Effect of hydrofluoric acid-based etchant at an elevated temperature on the bond strength and surface topography of Y-TZP ceramics

Abstract

Objectives: This study investigated the effects of a hydrofluoric acid (HA; solution of hydrogen fluoride [HF] in water)-based smart etching (SE) solution at an elevated temperature on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics in terms of bond strength and morphological changes.

Materials and methods: Eighty sintered Y-TZP specimens were prepared for shear bond strength (SBS) testing. The bonding surface of the Y-TZP specimens was treated with 37% phosphoric acid etching at 20°C-25°C, 4% HA etching at 20°C-25°C, or HA-based SE at 70°C-80°C. In all groups, zirconia primers were applied to the bonding surface of Y-TZP. For each group, 2 types of resin cement (with or without methacryloyloxydecyl dihydrogen phosphate [MDP]) were used. SBS testing was performed. Topographic changes of the etched Y-TZP surface were analyzed using scanning electron microscopy and atomic force microscopy. The results were analyzed and compared using 2-way analysis of variance.

Results: Regardless of the type of resin cement, the highest bond strength was measured in the SE group, with significant differences compared to the other groups (p < 0.05). In all groups, MDP-containing resin cement yielded significantly higher bond strength values than MDP-free resin cement (p < 0.05). It was also shown that the Y-TZP surface was etched by the SE solution, causing a large change in the surface topography.

Conclusions: Bond strength significantly improved when a heated HA-based SE solution was applied to the Y-TZP surface, and the etched Y-TZP surface was more irregular and had higher surface roughness.

Keywords: Bond strength; HA-based etchant; Temperature elevation; Y-TZP.

Figure 1. Shear bond strength values of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in each group etched under various conditions with different resin cements.

MDP, methacryloyloxydecyl dihydrogen phosphate; PA, phosphoric acid; HA, hydrofluoric acid; SE, smart etching. Identical uppercase letters indicate no statistically significant differences (p > 0.05).

Figure 2. Scanning electron microscopy (SEM) images at 30,000 times magnification of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surfaces etched under different conditions. (A) Etching-free specimen (control); (B) 37% phosphoric acid (PA)-etched specimen; (C) 4% hydrofluoric acid (HA)-etched specimen; (D) HA-based smart etching (SE)-etched specimen.

Figure 3. Atomic force microscopy images of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surfaces etched under different conditions. (A) Etching-free specimen (control); (B) 37% phosphoric acid (PA)-etched specimen; (C) 4% hydrofluoric acid (HA)-etched specimen; (D) HA-based smart etching (SE)-etched specimen.