In a well-known 1992 study of the gum between teeth, the gum filled the gap almost every time the distance from the point where two teeth touch down to the bone was 5 mm or less. At 7 mm or more, it filled the gap in about a quarter of cases or fewer. That small measurement explains most dark triangles at the gumline: either the bone has dropped, the teeth touch too far from the gum, or both. Dentists call these spaces open gingival embrasures, and they can often be reduced, although the right approach depends on which of those causes is at work.
The geometry behind the gap
Between each pair of teeth sits a small peak of gum called the papilla. It needs support from the bone beneath and a fairly short space to fill. The 1992 research by Tarnow and colleagues, published in the Journal of Periodontology, measured that space in patients and found the papilla was present in nearly all sites at 5 mm, in about half at 6 mm, and in 27 per cent or fewer at 7 mm or more. So a gap can appear because the bone level has fallen, or because the teeth are shaped or positioned so that their contact point sits high up, away from the gum.
Why the papilla shrinks
Gum disease and recession. Periodontal disease can destroy the bone that supports the papilla, and once the bone is lower, the gum peak flattens. Recession from other causes can do the same. Our guides to receding gums and gum disease treatment explain how this develops and what can be done.
Tooth shape. Teeth that are narrow at the neck and wide at the biting edge, sometimes described as triangular, touch only near the tips. That leaves a taller space at the gumline for the papilla to fill.
Tooth position. Crowded, rotated or tipped teeth can change where neighbouring teeth touch. When teeth are straightened, that hidden space can become visible.
Gaps that show up during braces or aligners
Many people first notice black triangles partway through orthodontic treatment. A 2026 systematic review by Angioni and colleagues in the International Journal of Dentistry brought together ten studies and found reported rates during treatment ranging from 18 to 78 per cent, depending on the study. The factors most often linked with them were the distance from the contact point to the bone, crown shape, crowding and age. The certainty of the evidence was low to very low, but the pattern is consistent: straightening crowded teeth with tapered crowns can uncover a space that was already there.
This does not mean the orthodontic work was done badly, and there are ways to manage it. Small adjustments to the shape of the contact between teeth, sometimes made by gently reshaping the enamel during treatment, can move the contact point closer to the gum. Your dentist can discuss whether that suits your teeth.
Ways to close or reduce a black triangle
Treating the gums first. If gum disease is active, it needs treatment before anything cosmetic is done, both to protect the remaining gum and bone and because inflamed gums change shape as they heal.
Composite bonding. Tooth-coloured resin can be added to the sides of the teeth to move the contact point closer to the gum and fill the space, usually without drilling healthy tooth. It suits many small to moderate gaps. Our guide to bonding versus veneers compares the two, and our bonding service page explains how we approach it.
Porcelain veneers or crowns. Where several teeth need reshaping, or the teeth are already heavily filled, ceramic restorations can change the outline of the teeth to reduce the gaps.
Orthodontic treatment. Moving teeth, sometimes combined with reshaping of the contact areas, can close spaces caused by tooth position. Our article on closing a gap between the front teeth covers related situations.
| Option | Typical market range in Australia |
|---|---|
| Composite bonding | $250 to $800 per tooth |
| Porcelain veneers | $1,500 to $2,500 per tooth |
| Orthodontic treatment | Varies widely with the case |
| Gum treatment | Varies with the extent of disease |
These are typical market ranges, not Lumi fees. For our current offers, see our current deals page.
Can the gum be regrown?
A lost papilla rarely rebuilds by itself, and regrowing it is one of the harder problems in gum treatment. Surgical techniques exist, and our guide to gum graft surgery explains grafting in general, but results between teeth are less predictable than along the front of the gum.
Injections of hyaluronic acid into the papilla have been studied. A 2026 systematic review by Jamjoom and Bakhshwain in Frontiers in Dental Medicine found three small trials in which hyaluronic acid reduced the visible area of black triangles compared with saline in the short term. The evidence was low to moderate in certainty, the trials were small and varied, and it was not clearly better than other regenerative approaches. It is an area to watch rather than a reliable fix.
Protecting the gum you still have
Brushing gently with a soft brush, cleaning between the teeth every day with floss or interdental brushes sized by your dentist or OHT, and having gum problems treated early all help keep the papillae you have. Black triangles can trap food, so good interdental cleaning matters even if you decide not to close them.
What patients ask about black triangles
Are they harmful?
They are mainly a cosmetic concern, but food and plaque can collect in them. If they are caused by gum disease, the disease itself needs attention.
Will whitening hide them?
No. Whitening changes tooth colour but does not fill the space.
Do I have to treat them?
No. If they do not bother you and you can keep the area clean, monitoring at check-ups is a reasonable choice.
If dark gaps at your gumline bother you, our dentists can check your gum health, explain what is causing the spaces and talk through options. Contact the team at Lumi Dental or see our current deals page.
