I had root canal work done on a tooth and it was completely painfree - it must depend on how skillful your dentist is with the anaesthetic. Presumably a dog would have a general so shouldn't feel anything. That said, I don't think I would put a dog through it for various reasons.

thanks to all who replyed. i guess now im leaning yowards extraction. what will the exrtaction site look like all healed. does anybody have a pic.

It will just look like bare gum.