E.max or Zirconia: Which Material for a Crown or Veneer?

The short answer: aesthetics on one side, strength on the other

Lithium disilicate (best known under the brand name e.max) is a highly aesthetic, translucent glass-ceramic that bonds strongly to the tooth: it is often preferred for veneers and front teeth. Zirconia is a polycrystalline ceramic with much greater fracture resistance and, in its classic forms, more opacity: it is often chosen for molars, bridges and patients who clench. Newer multilayer zirconias narrow the aesthetic gap, at the cost of slightly lower strength in their most translucent layers.

So there is no superior material in absolute terms. There is a material suited to a specific tooth, situation and mouth. The selection criteria are set out below; for an overview of every crown family (metal, porcelain-fused-to-metal, all-ceramic), see our article on dental crowns: steps and materials.

Lithium disilicate (e.max) in detail

Lithium disilicate is a reinforced glass-ceramic: a glassy phase that provides translucency contains elongated crystals that give it high strength for a ceramic of this type.

Strengths:

• translucency and light behaviour close to natural enamel;
• adhesive bonding: its surface can be etched with hydrofluoric acid and silanised, creating a very strong bond to enamel. This bond contributes to the strength of the whole restoration and allows thin designs;
• versatility: veneers, inlays and onlays, front-tooth and premolar crowns, sometimes molars when there is enough thickness;
• made by pressing in the laboratory or milling a CAD/CAM block, then crystallised in a furnace.

Limits:

• lower strength than zirconia, so a minimum ceramic thickness is required, which sometimes means slightly more preparation;
• less suitable for long bridges or back-tooth bridges;
• bonding requires careful isolation of the tooth, which is difficult when the margin lies deep under the gum.

Zirconia: monolithic, layered, multilayer

Zirconia (zirconium dioxide) is a very dense oxide ceramic with no glassy phase. It comes in several forms worth distinguishing:

• monolithic zirconia: the crown is milled from a single block with no cosmetic porcelain on top. This is the strongest version, with no risk of the surface layer chipping. Its shade comes from colouring and staining;
• layered zirconia: a zirconia framework veneered with feldspathic porcelain. Very aesthetic, but the veneering layer can chip;
• multilayer zirconia: a single block with a gradient of shade and translucency from the gumline to the edge. Some even combine stronger zones with more translucent ones.

So-called high-translucency zirconias (often labelled 4Y or 5Y according to their yttria content) are more aesthetic but less strong than classic zirconia (3Y). Choosing the zirconia generation is itself a trade-off.

Strengths: high strength, thin walls possible on back teeth, good ability to mask a dark tooth or metal post, and conventional cementation is possible when bonding is difficult.

Limits: relative opacity, cannot be etched with hydrofluoric acid (air abrasion and specific primers are used instead), and any bite adjustments must be carefully polished.

Which material for which tooth?

These are the generally accepted tendencies, to be adapted to each case:

• Incisors and canines: lithium disilicate is often preferred for its translucency and bonding, as a veneer or crown. If the underlying tooth is very dark, multilayer or layered zirconia may mask it better.
• Veneers: lithium disilicate or feldspathic porcelain. Zirconia is rarely used for thin veneers, as it does not bond as well and remains more opaque. Our page on dental veneers describes this treatment.
• Premolars: both materials work; the choice depends on how visible the tooth is in your smile, the available thickness and the forces involved.
• Molars: monolithic zirconia is often preferred, particularly with clenching or short teeth. Lithium disilicate remains possible when space and bite allow.
• Bridges: zirconia for back-tooth or multi-unit bridges; lithium disilicate is limited to three-unit bridges, at the front and as far back as the premolars, within the manufacturer's indications.
• Implant crowns: both are used, often on a titanium base; zirconia is common for back teeth.

Combining both in the same mouth is perfectly possible: lithium disilicate at the front, zirconia at the back, with matched shades.

Bruxism, opposing teeth and other deciding factors

Beyond tooth position, several factors can tip the balance:

• Bruxism (clenching, grinding): the strength of monolithic zirconia is an asset. A night guard is still advisable whatever the material.
• Wear of opposing teeth: a rough ceramic can wear the enamel it bites against. Well-polished monolithic zirconia is generally gentle; polish quality matters more than the material itself.
• Colour of the underlying tooth: on a grey root-filled tooth or a metal core, a more opaque material is needed.
• Depth of the margin: if it sits far below the gum, conventional cementation (possible with zirconia) can be more predictable than bonding.
• Available thickness: a short or heavily broken-down tooth leaves less room; zirconia tolerates thinner sections on back teeth.
• Future repairs: lithium disilicate can sometimes be repaired locally; fractured zirconia is usually remade.

The question of zirconia ageing in a moist environment is well known: current zirconias and a correct manufacturing protocol aim to limit it.

What digital dentistry changes

Both materials fit a digital workflow: an intraoral scan, computer-aided design and then milling of the block. Lithium disilicate is milled in a soft intermediate state and then crystallised in a furnace, which gives it its final shade and strength. Zirconia is usually milled in a pre-sintered state and then sintered at high temperature, with shrinkage calculated in advance by the software.

Some restorations can therefore be made at the practice, sometimes in a single visit depending on the material and the case: our article on the same-day ceramic crown explains when that is possible. Others, especially demanding aesthetic cases or layered zirconia, go through a dental laboratory for finer staining or layering.

Choosing with your dentist in Rabat

To make an informed choice, ask these questions at your consultation: which material for this particular tooth, and why? Will one of them need more tooth reduction? Is the underlying tooth dark? Do I clench? How will the crown be fixed, bonded or cemented?

At German Dental Clinic in Agdal, the choice between lithium disilicate and zirconia is made after an examination, X-rays and bite analysis, taking your aesthetic expectations into account. The practice has an intraoral scanner and an in-house milling unit (CAD/CAM) to make certain dental crowns on site. If you are in Rabat and unsure which material to choose for a crown or veneer, book an appointment to talk it through.