Angularis nigra Wikipedia
Angularis nigra, Latin for black angle (formerly known as the black triangle), is the space or gap seen at the cervical embrasure, below the contact point of some teeth. The interdental papilla does not fully enclose the space, leading to an aperture between adjacent teeth. This gap has many causes including gingival recession, and gingival withdrawal post orthodontic work. Possible treatments to correct angularis nigra include addition of composite resin in the space, veneer placement, or gum graft. Angularis nigra is generally only treated based on the aesthetic preference of the patient (although serious gum recession may warrant periodontal treatment).
Previously, lack of proper termology to report this condition was an issue, often colloquially termed the "black triangle"; angularis nigra was coined at the University of Toronto Faculty of Dentistry.