Modern dentistry says the old theory that root canals are a source of infection is major quackery.
Myth #3: Root canals cause illness.
It’s hard to miss this myth if you are searching for information on root canals online. This myth is based on poorly designed and long-since debunked research that took place almost an entire century ago! In the 1920s, Dr. Weston A. Price was responsible for disseminating the results of this study and using them to promote extractions (the permanent removal of a tooth) — one of the most traumatic treatments available. There is no valid scientific evidence supporting Dr. Price’s research to date. Not only are root canals safe and effective, they eliminate bacteria from the infected roots of teeth, improving both your oral health and your overall health.
I had many and didn't have any problems except when my immunity was impaired, then I had six infections from previously treated root canalled teeth that ended up having to be extracted and replaced with implants. Interestingly, none of them could be saved when in the past I had several re-treatments that were successful. After I restored the immunity problem I stopped losing teeth.
Back in the 1990s I had a holistic dentist remove my fillings to treat depression. It had no effect and the back composite fillings didn't last. He did a root canal with an alternative material Calcium Hydroxide that ended up getting reinfected. It was so hard to remove an endodontist had to grab my jaw painfully to dig it out. I avoid these dentists now.