Effects of surface treatments on the bonding properties of polyetherketoneketone to dentin: An in vitro study

Polyetherketoneketone (PEKK) has been recently introduced as a dental material for fixed dental prostheses. However, how surface treatments affect the bonding of PEKK to dentin is unclear.

The purpose of this in vitro study was to evaluate the effects of airborne-particle abrasion and acid etching on the bonding of PEKK to dentin.

Eighty-four PEKK specimens were fabricated, polished, and divided into 6 groups (n=14): no treatment (group NT), airborne-particle abrasion with 110-μm alumina particles (group Al), 98% sulfuric acid etching for 5 seconds (group SA5), 98% sulfuric acid etching for 30 seconds (group SA30), 98% sulfuric acid etching for 60 seconds (group SA60), and airborne-particle abrasion plus 98% sulfuric acid for 5 seconds (group AlSA5). Sixty PEKK specimens (n=10) were fabricated for the shear bond test. Another 24 PEKK specimens (n=4) were fabricated for surface element analysis and morphological observations. For each group, 2 specimens after surface treatments were randomly selected to examine scanning electron microscope (SEM) observations and surface element analysis. Another 2 specimens after bonding were randomly selected to examine cross-sectional observations. Airborne-particle abrasion with 110-μm alumina particles was performed to cobalt-chromium (Co-Cr) specimens (group Co-Cr, n=10). A light-polymerizing polymethylmethacrylate and composite resin primer (visio.link) was applied to the treated PEKK specimens and bonded with a resin cement (RelyX Ultimate) to dentin. The Co-Cr specimens were bonded with the resin cement to dentin. The shear bond strengths of all groups were tested by using a universal testing machine, and fracture analysis was performed. A statistical analysis was performed by using 1-way ANOVA, followed by the Student-Newman-Keuls-q post hoc test (α=.05).

The shear bond strengths of groups SA5 and AlSA5 were higher than those of groups NT, Al, SA30, SA60, and Co-Cr (P＜.05). Group SA5 achieved the highest shear bond strength (16.84 ±1.84 MPa). The SEM observations showed that after surface treatments, groups SA5 and AlSA5 had a uniform sponge shape with small pores, while groups SA30 and SA60 had a collapsed shape with large pits and pores. The sulfur element content and H₂SO₄-etched thicknesses of groups SA30 and SA60 were higher than those of groups SA5 and AlSA5. The cross-sectional SEM observations of groups SA30 and SA60 after bonding revealed that H₂SO₄-etched pores were deeper and not filled with the bonding material.

Compared with airborne-particle abrasion, the 98% sulfuric acid etching significantly improved the shear bond strength of PEKK to dentin. The surface treatment of 98% sulfuric acid etching for 5 seconds led to the high bond strength of PEKK to dentin, which meets the requirements for clinical use.