That black line is actually old technology. What that black line is, is years ago we had to put metal under a lot of the dental work, which we don't do anymore.
But that metal, you can't mask that out.
So they would try to bury the margin of that black line as deep under the gums as they could.
Well, the gums didn't like that, and eventually they start to recede. It exposes that black line, and there's nothing you can do except for remove that restoration.
Now the good thing is, is that we've got options that just don't require us to use that type of dentistry anymore.
► See also:Taking DENTAL IMPRESSIONS : Correction Impression
Fuente: Youtube / Atlanta Dental Spa