The margins look right, the shade matches, and then the patient closes and says the new crown feels high. Or floss drops straight through the mesial contact. Every minute of grinding costs chair time and removes material the crown was designed to have.
Most of these problems start before the case reaches the lab, in the bite record, the scan of the adjacent teeth and the Rx. Below: the causes, what adjustment is normal, how to adjust zirconia and e.max safely, and when to send a crown back.
Key Takeaways
- In a US study of 3,730 crowns, dual-arch impressions of teeth missing a neighbor gave excellent occlusion 57.9% of the time, against 66.2% with both neighbors present.
- A systematic review of 29 studies recommends a bilateral posterior bite record of at least 4 teeth.
- In an audit of 40,344 lab restorations, proximal-fit problems caused 23.2% of remakes, more often with monolithic zirconia.
- In randomized trials of implant crowns, the highest occlusal point was ground down by about 213 to 280 µm in digital workflows and 331 to 480 µm in conventional ones.
- Contacts next to implant crowns open over time: 41% cumulatively in a meta-analysis of 10 studies, most often mesially.
- After adjusting zirconia, polish rather than reglaze: in lab tests, glazing after grinding lowered flexural strength and polishing did not.
Quick Answer
Crowns come back high mostly because the lab worked from a bite that was not the patient's real bite: a one-sided or short bite scan, a dual-arch tray on an unbounded prep, or scan collisions trimmed in CAD. Contacts come back open or tight when adjacent teeth are incomplete in the scan or the Rx gives no contact preference. Prevent both with a bite recorded on both sides, complete adjacent teeth and a stated contact tightness.
Why Do Crowns Come Back High?
The bite record is short or one-sided
A digital bite aligns the two arch scans using a buccal scan of the closed teeth. A 2023 systematic review of 29 studies found that most studies showed no difference in bite accuracy between half-arch and complete-arch scans, but 2 or more missing teeth in the area reduced it. It recommends a bilateral posterior bite record of at least 4 teeth, or at least 4 posterior teeth on a half-arch scan. Dentsply Sirona's Primescan instructions also call for a buccal scan on both sides for a full-jaw scan, and a 2025 lab study found complete-arch scans located the bite more accurately than half-arch scans.
A dual-arch tray on an unbounded prep
In the National Dental Practice-Based Research Network, 205 US dentists documented 3,730 consecutive single crowns. With dual-arch trays, crowns on teeth lacking a mesial or distal neighbor reached excellent occlusion less often (57.9% against 66.2%). The authors explain that adjacent teeth give occlusal stops that help prevent tray flexure and stabilize the casts during mounting.
The arches overlap in the scan, and CAD trims them
Aligned arch scans can overlap slightly, and scanner or CAD software then "corrects" these occlusal collisions. The method matters: in a study with TRIOS 4 and i700 scans, corrections made in the scanner software gave a truer jaw relationship than corrections in the CAD program, and trimming in CAD changed the occlusal surfaces themselves. A crown designed against a trimmed antagonist can come out high.
The crown does not fully seat
A tight contact or an internal interference holds the crown up, and it reads as high. Cement adds a little too: in a lab study of monolithic zirconia crowns, the average vertical gap at the margin rose from 38 µm before cementation to 60 µm after. Seat fully, check contacts before occlusion, and recheck the bite after cementation.
Why Are Contacts Open or Too Tight?
Adjacent teeth are incomplete in the scan
The lab designs each contact against the neighbor surface it can see. If the scan stops halfway across the adjacent tooth, or its proximal surface is a hole in the mesh, the technician has to guess. Dentsply Sirona's Primescan instructions start the scan on the adjacent tooth and capture the approximal surfaces of the prep in both directions.
Nobody said how tight
In a 2026 audit of 40,344 restorations from seven labs, proximal-fit problems (poor adaptation at the mesial or distal) caused 23.2% of remakes. The authors recommend that prescriptions state the target contact location and intensity. On stone models, technicians commonly relieve the adjacent teeth to set contacts (Kim et al., 2023), so tightness also depends on how much stone was removed.
Material and seating tolerance
Proximal-fit problems were more frequent with monolithic zirconia, at 29.8% of its remakes. The audit authors link this to seating tolerance and to inadequate preparation or scanning, not to a defect in the material.
How Much Chairside Adjustment Is Normal?
For tooth-supported crowns, randomized trials favor intraoral scans: better occlusal contacts in one 42-patient trial (Gjelvold et al., 2016), shorter adjustment times in a 70-crown trial (Liu et al., 2024). Trials that measured the amount are on implant crowns.
| Randomized trial | Restorations | Digital workflow | Conventional impression |
|---|---|---|---|
| Ren et al., 2022 | 40 single cement-retained implant crowns | 213 µm maximum occlusal adjustment; 20.20 min total chair time | 331 µm; 26.65 min |
| Ren et al., 2024 | 24 patients, two adjacent implant crowns | 280 µm maximum occlusal deviation | 480 µm |
| Derksen et al., 2021 | 45 screw-retained implant crowns | 3.35 min adjusting; 39.1% needed none | 6.09 min; 18.2% needed none |
| Haghi et al., 2024 | 28 patients, splinted crowns on two implants | 5.31 min adjusting occlusion | 6.06 min |
In each of these trials, the digital workflow needed less occlusal grinding or less adjustment time. A few tenths of a millimeter at the highest point is typical; if you are removing much more, look upstream.
