New Adhesive Protocol to Improve Polyetherketoneketone (PEKK) Bonding.

Objectives: Polyetherketoneketone (PEKK) coating is a challenging process due to the inert surface of this polymer. Thus, a new experimental adhesive protocol was developed to improve PEKK adhesiveness and increase the longevity of the gingival esthetic coating.
Methods: PEKK blocks were milled and included in acrylic resin, The PEKK surface was polished at maximum roughness of 0.20 μm. Blocks were randomly assigned to the new protocol and controls (N=36). The new protocol was based on surface blasting (Al₂O₃ 110 μm and isopropyl alcohol at 60 psi), followed by washing with isopropyl alcohol and air drying. A PEKKBond (AnaxDent, USA) layer was then applied and dried on the stove (3 min at 77^oC). Then, a second layer of Visio.link (Bredent, Germany), was applied and dried on a stove (3 min at 60^oC). Both adhesive layers were light-cured (3 min 800 mW/cm²). Preopaque (GC Europe, Germany) and Opaque (AnaxDent) layers were applied, light-cured (5 min), and dried in a stove (3 min at 60^o C). Controls were performed to surface pre-treatments (no treatment, sandblasting with 110-µm Al₂O₃, and silica coating), and adhesive treatments (no adhesive, Visio. link, and PEKKBond). After SEM morphological topography analysis, flowable gingiva-colored composite (AnaxGum, AnaxDent) was bonded and aged (24 hs and thermocycling for 5000 cycles, 5 to 55 °C). The shear bond strength (SBS) was measured in a universal test machine (MPa) and data were analyzed with 2-way ANOVA followed by Tukey (α =0.05)
Results: The new protocol presented the highest SBS values, while thermocycling reduced the bond strength of all groups. In the controls, sandblasting with Al₂O₃ was more efficient than silica, and PEKKBond produced higher SBS than Visio.link.
Conclusions: The new protocol significantly improves PEKK adhesiveness and could be a useful option when fabricating prostheses using PEKK-based materials and indirect resin composites.