A dental material based on yttria-stabilized zirconia (Y-TZP) is being evaluated. How many crystalline phases does yttria-stabilized zirconia typically contain?

Correct answer: A. 3

• A. CORRECT. Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) typically contains 3 crystalline phases: monoclinic, tetragonal, and cubic. The tetragonal phase is maintained by yttria stabilization and is responsible for transformation toughening — the key mechanism that makes Y-TZP strong and fracture-resistant.
• B. Incorrect. 6 phases is not correct for this material.
• C. Incorrect. 4 phases does not match standard Y-TZP crystallography.
• D. Incorrect. 5 phases is not correct for yttria-stabilized zirconia.