The crown seats, the margins close, and the patient says it hits first. A few seconds with a diamond fixes the bite, but now a matte, scratched patch of zirconia sits against natural enamel. Do you polish it, ask the lab to reglaze it, or send the crown back?
The answer depends on what grinding does to zirconia, how each finish treats the opposing tooth, and what that zirconia's maker says now. Below: the evidence, burs, polishing sequences and a decision table.
Key Takeaways
- In a 2023 meta-analysis of 33 lab studies, polishing was the only finish after grinding that raised zirconia's flexural strength.
- In one lab test, ground zirconia showed 26% monoclinic phase, polished 23 to 24% and glazed 0%; only the glazed bars lost the strength gain.
- A meta-analysis of in vitro studies and a review of 16 articles found polished zirconia wore enamel less than glazed.
- Ivoclar's intraoral OptraGloss polishers run at up to 10,000 rpm with more than 50 ml/min of water spray.
- Dentsply Sirona's 2026 CEREC Zirconia+ instructions forbid glazing unpolished zirconia because opposing teeth may wear excessively.
Quick Answer
Polish it. After a small adjustment with a fine diamond, water and light pressure, a complete diamond polishing sequence restores a smooth surface, keeps the strength that grinding's transformed layer provides, and in lab studies wears enamel less than glaze. Reglaze only for esthetics, and only after polishing. Send the crown back when the fix needs material added, touches a bridge connector, or would take it below the material's minimum thickness.
What Does Grinding Do to Zirconia?
It roughens the surface and can leave microcracks
A 2016 systematic review of 30 lab studies found grinding generally lowers flexural strength and raises roughness; fine grit (under 50 µm), plenty of coolant and a slow-speed contra-angle limited the damage. On KATANA 3Y, 4Y and 5Y zirconia, a coarse diamond alone roughened the surface and dulled its gloss, while a fine bur and polisher sequence (Dialite ZR) left roughness unchanged. On a high-translucency zirconia, coarse grinding left a mean Sa of 0.95 µm with significant microcracks.
It transforms the surface, and polishing keeps the change
Grinding turns surface grains from the tetragonal to the monoclinic phase and builds a layer of compressive stress (Curtis et al., 2006); in that study, coarse grinding lowered strength and fine grinding did not. Glaze firing undid the transformation: in a test of five finishes, ground bars showed 26% monoclinic phase, polished bars 23 to 24%, and ground then glazed bars 0%. Ground and polished bars were the strongest; glazed bars were the weakest, no stronger than unground controls.
Lab studies in a 2023 meta-analysis of finishing after grinding: every method smoothed zirconia, but only polishing raised its flexural strength (da Rosa et al., 2023).
Glazing after adjustment lowered strength in a second study too, while polishing did not (Ozturk et al., 2022). The gain may shrink with yttria content: in a 2026 study, grinding plus three-step polishing raised the strength of 3Y zirconia significantly, of 5Y less, and of 6Y not significantly.
Polished, Glazed or Ground: Which Wears Enamel Least?
Reviews of lab studies agree. A meta-analysis (25 studies reviewed, 3 pooled) found polished monolithic zirconia wore enamel less than glazed zirconia, and a review of 16 full-text articles found the same for polishing versus glazing. Ground and unpolished is a poor option: in a chewing simulation against human enamel, clinically adjusted zirconia wore enamel as much as enamel opposing enamel and more than adjusted and repolished zirconia, which matched lab-polished and glazed surfaces.
Glaze is also temporary. In another chewing simulation, polished, ground and repolished zirconia showed no wear of its own, while the glaze layer was abraded. Dentsply Sirona's current CEREC Zirconia+ instructions forbid glazing unpolished zirconia, warning that opposing surfaces may wear excessively.
Clinical data are fewer: a 2024 network meta-analysis of 7 studies (261 crowns) found monolithic zirconia caused 40.1 µm more antagonist enamel loss than natural teeth over up to 24 months, and a US randomized trial found polished zirconia comparable to metal-ceramic at one year. Not every lab test agrees: a 2020 study found no significant difference in enamel wear between glazed, unglazed and polished zirconia. For bruxers, see Restorations for Bruxers.
Which Burs, Speeds and Water Settings?
