Comparison of shear bond strength of new and rebonded ceramic brackets with and without hydrofluoric acid conditioning: an in vitro study

BACKGROUND: Ceramic orthodontic brackets are widely used for their aesthetic advantages; however, their bonding strength, particularly upon rebonding, remains a concern. Effective surface-conditioning methods are essential to optimize shear bond strength (SBS) under laboratory conditions. Hydrofluoric acid (HF) conditioning and airborne particle abrasion (APA) are commonly employed techniques to enhance bracket adhesion. METHODS: Thirty monocrystalline ceramic brackets were randomly allocated into three groups (n = 10 each). Group A (control) consisted of new ceramic brackets; Group B included rebonded brackets treated with tungsten carbide burs, APA for ≥ 30 s, and 9.5% HF for 90 s; Group C included rebonded brackets treated with tungsten carbide burs and APA only. SBS was measured using a universal testing machine at 0.5 mm/min until bracket detachment, and values were recorded in MPa. RESULTS: The mean SBS for new brackets was 13.51 ± 5.61 MPa. Rebonded brackets with HF conditioning (Group B) showed 6.88 ± 2.55 MPa, and rebonded brackets without HF conditioning (Group C) showed 6.36 ± 3.60 MPa. One-way ANOVA revealed a statistically significant difference among groups (p = 0.0287). Tukey’s post hoc analysis indicated significantly higher SBS for Group A compared with Group B (p = 0.007) and Group C (p = 0.011), as well as a significant difference between Groups B and C (p = 0.009). CONCLUSIONS: New ceramic brackets demonstrated significantly higher immediate SBS than rebonded brackets under in vitro conditions. Although HF conditioning slightly enhanced immediate SBS compared with APA alone, both methods yielded lower bond strengths than new brackets. Within the limitations of this in vitro study, APA may be considered a practical alternative to HF conditioning for rebonded ceramic brackets.