Black triangles appeared between my teeth after orthodontic treatment. Can they be fixed?

There are ways to improve them. A black triangle is an empty space between teeth that appears when the gum has receded, and once receded the gum does not fill back in on its own. The options are 1) reshaping the sides of the teeth slightly (stripping) to bring them closer together, 2) filling the space with resin, and 3) changing the shape with a laminate veneer or crown when it is severe. However, the right option differs with the condition of your teeth and the size of the space, and sometimes leaving it alone is the best choice, so it is better to decide together with your dentist after an examination.