I Am on Trays 28/28 of my Invisalign Treatment and my Teeth. Are my Black Triangles Permanent? (photo)

In your particular case, your papillas have become blunted.  This can occur following orthodontic treatment in adults if the teeth were significantly overlapped and where then straightened out.  In adults, the gum tissue does not usually fill in the embrasure (triangular area between two teeth at the gum line). 

Another cause could be gum disease. 

These black triangles can sometimes be reduced in size by either mildly tipping the roots of the adjacent teeth towards each other, or by doing filing between the teeth which brings them closer together.  

I would suggest asking your treating doctor.  Orthodontists are often able to give you some suggestions and choices where black triangles can be reduced or minimized. 

Otherwise, a general dentist may be able to help by adding bonding material to help conceal the black triangles. 

Very often, the black triangles are permanent. It is one of the normal outcomes after Invisalign or Braces. Wait a few months after completion of Invisalign, and then your dentist can cosmetically improve them with some bonding or even with injections of dermal-filler into the gum papilla.

The black triangles are usually a sign of lost gum and/or supporting bone. There may be some small improvement in the next 18 months after treatment but usually not enough to say the triangles have disappeared.