Post-Invisalign Gap. Is This Normal Or Should I Seek a Second Opinion?

While there is some merit to each of the posts below, it is important to note that the inherent shape of the teeth may be responsible for the spaces.  Often times, the width of the teeth at the biting surface of the teeth is larger than that at the gum.  Therefore, even if the roots are moved and the teeth are in fact parallel/straight, unless there is gum coverage, you will expect these "spaces".

Keep in mind that the teeth themselves are actually touching each other, so there is no true "orthodontic space".   Therefore, if the gums do not grow back (which they may or may not, depending on a variety of periodontal criteria) you may need to have the teeth reshaped interproximally (IPR).

Hope this helps!

The reason you have these so called "black triangles" is because invisalign does a good job moving crowns of teeth but not so much moving the roots.  Reason for these areas with not gum coverage is that the crowns of the teeth were brought together with invisalign but since the roots did not move, you ended up with these black triangles.  Time may improve them but not appreciably in my experience.  I would ask your dentist about "refinement" which is part of invisalign treatment and have him order "attachments" to be placed on the involved teeth to try to bring the roots closer together.  This is a situation where conventional braces would handle the correction much better than invisalign.  Hope this helps.  Good luck!