Evaluation of wear characteristics and volumetric change in bi-layered hybrid PEEK/PEKK CAD-CAM implant supported fixed dental prostheses

Purpose: This study employed a technique-sensitive, anatomically precise full-arch design to investigate the wear behavior—specifically volumetric wear loss (ΔV) and vertical height loss (ΔH)—of two high-performance polymer frameworks: polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), each veneered with either a lithium disilicate ceramic (IPS® e.max Press) or a high-impact polymer composite (breCAM®.HIPC). The lower hybrid Toronto-designed implant-supported fixed dental prostheses (ISFDPs) were evaluated in opposition to full-anatomy maxillary monolithic zirconia (DD cube ONE®, 4Y-TZP) restorations. The study also compared these polymer-based systems to traditional materials—zirconia (ZIR) and cobalt-chromium (CoCr)—to assess how framework type and veneering choice affect long-term dimensional stability and wear performance under simulated clinical loading. Materials and Methods: A total of 84 CAD/CAM-fabricated ISFDPs were produced: 42 mandibular hybrid frameworks veneered with 504 anatomically contoured lithium disilicate or HIPC coping crowns, and 42 opposing full-anatomy zirconia maxillary prostheses. The mandibular samples were evenly divided into six groups (n = 7): PEKK\Comp, PEKK\Emax, PEEK\Comp, PEEK\Emax, ZIR\Emax, and CoCr\Comp. All specimens were mounted on identical stainless-steel arch forms using screw-retained epoxy resin models and subjected to five years of simulated function through thermocycling and mechanical loading (TCML): 1,250,000 loading cycles at 80 N, 1.2 Hz, with lateral (1.0 mm) and vertical (2 mm) movements, and 5/55 °C thermal cycling. Volumetric wear loss (ΔV) was quantified via 3D laser scanning and Avizo® software, while vertical wear loss (ΔH) was recorded in real-time using the Willytec CS-4.8 chewing simulator. Data were statistically analyzed using the Kruskal–Wallis and Dunn's post-hoc tests (α = 0.05). Results: PEKK\Comp exhibited the lowest mean volume loss (0.222 ± 0.04 mm³), while CoCr\Comp showed the highest (1.564 ± 0.14 mm³). PEKK-based combinations outperformed other groups in both ΔV and ΔH metrics, with PEKK\Comp and xxvi PEKK\Emax demonstrating significantly lower wear than PEEK\Comp, PEEK\Emax, ZIR\Emax, and CoCr\Comp (p < 0.05), except PEKK\Emax vs. PEEK\Emax, which showed no statistically significant difference. For vertical height loss, PEKK\Comp recorded the lowest mean (0.277 ± 0.03 mm), and CoCr\Comp the highest (0.643 ± 0.08 mm). ZIR\Emax demonstrated intermediate performance and significantly outperformed both PEEK\Emax and CoCr\Comp (p < 0.05). No fractures, veneer chipping, or structural failures were observed in any group throughout the TCML simulation. Conclusions: PEKK\Emax emerged as the most promising material combination, exhibiting strong positive wear correlation (r = 0.893, p = 0.007) and balanced performance across both wear metrics. Although PEKK\Comp demonstrated the lowest absolute wear values, PEKK\Emax offered more predictable performance under stress. ZIR\Emax and PEKK-based combinations demonstrated consistent and favorable wear behavior, suggesting that under appropriate conditions, polymer-based frameworks—particularly those using PEKK—can rival or exceed the performance of traditional metal-ceramic ISFDPs. These findings offer valuable implications for clinical material selection and the advancement of metal-free full-arch prosthetic solutions. Key Words: Wear, PEKK, PEEK, Toronto Bridge, ISFDP, CAD/CAM, 4Y-TZP, Chewing simulation, Chewing forces, Polymer frameworks, Lithium disilicate, breCAM HIPC, Volumetric loss, Vertical height loss, Full-arch prostheses, Willytec CS-4.8.