How can I fix black triangles after braces? (Photos)

I had very over crowded teeth and I had started with orthodontic treatment for the same around 2 years back. Now the treatment is in final stages and I am starting see black triangles in between my teeth due to missing papilla. I am currently 26 years old. What can be done to get this black triangle fixed. My orthodontist has already performed IPR on this region once and is concerned that we reduce the tooth width any further, the symmetry will be completely lost between my incisors.