Polishing Zirconia.
Zirconia is harder than enamel, and how it is finished determines whether that hardness matters. A polished zirconia surface is remarkably kind to the opposing dentition. A ground one is not.
Polished beats glazed
The intuition is that a glazed surface must be smoother and therefore kinder. The evidence points the other way: well-polished monolithic zirconia produces less wear on opposing enamel than glazed zirconia does.
The reason is durability rather than initial smoothness. Glaze is a thin glassy layer over a much harder substrate, and in function it wears away. What is then exposed is whatever surface the zirconia had beneath the glaze — frequently the as-milled or lightly finished surface, which is considerably rougher than a polished one.
A properly polished zirconia surface has no such layer to lose. It presents the same finish on the day it is seated and years later.
Adjustment technique
Adjust with a fine-grit diamond under copious water, using light intermittent pressure. Zirconia is hard and generates heat readily, and heat is the main risk during adjustment — both to the pulp through the tooth and to the material itself.
Heavy dry grinding creates surface damage and locally induces phase transformation, which is exactly the condition that makes the material more susceptible to degradation over time. It also produces a surface that is very difficult to bring back to a proper polish.
Remove the minimum necessary, and check frequently rather than adjusting in one long pass.
The polishing sequence
Polishing zirconia requires diamond-impregnated instruments — conventional ceramic polishers designed for glass ceramics are considerably softer than zirconia and will not cut it effectively.
Work through the sequence rather than jumping to the finest. A coarse diamond-impregnated polisher removes the grinding scratches, a medium refines, and a fine or high-shine instrument, often used with a diamond polishing paste, produces the final surface.
Skipping stages is the most common error. A high-shine polisher used directly on a coarsely ground surface produces a glossy appearance over the original scratches, which looks acceptable and behaves like a rough surface. Low speed and light pressure throughout, with water where the instrument allows.
Verify the result
Assess the polished surface under magnification and with the surface dry. Loupes are sufficient. A properly polished surface reflects a sharp, continuous highlight; an inadequately polished one produces a highlight that is broken or hazy.
Running a fine explorer across the surface is a reasonable secondary check, though it is less sensitive than looking at the reflection.
If the surface has been extensively adjusted and cannot be polished satisfactorily at the chair, returning the restoration for re-polishing and if necessary re-glazing is a legitimate option, and preferable to seating a rough occlusal surface.
Where adjustment is most consequential
Occlusal and guidance surfaces, because those are where the restoration contacts opposing enamel repeatedly. An adjusted and unpolished contact area on a functional cusp will wear the antagonist measurably over years.
Interproximal adjustment matters less for wear but affects plaque retention, and margin adjustment matters for tissue response. Both are worth polishing properly, though the antagonist argument applies specifically to occluding surfaces.
Keep a kit that actually works
The single most useful investment here is a dedicated zirconia polishing kit kept where the restorations are seated, rather than a general ceramic kit used for everything.
The instruments wear and should be replaced on a sensible schedule. A worn diamond polisher stops cutting and starts burnishing, which produces the glossy-over-scratched result described above.
It is a small cost against the alternative, which is opposing enamel worn by a restoration that was meant to protect the tooth it restored.
Polishing layered and glass-ceramic restorations
The sequence described here is specific to zirconia. Lithium disilicate and feldspathic porcelain are softer, and conventional ceramic polishing systems designed for glass ceramics work well on them — diamond-impregnated instruments intended for zirconia are unnecessarily aggressive.
Using the wrong kit in either direction produces poor results. Zirconia polishers on feldspathic porcelain remove material faster than intended; glass-ceramic polishers on zirconia burnish without cutting.
Keeping two labelled kits, and knowing which material is in the mouth, avoids the problem entirely. If you are unsure what a restoration is made from, the prescription or the laboratory will tell you.
Re-glazing as an alternative
Where a restoration has been adjusted extensively and chairside polishing cannot restore an acceptable surface, returning it to the laboratory for re-finishing is a reasonable course.
It costs an appointment, which is why it is often avoided, but the comparison is against a rough occlusal surface abrading opposing enamel for the life of the restoration. Where the adjustment has been substantial and the antagonist is intact natural enamel, the appointment is the better trade.
If a restoration is being returned for this reason, say what was adjusted and why — a pattern of heavy adjustment usually indicates a clearance issue worth addressing at source.
Tell the laboratory when you adjust
If a restoration required significant occlusal adjustment, that is information about clearance. A pattern of heavy adjustment on a particular tooth position or restoration type points to a reduction issue that can be addressed at source.
It also lets the laboratory know that the surface finish it produced is no longer the surface in the patient's mouth, which matters for anything assessed at review.
In short
- Well-polished zirconia wears opposing enamel less than glazed zirconia
- Adjust with fine diamonds under water; heat and dry grinding cause damage
- Use diamond-impregnated polishers and work through the full sequence
- Verify by the sharpness of the reflected highlight under magnification
- Return a heavily adjusted restoration rather than seating a rough surface
More on clinical
Discuss a case
Where a case sits between options, a short conversation before preparation is usually quicker than resolving it afterwards.