Enhancing Fracture Toughness of Dental Zirconia through Incorporation of Nb into the Surface

Background: Our previous study found that the addition of pentavalent cations like niobium (Nb) to yttria-stabilized zirconia increased fracture toughness but also raised the coefficient of thermal expansion (CTE), and opacity also increased undesirably. A new surface treatment is required to boost fracture toughness without altering CTE or translucency. Methods: The surfaces of pre-sintered 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 4.2 mol% yttria-stabilized partially stabilized zirconia (4.2Y-PSZ) were treated with a Nb sol solution containing Nb₂O₅ nanoparticles. After drying and sintering, a high-Nb-content surface layer formed with a depth of approximately 1 mm. Results: The Nb content in this surface layer matched that of a bulk material with 1 mol% Nb₂O₅. The tetragonality of the surface zirconia increased, enhancing the surface fracture toughness without changing the CTE or translucency. Conclusions: Adding Nb near the surface improved the fracture toughness without affecting the CTE or translucency. This method could strengthen zirconia prostheses, allowing more reliable dental restorations.