Abstract
Although sandblasting is mainly used to improve bonding between dental zirconia and resin cement, the details on the in-depth damages are limited. The aim of this study was to evaluate phase transformations and subsurface changes after sandblasting in three different dental zirconia (3, 4, and 5 mol% yttria-stabilized zirconia; 3Y-TZP, 4Y-PSZ, and 5Y-PSZ). Zirconia specimens (14.0 × 14.0 × 1.0 mm3) were sandblasted using different alumina particle sizes (25, 50, 90, 110, and 125 µm) under 0.2 MPa for 10 s/cm2. Phase transformations and residual stresses were investigated using X-ray diffraction and the Williamson-Hall method. Subsurface damages were evaluated with cross-sections by a focused ion beam. Stress field during sandblasting was simulated by the finite element method. The subsurface changes after sandblasting were the emergence of a rhombohedral phase, micro/macro cracks, and compressive/tensile stresses depending on the interactions between blasting particles and zirconia substrates. 3Y-TZP blasted with 110-µm particles induced the deepest transformed layer with the largest compressive stress. The cracks propagated parallel to the surface with larger particles, being located up to 4.5 µm under the surface in 4Y- or 5Y-PSZ subgroups. The recommended sandblasting particles were 110 µm for 3Y-TZP and 50 µm for 4Y-PSZ or 5Y-PSZ for compressive stress-induced phase transformations without significant subsurface damages.
Highlights
Zirconia ceramics doped with 3 mol% Y2 O3 (3 mol% yttria-stabilized tetragonal zirconia polycrystal; 3Y-TZP) play a key role in dentistry since they are used in diverse important applications such as crowns, endodontic posts, orthodontic brackets and dental implants
The tetragonal phase contents decreased while the rhombohedral phase contents increased as the blasting particle size increased for all zirconia grades
We have evaluated the crystallographic and microstructural subsurface changes after alumina sandblasting with five different particle sizes in three different dental zirconia grades
Summary
Zirconia ceramics doped with 3 mol% Y2 O3 (3 mol% yttria-stabilized tetragonal zirconia polycrystal; 3Y-TZP) play a key role in dentistry since they are used in diverse important applications such as crowns, endodontic posts, orthodontic brackets and dental implants.In addition, improvements in the manufacturing process of zirconia ceramics combined with computer aided design/computer aided manufacturing (CAD/CAM) technologies are capable of creating the repeatable fabrication of individualized dental prosthesis with high accuracy [1]. Zirconia is a metastable ceramic, consisting of monoclinic, tetragonal, and cubic phases depending on the temperature. Zirconia ceramics exhibited superior fracture toughness and strength, their inherent opacity often cannot satisfy patients’ esthetic demands. With higher yttria contents (4 or 5 mol% partially stabilized zirconia; 4Y-PSZ or 5Y-PSZ), the amount of isotropic cubic phase increases and a significant enhancement in translucency has been obtained due to the reduced light scattering at the grain boundaries [3]. Since the tetragonal to monoclinic phase transformation under tension is the main factor to determine the fracture toughness, the mechanical strengths of highly translucent zirconia would be compromised due to the limited amount of metastable tetragonal phase [3]
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