A fresh fine diamond, light pressure and water
Ivoclar's current grinding chart lists fine diamonds with water, at up to 15,000 rpm, for intraoral corrections on zirconia, and light pressure to avoid overheating; its ZirCAD Prime instructions require water whenever diamonds are used for adjustments. Dentsply Sirona's CEREC Zirconia+ instructions call for fine diamonds in a high-speed handpiece with water and low pressure, always followed by polishing, or soft diamond rubber polishers at low speed. Its Cercon xt ML instructions add minimal pressure and working in one direction. Ivoclar also asks for "immaculate" instruments: retire worn diamonds.
Minimum water spray in Ivoclar's instructions for its OptraGloss intraoral polishers, used at up to 10,000 rpm; dry polishing is for extraoral use (OptraGloss IFU, Rev. 3, 2024).
What not to touch
Leave bridge connectors alone: Dentsply Sirona says connectors should not be adjusted, and Ivoclar forbids separating them with a disc. Keep the minimum thickness after adjusting: for posterior crowns, 1.0 mm for KATANA Zirconia YML and IPS e.max ZirCAD Prime, 0.6 mm for ZirCAD LT and MO.
What Is the Best Polishing Sequence?
Use a diamond-impregnated rubber system made for zirconia, coarse to fine, and finish every step. In a 2025 study of 4Y and 5Y zirconia, three-step systems barely changed roughness after step two; the effect came with the third step. Kits differ: on a high-translucency zirconia, a three-step kit after a fine diamond gave a significantly smoother surface, a two-step kit left it no smoother than the diamond, and adding diamond paste gave the smoothest result (Sa 0.08 µm).
Kits named in current manufacturer instructions:
- Ivoclar OptraGloss (intraoral): dark blue pre-polisher, then light blue high-gloss polisher, with water spray.
- Ivoclar OptraGloss Extra Oral: the same two steps outside the mouth, dry at low speed, optional polishing paste.
- Meisinger Luster Kit for Zirconia: recommended by Dentsply Sirona for CEREC Zirconia+, five instruments at up to 12,000 rpm (Meisinger is a separate company).
Expect smooth, not glaze-like. Polished zirconia came in below Ra 0.2 µm, the threshold for plaque accumulation, in one 2026 study; in another, three kits left ground translucent zirconia at Ra 0.39 to 0.68 µm, against 0.02 µm for intact glaze.
What Do Zirconia Manufacturers Say Now?
| Zirconia (current document) | Adjusting | Finishing |
|---|---|---|
| Ivoclar IPS e.max ZirCAD (labside IFU, Rev. 3, 2026-02-11) | Keep to a minimum; light pressure, low speed, immaculate instruments | Keep minimum wall thickness and connector size |
| Ivoclar IPS e.max ZirCAD Prime (chairside IFU, Rev. 3, 2026-07-22) | Water-cool diamonds; low pressure | Polish at least occlusal contacts; polished surfaces protect opposing teeth |
| Ivoclar IPS e.max Zirconia (IFU, Rev. 0, 2026-04-27) | Only if absolutely necessary; low pressure, low speed | After cementing, check occlusion, polish adjusted contacts |
| Kuraray Noritake KATANA Zirconia YML (IFU, 08/2025) | Diamond bur as needed; check for cracks | Polish contacts to a high shine before glazing; for polish only, select one shade brighter |
| Dentsply Sirona CEREC Zirconia+ (IFU, REV 2026-07) | Fine diamond, water, low pressure; never connectors | Polish after every diamond adjustment; never glaze unpolished; no extra heat treatment |
| Dentsply Sirona Cercon xt ML (IFU, REV 2026-07) | Diamonds with irrigation only; minimal pressure, one direction | Polish or glaze adjusted sites before cementation |
Should You Adjust Before or After Cementation?
Do most of it before. At try-in, relieve contacts first, then adjust occlusion, and polish outside the mouth. Ivoclar's ZirCAD Prime guide says adjusted areas must be polished extraorally before final seating; the Cercon xt ML instructions want adjusted sites polished or glazed before temporary or definitive cementation; CEREC Zirconia+ try-in adjustments must be re-polished before delivery. Then clean the crown as described in How to Cement Zirconia and Bond E.max.
