Black triangles between your teeth: why they appear, what closes them

Black triangle fixes compared side by side

Swipe sideways on mobile. Suitability depends on the measured distance from contact point to bone and on gum health, which only an in-person exam can assess.

What a black triangle actually is, and why it looks dark

Between every pair of neighbouring teeth there is a small pointed wedge of gum called the interdental papilla. In a young, healthy mouth it fills the space from the gumline up to the point where the two teeth touch, so the smile reads as a continuous row of tooth and pink tissue. When that wedge shortens, a small triangular opening appears below the contact point. Light does not reflect back out of that space, it falls into the dark of the mouth behind, so the opening looks black even though it is simply empty. Dentists call it an open gingival embrasure. Most people just call it a black triangle, and they notice it first in photos, because a camera flash makes the contrast sharper than a bathroom mirror does.

The size varies a lot. Some people have a sliver only visible up close, others have openings wide enough to trap a sesame seed or whistle a little on certain words. Researchers grade the size by how much of the space the papilla still fills, from a small loss near the tip to a complete loss where the gum is flat between the teeth. That grading matters because the treatment options are different at each end of the scale. A small gap may close with a thin layer of bonding or with careful orthodontic finishing, while a large gap with significant bone loss usually needs a combination of approaches and realistic expectations.

It helps to understand that the papilla is not a separate flap that can simply be pulled back up. It is part of the gum tissue that rests on the bone between the teeth and attaches to the roots below the enamel. When the bone underneath drops, or the gum is inflamed and later shrinks, the papilla follows it down. That is why black triangles are often a visible sign of something that happened lower down: past gum inflammation, bone loss, or teeth being moved. The triangle itself does no harm, but its cause sometimes does, and that cause deserves attention before the cosmetic question does.

Black triangles are common, and they become more common with age. They are not a sign of poor hygiene by themselves, many people with excellent routines develop them after orthodontics, after successful gum treatment, or simply because their teeth are shaped like narrow-waisted triangles. They are, however, a spot where cleaning needs a different tool, because a toothbrush cannot reach into the space and floss pressed against a wide gap barely touches the side surfaces of the teeth. That practical point is often more important for your long-term oral health than how the gap looks.

The 5 mm rule, the number behind every fix

The most cited paper on this subject is short and simple. In 1992 Dennis Tarnow and colleagues at New York University measured 288 sites in 30 patients. They recorded the distance from the base of the contact point between two teeth down to the crest of the bone, and whether the papilla filled the space. Their results, published in the Journal of Periodontology, showed that when the distance was 5 mm or less, the papilla was present almost 100 percent of the time. At 6 mm it was present 56 percent of the time, and at 7 mm or more it was present 27 percent of the time or less.

Those few numbers explain almost every black triangle and every treatment for one. The gum can only stretch so far above the bone. If the distance it needs to cover grows, either because the bone dropped or because the teeth touch higher up, a gap appears. Every fix therefore works on one of two levers. You can bring the contact point down toward the bone, which is what bonding, crowns, veneers and some orthodontic movements do. Or you can try to add volume to the soft tissue or the bone underneath it, which is what injectable fillers and surgical grafts aim to do. Knowing which lever is realistic for your teeth is the first conversation to have with your dentist.

Later research has refined the picture without overturning it. Studies on implants have looked at the same relationship around crowns placed on implants, and the general principle, that soft tissue fills a short gap more reliably than a long one, has held up. The exact millimetre threshold varies a little between people, depending on how thick the gum is and how wide the space between the roots is. Thick, sturdy gum tissue tends to fill gaps more readily and to resist recession, while thin, delicate tissue is more prone to shrinking after inflammation, trauma or dental work.

The practical takeaway is that a black triangle is a measurement problem as much as a gum problem. A dentist can estimate the distance from the contact point to the bone with a probe and an X-ray, and that single measurement tells you much more about your options than any before and after photo. If the distance is only slightly over the threshold, small changes to tooth shape can be enough. If it is far over, because a lot of bone has been lost, then the honest answer is that soft tissue alone will not cover it, and a restorative approach becomes the main tool.

