A patient with #46 failed root canal treatment walks into my office a couple of days ago. He was so upset with his original dentist who had done the root canal followed by a crown (~11 years ago). The patient started having pain a few days prior to his consultation appointment at my office. He had seen a new dentist on an emergency basis for the pain since his long-term dentist was away on vacation. The new guy says to the patient “I think the dentist who did the root canal forgot to remove the cotton inside of your tooth before putting the crown on. And, this is the reason why the root canal failed!”
While I was listening to the patient, I was suspecting that the “empty” pulp chamber could have certainly been the main contributing factor to this failure besides slightly under-instrumented/-filled canals. The endodontic and restorative work looked solid otherwise. After all, the work had served the patient for 11 years. As usual, I kept the speculations to myself and talked to the patient about the pathways for the bacteria to the root canal system and the fact that every work, no matter how perfectly done such as this, requires maintenance after a long period of time. I accessed the tooth and expected a large, stinky cotton pellet inside the chamber. To my surprise, there was a solid bonded core material (translucent on the radiograph) with evidence of coronal leakage inside the chamber. There was absolutely no big void in the core material. Coronal leakage over a very long time was indeed the main contributing factor in this case.
So, do not be so quick and judge someone else’s performance based on a 2D x-ray. Always state the fact (“re-infection of the root canal system by micro-organisms that are much smaller than the gap between the best fitting crown and the tooth”) and stay away from your prejudices.