Last I spoke with a dentist, he stated that some root canals may not be clear of all bacteria when cleaning the hole prior to a root canal. If so, an infection will occur at the filled root. Some dentists will not do a thorough job of sealing the root and bacteria may enter the root area and infect it. Bacteria may find some way to enter the dead root and populate the prime real estate. Once you have that infection, the toxins released at the root leak to your vascular system (blood vessels) and, from what I've read, can affect the destination where they hit. So if the toxins leak to your heart area
This is why antibiotics are often given before and after many dental procedures. And if the toxins can seep in to the bloodstream then there is access of the bloodstream to carry antibiotics to the infection. Although I personally still prefer herbal antibiotics or ozone therapy.