Can Old Crowns Cause a Grey Line at the Gums?

A thin dark line at the gum edge of a crown is something people usually notice years after the crown was placed, often in a photograph or in bright light. It tends to be more visible to the person who has it than to anyone else, but it is a genuine and common concern.

In most cases the explanation is straightforward and relates to how crowns were constructed for several decades. Whether it needs anything doing about it depends on what is causing it, and that distinction is worth making before assuming replacement is required.

Why has a dark line appeared at the edge of my crown?

The commonest reason is that the crown has a metal substructure. Porcelain-fused-to-metal crowns were the standard for many years and consist of a metal coping with porcelain layered over it. The metal margin sits at the gum line, and as the gum recedes slightly over the years — which is normal — that margin becomes visible as a grey line. The tissue itself may also appear greyish where it is thin, because the metal shows through. This is usually a cosmetic finding rather than a sign of failure, and a sound crown with a visible metal margin does not necessarily need replacing. However, a dark line can occasionally indicate decay at the margin or a defective fit, so it should be assessed rather than assumed.

Porcelain-fused-to-metal. A metal coping provides strength; porcelain provides appearance. Reliable and long-serving, but the metal must be masked, and at the margin there is often either exposed metal or a layer of opaque porcelain that looks less natural than tooth structure.

Full metal crowns. Gold or other alloys, used mainly on back teeth. Strong and kind to opposing teeth, but obviously not tooth-coloured.

All-ceramic crowns. Modern materials including lithium disilicate and zirconia have no metal substructure, so there is no grey margin. They transmit light more like natural tooth and can be finished at the gum without a dark line.

Zirconia. Very strong, available in increasingly translucent formulations, and widely used where strength and appearance are both required.

The shift away from metal substructures for visible teeth is one of the more noticeable changes in restorative dentistry over recent decades — see dental crowns.

Gum recession. The primary cause. The gum margin migrates apically over years, exposing the crown margin that was originally hidden beneath it. See receding gums.

Thin gingival biotype. Where tissue is thin, the metal beneath shows through it, producing a greyish tinge even without frank recession.

Metal ion release. Over long periods, corrosion products from some alloys can discolour the adjacent gum tissue. This is more associated with older base metal alloys.

Marginal discrepancy. A crown that does not fit precisely leaves a margin where plaque accumulates and stains, and where decay may develop.

Decay at the margin. Recurrent caries beneath the crown edge appears as a dark area. This is the possibility that must not be missed.

Root surface exposure. Exposed root dentine is naturally darker and more yellow than enamel, which can contribute to the visual effect.

Staining. Simple extrinsic staining accumulating at the margin, which may be removable.

This is the useful part of an assessment. Several features help:

• Does a probe catch at the margin, suggesting a defect or a ledge?

• Is the surrounding gum inflamed or bleeding? See bleeding gums

• Is there sensitivity, or discomfort on biting?

• Does a radiograph show radiolucency beneath the margin?

• Is the discolouration removable with polishing, or does it persist?

• Is the crown mobile?

A grey line that is simply an exposed metal margin, with healthy tissue and no defect, can reasonably be monitored. A dark margin with inflammation, catching, or radiographic change is a different matter and needs treatment.

Monitoring. Entirely reasonable where the crown is sound and the concern is purely aesthetic. Replacement involves removing the crown, which is not without cost to the underlying tooth.

Replacement with an all-ceramic crown. Where appearance matters and the crown is nearing the end of its life anyway, this addresses the problem directly. The margin can be finished at or slightly below the gum without a metal edge.

Soft tissue grafting. Where recession is the main issue and the crown is otherwise good, thickening or repositioning the tissue can cover the margin. This suits some cases and not others.

Margin repair with composite. A conservative interim measure in some situations, though bonding to a crown margin is less predictable than bonding to enamel.

Addressing the cause of recession. Brushing technique, occlusal factors, and periodontal health all contribute. Replacing a crown without addressing ongoing recession may mean the same problem recurs.

Where several older crowns are involved, a broader discussion — potentially including full mouth reconstruction if extensive work is needed — may be more coherent than replacing them one at a time.

Arrange an assessment if you notice:

• A dark line at a crown margin, particularly if it has appeared or worsened recently

• Sensitivity around a crowned tooth — see tooth sensitivity

• Bleeding or tenderness of the gum around a crown

• A bad taste or odour around a crown

• The crown feeling loose or moving

• Food packing at the margin

• Discomfort when biting on the crowned tooth — see pain when biting

Any sensation of looseness should be reported promptly. Decay progresses quickly beneath a partially detached crown and often causes no discomfort until advanced, because many crowned teeth have been root treated.

The NHS provides general information about crowns at nhs.uk/conditions/crowns/.

• Brush gently with a soft brush; aggressive brushing contributes directly to recession

• Clean the margin daily with interdental brushes or floss — this is where decay begins

• Use a non-abrasive fluoride toothpaste, and consider a higher-fluoride product if advised

• Attend hygiene appointments so margins are cleaned and monitored

• Attend check-ups with radiographs at appropriate intervals

• Wear a night guard if you grind, as occlusal overload contributes to both recession and crown failure

• Report changes rather than waiting

Root surfaces exposed by recession are considerably more susceptible to decay than enamel, so cleaning at the margin becomes more important, not less, as recession progresses.

• Grey lines usually come from the metal substructure of older porcelain-fused-to-metal crowns

• Gum recession over time exposes a margin that was originally hidden

• Thin gum tissue can allow metal to show through without frank recession

• A dark line may also indicate decay or a defective margin, so assessment matters

• All-ceramic crowns have no metal substructure and avoid the problem

• A sound crown with a visible margin does not automatically need replacing

• Addressing the cause of recession matters, or the problem may recur

A grey line at the gum edge of an older crown is common, usually explicable, and often not a problem requiring treatment. It reflects the way crowns were built for many years combined with the normal migration of the gum margin over time.

What matters is distinguishing the cosmetic version from the clinical one. Those two look similar and are managed quite differently, and only examination — usually with a radiograph — reliably separates them. If the crown is sound, replacing it purely for appearance is a choice rather than a necessity, and one worth weighing against the tooth structure involved in redoing it.

If you have noticed a dark line at a crown margin, you are welcome to arrange an appointment at Wimpole Dental, 22 Wimpole St, London W1G 8GQ, or call 020 7183 0692.

Dental symptoms and treatment options should always be assessed individually during a clinical examination.

This article is for general educational information only and is not professional dental advice, diagnosis, or a treatment recommendation. Information here is general and cannot replace an in-person assessment by a qualified, GDC-registered dental professional. Symptoms, suitability, fees, timelines, and outcomes vary according to individual clinical circumstances. If you have pain, swelling, or other concerning symptoms, seek prompt professional dental care. Always request a written treatment plan and cost estimate before proceeding with treatment.

Written Date: 19 August 2026

Next Review Date: 19 August 2027