What does it mean if you have black lines on teeth near gums?

Black lines: It might be stain, it might be decay, it might be a build-up of calculus (tarter), it might be periodontal (gum) disease. It would be best if you had an examination at your dentist to be sure.

Time for check up: If you have black lines near the gumline it means you're long overdue for a dental check up and exam. Could be a number of different things, but guessing over the internet won't give you the proper answer. A local dentist can tell you exactly what is wrong and what treatment you need.