It seems to me that hair, finger nails, and the outer layers of skin remove and replace themselves on an ongoing basis. As far as I know, adult teeth do not replace themselves. root canals are not on the outside of the body, so you can't clean them if they get infected and you may not even know if there is an infection until severe damage is already done.

root canals can "fail". I did not have anything against root canals or any dental work, then I got deathly ill from a "failed" root canal and apicoectomy and its resulting deadly bacterial infection and Amalgam leaking into the gum tissue and bone and turning my gums black/blue/gray. These bacteria are toxic and do not respond well to prescription Antibiotics . I still suffer the adverse health effects 3 years afer having the metal post/rod removed. The dental surgeon said he could not even get out all the infected tissue nor all the Amalgam which had leaked.

Don't know much about the teeth but removing external parts of body like hair and nails can hurt skin of your body any how.