Crown materials

How crowns are cemented, and why E-max is bonded when zirconia often is not

The last ten minutes of a crown appointment get the least attention, but the cement holds the crown on and seals the edge for years. Different crown materials need different approaches.

Medically reviewed by Dt. Hüseyin Yavuz Özbek, implant surgeon · Updated October 2026

Short answer

Crowns are fixed either with conventional cement, which mainly fills the gap and relies on the shape of the tooth for grip, or with adhesive resin cement, which bonds chemically to both tooth and crown. Glass-ceramics such as E-max can be etched and bonded, and bonding is the long-standing standard for silica-based ceramics. Zirconia cannot be etched the same way; it can be bonded after air-abrasion and a special primer, but a 2019 systematic review found zirconia crowns survived similarly with adhesive or conventional cement.

By the time a crown is ready to fix, most of the hard work seems done. The tooth has been prepared, scanned and the crown made. But the way it is fixed affects how long it stays put, how well the edge is sealed, and, for some materials, how strong the crown itself ends up being. The dental term is "luting": the cement that attaches a crown to a prepared tooth is called a luting agent. There are two broad families, and which one is used depends a lot on what the crown is made of.

Two ways to hold a crown on

Conventional cement

Conventional cements include zinc phosphate, glass ionomer and resin-modified glass ionomer. A 2007 review by Hill in Dental Clinics of North America described these alongside newer resin-based luting agents. They mainly fill the microscopic space between crown and tooth and lock into the small irregularities of both surfaces. They do not form a strong chemical bond to the crown.

With conventional cement, most of the grip comes from the shape of the prepared tooth. A tall tooth with nearly parallel walls holds a crown far better than a short, cone-shaped stump. A 2001 review of tooth preparation by Goodacre and colleagues set out guidelines for this: walls tapering by a total of 10 to 20 degrees, and a minimum height of 4 mm for molars and 3 mm for other teeth. Below that, extra features such as grooves are needed to stop the crown rocking off.

Adhesive (resin) cement

Adhesive cements are resin-based and bond to the tooth and to the inside of the crown, provided both surfaces are treated first. That treatment depends on the crown material. Bonding needs more steps and a dry, clean working area, so it is more technique-sensitive than conventional cementation. A 2018 review in the Journal of Dental Research by Blatz and colleagues made this point: resin bonding requires multiple pretreatment steps, which increases complexity compared with conventional cement.

In between sit self-adhesive resin cements, which bond to some degree without the full sequence of separate steps.

Why E-max crowns are bonded

E-max crowns are made of lithium disilicate, a glass-ceramic. Because it contains a glass phase, its inner surface can be etched with hydrofluoric acid, which creates a microscopically rough surface, and then treated with a silane primer that helps resin cement attach chemically. A 2018 study in the Journal of Prosthetic Dentistry used exactly this etch-and-silane routine to bond lithium disilicate.

Bonding does two jobs here. It holds the crown on, and it supports the ceramic. Glass-ceramic is strong for its type, but well below zirconia, and a crown that is bonded to the tooth behaves more like one unit under load. Blatz and colleagues described resin bonding as the long-standing gold standard for retention and reinforcement of low- to medium-strength silica-based ceramics.

For completeness: Ivoclar, which makes IPS e.max CAD, states that restorations can be cemented adhesively, self-adhesively or conventionally depending on the clinical situation. At our clinic, E-max crowns are bonded.

Why zirconia often is not

Zirconia is a different kind of ceramic. It is a polycrystalline oxide with no glass phase, so hydrofluoric acid does not etch it the way it etches lithium disilicate. For years that made zirconia hard to bond to.

It can be done. A 2015 review by Matthias Kern in Dental Materials looked at the clinical trials of resin-bonded zirconia and alumina restorations and found strong evidence that air-abrasion at moderate pressure combined with primers or cements containing phosphate monomers gives durable long-term bonding. That matters most for restorations with little mechanical grip, such as resin-bonded bridges.

For a full crown on a well-shaped tooth, the extra effort may not change much. Zirconia is strong enough not to need the reinforcement that glass-ceramic gets from bonding. Blatz's 2018 review found that veneered zirconia and alumina crowns had high long-term survival when fixed with conventional cements, although most studies still recommended resin bonding and it noted there were no long-term clinical data yet on bonding monolithic zirconia.

