There is none. 100% of root canals are infected. All root canaled teeth are dead.
If you consider pain control, mechanical function and aesthetics to be the limit of good dental treatment, then you will have "SAVED" the tooth.
If systemic effects are included in your concept of dentistry, than you must understand that all that has happened, is that you have kept dead, infected tissue, buried in the bone, within a couple of inches from your brain.
For some obscure reason we are all conditioned to think that teeth are not a part of the body, but that they are inert calcified material, and that they are sort of dead anyway. Dentistry is the only one of all the medical & para-medical professions that thinks it is a good idea to keep dead, gangrenous tissue in the body. The way to do this is to perform a Root Canal Therapy .
One eminent Endodontist says:
"It is wrong to speak of (Root Canal Therapy) as a dead tooth; it is more correct to describe such a tooth as nonvital or , better, pulpless. Even though the central blood supply to the tooth has been lost, the tooth itself still retains it's connection to the body via the periodontal membrane and the cementum."
This is like saying that even though the blood supply to your leg may be completely cut off , it would be wrong to suggest that the leg is dead, because it is still connected to your body by your hip joint! The Oxford dictionary defines 'non-vital' as "Fatal To Life". It defines 'Dead' as "No longer Alive".