Troubleshooting High Crowns and Open Contacts
| Symptom | Likely cause | Fix at the chair | Prevention next time |
|---|---|---|---|
| Crown high, other teeth apart on both sides | Wrong or one-sided bite; collisions trimmed in CAD | Confirm seating; if seated and far off, send it back with a new bite scan | Bilateral bite, 4 or more teeth per side |
| High on an unbounded or last molar | Dual-arch tray without stops | Adjust small high spots, polish | Scan, or use a full-arch tray |
| Will not seat, feels high | Tight contact or internal interference | Relieve the contact first, then check internal fit | Full adjacent teeth; contact preference on the Rx |
| Fine at try-in, high after cementing | Cement film, incomplete seating | Recheck after the cement sets; adjust, polish | Firm seating pressure; tell the lab if it recurs |
| Open contact | Neighbor incomplete in the scan or impression | Send it back; it needs material added | Scan the full neighbor, proximal surface included |
| Contacts too tight | No stated preference; stone relieved differently | Adjust the crown, not the tooth; polish | Light, medium or heavy on the Rx |
| Implant crown contact open at recall | Natural teeth drift, mostly mesially; the implant does not | Retrieve a screw-retained crown so the lab can add to the contact | Inform the patient; recall checks; screw-retained design |
Why Do Contacts Open Next to Implant Crowns?
Cumulative rate of open contacts between implant restorations and adjacent natural teeth in a meta-analysis of 10 studies; 47% at the mesial contact (Bento et al., 2023).
Natural teeth keep drifting, mostly mesially, while an osseointegrated implant barely moves. A review of 19 studies found contact loss in 11% to 30% in studies shorter than 2 years, 13% to 65% at 2 to 5 years and 29% to 83.3% beyond 5 years, and called it frequent, inevitable and progressive.
The review authors advise telling patients about it, checking contacts at every recall, and choosing screw-retained crowns, so the crown can be retrieved and the contact built up without cutting it off.
How Do You Adjust Zirconia and E.max Safely?
Zirconia: fine diamond, water, then polish
Ivoclar's IPS e.max ZirCAD Prime guide calls for diamond tools with water cooling and says adjusted areas must be polished extraorally before final seating. Lab studies agree: coarse grinding without polishing caused phase transformation and lower strength (Lee et al., 2019), and glazing after grinding lowered flexural strength while polishing did not (Mohammadi-Bassir et al., 2017; Ozturk et al., 2022). Polished zirconia also wore opposing enamel less than glazed zirconia in a meta-analysis of lab studies (Aljomard et al., 2022).
E.max: no heat, keep the thickness, polish
Ivoclar's IPS e.max CAD instructions: avoid overheating when grinding, polish adjusted areas to a high gloss, and keep the minimum thickness after adjustment. For a monolithic e.max crown that means 1.5 mm occlusal with conventional or self-adhesive cement, 1.0 mm only if bonded (see our Crown Prep Guide). The kit matters: in one lab study, the OptraFine system named in those instructions matched glazed e.max for strength, while another system lowered it (Mohammadibassir et al., 2019). For an open contact, Ivoclar documents an Add-On material for minor shape adjustments such as proximal contact points, fired in a correction firing.
When Should You Remake Instead of Adjust?
Adjust when the crown is fully seated and the problem is a few high spots or a heavy contact. Send it back when:
- It still will not seat after the contacts are relieved.
- A margin is open.
- A contact is open: that needs material added, not removed.
- Reaching the bite would take it below the material's minimum thickness, or through the stain and glaze of an esthetic crown.
- It is high and the posterior teeth are apart on both sides: that points to the bite record, so send a new bite with it.
Checklist
- Scan: complete adjacent teeth, proximal surfaces included, no holes in the mesh.
- Bite: both sides, at least four teeth per buccal scan; full arches if teeth are missing; no dual-arch tray on an unbounded prep.
- Rx: contact preference (light, medium or heavy) and how you test it.
- Try-in: seat fully, contacts first, then occlusion; recheck after cementing.
- Finish: polish every adjusted surface.
- Remake request: photos of articulating marks, notes on adjustments, a new bite scan if needed.
Sending digitally? See How to Send a Scan to a Dental Lab.
Crowns at Elegant Dental Laboratory
- Digital scans are reviewed before production, and every case is made in house in Brooklyn by more than 35 technicians.
- Zirconia (solid, 9-layer and layered options), IPS e.max, PFM and screw-retained or cement-retained implant restorations.
- 5 business day standard turnaround on most restorative cases, rush options, and up to a 7-year warranty on final restorations (policies and warranties).
- Submit a digital case or send a case: our own drivers pick up in the New York area (call to confirm), and UPS labels work anywhere. Call 877-335-5221.
Related Guides
- Why Implant Screws Loosen, and How to Prevent It
- AI Crown Design in Dental Labs: What It Does Well, Where It Fails, and What It Means for Your Cases
- Shade Matching for the Lab: How to Take Shade Photos and Send a Stump Shade
FAQ
How much occlusal adjustment is normal on a new crown?
In randomized trials of implant crowns, the highest point was ground down by about 0.2 to 0.3 mm in digital workflows and 0.3 to 0.5 mm with conventional impressions. Much more suggests a bite or seating problem.
Should I adjust the contacts or the occlusion first?
The contacts. A tight contact keeps the crown from seating, and an unseated crown reads high.
Can I reglaze a zirconia crown after adjusting it?
Polish it instead. In lab studies, glazing after grinding lowered flexural strength and polishing did not.
Is a half-arch scan enough for a single crown?
Usually, if no more than one tooth is missing in the scanned area and the bite covers at least four posterior teeth. Otherwise, scan complete arches.
Why do contacts open next to implant crowns?
Natural teeth drift, mostly mesially, while the implant barely moves. Check implant contacts at every recall.
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Reviewed by Gary Fingerman, founder and CEO of Elegant Dental Laboratory, Brooklyn, New York (founded 2007). Last reviewed: September 27, 2026. Study values are from published research or manufacturer instructions; always follow the current instructions for use of the materials you adjust.
