The purpose of this in vitro study was to find ways of treating the zirconia surface without causing flaws, debris, pits, microcracks, or tetragonal to monoclinic phase transformation.
Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic surfaces were treated with gas plasma, argon-ion bombardment, 150-μm abrasive zirconia particles, and abrasive 150-μm alumina particles; untreated surfaces were used as the control group. X-ray diffraction (XRD) and confocal Raman spectroscopy were used to study the phase transformation. The roughness of specimens was measured with a confocal 3D laser scanning microscope. Modification of surface topography was analyzed with field emission scanning electron microscopy (FESEM), and the flexural strength was measured with a universal testing machine. Statistical analyses were performed with 1-way ANOVA, followed by comparison of means with the Tukey honest significant difference test. The standard deviation was calculated with descriptive statistics.
The sintered Y-TZP ceramic used in this study showed 2 phases, tetragonal and cubic. Specimens abraded with 150-μm alumina particles showed a higher monoclinic volume fraction (VmXRD=8.68%) and roughness (Ra=0.91μm) than specimens abraded with 150-μm zirconia particles (VmXRD=1.22%, Ra=0.08μm). One-way ANOVA indicated a significance difference in roughness among groups (P<.01). No phase transformation was observed in specimens treated with argon-ion bombardment or plasma. According to the Raman results, the volume fraction of the monoclinic phase for the specimens treated with airborne-particle abrasion depended on the distance from the ceramic surfaces and decreased with the increase in this distance. A slightly higher flexural strength was observed for untreated specimens (1009 MPa), followed by specimens treated with gas plasma (1000 MPa) and those airborne-particle abraded with 150-μm zirconia particles (967 MPa). The flexural strength of other specimens was lower (940 MPa for specimens abraded with 150-μm alumina particles and 916 MPa for specimens subjected to argon-ion bombardment). One-way ANOVA analysis indicated no significant difference in flexural strengths among all groups (P>.2). FESEM measurements showed that airborne-particle abrading Y-TZP surfaces with 150-μm alumina particles caused more damage to this area than the other methods.
Y-TZP ceramic surfaces treated with zirconia particles, argon-ion bombardment, and gas plasma were damaged less in comparison with surfaces abraded with alumina particles.