Restor Dent Endod.  2021 Nov;46(4):e54. 10.5395/rde.2021.46.e54.

Change of phase transformation and bond strength of Y-TZP with various hydrofluoric acid etching

• Yu MK
• Oh EJ
• Lim MJ
• Lee KW

• KMID: 2548098
• DOI: http://doi.org/10.5395/rde.2021.46.e54

Abstract

Objectives
The purpose of this study was to quantify phase transformation after hydrofluoric acid (HF) etching at various concentrations on the surface of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), and to evaluate changes in bonding strength before and after thermal cycling.
Materials and Methods
A group whose Y-TZP surface was treated with tribochemical silica abrasion (TS) was used as the control. Y-TZP specimens from each experimental group were etched with 5%, 10%, 20%, and 40% HF solutions at room temperature for 10 minutes. First, to quantify the phase transformation, Y-TZP specimens (n = 5) treated with TS, 5%, 10%, 20% and 40% HF solutions were subjected to X-ray diffraction. Second, to evaluate the change in bond strength before and after thermal cycling, zirconia primer and MDPcontaining resin cement were sequentially applied to the Y-TZP specimen. After 5,000 thermal cycles for half of the Y-TZP specimens, shear bond strength was measured for all experimental groups (n = 10).
Results
The monoclinic phase content in the 40% HF-treated group was higher than that of the 5%, 10%, and 20% HF-treated groups, but lower than that of TS-treated group (p < 0.05). The 40% HF-treated group showed significantly higher bonding strength than the TS, 5%, and 10% HF-treated groups, even after thermal cycling (p < 0.05).
Conclusions
Through this experiment, the group treated with SiO₂ containing air-borne abrasion on the Y-TZP surface showed higher phase transformation and higher reduction in bonding strength after thermal cycling compared to the group treated with high concentration HF.

Keyword

Y-TZP; Hydrofluoric acid; Phase transformation; Thermal cycling; Bond strength

Figure

• 

  Figure 1 X-ray diffraction patterns of yttria-stabilized tetragonal zirconia polycrystal surfaces etched with various concentrations of hydrofluoric acid or treated with tribochemical silica abrasion.TS, tribochemical silica air-borne abrasion; AS, after sintering.

• 

  Figure 2 Monoclinic phase content (Fm.%) of yttria-stabilized tetragonal zirconia polycrystal when treated with hydrofluoric acid depending on concentration conditions. Identical capital letters in figure indicate no statistically significant differences (p > 0.05).TS, tribochemical silica air-borne abrasion; HF, hydrofluoric acid.

• 

  Figure 3 Shear bond strength before and after thermal cycling for HF etched yttria-stabilized tetragonal zirconia polycrystal at various concentration conditions. Identical lowercase letters indicate no statistically significant differences (p > 0.05).TS, tribochemical silica air-borne abrasion; TC, thermal cycling; HF, hydrofluoric acid.

• 

  Figure 4 Scanning electron microscopic views of debonded Y-TZP specimens without thermal cycling after surface treatment with various concentrations of hydrofluoric acid. (A-E) Y-TZP specimens treated with tribochemical silica abrasion, 5%, 10%, 20%, and 40% HF at magnification X30. (F, J) Y-TZP specimens treated with tribochemical silica abrasion, 5%, 10%, 20%, and 40% HF at magnification ×10,000. The white arrow indicates the primed layer.Y-TZP, yttria-stabilized tetragonal zirconia polycrystal.

• 

  Figure 5 Scanning electron microscopic views of debonded Y-TZP specimens thermally cycled after surface treatment with various concentrations of hydrofluoric acid. (A-E) Y-TZP specimens treated with tribochemical silica abrasion, 5%, 10%, 20%, and 40% HF at magnification X30. (F, J) Y-TZP specimens treated with tribochemical silica abrasion, 5%, 10%, 20%, and 40% HF at magnification ×10,000. The white arrow indicates the primed layer.Y-TZP, yttria-stabilized tetragonal zirconia polycrystal.

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