The most direct comparison is a 2019 systematic review for the American Academy of Fixed Prosthodontics, which included 17 clinical studies and 2,436 zirconia and lithium disilicate crowns. Survival of adhesively cemented zirconia crowns ranged from 83.3% to 100%, and of conventionally cemented ones from 82.0% to 100%. The authors concluded that zirconia and lithium disilicate crowns had comparable survival and complication patterns with either cement type, while warning that the quality of evidence was poor.

Does the bond last?

Bond strength measured on day one is not the same as bond strength years later in a wet mouth. The 2018 laboratory study tested resin cement bonded to 3Y zirconia, 5Y zirconia and lithium disilicate after 1 day and after 150 days in water. Every material lost some bond strength over that time: 3Y zirconia went from about 34 to 28 MPa, 5Y zirconia from about 35 to 25 MPa, and lithium disilicate from about 36 to 22 MPa. The authors found no significant difference between the materials overall, which suggests that, with the right surface treatment, zirconia can be bonded about as well as glass-ceramic in the lab.

In clinical studies, the common problems reported across both cement types were broadly the same. The 2019 review listed fracture of the veneering ceramic, fracture of the crown and loss of retention as the most commonly reported complications. Only the last of those is really about cement, and the evidence did not show that one cement type clearly prevented it.

When the choice of cement matters more

Retention is the main reason to think harder. A 2015 systematic review of single crowns found zirconia crowns had significantly more loss of retention than metal-ceramic crowns. Situations where a dentist is more likely to bond a zirconia crown, or to add retention in other ways, include:

short teeth, or teeth that had to be prepared with a steep taper
teeth with little sound structure left after decay or fracture
front teeth where a tooth-coloured resin cement helps the final shade

Where a tooth is too short to hold any crown well, the gum and bone may need reshaping first. That is covered in crown lengthening.

What happens on fixing day

At our clinic, fit, bite and shade are checked at a try-in before anything is fixed for good. In general, the fixing itself follows the material: surfaces of crown and tooth are cleaned and, for bonding, treated as the material requires; the tooth is kept dry; cement goes into the crown; the crown is seated; excess cement is cleared away from the edges and between the teeth; and the bite is checked again. Removing excess cement properly matters because it sits right at the edge of the crown and the gum, the area explained in crown margins explained.

Questions worth asking

Which cement will be used for each crown, and is it bonded or conventional?
Is my tooth tall enough to hold a crown well, or does it need extra retention?
If a crown is bonded, what happens if it ever needs to come off? Bonded crowns are usually harder to remove intact than conventionally cemented ones, which can matter if a root canal or repair is ever needed.
How will excess cement be cleared from below the gumline?

None of these have a single right answer for everyone. They are about matching the method to the material and the tooth, which is what the research above keeps pointing back to.

It is fair to ask which cement is planned for each of your crowns and why. If you would like a free written plan for your own teeth, contact us through our contact page.

Common questions

Is a bonded crown stronger than a cemented one?

For glass-ceramics like E-max, bonding helps support the ceramic as well as holding it in place, which is why it has long been the standard for that material. For strong zirconia crowns on a well-shaped tooth, clinical studies have not shown a clear survival difference between bonding and conventional cement.

Can a crown be fixed with temporary cement first?

Sometimes, to test comfort or appearance before final fixing. It is a clinical decision, and temporary cement is not designed to last. At our clinic, fit, bite and shade are checked at a try-in before the crowns are fixed permanently.

What if my tooth is very short?

Short or very tapered teeth give a crown less grip. Bonding, extra grooves in the preparation, or gum and bone reshaping may help. Our article on crown lengthening explains the surgical option.

My crown came out. Can it just be re-cemented?

Often, if the crown and tooth underneath are sound. Keep the crown safe and see a dentist rather than gluing it at home. See what to do if a crown comes off or chips.

Does the cement show?

It should not. Cement sits in a very thin layer inside the crown and at the edge. Resin cements also come in shades, which matters more under translucent crowns such as E-max on front teeth.

Sources

Checked October 2026. Where we give our own view as a clinic, we say so.

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