Dr J Tennant is an interesting and good example of the potential impact of root canals on health.
Dr T did most of the testing of the Lasik eye surgery procedure. He nearly died because of it. His doctor gave up on him and left him terminally ill. The Science related to his recovery is quite fascinating. This is a talk he gave at an IAOMT--mercury free dentistry--conference a few years ago. https://www.youtube.com/watch?v=6XicmDDmVBs