Zirconia veneers: the material behind every Xiluet smile.

Zirconia is zirconium dioxide, a white crystalline ceramic. It is not a metal and contains none, which is why it does not corrode, does not show a dark line at the gum and does not trigger metal sensitivities. Dentistry adopted it for crowns and bridges two decades ago because it was the first ceramic strong enough to replace metal frameworks. For most of that time it was too opaque for a front tooth.

That changed with multilayer discs. A modern disc is pressed in five layers of shade, warmer and more opaque at the base, lighter and more translucent toward the edge, so the gradient of a natural tooth is already inside the material before anything is cut. Every veneer, crown and bridge we make is zirconia milled from German-made discs in our own lab.

Zirconia comes in grades named for the amount of yttria that stabilises the crystal. The lower the number, the stronger and more opaque the ceramic; the higher, the more translucent and the less strong. A molar crown wants strength; a front veneer wants light to pass through it the way it passes through enamel. Multilayer discs resolve the trade inside one piece: the strong, warm, opaque grade at the base where a tooth is thickest near the gum, the translucent grade toward the biting edge, where light should pass through. The ceramist positions each veneer in the disc so that gradient falls in the right place.

• 3Y

  The strongest grade, roughly 1,000 to 1,200 MPa. Opaque. The material for molars, bridges and the base of a multilayer disc.

• 4Y

  A middle grade: more translucent than 3Y with most of its strength. Used where a crown has to look natural and still take a heavy bite.

• 5Y

  The most translucent grade, closer in look to glass ceramic, with lower strength. The outer layer of a disc, where the edge of a veneer catches the light.

• Multilayer

  Five layers from opaque base to translucent edge in one disc. The gradient is in the material itself, not painted on afterwards.

Strength in ceramics is measured as flexural strength, in megapascals. The manufacturer's figure for IPS e.max is about 470 MPa. Standard 3Y zirconia is rated at roughly 1,000 to 1,200 MPa, two to three times higher. That gap is why zirconia is the default for molars, bridges and patients who grind, and why e.max is usually limited to single front teeth.

Strength also decides how much of your tooth is kept. An e.max crown needs 1.0 mm walls; a zirconia crown can be made with 0.5 mm walls, half a millimetre of your own tooth kept all the way round. For veneers both can be made at 0.3 mm, though most labs ask for 0.5 to 0.7 mm of e.max to be safe; ours are 0.3 mm as standard, and at that thickness zirconia has strength to spare, which is what lets the preparation stay inside the enamel on every tooth. On a dark tooth the ceramist uses a little more of the opaque base of the disc so the grey does not show through; you see that on the preview at Visit 1. The zirconia vs e.max article goes through the numbers tooth by tooth.

• Zirconia vs e.max, in detail
• Zirconia vs composite

Milling is the start, not the end. Straight off the machine a zirconia piece rarely fits, and it has none of the surface a natural tooth has. In our lab each veneer is seated on the model and adjusted under magnification with fine burs until it sits without pressure. The margin is polished into a closed seal at the gum line so bacteria cannot get under it. Then the ceramist builds the surface by hand: the faint vertical texture of enamel, the translucency at the edge, the small irregularities that stop a set from reading as uniform.

The shade is matched in person. At Visit 3 the ceramist comes down to the chair, holds the veneers against your teeth in daylight, and corrects anything that is off before bonding. If a veneer needs a change on delivery day, it goes upstairs and comes back the same afternoon. That is what makes the Monday-to-Thursday week possible.

• Inside the in-house lab
• Edgar Castaños, lab manager

We would be doing what we criticise if we pretended zirconia wins every case. e.max is a fine material for a single veneer on a front tooth with a healthy bite, especially when the tooth underneath is already bright and the goal is a small change of shape. Its glass structure gives a depth of translucency that is hard to beat on one tooth next to natural neighbours.

Where it stops being the honest choice is under load: long bridges, molars, grinders, dark teeth that need masking, and full sets where every tooth has to match and the bite is being rebuilt. There the strength and the margin advantages of zirconia are worth more than a fraction more translucency. That is most of our work, which is why our lab is set up for zirconia. If your case is the single bright front tooth, we will say so in your written plan.