Shear bond strength of adhesive systems on PEEK, PEKK, and fiber-reinforced composites: an in vitro study

Strong and durable bonding between composite resins and high-performance polymers (HPPs) is difficult to achieve because of HPPs’ low surface energy and chemical inertness, which limit their clinical applicability. This in vitro study aimed to evaluate the shear bond strength (SBS) between a composite resin and HPPs using different adhesive systems. Disc-shaped specimens of polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and fiber-reinforced composite (FRC) (n = 50 per group) were fabricated and sandblasted with 50 μm aluminum oxide (Al₂O₃) particles. Surface roughness (Ra) was measured using a profilometer, and surface topography was evaluated using scanning electron microscopy (SEM). Each polymer group was divided into five subgroups (n = 10) according to the adhesive system used: Scotchbond Universal, G-Premio BOND, Tokuyama Universal Bond, visio.link, and PEKK Bond. Following the adhesive application, a composite resin was applied to each specimen surface and then light-polymerized. All specimens were subjected to thermocycling for 5,000 cycles. After thermocycling, SBS was measured using a universal testing machine. Data were analyzed using a two-way and one-way ANOVA with Tukey’s HSD test (α = 0.05). FRC demonstrated the highest Ra and SBS values, followed by PEKK and PEEK. The 10-methacryloyloxydecyl-dihydrogenphosphat (MDP) - and silane-containing adhesive (Scotchbond Universal) showed significantly higher SBS values compared to the other adhesive systems. Cohesive failure represented the predominant type of failure in most groups. Universal adhesives containing functional monomers such as MDP and silane may provide reliable bonding to HPP materials after airborne-particle abrasion. Within the limitations of this in vitro study, these findings support the clinical use of universal adhesives for chairside repair and veneering procedures of HPP-based restorations. Additionally, the selection of appropriate surface conditioning and adhesive protocols may help improve the longevity and predictability of polymer-based prosthetic restorations.