Black triangles between crowns: why the gaps appear and what can be done

You smile in a photo and notice small dark gaps between your front teeth, right next to the gum. Dentists call them open gingival embrasures. Everyone else calls them black triangles. They are common around crowns, around natural teeth after braces, and in most mouths as people get older. They are not usually harmful, but they can bother people a lot, especially after spending money on a new smile. Here is what causes them, the one measurement that explains most of it, and what can realistically be done.

What is missing: the papilla

Between each pair of teeth, the gum rises into a small pointed peak called the interdental papilla. In a young, healthy mouth it fills the space under the point where the teeth touch. A black triangle is simply the dark space you see when that papilla no longer reaches the contact point, so you are looking into the shadow of the mouth behind (Sharma and Park, 2010).

The papilla is soft tissue supported by bone. It cannot stretch indefinitely. That leads to the most useful piece of research on this subject.

The 5 mm rule

In 1992, Tarnow and colleagues measured 288 sites between teeth in 30 people. For each, they measured the distance from the bottom of the contact point down to the top of the bone between the teeth, and noted whether the papilla filled the space. The results were striking (Tarnow et al., 1992):

A millimetre or two makes the difference. This explains nearly every cause of black triangles. Either the bone has dropped, so the distance grew from below, or the contact point sits too far from the gum, so the distance grew from above.

Between two implants, the numbers are less forgiving. A later study found that the soft tissue between adjacent implants averaged only 3.4 mm in height above the bone (Tarnow et al., 2003). That is why two implant crowns side by side at the front are one of the hardest places to avoid a dark gap.

Why black triangles appear around crowns

Bone and gum loss

Gum disease destroys the bone between teeth, and the papilla shrinks with it. The NHS lists gums shrinking among the effects of gum disease. Smoking adds to the risk; see our article on vaping, smoking and crowns. Reviews of the subject also list ageing and loss of bone height relative to the contact point among the main risk factors (Sharma and Park, 2010).

Swollen gums that settle

If your gums were puffy and inflamed before treatment, they may have filled the spaces only because they were swollen. Once the gums become healthy after cleaning and good care, they tighten and shrink slightly, and a gap can appear. This is healthy gum revealing a shape that was already there.

Tooth and crown shape

Triangular teeth, wide at the biting edge and narrow at the gum, leave a bigger space near the gum. A study of 337 adults after orthodontic treatment found black triangles in 38%, and linked them to triangular crown shapes, contacts that were short and placed too near the biting edge, more divergent roots, and a bone-to-contact distance above 5.5 mm (Kurth and Kokich, 2001). Those are natural teeth after braces, but the same geometry applies to crowns. A crown with a short contact high up, or a narrow neck at the gum, recreates the problem.

Root angle

If two roots tip away from each other, the space between them near the gum is wider, and the papilla has more to fill. Kurth and Kokich found this was one of the strongest associations with black triangles.

What can be done

A 2026 review of how to manage black triangles stresses that treatment depends on the cause, and may involve gum treatment, orthodontics, restorative work or a combination (Ogawa et al., 2026). In practice, the order usually looks like this.

1. Get the gums healthy first

If gum disease is part of the story, treating it comes before anything cosmetic. Changing crowns to cover a gap while the bone is still being lost does not last. The NHS advises seeing a dentist if your gums bleed when you brush or are swollen and sore.

2. Reshape or remake the crowns

This is the most direct fix for crowns. If the contact point can be lengthened and moved closer to the gum, so the distance to the bone comes down towards 5 mm, the papilla has a much better chance of filling the space, or the gap becomes too small to notice. Crowns can also be made slightly wider at the neck.

There are limits. Push the contact too far and teeth look long and square, and a crown bulging at the gum line is hard to clean, which can inflame the very papilla you are trying to keep. Good crown design is a balance between closing the gap and keeping a natural shape. If you are considering crowns versus veneers for this, our crowns vs veneers page explains where each fits.

