Hi Jenny,
Here's a thought. Before I had my root-canaled tooth extracted, I had gone to a dentist who did "replacement root canals" using a product called Endocal, or Biocalex, or something like that. This material is apparently used almost exclusively in Europe for root canals, and has apparently been shown to seal better than the gutta perca most often used in the US. The "sealing" action of the material apparently eliminates the "open pockets" left behind by gutta perca, the open pockets apparently being what gives rise to the problematic anaerobic bacteria being able to take hold. The downside for this material is that if too much is inserted into the tooth, it expands too much, can create pressure, and makes the tooth become brittle.
I had to travel over 200 miles to the only dentist in Oregon who did this, and was extremely wiped out and had a terrific headache by the time I arrived. As the dentist began to drill on the tooth, he stopped momentarily and asked whether I smelled something, which he then said was the smell of infection. As he continued, I noticed that even though I was undergoing some very stressful dental work, right after such a long and difficult road trip, I actually began to feel better. My headache went away, and the stress level in my body went way down. And my chronic daily headaches almost went completely away for the next several weeks. After the dentist finished drilling out the tooth, he then disinfected it thoroughly with some kind of laser device.
I ended up not doing the replacement, because I didn't have a lot of tooth left, and it would have taken a fair amount of time and expense to pull down the tooth enough to do a reliable root canal. So getting back to my thought at the beginning, I wonder if my story would indicate it might be worthwhile for somebody concerned about their own root canals to consider doing a replacement. Perhaps if it was done one at a time, it might become discernible as to whether the process of drilling out the inside of old root canals makes a difference. --- Seems like with most everything we deal with, there's no easy answers.
Best Regards, Wayne