Effect of Al2O3 Sandblasting Particle Size on the Surface Topography and Residual Compressive Stresses of Three Different Dental Zirconia Grades

Abstract

This study investigated the effect of sandblasting particle size on the surface topography and compressive stresses of conventional zirconia (3 mol% yttria-stabilized tetragonal zirconia polycrystal; 3Y-TZP) and two highly translucent zirconia (4 or 5 mol% partially stabilized zirconia; 4Y-PSZ or 5Y-PSZ). Plate-shaped zirconia specimens (14.0 × 14.0 × 1.0 mm³, n = 60 for each grade) were sandblasted using different Al₂O₃ sizes (25, 50, 90, 110, and 125 μm) under 0.2 MPa for 10 s/cm² at a 10 mm distance and a 90° angle. The surface topography was characterized using a 3-D confocal laser microscopy and inspected with a scanning electron microscope. To assess residual stresses, the tetragonal peak shift at 147 cm^-1 was traced using micro-Raman spectroscopy. Al₂O₃ sandblasting altered surface topographies (p < 0.05), although highly translucent zirconia showed more pronounced changes compared to conventional zirconia. 5Y-PSZ abraded with 110 μm sand showed the highest Sa value (0.76 ± 0.12 μm). Larger particle induced more compressive stresses for 3Y-TZP (p < 0.05), while only 25 μm sand induced residual stresses for 5Y-PSZ. Al₂O₃ sandblasting with 110 μm sand for 3Y-TZP, 90 μm sand for 4Y-PSZ, and 25 μm sand for 5Y-PSZ were considered as the recommended blasting conditions.

Keywords: air abrasion; dental stress analysis; phase transition; surface properties; zirconium oxide.

Figure 1

Flow chart of the experimental procedure; specimen preparation and Al₂O₃ sandblasting conditions as well as the analytical methods associated with surface topography, residual stresses, microstructure, and Al₂O₃ particle analysis are depicted. 3Y-TZP: 3 mol% yttria-stabilized tetragonal zirconia polycrystal; 4Y-PSZ: 4 mol% partially-stabilized zirconia; 5Y-PSZ: 5 mol% partially-stabilized zirconia; CLSM: confocal laser scanning microscopy; ICP OES: inductively coupled plasma optical emission spectrometry.

Figure 2

Characteristics of the alumina particle size distributions. There were significant differences among all particle size specifications and the measured particle sizes increased as the particle size specification increased (p < 0.05).

Figure 3

Particle size distributions and scanning electron micrographs of Al₂O₃ particles. The finest particles were observed in the 25 μm specification, while the largest particles prevailed in the 125 μm specification. Most of the particles had a grit shape with sharp edges and rarely a spherical shape. (A) 25 μm specification; (B) 50 μm specification; (C) 90 μm specification; (D) 110 μm specification; (E) 125 μm specification.

Figure 3

Particle size distributions and scanning electron micrographs of Al₂O₃ particles. The finest particles were observed in the 25 μm specification, while the largest particles prevailed in the 125 μm specification. Most of the particles had a grit shape with sharp edges and rarely a spherical shape. (A) 25 μm specification; (B) 50 μm specification; (C) 90 μm specification; (D) 110 μm specification; (E) 125 μm specification.

Figure 4

Three-dimensional representations obtained by confocal laser scanning microscopy and scanning electron microscopic images (magnification 10,000×) of each subgroup. For the SEM images, the white arrow indicates a micro-crack; the red arrow indicates Al₂O₃ particle debris deposited on the abraded zirconia surface; the white circle indicates plastic deformation; the red circle indicates surface melting. (A) 3Y-con.; (B) 3Y-25.; (C) 3Y-50.; (D) 3Y-90.; (E) 3Y-110.; (F) 3Y-125.; (G) 4Y-con.; (H) 4Y-25.; (I) 4Y-50.; (J) 4Y-90.; (K) 4Y-110.; (L) 4Y-125.; (M) 5Y-con.; (N) 5Y-25.; (O) 5Y-50.; (P) 5Y-90.; (Q) 5Y-110.; (R) 5Y-125.