3. Small additions to existing crowns or teeth

Where a gap is small and next to a natural tooth, tooth-coloured bonding can sometimes be added to the natural tooth to close it. On ceramic crowns, additions are less predictable. Ask your dentist what is realistic for your particular crowns.

4. Orthodontics

If roots are tipped apart, or teeth are spaced, aligners or braces can bring the roots more parallel and the contacts closer to the gum. That changes the geometry rather than covering it. It often has to happen before new crowns are made, not after.

5. Gum surgery

Techniques exist to rebuild or graft gum in this area, and reviews describe them as part of the toolkit (Ogawa et al., 2026). Results are less predictable than changing tooth shape, because you are asking a small amount of tissue with a limited blood supply to grow into a space. A periodontist is the right person to advise.

Preventing black triangles with new crowns

If you are planning crowns on your front teeth, especially full mouth crowns, it is worth asking about this before treatment, not after.

• Have any gum problems treated and stable before crowns are made.
• Ask how the contact points and crown shape near the gum will be designed.
• Look closely at the gaps near the gum at the try-in. At Precious Dental, fit, bite and shade are checked at a try-in before crowns are permanently fixed, and that is the moment to raise it.
• Be realistic if you have had gum disease in the past. Where bone has been lost, a little dark space may be the price of a crown shape that can still be cleaned.

Living with a small gap

Black triangles are mostly a cosmetic issue. From a cleaning point of view, they can even be an advantage, because an interdental brush fits easily. The Oral Health Foundation advises cleaning between teeth once a day and asking your dental team which brush size suits each gap. Keeping the papilla healthy is the best protection against the gap getting bigger.

A black triangle is different from food packing between teeth when you chew, which is usually about the contact point being too loose. That is covered in our article on food stuck between crowns.

Bothered by gaps between your crowns?

Send us a clear, close photo of your smile and any recent X-rays through our contact page or on WhatsApp. We will tell you what seems to be causing the gaps and which options are worth discussing, including when the honest answer is to leave them alone. You can see examples of our crown work on real results.

Common questions

Will the gum grow back to fill a black triangle?

Sometimes partly, if the gap is due to swelling settling or a contact point that can be moved closer to the bone. Gum that has been lost with bone through gum disease does not reliably grow back on its own. The distance from the contact point to the bone is the key.

Can new crowns close black triangles?

Often, yes, at least partly. Crowns can be shaped with longer contacts that sit closer to the gum, making the gap smaller. The trade-off is that over-filling the space makes teeth look square and can be hard to clean, so it has to be done carefully.

Why did black triangles appear after my crowns were fitted?

Common reasons are gums that were swollen before treatment settling down, gum recession, crown shapes that taper towards the gum, or contacts placed too high. If it is new and you also have bleeding gums, get your gums checked first.

Are black triangles a sign of gum disease?

They can be. Gum disease destroys the bone between teeth, and the papilla shrinks with it. They can also come from tooth shape, age or orthodontic treatment in a healthy mouth. A dentist can tell the difference with a check and X-rays.

Do black triangles trap food?

They can collect plaque and small bits of food, but a black triangle usually makes the gap easier to clean with an interdental brush. Food packing into a gap when you chew is more often a problem with the contact point itself.

Sources

1. Tarnow DP, Magner AW, Fletcher P (1992). The effect of the distance from the contact point to the crest of bone on the presence or absence of the interproximal dental papilla. Journal of Periodontology
2. Tarnow D et al. (2003). Vertical distance from the crest of bone to the height of the interproximal papilla between adjacent implants. Journal of Periodontology
3. Kurth JR, Kokich VG (2001). Open gingival embrasures after orthodontic treatment in adults: prevalence and etiology. American Journal of Orthodontics and Dentofacial Orthopedics
4. Sharma AA, Park JH (2010). Esthetic considerations in interdental papilla: remediation and regeneration. Journal of Esthetic and Restorative Dentistry
5. Ogawa Y et al. (2026). Interdisciplinary management of open interproximal embrasures. Journal of Esthetic and Restorative Dentistry
6. NHS. Gum disease
7. Oral Health Foundation. How to clean between your teeth

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