I was at my dentist last week and she pointed out a white mark on my gum. I hadn't noticed it before but she asked me to go back if it hadn't gone within 10 days. It hasn't gone and I'm due to go back to the dentist next week but now I'm getting paranoid about what it is. It's a clearly defined but painless white mark, about 5mm long and 2mm wide. I should also point out that I am a smoker. Has anyone else had anything like this?