Effect of surface treatments on the shear bond strength of PAEK polymers to composite resin: an in vitro study

BACKGROUND: Polyaryletherketone (PAEK) polymers, including polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), are increasingly used in prosthodontics because of their favorable mechanical and biological properties. However, their chemically inert and low-surface-energy characteristics result in insufficient bonding to veneering composite resins. Therefore, effective and clinically safe surface treatment protocols are required to enhance adhesion. METHODS: Square specimens were fabricated from three Computer Aided Design/ Computer Aided Manufacturing (CAD/CAM) PAEK polymers: unfilled PEEK (Copra Peek), ceramic-reinforced PEEK (BioHPP), and PEKK (Pekkton Ivory). Specimens were allocated to six surface-treatment groups: untreated control, CoJet, 98% sulfuric acid etching, Er: YAG laser irradiation, CoJet plus laser, and sulfuric acid plus laser. A methyl methacrylate-based adhesive and veneering composite resin were applied. Half of the specimens were subjected to 10,000 thermocycles. Shear bond strength (SBS) was measured using a universal testing machine. Surface roughness, wettability, and morphology were evaluated using profilometry, contact angle measurements, and scanning electron microscopy. Data were analyzed using ANOVA and Tukey post-hoc tests (α = 0.05). RESULTS: Most experimental groups demonstrated SBS values above clinically acceptable thresholds; however, lower values were observed in certain laser-treated and thermocycled subgroups. Sulfuric acid etching produced the highest mean SBS values across all three materials, followed by CoJet. Laser irradiation alone consistently yielded the lowest bond strengths (range: 12.07-14.69 MPa) despite generating the highest surface roughness, and a significant moderate negative correlation was identified between surface roughness and SBS (r = - 0.39, P < 0.001). Three-way ANOVA confirmed significant main effects of surface treatment (P < 0.001), material type (P = 0.002), and thermocycling (P = 0.015). CONCLUSIONS: Durable adhesion between PAEK polymers and veneering composite resin may be achieved through appropriate surface treatment. Within the limits of this in vitro study, sulfuric acid etching appeared the most effective method, possibly generating a microporous surface that may contribute to enhanced bond strength; however, its clinical application is limited by the hazardous nature of 98% sulfuric acid, and safer alternatives should be explored. Among clinically feasible treatments, CoJet produced consistently high bond strengths and may represent the most clinically translatable protocol. In contrast, laser irradiation alone caused surface degradation and resulted in inferior bonding performance.