How to cement e.max crowns and onlays: HF etch and silane

When can e.max go in with a self-adhesive or conventional cement?

e.max takes a self-adhesive or conventional cement only as a crown or a three-unit bridge on a retentive prep, according to the IPS e.max CAD IFU (Ivoclar, 2026). Veneers, inlays, onlays and minimally invasive crowns must be bonded, and adhesive cementation is also the only option on a non-retentive prep.

The same IFU puts more limits on minimally invasive crowns: nothing under 1 mm, composite resin cores only, canine guidance present and never on implants. Minimum thicknesses for each restoration are in monolithic, multilayer zirconia or e.max.

A retentive prep has 10 to 20° of total occlusal convergence and at least 4 mm of occlusocervical height on molars and 3 mm on other teeth. Those are the values in Goodacre and colleagues’ classic review (The Journal of Prosthetic Dentistry, 2001).

Clinically, the cement makes little visible difference. Maroulakos and colleagues’ review (The Journal of Prosthetic Dentistry, 2019) found survival of 83.5% to 100% for bonded lithium disilicate crowns and 98.5% in the single conventionally cemented group, with poor-quality evidence.

What hydrofluoric acid should you use on e.max, and for how long?

e.max (lithium disilicate) is etched with 5% hydrofluoric acid for 20 seconds, according to Ivoclar’s Monobond Plus and Variolink Esthetic LC instructions. Leucite glass-ceramics such as IPS Empress get 60 seconds; lithium disilicate gets only 20.

More time and a stronger acid don’t help. May and colleagues (The Journal of Prosthetic Dentistry, 2022) ran a meta-analysis of lab studies: acid above 4.9% for 20 seconds or longer lowered the flexural strength of lithium disilicate without changing roughness. On feldspathic and leucite ceramics, 5% for 30 to 120 seconds increased roughness with no loss of strength.

Etching happens outside the mouth. Özcan and colleagues’ review (Clinical Oral Investigations, 2012) describes hydrofluoric acid as aggressive to soft tissue, with symptoms that may not show right away, and urges precautions for clinicians who use it chairside.

The IPS e.max CAD IFU also says the restoration must not be blasted with alumina. Air abrasion is the zirconia treatment.

What does silane do on e.max?

Silane is the primer that promotes the bond between etched e.max and the resin cement. In the Monobond Plus IFU, it stays on the etched surface for 60 seconds and is dispersed with a strong air stream; in crowns, without pooling.

A separate primer outperforms a silane-containing universal adhesive. Lima and colleagues’ meta-analysis (The Journal of Prosthetic Dentistry, 2024) pooled 26 lab studies. On lithium disilicate, hydrofluoric acid followed by a ceramic primer bonded better than acid followed by a silane-containing universal adhesive.

There is an alternative to the acid: a self-etching ceramic primer, which etches and silanates from one bottle. In the same meta-analysis, its bond was similar to acid plus silane. Ivoclar describes Monobond Etch & Prime in the Variolink Esthetic LC IFU: scrub for 20 seconds, leave for another 40, then rinse until the green color is gone.

With a self-adhesive cement, silane stays in the protocol. In its RelyX cement pretreatment guide, 3M calls for hydrofluoric acid and silane on glass-ceramics with its self-adhesive cement too.

What do you do when e.max is contaminated at try-in?

Contaminated e.max is cleaned before silane, and how depends on whether it was already etched. A restoration that wasn’t etched is rinsed, dried and etched after try-in, which also cleans the surface. A restoration etched before try-in gets a cleaning paste, per the Variolink Esthetic LC IFU: rinse, apply Ivoclean for 20 seconds, rinse, dry and then prime.

If silane was already on, it goes on again after cleaning, according to the Ivoclean IFU. And if the restoration is contaminated with saliva, blood or water after priming, the Monobond Plus IFU says to repeat the whole treatment.

The cleaning paste has one limit: the Ivoclean IFU contraindicates it on a restoration that has touched a silicone-based material.

How do you cement an e.max onlay?

An e.max onlay can only be bonded: the IPS e.max CAD IFU doesn’t allow self-adhesive or conventional cement for inlays, onlays, occlusal veneers or partial crowns. The Variolink Esthetic LC IFU requires relative or absolute isolation, and the Monobond Plus IFU says not to use the primer without a dry field.

At try-in, Ivoclar asks for care when checking the occlusion of a ceramic restoration that isn’t cemented yet, because it can fracture. Any adjustment is done with a fine diamond at medium speed, light pressure and water cooling, and the adjusted area is polished.

A light-cure-only cement fits a thin onlay. Variolink Esthetic LC is indicated for translucent inlays, onlays and veneers under 2 mm; for a thicker or opaque restoration, Ivoclar doesn’t indicate it.

The studies behind e.max onlays used adhesive cementation, and the numbers are on the e.max or zirconia onlay page.

How does cementing e.max differ from zirconia?

The difference between cementing e.max and zirconia is the intaglio: e.max is etched with hydrofluoric acid and silanated; zirconia is air-abraded with alumina and, for adhesive cementation, primed with MDP.

The zirconia steps, including RelyX U200, zinc phosphate and implant crowns, are in how to cement zirconia crowns.

What mistakes compromise e.max cementation?

The mistakes that most compromise e.max cementation are in etching the restoration and in matching the cement to the type of restoration.

What comes from the lab, and what goes on the Rx?

Smile Digital Lab makes e.max restorations from IPS e.max CAD, by Ivoclar, in its own ceramics department in São Paulo, Brazil, stained and glazed by hand. The restoration arrives ready for try-in; etching, silane and cementation happen chairside. Ask the lab whether the intaglio comes etched, because that changes the cleaning after try-in.

On the Rx, include:

• The cement you plan to use. With a self-adhesive or conventional cement, the restoration has to be a crown on a retentive prep; a minimally invasive crown only exists with adhesive cementation.
• The stump shade, especially with a metal core or a discolored tooth. Ivoclar says to pick the block by the shade of the prep at its most discolored area.
• Bruxism. In the IPS e.max CAD IFU, untreated bruxism is a limitation of use, with a splint indicated after placement.

If the space falls short of the material’s minimum thickness, we contact you before milling. We check every case when it arrives and on eight points before it ships. The restorations are on the e.max crown and e.max or zirconia onlay pages, and stump shade in the shade guide.