Recheck after cementing. Ivoclar's 2026 IPS e.max Zirconia instructions list checking static and dynamic occlusion after cementation, then polishing the adjusted contacts. Intraorally, use water with both the diamond and the polisher: OptraGloss instructions warn that excessive pressure or insufficient water cooling can damage the restoration and surrounding tissue.
Polish, Reglaze or Send It Back?
| Situation | Recommended action | Why |
|---|---|---|
| One or two high spots on a posterior crown at try-in | Fine diamond, water, light pressure; full polishing sequence outside the mouth; then cement | Only polishing raised strength after grinding (da Rosa 2023); Ivoclar requires extraoral polishing before seating |
| Small touch-up after cementation | Fine diamond with water; intraoral diamond polisher with water spray | Ivoclar e.max Zirconia IFU; OptraGloss: up to 10,000 rpm, over 50 ml/min water |
| Ground area, no zirconia kit at hand | Do not leave it rough or cover it with spray glaze; polish before delivery | Ground zirconia wore enamel more than repolished (Chong 2015); glaze abrades (Preis 2013) |
| Adjustment cut through stain and glaze on a visible surface | Send it back for re-polishing and a stain and glaze firing | Adjusted stained areas can look brighter (Cercon xt ML IFU); polishing shifted zirconia color past a ΔE of 3.7 (Koch 2025) |
| Open contact | Send it back; it needs material added | Ivoclar's ZirCAD Prime IFU uses an Add-On material and a corrective firing for proximal contacts |
| Bridge connector or embrasure needs reduction | Do not adjust; send it back | Connectors should not be adjusted (CEREC Zirconia+ IFU); no separating discs (Ivoclar) |
| The bite needs more reduction than the minimum thickness allows | Send it back with a new bite record | Minimum thickness must be kept after adjusting (Ivoclar, Kuraray Noritake IFUs) |
Reglazing has a place, as an esthetic step after polishing, not as a cure for a ground surface. Ivoclar, Kuraray Noritake and Dentsply Sirona all want at least the contacts polished before glaze, and a separate "healing" firing is not needed: Dentsply Sirona calls one unnecessary and inappropriate for Cercon xt ML.
How Do You Avoid Adjusting in the First Place?
Heavy adjustment usually traces back to the records: a one-sided or short bite, incomplete adjacent teeth in the scan, or no contact preference; see High Crowns and Open Contacts. On the Rx, name the zirconia, the occlusal clearance you prepared and how tight you like contacts (How to Fill Out a Dental Lab Rx). Grades and minimum thicknesses: Types of Zirconia Explained.
Zirconia Crowns at Elegant Dental Laboratory
- Solid 3Y, 9-layer 5Y, solid with buccal porcelain, and zirconia copings with layered porcelain; we follow the brand or grade written on the Rx.
- Digital scans are reviewed before production, and every case is made in house in Brooklyn by more than 35 technicians.
- 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: free pickup and delivery by our own drivers in all five New York City boroughs and 13 northern New Jersey counties, and UPS labels anywhere. Call 877-335-5221.
FAQ
Can I just reglaze an adjusted zirconia crown?
Not over a ground surface. Polish first; glaze abraded in chewing tests, and Dentsply Sirona forbids glazing unpolished zirconia.
Should I adjust zirconia wet or dry?
Wet in the mouth: Ivoclar requires water with diamonds and over 50 ml/min with its intraoral polishers.
Does polishing change the shade?
It can. One study measured a color shift past a ΔE of 3.7, and Kuraray Noritake suggests one shade brighter for polish-only crowns.
Two-step or three-step kit?
The kit matters more than the count. Three-step kits worked only after step three in one study; in another, a two-step kit was no smoother than the diamond.
Is an adjusted zirconia crown weaker?
Not necessarily. In lab tests, fine grinding plus polishing kept or raised strength; coarse grinding, and glaze firing after grinding, lowered it.
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- Dentsply Sirona (DeguDent). Cercon xt ML Instructions for Use, REV 2026-07 (finishing, polishing in the dental office). PDF
Reviewed by Gary Fingerman, founder and CEO of Elegant Dental Laboratory, Brooklyn, New York (founded 2007). Last reviewed: October 1, 2026. Study values are from published research or manufacturer instructions; always follow the current instructions for use of the zirconia you adjust.
