Why is there a black line at the gum on my old crowns?

A black line at the gum on an old crown is something many people notice in the bathroom mirror years after the crown was made. You may have had the crown fitted in the 1990s or 2000s, it looked fine at the time, and now there is a dark rim right where tooth meets gum. In this article our dentists explain why that black line appears, what else it could be, and what metal-free crowns can and cannot change.

What an old metal-ceramic crown is made of

For several decades the standard crown in the UK and across Europe was the metal-ceramic crown, often called a porcelain-fused-to-metal crown or PFM. It is built in layers. A thin metal shell, called a coping, fits over the prepared tooth. On top of the metal the technician bakes an opaque layer to hide the metal colour, then several layers of tooth-coloured porcelain.

These crowns were popular for good reasons. The metal gives strength, and the porcelain gives a tooth-like look from the front. The Oral Health Foundation still describes them as one of the most common types of crown. Many of them have lasted 15 or 20 years, which is a good result by any measure.

The weak point is the edge. Where the crown finishes at the gum, the porcelain has to get very thin, and at the very margin there is often a collar of bare metal. When the crown was new, that edge sat just under the gum and nobody could see it.

Why the black line appears

There are three common reasons, and often more than one is at work.

1. The gum has receded

Gums shrink back slowly with age, with brushing too hard, and after gum disease. Even a millimetre of recession is enough to bring the metal collar of an old crown into view. Because the metal is grey, it reads as a dark line next to the pink gum and the pale porcelain.

2. The metal shows through thin gum

Some people have naturally thin, delicate gum tissue, especially over the front teeth. Even if the edge of the crown is still hidden, the metal underneath can cast a blue-grey shadow through the gum. This is why some patients say the gum itself looks dark rather than the tooth.

3. The root of the tooth is dark

Many crowned teeth have had root canal treatment. A root-filled tooth can darken over time, and an exposed dark root just above the crown edge looks very similar to a metal line. Some older crowns also sit on a metal post inside the root, which can add to the grey shadow.

When the line is a sign of something more

A line that is simply metal is mostly about looks. A few things change the picture, and our dentists look for them on every old crown before suggesting anything:

• Decay under the edge. If the cement has washed out over the years, bacteria can get in under the margin. Decay there is often brown or black and can be hard to see without an X-ray.
• A ledge or gap. If you can catch a fingernail or floss on the edge, plaque collects there. That raises the risk of decay and inflamed gums.
• Sore or bleeding gum. Gum that bleeds when you brush around one crown may be reacting to plaque trapped at a rough edge.
• Infection at the root tip. An X-ray may show a dark area at the end of the root, which points to an old root filling that has failed.

This is why we always ask for a recent X-ray or clear photos first. The answer to “why is it black?” decides whether the fix is a new crown alone, or a new crown plus work on the tooth underneath.

What metal-free crowns change

Modern crowns can be made without any metal at all. The two we use most are zirconia and E-max (lithium disilicate). Both are tooth-coloured all the way through, so if the gum recedes a little in future, there is no grey collar to appear.

Research supports this. A 2018 systematic review of crowns on implants by Pjetursson and colleagues found zirconia crowns had fewer aesthetic complications than metal-ceramic crowns, with similar rates of gum problems. A 2026 review of crowns on natural teeth found five-year survival for lithium disilicate and zirconia crowns comparable to metal-ceramic ones. In plain terms, you are not giving up strength by leaving metal behind.

Which one suits you depends on where the tooth is, how heavily you bite, and how much colour the tooth underneath has. A very dark root-filled tooth may need a more opaque material to hide it. Our team includes Dt. Şeyda Yılmaz, whose work focuses on zirconia and full-ceramic restorations. You can read more on our zirconia crowns page and our general crowns page.

What a new crown cannot change

It is fair to be clear about the limits.

