I can see a brownish line along the top of the gum just above the dental bridge, should I be concerned? (Photo)

What you're seeing is the root that is not covered by your crown on the bridge. Whether it was covered and your gums receded, or it wasn't covered, are separate issues. The reason it is brown is most likely because you once had a root canal on that tooth. If not, you just have darker roots than normal.Is this likely to cause you any problem? Probably not.If you don't like it, then you can always have the bridge redone and demand that the entire root surface be covered by the back crown on the bridge. Ask to see it prior to giving your dentist permission to cement the bridge into place.Dentists don't have any control on whether your gums recede or how. It could recede because of your bite, any clenching or grinding habits, condition or health of your gums, your oral hygiene habits, are you a "hard brusher" and/or use hard tooth brush and abrasive tooth paste?What you might consider is seeing a periodontist (gum/bone dental specialist) and see if he can graft new gum tissue over the brown roots that are showing.

That is just where the crown ends and the tooth begins. It is probably a tooth that has had a root canal, that has turned dark. That happens sometimes.

The line you see is a gap between the crown and the gum. It can lead to problems down the road. Have your dentist remove any decay and fill the area.