Effect of Airborne Particle Abrasion and Nitric-Hydrofluoric Acid Etching on the Mechanical and Structural Properties of 3Y- and 5Y-TZP Zirconia.

Abstract

Introduction: Surface treatment is essential for optimizing zirconia bonding, but conventional airborne-particle abrasion (APA) may compromise its mechanical properties, particularly in highly translucent materials. Nitric-hydrofluoric acid (HF) etching has recently emerged as a potential alternative, yet its influence on the surface characteristics and mechanical performance of different zirconia generations remains inadequately understood. Therefore, this study evaluated the effects of APA and nitric-HF etching on the surface roughness, crystalline structure, and biaxial flexural strength (BFS) of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 5 mol% Y-TZP (5Y-TZP) zirconia.

Methods: Ninety-six disc-shaped specimens (10 mm diameter × 1.5 mm thickness) were milled from 3Y-TZP (ZI) (n = 48) and 5Y-TZP (FX) (n = 48). Each zirconia type was randomly allocated into four treatment subgroups (n = 12 per subgroup; 8 subgroups in total): (1) untreated control, (2) APA-50, (3) APA-120, and (4) Zircos E etching. Surface roughness (Ra) was measured using a Marsurf Ps10 surface roughness analyzer, while the crystalline structure was assessed by X-ray diffraction (XRD) diffraction and BFS was evaluated using a universal testing machine according to ISO 6872. Data were statistically analyzed using ANOVA (α = 0.05), followed by posthoc tests.

Results: APA-120 showed the highest Ra values (ZI = 1.09 ± 0.29 µm; FX = 0.69 ± 0.12 µm), significantly higher than those of all other treatments (p  < 0.001). Acid etching produced Ra values comparable to the controls (ZI = 0.38 ± 0.06 µm; FX = 0.47 ± 0.03 µm; p  > 0.05). for XRD, 5Y zirconia remained stable across all treatments, while 3Y zirconia showed slight peak intensity changes and minor tetragonal-to-monoclinic transformation after APA, with no change after acid etching. BFS was consistently higher in ZI than in FX (p  < 0.001). The highest strength was recorded for untreated ZI (1059 ± 103 MPa), whereas the lowest was observed for FX after APA-120 (420 ± 80 MPa). Zircos-E preserved 84.7% of the control strength in ZI (897 ± 153 MPa) and 96% in FX (479 ± 97 MPa), whereas APA-120 reduced strength by ~20% in 3Y-TZP and 16% in 5Y-TZP.

Conclusions: APA with 120 µm Al₂O₃ maximizes microroughness but compromises the flexural strength. Zircos E etching produced limited surface roughness changes while preserving crystalline stability and flexural strength in both zirconia generations.