A crown that fit perfectly at try-in comes off a few months later, or an e.max onlay lifts at one margin. The crown itself may be fine. Zirconia and lithium disilicate need nearly opposite treatment: hydrofluoric acid etches e.max but zirconia has no glass to etch, sandblasting roughens zirconia but can crack e.max, and phosphoric acid cleans e.max but contaminates zirconia.
This protocol combines the instructions for use (IFUs) of Ivoclar, Kuraray Noritake, 3M and GC with systematic reviews from 2019 to 2026. Brands differ in the details, so follow the IFU of the product in your hand.
Key Takeaways
- Zirconia: air-abrade the intaglio with alumina (Ivoclar: 25 to 70 µm at 1 bar; 3M: 30 to 50 µm at 2 bar), then use an MDP primer or an MDP-containing cement.
- E.max: etch with hydrofluoric acid for 20 seconds (Ivoclar's gel is 4.5% HF), rinse, dry, then silane for 60 seconds (Monobond Plus). Never sandblast it.
- Never clean zirconia with phosphoric acid: in a 2022 meta-analysis it did no better than water, and re-blasting did best.
- RMGI and self-adhesive cements need a retentive prep: Ivoclar specifies a 4 to 8° taper and, for self-adhesive cement, at least 4 mm of height.
- E.max veneers, inlays, onlays and minimally invasive crowns (1 mm) must be bonded with adhesive resin cement.
- In 2,436 zirconia and lithium disilicate crowns, adhesive and conventional cementation showed comparable survival.
Quick Answer
Zirconia: try in, then re-blast the intaglio with alumina at moderate pressure or clean it with a zirconia cleaning paste, apply an MDP primer (often optional with an MDP cement), and seat with RMGI, self-adhesive or adhesive resin cement depending on retention. E.max: try in, etch with about 5% hydrofluoric acid for 20 seconds, rinse, dry, silanate, and bond with adhesive resin cement; use self-adhesive or conventional cement only for crowns on retentive preps.
Why Do Zirconia and E.max Need Different Protocols?
IPS e.max is a lithium disilicate glass-ceramic: hydrofluoric acid etches its glass phase into a retentive pattern, and silane bonds to the etched glass. Zirconia has no glass phase, so Ivoclar notes that silane primers do not work on it. It is roughened with alumina and bonded through phosphate monomers such as MDP. Still choosing a material? See Zirconia vs. E.max: When to Use Each.
What Is the Step-by-Step Protocol?
| Step | Zirconia | E.max |
|---|---|---|
| 1. Try in | Check fit and occlusion. Polish adjusted areas before seating (Ivoclar). | If the crown is not yet etched, try in first and etch afterward (GC). |
| 2. Clean | Re-blast (GC) or use a zirconia cleaning paste (Ivoclar). No phosphoric acid. | Unetched: the etch also cleans. Pre-etched: 37% phosphoric acid for 60 s (GC) or Ivoclean; do not etch again (Ivoclar). |
| 3. Treat the surface | Alumina air abrasion at the zirconia maker's setting (below). | Hydrofluoric acid for 20 s. Never sandblast. |
| 4. Rinse and dry | Rinse and air-dry; Kuraray adds 2 minutes in an ultrasonic cleaner. | Wash the acid off thoroughly and dry. |
| 5. Prime | MDP-containing primer, e.g. Monobond Plus for 60 s. Optional for crowns under some cements (G-CEM ONE, RelyX Universal). | Silane, e.g. Monobond Plus for 60 s. Needed for adhesive and self-adhesive cement, not conventional (Ivoclar). |
| 6. Prepare the tooth | Remove all temporary material; avoid eugenol and ferric hemostatics (Kuraray). | Same. For veneers and onlays, GC etches enamel with 35 to 40% phosphoric acid for 10 to 15 s. |
| 7. Cement | RMGI, self-adhesive or adhesive resin, chosen by retention. | Adhesive resin for veneers, inlays, onlays and thin crowns; other cements only for crowns on retentive preps. |
Air abrasion settings for zirconia
Ivoclar: 25 to 70 µm alumina at 1 bar (or 70 to 110 µm at 1.5 bar). GC: 25 to 50 µm at 1.5 bar. 3M: 30 to 50 µm at 2 bar. Kuraray Noritake: 30 to 50 µm at 1 to 4 bar, unless the restoration's own IFU says otherwise. A 30 to 50 µm alumina fits every range; take the pressure from the zirconia's maker.
