Re: Gum Pockets!
If they did a deep cleaning (root planing and scaling) the irritation can last for several days. Keeping the area clean will go a long way to it healing faster. Salt water rinses (1/4tsp to 8oz warm water) can help greatly also.
Once a black triangle has formed there is nothing short of surgical gum replacement that can fix it. The gum has receded past the "waist" of the tooth and the space there is permanent. A crown may make it look more esthetically appealing but the only permanent solution would be gum replacement. Even then, without bone below it, the gum won't attach.
Be sure you are flossing between the teeth and keeping that area clean. When the gum recedes it exposes the tooth dentin, sort of a deeper yellow color as you go to the base of the tooth. The dentin contains small tubules that can allow painful sensations to reach the nerve (hot, cold, sweet etc.). Using toothpaste for sensitive teeth can greatly help this as it contains ingredients to plug the tubules up. It does take a few weeks to work though. I would recommend you start using this as it sounds as though there is recession there.
Hope this helps!
GOOD LUCK and let us know how you are doing.
My best to you,