Dental health

I know this is a long shot and not the right forum for this. But I have black lines on the chewing part of my molar teeth. I don't think they're cavities cuz they don't hurt. But they don't brush off either. I know, you're all gonna say "go to a dentist". I know I need to. Just curious if you guys know what it might be. It doesn't hurt and there's no cold or heat sensitivity