The worst thing you can do to an already bad situation (root canal),is fill it in with amalgam,i've have a root canal filled all the way to the root with amalgam myself.
A few months ago i went to a naturopath doctor who did some muscle testing,and clearly told me i would probably never get all the mercury out by drilling out the amalgam and refilling with compatible replacement,so i have the tooth pulled and all tissues cleaned out.
I have since had the digital exrays,that show any kind of disturbance/infection from the base of the tooth to jaw area,and it was free,so i'm keeping my fingers crossed.