Diazonium chemistry for bonding between PEEK and resin cement

Statement of problem. Polyetheretherketone (PEEK) is an excellent restorative material, but its hydrophobicity and inertness prevent strong adhesion to resin cements.
Purpose. The purpose of this in vitro study was to examine the use of diazonium reactions for priming PEEK surfaces to improve their adhesion to resin cements. Material and methods. Polished PEEK specimens were exposed to 7 different treatments: airborne-particle abrasion (50 mu m) (APA), diazonium priming (D), adhesive (visio-link) application (A), APA followed by A (APAA), D and A (DA), APA and D (APAD), and APA followed by D and A (APADA). Nontreated specimens served as controls (C). The surface composition, roughness (Ra), and contact angle of the specimens were examined before and after treatment using X-ray photoelectron spectroscopy (XPS), profilometry, and goniometry respectively. The tensile bond strength between the treated specimens and resin cement (Panavia SA) was evaluated with a mechanical testing machine after incubation in distilled water (24 hours, at 37 degrees C). The fracture surfaces were examined by using a stereomicroscope at x40 magnification. The Kruskal-Wallis, 1way analysis of variance, Tukey HSD, and Fisher-Freeman-Halton tests were used for statistical analysis (alpha=.05). Results. Surface characterization revealed that the APA treatment resulted in the highest surface concentration of oxygen and the highest contact angle (81.3 +/- 4.9 degree), the D treatment resulted in the highest surface concentration of nitrogen, the DA treatment resulted in the lowest roughness and contact angle (49 +/- 6.2 degree), and the APAD treatment resulted in the highest roughness. Tensile test results showed the lowest tensile bond strength in the control group (0.1 +/- 0.1 MPa) and the highest in the APADA group (13.9 +/- 1.6 MPa) (P<.001). Differences were not observed among the APAA (10.8 +/- 0.9 MPa), DA (10.4 +/- 1.6 MPa), and APAD (9.8 +/- 1.7 MPa) treatments (P>.05). The failures of the groups were different (P<.05), with group C showing 100% adhesive failure and the APADA group showing 70% mixed failure.
Conclusions. The surface treatment of PEEK with a diazonium primer increased the bonding strength of resin cement to PEEK.