Teeth Shaving and Black Triangles w/ Invisalign?

Depending on the level of bone between teeth, some black triangles can only be hidden by restorative means (bonding composite or porcelain veneers).  You are correct that contouring the teeth to be more rectangular can help, but if the triangles are severe the contouring may not be enough.

Many year ago a Norwegian orthodontist talked about "slenderizing" the anterior teeth when a person gets older, since as a person ages, recession of the gums cause the dreaded black triangles you refer to.  The reduction of the width of the teeth where they contact can allow closing of the gaps with orthodontics, braces or Invisalign.  I have performed this procedure many times resulting in dramatic improvement in a persons smile.  Yes, Invisalign can be used for this procedure with great predictable results.

If the black triangles are not too severe and your bite allows it, "slenderizing" the teeth and then closing the resulting spaces with Invisalign or braces may resolve the problem.  It is surprising how much better it can appear if the triangles are reduced, even if they are not eliminated.  Asking your orthodontist or dentist about how to achieve the best result is your best course of action.