Influence of surface treatments and cyclic fatigue on subsurface defects and mechanical properties of zirconia frameworks

Objectives: To evaluate the effect of laser fused and air abraded fluorapatite particles on flexural strength σf and fracture toughness (K _IC) of Yttria tetragonal zirconia polycrystal (Y-TZP). Methods: 160 polished Y-TZP bars received one of the following surface treatments: airborne particle abrasion (APA) with fluorapatite glass-ceramics (FGC), APA with tribochemical silica-coated alumina (CoJet), laser fused FGC using Nd:YAG Laser (FGC + Laser), while as-sintered polished specimens served as control. Initial flexural strength σfI was measured to half of the specimens, while the rest underwent cyclic fatigue (1,000,000 cycle of 15N load and 3 s contact time) followed by measuring residual flexural strength σfR. Fractographic analysis was performed and K _IC was calculated. The effect of surface treatment and fatigue on flexural strength was statistically analysed using 2-way ANOVA (α = 0.05). Weibull probability was measured to assess the reliability of flexural strength. Results: The highest σf before or after the fatigue was reported for the control group while the lowest was for FGC + Laser group. Cyclic fatigue significantly decreased the flexural strength of all groups except for FGC + Laser group. There was no significant difference between the K _IC between the control and FGC groups, however, a significant reduction of K _IC was found in the CoJet group, while FGC + Laser reported the significant lowest value compared to all groups (P = 0.00). Significance: Fluorapatite glass-ceramic powder offers a promising alternative for particle abrasion of zirconia-based frameworks.