (SEM) was employed to analyse their topography. Post-debonding, the adhesive residue and ceramic surface condition were assessed using the Adhesive Remnant Index (ARI) and the Porcelain Fracture Index (PFI). Ethical approval was obtained from the Institutional Review Board (SRMDC/IRB/2021/MDS/NO.101).
Results: Sandblasting and HFA treatment showed significantly higher mean SBS (14.94 MPa and 13.94 MPa,
respectively) compared to diamond bur treatment (8.38 MPa) and the control group (3.21 MPa). SEM analysis revealed effective surface roughening in sandblasted and HFA-treated groups. Statistical analysis demonstrated significant differences in SBS between the groups and distribution of ARI and PFI scores across treatments.
Conclusion: Combining silane with mechanical or chemical roughening enhances SBS, with sandblasting and HFA
being effective. However, mechanical roughening risks ceramic damage, highlighting the need for careful surface
preparation. Adhesive failures that occur primarily at the ceramic–composite resin interface can help protect against
ceramic fracture and preserve the restoration’s longevity.