People have root canals all the time. Not all of them succeed. Sometimes they are successful for years and then the root fractures and the tooth must be extracted. Root canal teeth can get brittle. Habits like grinding and clenching from stress can sacrifice your tooth.
First, choose to have your treatment done by a dentist who does a lot of root canals. Endodontics is the specialty in dentistry that focuses on root canals.
Knowing if the root canal is failing is tricky-You most likely be suspicious if you have pain or a gum boil - you need to see the dentist.
A dentist will look for a gum boil, look at the gum pocketing, check your bite and can take an radiograph to check for an abcess.
Options for failing root canals are to re-treat the tooth. Sometimes there is a root that was missed and a retreat cleans up the infection. Another option can be an apioectomy. The root canal specialist goes up at the top of the root, cuts off the edge, cleans out the infection and seals it. There are some instances where that is successful.
Otherwise, you need the tooth removed and replace it either with an Implant, Bridge or Maryland Bridge. Get a good opinion on your options. Failing root canals do happen.