Effect of Surface Treatment on the Mechanical Properties of Zirconia

Objectives: The present study aimed to evaluate the shear bond strength (SBS) and biaxial flexural strength (BFS) of resin cements according to the surface treatment methods using low-concentration hot-etching with hydrofluoric acid on the yttrium-stabilized tetragonal zirconia (Y-TZP) surface.
Methods: Ninety-six Y-TZP discs were divided into 4 groups for the BFS test, and 72 Y-TZP cubes were classified into 3 groups for the SBS test according to the surface treatment methods. A total of 4 kinds of surface treatment methods were applied as follows: 1) no treatment (C, included only in the BFS group), 2) air abrasion with 50um Al₂O₃ particles (A), 3) hot etching with hydrofluoric acid in 100°C for 10 minutes (E), 4) air abrasion + hot-etching (AE). The cubic specimens were coated with primer and followed by the application of resin cement with the aid of a plastic mold. Half of the specimens in each group were stored in 37°C distilled water for 24 hours, and the other half of the specimens underwent 1,000 thermocycles. All specimens were observed with a scanning electron microscope, and the SBS, BFS, roughness (Ra) of the specimens were measured. Additionally, the phase composition of Y-TZP was determined by X-ray diffractometer. All data were analyzed with analysis of variance or Kruskal-Wallis tests (α=.05)
Results: Regardless of thermocycling process, group E exhibited significantly higher SBS value than the other 2 groups (p<.05). Groups C and E exhibited significantly higher BFS values compared to groups A and AE after thermocyclinig (p<.05), whereas no significant differences were observed for the BFS values among the 4 groups before thermocycling (p>.05). For all groups, phase transformation occurred from tetragonal to monoclinic phase.
Conclusions: Low-concentration hot-etching for 10 minutes produced significantly higher SBS and BFS values compared to airborne particle abrasion and simultaneous application of airborne particle abrasion and hot-etching treatment.