I Have Large "Black Triangles" 3 mm Wide Between my Front Teeth, Are Crowns a Good Option?

Veneers and crowns are options to improve your smile, it depends mostly where the problem is coming from. I always recommend to patients to have a comprehensive evaluation of your smile. It sounds like your feel untrusted of your dentist explanation, if you feel so. Go ahead and search for a dentist that focus on cosmetic dentistry and provides an aesthetic vision. Look for before and after photos similar to your case. That will give you and idea and for you to be easier to make a decision. I do not like the fact i can not give you a straight answer, but i least some guidance will help you. 

If you are presenting to your dentist with a cosmetic concern as this, it can be a difficult situation to correct.  Depending on th esize of your front teeth, you have a few options.  First, if your teeth are of normal size, veneers can be placed to close the space. Also a gum graft by a periodontist (gum and bone specialist) can be considered.  This is not an easy fix but if it can be done then it is very cosmetically natural looking.  Often when teeth have such a large area of missing gum tissue, there is bone loss underneath the gums as well.  I would tell you to visit a cosmetic dentist in your area for a complete evaluation and a potential referral to a periodontist.