Why yours appeared, the five common causes

1. Gum disease and the bone loss it leaves behind. Periodontitis is the most important cause to rule out, because it is the one that keeps getting worse if left alone. Plaque bacteria along and below the gumline trigger inflammation, and over time that inflammation destroys some of the bone that holds teeth in place. The National Institute of Dental and Craniofacial Research describes how gums affected by the disease can pull away from the teeth and make them look longer, and it names smoking as the most significant risk factor. When the bone ridge between two teeth drops, the papilla drops with it. Ironically, black triangles often become most visible right after successful gum treatment, because swollen tissue that was hiding the gap shrinks back once the inflammation calms down.

2. Orthodontic treatment that straightened overlapping teeth. This is the cause that surprises adults most. Crowded front teeth often overlap, and the overlap hides the space near the gum. Once the teeth are lined up, that hidden space is exposed. A retrospective cohort study of adults treated with clear aligners and fixed braces and a study of risk factors after clear aligner treatment both examined how often these gaps appear and which patients are most likely to develop them. Age, the amount of crowding before treatment, tooth shape and the angle of the roots all play a role. This is usually a geometry change, not damage, and an orthodontist can often reduce it during the finishing stage.

3. Triangular tooth shape. Teeth come in broadly square, oval and triangular outlines. Triangular crowns are wide near the biting edge and narrow toward the gum, so the contact point between two of them sits high, close to the edge, leaving a long distance down to the bone. People with this tooth shape may have black triangles even with perfectly healthy gums and no bone loss at all. In that case the gap is purely about shape, and it responds well to treatments that make the teeth a little wider near the gum, such as composite bonding or careful reshaping combined with orthodontics.

4. Age and thinning gum tissue. Gums tend to recede gradually over decades, even in people without significant gum disease. Wear, years of brushing, small inflammatory episodes and natural tissue changes add up. Thin gum tissue is more likely to shrink than thick tissue. That is why someone may notice their first black triangle in their forties or fifties without any obvious trigger. The change is slow, and its progress can be slowed further with gentle, thorough cleaning and regular checkups, but the tissue that has already been lost does not grow back by itself.

5. Trauma from cleaning tools or habits. Pushing oversized interdental brushes or toothpicks into a tight space, snapping floss down hard into the gum, or scrubbing with a hard brush can wear the papilla down over time. The same goes for habits like picking at the gum with a fingernail. This cause is easy to fix once you know about it, and it is a good reason to have a hygienist show you the correct interdental brush size rather than guessing. A tool that is too large for the space does not clean better, it bruises the tissue it is supposed to protect.

Why a black triangle matters, beyond how it looks

For most people the first concern is appearance, and that concern is legitimate. Dental surveys of how people judge smiles regularly place visible gaps near the gumline among the features people like least. But the space also changes how your mouth handles food and plaque. A papilla that fills the gap acts like a seal: food slides past it during chewing. Once the seal is gone, fibrous food such as meat, leafy greens and popcorn husks can wedge into the opening. Trapped food feeds the bacteria that live there, and if it sits for hours, it irritates the gum and keeps the area acidic.

The side surfaces of teeth are already the hardest places to keep clean and the most common sites for hidden decay, which is why we wrote a separate guide on cavities between teeth. A black triangle adds root surface to that area, since the gum that used to cover part of the root has moved away. Root surfaces are covered by cementum and dentin rather than enamel, and they are softer and more easily demineralised by acid. That combination, more exposed root, more trapped food and harder access for the brush, is why dentists pay attention to these gaps even when the patient only asked about appearance.