• Lost gum does not grow back. A new crown can finish neatly at the gum line, but it will not raise the gum to where it was 20 years ago.
• Stained gum may stay a little dark. If metal particles have stained the gum tissue itself, some colour can remain after the metal crown is gone. It often looks much better, but not always perfect.
• A dark root may need covering. If the root above the crown is exposed and dark, the new crown edge may need to sit slightly differently to hide it, and this is discussed with you in advance.

How replacing an old crown works

1. Photos and X-ray You send us a recent X-ray or clear photos on WhatsApp. A dentist reviews them and sends a preliminary written plan with an itemised price.
2. Examination in Antalya On day one we examine every crown, take a 3D scan and confirm the final plan in writing. Nothing starts until you agree.
3. Removing the old crown Under local anaesthetic the old crown is cut off. It cannot usually be unscrewed or reused.
4. Checking the tooth With the crown off, we can see the tooth properly. Any decay is removed and the core is rebuilt if needed. If the root filling has failed, we tell you before going further.
5. Scan and temporary The tooth is scanned with an intraoral scanner and a temporary crown is fitted while the lab makes the new one. See what to expect from temporary crowns.
6. Fitting The new crown is tried in, checked for fit, bite and colour, then fixed in place.

For most patients this fits into one trip of about five to seven days. Your written aftercare explains how to clean the new edge and when to have it checked.

Should you replace one crown or several?

If only one front crown shows a line, replacing just that one is often enough, as long as the new shade can match the teeth next to it. If you have several old crowns across the front, replacing them together usually gives a more even result, because the shade and shape are planned as a set. That is the starting point for a wider smile makeover, but it is never automatic. We prefer to leave a healthy, unseen crown alone rather than replace it for the sake of it.

Old crowns at the back of the mouth that nobody sees, that fit well and cause no trouble, can often stay as they are. Your plan will list each tooth and our reason for treating it or not.

Looking after the new crown edge

The edge of any crown is where problems start, metal or not. Keeping it clean is the best way to make the new crown last:

• Brush twice a day for two minutes with fluoride toothpaste, angling the brush gently at the gum line.
• Clean between the teeth once a day with floss or interdental brushes.
• Use a soft brush and light pressure, as hard scrubbing speeds up gum recession.
• Keep up regular check-ups and hygiene visits with your dentist at home.

Ask us about your old crowns

If you have a black line at the gum on one or more old crowns, send us a recent X-ray or a few clear photos in good light. A dentist will look at them and send you a written plan explaining what is causing the line and what we would suggest, with an itemised price. There is no charge for the plan. You can use our contact form or message us on WhatsApp.

Common questions

Is the black line at the gum dangerous?

Usually not. On its own it is a cosmetic problem. It becomes a health concern if there is decay under the edge of the crown, a gap where food collects, or sore, bleeding gum around it. A dentist can tell which by examining the tooth and taking an X-ray.

Will a new crown make my gum grow back?

No. A new crown does not regrow gum that has receded. What it can do is end the grey shadow from metal and give a cleaner edge that is easier to keep healthy. Gum grafting is a separate treatment and is not right for everyone.

Can the line be polished or covered without replacing the crown?

Not really. The line is the metal itself or the shadow it casts, so polishing does not remove it. In a few cases a small tooth-coloured filling can cover an exposed root edge, but on an old metal-ceramic crown replacement is usually the lasting answer.

Should I replace all my old crowns at once?

Only the ones that need it. We look at each crown on the X-ray and in the mouth. If some are sound and out of sight at the back, there may be no reason to touch them. Your written plan will list which ones we suggest replacing and why.

How much does it cost to replace an old crown?

A zirconia crown is £150 and an E-max crown is £225 per tooth. If the tooth underneath needs extra work, such as a new root filling, we give you a written price after seeing your X-ray. See our prices page.

Sources

1. Oral Health Foundation: Crowns
2. Pjetursson et al. (2018), Clinical Oral Implants Research: survival and complication rates of zirconia-ceramic and metal-ceramic single crowns
3. International Journal of Prosthodontics (2026): survival of metal-ceramic, veneered and monolithic all-ceramic tooth-supported single crowns

Checked October 2026. Where we give our own view as a clinic, we say so.