Promoting porcelain–zirconia bonding using different atmospheric pressure gas plasmas

Objectives: To evaluate the effects of different atmospheric-pressure plasma (APP) on the physicochemical properties of yttria-stabilized zirconia, and promoting the adhesion of veneering porcelain. Methods: Cercon base zirconia disks were prepared to receive different treatments: as-polished, three APPs (oxygen, OP; argon, AP; and CF₄, CP), and grit-blasted (GB). Their surface roughness and hydrophilicity were measured, and surface morphology was examined either after treatments, after simulated porcelain firing, or additional thermal etching. X-ray photoelectron spectroscopy (XPS) analysis characterized the surface chemical compositions. Shear bond strength (SBS) tests examined the adhesion between veneering porcelain and zirconia either before or after thermocycling. The layered ceramic disks were also sectioned to inspect the porcelain–zirconia interfaces. Statistical analysis was performed with one-way ANOVA and post hoc Duncan's test. Results: Grit-blasting caused surface damage and increased roughness. All APP-treated disks exhibited deeper grain boundaries and enlarged grain sizes after thermal etching, while CP disks revealed additional particle dispersions. Three APPs rendered the zirconia surface superhydrophilic. XPS spectra of three APP groups revealed increased hydroxyl groups and reduced C–C contents, and CP group especially showed the existence of Z–F bonds. CP exhibited the highest SBS both before and after thermocycling, while AP and GB also showed improved SBSs compared to the as-polished. OP presented reduced SBS, and its cross-sections showed increased microporosities in the veneering porcelain. Significance: APP did not change surface morphology but enhanced wettability. CP and AP improved porcelain–zirconia SBSs, primarily through surface hydroxylation. OP induced the microporosities in porcelain and adversely affected the adhesion.