Quick answer
Dental zirconia is not one material. It is zirconium dioxide stabilised with different amounts of yttria, and that amount decides whether a restoration is built for strength or for appearance. Knowing the grade on your quote tells you far more than the word "zirconium".
What the numbers mean
The "Y" number is the yttria content in mol%. More yttria keeps more of the material in its cubic crystal form, which scatters less light and looks more translucent, but gives up some of the toughening that makes zirconia so strong.
| Grade | Typical flexural strength | Translucency | Typical uses |
|---|---|---|---|
| 3Y-TZP | About 1,000–1,200 MPa | Low, fairly opaque | Molar crowns, bridges, implant frameworks, masking dark teeth |
| 4Y-TZP | About 750–900 MPa | Medium | Premolar and some front crowns, short bridges |
| 5Y-TZP | About 600–750 MPa | High | Front crowns and veneers on light teeth |
| Multilayer blanks | Graded within one crown | Graded | Crowns needing strength at the gum and translucency at the edge |
Why strength and translucency trade off
3Y zirconia resists cracks through transformation toughening: under stress at a crack tip, the crystals change shape, expand slightly and squeeze the crack closed. The cubic phase that makes 4Y and 5Y more translucent does not do this, so those grades are less tough. That is why highly translucent 5Y should not be used for long bridges or heavily loaded molars, even though it is still stronger than glass-ceramics such as lithium disilicate.1
Masking dark teeth
Opacity is sometimes an advantage. Over a dark root-treated tooth, a metal post or tetracycline staining, opaque 3Y or a multilayer blank hides the colour far better than 5Y. Translucent 5Y over a dark core can look grey.
Wear on opposing teeth
All grades are very hard. When highly polished, monolithic zirconia causes little wear on opposing enamel; when left rough after adjustment, or once its glaze has worn away, it becomes abrasive. Every adjusted surface should be re-polished.
Bonding
Zirconia has no glass phase, so it cannot be etched with hydrofluoric acid like porcelain. Crowns with good retention can be cemented conventionally; veneers and short crowns need air abrasion, a 10-MDP primer and an MDP-containing resin cement.2 See our adhesive bonding guide.
Questions to ask about your quote
- Which grade, or which multilayer blank, will be used for each tooth?
- Which manufacturer made the blank (for example Kuraray Katana, Ivoclar IPS e.max ZirCAD, Zirkonzahn Prettau, Dentsply Sirona Cercon or 3M Lava)?
- Will the crowns be monolithic, or layered with porcelain?
Related guides
Zirconia crowns · Zirconium veneers · Dental bridge · Adhesive bonding
References
- Zhang Y, Lawn BR. Novel zirconia materials in dentistry. J Dent Res. 2018;97(2):140–147. PubMed
- Özcan M, Bernasconi M. Adhesion to zirconia used for dental restorations: a systematic review and meta-analysis. J Adhes Dent. 2015;17(1):7–26. doi:10.3290/j.jad.a33525