How Should You Clean Zirconia After Try-In?
Saliva contains phosphates, and zirconia binds phosphate readily. In the study Ivoclar cites, water, isopropanol and phosphoric acid all left an organic film on saliva-contaminated zirconia; air abrasion cleaned best (Yang et al., 2008). Two systematic reviews agree: in one, sandblasting beat Ivoclean cleaning paste, both beat water, and phosphoric acid did no better than water (da Silva et al., 2022). In the other, covering 25 studies, alumina air abrasion (and sodium hypochlorite) matched uncontaminated zirconia after long-term aging; water, alcohol, acid etching and cleaning agents fell short (Thammajaruk et al., 2023).
Manufacturers split on the next step. GC re-blasts every zirconia crown after try-in, even if the lab blasted it. Ivoclar advises against re-blasting a lab-pretreated restoration, which it says could damage it, and recommends Ivoclean paste (outside the mouth only), then Monobond Plus. KATANA Cleaner, an MDP-salt cleaner at pH 4.5, works in 10 seconds inside or outside the mouth. Follow the zirconia maker's IFU, then prime again.
Which Cement Fits Which Case?
| Cement type | Zirconia | E.max | Prep needed |
|---|---|---|---|
| Conventional (RMGI or glass ionomer) | Crowns and bridges (Ivoclar, 3M, GC) | Crowns and 3-unit bridges, still etched (Ivoclar); 3M does not list its RMGI for glass-ceramics | 4 to 8° taper (Ivoclar) |
| Self-adhesive resin | Crowns and bridges; some contain MDP (PANAVIA SA Cement Universal, G-CEM ONE) | Crowns and 3-unit bridges, etched and silanated | 4 to 8° taper, at least 4 mm high (Ivoclar) |
| Adhesive resin with primer and bonding agent | Any case; the option for short or non-retentive preps | Required for veneers, inlays, onlays, partial crowns and minimally invasive crowns | No retentive form needed |
For IPS e.max, Ivoclar's IFU governs: adhesive cementation increases the overall strength of the seated restoration; conventional and self-adhesive cementation do not.
What the evidence says about debonding
Lab studies favor MDP: a 2025 network meta-analysis of 21 in vitro studies found the highest bond strengths to zirconia with MDP-based cements, and mechanical or mechano-chemical pretreatment helped with every cement type (Mazaheri Tehrani et al., 2025).
A review of 17 clinical studies covering 2,436 zirconia and lithium disilicate crowns found comparable survival and complications with adhesive and conventional cementation, though evidence quality was poor; mean follow-up ranged from 25.5 to 121.2 months (Maroulakos et al., 2019).
For veneered zirconia crowns and bridges, fracture or chipping was about four times as likely as loss of retention across 52 clinical studies (Gonzaga et al., 2022).
In practice: on a retentive prep, a blasted zirconia crown can take any of the three cement types. On a short or over-tapered prep, choose adhesive cementation, which Ivoclar says needs no retentive preparation.
How Do You Etch and Bond E.max?
Ivoclar's sequence for IPS e.max CAD: etch the intaglio with IPS Ceramic Etching Gel (4.5% hydrofluoric acid, per its 2024 safety data sheet) for 20 seconds, then Monobond Plus for 60 seconds, dried with air. Rinse the acid off and dry thoroughly before priming. GC's lithium disilicate protocol is 5% for 20 seconds. Ivoclar stresses that lithium disilicate needs a shorter etch than conventional glass-ceramics, timed exactly to prevent over-etching, and that the intaglio must be conditioned whatever the cement.
Etch time for lithium disilicate with Ivoclar's gel. A 2023 meta-analysis found 4 to 5% HF bonded as well as 7 to 10% HF at this time in short-term lab tests (Araújo-Neto et al., 2023).
Never sandblast lithium disilicate: GC warns it creates micro-cracks and weakens the restoration. To avoid hydrofluoric acid, Ivoclar offers a one-step etching silane (Monobond Etch & Prime); a 2024 meta-analysis of in vitro studies found no bond-strength difference from acid plus silane (Brunetto et al., 2024).
Cleaning e.max after try-in
An unetched crown is tried in first and etched afterward; the etch also cleans (GC). If the lab already etched it, GC advises 37% phosphoric acid for 60 seconds, then silane. In a 2025 network meta-analysis of 15 studies, phosphoric acid held up after long-term aging, water and alcohol did not, and ceramic cleaners lost performance over time (Thongkaemkaew et al., 2025).
