The influence of sandblasting conditions on 3Y-TZP ceramics

Abstract

3Y-TZP ceramics are a high performance material with excellent biocompatibility and mechanical properties, which suggest its suitability for dental restorations and total hip replacement. These ceramics have a tendency to transform from tetragonal to monoclinic phase in the surface at temperatures close to room temperature. This phenomenon, referred as hydrothermal degradation, leads for example to the failure of femoral heads in vivo. For dental restorations, it is known that the strength and reliability of 3Y-TZP zirconia ceramics are affected by the inner surface sandblasting of crowns. The goal of this work is to study the effect of sandblasting conditions (angle, particle size) on the strength and degradation of 3Y-TZP. Zirconia ceramics doped with 3 molar % of yttria are used in this study. Samples sintered at 1450°C. Sintered samples were sandblasted with 110 and 250-μm alumina particles at 2 bars. Samples with polished surfaces were used as a control. The roughness decreased when the sample was tilted. For all angles, roughness of samples sandblasted with 110μm particles was about 40% less than with 250μm. This was explained by the decrease of surface area of contact when the sample was tilted or the particle size decreased. For both particle sizes, when the sample was tilted at an angle of 30°, the monoclinic volume content didn’t vary. However, it decreased of about 30% when the sample was tilted at 60°. Only one surface treatment (250-2B) didn’t improve the biaxial strength of 3Y-TZP. In the other cases, the sandblasting improved the biaxial strength between 8% (250-2B-30) to 21% (110-2B). For 110μm particles, tilting the sample didn’t improve the biaxial strength of the material. But, for 250μm particles, tilting the sample at 30° or 6 0° improved the biaxial strength of 8% and 10% respectively. Sandblasting with 250μm particles created larger flaws at the surface than 110μm particles (confirmed by the roughness values). Therefore, samples sandblasted with 250μm particles had biaxial strength lower. For samples sandblasted with 110μm particles, defects of about 30μm were found at the surface of samples which broke at low biaxial strength. These defects were due to the impingement of particles during the sandblasting. The surface treatments which appeared to be the best were 110-2B (Ra=0.75μm and _max=1547MPa) and 250-2B-30 (Ra=1.05μm and _max=1375MPa) because they had both high roughness and high biaxial strength.