Yeah I figured the "margin" had some role in this. In fact after I got the back of my tooth shaved down, on my next visit the dentist remarked "hmm, were gonna have to take another look at that...". Unfortunately I couldn't make my set appointment and I'm here now putting this 1000 piece puzzle together. I should have known better than to have him shave it down but I had no idea the cauldron of bacteria brewing under it in my dead tooth. I wasn't even aware root canals were even the slightest bit unhealthy until a month or so ago.
Thanks for your pro input
Do you think I should have the tooth extracted as well as my single mercury filling?