A black triangle in between the teeth can indicate a number of issues. While it may start out small at first, it can widen into a larger triangle shaped gap if not treated. This black triangle most likely indicates that the gums are starting to recede, which is often due to periodontal disease. A deep cleaning, or a scale and root planing, may be necessary to remove plaque and debris far up underneath the gum line. A black triangle in between the teeth can also be an indicator that bone loss is beginning to occur, which may go hand in hand with periodontal disease. Advanced periodontal disease can cause bone loss, which in turn weakens the entire structure of the jaw and teeth. Patients that notice black triangles in between their teeth should see a dentist promptly, particularly if it appears that the black triangles started out small and are beginning to get larger in size.