Surface modification of polyether ether ketone (PEEK) via sulfonation and hydroxyapatite coating: impact on shear bond strength with resin composite

Purpose This study evaluates the effects of various polyetheretherketone (PEEK) surface treatments on its shear bond strength (SBS) with flowable resin composite. Methods A total of 120 PEEK disks were categorized into five groups: untreated PEEK (control), sandblasted with 50 mu m alumina (Sa PEEK), etched with 98% sulfuric acid for 1 min (S PEEK), hydroxyapatite-coated sulfonated PEEK (HA PEEK), and phosphoric acid-etched HA-coated PEEK (HAP PEEK). Each group was subdivided into two groups (n = 12): Scotchbond Universal Plus (Scb) and Single Bond Universal (Sib) adhesive application and bond with flowable resin composite. SBS was evaluated after thermocycling for 5000 cycles and the results were analyzed using two-way and one-way ANOVA, followed by Tukey's HSD (alpha = 0.05). Failure mode was analyzed using light and scanning electron microscope. Surface roughness and contact angle analysis of each surface treatment were also done. Results HA PEEK exhibited the highest SBS in both Scb and Sib, while untreated PEEK showed the lowest. The effect of bonding agent can be seen only in S PEEK group where Sib demonstrated significantly higher SBS (P < 0.05) than Scb. Cohesive and mixed failures were observed in HA PEEK and HAP PEEK groups and others showed mostly adhesive failure. The wettability of PEEK increased after surface treatment except for Sa PEEK. Conclusions HA PEEK consistently achieved the highest SBS, indicating that combining sulfonation with HA coating is an effective strategy to enhance bonding between PEEK and flowable resin composite.