Q. My gums started bleeding recently when i brushed my teeth, so i started using a mouthwash specially for gingivitus and thankfully it stopped. However when i looked closly at my bottom teeth in the mirror earlier i noticed they have black lines randomly across the inside. They look like lots of little thunderbugs. Theyre only on my molar and bicuspid teeth (think thats what theyre called) There arent any marks on the front or back of the teeth, just the top. What is this??