For what it may be worth to you: I have two root canals on back-most teeth, done in 2002 and 2009. They have never bothered me, BUT: I ingest a Bowel Tolerance dose of ascorbic acid every day [and have for the past 20 years], i.e. I believe all of that supplemental ascorbic acid has solved any toxicity issue(s) that root canals are strongly suspected to cause.
If you have any questions, comments, and/or concerns about ascorbate/vitamin C therapy, please feel free to post them here and/or contact me privately.