Effect of surface treatments on the properties and morphological change of dental zirconia

Abstract

Statement of problem: Creating a rough surface for bonding with airborne-particle abrasion with alumina may damage the surface of zirconia. Other treatment methods for creating a bonding surface without causing damage require investigation.

Purpose: 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.

Material and methods: 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.

Results: 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.

Conclusions: 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.