What are some signs or symptoms that I need a root canal?
Is it painful after the procedure? If so, for how many days after should I expect?

You need a root canal when your dentist say's "You need a root canal." This is because Xrays must taken and teeth must be examined to determine that the nerve in your tooth is so badly infected that it must be removed. The pain which may have could seem severe yet just be a regular cavity.