Influence of different low-pressure plasma process parameters on shear bond strength between veneering composites and PEEK materials

The aim of this study was to evaluate the impact of oxygen and argon/oxygen low-pressure plasma on the shear bond strength (SBS) between dental PEEK compounds and veneering composites as a function of plasma process time. Of an unfilled PEEK (“Juvora”) and two pigment powder filled PEEK compounds (“DC4420”, “DC4450”), 273 rectangular plates were prepared and polished up to 1200 grit. Afterwards the samples were sandblasted and randomly assigned to five different surface pre-treatment groups (1. No plasma (control); 2. O2 plasma for 3min; 3. O2 plasma for 35min; 4. Ar/O2 plasma for 3min; 5. Ar/O2 plasma for 35min). Surface roughness and water contact angles were recorded using three samples of each PEEK compound for each of the plasma treatment groups. An adhesive (visio.link, Bredent GmbH & Co KG, Senden, Germany) was applied onto the specimen surfaces and light cured. A mold was used to shape three different veneering composites (a) Vita VM LC, “Vita” (Vita Zahnfabrik, Bad Säckingen, Germany); (b) GC GRADIA, “Gradia” (GC Europe, Leuven, Belgium); (c) GC GRADIA DIRECT Flo, “Gradia Flo” (GC Europe, Leuven, Belgium)) into a cylindrical form on the sample surface before light curing. SBS was measured using a universal testing machine after 24h of incubation in distilled water at 37°C. The two pigment filled PEEK compounds treated with O2 plasma and veneered with Gradia Flo showed the highest SBS values (34.92±6.55MPa and 34.2±1.87MPa) followed by the combination of the unfilled PEEK material with Gradia Flo (29.57±3.71MPa). The SBS values of the samples veneered with Gradia were lower, but not significantly so. The SBS values of the specimens with Vita were for the most part associated with significantly lower results. A low-pressure plasma process using oxygen plasma for a duration of 35min, preceded by sandblasting, seems to be the most effective in increasing shear bond strength between veneering composites and PEEK materials.