Objectives: Although air-particle abrasion delivers advantages for improved adhesive strength of resin cements to yttria-stabilized tetragonal-zirconia-polycrystalline (zirconia), it is not widely studied whether this process impairs the mechanical properties of such ceramics. The objective of this study was to evaluate the effect of different particle deposition protocols on the biaxial flexural strength of a commercial zirconia after long term cyclic loading.

Materials and methods : Disc shaped sintered zirconia specimens (diameter: 15 mm, thickness: 1.2 mm) ( N = 64/ n = 8 per group) were obtained from the manufacturer (Vita YZ, Vita). Three air-abrasion protocols, namely (1) 50 μm Al ₂ O ₃ particles, (2) Laboratory silica coating (110 μm alumina particles coated with silica-Rocatec Pre and Plus, 3M ESPE) and (3) Chairside silica coating (30 μm alumina particles coated with silica-CoJet, 3M ESPE) were employed on the cementation surface of the specimens under standardized conditions (distance: 10 mm; pressure: 2.9 bars, duration: 20 s). Control group received no surface treatment. All specimens were tested for biaxial flexural strength (ISO 6872) after being subjected to mechanical cyclic loading (20,000 cycles under 50 N load, immersion in distilled water at 37 °C) in a universal testing machine (1 mm/min).

Results : The air-abrasion protocols ( p = 0.001) showed significant effect on the results (two-way ANOVA, Tukey’s test, α = 0.05). The highest results (MPa) were obtained with 30 μm CoJet-Sand (1266 ± 158) being not significant than that of 110 μm Rocatec (1179 ± 216) ( p > 0.05). Air abrasion with 50 μm Al ₂ O ₃ particles (915 ± 186) showed the lowest biaxial flexural strength results.

Conclusions : Particle morphology has a significant effect on the flexural strength of zirconia. Mechanical properties of zirconia may not be impaired with adequate choice of application of the particle deposition methods prior to cementation.