How many times can a root canal be redone?

[reminisce214]

I've had about 5 root canals done about 20 years ago, one I had redone 8 years ago, another two are failing. I'm wondering how many times can a root canal be done, and at what point would an implant be better instead?

 

[Dr M]

It depends on the reason for the failed root canal. Does it have a crack? Is there re-infection in one of the roots?