There are also smaller, everyday effects. Some people notice a slight whistle or lisp on sounds like s and f when a gap between the upper front teeth is large, because air escapes through the opening. Others find saliva bubbles at the gap when they speak. Sensitivity to cold is possible when root surface is exposed, especially just after a dental cleaning. None of these is dangerous, but they are part of the reason people seek treatment, and they help a dentist judge how much the gap matters to the patient's daily life rather than only to photos.

Finally, a black triangle can be the first visible clue to an underlying gum problem that has been progressing quietly. Periodontitis is usually painless until late. If the gap is new, if the gums bleed when you clean between the teeth, if a tooth feels slightly mobile or if your bite seems to have changed, treat the triangle as a signal and book a gum assessment. Cosmetic treatment on top of active disease tends to fail, because the tissue keeps changing underneath the repair.

Keeping the gap from growing, the at-home routine

Nothing you do at home will make a lost papilla grow back. What home care can do is stop further loss and keep the exposed surfaces free of plaque and decay. The best evidence on cleaning between the teeth comes from a 2019 Cochrane review of interdental cleaning devices, which concluded that using floss or interdental brushes in addition to toothbrushing may reduce gingivitis and plaque more than brushing alone, and that interdental brushes may be more effective than floss. The authors also noted that much of the evidence is low certainty and short term, which is an honest reminder that technique and consistency matter as much as the choice of tool.

Two habits are worth stopping for anyone with black triangles. The first is using toothpicks or tools that are too large for the space, as described above. The second is smoking or any tobacco use, which the NIDCR lists as the most significant risk factor for gum disease. Smoking also reduces blood flow to the gums, which hides bleeding, the most obvious early warning sign. People who stop often notice their gums bleed more at first. That is not a reason to worry, it is the tissue's normal response to plaque becoming visible again.

Professional fixes, from simplest to most involved

1. Composite bonding. This is the most common fix and often the most predictable. A dentist adds tooth-coloured resin to the sides of the teeth near the gum, which makes them wider at the neck and moves the contact point down toward the bone. Because it changes the measurement in the 5 mm rule, it works regardless of whether the gum can regrow. It is usually done in one visit, without drilling healthy tooth structure, and it is reversible. The trade-offs are that resin can stain over years, edges may need polishing or repair, and bonding done badly can create ledges that trap plaque. A skilled operator matters more than the material.

2. Orthodontic finishing and reshaping. If the triangle appeared because teeth were straightened, an orthodontist can often reduce it before treatment ends. One technique is to slightly reshape the sides of the teeth, sometimes called interproximal reduction, so the teeth can be moved closer together and the contact becomes longer and lower. Another is adjusting the angle of the roots so they sit more parallel. These changes are small, measured in fractions of a millimetre, and they work best when planned into treatment rather than added afterwards.

3. Hyaluronic acid injections. This is the newest option and the one with the most marketing around it. Small amounts of hyaluronic acid gel are injected into the papilla to add volume. A 2024 systematic review pooled 24 studies covering 898 injected papillae and reported promising results with few adverse reactions for front teeth. Another systematic review found that success varied, results were better in the upper jaw and in people with thicker gums, multiple injections are often needed, and long-term durability is still not established. In plain terms, it can help small to moderate gaps in suitable patients, but it is not permanent and it is not a fix for large gaps with major bone loss.

4. Veneers and crowns. Porcelain or composite veneers and crowns can be designed with contact points that sit lower and with a shape that fills the space near the gum. They make sense when the teeth also need work for other reasons, such as wear, chips or old discoloured fillings. They are not a sensible first choice purely to close a small gap on otherwise healthy teeth, because they remove tooth structure and commit you to future replacements.

5. Gum and bone surgery. Periodontal surgeons have developed techniques to rebuild the papilla using connective tissue grafts and, in some cases, bone grafts underneath. These procedures are technically demanding, and results for the papilla specifically are less predictable than for covering recession on the front of a root, because the papilla has a poor blood supply and sits in a narrow space. Surgery is usually reserved for cases where the patient is highly motivated and other options have been considered. A specialist consultation will give you an honest estimate for your specific site.