Veneers and other thin restorations
E.max veneers, inlays, onlays, partial crowns and minimally invasive crowns are adhesive-only. Ivoclar requires at least 1 mm of material for minimally invasive crowns and lists conventional and self-adhesive cementation among the limitations of use. For veneers, Ivoclar positions the light-cure Variolink Esthetic LC for restorations under 2 mm thick with adequate translucency; 3M rates its dedicated veneer cement highest and does not indicate RelyX Unicem 2 or its RMGI; GC says veneers require adhesive solutions.
What Mistakes Cause Debonds or Sensitivity?
| Problem | Likely cause | Fix |
|---|---|---|
| Zirconia crown debonds | Phosphoric acid after try-in; intaglio not blasted; no MDP | Re-blast or clean with zirconia paste; MDP primer or cement |
| Crown lifts off a short or steep prep | RMGI or self-adhesive cement without retentive form | Adhesive resin cement |
| E.max crown debonds | Etch skipped or cut short; no silane; saliva after priming | 20 s etch, 60 s silane; if contaminated after priming, clean and silanate again |
| E.max veneer or thin crown fractures | Non-adhesive cement where Ivoclar requires bonding; sandblasted intaglio | Adhesive cementation; never blast lithium disilicate |
| Inlay or partial crown debonds | Self-adhesive resin cement | Self-etch or selective-etch protocols did better in randomized trials (Alghauli et al., 2022) |
| Resin cement sets slowly or bonds poorly to tooth | Eugenol temporary cement or ferric hemostatic residue | Remove all temporary material; avoid both (Kuraray) |
| Sensitivity after seating | Randomized trials found no link to the adhesive protocol; pulpal response relates to remaining dentin thickness and material | Isolate with a rubber dam; use a pulp-capping agent close to the pulp (Kuraray) |
If a case still fails, work through Crown Remakes: What Really Causes Them and How to Prevent Them.
Zirconia and E.max From Elegant Dental Laboratory
- Zirconia: solid, 9-layer, solid with buccal porcelain, and zirconia copings with layered porcelain. See our zirconia options.
- IPS e.max: full-contour crowns, veneers, layered crowns, and inlays and onlays. See our e.max options.
- Every case is made in house by more than 35 technicians in our 7,000 sq. ft. facility at 2308 McDonald Ave, Brooklyn, NY: 5 business day standard turnaround on most restorative cases, rush options, and up to a 7-year warranty on final restorations (policies and warranties).
- We review digital scans before production. Submit a digital case or send a case: our own drivers pick up in the New York area (call to confirm availability), and we provide UPS shipping labels for practices anywhere. Phone: 877-335-5221.
Related Guides
- Crown Prep Guide: Reduction, Margins and Taper for Zirconia, E.max and PFM
- Maryland Bridges in 2026: Zirconia Cantilevers, Metal Wings and What the Evidence Says
- E.max Press vs. E.max CAD: Which Lithium Disilicate Should You Prescribe?
FAQ
Can I clean a zirconia crown with phosphoric acid after try-in?
No. Phosphate binds to zirconia and blocks the primer; in a meta-analysis phosphoric acid did no better than water. Re-blast or use a zirconia cleaning paste, then prime again.
Do I need a separate MDP primer if my cement contains MDP?
Often not for crowns. GC calls its primer optional for zirconia under G-CEM ONE, which contains MDP; 3M lists priming as optional for zirconia under RelyX Universal but recommended for veneers, table tops and adhesive bridges.
Can I cement e.max crowns with RMGI?
Ivoclar allows conventional cementation for e.max crowns and 3-unit bridges on a retentive prep, with the intaglio still etched, but not for veneers, inlays, onlays or minimally invasive crowns. 3M does not list its RMGI for glass-ceramics.
How long should I etch e.max with hydrofluoric acid?
20 seconds with Ivoclar's gel, then wash, dry and apply silane. Time it exactly; stronger 7 to 10% HF gave no better bond in a meta-analysis.
Is self-adhesive cement enough for a zirconia crown?
On retentive preps, yes: Ivoclar recommends a 4 to 8° taper and at least 4 mm of height, and several self-adhesive cements contain MDP. On shorter preps, use an adhesive protocol.
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Reviewed by Gary Fingerman, founder and CEO of Elegant Dental Laboratory, Brooklyn, New York (founded 2007). Last reviewed: September 28, 2026. Protocol values are manufacturer instructions or published studies; always follow the current instructions for use of the products you use.
