Seeing an oral pathologist or oral medicine specialist is advised.
Hi,
For self-diagnosis on tooth/mouth problem i use the following site: www.doctorspiller.com
The white section of 'oral images' is particularly useful. (btw the images of infections etc are NOT pleasant - you have been warned)
However - after a quick browse and not knowing much about your condition i would agree with Scottma to seek specialist advice. Hope the site can help alleviate any worry in the meantime or give you ideas to question your dentist with.
Hope you get it sorted, all the best.
Did you ever get an answer to this question? I also have a red, sore line on the inside of my lip.