Often the best result comes from combining approaches. Treat any gum disease first, let the tissue settle for a few months, then finish with orthodontic adjustments or bonding. Ask to see the treatment plan in terms of what it does to the contact point and the bone level, not only in terms of before and after pictures. And ask how the result will be maintained, because a repair that makes cleaning harder can create new problems in a space that already traps food.

Claims to be careful with, what will not regrow gum

Search results for black triangles are full of promises that the gap will close on its own with the right product. It helps to separate what is plausible from what is not. Oil pulling, herbal rinses, special toothpastes, supplements and serums do not regrow a lost papilla. Some of them can reduce gum inflammation, and when a swollen, bleeding gum calms down it may look tidier, but they do not rebuild bone or move the contact point, which are the two things that determine whether the space fills. If a product claims to grow gum tissue back, look for clinical evidence on lost papillae specifically, not on general gum health.

A few things can look like improvement but are not regrowth. Gum that was swollen from inflammation can look fuller, then shrink back after a cleaning, revealing a bigger gap. Food or plaque packed into the space can make it less visible until it is cleaned out. Lighting and camera angles change how dark the gap appears. Track a gap with consistent photos taken in the same light, or better still, ask your dentist to note its size at each checkup, so you know whether it is stable.

Similarly, remineralising products, including toothpastes and gums containing hydroxyapatite or fluoride, work on the hard surfaces of teeth. They can help protect exposed root surfaces and the sides of teeth from acid and early decay, which is useful when a black triangle has left more root exposed. They do nothing to the soft tissue of the papilla and will not close the gap. We say that plainly about our own gum too: Minvelle is designed to support saliva and supply hydroxyapatite to tooth surfaces after meals, not to change your gums. Our guide to hydroxyapatite gum benefits sets out what the evidence does and does not support.

The most reliable protection for a black triangle is a set of unglamorous habits: cleaning the space every day with the right tool, fluoride toothpaste twice a day, limiting how often you snack on sugary or acidic food, regular professional cleanings, and not smoking. These protect the bone and gum you still have, which matters more than any cosmetic fix, because every treatment works better when the foundation underneath is stable.

Questions to ask your dentist, before you choose a fix

Going into the appointment with a short list of questions makes it much easier to compare options. Start with the cause: ask whether the gap is due to bone loss, tooth shape, orthodontic movement, recession or a mix. Ask whether there is any active gum inflammation or pocketing around those teeth and whether that needs treatment first. Ask what the distance from the contact point to the bone is, or at least whether it is close to or far from the range where the gum would normally fill the space. Those answers tell you whether you are looking at a soft-tissue problem, a tooth-shape problem or both.

Then ask about the options in practical terms. How many visits will it take, how long is the result expected to last, what maintenance will it need, and what happens if it fails? For bonding, ask how the margins will be shaped so you can still clean between the teeth. For injections, ask how many sessions are typical, how long results last in the dentist's experience and what the cost is per session. For veneers or crowns, ask how much tooth structure will be removed and how often they usually need replacing. For surgery, ask for a realistic success estimate for your particular site, not a general one.

If you have an old filling or crown next to the gap, ask the dentist to check its edges as well. Food trapped in a black triangle sits right against restoration margins, and decay can start at those margins without any pain, and a dentist checking the gap is the best moment to catch it. Sometimes the right plan is to replace an old restoration with one shaped to close the gap at the same time, solving two problems with one procedure.

Finally, it is perfectly reasonable to decide not to treat a black triangle at all. If the gum is healthy, the gap is stable and it does not bother you, careful cleaning is a complete plan. Many people choose to keep things as they are and revisit the question later. What matters is that the decision is made with the cause understood and the gum health confirmed, so that a small cosmetic gap does not hide a larger problem.

The things people actually ask