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 (sigma(f)) 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 (sigma fI) 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 (sigma fR). Fractographic analysis was performed and KIC was calculated. The effect of surface treatment and fatigue on flex-ural strength was statistically analysed using 2-way ANOVA (alpha = 0.05). Weibull probability was measured to assess the reliability of flexural strength. Results. The highest sigma f 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. Published by Elsevier Inc. on behalf of The Academy of Dental Materials.