Figure 4

Three-dimensional representations obtained by confocal laser scanning microscopy and scanning electron microscopic images (magnification 10,000×) of each subgroup. For the SEM images, the white arrow indicates a micro-crack; the red arrow indicates Al₂O₃ particle debris deposited on the abraded zirconia surface; the white circle indicates plastic deformation; the red circle indicates surface melting. (A) 3Y-con.; (B) 3Y-25.; (C) 3Y-50.; (D) 3Y-90.; (E) 3Y-110.; (F) 3Y-125.; (G) 4Y-con.; (H) 4Y-25.; (I) 4Y-50.; (J) 4Y-90.; (K) 4Y-110.; (L) 4Y-125.; (M) 5Y-con.; (N) 5Y-25.; (O) 5Y-50.; (P) 5Y-90.; (Q) 5Y-110.; (R) 5Y-125.

Figure 5

The surface texture parameters of each subgroup for three different zirconia grades. Mean values represented with same uppercase letters (within each row) or lowercase letters (within each column) are not significantly different based on the results of pairwire comparisons for simple main effects using Sidak adjustment (p > 0.05). The values of the Sa, Sq, or Sv parameters increased with an increase in the particle size up to 110 μm, whereas those values decreased with 125 μm alumina sand, lying between those with 50- and those with 90 μm alumina sand for all zirconia grades.

Figure 6

Representative μRaman spectra for each subgroup of three zirconia grades. (A) 3Y-TZP.; (B) 4Y-PSZ.; (C) 5Y-PSZ. The shapes of the spectra for 3Y-TZP specimens are clearly different from those for 4Y- or 5Y-PSZ specimens. In order to confirm the crystalline structures of the specimens, Raman peaks from 130 to 190 cm⁻¹ and from 440 to 660 cm⁻¹ are shown. For 3Y-TZP, the tetragonal peaks at 147, 456, and 641 cm⁻¹ decreased, while the monoclinic peaks at 178 and 506 cm⁻¹ increased as the particle size increased. For 4Y- and 5Y-PSZ, the tetragonal peaks at 641 cm⁻¹ decreased, whereas the cubic peaks at 625 cm⁻¹ were maintained.

Figure 6

Representative μRaman spectra for each subgroup of three zirconia grades. (A) 3Y-TZP.; (B) 4Y-PSZ.; (C) 5Y-PSZ. The shapes of the spectra for 3Y-TZP specimens are clearly different from those for 4Y- or 5Y-PSZ specimens. In order to confirm the crystalline structures of the specimens, Raman peaks from 130 to 190 cm⁻¹ and from 440 to 660 cm⁻¹ are shown. For 3Y-TZP, the tetragonal peaks at 147, 456, and 641 cm⁻¹ decreased, while the monoclinic peaks at 178 and 506 cm⁻¹ increased as the particle size increased. For 4Y- and 5Y-PSZ, the tetragonal peaks at 641 cm⁻¹ decreased, whereas the cubic peaks at 625 cm⁻¹ were maintained.

Figure 7

The 147 cm⁻¹ of the t-ZrO₂ Raman peak shift for each subgroup of three zirconia grades as a function of Al₂O₃ particle size. Mean values represented with the same uppercase letters (within each zirconia grade) or lowercase letters (within each particle size) are not significantly different based on the results of pairwire comparisons for simple main effects using the Sidak adjustment (p > 0.05). For 3Y-TZP, the peak shift increased with increasing particle sizes up to 125 μm (p < 0.05). The tetragonal peak at 147 cm⁻¹ shifted to a higher wavenumber up to 90 μm for 4Y-PSZ (p < 0.05), while the peak shifted to a higher wavenumber up to 25 μm for 5Y-PSZ (p < 0.05).