Changes in bond strength and topography for y-tzp etched with hydrofluoric acid depending on concentration and temperature conditions

Background and objectives: This study aimed to investigate the change in bond strength between resin cement and tetragonal zirconia polycrystalline stabilized with 3 to 8 mol% yttrium oxide (Y-TZP) and observe the topographical change of the Y-TZP surface when etched with hydrofluoric acid (HF) solution under different concentration and temperature conditions. Materials and Methods: Non-etched sintered Y-TZP specimens under two different temperature conditions (room temperature and 70–80^◦ C, respectively), were used as a control, while experimental groups were etched with 5%, 10%, 20%, and 40% HF solutions for 10 min. After zirconia primer and MDP-containing resin cement were applied to the Y-TZP surface, the shear bond strength (SBS) of each experimental group was measured. Results: Under room temperature conditions, the highest SBS value was measured in the 40% HF etching group, representing a significant deviation from the other groups (p < 0.05). In the 70–80^◦ C tests, the 40% HF etching group also had the highest SBS value, but there was no significant difference when compared to the 20% HF etching group (p > 0.05). From SEM and AFM observations, the HF solution increasingly dissolved the Y-TZP surface grain structure as the concentration and application temperature rose, resulting in high surface roughness and irregularities. Conclusions: Pretreating with either 20% HF solution at 70–80^◦ C or 40% HF solution at room temperature and 70–80^◦ C effectively acid etched the Y-TZP surface, resulting in more surface roughness and irregularities. Accounting for the concentration and temperature conditions of the HF solution, using 40% HF solution at room temperature will result in improvements in adhesion between resin cement and Y-TZP.