sores in mouth and painful incisor

I have already posted. I would like to hear from a Doctor. I am scheduled for a surgery on tooth #11. I had the RC last August, and all was fine...so I thought.
Then I had a $1250-cash crown, all porcelain))) put on. Then I was having another RC done two teeth down that chipped too.!
During that time I started to complain to the Endo that I was having Pressure pain on the 1st RC he did. He took a pic and consulted with my Dentist. The 2 of them decided I needed a re-do.. Apparently they are seeing a circular ring at the top of the root..which usually indicated the RC has failed. In the meantime I have bad pain now, I have sores in my mouth, my lips hurt on the inside, can't eat anything like Tomatoes. and I am on a very strong Anti-biotic, which will indeed cause Yeast infection eventually !! The reason for going in and redoing it thru the gum is they are afraid I may lose the very, very expensive crown I put on !! ....They just said I am one of the unlucky 10% of people who has had a RC that didn't work. I had no infection going in. That I am aware of..But I do remember the Endo saying something about the root already in bad shape when he opened the tooth, but I didn't smell anything, like in some cases.
I just don't know what to do. I am reading about this surgery and the success rate is not good. should I take the chance and go thru the All-Porcelain Princess Crown??
please help, plus what is this horrible taste in my mouth? and the bumps.?

[Ania778]

Cindy try dentalcom.net.   There is a forum there with an endo section where dentists discuss such problems as yours.