What Can I Do About "Black Triangles" Caused by Invisalign Treatment?

Chances are that your Invislaign treatment did not "cause" the black triangles. It is common for gum tissue between severely rotated teeth to be less bulky than between properly aligner teeth. Then when the rotated teeth are corrected, the gum tissue is not bulky enough to fill the space. This is particularly true with adults. In adolescents, we typicaly see that the gum tissue will adapt to the space that is created by rotation correction. ( Good argument for early bite correction!)

When this problem arises there are generally two solutions. one is to narrow the teeth a bit so they can be movedcloser together. This should be done very carefully to be certain that there is not a tendency for tooth contacts to remain open. The second solution is to have your dentist build the teeth up in width with composite filling material. These materials have been much improved in recent years so such build-ups have good longevity. Follow your orthodontists recommendation as to which of these alternatives will best suit your needs.

Suggest additional Invisalign aligners to correct the rotated teeth. Attachments and interproximal reduction may be needed.
Interproximal reduction may also be an option to change the contact point of the two teeth, reshaping them to reduce the black triangles. You may require additional Invisalign refinement aligners in order to close any residual space.
The good news is that once new contact points are formed following your Invisalign, there may be some reestablishment of your papillae (gums near the black triangle) over time.
Good Luck!