Translucent and Highly Toughened Zirconia Suitable for Dental Restorations

Background: There is a limit to improving the characteristics of zirconia with only one kind of stabilizing element such as yttrium. The purpose of this study is to systematically evaluate the effects of various co-doped elements on mechanical and optical properties and to develop a novel composition of zirconia with enough properties to apply to dental restorations. Methods: Forty-four kinds of zirconia were prepared by combining trivalent cations yttrium (Y) and ytterbium (Yb), and pentavalent cations niobium (Nb) and tantalum (Ta) oxide as stabilizers. The combined contents ranged from 0 to 5.6 mol% for Y2O3, 0 to 4.2 mol% for Yb2O3, 0 to 1.5 mol% for Nb2O5, and 0 and 1.2 mol% for Ta2O5. These specimens were determined for fracture toughness and opacity. X-ray diffraction studies were undertaken to evaluate the microstructural change. Results: The present study revealed that adding of the trivalent cations Y and Yb reduced fracture toughness and opacity, whereas the addition of pentavalent cations Nb and Ta to zirconia stabilized with trivalent cations increased both properties. There was no clear difference in the effects of Y and Yb, Nb, and Ta. Conclusions: Considering many factors, the following composition is optimal: 3-4.2 mol% Y2O3 and/or Yb2O3 stabilized zirconia with up to 1.5 mol% Nb2O5 has sufficiently high fracture toughness values and sufficiently high translucency suitable for dental restorations.