Effect of Bioactive Adhesives on Shear Bond Strength at the Enamel-Orthodontic Bracket Interface

Objectives: This study aimed to assess the bonding effectiveness of bioactive restorative materials when used for orthodontic bracket placement. Specifically, it evaluated whether these materials could provide shear bond strength (SBS) comparable to that of conventional resin-based adhesives, while also minimizing residual adhesive and preserving enamel integrity after bracket debonding. Methods: Forty-five extracted, caries-free premolars were randomly assigned into three main groups (n=15) based on the restorative material used: ACTIVA Bioactive-Restorative (AB), Beautifil II (BF), and Transbond XT (TB XT) — with TB XT serving as the control. Each group was further subdivided into three adhesive primer subgroups (n=5): FL-Bond II, BeautiBond Xtreme, and Transbond XT Primer. After standardized enamel cleaning and etching procedures, orthodontic metal brackets were bonded to the tooth surfaces and light-cured as per manufacturer guidelines. Specimens were stored in distilled water at 37°C for 24 hours before being subjected to shear bond strength testing using a universal testing machine. Following debonding, residual adhesive was evaluated under a stereomicroscope and scored using the modified Adhesive Remnant Index (ARI). Results: Two-way ANOVA revealed a statistically significant interaction between the type of adhesive and restorative material on SBS values (p<0.001). Among all combinations, the group using FL-Bond II with Transbond XT exhibited the highest mean SBS (19.44±3.90 MPa), while the Beautifil II group paired with BeautiBond Xtreme showed the lowest bond strength. ARI score analysis demonstrated significant differences across groups, with FL-Bond II generally resulting in minimal adhesive remnants on the enamel surface. Conclusion: The combination of FL-Bond II adhesive with conventional Transbond XT composite resin exhibited superior shear bond strength and favorable ARI scores, making it an optimal choice for orthodontic bracket bonding. ACTIVA Bioactive, when used with suitable primers, demonstrated promising results in terms of bond strength and enamel preservation, indicating its potential as an alternative to conventional systems. However, further in vivo and long-term clinical studies are warranted to validate these findings under dynamic oral conditions.